DCA Seasonal Snowfall, Blocking, and ENSO

[donsutherland1]

The following are some statistics related to the AO, ENSO and Washington DC's seasonal snowfall (1950-51 through 2012-13):

 

[Fozz]

So if the AO averages + for the season, then there's pretty much no chance of a good (20"+) winter. Thanks for the stats.

 

I wonder why the ≤ -0.5 AO is more likely bring have a 30"+ winter than a ≤ -1.0 AO. Is the sample size reliable enough for this difference to matter?

[donsutherland1]

So if the AO averages + for the season, then there's pretty much no chance of a good (20"+) winter. Thanks for the stats.

 

I wonder why the ≤ -0.5 AO is more likely bring have a 30"+ winter than a ≤ -1.0 AO. Is the sample size reliable enough for this difference to matter?

On the first question, you are correct. That's been the case since winter 1950-51.

 

On the second, it might have to do with systems being suppressed to the south.

[ravensrule]

Don is there anyway you can show a chart like that for Baltimore. Thanks in advance.

[Fozz]

Don is there anyway you can show a chart like that for Baltimore. Thanks in advance.

 

I always felt that BWI's snow stats are much more representative of the whole area than DCA's.

[ravensrule]

I always thought BWI's snow stats are much more representative of the whole area than DCA's.

Totally agree.

[WxUSAF]

Don is there anyway you can show a chart like that for Baltimore. Thanks in advance.

The numbers will change, but the message probably won't.  Don posted a similar chart for Philly in their subforum and the message is pretty similar.  We want a -AO/El Nino winter.  

[donsutherland1]

Don is there anyway you can show a chart like that for Baltimore. Thanks in advance.

 

Yes. I'll do that tonight.

[snow.]

The numbers will change, but the message probably won't.  Don posted a similar chart for Philly in their subforum and the message is pretty similar.  We want a -AO/El Nino winter.  

 

 

and there is  tendency toward that...El Ninos have a tendency to have a neutral or negative AO...only 4 ninos since 1950 have had a marked +AO...72, 91, 94, 06....the other 18 were around neutral or negative...so chance are if we get a NINO we will have a neutral or negative AO

[usedtobe]

Don,  good stuff.  I have a Capital Weather Gang piece coming out either today or tomorrow that discusses the PNA and AO and dc snowstorms.  There have been a few AO+  8" or greater storms but no such storms when the AO is positive and the PNA is negative.  I break it down for 4 inch or greater and 8 inch or greater in the piece.  I have a scatter diagram of 20 inch or greater events by AO and ONi. If you want 20 inches of snow you better root for a negative AO. 

 

 

 

[mitchnick]

12/99-2/00 had a pretty positive AO and BWI managed a 14.9" snow storm and received 25.7" during 1-2/00

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/month_ao_index.shtml

there are exceptions to every rule

the only thing we need to know, and pretty much all of us do, is we generally want an El Nino in the MA if we want a decent shot at an above normal snow season, but flukes can and do happen and explain why we don't have single digit snow fall numbers for every non-NINO winter

we'd all be happy with a very near normal snow fall year this year and nobody can predict whether we will or won't with any certainty using any index

[Bob Chill]

I can probably speak for a handful of folks here....we aren't expecting climo+ or a big storm unless things line up for a fluke in an overall notsogreat storm track.

I think the prize would be a couple of 2-4s or 3-6s. That's my bar at least. And I hope my hunch about having some sort of real op each month is right. Keep it fun and interesting with modest expectations.

[mitchnick]

I can probably speak for a handful of folks here....we aren't expecting climo+ or a big storm unless things line up for a fluke in an overall notsogreat storm track.

I think the prize would be a couple of 2-4s or 3-6s. That's my bar at least. And I hope my hunch about having some sort of real op each month is right. Keep it fun and interesting with modest expectations.

I agree

Index lr forecasting has its limitations, most of which no one understands or identifies until after the season....he!!!, even NINOs can suck around here

[snow.]

12/99-2/00 had a pretty positive AO and BWI managed a 14.9" snow storm and received 25.7" during 1-2/00

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/month_ao_index.shtml

there are exceptions to every rule

the only thing we need to know, and pretty much all of us do, is we generally want an El Nino in the MA if we want a decent shot at an above normal snow season, but flukes can and do happen and explain why we don't have single digit snow fall numbers for every non-NINO winter

we'd all be happy with a very near normal snow fall year this year and nobody can predict whether we will or won't with any certainty using any index

 

 

the AO did go briefly negative starting a week before 1/25....the NAO was positive because the block was too far east, but I don't think the Atlantic pattern was necessarily adverse

[Bob Chill]

I agree

Index lr forecasting has its limitations, most of which no one understands or identifies until after the season....he!!!, even NINOs can suck around here

 

The one very clear part of lr forecasting is that it's starkly obvious what enso/teleconnections need to show in order to have high expectations. We don't get big years often for a reason. It requires specific ingredients that don't occur but every 5+ years on average. 

 

I do take some comfort in the fact that it's now mid nov and there is no reason to even remotely think we'll 3peat. If anything, things look better than worse at this point. Just need to have things hold together and continue into Dec. 

[ORH_wxman]

the AO did go briefly negative starting a week before 1/25....the NAO was positive because the block was too far east, but I don't think the Atlantic pattern was necessarily adverse

 

 

It was a pretty good pattern for cold but hostile for a big east coast storm...but the dice came up snake eyes and a big storm was able to thread the needle with a very lucky phase job.

 

The Atlantic had a pretty solid block going on around the time of the storm. I don't have the numbers in front of me, but if the NAO was positive, it was basically a technicality on CPC's part versus a true +NAO pattern. It was indeed an east-based block though.

 

[snow.]

It was a pretty good pattern for cold but hostile for a big east coast storm...but the dice came up snake eyes and a big storm was able to thread the needle with a very lucky phase job.

 

The Atlantic had a pretty solid block going on around the time of the storm. I don't have the numbers in front of me, but if the NAO was positive, it was basically a technicality on CPC's part versus a true +NAO pattern. It was indeed an east-based block though.

 

 

 

I always thought at least in terms of the split flow the pattern was pretty good....

 

[mitchnick]

the AO did go briefly negative starting a week before 1/25....the NAO was positive because the block was too far east, but I don't think the Atlantic pattern was necessarily adverse

that winter clearly qualifies as one ranked as a mod+ AO per this graph

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/monthly.ao.index.b50.current.ascii.table

 

regardless, your statement proves my point that even correctly predicting an index that is normally hostile to us for snow doesn't mean it can't snow because it does

our odds may be lower but like I said above, there have been plenty of NINOs that have kicked us in the nutz

[snow.]

that winter clearly qualifies as one ranked as a mod+ AO per this graph

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/monthly.ao.index.b50.current.ascii.table

 

regardless, your statement proves my point that even correctly predicting an index that is normally hostile to us for snow doesn't mean it can't snow because it does

our odds may be lower but like I said above, there have been plenty of NINOs that have kicked us in the nutz

 

ok?...that doesn't contradict what I said at all...

[ORH_wxman]

I always thought at least in terms of the split flow the pattern was pretty good....

 

 

 

The split flow is probably the only reason the storm happened...so yes, I agree that helped. Everything else was kind of ugly including no 50/50 low at all.

[ravensrule]

Yes. I'll do that tonight.

Thank you very much.

[donsutherland1]

Don,  good stuff.  I have a Capital Weather Gang piece coming out either today or tomorrow that discusses the PNA and AO and dc snowstorms.  There have been a few AO+  8" or greater storms but no such storms when the AO is positive and the PNA is negative.  I break it down for 4 inch or greater and 8 inch or greater in the piece.  I have a scatter diagram of 20 inch or greater events by AO and ONi. If you want 20 inches of snow you better root for a negative AO. 

 

ao_enso_seasonal.png

Thanks for posting this chart, Wes. The scatter diagram is what I would have expected, but I probably spend too much time looking at such data. 1982-83 (Blizzard of '83) is still very "lonely" at the top right of the chart, though February 1983 featured a lot of blocking in a winter with not much blocking.

[donsutherland1]

It was a pretty good pattern for cold but hostile for a big east coast storm...but the dice came up snake eyes and a big storm was able to thread the needle with a very lucky phase job.

 

The Atlantic had a pretty solid block going on around the time of the storm. I don't have the numbers in front of me, but if the NAO was positive, it was basically a technicality on CPC's part versus a true +NAO pattern. It was indeed an east-based block though.

 

Prior to the January 2000 storm, the AO had been negative during the 1/17-1/23 period. The storm occurred during a negative NAO. The NAO was negative during the 1/16-1/27 period).

[snow.]

Prior to the January 2000 storm, the AO had been negative during the 1/17-1/23 period. The storm occurred during a negative NAO. The NAO was negative during the 1/16-1/27 period).

 

you're right of course...I must have looked at the wrong data....

[ORH_wxman]

Prior to the January 2000 storm, the AO had been negative during the 1/17-1/23 period. The storm occurred during a negative NAO. The NAO was negative during the 1/16-1/27 period).

 

 

Thanks for the data, it makes sense looking at the chart. I would have been surprised if that 5H pattern numerically led to a positive NAO, even using CPC's larger domain method.

[snow.]

Thanks for the data, it makes sense looking at the chart. I would have been surprised if that 5H pattern numerically led to a positive NAO, even using CPC's larger domain method.

 

 

which is why I got confused, but just assumed it was because it was east based and the downstream trough was too far east....also knowing that the data doesn't always make sense when looking at the pattern...I was obviously looking at the wrong dates or wrong data

[ORH_wxman]

which is why I got confused, but just assumed it was because it was east based and the downstream trough was too far east....also knowing that the data doesn't always make sense when looking at the pattern...I was obviously looking at the wrong dates or wrong data

 

Yeah sometimes CPC has weird values because their NAO domain goes back into Hudson Bay and up to the north pole region...so if you have a block over iceland or even part of Greenland and there is a huge vortex digging into Hudson Bay and SE Canada, it can show a value more positive than you would expect. That's sometimes where the old SLP method excels in "describing the pattern" over the CPC number....but both have their strengths and weaknesses.