JANUARY 2018 - Seasonal WX Week/Pacific Front Saturday

[WWxHopeful]

About what timeframe would any city officials in the northwestern areas of Harris County most of Montgomery County start to think about issuing warnings, possible school delays or closures, etc. Last thing I want is someone to take this lightly and people to head out to work/school Tuesday and get stuck due to roads being in poor condition.

Tomorrow is a Federal Holiday and TXDOT has pretreated some roads/flyovers/overpasses since last Friday. As is usually the case around here with these borderline events, look for tomorrow afternoon to be decision time for exactly where wintry precipitation may impact traveling. I wouldn't be surprised to see a Special Weather Statement issued this afternoon from HGX for our SE Texas Forecast Area.

Great. Thank you for the response.

[TexasMetBlake]

12z Sunday Euro certainly is the most impressive run yet as far as winter weather goes. Here's a snap shot at 48 hrs:

[TexasMetBlake]

12z Euro (Sunday) 54 hrs:

[TexasMetBlake]

12z Euro (60 hrs)

[srainhoutx]

SPECIAL WEATHER STATEMENT
National Weather Service HOUSTON/GALVESTON TX
239 PM CST Sun Jan 14 2018

Houston-Trinity-Madison-Walker-San Jacinto-Polk-Burleson-Brazos-
Washington-Grimes-Montgomery-Liberty-Colorado-Austin-Waller-
Harris-Chambers-Wharton-Fort Bend-Jackson-Matagorda-Brazoria-
Galveston-
Including the cities of Crockett, Trinity, Groveton,
Madisonville, Huntsville, Shepherd, Coldspring, Livingston,
Corrigan, Onalaska, Caldwell, Lake Somerville, College Station,
Bryan, Brenham, Navasota, The Woodlands, Conroe, Willis, Liberty,
Cleveland, Dayton, Columbus, Eagle Lake, Weimar, Sealy,
Bellville, Hempstead, Prairie View, Brookshire, Houston,
Pasadena, Katy, Tomball, Humble, Winnie, Mont Belvieu, Anahuac,
El Campo, Wharton, Pierce, Sugar Land, Missouri City, Richmond,
Rosenberg, Edna, Bay City, Palacios, Pearland, Lake Jackson,
Alvin, Angleton, Freeport, League City, Texas City, Friendswood,
and Galveston
239 PM CST Sun Jan 14 2018

...COLD TEMPERATURES AND WINTRY MIX POSSIBLE TUESDAY...

A strong cold front will push through the area early Tuesday
morning with periods of rain beginning overnight Monday night.
Temperatures will fall throughout the day on Tuesday with the rain
gradually changing over to a wintry mix starting early Tuesday
morning across the Brazos Valley and Piney Woods region. The
change over to a wintry mix will gradually work its way southward
throughout the day on Tuesday, even approaching the coast by
Tuesday night. Light ice accumulations of under 0.1 inch will be
possible area-wide, but are more likely across the northern and
western portions of the area. Light snow accumulations are also
possible across the Brazos Valley and Piney Woods region. A Winter
Weather Watch could be issued in the next day or so.

Cold temperatures are expected Tuesday night in the wake of the
front, with lows reaching the low/mid 20s inland and near freezing
at the coast. Any remaining water could freeze and create
additional ice issues. A Hard Freeze Warning may be required for
portions of the area. Please keep up with the latest forecasts.

[don]

The latest Nam and many of its suite of mesocale models are now more agressive with many of them bringing a decent swath of frozen precip into the Houston area.

[srainhoutx]

URGENT - WINTER WEATHER MESSAGE
National Weather Service Austin/San Antonio TX
250 PM CST Sun Jan 14 2018

...SIGNIFICANT IMPACTS POSSIBLE DUE TO WINTRY PRECIPITATION LATE
MONDAY NIGHT THROUGH TUESDAY AFTERNOON...

.A cold front will move through Monday night and bring with it
cold temperatures, strong winds, and a wintry mix of
precipitation. Wintry precipitation will begin across the northern
Hill Country and Austin between midnight and 6am Tuesday spreading
south through the day. Precipitation will begin as a mix of sleet
and freezing rain with some snow mixing in across the Hill
Country, Austin metro area, and the Rio Grande Plains Tuesday
afternoon. With ice accumulations of around one tenth of an inch
expected significant travel impacts are possible during the day on
Tuesday not just on bridges and overpasses, but also on surface
streets as well due to the cold temperatures. With temperatures
remaining below freezing overnight Tuesday into Wednesday any
accumulated frozen precipitation could remain into Wednesday
morning.

Llano-Burnet-Williamson-Val Verde-Edwards-Real-Kerr-Bandera-
Gillespie-Kendall-Blanco-Hays-Travis-Bastrop-Lee-Kinney-Uvalde-
Medina-Bexar-Comal-Guadalupe-Caldwell-Fayette-Wilson-Gonzales-
Including the cities of Llano, Burnet, Georgetown, Del Rio,
Rocksprings, Leakey, Kerrville, Bandera, Fredericksburg, Boerne,
Blanco, San Marcos, Austin, Bastrop, Giddings, Bracketville,
Uvalde, Hondo, San Antonio, New Braunfels, Seguin, Lockhart,
La Grange, Floresville, and Gonzales
250 PM CST Sun Jan 14 2018

...WINTER STORM WATCH IN EFFECT FROM LATE MONDAY NIGHT THROUGH
TUESDAY AFTERNOON...

* WHAT...Significant icing possible. The ice will result in
dangerous travel conditions for late Monday tonight through the
day on Tuesday. Total ice accumulations of up around one tenth
of an inch are expected with isolated totals up to one quarter
inch.

* WHERE...Most of South Central Texas.

* WHEN...From late Monday night through Tuesday evening.

* ADDITIONAL DETAILS...In addition to the wintry precipitation and
the impacts of accumlating freezing rain, sleet, and snow
temperatures will be very cold. Temperatures will drop into the
upper 20s by Tuesday afternoon and with strong north winds
windchill values could drop into the teens. Overnight Tuesday
into Wednesday as temperatures continue to drop some single
digit windchill values will be possible in the Hill Country.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Winter Storm Watch means there is potential for significant
snow, sleet or ice accumulations that may impact travel. Continue
to monitor the latest forecasts.

[srainhoutx]

Looking at the afternoon WPC Updated graphics for QPF and Winter Weather, we can see an significant increasing in precipitation amounts and probabilities of seeing wintry precipitation across Central, S Central and SE Texas extending into Louisiana compared to the morning graphics I posted earlier today. If these trends continue into the overnight suite of guidance and the 12Z tomorrow runs, Winter Weather Watches may be required across portions of our immediate SE Texas Region extending East into portion of Louisiana. Looks like the Edwards Plateau could be the jackpot area for significant snow accumulations.

[harp]

The NAM, GFS and now the CMC dry up the moisture before it reaches S.E. La. The Euro still gives us hope. Good luck to you winter weather lovers in SE Texas. We may have to live vicariously through you!

[TexasMetBlake]

The 12z GFS forecast sounding looks about as close to an all-snow event as you can get. Maybe a bit of melting around 800 mb but very little.

[TexasMetBlake]

Winter Storm Watch possible for Corpus Christi:

Special Weather Statement
National Weather Service Corpus Christi TX
321 PM CST Sun Jan 14 2018

TXZ229>234-239>247-142330-
La Salle-McMullen-Live Oak-Bee-Goliad-Victoria-Webb-Duval-
Jim Wells-Kleberg-Nueces-San Patricio-Aransas-Refugio-Calhoun-
Including the cities of Cotulla, Calliham, Cross, Loma Alta,
Tilden, George West, Three Rivers, Beeville, Goliad, Victoria,
Laredo, Freer, Benavides, San Diego, Alice, Orange Grove,
Kingsville, Corpus Christi, Portland, Ingleside, Aransas Pass,
Sinton, Mathis, Rockport, Refugio, Woodsboro, and Port Lavaca
321 PM CST Sun Jan 14 2018

...FREEZING RAIN AND SLEET POSSIBLE TUESDAY INTO WEDNESDAY
MORNING...

...DANGEROUS WIND CHILLS POSSIBLE TUESDAY THROUGH WEDNESDAY
MORNING...

A strong arctic cold front will push through South Texas early
Tuesday morning, bringing falling temperatures throughout the day.
Significantly colder air will filter in behind the front as
precipitation lingers across the region. A wintry mix of sleet
and freezing rain will be possible across South Texas beginning
in the northern inland counties during the early afternoon
Tuesday. Anticipate the potential wintry mix to spread further
south to the southern inland counties during the late afternoon,
and into the coastal counties by Tuesday evening into Wednesday
morning. Some light sleet or ice accumulations will be possible
through Wednesday, so roads, bridges, and overpasses could become
hazardous, especially for those traveling Tuesday night or
morning commuters on Wednesday. A Winter Storm Watch may be needed
by Monday as the forecast evolves and confidence increases.

Precipitation chances are expected to diminish by Wednesday
afternoon. However, another potential round of freezing rain will
be possible late Wednesday night into early Thursday morning
across portions of the Brush Country and Coastal Plains, as an
upper level disturbance approaches the area.

In addition to the freezing temperatures and wintry mix, wind
chill values will dip down into the upper teens to lower 20s
during the day on Tuesday, and remain there until Wednesday
morning as low temperatures will be below freezing with a brisk
north wind.

Begin preparing now for any changes in plans that a wintry mix
would cause on Tuesday and Wednesday, and take steps to protect
people, plants, pets, and your home from the expected cold weather.
Motorists should be cautious and slow down over bridges and over-
passes, as roads may become slick in spots. Make sure to allow
extra distance between you and the driver ahead of you, and
consider allowing extra time to reach your destination.

Stay tuned to NOAA Weather Radio, commercial radio or television
on this impending winter weather event. You can also keep updated
on the latest forecasts by visiting our website at:

www.weather.gov/corpuschristi

[MontgomeryCoWx]

I would assume (at the very least) HGX will issue a WWA in the next 18-24 hours. We could
Possibly see a WSW if the trend of wetter continues.

[TexasMetBlake]

Winter Storm Watch possible for Houston within the next day or so.

.Tonight through Wednesday...
Cool but benign weather is expected through Monday. A strong cold
front will push through the area early Tuesday morning with
periods of rain beginning overnight Monday night. Temperatures
will fall throughout the day on Tuesday with the rain gradually
changing over to a wintry mix starting early Tuesday morning
across the Brazos Valley and Piney Woods region. The change over
to a wintry mix will gradually work its way southward throughout
the day on Tuesday, even approaching the coast by Tuesday night.
Light ice accumulations of under 0.1 inch will be possible area-
wide, but are more likely across the northern and western portions
of the area. Light snow accumulations are also possible across
the Brazos Valley and Piney Woods region. Forecast confidence
continues to increase, and we now have moderate to high confidence
of at least some wintery precipitation falling. The finer details
of precisely what type of mix, accumulations, and timing will
likely change some as we get closer to the event. A Winter Storm
Watch could be issued in the next day or so.

Cold temperatures are expected Tuesday night in the wake of the
front, with lows reaching the low/mid 20s inland and near freezing
at the coast. Any remaining water could freeze and create
additional ice issues. A Hard Freeze Warning may be required for
portions of the area. Temperatures should gradually warm through
the day Wednesday, eventually climbing into the upper 30s to low
40s during the afternoon. 11

.Wednesday Night through Monday...
Onshore flow returns Wednesday night as the surface high pressure
system moves eastward over the Tennessee Valley. Isentropic
upglide takes place ahead of an upper-level shortwave trough that
will cross the area Thursday night. The big question is whether or
not the moisture and lift will align with the sub-freezing
temperatures early Thursday morning. At this time, a slight chance
for a wintry mix is possible along the northernmost counties
Thursday morning. Models have trended drier and colder, so
confidence at this time is low. If any wintry precipitation
occurs, accumulations and impacts should be minimal.

The shortwave trough will linger in the Gulf and develop a weak
surface low off the Texas coast, which will keep rain chances
along the coast and offshore throughout the day Friday. Otherwise,
the warming trend will continue until a cold front passes during
the day Sunday. 22

[srainhoutx]

Even in the Rio Grande Valley winter weather is possible...


Area Forecast Discussion
National Weather Service Brownsville TX
324 PM CST Sun Jan 14 2018


...Freezing rain possible Tuesday night and Wednesday...
...Very cold temperatures and low wind chills Tuesday night
through Thursday morning...

.SHORT TERM (Tonight through Monday night):
500mb low/trough across the Midwest United States tonight will
deepen across the north- central U.S. Monday into Mon night
allowing a blast of cold Canadian air to move into the northern
plains tonight and into the southern plains Monday before moving
into central Texas Mon night behind a strong cold front. An
onshore flow tonight through Mon night will allow temperatures to
warm to near normal tonight and Monday and slightly above normal
Mon night before the polar airmass arrives Tues morning. In
addition...moisture will increase across the CWA Monday into Mon
night to mention isolated to scattered showers Mon night as the
front approaches from the north.


.LONG TERM (Tuesday through Sunday):Very challenging forecast for
the first half of long term with an Arctic surge to overspread all
of Deep South Texas and the Rio Grand Valley from Tuesday through
Thursday. Latest model package coming in colder as a 1052mb High
pressure area moves out of Canada Monday and spreads into the
Central/Southern Plains and North Texas Tuesday. The cold air will
continue to surge into our CWA through at least Thursday before
the surface ridge moves east and the airmass modifies rather
rapidly for next weekend.

Without much detail expecting the cold front to move through the
region early Tuesday morning but could reach the Northern
Ranchlands after midnight Monday night. In any case, temperatures
will be falling and rain/drizzle chances increasing through the
day and into Wednesday morning. The main issue and impact with
this system will the rapid drop in temperatures, wind chills and
the chance of freezing rain/drizzle. Models temperature guidance
and forecast soundings show surface temperatures dipping below
freezing over the north and west and into portions of Northern
Hidalgo county. Atmosphere becomes saturated from the surface to
around 700mb as the overrunning machine, isentropic lift, turns
on. A reasonable worse case scenario is if models continue to
trend colder, and some ensemble members are colder, freezing
temperatures along with some patches of freezing rain are possible
along the Rio Grande River Wed from McAllen to Brownsville
Wednesday morning. Confidence is increasing that some winter
weather impacts will be felt across portions of DSTX but with
onset still more than 48 hours away winter storm watches or
warning will not issued at this time. Winds chills to drop below
the 30 degrees Tuesday evening and may not rise above 30 until
later Thursday morning.

As drier air moves into the Northern and Western Ranchlands rain
chances may temporary lower Wednesday afternoon and evening but it
will remain very cold with the EC the coldest and will be trending
in this direction. Models suggest a coastal trough to rapidly
develop Wednesday night and strengthen Thursday with the approach
of a moderately strong mid level shortwave trough. Rain and
drizzle to increase with Thursday possibly being the wettest day
of the week. Not expecting winter weather impacts, although a few
patches of freezing rain is still possible across northern
counties Wednesday night/early Thu, but as temperatures trend to
moderate slightly as east/SE winds at 925-850mb increase the
threat of freezing rain lessens. Overall, it will still be a west
raw Wed night and Thursday.

[srainhoutx]

Sunday afternoon briefing from Jeff:

Winter Storm Watches are issued N/W of SE TX for Tuesday

Winter Storm Watch or Winter Weather Advisory will likely be required for portions of SE TX for Tuesday

Accumulations of ice on Tuesday across portions of SE TX will make driving conditions increasingly dangerous throughout the day

Developing winter weather situation for SE TX for Tuesday. It is important to remember that while confidence is increasing, minor details in temperatures can result in significant variations of P-type and any accumulation amounts. Residents are urged to check forecast frequently over the next 24-36 hours for forecast changes.

Discussion:
Strong arctic high pressure system will drop southward out of Canada later tonight and into Monday sending a powerful frontal boundary into the region late Monday and early Tuesday. Front will blast off the coast early Tuesday morning with a very cold arctic air mass surging southward into the region. Surface freezing line will approach College Station just before sunrise and then slowly progress southward during the day reaching HWY 105 by late morning and possibly I-10 by mid afternoon and the coast by mid evening. This is a slightly faster progression of the freeze line into the region on Tuesday and this requires an extension of potential winter mix of precipitation southward deeper into the area on Tuesday afternoon. While confidence is increasing that winter precipitation will impact portions of SE TX on Tuesday and Tuesday evening, amounts, types, and locations of maximum accumulations remain low confidence.

P-type:
Expect rain to develop Monday night ahead of the arctic cold front and continue in the post frontal air mass. An upper level disturbance will move across the region Tuesday afternoon and evening helping to lift warm and moist air over top of the cooling surface layer. Where surface temperatures fall below freezing during the day on Tuesday rain will change to freezing rain. As the air column cools during the day freezing rain may mix with or change to sleet generally along and NW of a line from Columbus to Hempstead to Livingston. The warm layer above the surface will continue to shrink on Tuesday evening and if there remains enough moisture in place freezing rain/sleet may mix or transition to snow. The highest potential for a snow transition will be across the Brazos Valley from Lake Somerville toward Huntsville.

Accumulations:
There is increasing confidence that accumulations of ice from freezing rain will occur across portions of SE TX. Given the trajectory of the arctic air mass expect accumulations of freezing rain/ice to begin Tuesday morning along and NW of a line from LaGrange to College Station and then expand south and east during the day reaching a line from Columbus to The Woodlands to Coldspring by mid afternoon and then Wharton to Houston to Cleveland by late afternoon and all the way to the coast during the evening hours. Accumulations of ice up to .10 of an inch will be possible NW of a line from Columbus to Livingston where the longest duration of sub freezing temperatures and precipitation will occur. Accumulations of ice is possible as far south as US 59 by late afternoon/early evening, but should average a few .01’s of an inch to maybe .05 of an inch. While these amounts of ice are generally low…any ice on any bridge or overpass is dangerous!

Travel conditions will deteriorate throughout the day on Tuesday from the N and W as the freezing line moves southward. Bridges and overpasses will become icy NW of a line from Columbus to Livingston during the day and icy conditions will spread southward and across at least the northern 2/3rds of the area by early evening Tuesday.



Key Messages:

· Increasing threat for winter precipitation and ice accumulation NW of a line from Columbus to Livingston on Tuesday

· Freezing rain/sleet may progress as far south as US 59 by late afternoon/early evening

· Increasing threat for hazardous travel over portions of SE TX Tuesday spreading S and E with time

· Hard freeze may occur over portions of the area Wednesday morning…make preparations on Monday

· Wind chills Tuesday and Tuesday night will fall into the 20’s and 10’s over the region

Uncertainty:

· How far south and how quickly the freezing line progresses on Tuesday. Confidence is increasing the freezing line will move southward to near I-10 west of Houston by midday and near US 59 by late afternoon

· P-type and accumulation amounts will be tied to moisture in the post frontal air mass and when a location falls below freezing. At this time expecting accumulations of ice to average generally less than .10 of an inch

· Ending of precipitation on Tuesday evening…this will be tied to the exiting of the disturbance to the east and drier air arriving from the north.

WPC Probability of .01 of an inch of ice accumulation valid for 600am Tuesday morning to 600am Wednesday morning:

01142018 20Z Tuesday 24 Hour ZR Probs prb_24hicez_ge_01_2018011500f060.gif

[Andrew]

Seeing a better and better chance of frozen precip from I-10 North. Models are usually notorious for underestimating the advance/intensity of cold air in these type of situations. I suspect the trend of colder will only continue over the next day or two. With that said, models also underestimate the thickness of the warm nose. Paired with little room for wet bulbing makes it even harder to get a below freezing profile. I think eventually the warm nose will erode but I am not sure if moisture will still be around. Either way I suspect advisories/watches will be issued for the northern part of the CWA here tonight or tomorrow morning.

[srainhoutx]

Looking like the NAM is holding steadfast regarding our wintry weather threat. HGX is slowly ramping up this treat and I suspect laying the groundwork for potential Winter Weather Watches/Advisories possibly as soon as tomorrow morning.

[TexasMetBlake]

After speaking with HGX, it appears as though no modifications will be made to the Winter Storm Watch to our northwest. In fact, a winter storm watch will NOT be issued at all (at least right now) as accumulations of ice or snow is expected to remain below watch criteria.

However, per the latest AFD, a Winter Weather Advisory may be required for ALL of southeast Texas by Monday.

[MontgomeryCoWx]

Well done Blake!

[don]

The 0z NAM suite of mesoscale models are coming in stronger for Southeast Texas