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

[jhamps10]

 

FWD going gung ho on this now... 1-2" of sleet for Ft Worth, Grapevine, Frisco West/North

[Srain]

Morning briefing from Jeff:

 

Winter Storm heading for TX.

 

Increasing threat for ice accumulation over portions of SE TX Monday evening-Tuesday morning.

 

Surface cool front currently lies along a line from Columbus to BUSH IAH to Cleveland with temperatures falling into the 50’s north of this boundary and rising into the 70’s south of the boundary. Front has shown very little movement this morning and do not expect much more southerly progress for much of today…in fact some of the high resolution guidance actually lifts the front back northward midday. Of bigger importance is the arctic front currently plowing through the panhandle. Temperatures behind this boundary are in the 10’s and this air mass is moving quickly southward and should push across SE TX and off the coast this evening with a much more significant temperature fall.

 

Strong cold air advection will onset this evening and continue Monday. Temperatures will fall from this evening through the day on Monday. Temperatures Monday morning in the lower 40’s will gradually fall during the day toward the mid 30’s by late afternoon as ice/sleet accumulation develops over north TX on Monday. Model guidance has trended a degree or two colder for Monday night and Tuesday morning which requires the freezing line to be shifted southward bringing more of the area under the threat for freezing drizzle. Additionally, what seemed marginal freezing temperatures yesterday (30-32) are now expected to be closer to 28-30 over our northern counties Tuesday morning and this is certainly into the critical threshold for ice accumulation on bridges and overpasses. Forecast profiles continue to support a very strong warm layer aloft over top of a shallow surface freezing layer (maybe 1000-2000 ft thick). This continues to support a rain/freezing rain P-type…however some of the latest soundings are showing a smaller warm layer aloft from Huntsville to Livingston Tuesday morning and this could support a mixture of freezing rain and sleet over Walker, Polk, Trinity, and San Jacinto Counties.  

 

Freezing Line:

Of course the critical factor is how far south the freezing line progresses into the region. Current indications suggest the freezing line will extend from Columbus to Waller to between Conroe/The Woodlands to Cleveland from late Monday evening through Tuesday morning. This line has been shifted southward about 50 miles since yesterday. Both GFS and NAM guidance do suggest BUSH IAH does fall to 31-32 for a window Tuesday morning and this is possible between roughly 1100pm Monday and 900am Tuesday. Official forecast has IAH falling to 32 Tuesday morning so pockets of freezing temperatures are possible over northern and northwest Harris County overnight Monday into Tuesday morning. Best thinking at the moment is that the north and west portions of Harris County will fall to 32-33 with the rest of the county and metro Houston falling to 33-34. A degree or two could make all the difference between minor ice accumulation in Harris County and no ice at all.  

 

Ice Accumulation:

Forecast models show general lift being maintained Monday night into early Tuesday when critical temperatures will be reached over portions of the area. Liquid QPF amounts range from .05-.10 of an inch in mainly a drizzle or light rain. Ice accumulation will be greatest from Huntsville to Livingston where temperatures will be colder the longest and likely fall into the upper 20’s resulting in effective freezing of the liquid precipitation. Accumulations in this area will likely average .05-.10 of an inch which is just under the .12 of an inch for our local winter storm warning criteria. North of a line from Columbus to Waller to Conroe to Cleveland ice accumulation of .03-.06 of an inch is possible. Temperatures in this area will be in the 30-32 degree range resulting in a less effective freezing process since the falling precipitation will need to be cooled after passing through the warm layer aloft. Bridges and overpasses are also fairly warm from the recent warmth and will take time to cool to freezing so this region has a more conditional ice accumulation threat especially on bridges and overpasses.

 

Decision Support Matrix:

 

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

                Ice Accumulation: .05-.10 of an inch

                Timing: 600pm Monday-1000am Tuesday

                Temperatures: 28-30 degrees

                Winds: NNE 10-15mph

                Confidence: high

 

                Transportation: prepare for anti-ice operations

                Education: delays and cancellations possible

                Aviation: anti-ice operations likely

                Power: isolated outages possible

 

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

Ice Accumulation: .03-.06 of an inch

                Timing: 1000pm Monday-1000am Tuesday

                Temperatures: 30-32 degrees

                Winds: NNE 10-15mph

                Confidence: moderate

 

                Transportation: standby for anti-ice operations

                Education: delays and cancellations possible

                Aviation: anti-ice operations likely

                Power: isolated outages possible

 

Austin, Colorado, north Harris, central Liberty:

Ice Accumulation: patchy ice accumulation possible

                Timing: 1100pm Monday-900am Tuesday

                Temperatures: 31-33 degrees

                Winds: NNE 10-15mph

                Confidence: low to 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

 

Will update again this evening.

 

[bubba hotep]

is it earlier than anticipated?

 

The intensity of those cells up there probably played a bigger roll in that sleet than the cold air filtering in.  It looks like everyone is still safely above freezing at this point. 

[Captmorg70]

Right now the models are still looking the same as the last day. This first wave has always been showing rain. It does seem like it has really got lift and brining good moisture. We should only start worrying about a bust if the temps don't start dropping this afternoon because most models haven't shown freezing temps until 6 to midnight through ours.

[bubba hotep]

Will have to wait for text output but it looks like the 12z GFS is 0.25" - 0.30" across DFW after temps drop below freezing. That is taking the GFS at face value and not accounting for temps probably cooling faster than depicted. So about 1" of sleet?

[DFWWeather]

The National Weather Service is now saying that travel will become nearly impossible, with roads and bridges and overpasses becoming impassable, across a large portion of the Metroplex and for residents to not get on the roads unless it is an emergency.

[vwgrrc]

image_full3.gif

 

FWD going gung ho on this now... 1-2" of sleet for Ft Worth, Grapevine, Frisco West/North

[David Reimer]

Will have to wait for text output but it looks like the 12z GFS is 0.25" - 0.30" across DFW after temps drop below freezing. That is taking the GFS at face value and not accounting for temps probably cooling faster than depicted. So about 1" of sleet?

 

The typical sleet to liquid ratio is 3:1 so about an inch of sleet - yup!

[aggiegeog]

Glancing through the 12Z models I see no reason to change anything.

[vwgrrc]

The typical sleet to liquid ratio is 3:1 so about an inch of sleet - yup!

So that doesn't include freezing rain? I think FR causes more troubles than sleet.

[bubba hotep]

Freezing line is about to push through Ardmore, Ok on its march south this afternoon. 

[DFWWeather]

So that doesn't include freezing rain? I think FR causes more troubles than sleet.

 

It depends, but eventually it all forms a solid hard coat of ice on the roadways from melting and refreezing. With sleet you get more of the cobblestone ice as they call it. Freezing rain is smoother and slippery with no traction at all. Its all bad. An inch or more of ice whether from sleet or freezing rain is severe icing.

[Roy]

In my personal experience growing up in Kansas, where we had this stuff a lot more often, IF IT'S BEEN WARM FOR DAYS BEFORE THE EVENT, sleet at marginal temps is pretty pitiful, even if it's a lot....you want freezing rain for any big travel impacts there. We had plenty of sleet days with temps barely below 32 where the sleet didn't even freeze on the roads....it just stayed loose ice pellets at first (or melted immediately), which frankly wasn't dangerous at first at least unless it froze into a sheet of ice later, which it often did, so in those cases, often the day after the storm was the more dangerous day. But, if it gets colder and stays cold for a long time, sleet is better at cooling the roads faster. With temps dropping into the mid-upper 20s, I think sleet COULD be worse for the roads than freezing rain at least initially and start the roads freezing more quickly than FZR. But, I am not a met, and other factors might be at play there. Now, if it's been warm before the event and you only get a little tiny coating of sleet, if temps are marginal, there is a chance it mostly evaporates before it has a chance to refreeze after melting. Doesn't look like that will happen this time unless the later impulse ejects too far north or something. Regardless, the NWS folks who are the experts think this WILL freeze badly on the roads. I see no reason to think otherwise. It could be bad well into Tuesday.

[vwgrrc]

Am i the only one found the temps running a few degree lower than anticipated?

[vwgrrc]

In my personal experience growing up in Kansas, where we had this stuff a lot more often, IF IT'S BEEN WARM FOR DAYS BEFORE THE EVENT, sleet at marginal temps is pretty pitiful, even if it's a lot....you want freezing rain for any impacts there. We had plenty of sleet days with temps barely below 32 where the sleet didn't even freeze on the roads....it just stayed loose ice pellets (or melted), which frankly wasn't dangerous at first at least unless it refreezes into a sheet of ice later. But, if it gets colder and stays cold for a long time, sleet is better at cooling the roads faster. With temps dropping into the mid-uper 20s, I think sleet COULD be worse for the roads than freezing rain at least initially. But, I am not a met, and other factors might be at play there. Now, if it's been warm before the event and you only get a little tiny coating of sleet, if temps are marginal, there is a chance it goes away before it has a chance to refreeze after melting. Doesn't look like that will happen this time unless the later impulse ejects too far north or something.

Thinking about the last winter, I guess FR causes more troubles here because it sticks to even vertical surface like trees, power lines, and keep adding the thickness as it falls (Dec 2013). Sleet should bounce off to the ground and easier to plow away (Mar 2014). Just my thought

[bubba hotep]

12z GFS at DFW is 0.31" after temps drop below freezing, an additional 0.07" falls right before temps drop below freezing.  

[Captmorg70]

Am i the only one found the temps running a few degree lower than anticipated?

It's sorta hard to tell but seems close ATM. Heres the NAM temps at Noon. GFS temps are pretty similar.

[vwgrrc]

Sounds like they upgraded the accumulations 

 

URGENT - WINTER WEATHER MESSAGE...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
1051 AM CST SUN FEB 22 2015

 

ACCUMULATIONS...SLEET ACCUMULATIONS AROUND 1 INCH WITH LOCALLY
HIGHER AMOUNTS OF 1.5 TO 2 INCHES THROUGH MONDAY.

[DFWWeather]

Thinking about the last winter, I guess FR causes more troubles here because it sticks to even vertical surface like trees, power lines, and keep adding the thickness as it falls (Dec 2013). Sleet should bounce off to the ground and easier to plow away (Mar 2014). Just my thought

 Not really. Here sleet gets slushy and forms a hard coat of solid ice when enough of it falls and temperatures are cold enough (i.e. below 28°F). Cannot really plow that off the roads with out tearing up the roads. You need to read the cobblestone ice report that the NWS posted back in December remembering the Dec. 2013 event. That was all mostly sleet. Very informative.

[Roy]

Thinking about the last winter, I guess FR causes more troubles here because it sticks to even vertical surface like trees, power lines, and keep adding the thickness as it falls (Dec 2013). Sleet should bounce off to the ground and easier to plow away (Mar 2014). Just my thought

True. When it comes to higher impacts with power outages, not just the roads, freezing rain is much worse. I hadn't really thought about plowing, but if you do it when it first falls, they probably could....wait any time at all though and don't think that's possible as it's already frozen.

[bubba hotep]

Am i the only one found the temps running a few degree lower than anticipated?

 

Temps are running a degree or two cooler across DFW when compared to the 16z HRRR 

[David Reimer]

Temperatures up here in Norman were already below freezing at 9:30 AM when most models only now had us hitting freezing at noon (18Z). It's not going to be good in Oklahoma or Texas tonight, Monday, or even Tuesday. Return of the cobblestone ice is probable in northern parts of D/FW (again). Keep in mind we'll be dealing with thundersleet tonight too - that's what really gives us the major sleet accumulation problems and rapid accumulations. 

[vwgrrc]

David Finfrock ‏@DavidFinfrock  6m6 minutes ago

TXDOT reporting ice beginning to accumulate on brdidges/overpasses on Hwy 287 E of Wichita Falls towards Bowie.

[vwgrrc]

Temperatures up here in Norman were already below freezing at 9:30 AM when most models only now had us hitting freezing at noon (18Z). It's not going to be good in Oklahoma or Texas tonight, Monday, or even Tuesday. Return of the cobblestone ice is probable in northern parts of D/FW (again). Keep in mind we'll be dealing with thundersleet tonight too - that's what really gives us the major sleet accumulation problems and rapid accumulations. 

How do you think this comparing to Dec 2013?

[bubba hotep]

Temperatures up here in Norman were already below freezing at 9:30 AM when most models only now had us hitting freezing at noon (18Z). It's not going to be good in Oklahoma or Texas tonight, Monday, or even Tuesday. Return of the cobblestone ice is probable in northern parts of D/FW (again). Keep in mind we'll be dealing with thundersleet tonight too - that's what really gives us the major sleet accumulation problems and rapid accumulations.

That will be the key, where does the best instability cross the region tonight and tomorrow morning.

[Quixotic1]

Initially freezing rain is worse. It's impossible to get traction on and it brings down trees onto power lines. Skeet is more permanent around here because it is compact dense and has a high albedo. The ground underneath doesn't warm as much. Frozen rain is translucent and lets the coated surface absorb any sunlight.

[bubba hotep]

12z Euro looks like it contracts the northern extent of the precip, but that is mainly an issue up in Oklahoma, and has about 0.30" across DFW after temps fall below freezing. 

[bubba hotep]

Initially freezing rain is worse. It's impossible to get traction on and it brings down trees onto power lines. Skeet is more permanent around here because it is compact dense and has a high albedo. The ground underneath doesn't warm as much. Frozen rain is translucent and lets the coated surface absorb any sunlight.

 

The best thing about sleet, not that there are many, is that we shouldn't see major power issues.  To me this all a waste - snow or bust!

[DFWWeather]

12z Euro looks like it contracts the northern extent of the precip, but that is mainly an issue up in Oklahoma, and has about 0.30" across DFW after temps fall below freezing. 

 

How do you get the 12z ECMFW so early? I don't usually get access to it for another couple hours or so.

[David Reimer]

How do you think this comparing to Dec 2013?

 

The December 2013 storm was 'so bad' in retrospect because temperatures remained below freezing for nearly a week. Any sort of melting that occured quickly froze into a solid block of ice (cobblestone ice). Whoever ends up under thundersleet tonight will likely see rapid accumulation. Some locations, especially D/FW and points north and west, could have similar impacts with nearly impossible travel conditions. With temperatures staying well below freezing on Monday and into most of Tuesday it will certainly be interesting to see how things go.