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

Portastorm

By Portastorm,
in Central/Western States

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Srain

Srain

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Morning briefing from Jeff:

 

Colder air mass has moved in faster than expected requiring changes to Freezing Rain Advisory start times.

 

Freezing Rain Advisory will begin at noon today-600am Tuesday for: Burleson, Brazos, Madison, Walker, Houston, Trinity, and Polk Counties

 

Freezing Rain Advisory will begin at 600pm today-600am Tuesday for: Washington, Grimes, Montgomery, San Jacinto, and Liberty Counties.

 

600am temperatures range from 35 at College Station to 43 at BUSH IAH to 27 at Dallas. Freezing line currently extends from near Austin to Texarkana and has been steadily progressing southward this morning. High temperatures for today have already been reached and temperatures will continue to slowly fall into the 30’s area wide by early afternoon. Freeze line will move into our northern counties between noon and 200pm and then progress southward to a Brenham to Conroe to Cleveland line by 600pm.

 

Regional radars show extensive freezing rain and sleet across much of N TX into the Hill Country and this is confirmed by hazardous road conditions in those areas. Short wave in the flow aloft over New Mexico will move across TX today helping to enhance the precipitation across the region. Where surface temperatures fall to freezing, light rain and drizzle will change to light freezing rain and freezing drizzle. Elevated objects such as trees, power lines, and bridges/overpasses will be cooling to freezing with the air temperature allowing ice accumulation on these surfaces. Soundings and profilers show the forecasted strong warm layer aloft in place with temperatures above 40 degrees a few thousand feet above the surface. Since rainfall is expected to be very light, not sure much if any of the warm layer aloft will mix down helping to offset the cold air advection…this was a concern yesterday that would prevent temperatures from falling as much…but this does not appear to be the case today. Fairly high confidence that the ongoing strong cold air advection will push the freezing line into the area this afternoon.

 

Question then becomes how far south does the freezing line progress tonight into Tuesday morning and how much precipitation falls during this period. 00Z model guidance has trended a degree warmer for tonight even though all guidance is running about 3-4 degrees too warm at the moment. Expect the freezing line tonight to move as far south as a Columbus to Waller to The Woodlands to Splendora line. Forecast models show the best precipitation chances in the noon-midnight time period today with chances decreasing between midnight and 600am on Tuesday.

 

Accumulations:

Ice accumulations in the advisory area will average .01 to .05 of an inch with possibly higher amounts in the Huntsville to Livingston area where temperatures will be below freezing the longest. Road temperatures are fairly warm from the 80 degree highs yesterday and will slowly cool through the day. Suspect surface air temperatures will need to reach at least 30-31 for ice formation on bridges and overpasses. With that said, freezing drizzle is historically the most dangerous of winter precipitation as roadway surfaces can appear dry, but actually have a thin coating of ice…so caution is advised even if the bridge deck appears dry.   

 

Wednesday Morning:

Forecast models show the main upper level storm system moving nearly overhead early Wednesday morning with rapid cooling of the warm layer aloft. While surface temperatures will have warmed into the mid 30’s by this time early Wednesday, sounding profiles suggest rain may change to or mix with sleet. Precipitation in this time period looks much heavier than today. Not expecting any accumulations with surface temperatures above freezing, but will need to monitor for any additional P-type changes or changes in surface temperatures.

 

Freezing Rain/ice accumulation (>.01 of an inch) threat probabilities:

http://www.hpc.ncep.noaa.gov/pwpf/wwd_accum_probs.php?fpd=24&ptype=icez&amt=1&day=1&ftype=probabilities

 

Decision Support Matrix:

 

Burleson, Houston, Madison, Walker, Trinity, San Jacinto, Polk:

                Ice Accumulation: .03-.06 of an inch

                Timing: noon Monday-600am Tuesday

                Temperatures: 28-30 degrees

                Winds: NNE 15-20mph

                Confidence: high

 

                Transportation: anti-ice operations likely

                Education: delays and cancellations possible

                Aviation: anti-ice operations likely

                Power: isolated outages possible

 

Brazos, Grimes, Washington, Montgomery, Waller, northern Liberty:

Ice Accumulation: .03-.05 of an inch

                Timing: 600pm Monday-600am Tuesday

                Temperatures: 30-32 degrees

                Winds: NNE 10-15mph

                Confidence: moderate

 

                Transportation: prepare for anti-ice operations

                Education: delays possible

                Aviation: anti-ice operations likely

                Power: isolated outages possible

 

Austin, Colorado, north Harris (Cypress-Spring-Kingwood), central Liberty:

Ice Accumulation: patchy ice accumulation possible

                Timing: 1000pm Monday-600am Tuesday

                Temperatures: 32-33 degrees

                Winds: NNE 10-15mph

                Confidence: moderate

 

                Transportation: monitor trends/standby equipment and personnel

                Education: delays possible

                Aviation: anti-ice operations possible at Hooks and IAH

                Power: None

 

Fort Bend, southern Harris, Wharton, Jackson, Matagorda, Brazoria, Galveston, Chambers:

Ice Accumulation: None expected at this time

                Timing:  N/A

                Temperatures: 33-35 degrees

                Winds: NNE 14-18mph

                Confidence: moderate

 

                Transportation: None

                Education: None

                Aviation: None

                Power: None

 

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Srain

Srain

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MESOSCALE DISCUSSION 0093
   NWS STORM PREDICTION CENTER NORMAN OK
   0735 AM CST MON FEB 23 2015

   AREAS AFFECTED...PARTS OF E-CNTRL AND NE TX INTO NWRN LA

   CONCERNING...FREEZING RAIN

   VALID 231335Z - 231700Z

   SUMMARY...FREEZING RAIN RATES AROUND 0.05 INCH PER 3 HOURS ARE
   POSSIBLE THIS MORNING.  A MIX P-TYPE WITH SLEET/FREEZING RAIN IS
   POSSIBLE IN AREAS CLOSEST TO THE DFW METROPLEX AND FAR NERN TX.

   DISCUSSION...RADAR MOSAIC AT 1330Z SHOWS A DISCONTINUOUS
   PRECIPITATION SHIELD ACROSS N-CNTRL INTO E-CNTRL AND NERN TX.  KCRS
   RECENTLY OBSERVED A FREEZING RAIN RATE IN EXCESS OF 0.05 INCH/HOUR.
   THIS ACTIVITY APPEARS PARTLY IN RESPONSE TO WEAK WARM ADVECTION
   AROUND H7 AND IS IMPLIED VIA CHANGES AROUND THE MELTING LAYER WHEN
   COMPARING THE 00Z AND 12Z FWD RAOBS.  WEAK ELEVATED INSTABILITY IS
   CONTRIBUTING TO LOCALIZED HEAVIER BURSTS OF SLEET WITH
   SHOWERS/THUNDERSTORMS OVER N-CNTRL TX EARLY THIS MORNING.  MODELS
   ARE IN GENERAL AGREEMENT IN SHOWING THIS AREA OF MID-LEVEL ASCENT
   OVER N-CNTRL TX MOVING TO THE ENE TOWARDS THE ARKLATEX DURING THE
   MORNING HOURS.  THE SRN FRINGE OF THE PRECIPITATION SHIELD SHOULD
   OVERSPREAD THE DISCUSSION AREA THIS MORNING.  INTERPOLATED THERMAL
   PROFILES FROM THE 12Z AREA RAOBS SUGGEST A CORRIDOR OF FREEZING RAIN
   IS POSSIBLE TO THE S OF WHERE SLEET IS FORECAST MAINLY FROM PARTS OF
   N-CNTRL TX INTO SWRN AR.  WET BULB COOLING AND LOW-LEVEL CAA WILL
   LIKELY DROP TEMPS BELOW FREEZING ACROSS PARTS OF NERN TX OVER THE
   NEXT FEW HOURS.  AS A RESULT...FREEZING RAIN RATES FROM E-CNTRL TX
   INTO NWRN LA MAY REACH AROUND 0.05 INCH PER 3 HOURS /LOCALIZED
   HEAVIER AMOUNTS ARE POSSIBLE OVER NERN TX INTO NWRN LA/.

   ..SMITH.. 02/23/2015


   ATTN...WFO...SHV...HGX...FWD...
 

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Srain

Srain

Posted
Posted

Cold Core Upper Low equals Weatherman's Woe. NWS FWD will have an interesting AFD about Wednesday morning up shortly. Interesting discussion going on right now in NWSChat. Concern is certainly there. 

It's certainly worth monitoring. I cannot recall how many times over the years these 5H lows have thrown wrinkle in the best forecast even 6 hours out and with sounding data that was very recent and warm yet still busted with a burst of snow.

 

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bubba hotep

bubba hotep

Posted
Posted

It's certainly worth monitoring. I cannot recall how many times over the years these 5H lows have thrown wrinkle in the best forecast even 6 hours out and with sounding data that was very recent and warm yet still busted with a burst of snow.

 

attachicon.gif02232015 12Z GFS gfs_namer_051_500_vort_ht.gif

 

It will be interesting to see what the 12z Euro has to say.  The 12Z NAM is deeper and has it going neutral as it moves across Texas but the GFS is weaker and keeps a positive tilt.  Now, if the was depicted on the NAM could trend deeper and go negative across... but when was the last time we saw one go negative? It seems like it has been forever but maybe I'm missing a non-fronzen event. 

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