DFW: Arctic Blast Wednesday with a Chance of Winter Precipitation on Thursday

Special Update #2 (Wednesday 12/31 3:30 pm CST)

Note: A new forecast update has been posted.  Click here for more information.

Special Update #1 (Tuesday 12/30 10 pm CST)

The freezing line is now approaching Denton and Tarrant Counties (at 10 pm CST 12/30).  Temperatures will begin to fall sharply in the metroplex over the next couple of hours as the Arctic air infiltrates North Texas.  I still do not expect temperatures to rise above freezing on Wednesday (as indicated in the previous forecasts below).  There are also no changes to the freezing rain/sleet forecast.

Note: Based on current trends, it wouldn’t surprise me at all to see a Winter Storm Watch/Warning issued for parts of N. TX for tomorrow night/Thursday. In fact, given that we are going to be dealing with a freezing rain event, an Ice Storm Warning may be warranted for parts of the area. Pay very close attention to the forecast updates tomorrow (Wednesday 12/31), because freezing rain events tend to be narrow in nature (spatially speaking) and D/FW will be in a critical location relative to the heaviest rain and the freezing line. I will resume updates with new data tomorrow (Wednesday 12/31). All of the current forecasts that I posted yesterday (below) remain unchanged. /Chris Robbins

The main round of precipitation should begin to affect North Texas Wednesday night, but there may be some light winter precipitation around the area late tonight (Tuesday night – see the 9:30 pm CST radar image below, which indicates light precipitation forming to the west at the time of this special update) and very patchy freezing drizzle tomorrow (Wednesday).  At this time, I see no reason to modify the precipitation graphics.

The first two maps below show CURRENT temperatures (the first map is for the entire Southern Plains using temperature data at 8 pm CST, the second map is a closer look at North Texas using temperature data from 9 pm CST).

The third image in this Special Update is the 9:30 pm CST radar image, which shows freezing drizzle developing to the west of the metroplex (as of the time of this update, it is already down to 22º in Abilene).  Light sleet or light snow will be possible across the western and northern portions of the area light tonight, but this should not accumulate.

OBSERVED: Southern Plains Temperatures 8 pm CST Tuesday 12/30
OBSERVED temperatures over the Southern Plains (8 pm CST, Tuesday December 30).

OBSERVED temperatures over the Southern Plains at 8 pm CST (Tuesday December 30)

OBSERVED: North Texas Temperatures 9 pm CST Tuesday 12/30
OBSERVED temperatures over North Texas at 9 pm CST (Tuesday, December 30)

OBSERVED temperatures over North Texas at 9 pm CST (Tuesday, December 30)

OBSERVED: Radar at 9:30 pm CST Tuesday 12/30

Weak isentropic lift to the west of D/FW spreading northeast.  Models indicate some weak frontogenetical forcing and some isentropic lift that may cause very light sleet/snow and freezing drizzle over western and northern parts of North Texas tonight (12/30).  This activity will be insignificant.

Radar image at 9:30 pm CST (Tuesday, December 30) indicating freezing drizzle developing west and southwest of the metroplex

Radar image at 9:30 pm CST (Tuesday, December 30) indicating light precipitation developing west and southwest of the metroplex… possibly in the form of light freezing drizzle, flurries, and ice pellets

OBSERVED: Radar at 11:55 pm CST Tuesday 12/30…

Weak isentropic lift and bands of frontogenetic forcing over North Texas.  These forcing mechanisms are weakening and precipitation will dissipate.

Posted on Facebook (WeatherNet page) at 1:07 am 12/31:  If you’re seeing some light sleet or light snow from D/FW northward right now, it will not last long. The atmospheric models have been indicating some narrow/weak frontogenesis and isentropic lift over North Texas tonight. The forcing caused by those mechanisms and the resulting VERY light precipitation will dissipate soon. The main precipitation event will be tomorrow night (Wednesday night into Thursday).  /Chris Robbins

Radar image Tuesday night (12/30) at midnight.  Very light sleet and some snow flurries were reported from D/FW northward.  No accumulations occurred.

Radar image Tuesday night (12/30) at midnight. Very light sleet and some snow flurries were reported from D/FW northward. No accumulations occurred.


Previous Forecast Discussion Posted on Monday, December 29, 2014

I am closely monitoring a significant Arctic airmass that is poised to move south over the next few days.  The Arctic front will move into North Texas Tuesday night, with temperatures on Wednesday struggling to rise above freezing.  I expect highs on Tuesday to be in the upper 40s to near 50º ahead of the Arctic front.

Forecast high temperatures for Tuesday 12/30, ahead of the Arctic front.

Forecast high temperatures for Tuesday 12/30, ahead of the Arctic front.

By 7 pm Tuesday, the Arctic front will be moving through Oklahoma, approaching the Red River.  It should arrive in the DFW metroplex around midnight.  At 7 pm on Tuesday, the center of the surface high will be located over northwest Nebraska, with surface pressures in the range of 1050 to 1055 mb. This is very impressive and signals to me that this airmass may be colder than the NWP model guidance are indicating.

Position of the Arctic front at 7 pm Tuesday (December 30)

Position of the Arctic front at 7 pm Tuesday (December 30)

The front will move through D/FW Tuesday night (around midnight), with temperatures falling rapidly through the 30s, and eventually into the 20s.  As mentioned above, surface pressures in the range of 1050 to 1055 mb over northwest Nebraska at 7 pm Tuesday suggest to me that the airmass is not only extremely cold, but will likely be much colder for North Texas than most of the atmospheric models are (have been) indicating.  For this reason, the coldest model solution (NAM) is favored given its propensity for best handling Arctic airmasses.  Thus, my forecast for Wednesday (12/31) is for high temperatures to hold near to below freezing all day.

This map shows my forecast high temperatures for Wednesday, December 31:

High temperatures over N. TX, behind the Arctic front. Most locations at or below freezing, especially the northwestern 1/2 of the area.

High temperatures over N. TX, behind the Arctic front. Most locations at or below freezing, especially the northwestern 1/2 of the area.

After the cold air arrives, a series of disturbances will move across Texas, beginning as early as Wednesday morning.  This is an extremely difficult forecast, and it will be subject to change over the next few days.  For now, I am forecasting an initial disturbance on Tuesday night/Wednesday to bring a mixture of freezing rain/sleet/snow in the highlighted area on this map (well west of the metroplex, but affecting areas such as Abilene, Lubbock, and Amarillo):

Light sleet/snow mixture possible well west of D/FW on Wednesday. Overcast expected in N. TX.

Light sleet/snow mixture possible well west of D/FW on Wednesday. Overcast expected in N. TX.

This next map shows the 500-mb pattern for 4 am Thursday 1/1.  The main forcing associated with the upper low to the west is the culprit, sending waves of precipitation into Texas Wednesday night through early Friday.

500-mb geopotential height and vorticity at 3 am CST on Thursday, January 1, 2015

500-mb geopotential height and vorticity at 3 am CST on Thursday, January 1, 2015

The main round of precipitation will move into the metroplex Thursday morning, spreading from south to north across the area.  With wet-bulb temperatures in the 20s, there will be sufficient evaporative cooling to support sleet/freezing rain.  This portion of the forecast is extremely complicated, and I will update the forecast with future data.

Freezing rain and sleet possible Thursday, mainly before noon. Changing to rain in the afternoon. Forecast subject to change.

Freezing rain/sleet possible Thursday. Changing to rain in the afternoon. Forecast subject to change.

I believe that warm air advection will eventually take over, and cause temperatures to rise (Thursday afternoon/night).  If this happens as expected, it would bring the winter precipitation to an end.  This will be monitored closely.

Although we are still three days out, now is the time to start paying attention to the forecasts.  I will update as frequently as I possibly can, so please bookmark this page.  This event has the potential to bring a significant accumulation of ice to portions of North Texas.  Unfortunately, predicting the exact temperature within a degree or two of 32º is an extremely challenging task in these situations (especially three days in advance).  If the temperatures do not warm as expected, ice amounts could be significant.  If the precipitation arrives later than expected (i.e., after temperatures rise above freezing), then there will be little to no ice.  This forecast is certainly subject to change as I analyze future data.

Remember: Stay tuned for future weather statements and possible weather watches for the affected areas.  If you have New Year’s Eve or New Year’s Day travel plans, consider the forecast and call ahead to confirm your flight status. If traveling by automobile, keep an eye on the radar and pay attention to road conditions along your route.

 

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