Texas/New Mexico/Louisiana/Mexico Obs And Discussion Thread Part 5

[Ed Lizard]

Euro a smidge too warm, 6Z GFS still shows potential school cancel Friday.

[bubba hotep]

Us up here in the Metroplex need that piece of energy to come onshore stronger and dig deeper before getting sheared out.  The only ray of hope that I see is that the GEFS indicates there is still a lot of uncertainty surrounding the actual strength and track of that shortwave.  

[Srain]

The 12Z GFS suggests a fairly widespread freezing rain and sleet event from Del Rio to Beaumont. Portions of the Edwards Plateau may see some light snow accumulations. If the GFS is correct, freezing rain and sleet may extended to near the Coastal Counties from Corpus Christi to near Galveston.

[Srain]

Afternoon Update from Meteorologist Jeff L (Harris County Flood Control District):

 

Powerful arctic cold front will arrive after mid week with some potential for wintery precipitation.

 

It does not get much better than this in mid-January…current afternoon temperatures at 300pm range from 80 at Victoria to 76 at BUSH IAH and 79 at Brenham. As is usually the case when it gets this warm in January cold air is not far behind and this week will be no different.

 

Upper air pattern is currently undergoing amplification along the US west coast with large scale ridging building into Alaska and the downstream trough located over the Midwest into NE US. A shot of cold air will pass across the region tonight into Tuesday with highs on Tuesday running 15-20 degrees colder than today (55-60) versus (75-80). Will see gusty NW winds on Tuesday along with lower RH so fire danger will be elevated. Cold Wednesday morning with lows in the upper 20’s and lower 30’s across the region rebounding into the mid 60’s by afternoon with SSW winds.

 

Thursday-Friday:

Forecast challenges are plenty in this period as a strong arctic air mass plows down the plains into TX and an upper level storm system then moves across the state with the cold arctic dome in place bringing P-type questions into the forecast. Arctic boundary should plow southward on Wednesday and push off the TX coast on Thursday with little appearing to slow the boundary or prevent the cold air from penetrating southward. Latest model guidance appears to be trending colder with the front as is common with shallow and fast moving arctic boundaries. Temperatures will fall rapidly on Thursday with the passage of the boundary and onset of cold air advection off the plains. Highs near 60 prior to the front will fall into the 40’s by late afternoon under gusty NW winds…and then into the 30’s and possibly 20’s by Friday morning.

 

While the cold air is filtering southward and upper level trough will be approaching the state from the WSW which will help induce a coastal surface trough slinging moisture northward over the cold dome. There will be a battle as to how much moisture can work northward against the southward moving dry air and what will the temperatures profile look like if and when the northward moving moisture wins out and the air mass over the area is able to produce precipitation.

 

Current thinking is that moisture may be just enough along with favorable lift to produce some amount of precipitation when the air mass at the surface is at or below freezing. Current forecast soundings support a mixture of sleet and freezing rain. Of course the position of the 32F line at the surface becomes very critical is determining what surface impacts of falling sleet or rain would have. Below 32F would possibly result in some accumulation of ice (freezing rain) or sleet and above 32 would result in sleet melting or just plain rain. Current indications suggest most of the area except the immediate coast could be at or below 32F by Friday morning. Good news is that currently the precipitation amounts look fairly light (below .05 of an inch)…but as we saw back in early December even .01 of an inch of freezing drizzle can cause some big problems on bridges. Given thick cloud cover and cold air advection think temperatures will go nowhere on Friday with a very small range between lows and highs and most likely temperatures hovering in the low to mid 30’s all day.

 

As with all winter weather episodes in this area the uncertainty is large especially at this range and will probably not get much better until about 24-36 hours before the onset of the event (late Wednesday into Thursday AM).  

 

GFS model brings more precipitation into the area on Saturday again with very cold surface temperatures in place especially in the morning however other guidance is not as wet and think the GFS may be overdoing the rainfall. Still looks cold with highs on Saturday possibly only in the 40’s if it stays cloudy….50’s if the sun is able to break through.  

[DoctorMu]

verrrrrrrry interesting on the GFS 00Z run

 

 

[Srain]

Heh...

[DoctorMu]

[Srain]

[bubba hotep]

DFW, esp. northern burbs, gets NAM'ed at 12z

[wxmx]

DFW, esp. northern burbs, gets NAM'ed at 12z

 

I'm on the fringe of seeing a few flakes on all models...with the GEM being the coldest and wetter(as always) and the GFS the warmest and drier (as always)

[DFWWeather]

DFW, esp. northern burbs, gets NAM'ed at 12z

 

The DFW area should not see much if any precip with this event. Coastal lows are notorious for robbing us of valuable moisture. This disturbance looks to be weakening as it moves across the state. Furthermore, there has been no appreciable moisture return due to the persistent northwest flow aloft and multiple cold fronts the entire month of January, keeping the Gulf largely shut down. The stout Arctic airmass will dry out the atmosphere even further. Any measurable precip should stay well south and east of the DFW Metroplex. Not saying there couldn't be some freezing drizzle or flurries, but not much more than that. However, it will be very cold. When was the last time you saw forecasted temps in the teens with cloud cover? Could you imagine how much colder it would be if we had ideal radiational cooling conditions? If we did get a snow pack, could it be even colder? More Arctic air is on tap for next week that looks even colder!

[Ed Lizard]

24 hours of .01 in ice would not even effect bridges and overpasses much.

 

GFS Houston less than a hundredth per hour once below freezing is trivial, I think one could sublimate that much, again, probably even bridges and overpasses.  (Houston area).

 

NAM would be a big deal here Friday, but it is the NAM on Friday from a Tuesday.

[Srain]

Updated 3 day qpf...

[Srain]

 

 

 

 

[bubba hotep]

The DFW area should not see much if any precip with this event. Coastal lows are notorious for robbing us of valuable moisture. This disturbance looks to be weakening as it moves across the state. Furthermore, there has been no appreciable moisture return due to the persistent northwest flow aloft and multiple cold fronts the entire month of January, keeping the Gulf largely shut down. The stout Arctic airmass will dry out the atmosphere even further. Any measurable precip should stay well south and east of the DFW Metroplex. Not saying there couldn't be some freezing drizzle or flurries, but not much more than that. However, it will be very cold. When was the last time you saw forecasted temps in the teens with cloud cover? Could you imagine how much colder it would be if we had ideal radiational cooling conditions? If we did get a snow pack, could it be even colder? More Arctic air is on tap for next week that looks even colder!

 

We always needed that shortwave to be stronger and dig deeper before getting sheared out.  The Sunday 12z GFS showed how that could happen and to a lesser extent the 12z NAM from today.  I’m a sucker for the long shot and, even though I know everything is working against it, I keep checking the 500 mb charts looking for a trend in our favor

[Quixotic1]

Feb 2010. March 2010. 2" became 14". Flurries became 7"

[bubba hotep]

Feb 2010. March 2010. 2" became 14". Flurries became 7"

I would have to go back and dig through old post to get the exact date but last January we had a forecast for cloudy skies. I heard some thunder that morning and was like, " that can't be?!" and sure enough unforecasted thunder snow! We got a quick 2" of snow, pure awesomeness

[Quixotic1]

I would have to go back and dig through old post to get the exact date but last January we had a forecast for cloudy skies. I heard some thunder that morning and was like, " that can't be?!" and sure enough unforecasted thunder snow! We got a quick 2" of snow, pure awesomeness

 

Here's a link of one 6 years ago.  I think it was supposed to be a "snow little to no accumulation" event.  It was awesome.  At the time I lived in Tarrant and it was no joke.  The flakes were wet and huge.  

 

http://www.srh.noaa.gov/fwd/?n=2008march6snow

 

This year's a bit different.  Nothing that dynamic like 09-10, 10-11 or even the Christmas day event in 2012.  Everything has been kinda steady as she goes.  Need some strong shortwaves and they look lacking with that giant PNA.  It's going negative though and the EPO is staying positive.  Hope that will push troughs to the middle of the country rather than east.  We'll see.  February is my hope.  things slow down and stuff starts to stack up.  

[DFWWeather]

Next week's airmass for Monday/Tuesay is much colder on the 0z ECMWF and Control than on the 0z GFS, which looks right considering its source region. This airmass traveled over the top of the pole. H85 temps approach -14°C at DFW according to the ECMWF, and this looks correct. If I were to perfect prog the ECMWF for lows at DFW they would drop to 10“F or lower next week without snow.

[Srain]

Morning Update from Jeff:

 

Ingredients appear to be coming together to produce a mixture of light winter precipitation across much of the area Thursday night into Friday.

 

A strong arctic cold front will move southward down the plains today and into TX on Thursday. Temperatures behind this front originate in central Canada and are very cold. While this arctic boundary moves southward, a piece of upper level energy within the mean flow of the upper level trough will break off and develop into an upper level storm system over the SW US on Thursday. This storm system helps to bring a plume of sub-tropical moisture NE from the Pacific as well as some Gulf moisture. This moisture rides back over the top of and into the arctic cold dome over the region by Thursday evening. The overall large scale setup is fairly straight forward….but the details will make all the difference in P-type and accumulation amount.

 

Temperatures:

 

Will take the easiest aspect first. Strong cold air advection will onset post front with temperatures quickly falling into the 30’s and 40’s Thursday. Freezing line will advance rapidly southward on Thursday and reach a College Station to Huntsville line likely by sunset and continue to push southward overnight all the way to the coast. Temperatures by Friday morning will range from the mid 20’s north to near 30 at the coast with strong north winds of 15-25mph and gusty pushing wind chills into the teens. Will likely see very little recovery of temperatures on Friday and highs may not get much above freezing if at all with continued cold air advection and clouds/light precipitation which could prolong the threat of winter precipitation into much of Friday.

 

Precipitation:

 

Increasing weak large scale ascent and moisture will begin to produce periods of light rain on Thursday as the arctic boundary crosses the area. Suspect a brief break Thursday afternoon before lift increases again on Thursday night into Friday. Large scale models such as the GFS, NAM, and ECMWF show dry attempting to undercut the moisture below the cloud bearing level suggesting that rain falling from the cloud bases will have to saturate the near surface layer before reaching the ground. Current dry layer does not look overly deep and would be overcome with a few hours of precipitation falling. This will however help to “wet bulb” or cool temperatures in the air column toward the dewpoints which will likely play havoc with potential P-types. Overall amounts look greatest over our SW counties around Matagorda Bay and least around Lake Livingston. Do not expect liquid ratio precipitation amounts greater than about .25 of an inch.

 

P-type:

 

While surface temperatures will likely be well below freezing, it is what is happening above the surface which determines the type of precipitation that falls at a given location. A freezing surface layer with warmer air aloft results in freezing rain …liquid rain that freezes on contact with the surface forming a glaze of ice. If the warm air aloft is fairly shallow then the snow from aloft will only partially melt through the warm layer and then refreeze into a pellet of ice prior to reaching the surface…sleet. If the column from the surface to aloft is all below freezing then snow is most likely.

 

Current forecast soundings for Thursday night into Friday show a freezing surface layer up to around 1500 ft deep with a warm layer above that and then freezing aloft. This is pointing toward a freezing rain and sleet mixture across nearly the entire area. These soundings change with time and are different at locations across the area. For example the College Station sounding by Friday morning is nearly all below freezing suggesting more snow than freezing rain. Soundings at IAH and HOU keep a defined warm layer aloft through the period suggesting freezing rain mixed with some sleet.

 

Best attempt at the moment is:

 

North of a line from Rockport to Port O Connor to Galveston to High island: rain changing to freezing rain.

 

North of US 59: freezing rain mixed with periods of sleet

 

NW of a line from Columbus to Brenham to Huntsville: freezing rain mixed with sleet changing to sleet mixed with snow.

 

Accumulations:

 

It is pretty hard to get accumulations correct unless the P-type is right as freezing rain, sleet, and snow all produce different accumulations…start mixing them together and it gets even more challenging. Taking the models QPF models (liquid precip amounts) it appears areas west of I-45 could see upwards of .10 to .20 of liquid. This would equate to 1-2 inches of snow using standard liquid to solid ratios. Sleet amounts would be significantly lower in the ¼ to ½ of an inch range. Freezing rain amounts would be fairly equal to the liquid amount…maybe a little less. Liquid QPF amounts drop off quickly to the NE of Houston as this appears to be where the dry layer below the cloud bases wins out. Would not rule out a trace to .05 of an inch of accumulation in this region, but the main focus will be from Houston to the west and southwest.

 

Going with the main P-type of freezing rain mixed with sleet for much of the area suggest a possible accumulation of .05 to .15 of an inch of ice and sleet mix which will produce a crusty glaze on elevated objects including bridges and overpasses.

 

Over the NW counties where more sleet is possible and possibly some snow mix, accumulations may reach ¼ to ½ inch of sleet with possibly a dusting of snow. Would not discount a period of freezing rain and glazing in this region also under a thin layer of sleet/snow which will make bridges and overpasses extremely dangerous.

 

If should be clearly noted that precipitation amounts look to be on the light side…while not expecting heavy icing…it only takes a very small amount of ice on roadways to cause major problems.

 

Uncertainty:

 

Still a lot of uncertainty with respect to the P-type and accumulations across the region and likely this will continue up to the start of the event. Appears that the area will see enough of both cold and moisture at the same time to potentially cause some problems on bridges and overpasses across much of the area. Do not expect enough ice accumulation to result in any large scale power outages. Forecast changes are likely over the next 24 hours both to P-types and accumulation amounts.

 

A Winter Storm Watch will likely be needed for parts of the area by late today or early Thursday.   

[bubba hotep]

So you are saying there is a chance?

 

 

[Srain]

So you are saying there is a chance?

 

 

[Ed Lizard]

SREF guidance based on 0.01 ice in a day is almost useless.  Like the severe weather season SREF guidance that uses 0.01 3 hour precip as a discriminator to show MUCAPE and deep shear combos (a menu, that all use 0.01), the MU over 2000 J/Kg and deep shear over 40 knots would be more useful if it wasn't insignificant rain as a discriminator.

 

 

Both GFS and NAM are right on the edge of a bridges and overpass style minor ice storm.

Thermal profile suggests partly melted snowflakes mixed with some drizzle (temps barely cold enough where saturated to make snow versus sub-cooled water) that refreeze. Or some sleet and freezing drizzle, Very light, But maybe just enough to make cancelling school a good idea.
 

[Srain]

Odds have increased today suggesting a fairly wide spread Winter Weather event will unfold across Central and The Coastal areas of Texas into SW Louisiana. While there still remains some uncertainty and the amount of precip looks light, it appears Winter Storm Watches will be hoisted with the afternoon updates across the Southern half of Texas.

[Quixotic1]

WS Watch out.

[Quixotic1]

First threat in awhile for Houston. Anybody besides steve excited? I know ed is steeling himself for disappointment but things are looking really good.

[1900hurricane]

I'm excited here in College Station, but I'm not trying to get too excited in case of another letdown. The last few events (November and December ice plus the Solstice Outbreak) didn't preform up to par around here, but hopefully that means we're due.

[bubba hotep]

First threat in awhile for Houston. Anybody besides steve excited? I know ed is steeling himself for disappointment but things are looking really good.

 

Based on 18z GFS, it looks like IAH gets about 1/3" but only about 0.10" with temps below freezing.  Factor in the fact that the cold air will probably bleed in faster than modeled and that amount goes up but temps will still be borderline.  Things will be more interesting on the northern fringe where someone might pick up 1/4 - 1/2” of snow.  Looks like maybe Austin over to College Station could be in that window.  I’m holding out hope for a flizzard up this way

[DoctorMu]

Just because it looks cool

 

 

 

 

I have a much better feeling about this that the last few duds.  The column's darn cold.  When precip starts I think sleet/snow mix are possible early.  The timing Thu night might be ideal

 

I need Friday to write anyway...

[Quixotic1]

I know I beat this to death but the big events rarely get forecasted well because it IS better to be conservative unless you're a hype master like some national guy i won't mention. Pretty sure the December 2004 miracle or the January 1985 event for the Hill Country were never called. Get enough chances and the worm will turn.