WHY the +AO = WARM WINTER argument is in deep Doo

[HM]

No. What is BS is to state that "what made November cold will make Dec and Jan warm" and then tap dance when questioned on it. It's also a statement that has no way to dissect no matter what the outcome is.

Do you even know what it means to tap dance? Heck, do you even know that you were the one questioned? How should we conmunicate if you believe the actual science I'm posting is tap dancing, while your stuff is opinion and anecdotal? You tell me.

[NJwinter23]

Perhaps I'm a bit misguided with this, but how much different are the wavelengths in mid and late November vs December, anyway? The wavelengths are a tad longer in December, so even if the forcing is a tad too far west, perhaps larger wavelengths would help any subsequent ridging "move" eastward a bit into a more favorable position Plus, there are +SST anomalies in the west-based ENSO regions, which could lead forcing to migrate east a bit into a more favorable location to help out with better EPO ridging to begin with. 

 

Based on the wavelengths and current regime, I would actually favor a cold December. But perhaps in January when the wavelengths begin to shorten again, the east could be quite mild given the +AO and potential EPO ridging being too far west because of the shorter wavelengths. 

 

February would be a bit more uncertain...but maybe some weak +ENSO effects could set in, hopefully leading to blocking at some point along with a split flow and hopefully a continued -EPO regime...perhaps this favors a cold month. 

 

Long-range forecasting is not my forte, but those are my leanings. 

 

Hey Doug,

 

To be clear I did not portray any December forecast in this thread, I was just defending the claims that tropical forcing in any given region leads to different pattern results in November than it does in December, due to different wavelengths. I think the phase composites for each month capture this variation

[HM]

Perhaps I'm a bit misguided with this, but how much different are the wavelengths in mid and late November vs December, anyway? The wavelengths are a tad longer in December, so even if the forcing is a tad too far west, perhaps larger wavelengths would help any subsequent ridging "move" eastward a bit into a more favorable position Plus, there are +SST anomalies in the west-based ENSO regions, which could lead forcing to migrate east a bit into a more favorable location to help out with better EPO ridging to begin with.

Based on the wavelengths and current regime, I would actually favor a cold December. But perhaps in January when the wavelengths begin to shorten again, the east could be quite mild given the +AO and potential EPO ridging being too far west because of the shorter wavelengths.

February would be a bit more uncertain...but maybe some weak +ENSO effects could set in, hopefully leading to blocking at some point along with a split flow and hopefully a continued -EPO regime...perhaps this favors a cold month.

Long-range forecasting is not my forte, but those are my leanings.

MJO waves are not just influenced by SST. As for planetary waves, they are significantly more equatorward next month and are at their longest in Jan. They do not shorten in the dead of winter.

[HM]

Most outlets are changing December calls to cold, that's 1/3rd of the winter.... So this is relevant to the OP.

The OPs were flawed. It's not necessarily his fault either. Sometimes you have to dig deeper into the CDC tool he used. If Dec ends up cold, it wasn't for this reasoning.

[WEATHER53]

Most outlets are changing December calls to cold, that's 1/3rd of the winter.... So this is relevant to the OP.

Some of the scrambling is simply folly.

[Jonger]

Most outlets are changing December calls to cold, that's 1/3rd of the winter.... So this is relevant to the OP.

Some of the scrambling is simply folly.

I respect people who put effort into seasonal forecasting, but man is it dangerous.... The best met on earth can only nail it 55% of the time in a neutral ENSO year. 1997-1998 should have been the only slam dunk winter I can remember.

[WEATHER53]

I respect people who put effort into seasonal forecasting, but man is it dangerous.... The best met on earth can only nail it 55% of the time in a neutral ENSO year. 1997-1998 should have been the only slam dunk winter I can remember.

It's one reason to do a long range forecast in the long range.

[uncle W]

don't count the chickens before they hatch...On December 31st the the verdict comes in...that goes for the ao also...Nothing is set in stone...maybe wet cement for our neutral enso...latest weekly 3.4 oni was +0.1...there is a chance DJF oni won't be in the negative...

[The_Global_Warmer]

don't count the chickens before they hatch...On December 31st the the verdict comes in...that goes for the ao also...Nothing is set in stone...maybe wet cement for our neutral enso...latest weekly 3.4 oni was +0.1...there is a chance DJF oni won't be in the negative...

 

I think the AO is set in stone.  The OPI is predicting a 1.64 AO+.  Which is quite ridiculously high.  Now the GFS ensembles are showing around a 2-3SD AO+ at the start of December.  We know pattern changes are typicallty modeled to fast. 

 

I don't know about your neck of the woods.  But during the record AO+ in the 88-89 season we had 24" which is 5" above normal.  Which is pretty interesting.  I believe we also went down to -20F as well(all time record low) in December of that year.

 

 

 

 

This is years with a AO+ of 1.5 or more for the DJF period.  Interestingly they both featured a large HP over the GOA.  But also a trough over the West coast.  This goes back to 1948.  So it looks like it has only happened twice.

 

 

Here is the AO+ of 1.0 or higher years.  Much more muted SE ridge. 

As far as the ONI.  I totally agree. Sub-surface OHC is way above 12 month highs.  We can see the sub-surface warmth making it's way to the surface between 120-140W.

 

TAO is a bit cooler which is probably more reaslistic than the CPC charts.  As far as winds or trends I certainly cannot talk about them. 

 

 

[Jonger]

don't count the chickens before they hatch...On December 31st the the verdict comes in...that goes for the ao also...Nothing is set in stone...maybe wet cement for our neutral enso...latest weekly 3.4 oni was +0.1...there is a chance DJF oni won't be in the negative...

 

I think the AO is set in stone.  The OPI is predicting a 1.64 AO+.  Which is quite ridiculously high.  Now the GFS ensembles are showing around a 2-3SD AO+ at the start of December.  We know pattern changes are typicallty modeled to fast. 

 

I don't know about your neck of the woods.  But during the record AO+ in the 88-89 season we had 24" which is 5" above normal.  Which is pretty interesting.  I believe we also went down to -20F as well(all time record low) in December of that year.

 

 

 

 

This is years with a AO+ of 1.5 or more for the DJF period.  Interestingly they both featured a large HP over the GOA.  But also a trough over the West coast.  This goes back to 1948.  So it looks like it has only happened twice.

 

 

Here is the AO+ of 1.0 or higher years.  Much more muted SE ridge. 

As far as the ONI.  I totally agree. Sub-surface OHC is way above 12 month highs.  We can see the sub-surface warmth making it's way to the surface between 120-140W.

 

TAO is a bit cooler which is probably more reaslistic than the CPC charts.  As far as winds or trends I certainly cannot talk about them. 

 

 

How can the AO be set in stone?.... Its switches between positive and negative almost weekly, all year.

[Stebo]

How can the AO be set in stone?.... Its switches between positive and negative almost weekly, all year.

It isn't set in stone, it should very well average positive for the winter, but it shouldn't remain positive all winter. That would be unheard of.

[SnowGoose69]

It isn't set in stone, it should very well average positive for the winter, but it shouldn't remain positive all winter. That would be unheard of.

 

As well all know the NAO/AO can be heavily overrated anyway, with a poor Pacific they don't matter all that much and with a good Pacific they can not matter much as well, although odds are they will help make your pattern better if the Pacific is good and make it even worse when its bad.

[Isotherm]

As well all know the NAO/AO can be heavily overrated anyway, with a poor Pacific they don't matter all that much and with a good Pacific they can not matter much as well, although odds are they will help make your pattern better if the Pacific is good and make it even worse when its bad.

 

 

Strongly agree. I find it interesting that we're having the second consecutive December where the AO is liable to NOT produce the traditional pattern in the CONUS. The negative AO last December was masked by the strong AK vortex/+EPO and the likely positive AO this December might be masked by the AK ridge/-EPO signal.

 

I don't like the phrase "set in stone" with long range forecasting as that displays too much confidence. But the correlations dictate that yes, most likely, the AO will be positive this winter. However I don't think guarantees should be made about anything that far out.

[Stebo]

As well all know the NAO/AO can be heavily overrated anyway, with a poor Pacific they don't matter all that much and with a good Pacific they can not matter much as well, although odds are they will help make your pattern better if the Pacific is good and make it even worse when its bad.

Oh I completely agree, if the Pacific isn't assisting in the pattern you could end up in trouble, especially if you are west of the Appalachians.

[tacoman25]

Oh I completely agree, if the Pacific isn't assisting in the pattern you could end up in trouble, especially if you are west of the Appalachians.

 

And vice versa.

[The_Global_Warmer]

I think it's pretty obvious set it stone is in reference to the fact that it will be positive in gerneral for the DJF period.  No one ever said it wouldn't be negative at times.  No one has said people wont get snow.  No one has said the winter won't be cold.

 

The poster I replied to made a comment about the AO.  My response was about the AO and the OPI predictive index.  Nothing else.  I posted the analogs because our recent pattern and upcoming pattern this week as the AO goes back way positive looks a whole lot like those two years with the highest AO's.  I have no idea if a super AO+ goes hand in hand with a GOA HP. 

 

Jonger is trolling.  If you can't see that then you guys just want to hate me or let it go and let him keep crapping on the discussion because he constantly along with a hand-full of others for whatever reason can not emotionally handle this topic so they sabotage it.  Jonger impying I tried to say the AO would be positive all winter is total crap and completely disengenous.   My post was well laid out and obvious to everyone.  All of you.  My point as backed with medium to long range weather models talking about the AO being highly positive at the start of December.  I included the OPI graph to illustrate the incredible accuracy of the OPI.  Then I broke out the analogs based on the AO for the DJF period for 1.0 and 1.5+ which is the likely range for this winters AO.  Then to throw a cherry on top I made my second point totally agreeing with the person I replied to.  Jonger ignored that because it was a snow friendly talking point.  Then instead of over stepping myself I admit I have zero idea where ENSO will be headed because I have zero knowledge of predicting it.  Everybody in this thread loves snow.  I really don't know why.  I do nothing with it except enjoy tracking winter events.  Of course when you make excuses to go outside and shovel the driveway 3 or 4 times during a 6 inch snow event just to be immersed in the winter wonderland.  Or from 5 days out you get 2-3 hours of sleep per night.  You wake up 3 hours into sleep wide awake and have to check the 06Z model runs.  When your at work or home you get nothing done. You show up for the NAM at 7:51 Central waiting for those first six hours to show up.  You always open the previous run to compare images.  You flip back 10 times wondering if that 25 mile shift is real or if your hoping to much.  The model comes out to slow.  So you try to do something else for 10, 20 minutes so when you come back you have another six panels to check out.  You won't read the message forum incase someone spoils it for you.  If your favorite site is slower than others you will try so hard to not look ahead and stick with the graphics you like the best. 

 

When the storm is in the 24-36 hour range.  It can get hard.  The NAM will be out to that by 8:20am or so.  The RAP isn't in range.  So you then have to wait for the RGEM.  Which won't be out for another 45 min.  Once you are done with the RGEM.  You feel dissapointment because the next model out is the GFS which sucks and is worthless.  But you cant help but check it.  If you have source the UKmet is out around that time as well.  After that another big lull takes place until the GGEM comes out.  In the meantime you can pick up the GFSENS.  Then the longer wait for the EURO comes. While you wait or that you will get the 4KM NAM, ARW, NMM.  If you are really desperate for more model info you can look at the FIM and JMA.  If you get free time you can do real time OBS comparisons to the models and you read the forums.  Then you likely have only free Euro so you look at that while following the folks who post real time updates of what the King says. 

 

So after 4 hours of model digestion.  You have like 30-45 mins to take a break before the18z NAM is running.  The 18z model watch is much lighter.  Nam, GFS, GFSENS, 12z EUROEnsemble, 18z ukmet, 18z RGEM, 18z DGEX(if needed).  However by then the AFDs are in so you read yours and probably all of the ones near you like 4-5.  If there is still quite a bit uncertainty you may read ones even further away since they may have important info for you. 

 

It's never enough.  Expecially when the odds become very high by day 3-4 that you will get a moderate to strong event.  You feel more and more excited all day. 

 

When the day finally comes.  It's constant radar watching, every little thing can give you hope or fear.  It feels at times that the snow will never start that everyone around you is getting snow and you aren't.  Like you wil get 2-3 inches less because it started later or there is dry air. 

The worst is when a band of snow sets up just North or South of you and doesn't move.

 

I am tired and don't feel like explaining that I suffer from the snow addiction too any further.  I am just not obssesive about it like a child.  It does not compel me to go to great lengths to create an altered reality because the thought that the up coming winter will be one of the crappy ones is to much to bear.  So I don't drop into every legit discussion on a message forum that isn't pro cold and snowy winter and try to wreck it and discredit the people talking about it.  It obvoiosly does not cause me to go to the climate change forum even though I have no interest in CC so I can ruin the discussion because some how the idea of the Earth warming threatens my snow.  I don't write 1200 worthless posts there about nothing.  I don't run to every thread discussing the up coming winter and troll them if the disscussion doesn't fit my idea that every winter will be very cold and above average snow.

 

And yet I clearly get just as excited as everyone else.  You can't make up my description above.  But it's far more important to me to uphold Scientific integrity before my desire for snow. 

 

 

 

 

I rather enjoy these conversations because it's when I learn the most about the weather side of the Earths atmospheric system vs the climate side.  I have openly admitted that I am rooting for the OPI to nail it because it will be a major advancement in long range forecasting. 

 

 

Mutiple people well lots of people have predicted teh DJF AO being slightly positive, nuetral, or even negative. 

 

I believe if you read through these links you will see how legit this OPI is.

 

Perhaps some of you don't know what this even is. And myself just learnt about it before 3 days.

So here is some read(unfortunately it is in Italian so you will have to use a translator whatever that implies):

 

http://www.meteogiul...-invernale.html

http://forum.meteone...-paper-opi.html

http://www.centromet...hp?topic=7356.0

http://www.centromet...?topic=7364.msg

http://forum.meteone...tern-index.html

 

The original link with the complete researce paper(which is 28 pages and it is also in Italian) was available for downloading but now it isn't. The reason if i understood correctly from the crappy google translation, is that the 3 authors will publish their research to a scientific journal and in order to do so, a free available copy is forbidden to exist.

 

 

 

[Harry]

Strongly agree. I find it interesting that we're having the second consecutive December where the AO is liable to NOT produce the traditional pattern in the CONUS. The negative AO last December was masked by the strong AK vortex/+EPO and the likely positive AO this December might be masked by the AK ridge/-EPO signal.

 

I don't like the phrase "set in stone" with long range forecasting as that displays too much confidence. But the correlations dictate that yes, most likely, the AO will be positive this winter. However I don't think guarantees should be made about anything that far out.

 

 

More often then not the -AO is not good for my backyard unless you like cold and or more importantly DRY. So yeah i'll pass on it.

[Alessandro]

Hello guys. First of all, forgive me the language .. I do not speak well English. My name is Alessandro and I am the co-author of the research OPI together with Riccardo .

I want to compliment you for the wonderful topic and specify only a concept about the difference between OPI and SAI .

OPI essentially measure the position and degree of intrusiveness of the planetary waves in the month of October by two parameters:

1) degree of ellitticizzazione / elongation

2) axis of vp

When we have a very tilted axis ( iceland -east Siberia / Aleutine ) and a vp stretched in October, like 2005/2006, a part of the rate of snow cover can not be measured as the snowfall occurring in the sea under the 60th parallel. In these cases the SAI approximates very well unless the AO . For this reason it is important to measure the position and the intrusiveness of the planetary waves rather than the snow which is nothing other than a consequence of the pattern of October.

Soon we'll end the English translation and will submit to the competent authorities in the USA .

 

Best regards ;

Alessandro

[uncle W]

It isn't set in stone, it should very well average positive for the winter, but it shouldn't remain positive all winter. That would be unheard of.

1988-89 had only two days when the AO was in the negative side (barely) from from late November to April...

[The_Global_Warmer]

 

Hello guys. First of all, forgive me the language .. I do not speak well English. My name is Alessandro and I am the co-author of the research OPI together with Riccardo .

I want to compliment you for the wonderful topic and specify only a concept about the difference between OPI and SAI .

OPI essentially measure the position and degree of intrusiveness of the planetary waves in the month of October by two parameters:

1) degree of ellitticizzazione / elongation

2) axis of vp

When we have a very tilted axis ( iceland -east Siberia / Aleutine ) and a vp stretched in October, like 2005/2006, a part of the rate of snow cover can not be measured as the snowfall occurring in the sea under the 60th parallel. In these cases the SAI approximates very well unless the AO . For this reason it is important to measure the position and the intrusiveness of the planetary waves rather than the snow which is nothing other than a consequence of the pattern of October.

Soon we'll end the English translation and will submit to the competent authorities in the USA .

 

Best regards ;

Alessandro

 

 

 

Thanks for the post and the good work.

 

Do you guys have any ideas on why from 2000 on the OPI has been at an incredible 97% correlation?  That is almost perfect every year. 

[Alessandro]

Thanks for the post and the good work.

 

Do you guys have any ideas on why from 2000 on the OPI has been at an incredible 97% correlation?  That is almost perfect every year. 

Thanks for the compliments .

I have an idea about this..but I do not know if it is shared by Riccardo .

I think that the very high correlation of recent years has depended on the following reason:

when we have a long series of winters in AO - , like 2000-1012 except for a few years, we are able to approximate the value of the AO much better because we have both the elongation factor that the inclination of the axis of vp / position of the planetary waves  ( that is synthesized in a further numerical factor by a trigonometric function ) .

But when, as in the 90's , we have a predominance of years in AO + , loses importance both the component relative to elongation (anomaly 500MB ) but above all the component relative to the axis of vp (for a concentric polar vortex  does not have sense to speak of axis).For this reason the correlation decreases while remaining very high.

However , while considering that the correlation between OPI and AO is very important , what we are really proud  is that we have found a close correspondence between the pattern of October and pattern of the winter  and the possibility ( these hypothesis will be developed in other research ) to identify subseasonal variations of the winter pattern.

The forecast for winter 2013/2014 that we made, it based on these hypothesis : it tries to predict not only the  pattern of average winter , but also the subseasonal variations.

[The_Global_Warmer]

I completely agree with what you guys are trying to accomplish. And have accomplished so far.

I believe your work will help take our current weather model limits way beyond once we can start getting subseasonal variations as accurate as the OPI currently is.

That can be a template for the weather model to eliminate solutions say 15 days out that don't fit say the predictive pressure patterns.

While its part coincidence. The Models keep showing a stronger AO during the first 1/3rd of December.

I am not surprised one way or another come Feb 28th the AO will be almost surely above 1.0 and likely right around the 1.5 mark.

I think this knowledge can be used now. If December is a 2.5-3 AO+. We know over the next 60 days(jan-feb) the AO will be closer to 0.0 to reach the 1.5 the OPI is showing.

We can't predict the variation but we can use the process of elimination to increase our medium range forecast because of the OPI being so accurate.

It also appears extreme ENSO events can play a role in the OPI being off.

Do you guys agree? And If so have you thought of anyways to correct for this?

[Alessandro]

I completely agree with what you guys are trying to accomplish. And have accomplished so far.

I believe your work will help take our current weather model limits way beyond once we can start getting subseasonal variations as accurate as the OPI currently is.

That can be a template for the weather model to eliminate solutions say 15 days out that don't fit say the predictive pressure patterns.

While its part coincidence. The Models keep showing a stronger AO during the first 1/3rd of December.

I am not surprised one way or another come Feb 28th the AO will be almost surely above 1.0 and likely right around the 1.5 mark.

I think this knowledge can be used now. If December is a 2.5-3 AO+. We know over the next 60 days(jan-feb) the AO will be closer to 0.0 to reach the 1.5 the OPI is showing.

We can't predict the variation but we can use the process of elimination to increase our medium range forecast because of the OPI being so accurate.

It also appears extreme ENSO events can play a role in the OPI being off.

Do you guys agree? And If so have you thought of anyways to correct for this?

The identification of subseasonal variations is a argument  that I can not treat because  we are still studying and  we must develop it before speaking. 

However, it would not be a statistical fact..as well as it would not be a statistical fact the correspondence between the pattern of October and winter pattern.

We, although engineers, we do not have sufficient knowledge in the physical of the atmosphere to explain  rigorously a similar correspondence. However, and you can read it in the research, we hypothesized that this feedback mechanism involving the Brewer-Dobson Circulation...but I can not anticipate more...except that, for the reasons placed at the base of the possible explanation, the great events of nino(ENSO in general like 82 and 98) may invalidate the feedback mechanism. In fact 82( also the QBO changes sign in october/november) e  98 are the only years anticorrelati with OPI. Therefore, I agree with you..and there is no way to eliminate the "error", but only the awareness of not having to use the OPI in those cases. 

[donsutherland1]

 

Hello guys. First of all, forgive me the language .. I do not speak well English. My name is Alessandro and I am the co-author of the research OPI together with Riccardo .

I want to compliment you for the wonderful topic and specify only a concept about the difference between OPI and SAI .

OPI essentially measure the position and degree of intrusiveness of the planetary waves in the month of October by two parameters:

1) degree of ellitticizzazione / elongation

2) axis of vp

When we have a very tilted axis ( iceland -east Siberia / Aleutine ) and a vp stretched in October, like 2005/2006, a part of the rate of snow cover can not be measured as the snowfall occurring in the sea under the 60th parallel. In these cases the SAI approximates very well unless the AO . For this reason it is important to measure the position and the intrusiveness of the planetary waves rather than the snow which is nothing other than a consequence of the pattern of October.

Soon we'll end the English translation and will submit to the competent authorities in the USA .

 

Best regards ;

Alessandro

 

Welcome to AmericanWx, Alessandro. I wish Ricardo and you all the best with your research Hopefully, the paper will be accepted and published in the not too distant future. Your work certainly seems very promising.

[Lorenzo]

Absolutely echo the above, thanks for the update and a little more insight into the telemappa software.  Your comments re: mapping planetary waves influence on the core vortex and considering the BDC may go some way to alleviating those more sceptical prior to that publication.

 

Best of Luck !

[wxhstn74]

Josh,

 

It's an interesting outlook. One thing confused me, though. Deedler wrote:

 

Best below normal chances would be at Detroit but that's only because of the inflated heat island norms.

 

The norms are from the 1981-2010 base period. They are the product of all temperatures that occurred during that timeframe, all of which were recorded in the heat island environment. If that's the case, then why wouldn't the 2013-14 temperatures also be affected by the same heat island effect?

 

Was the station at which Detroit's temperatures are presently recorded moved from where they were recorded during the 1981-2010 base period?

 

Detroit temps have been at present-day location (DTW) since 1966. From 1874-March 1966 they were at various locations in Detroit (first downtown then City Airport, DET) then from April 1966 to present they have been at Detroit Metro Airport (DTW) in suburban Romulus (approx 20 miles SW of downtown Detroit and 25 miles SW of City Airport). From the 1960s to at least the early 1980s, the place was a radiating magnet, often one of the lowest low temps in the area. While its still a somewhat rural area, the concrete/runways and general buildup of the area has caused definite UHI at the airport so that nowadays, on a great radiating night DTW is on the higher end of low temps in the area, often the highest, a complete reversal from the 1960s-70s. Obviously, this has been reflected in the most recent 1981-2010 norms.

 

You pose a good question, and my GUESS would be that Deedler was implying that UHI is less defined in a true arctic airmass. For instance, DTW got down to -15F in Jan 2009, and -20F in Jan 1994....when an arctic airmass packs that much punch, UHI is more of a nonfactor. In your more "typical" winter coldblast, the outlying areas may come up in the -5F to 0F range while DTW will be, say, 2F to 5F. So if indeed its a very cold winter, UHI wont be as much of a factor. Detroits present 30-yr average temp is 27.9F, but the 100-yr average is 26.7F, the difference almost entirely made up of low temps rather than high temps.

-------------------------------

Hi Josh & donsutherland1

 

I saw your disc about my outlook and reply about confusion about larger departures below norm likely at DTW. Looking at the new norms for the region, I feel DTW's norms have warmed enough to cause a bigger departure in the case of below normal temperatures than FNT or MBS.

 

You are right when you say "wouldn't the temperatures this winter be affected by the same heat island" Yes, somewhat but not to the extent to negate the larger departures because of the new normals. I don't have to type about it...I can show you with November's departures thus far (they prove it)...and already a big difference when looking at DTW against FNT or MBS because of the warmer norms @ DTW. You will see that even though all three cities jive fairly close in temps, it's the departs (because of new norms) that screws it up and thus "Detroit has the best chance to have the largest departures below normal when colder". This will be most apparent on good CAA days with wind when temps are fairly uniform at night too.

 

As of 11/26 these are the temps/departs from all three cities...( note big dif in depart data even though ave temps close).

 

DTW

AVERAGE MONTHLY: 39.1   DPTR FM NORMAL:  -3.3

FNT

AVERAGE MONTHLY: 38.8   DPTR FM NORMAL:  -1.0 

MBS

AVERAGE MONTHLY: 38.5   DPTR FM NORMAL:  -0.9 

Bill Deedler

[famartin]

You pose a good question, and my GUESS would be that Deedler was implying that UHI is less defined in a true arctic airmass. For instance, DTW got down to -15F in Jan 2009, and -20F in Jan 1994....when an arctic airmass packs that much punch, UHI is more of a nonfactor. In your more "typical" winter coldblast, the outlying areas may come up in the -5F to 0F range while DTW will be, say, 2F to 5F. So if indeed its a very cold winter, UHI wont be as much of a factor. Detroits present 30-yr average temp is 27.9F, but the 100-yr average is 26.7F, the difference almost entirely made up of low temps rather than high temps.

 

I am not as familiar with weather in Michigan as I'd like to be before making this post, but I know in other places, the key to defeating the UHI is wind.  Keep a steady wind blowing and it will be like the UHI isn't even there.  During 1994 the wind was 10 knots or higher pretty much the entire night. 

http://www.wunderground.com/history/airport/KDTW/1994/1/19/DailyHistory.html

 

It was not quite as strong in 2009 but it certainly never went calm.  Calm nights, with the high pressure nearby, would be when you are most likely to see the UHI show itself, at least in my experience elsewhere in the country.

[Jonger]

I am not as familiar with weather in Michigan as I'd like to be before making this post, but I know in other places, the key to defeating the UHI is wind.  Keep a steady wind blowing and it will be like the UHI isn't even there.  During 1994 the wind was 10 knots or higher pretty much the entire night. 

http://www.wunderground.com/history/airport/KDTW/1994/1/19/DailyHistory.html

 

It was not quite as strong in 2009 but it certainly never went calm.  Calm nights, with the high pressure nearby, would be when you are most likely to see the UHI show itself, at least in my experience elsewhere in the country.

 

That was the coldest day of my life.

[donsutherland1]

Detroit temps have been at present-day location (DTW) since 1966. From 1874-March 1966 they were at various locations in Detroit (first downtown then City Airport, DET) then from April 1966 to present they have been at Detroit Metro Airport (DTW) in suburban Romulus (approx 20 miles SW of downtown Detroit and 25 miles SW of City Airport). From the 1960s to at least the early 1980s, the place was a radiating magnet, often one of the lowest low temps in the area. While its still a somewhat rural area, the concrete/runways and general buildup of the area has caused definite UHI at the airport so that nowadays, on a great radiating night DTW is on the higher end of low temps in the area, often the highest, a complete reversal from the 1960s-70s. Obviously, this has been reflected in the most recent 1981-2010 norms.

 

You pose a good question, and my GUESS would be that Deedler was implying that UHI is less defined in a true arctic airmass. For instance, DTW got down to -15F in Jan 2009, and -20F in Jan 1994....when an arctic airmass packs that much punch, UHI is more of a nonfactor. In your more "typical" winter coldblast, the outlying areas may come up in the -5F to 0F range while DTW will be, say, 2F to 5F. So if indeed its a very cold winter, UHI wont be as much of a factor. Detroits present 30-yr average temp is 27.9F, but the 100-yr average is 26.7F, the difference almost entirely made up of low temps rather than high temps.

-------------------------------

Hi Josh & donsutherland1

 

I saw your disc about my outlook and reply about confusion about larger departures below norm likely at DTW. Looking at the new norms for the region, I feel DTW's norms have warmed enough to cause a bigger departure in the case of below normal temperatures than FNT or MBS.

 

You are right when you say "wouldn't the temperatures this winter be affected by the same heat island" Yes, somewhat but not to the extent to negate the larger departures because of the new normals. I don't have to type about it...I can show you with November's departures thus far (they prove it)...and already a big difference when looking at DTW against FNT or MBS because of the warmer norms @ DTW. You will see that even though all three cities jive fairly close in temps, it's the departs (because of new norms) that screws it up and thus "Detroit has the best chance to have the largest departures below normal when colder". This will be most apparent on good CAA days with wind when temps are fairly uniform at night too.

 

As of 11/26 these are the temps/departs from all three cities...( note big dif in depart data even though ave temps close).

 

DTW

AVERAGE MONTHLY: 39.1   DPTR FM NORMAL:  -3.3

FNT

AVERAGE MONTHLY: 38.8   DPTR FM NORMAL:  -1.0 

MBS

AVERAGE MONTHLY: 38.5   DPTR FM NORMAL:  -0.9 

Bill Deedler

Thanks for your response, Bill. I greatly appreciate it and now understand what you were writing.

 

Very best wishes.

[tacoman25]

Any question now as to what is more important for CONUS cold, the AO or EPO?