SW LA/SE TX Winter 2013-2014

[PTrackerLA]

I'm afraid the trend has been less and less moisture in the models as temps have trended down somewhat. Two days ago things looked REALLY interesting on the GFS but sadly that is gone. Still some time tomorrow for things to change but as of right now almost all of the moisture will remain to our SW and south over the gulf. If a surface low were to form that would change things significantly but I can't even recall a western gulf "winter-time" low forming this season so I have no reason to believe one will just pop up now. Enjoy the hard freezes!

[stormlover2013]

Euro and 12 gfs run had moisture and cmc had moisture, the 18 runs have been really inconsistent even the name 00 and 12 run has been fairly consistent

[vbhoutex]

Latest from Jeff Lindner:

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 amounts.

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.

[CYCLONE MIKE]

I don't know what to believe anymore with the gfs. It gives us hope in the 6z run but no sooner the 12z comes out takes it all away. Im thinking we end up just getting teased. Watch everything unfold for you guys in tx, it clouds up over here, then poof all the moisture goes.

[BigB0882]

The GFS is showing very light amounts of snow in southwest and even south-central Louisiana and eventually SETX. It is not showing nearly the amounts in Central Texas that some other models are showing. Maybe this is the beginning of a last minute trend, pushing some snow into Louisiana? NWS still has a 20% chance for us but it isn't very likely.

By the way, this is the current 18z. It shows even more snow (not amounts, just in area) for Louisiana than the 6z that Cyclone mentioned.

[Stormcenter]

The trend eastward begins?

The GFS is showing very light amounts of snow in southwest and even south-central Louisiana and eventually SETX. It is not showing nearly the amounts in Central Texas that some other models are showing. Maybe this is the beginning of a last minute trend, pushing some snow into Louisiana? NWS still has a 20% chance for us but it isn't very likely.

By the way, this is the current 18z. It shows even more snow (not amounts, just in area) for Louisiana than the 6z that Cyclone mentioned.

[CajunMama]

We'll just have to STAY UP ALL NIGHT!!! and watch the sky!

[Stormnut]

The 21z SREF looks much better for Baton Rouge seeing some sort of frozen precip than the earlier runs

[LaBreeze]

We'll just have to STAY UP ALL NIGHT!!! and watch the sky!

CajunMama, I suppose that you are correct - we'll stay up and see a flake or two. Hmm, I guess I'll take an early nap and then check the sky later. I'm thinking that we will not see much, but, hey - I'm not a weatherman. Rest your eyes for the squinting we'll be doing tomorrow night.

[BigB0882]

The 21z SREF looks much better for Baton Rouge seeing some sort of frozen precip than the earlier runs

Do you have the ability to post a link or the actual graphic?

[Stormnut]

http://www.spc.noaa.gov/exper/sref/sref ... ditional__

[Stormnut]

You can click on previous runs on the right side of screen. Earlier runs were keeping everything west of us

[BigB0882]

Thanks. That is interesting although I have no idea how reliable the SREF model is. Someone is going to be wrong. The NAM, for example, keeps everything MUCH further West, well into Central Texas. The GFS is kinder to SELA (at least the 18z was) and almost nothing for central Texas. Model Wars...commence!

[LaBreeze]

Thanks. That is interesting although I have no idea how reliable the SREF model is. Someone is going to be wrong. The NAM, for example, keeps everything MUCH further West, well into Central Texas. The GFS is kinder to SELA (at least the 18z was) and almost nothing for central Texas. Model Wars...commence!

I suppose we, here in SW LA, are caught in the middle

[Jagno]

What I cannot understand is how snow and sleet are predicted for Texas all the way to the Sabine as well as points east of me but not us. I've never known cold weather events to bounce around like a tornado.

[ROCK]

Though I weigh the GFS more so than the NAM I think a blend of both 0Z runs look about right as far as precip goes. Pretty close to ditching the models anyway and just wait for it really.

IMO, Jeff did I excellent sum up above. I recall in 2009 I got about .25 of heavy snow here in Pearland and nothing else over Houston that heavy. Luck of the draw...

[CajunMama]

NWS now has south central LA (Lafayette) with a 60/60 chance of snow/sleet and then freezing rain Thursday night and Friday morning. Flip flop! Flip flop!

ETA at 1:30am: Darn NWS. Dropped back to 40/30 snow/sleet and sleet. MAKE UP YOUR MIND!!!!!!

[Jagno]

Okay, they corrected the graphic portion of the NWS forecast for our area. It is in fact calling for a 50% chance of wintry precip Thursday night and Friday. When they uploaded the graphics they simply had cloudy on there with no change of precip however when I went to the discussion they were calling for it. Whew, they need to stop playing with my emotions like that. LOL

[BigB0882]

It looks like next week could be our really big chance. Major cold coming and the GFS showing a few inches of snow for most of Louisiana and much of SETX. It is about 200 hours out so not close enough to trust, by any means, but not exactly way out in Lala land. It depends on a coastal low forming so that will be key.

[BigB0882]

Winter weather advisory for Baton Rouge and points westward. Very surprised! May be for some places east of us as well but haven't checked yet. Wonder what the schools will do now? Do you hold classes with a winter weather advisory? Lol. I have to cross the MS bridge to go to work everyday.

By the way, GFS is forecasting .04 of QPF for us with .02 being frozen (they predict snow, but it is very close to sleet). I suppose that is reason enough for the advisory especially if they are under on the QPF. As someone said in the Texas thread, all it takes is about .05 of freezing rain/ice to wreak havoc on bridges.