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Winter Storm heading for TX

Accumulations of snow possible over portions of SE TX Tuesday-Tuesday night.

Significant snow accumulations possible for N of Austin toward Waco (4-8 inches).

Discussion:
Strong cold front heading for SE TX this afternoon...ahead of this boundary temps. have soared into the mid 70's across the region...and it will all end tonight.

Cold front will cross the area overnight with cold air advection in progress on Monday with highs 10-15 degrees colder than today. Next in a new series of upper level storms will arrive into the 4 corners on Monday and head for TX Tuesday while arctic air over the central plains pours southward into the region Monday night.

Upper level storm brings moisture over and into the cold arctic dome starting Tuesday with light band of winter mix starting around mid morning over our NW counties and spreading to other areas of SE TX by Tuesday evening. Dynamics look fairly impressive with this system and some of the short range models are showing decent 700mb instability supportive of meso scale snow banding and burst of heavy snow.

P-type:
Forecast soundings support numerous P-type issues over the region Tuesday/Tuesday night with favorable critical thickness for SN and favorable cold profiles for SN to make it to the surface first up north and then dropping southward. Will break out the following three grid lines for P-type in a first attempt with this event....changes are for sure with this in the coming 24 hours.

N of a line from Columbus to Conroe to Livingston:
Expect a RA/SN/IP mix at the onset of precip with cooling of the air column to below freezing by Tuesday afternoon and change to all SN.

N of a line from Wharton to Downtown Houston to Liberty:
Mostly RA Tuesday then a mix of RA/SN Tuesday evening into Tuesday night...could see a complete change to all SN across Austin, Waller, N Harris, N Liberty Counties.

Coastal Areas:
All RA Tuesday with a possible RA/SN mix late Tuesday night...but mainly RA.

Accumulations:
Surface temperatures with this event will be in the mid to upper 30's based on the GFS sounding data. Dewpoints in the upper 20's to 30 at the start of the precip. do not bode well for evaporative cooling to or below freezing. Feel it is going to be hard to get the surface temp to freezing...which means a lot of melting on contact. On the other hand, meso models are pointing toward banding features over the northern part of the area...which may support heavy snow and rapid accumulations as seen over the DFW area 2 weeks ago even with surface temps. in the 32-35 range.

Needless to say this is a low confidence forecast!

N of a line from Brenham to Coldspring:
Slushy accumulations of 1-2 inches mainly on grassy surfaces.

Columbus to The Woodlands:
A dusting to .5 inch of accumulation.

Little to no accumulation is expect south of this line at this time...most of what falls in this region will melt on contact.

Some significant changes can be expected with accumulations as this event unfolds.

Temperatures may make it to freezing along and N of I-10 by Wednesday morning supporting the freezing of melted snow on bridges and overpasses.

At this time the NWS is holding off on the issuance of Winter Storm products, but they will likely be coming in the next 12 hours or so...especially for areas N of HWY 105.

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Significant Winter Storm event heading for SE TX.



Accumulating snowfall expected Tuesday over portions of SE TX.



Winter Storm Watch issued for the following counties: Brazos, Burleson, Grimes, Washington, Montgomery, Walker, Houston, Madison, Trinity, San Jacinto, and Polk.



Discussion:

Cold air advection in progress this morning behind the late Sunday cold front. Cold arctic dome over the central plains will filter southward today while the next upper level storm noted over NV this morning makes the eastward turn and begins it treck toward TX. Stratus deck this morning may break up some this afternoon, before high clouds begin to arrive from the west. Clouds will thicken and lower tonight as moisture and lift increase.



Tuesday:

Strong upper level storm drops toward the Big Bend area with a developing shield of winter precip. Over much of central TX by morning. Forecast soundings show the air mass over the area dry and cold by Tuesday morning. A dry layer in the 900-800mb level will support some room for evaporative cooling of the air column with the onset of rain/snow Tuesday morning over our NW counties first and then spreading SE during the afternoon hours. Meso scale models continue to point toward a fairly unstable layer in the snow growth area around 700mb over the northern portions of SE TX Tuesday afternoon. Past events and studies with such instability (Dallas 2 week ago, and Victoria in Dec 2004) suggest the formation of meso scale banding and potential for very heavy snowfall rates. 700mb front will also be introduced into the mix to add forcing over our northern counties. May see a band of very heavy snow develop from College Station to Huntsville Tuesday afternoon/evening with significant accumulations.



Tuesday night:

Rain/snow mix will spread toward the coast with a change over to all snow across inland SE TX. At this time it appears the rain will mix with snow by mid afternoon toward Harris County and then change to snow after dark Tuesday as far south as US 59. Surface temperatures will fall toward freezing during the early evening hours as far south as I-10 as accumulating snow pack just to the north advects colder surface air southward. The southward extent of accumulation will likely end up over Austin/Waller/Harris/Liberty counties.



Accumulations:



College Station to Trinity northward:

Models are really pegging this area for some significant accumulations. For now will go all snow Tuesday/Tuesday night with accumulations of 2-4 inches and isolated locations of 6+” possible.



Austin to Brenham to Conroe to Coldspring northward:

Rain/snow mix will begin Tuesday morning and change to all snow Tuesday afternoon. Accumulations of 2-3” is likely with isolated totals of 3-5” possible.



Columbus to Downtown Houston to Liberty northward:

Rain will start the event changing to a rain/snow mix during the mid afternoon and all snow after dark. Accumulations of generally less than 1 inch is likely.



Columbus to Downtown Houston to Liberty southward:

Rain will start the event changing to rain/snow after dark Tuesday and possibly all snow before ending late Tuesday. Most of what falls in this region will melt on contact as surface temperatures struggle to get to freezing.



Impacts:



Surface temperatures are forecast to be in the 32-35 degree range for much of the day Tuesday as the snow falls which indicates a lot will melt on impact, except where heavy snow bands develop. Temperatures will drop Tuesday evening to or below freezing along and N of I-10 where melted snow on bridges and overpasses may begin to freeze. Additionally as surface temperatures fall toward/below freezing Tuesday evening snowfall will begin to accumulate faster mainly on elevated and grassy surfaces. Could see some icing/glazing of bridges and overpasses Tuesday evening into Wednesday morning over the northern ½ of the area.





While confidence is growing in this event, the amount of accumulation and where the rain/snow line ends up remains in some question. Forecasting meso banding location is extremely difficult, but very high impact and much of this will not be known until the event is underway.

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(If Katy is planning to evacuate, do not go northwest on 290).

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Major Winter Storm heading for SE TX



Significant accumulations of snow expected on Tuesday/Tuesday night over the area.



Winter Storm Warning issued for Tuesday: Brazos, Burleson, Madison, Houston, Trinity, Polk, San Jacinto, Grimes, Montgomery, Walker



Winter Weather Advisory issued from 200pm Tuesday to 600am Wednesday: Harris, Austin, Colorado, Fort Bend, Liberty, Waller, Wharton



Discussion:



Overall consensus today has been to push the snowfall and accumulations southward which now brings Harris County more under the threat for accumulations. Models are still hammering away at some fairly hefty banding features over the northern ½ to 1/3 of the area and feel some surprisingly high totals may be had in the area bounded by College Station to Livingston. Will likely also see snow all the way to the coast mixed with the rain Tuesday night.



Will start to see accumulations by mid morning Tuesday up north and then spread southward during the day on Tuesday. Will see rain start to mix and change to snow from NW to SE during the afternoon on Tuesday with many areas having all snow by Tuesday evening. Ground temperatures are warm and some of the snow will melt on impact. Heavy snow bands will help mitigate the warm ground allowing for quick accumulations over our northern counties. Additionally, as surface temperatures fall toward and to freezing Tuesday evening greater accumulation and formation of glazing of area bridges/overpasses appears likely. Would like to see lower dewpoints for IAH on Tuesday to support accumulations, but it looks close enough especially if moderate/heavy snow falls for some quick accumulation even with surface temperatures above freezing…similar to Dec 4, 2009.



Accumulations:



College Station to Livingston northward:

Accumulations of 2-4” with higher amounts (6+” possible).



Columbus to The Woodlands to Humble northward:

Accumulations of 1-3” with isolated amounts to up 4 inches



Katy to downtown Houston to Liberty northward:

Accumulations of .5-1”



Sugar Land to Pearland to High Island northward:

A dusting to ½ inch of accumulation.



South and West of Sugar Land to High Island:

Snow will mix with the rain, but no accumulation is expected



Snowfall Measuring:

http://www.cocorahs.org/Media/Training/Training_Snow.html

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Only change this evening is to extend .5 to 1 inch accumulation to include all of Fort Bend and Wharton counties to match with NWS issued WWA. Wharton County will probably be closer to the lower end of this scale.

Other thing to note is that this will be a very wet now...great big large flakes, but very poor ratios so that may help trim down some on the overall accumulations. It is also important to point out that for much of the event temperatures will be at or above freezing so heavy burst will result in accumulations that will then melt and so on until it ends. Very similar to Dec 4th, 2009 although surface temperatures may be a touch higher than that event given current high dewpoints. This will make it very difficult to measure accumulations...especially total accumulations.

See no significant reason to alter other accumulations or onset timing at this time...although N Harris accumulations could be a tad high at the moment...but will just let it ride for now. Little doubt we will see snow...not as confident on accumulations south of HWY 105. Still looking good for heavy banding N of HWY 105 where +SN is likely Tuesday PM.

Take the camera tomorrow it will be one of those days across SE TX!

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….And here we go….



Winter Storm Warning remains in effect for the northern 1/3rd of SE TX.



Winter Weather Advisory will go into effect at 200pm for the following counties: Liberty, Harris, Waller, Austin, Fort Bend, Wharton, and Colorado.



Discussion:

Cold arctic air dome spilling into TX from the NNE this morning while potent upper level storm system near Big Bend begins its eastward track. Winter weather radar already shows a large shield of SN and RA/SN mix over much of central TX moving eastward. Surface observations and public reports from Austin indicate a RA/IP mix at the moment with San Antonio having SN within the last hour. Current temperatures over the area range from the upper 30’s up north to the upper 40’s along the coast under brisk cold air advection regime with dewpoints in the mid to upper 30’s. Upstream temperatures over the Waco/Dallas area are in the mid 30’s with dewpoints in the mid 20’s and this air mass will continue to advect southward today.



Current surface temperature/dewpoint regime over SE TX leaves little room for evaporative cooling and only our northern counties the potential to reach freezing…however upstream air mass advecting southward should help to cool the air column additionally today allowing a slow dewpoint fall this afternoon. Still feel we will not reach freezing until Wed AM south of a Brenham to Conroe to Livingston line…it is just too warm to start off this event.



Other item to be concerned with is the amount of instability likely over our northern counties this afternoon. Expect to see meso scale banding develop and with the amount of elevated instability may see a few lightening strikes. Expect to see heavy snow under these bands with visibilities falling to less than 1/4th of a mile at times and rapid accumulations.



See no reason to mess with accumulations at this time…could push them up a little bit over the northern areas…but feel some of what falls this morning will melt on contact before the onset of the heavier snowfall and also getting more reports of IP than expected which may help lower accumulations some…will have to see how things play out over the next few hours.



Accumulations:



College Station to Livingston northward:

Accumulations of 2-4” with higher amounts (6+” possible).



Columbus to The Woodlands to Humble northward:

Accumulations of 1-2”



Katy to downtown Houston to Liberty northward:

Accumulations of .5-1”



Wharton to Pearland to High Island northward:

A dusting to ½ inch of accumulation.



South and West of Sugar Land to High Island:

Snow will mix with the rain, but no accumulation is expected



Wednesday AM:



Freeze line will drop southward overnight and should be along a line from Columbus to Richmond to Jersey Village to Liberty by early Wednesday morning. Mel****er from falling snow on bridges and overpasses will likely freeze into a glaze of ice especially N and W of downtown Houston. Extreme caution should be used on any bridges and overpasses Wednesday morning. Anti-ice agent is has been deployed on many of the major freeways to help prevent ice formation.



Just had a report e-mailed of IP starting to accumulate in N Austin…should see this mix reach CLL within the next 1-2 hours.

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highwayman
posted 8:26a, 02/23/10



facebook friend in Austin just poseted that its snowing there right now

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Where are you finding these updates Jed? Google doesn't reveal much other than his current role.

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I think I'd turn that hot tub on and get in.

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