February: Tracking Rain/Wintry Mix & Arctic Front

[unome]

From their site: "Please note: The graphics depicted here do not depend on the WPC forecasts. They are derived only from Numerical Weather Prediction model data; therefore, noticeable disagreements with WPC forecast products are possible."

http://www.wpc.ncep.noaa.gov/wwprobs/lo ... _loop.html

[TexasBreeze]

I thought the front was going to be gradual, but it got cold quick and it is 50 now from the mid 70's a few hours ago.

[Ptarmigan]

Currently 44 at CLL. 18Z GFS did not have CLL reaching 43 until 09Z Monday morning. It was forecasting a 00Z temperature of 51 (off by 7 degrees).

12Z NAM was forecasting a 00Z temp of 51 also and CLL not reaching 44 until 12Z Mon. OUCH.

If it is off by 7 degrees, that is rather significant. I think we could see lows in the upper 20s.

[BlueJay]

We are down to 47F.
I hope it doesn't get down to the 20's but...we'll see.

[WeatherDuck]

Here in eastern Williamson County, the temperature has dropped from 42 to 38 in the past hour.

[BlueJay]

Do y'all have rain, Weather Duck?

[WeatherDuck]

Just a fine mist.

[Andrew]

Currently 44 at CLL. 18Z GFS did not have CLL reaching 43 until 09Z Monday morning. It was forecasting a 00Z temperature of 51 (off by 7 degrees).

12Z NAM was forecasting a 00Z temp of 51 also and CLL not reaching 44 until 12Z Mon. OUCH.

I have been keeping an eye on temps all across the state and even the hi-res models such as the HRR and NAM can't keep up with the temperature drop for both timing and intensity. DFW is already at 30 and Lubbock is already at its expected low for tonight.

[BlueJay]

I would appreciate any reports on road conditions from the Magnolia area (FM 1488) up to Austin.
Thank you!

[Ptarmigan]

Here in eastern Williamson County, the temperature has dropped from 42 to 38 in the past hour.

That is quite a drop!

[srainhoutx]

NWS Lake Charles extends Freezing Rain Advisories S to include the I-10 Corridor to just W of Lafayette.

[srainhoutx]

HGX suggesting the freezing line my drop precariously close to NW and N Harris County overnight as the latest short range guidance is coming in a bit colder than expected. Also there is a chance that the upper trough may become more negative tilted on Wednesday as it crosses the area and lift increases with a deeper cold layer suggesting sleet and possibly some grauple may fall Wednesday into the afternoon hours.

[unome]

from TxDot - HOU District's Twitter : https://twitter.com/TxDOTHoustonPio

At this time we will continue to monitor conditions. Crews and resources are ready to mobilize if needed.

For statewide road conditions as wintry weather comes into TX go 2 http://www.drivetexas.org

For local conditions go 2 http://www.houstontranstar.org

[BlueJay]

Thanks for these links unome!

[srainhoutx]

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_a ... babilities

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

[srainhoutx]

02232015 mcd0093.gif

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...

[srainhoutx]

Reports coming in across Travis and Williamson Counties of icing of flyovers and bridges. Accidents being worked in several locations across Metro Austin.

[srainhoutx]

Snow flurries reported in Del Rio.

[tireman4]

This event just might surprise some folks. Please be careful today (slick streets) and tomorrow folks. Please keep a weather wary eye to the sky and monitor all media outlets, the NWS and here. This is an ever changing situation and a few degrees either way will make all the difference in the world.

[BlueJay]

Reports coming in across Travis and Williamson Counties of icing of flyovers and bridges. Accidents being worked in several locations across Metro Austin.

Thank you for this report, srain.