Texas winter wx thread#5 - big changes on the way eventually

[jeff]

Potential for long duration of sub-freezing temps.


Potential for extensive winter precip. over several days including threat of widespread and heavy ice event.


Discussion:

Large scale pattern amplification is underway with high pressure building into Alaska where very cold Siberian air is located. Current temps. are -47 and -46 at ATA and AMC respectively. Building EPAC and west coast ridge will dig a deep downstream trough over the western US which over time spreads east into the plains. Arctic air mass plows southward into the plains Wednesday and Thursday as trough deepens over the western US. Bitter cold air mass with surface temps. in the -20’s and -30’s drops into Montana and the northern plains. Front slows some as it meets increasingly unfavorable flow aloft. However, experience with such setups and bitter cold/dense air mass will likely ooze on southward undercutting the unfavorable flow. Will continue frontal passage late Saturday night/early Sunday morning across SE TX even though the GFS is slowing until Sunday evening. Additionally, will knock 10-15 degrees off guidance values post frontal passage as snow cover over the plains will limit air mass modification.


Temps:


Temps. in the mid to upper 70’s on Saturday will crash 30-40 degrees on Sunday. Expect a good 20-30 degree temp. fall within the first 30 minutes of frontal passage with powerful cold air advection. Highs will be early Sunday with temps. falling into the 30’s and to near freezing by Sunday evening. Cold air advection continues for several days as large arctic high sits over the high plains with multiple reinforcing surges of cold air. Will go with temps. falling below freezing early Monday and remaining at or below freezing through Thursday due to clouds and precip. Expect temps. to hover in the upper 20’s to around 30 for most of this period.


Precip and P-type:


The following is very preliminary and subject to large changes.


Overrunning rains begin almost immediately behind the front as large upper trough hangs back over the western US. Shallow but freezing air mass at the surface overrun by warmer air aloft suggests a significant freezing rain/ ice threat. Should be all liquid Sunday and then things go downhill Sunday night. As temps. falls to freezing and below from north to south across the area, rain will begin to freeze on contact with the ground. Expect glazing to begin early Monday across the northern counties and sink southward during the day. Models continue precip. through Tuesday and as the cold air deepens over time rain may mix with or change to sleet and snow. Main P-type at this time appears to be freezing rain with potential for heavy ice accumulations especially northern counties. GFS continues precip into Wednesday and Thursday as short waves rotate through the mean trough…however feel we will not have freezing rain or sleet the entire time…if we do it will be nothing short of an historic event with devastating effects.



Residents should pay close attention to the forecast over the next several days. Long duration period of sub-freezing temps. may cause exposed pipes to freeze and precautions should be taken while the weather is warm to protect outside pipes and sprinkler systems. As we get closer to the event, accumulations will become the main topic along with differing P-types. Should the current forecast hold…icing will be enough to cause widespread power failures as trees collapse under the weight of the ice and take out power lines. As one would expect in TX surface travel could be extremely difficult if not impossible by this time next week. Should the forecast continue to suggest the threat of winter precip. TXDOT will begin applying anti-ice chemical to area interstates starting with the bridges and overpasses north and west. This chemical lowers the freezing temp. of water making ice harder to form although applications in N TX have had only modest results.



As with any winter weather threat, timing and moisture considerations are key. Temp and moisture changes over the next 4-5 days will help define the potential threats and large forecast changes should be expected.

[Tireman4]

Yikes. A major league yikes. I will be wrapping pipes this week.

[jasons2k]

All Ican say after looking at the models, etc., is what a MESS!

To me, this looks like an classic icing event setting-up for at least the northern half of SE Texas. Since this is a wet system I don't think we'll see some of the diurnal swings noted on some of the posted forecasts. I'd look for the temp. to just hover in the low 30's. Hopefully the moisture will prevent a devastating freeze.

I'm going to wrap my palms on Saturday and buy some chemical freeze protector and hope for the best. I REALLY don't have time for this - not with my wife in the hospital.

[Johnny]

Prayers outbound for your wife jcchlitz!

[Tireman4]

My prayers are with you. Hang in there.

[Portastorm]

12z GFS run coming in now ... still looks bogus. Hardly moves arctic boundary in Texas panhandle from 96 hrs to 114 hrs.

http://www.nco.ncep.noaa.gov/pmb/nwprod ... /fpc.shtml

EDIT: it's also looking much drier from previous runs.

[Tireman4]

Our local affliate, KHOU is still talking about this event.

http://www.khou.com/weather/


. David Paul likened to Houston being on the outer edge of the cone of uncertainty. He is sounding the caution flag now. Interesting.

[Johnny]

Yep, all in good fun burn1...now be quiet for crying out loud! j/k

[Lindaloo]

If any of you have a problem please contact an Admin or a moderator. Keep it off the board.

[aggiecutter]

Predicting precipitation areas-amounts this far out is a crap shoot with this type of situation. It wouldn't surprise me if there was anything from no post frontal precipitation to a major winter storm. Right now it's just too hard to tell. It'll probably be saturday or sunday before we really know what is going to happen. However, the cold is coming. You can cash that check.

[HouTXmetro]

Predicting precipitation areas-amounts this far out is a crap shoot with this type of situation. I wouldn't surprise me if there was anything from no post frontal precipitation to a major winter storm. Right now it's just too hard to tell. It'll probably be saturday or sunday before we really know what is going to happen. However, the cold is coming. You can cash that check.

So can we be positive in terms of temperature that there will at a minimum be a hard freeze in Houston sometime next week? Will there be a day next week where we don't reach 40 for a high?

[Burn1]

If any of you have a problem please contact an Admin or a moderator. Keep it off the board.

Thank you!

[jasons2k]

Hey HouTX,

As aggiecutter said, it's too early to know yet. I think the chances of a day (or days) below 40F for highs is better than the prospects of a hard freeze. That is more difficult to forecast at this point. We may have a very prolonged light freeze for several hours or even a couple of days - which can be just as devastating as a hard freeze. If we dry out, the chances of a hard freeze go up. If we stay wet, we may hover at 30 with freezing rain, etc., for 24-48 hours. At this point though it's anyone's guess....I'm just posting the possibilities....but based on the current models I'd lean towards the wetter/light freeze scenario.

[Tireman4]

I agree with Jschlitz. I am hearing that as well (wetter/lighter freeze- if there is a lighter freeze..LOL)

[TexasStooge]

Here's the next AFD from the NWS in Fort Worth:

.DISCUSSION...
406 AM
THE WEATHER WILL BE QUIET FOR THE NEXT COUPLE OF DAYS BEFORE THE
EXCITING TIMES BEGIN. A SURFACE RIDGE THAT EXTENDS FROM WESTERN
NEBRASKA SOUTH INTO WEST TEXAS THIS MORNING WILL MOVE EAST DURING
THE NEXT 24 HOURS AND A LEE SIDE TROUGH WILL DEVELOP. LIGHT
NORTHERLY WINDS TODAY WILL COME AROUND TO THE SOUTH TONIGHT...AND
INCREASE IN SPEED DURING THE DAY WEDNESDAY. BY THURSDAY...WE WILL
SEE A CHANCE OF SHOWERS...WITH A BETTER A CHANCE OF SHOWERS AND
SOME ISOLATED THUNDERSTORMS ON FRIDAY.

THE MAIN WEATHER PROBLEM COMES WITH THE TIMING A STRONG ARCTIC
COLD FRONT AND THE CONTINUING PRECIPITATION THIS WEEKEND. AN UPPER
TROUGH IS FORECAST TO SINK SOUTH AND SOUTHEAST FROM THE PACIFIC
NORTHWEST THURSDAY...INTO THE ROCKY MOUNTAINS ON FRIDAY. AN ARCTIC
COLD FRONT WILL MOVE SOUTHWARD TOWARD NORTH TEXAS FRIDAY NIGHT.
GIVEN THAT THIS WILL BE A SHALLOW COLD AIRMASS...WE ARE ASSUMING
THAT THE GFS IS NOT HANDLING IT WELL. THUS WE ARE BRINGING THE
FRONT THROUGH NORTH TEXAS ON SATURDAY. THIS IS OVER 24 HOURS AHEAD
OF THE GFS SOLUTION...SO THERE IS A POTENTIAL FOR A BIG
TEMPERATURE BUST IF WE ARE WRONG...AS WE ARE GOING WELL BELOW THE
GFS MOS GUIDANCE. THE RAIN MAY CHANGE TO FREEZING RAIN SATURDAY
NIGHT INTO SUNDAY ACROSS PARTS OF NORTH TEXAS...WITH SOME FREEZING
RAIN AND SLEET POSSIBLE SUNDAY NIGHT INTO MONDAY.

IF THAT WASN/T BAD ENOUGH...THE GFS FORECASTS ANOTHER CHANCE OF
PRECIPITATION MONDAY NIGHT AND TUESDAY. THE HEAVIEST
PRECIPITATION IS EXPECTED TO BE ACROSS THE SOUTHERN SECTIONS OF
NORTH TEXAS INTO THE HILL COUNTRY. SOME LIGHT SNOW WILL BE
POSSIBLE ACROSS THE NORTHERN HALF/TWO-THIRDS OF NORTH TEXAS...AND
SLEET MOST LIKELY ACROSS THE SOUTH.

Seems we'll see some wintry precip be placed, removed, and replaced from the North Texas forecasts before the week is over.

[Portastorm]

This is from NWSFO Fort Worth, mid-morning forecast discussion:

"MAIN FORECAST ISSUE OBVIOUSLY CONTINUES TO BE THE ARCTIC AIR THIS
WEEKEND. TIMING CONTINUES TO BE RATHER ILL DEFINED IN THE
MODELS...BUT IT DOES LOOK LIKE IT WILL BE VERY COLD BY SUNDAY AND ON
INTO EARLY NEXT WEEK. 0Z GFS APPEARS TO BE AN OUTLIER WITH THE
EARLY WEEK SNOW/SLEET STORM...AND 12Z RUN HAS COME IN WITH A MORE
PROGRESSIVE TROUGH LIKE THE OTHER MODELS. THEREFORE THE CHANCE OF
ANY WINTER PRECIP APPEARS TO BE ON SUNDAY...WITH THE PRECIP TYPE
BEING RAIN OR FREEZING RAIN AS VERY SHALLOW LAYER OF SUB FREEZING
AIR UNDERCUTS THE MOISTURE/LIFT ALOFT. CURRENT FORECAST HAS THIS
COVERRED WELL...AND WILL MAKE NO CHANGES AT THIS TIME. WILL AWAIT
THE 12Z ECMWF/UKMET BEFORE DECIDING ON WHETHER TO PULL OUT PRECIP
CHANCES EARLY NEXT WEEK."


My question: What models are they talking about? The Euro holds the trough back west of us. Maybe the UKMet? This 12z GFS run is the first time I have seen a "progressive trough" depicted.

Boy am I confused now.

I'm not sure anyone yet has a good fix on this situation ... other than it's going to get "abnormally cold" as aggiecutter reiterated earlier.

[HouTXmetro]

What does a Progressive trough mean... It will hold back? If so doesn't that mean the front should arrive sooner with less resistance from the trough (SW flow aloft)?

[wxman57]

What does a Progressive trough mean... It will hold back? If so doesn't that mean the front should arrive sooner with less resistance from the trough (SW flow aloft)?

"Progressive" means moving on, not holding back. I see two classic GFS errors in the 12Z run. I'd prevace that by saying that the GFS often does a good job with these situations in the long-range but loses them in the mid range. What the GFS did at 12Z was to fiirst develop a bogus lee-side low that "holds" the Arctic air back until it kicks out. That's almost certainly an error. The Arctic air win't be making any detours, it's coming south.

The second likely error is that the 12Z GFS takes that strong disturbance which was to move across the Gulf Coast states next Monday-Tuesday to the west and off the west U.S. Coast. Then it moves the trough axis on to our east. Thus the discussion of a more progressive trof with the 12Z GFS. If that actually happened, then the Southern Plains and Gulf Coast would get a shot of very cold air but no precip behind the front. I think this solution is probably unlikely. Let's see how the 12Z EC handles it in a few hours.

[southerngale]

How long until the 12z EC comes out?

Btw, we really appreciate your input, wxman57. Thanks.

[wxman57]

I'm more sure about the first GFS error (leeside low holding back Arctic air) than the 2nd error (trough not moving across the cold air early next week). It is possible that there will be no post-frontal precip. However, I do know that the GFS and the old MRF had a difficult time in the 3-5 day time frame before such an event.