SW LA/SE TX Winter 2013-2014

[vbhoutex]

Woke up to a sunny(FINALLY!!) 34F this am after a low of 33f. Added another .15" to the gauge-baby steps, baby steps-another small dimple in the ongoing drought. Yesterday the temp dropped all day long under drizzly skies and was down to 36f by sunset.

[PTrackerLA]

Another official freeze in the books with 32 this morning. It was absolutely beautiful today though. The sun really has been a rare sight the past few weeks...you could tell everyone seemed to be in a better mood today .

[vbhoutex]

Jeff's email about upcoming possible severe weather and more cold:

Severe thunderstorms possible Sunday afternoon and evening.
A strong storm system currently moving through the SW US will eject across TX on Sunday. At the surface strong southerly flow is pumping Gulf moisture northward from the Bay of Campeche, while to the north a strong late season arctic high pressure dome is moving southward down the plains. Impressive cold front will slice across the region late Sunday afternoon returning winter to the area for much of next week.

Upper level system currently over the SW US will shear into TX on Sunday with fairly strong dynamics forecasted aloft. Low level jet increases to near 40kts from Matagorda Bay NNE across SE TX by early Sunday afternoon. Increased dewpoints in the mid to upper 60’s and steepening lapse rates support instability values of 1000 to 1500 J/kg of CAPE by mid afternoon. Think mid level warm layer (cap) will hold through at least 1-2pm and then begin to erode from both increasing lift and modest surface heating. GFS and ECMWF develop a line of strong the severe thunderstorms from near Austin ENE toward W LA by mid afternoon as the cap is overcome…however the NAM and some of the other short range guidance holds the cap longer over the region and does not develop as much activity. 0-6km shear values will be on the order 50-60kts across the region and this combined with the expected instability would result in severe thunderstorms.

Forecast models that do develop storms show initial mode east of I-35 as supercells with a large hail threat and then quickly transition toward a line with bowing segments which seems likely given the wind energy aloft. Initial supercells could have a slight tornado risk…but think the main threat will be large hail. Storms will move ESE across at least the northern ½ of the region Sunday evening likely becoming increasingly linear. Linear mode favors strong straight line wind damage along the leading edge of the line and in any bowing segments. If a well defined line develops could see a few corridors of wind damage in the region from east of Austin ESE north of US 290 northward toward Huntsville. Will have to watch for the potential for the arctic front to undercut the leading edge of the line and reduce the severe weather threat Sunday evening.

Timing continues to look from mid afternoon into mid to late evening. SPC slight risk includes about 75% of the area, but think capping to the SW will be too much to overcome and the main severe threat will be NE of a line from Austin to Columbus to Houston to High Island.

Other item is fairly impressive cold air advection with this system and expect cold temperatures Monday-Wednesday. Modified arctic air mass will be fully entrenched by Monday morning with lows in the 30’s across the entire area and possibly upper 20’s northern counties. Will see only modest recovery on Monday as strong north winds continue to transport cold air southward with highs likely in the upper 40’s and low 50’s….a big difference from the highs near 80 on Sunday.

[vbhoutex]

Jeff's email for today:

Powerful arctic cold front will sweep across the region today with a significant drop in temperatures.

Arctic boundary is moving quickly southward this morning with a 30-40 degree temperature drop across the boundary (Austin is 72 while Waco is 35). Boundary will race southward and reach our NW counties before noon and push to near US 59 by 300-400pm and off the coast by early evening. Upstream temperatures at Amarillo are 8 and in the teens across much of OK so this air mass is very cold for early March.

Severe Threat:

Mornings soundings from LCH and CRP showed a fairly impressive capping inversion in place across the region with saturation of the air mass below the cap. With better moisture in place today…it will be hard to mix out the low stratus clouds over the region and suspect there will only be a few breaks in the overcast across the region which will keep instability on the lower side in the 800-1000J/kg instead of closer to 1500J/kg. Forecast models erode the cap this afternoon and allow convection to develop along the leading edge of the frontal lift. Think the arctic boundary will move too fast southward and outrun the developing storms cutting the updrafts off from the surface and making them quickly elevated which lessens the severe threat over the region. Could still see a few severe hail and wind reports especially NE of a line from College Station to Conroe to Liberty where capping will be weakest and storms have the best chance of being rooted near the surface.

Winter Precipitation:

Incoming air mass is very cold and forecast models have been too warm with upstream temperatures which raises the concern this evening that light rain following the frontal passage could change to freezing rain along a north of a HWY 105 line. Warm temperatures since Friday has greatly warmed both ground and roadway surface temperatures and even if temperatures fall into the 30-32 range do not think ice accumulation will be significant. With that said overnight lows will fall into the upper 20’s north of HWY 105 which may result in freezing over residual water on bridges and overpasses after the precipitation ends around midnight. Given very warm roadway surface conditions, think surface temperatures will need to fall into the 27-29 range for ice to form and this will be possible in the region from College Station to Lake Livingston after midnight.

Other aspect will be the potential for a freeze warning for areas N of I-10 tonight. While the area has had several hard freezes this winter the recent warm spells have allowed vegetation to bud and freezing temperatures will damage the new sensitive growth which would fall within the range of a late season freeze warning. Wind chills tonight will run 15-25 degrees across the area.

Early Week:

Cold arctic dome will entrench over the area for much of the week with active flow remaining in place from the WSW. This flow will bring several disturbances across the area and generate periods of rainfall. First disturbance will cross the area late Monday into Tuesday. Surface temperature profiles suggest mainly a rain event, but surface temperatures could be very near freezing Tuesday morning north of HWY 105 for a brief period of freezing rain or sleet. Highs on Monday will only reach the mid 40’s under north winds and cloudy skies (about 35 degrees colder than today). Next system approaches late Tuesday into Wednesday with another chance of rainfall across the area. Temperatures will remain cold for early March for most of the week with lows 30-35 Monday and Tuesday and highs only in the 40’s both Monday and Tuesday. Wednesday will again be cold with clouds and rain with lows in the upper 30’s and highs in the lower 50’s.

Should start to see a warming trend toward the end of the week ahead of yet another weather system next Saturday.

[vbhoutex]

Currently 32f at my house and still falling. Yep it was as quick as Jeff said. Quite impressive really.
Latest from Jeff Lindner:

Impressive arctic cold front has crossed the area this afternoon switching from spring to winter in about 30 minutes.

Strong arctic air mass is pouring into the region with 700pm temperatures ranging from 28 at College Station to a balmy 69 at Galveston….even better is the 7 at Amarillo and 75 at Brownsville. Freezing line has quickly advanced southward this evening and is currently along a line from Columbus to Brenham to Huntsville. Winds continue to howl in the 25-35mph range as the pressure gradient remains strong over the area forcing wind chill readings into the 20’s and 10’s across the area currently. Lift associated with the departing upper level trough is starting to move eastward out of the region and expect only brief light rain/drizzle for the next few hours prior to all precipitation ending by 1100pm. Winds at both Caldwell and Crockett are reporting calm winds indicating the annomometer has glazed over from freezing rain and this has been confirmed by law enforcement reports of ice on elevated surfaces in Brazos and Madison counties. While pavement is still warm from the recent warmth think surface temperatures north of HWY 105 are right at the cusp of forming ice on wet bridges and overpasses….however TXDOT is not reporting any ice on bridges and overpasses in SE TX at the moment. Luckily addition rainfall will be extremely light and the main threat will be from water freezing on elevated roadways as the pavement cools overnight.

Other item is the issuance of a wind chill advisory for the following counties until 800am: Brazos, Burleson, Washington, Grimes, Walker, Trinity, Madison, and Houston.

Winds of 20-30mph overnight with temperatures in the 26-28 degree range will produce wind chill values of 10-15 degrees over these counties.

[vbhoutex]

More from Jeff Lindner:

Hard Freeze Warning issued north of a line from Columbus to Conroe to Livingston for tonight.

Temperatures continue to tumble across the region and guidance has been of little use with this invading arctic air mass. Freezing line at 900pm extends from Columbus to Katy to The Woodlands to Livingston and continues to progress southward. Scattered showers continue to develop within the cold air mass resulting in freezing rain over Waller and Montgomery Counties. Should see all precipitation end within the next 1-2 hours and do not expect any significant ice accumulation as very gusty north winds are quickly drying what falls and roadway temperatures remain very warm. TXDOT continues to report no ice formation on bridges and overpasses across SE TX at this time even with surface temperatures in the 27-29 range north of HWY 105 and this is likely from the very warm temperatures yesterday and today which the roadways are holding some of that warmth.

As for temperatures…upstream readings are extremely cold for early March ranging from the 10’s to 1’s over NW TX and OK. This air mass continues to push southward ahead of the arctic high over the Dakotas. Many locations across SE TX are already near forecasted overnight lows and expect another 2-4 degrees of cooling from cold air advection processes pushing areas under the Hard Freeze Warning into the 20’s for 3-5 hours tonight. Damage to sensitive vegetation and vegetation in bloom is likely with surface temperatures in the 20’s.

Next concern is the potential for a winter mix of precipitation Monday night into Tuesday morning across portions of SE TX as another disturbance moves across and the cold arctic dome which is colder than expected remains locked in place. Will have to take a close look at the incoming 00Z guidance product early Monday to attempt to define where this threat may exist across the area.

[BigB0882]

I notice our chances for precip begin going up right as temps hover at freezing tomorrow morning. Could be a close call for some in the area!

[BigB0882]

Reports of snow in Tyler county and also in Jasper. This is in northern portions of SETX.

[vbhoutex]

From Jeff Lindner:

NWS has issued a Winter Weather Advisory for areas along an north of US 59 starting at 1100pm tonight for accumulations of freezing rain and sleet.

Bitter cold arctic air mass is entrenching over the region and light to moderate rainfall is expected to begin to develop after 1100pm along US 59 and overspread the region overnight. Freezing rain and ice accumulations of .03 to .10 of an inch are possible in the advisory area along and north of US 59 making travel potentially extremely dangerous on Tuesday morning….including the NW ½ of Harris County.

Air temperatures in the low to mid 20’s have cooled roadway surfaces to near/below freezing (US 290 at SH 6) is currently reporting a roadway temperature of 25.6 degrees. While there will be some recovery today with the high March sun angle…think roadway surfaces will cool quickly to freezing this evening.

There is still some uncertainty on exactly where the freezing line ends up tonight…but it is looking increasingly likely that some degree of ice accumulation is possible over portions of the area including the western and northern parts of Harris County Tuesday morning.

BTW, woke up to 24f this am!! Now up to a scorching 31f with some sun peaking out.

[Stormnut]

WWA for sw LA

[PTrackerLA]

Winter WX Advisory just issued. Pretty amazing. From NWS Lake Charles:

...WINTER WEATHER ADVISORY IN EFFECT FROM 3 AM TO NOON CST
TUESDAY...

THE NATIONAL WEATHER SERVICE IN LAKE CHARLES HAS ISSUED A WINTER
WEATHER ADVISORY FOR FREEZING RAIN...WHICH IS IN EFFECT FROM 3 AM TO
NOON CST TUESDAY.

* TIMING...FREEZING RAIN...MIXED WITH SOME SLEET...WILL DEVELOP
FROM 3 TO 6 AM TUESDAY MORNING...AND CONTINUE UNTIL NOON TUESDAY
WHEN TEMPERATURES ARE EXPECTED TO RISE ABOVE FREEZING.

* MAIN IMPACT...ICE ACCUMULATION UP TO ONE TENTH OF AN INCH WILL
CAUSING HAZARDOUS DRIVING CONDITIONS...MAINLY WHEN TRAVELING
ACROSS BRIDGES AND OVERPASSES. SOME THIN GLAZING ON TREE LIMBS
AND POWER LINES WILL ALSO BE NOTED.

[CajunMama]

I'm not Mardi Gras'ing tomorrow if it's going to be that cold! I'll stay in my warm house and eat my gumbo I'm cooking today. Though I bet if I would go to the parade I'd get a boatload of nice beads and wouldn't have to buy as much next year for our parade!

[BigB0882]

Any chance the WWA will extend to SELA? Or is the precip going to miss us or get here late enough in the day that we will be above freezing?

[Kennethb]

Any chance the WWA will extend to SELA? Or is the precip going to miss us or get here late enough in the day that we will be above freezing?

While I would not underestimate this winter's dominance, I do not think that we have low enough dewpoints to support wet bulb cooling to get any significant wintry precipitation in Baton Rouge. A few ice pellets are not out of the questions though.

[PTrackerLA]

Well the temperature and dewpoint has been dropping here all day. Currently 40 with a DP of 32. Could get interesting around sunrise tomorrow.

[BigB0882]

It was 36 degrees here in Baton Rouge last I checked at 6:30 local time. It was supposed to be 39 as of 7:00 according to the hourly forecast. If we are 3-4 degrees colder than normal and this carries through all night, then when any precip moves through tomorrow morning we may still be at or below freezing. As of now it looks like they think the precip will come through when it is about 35-36 but those 3-4 degrees could make a big difference. I don't think it will be a major problem and unless the precip is ahead of schedule we should only be below freezing for a limited time but it would be neat to have a few sleet pellets for a 4th time this season!!!

[vbhoutex]

We are already below freezing at my house and radar is showing increasing returns to our SW moving NE. Some are already showing up as frozen precip. This could get interesting!!

Jeff's update.:

Winter Storm heading for SE TX with accumulations of ice increasingly likely over portions of the region.

Winter Storm Warning: Burleson, Brazos, Grimes, Montgomery, Waller, Austin, Washington, Colorado counties

Winter Weather Advisory: Jackson, Wharton, Calhoun, Victoria, Fort Bend, Harris, Liberty, Polk, San Jacinto, Trinity, Walker, Madison, and Houston Counties.

Discussion:

Water vapor images, visible satellite images, and radar data west and southwest of Houston indicate a weak short wave crossing the Rio Grande currently near Del Rio with increasing radar echoes north of Victoria to south of Laredo. Secondary and stronger short wave is poised south of Tucson, AZ and moving eastward toward west TX. Initial short wave will result in moistening of the mid and lower levels this evening and the HRRR meso model even attempts to generate some rainfall this evening. Incoming secondary short wave will really get things going in the 300-600am time period when lift becomes maximized and PWS surge to 1.0-1.2 inches which is very impressive for this cold of an air mass. It is almost certainly going to rain and QPF trends have been increasing today suggesting greater amounts of liquid amounts. In fact HPC guidance is showing upwards of .50 to .75 of an inch of liquid accumulation overnight south of I-10.

Temperatures:

Current temperatures have failed to reach freezing north of HWY 105 this afternoon and range from 31 at College Station to 37 at Tomball to 41 at BUSH IAH and 46 and Pearland. Dewpoints are running in the mid 20’s across the area. A review of the 12Z guidance indicates the models have not performed well at all with highs today with a bust of 11 degrees too warm at College Station on the GFS and 5-7 degrees too warm at IAH. Do not think the model guidance has a very good handle on the surface air temperatures across the region nor much handle on potentially how cold it could get overnight. Using evaporative cooling forecasting techniques suggest a surface air temperature of between 29 and 31 across Harris County around 600am Tuesday….but this is subject to some change given warm air advection aloft. Dewpoints have actually increased today from 22 to 26 at IAH which does lend some degree of uncertainty on if the evaporation process will be fully capable of lowering the surface temperature to freezing…simply put will have to watch evening temperature and dewpoint trends.

P-type:

Forecast soundings show a shallow (1500-2500ft) sub-freezing layer near the surface with a large area of above freezing temperatures above about 2500ft. This is a freezing rain sounding and do not expect to see any snow and very little sleet mixed with the freezing rain. Critical element becomes the surface temperature as the 32F line will dictate the location where rain turns over the freezing rain. Evaporative processes will bring the low levels to saturation in the 300-600am range and that will effectively end the cooling. Freeze line should set up very near the US 59 corridor at some point between 200-500am. Freezing rain and ice accumulation will be ongoing north of the freeze line with just plain rain south of the line.

Accumulation:

Warning area:

Accumulations in the warning area will range from .10 to .25 of an inch as this area will be colder and sub freezing longer with less onset precipitation “wasted”. Ice development will onset quickly as the precipitation starts late this evening and worsen during the morning hours. Some of the meso models are fairly aggressive with elevated instability and suggest some convective banding which could result in some slightly higher amounts locally. Icing in the warning area is going to be a problem possibly even on surface streets with temperatures falling into the mid to upper 20’s.

Advisory area including metro Houston:

Liquid QPF numbers are higher in this region, but onset of freezing temperatures is delayed a few hours allowing the initial precipitation to remain liquid which cuts down on overall ice accumulation. Expect ice accumulation of .01 to .08 in this area mainly on elevated surfaces including some bridges and overpasses. Pretty much cutting Harris County nearly in half from Kingwood to Katy with ice accumulation NW of this line and then back SW toward Richmond and Wharton along US 59. Extremely hard to pin point exactly where that freezing line will establish and it could be further southward or further north. Travel in the advisory area could be impacted especially on bridges and overpasses…but it all depends on where the surface temperature falls to freezing.

Impacts:

Main impacts look to be to elevated roadway surface accumulating ice…but will have to see how quickly pavement cools tonight and how far south the ice development of bridges extends. Solar insolation today has warmed pavement temperatures into the low 40’s, but expect the cooling to begin with sunset and will have to watch trends overnight.

A few scattered power outages may be possible in the warning area Tuesday morning if ice accumulation approaches .20-.25 of an inch.

Icing on aviation control surfaces is likely Tuesday morning requiring de-icing especially from I-10 northward so delays can be expected.

[CajunMama]

Yes, I was out on the parade route this evening. The windchill was only 21F.

[gboudx]

If anyone is interested in reading about Mardi Gras impacts, you can read T. Scott Barry's update on his FB page.

https://www.facebook.com/SoutheastLouisianaWeather

I can remember a Mardi Gras camped out along St. Charles in Uptown New Orleans, waiting for Zulu, Rex and the truck parades to start. It was cloudy, temps in the 30's and raining lightly. Luckily for us, my grandmother worked for the Red Cross which had setup in a building across from us. We had bathroom and a warm place to go. The crowds were thin that day and we racked up 3 Schwegmann's paper bags full of beads and stuff. Good times.

[BigB0882]

32 degrees and according to the hourly forecast we were supposed to have a low of 33 around 3 am this morning. Haha