Texas/New Mexico/Louisiana/Mexico Obs And Discussion Thread Part 6

[bubba hotep]

It seems odd to me for the upper trough to dig into the middle of the huge west coast ridge.

Look out over the Pacific

[Srain]

Folks along the Middle/Upper Texas Gulf Coast extending E into SW/Central and SE Coastal Louisiana will need to monitor for the potential of some stronger storms just offshore and possibly just inland tomorrow as the next storm system approaches.

 

 

[Srain]

Afternoon briefing from Jeff:

 

Next storm system heading for TX over the next 36 hours.

 

Arctic cold front likely middle of next week.

 

Moisture advection is underway across SE TX this morning with light rain and drizzle covering much of the area. Marine front offshore is attempting to lift toward the coast and may push slightly inland this evening. Cold front extends from KS to WC TX and will slowly move eastward over the next 24 hours helping to bring SE TX a round of showers and thunderstorms. Expect light rain and drizzle to continue much of the day and into the overnight hours. Lift increases ahead of the cold front on Saturday helping to promote heavier showers and thunderstorms. Warm sector air mass may attempt to push inland early Saturday, but this remains only slightly likely with the best potential for any warm sector strong to severe convection being right near the coast and offshore. Most of the area will see mainly showers and a few thunderstorms. Front should reach the coast by early evening with some potential for post frontal rains to continue into Sunday as upper level flow remains out of the SW pushing moisture over the top of the surface cold dome. Sunday will be cloudy with periods of rain and temperatures likely remaining in the 40’s with N winds.

 

Next Week (Arctic Intrusion):

Monday will likely be the best day of the next week as clouds clear allowing some sun and a modest warm up into the lower 60’s from a cold and cloudy Sunday. However this will be short lived as significant upper air jet stream amplification pumps strong ridging deep into Alaska dislodging a large arctic high pressure cell out of NW Canada. Various global model solutions are all in agreement with the upper air pattern which is favorable for arctic air masses to move southward into TX. Agreement is also that the arctic surface high pressure cell will be on the order of a 1050-1060mb pressure at the surface and enter the US through Montana early next week. Simply stated that is a mighty strong arctic high pressure cell that will dam against the Rocky Mountains and funnel its cold air southward rapidly down the front range.

 

The problems lie within the model guidance output of temperature forecast post arctic front next week. It is well known that global models handle shallow dense arctic air masses poorly especially those that dam against the front range of the Rocky Mountains. Models tend to be too slow and too weak with the air mass especially in this time frame and once the dense cold air is on the move try and grasp what is happening and have significant temperature decreases in the 72-48 hour time period. Forecasters and media output of raw model guidance are significantly too warm for the Wednesday-Friday period of next week given the gravity of the high pressure being forecast, which is actually in good model agreement. For example the GFS model is forecasting a high of 49 next Thursday (1/1) for IAH. I would easily undercut this by 10 degrees and maybe more. Experience tells us that these shallow dense arctic air masses will arrive faster and colder than model guidance. With that said, will show the arctic front through the area and off the coast by Tuesday evening with strong cold air advection following. Will undercut guidance by at least 5 degrees and that is likely not enough from Wednesday through Friday with lows in the 30’s (possibly upper 20’s) and highs in the upper 30’s to low 40’s. Again these numbers may need to be lowered more in the coming days and highs on New Year’s Day may struggle to reach the mid 30’s.

 

Arctic fronts are notorious for being shallow in nature (usually only a few thousand feet deep) which typically makes for a very cold surface layer which is then overrun by warm air in the mid levels. This creates an overrunning situation not all that different from today or what is expected on Sunday, but with significantly colder surface temperatures. This pattern tends to support lots of thick clouds and at times precipitation in the arctic air mass. Additionally, it can help keep the cold air locked in place longer and slow air mass modification. Global forecast models are struggling with how to handle the base of the longwave trough which digs deep into the SW US toward the middle and end of next week. A few days ago models were ejecting this system into the arctic air mass over TX on New Year’s Eve and New Year’s Day, but they now delay that until the 2^nd and 3^rd of Jan. giving the shallow arctic air mass a bit of time to moderate. This appears to cut back on the potential for a winter storm across TX on New Year’s Eve and Day at the moment if the models are correct on the timing of this upper air system…delaying it. There is a lot of uncertainty in this part of the forecast (31^st -3^rd) with respect to the modification of the arctic cold dome and when any upper level system will cross the state. The pattern thus far has been very progressive, so I am not sure the slowing and cutting off of the upper system over the SW US is in fact correct. Likely something in the middle will be what actually transpires and then the question becomes how much if any has the downstream arctic air mass over TX warmed.  

 

[aggiegeog]

That matches my thoughts. We will see the cold setting in by Tuesday afternoon and by Wednesday and especially Thursday we will see the SW trough getting near enough to produce overrunning precip. With this timing we will stay plenty cold enough for frozen precip down into SE TX and especially areas further north.

[bubba hotep]

Very well could be...

 

12262014 12Z P GFS gfs_namer_360_500_vort_ht.gif

 

12262014 12Z P GFS gfs_namer_360_10m_wnd_precip.gif

Down here for the Holidays and certainly looking forward to it.  From the New Orleans AFD 

AFTER EVERYTHING IS SAID AND DONE THERE IS THE POTENTIAL FOR

WIDESPREAD 3-5 INCHES OF RAIN WITH LOCALLY HIGHER AMOUNTS POSSIBLY

RANGING FROM 6 TO AS MUCH AS 10 INCHES.

[vwgrrc]

That matches my thoughts. We will see the cold setting in by Tuesday afternoon and by Wednesday and especially Thursday we will see the SW trough getting near enough to produce overrunning precip. With this timing we will stay plenty cold enough for frozen precip down into SE TX and especially areas further north.

Looks like our main precip period will be Thursday and Friday. But with less than 7days reminds, it's still kinda of hard to believe we'll be cold enough for frozen precip, even for N TX. Actually I would say just above freezing for dfw on Thursday and warmer on Friday... 

[vwgrrc]

Well~ The next blast looks even stronger?

[aggiegeog]

A chance of light accumulations of snow this weekend across North Texas then a better chance for frozen precip Tuesday through Friday. There will be plenty more chances this month if you don't get it this time around though I expect many will get some this week especially in the northern half of Texas.

[DFWWeather]

I'm beginning to seriously question the projected magnitude of the Arctic high pressure cell being ejected into the CONUS this week. Models have consistently been showing an Arctic high on the order of 1055 to 1060 mb, when in reality I think it is going to be closer to 1046 to 1052 mb. The reason I say this is both H85 temps and 2m temps look much too warm for a 1060mb high. If this were true, given the pattern, temps at DFW would be a good 10 degrees colder than what is being forecasted by the NWS. We would typically see lows in the teens with highs struggling to get out of the 20s under such conditions, even with cloud cover. I'm still not buying the impingement of the Arctic air (especially a 1055 mb high) coming down the spine of the Rockies as much as the operational models are showing (though this has already been discussed). So either the high pressure is overdone by the models (no surprise), or the surface temperatures are not cold enough in forecasts (no surprise).

 

WOW the 10 day pattern H5 mean off the Penn State Ewall show a monster southeast ridge overwhelming the pattern over the entire CONUS on all 3 global models. Almost laughable. If CMC is correct, cancel winter altogether along the east coast.

[Srain]

I don't know DFWWeather. Even the very short range meso guidance is throwing out some impressive 1065mb reading in its wheel house range. Also if we look to California across the Sacramento/San Joaquin Valley into Southern Arizona, Freeze and Hard Freeze Warnings are up and this is in the wake of the current storm that is busting right and left and has caused the expansion of Winter Weather Advisories across W/NW and N Central Texas over that past couple of hours.

[bubba hotep]

Down here for the Holidays and certainly looking forward to it.  From the New Orleans AFD 

AFTER EVERYTHING IS SAID AND DONE THERE IS THE POTENTIAL FOR

WIDESPREAD 3-5 INCHES OF RAIN WITH LOCALLY HIGHER AMOUNTS POSSIBLY

RANGING FROM 6 TO AS MUCH AS 10 INCHES.

 

This rain event is under way and water is already rising in the bayou on the back of our property

 

[DFWWeather]

I don't know DFWWeather. Even the very short range meso guidance is throwing out some impressive 1065mb reading in its wheel house range. Also if we look to California across the Sacramento/San Joaquin Valley into Southern Arizona, Freeze and Hard Freeze Warnings are up and this is in the wake of the current storm that is busting right and left and has caused the expansion of Winter Weather Advisories across W/NW and N Central Texas over that past couple of hours.

 

Then the 29 and 39 for New Year's Eve by NWS at DFW is no where near cold enough.

[Srain]

Then the 29 and 39 for New Year's Eve by NWS at DFW is no where near cold enough.

Even down here in Houston the trend since yesterday is the MOS/MEX data is way too warm and they are undercutting the temperatures with each update. There is some 'chatter' down here that the upper 30's/low 40's may be too conservative for highs.

[DFWWeather]

Even down here in Houston the trend since yesterday is the MOS/MEX data is way too warm and they are undercutting the temperatures with each update. There is some 'chatter' down here that the upper 30's/low 40's may be too conservative for highs.

 

I agree with that logic. However at DFW the NWS actually raised temps from before. They originally had 35 for a high on New Year's Eve now 39. (guidance at 43)

 

Latest trend on the operational models (GFS and see this happening on NAM too) is splitting the cold air and sending a good chunk on the other side of the Rockies into the upper low/trough hanging back over the 4 corners. So it is actually getting colder along the west coast. This is bad for Texas as this leaves less cold air sinking into Texas along the spine of the Rockies. Which explains the warmer temps. However, when the upper low moves across in later periods it may be deeper with a good shot a snow next weekend for North Texas, but there will be all kinds of boundary layer issues with that system. So, we may have to consider this.

[Srain]

That upper trough and the cold core upper low has always been the wild card. It is a common modeling error to warm things up too quickly after the cold air is entrenched. NE winds with cloudy skies tends to mean much less moderation. Let's see if the guidance finally latches on to things being a tad more progressive than is currently progged. The theme all year has been a faster flow than some of the guidance suggested even 4 to 5 days out. Example, the current front is about 12 to 18 hours ahead of forecasted schedule.

 

[bubba hotep]

I agree with that logic. However at DFW the NWS actually raised temps from before. They originally had 35 for a high on New Year's Eve now 39. (guidance at 43)

Latest trend on the operational models (GFS and see this happening on NAM too) is splitting the cold air and sending a good chunk on the other side of the Rockies into the upper low/trough hanging back over the 4 corners. So it is actually getting colder along the west coast. This is bad for Texas as this leaves less cold air sinking into Texas along the spine of the Rockies. Which explains the warmer temps. However, when the upper low moves across in later periods it may be deeper with a good shot a snow next weekend for North Texas, but there will be all kinds of boundary layer issues with that system. So, we may have to consider this.

Taken verbatim, the 500mb evolution has been all kinds of fail for N. Texas snow lovers. The cold will either have to way over perform or the cutoff will have to kickout faster.

[aggiegeog]

I have been watching for some snow with the current system in North Texas for a while now and though the models never showed it except a couple short range ones on sporadic runs it is occurring with up to 3 inches already around Wichita Falls. Even now the short range models are still behind so I have trouble believing them that the freezing surface and upper levels will not move at least a bit east and maybe into the DFW area.

[bubba hotep]

That upper trough and the cold core upper low has always been the wild card. It is a common modeling error to warm things up too quickly after the cold air is entrenched. NE winds with cloudy skies tends to mean much less moderation. Let's see if the guidance finally latches on to things being a tad more progressive than is currently progged. The theme all year has been a faster flow than some of the guidance suggested even 4 to 5 days out. Example, the current front is about 12 to 18 hours ahead of forecasted schedule.

12272014 12Z GFS 114 gfs_z500a_nhem_20.png

Totally agree, there is plenty of wiggle room based on past experience. The different area offices are taking a conservative approach and that is totally understandable given what the models are showing.

[DFWWeather]

That upper trough and the cold core upper low has always been the wild card. It is a common modeling error to warm things up too quickly after the cold air is entrenched. NE winds with cloudy skies tends to mean much less moderation. Let's see if the guidance finally latches on to things being a tad more progressive than is currently progged. The theme all year has been a faster flow than some of the guidance suggested even 4 to 5 days out. Example, the current front is about 12 to 18 hours ahead of forecasted schedule.

 

12272014 12Z GFS 114 gfs_z500a_nhem_20.png

 

Hang with me here (agree with what your saying), just trying to justify the models output in my mind. The other thing I'm seeing is the apparent fight of the southeast ridge not allowing the cold air spreading further east quite as deep or readily into the state as in the western areas, that could also help explain the warmer temps further east. I've seen this happen before too.

 

Lows 20 to 25 with highs around freezing, if not a bit colder, seem a bit more reasonable to me right now in the coldest portion of this outbreak for DFW.

[bubba hotep]

Hang with me here (agree with what your saying), just trying to justify the models output in my mind. The other thing I'm seeing is the apparent fight of the southeast ridge not allowing the cold air spreading further east quite as deep or readily into the state as in the western areas, that could also help explain the warmer temps further east. I've seen this happen before too.

Lows 20 to 25 with highs around freezing, if not a bit colder, seem a bit more reasonable to me right now in the coldest portion of this outbreak for DFW.

Yep, as the cutoff sinks into the SW we get increased ridging.

[Srain]

Hang with me here (agree with what your saying), just trying to justify the models output in my mind. The other thing I'm seeing is the apparent fight of the southeast ridge not allowing the cold air spreading further east quite as deep or readily into the state as in the western areas, that could also help explain the warmer temps further east. I've seen this happen before too.

 

Lows 20 to 25 with highs around freezing, if not a bit colder, seem a bit more reasonable to me right now in the coldest portion of this outbreak for DFW.

No problem DFW...I know what you are saying. We have folks in SE Louisiana that are having a difficult time wrapping their head around the idea that they will miss out on this cold air. Typically in these dense shallow Arctic outbreaks, we see Brownsville get the front before Houston. I believe what we have working in our favor including the Metroplex is that the 700mb flow is our of the E versus the typical down sloping we usually see as the Arctic High build into the Plains. The positive tilted upper trough is probably more of a favorable pattern for days of over running. I just do not see us clearing out as we would typically see with a 'blue norther' afer that cold arrives. This has never been a historic Arctic Outbreak as I seen mentioned elsewhere across the web.

[Portastorm]

Yep, as the cutoff sinks into the SW we get increased ridging.

It may be worth throwing out there that one of the known biases of the GFS is pumping the ridge too much ahead of these desert SW lows. And as srainhoutx notes, the flow has been more progressive this season than what the GFS usually shows.

[Srain]

Nice webcam shot via TxDot of Wichita Falls were no snow was forecast and certainly was expecting anything to stick...

 

[3monkeymom]

No problem DFW...I know what you are saying. We have folks in SE Louisiana that are having a difficult time wrapping their head around the idea that they will miss out on this cold air. Typically in these dense shallow Arctic outbreaks, we see Brownsville get the front before Houston. I believe what we have working in our favor including the Metroplex is that the 700mb flow is our of the E versus the typical down sloping we usually see as the Arctic High build into the Plains. The positive tilted upper trough is probably more of a favorable pattern for days of over running. I just do not see us clearing out as we would typically see with a 'blue norther' afer that cold arrives. This has never been a historic Arctic Outbreak as I seen mentioned elsewhere across the web.

I'm in SE Louisiana, and suffice it to say that I'm one of the ones having a difficult time wrapping my head around the medium-range forecasts. (Although I'm very much an amateur.) Any forecast outside of 72 hours looks like a toss-up to me.

[bubba hotep]

It may be worth throwing out there that one of the known biases of the GFS is pumping the ridge too much ahead of these desert SW lows. And as srainhoutx notes, the flow has been more progressive this season than what the GFS usually shows.

 

There is also the lone wolf solution spit out by the 00z Euro that appears to have no support, not even from the Euro EPS.  However, if the energy were to hang back as long as depicted then it allows another window for the cold air to surge in.  It will be interesting to see if the 12z continues that trend or if it trends towards the other models.  

[cheese007]

So I've got plans to drive from McKinney to Austin on the 3rd. With all the uncertainty about if/when the cold/snow arrive should I head down Tuesday instead or wait it out?

[Quixotic1]

I dont see a 1050 mb high eroding as fast as depicted.

[Portastorm]

Scattered sleet in AUS area this morning. Wasn't in guidance last night. If models can't get a cold airmass right less than 24 hours out, how can we trust them for Wed-Thurs with Arctic airmass coming down?! Still believe guidance way too warm but noticed 12z NAM headed in right direction, trending colder.

[bubba hotep]

The 00z guidance was a total torch for the New Years day through the 3rd window when most models have moisture moving through. If guidance is off, then there might be some front end freezing rain in some areas but it looks like temps will slowly rise overnight with strong WAA. The 27th 00z Euro had a good look for winter weather with the 500mb cutoff coming out slower and passing south of DFW but the Euro has trended towards the faster more northerly track of the GFS. It seemed like we needed a much faster or slower ejection and we are getting muddled middle of the road solution.

The EPO looks to stay negative, so we should see cold anomalies continue to build in W. Canada. Just need to get lucky with the timing on one of the cold dumps.

[vwgrrc]

From Steve McCauley in dfw this afternoon:

 

The latest data now starts the precip in the Metroplex a little earlier when we are still very close to freezing, so a wintry mix is looking more possible not just for the western areas of north Texas but for the Metroplex as well. It will turn to all rain Friday.