Texas/New Mexico/Louisiana/Mexico Obs And Discussion Thread Part 5

[Srain]

Update from Jeff:

 

NWS will be issuing a Winter Storm Watch effective from 300am Tuesday until midnight Wednesday for all SE TX counties.

 

High impact winter storm appears likely Tuesday and Wednesday.

 

Discussion:

Forecast models have come into much better agreement today with increasing threat of accumulating ice and snow across all of SE TX starting early Tuesday and lasting into early Wednesday. Nearly all global models agree that moisture and cold air will be in place at the same time to produce a period of mixed precipitation across nearly the entire area. Still some uncertainty in when exact locations fall to and below freezing on Tuesday which will dictate when exactly accumulations begin.

 

Temperatures:

Arctic front will push off the TX coast Monday afternoon with temperatures falling into the 30’s and 40’s for most areas by sunset. Freezing line will reach the northern counties between 1000pm and midnight and progress to the I-10 corridor by 300-400am and close to the coast by 800-1000am Tuesday. Do not expect much if any temperature recovery on Tuesday as increasing precipitation along with ongoing cold air advection will result in evaporative cooling of the air column and surface temperature. Think any amount of potential warm up will be under-cut by this process. Very cold Tuesday night into Wednesday morning with lows falling into the mid 20’s at many locations. Wednesday warm up will be slow and is highly dependent on the degree of cloud cover and when clouds begin to break. Way too soon to attempt to give any kind of feeling on when certain areas will rise back above freezing on Wednesday, but it will likely be after noon and if clouds do not thin and with ice/snow on the ground it may not happen at all.

 

P-type:

Going to be a mess trying to time P-types and changes at locations. Air mass is colder than the last event which would support more snow, but pesky warm layer is seen in soundings which has burned us before in this area (Feb 2011) keeping P-type more in the freezing rain category. Models want to produce more snow, but I am just not completely sold on it yet. Best P-type attempt and changeover right now:

 

North of Brenham to Conroe to Cleveland: sleet and snow starting prior to 600am Tuesday and changing to all snow during the day.

 

North of I-10: freezing rain and sleet starting around 900-1100am changing to sleet and snow in the late afternoon.

 

Coast to I-10: freezing rain starting around noon. Freezing rain mixing with sleet by mid afternoon. Possible change to snow after 800pm Tuesday.

 

There is going to be changes with these P-types over the next 24 hours and this will affect accumulation amounts.

 

Accumulation:

Since the air mass and surface temperatures look colder with this event than the last…expect much more efficient ice/snow accumulation with much less melting. Appears most of the area will be at or below freezing at the onset of the precipitation which will help increase accumulation over last week. With that said…mixed phase precipitation is extremely hard to get good accumulation amounts on. Will keep things fairly general at this point

 

Freezing rain and ice accumulations of .10 to .20 across the area….mainly south of I-10

Snow accumulations of 2-4 inches north of Hwy 105…likely little freezing rain in this area

Snow accumulations of 1-2 inches all other areas on top of possible ice accumulation

 

Another aspect to keep in mind is the potential for meso scale snow banding which has been seen in past events (Dec 2004, Dec 2008, and Dec 2009) in which favorable lift can focus a period of moderate to heavy snow across certain locations. This is very much like trying to forecast training heavy rainfall in the summer months and is nearly impossible to determine until it is underway but can result in very quick and more significant accumulations.  

 

Impacts:

 

Big impact is going to be onset of precipitation during the daytime hours versus overnight/morning. For the most part Tuesday morning 400-800am looks dry, with precipitation breaking out during the day. This will likely result in a fairly uneventful morning rush hour with conditions going quickly downhill in the afternoon hours and a potentially very difficult evening rush hour.

 

A note to be said about snow…most people think it is easier to drive on snow…and this is usually true, but only if the ground below the snow is at or below 32…which here is not the case compared to up north. Ground and roadway surface temperatures will be hovering in the 31-35 range which will melt falling snow into a layer of ice over top the pavement which then becomes snow covered. This produces extremely hazardous driving conditions and is very common in the southern states during snow events.

 

Given the colder surface air temperatures, may be looking at icing and accumulation on surface streets and just not bridges/overpasses. A layer of ice can form on surface streets even if the ground is above freezing due to surface cold air. Typically this will happen when temperatures are in the mid to upper 20’s for a period of time. This happened in Dallas in early December with air temperatures in the mid 20’s yet ground temperatures were in the mid 30’s.

 

Freezing rain looks likely especially south of I-10 to start the event and then it becomes important how quickly precipitation changes over to sleet or snow or some combination. Do not think accumulations will be enough to cause widespread disruption of power, but if the change was slower or does not happen amounts could be very near the .25 of an inch threshold to start to cause power problems. Other comment is that it is going to be colder, so almost all the freezing rain is going to glaze into ice very effectively with little moisture lost….this is a big difference from last week when the first .10-.20 of liquid was lost due to surface temperatures being above freezing..    

 

[wxmx]

18z NAM is wintry precip heaven from here to lower Rio Grande valley. Not saying it was expected, but what I expected was the slowing down and strengthening of the s/w at the base of the trough, more in line with the rest of the guidance. I expect the same for the GFS...hopefully not by much.

[DoctorMu]

Who do I need to see about locking in the 12z GFS from hour 204 on?

 

 

 

[DoctorMu]

sRain - just about to post the Winter Storm Watch advisories are out and scrolling across local CBS station

 

[wxmx]

On a bit of good news, or so I think, the GGEM Ens and ECMWF Ens are  more progressive with the shortwave than their operational counterparts.

[Srain]

LCH and LIX issue Winter Storm Watch.

[wxmx]

18z NAM is wintry precip heaven from here to lower Rio Grande valley. Not saying it was expected, but what I expected was the slowing down and strengthening of the s/w at the base of the trough, more in line with the rest of the guidance. I expect the same for the GFS...hopefully not by much.

Wrong...faster with the 18z run. Probably too fast.

[1900hurricane]

HGX is somewhat aggressive with their wording in the discussion.

 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
343 PM CST SUN JAN 26 2014

.DISCUSSION...
HIGH IMPACT WINTER WEATHER EVENT ACROSS ALL OF SOUTHEAST TEXAS ON
TUESDAY! WINTER STORM WATCH IS IN EFFECT FOR TUESDAY.

 

...THE MUCH ANTICIPATED ARCTIC FRONT SET TO ARRIVE TOMORROW IS

CURRENTLY MOVING THROUGH NEBRASKA WITH TEMPERATURES BEHIND THE
FRONT IN THE SINGLE DIGITS TO LOW 20S BEHIND THE FRONT ACROSS
NORTH AND SOUTH DAKOTA. A PREFRONTAL TROUGH NOW ACROSS OKLAHOMA
WILL ARRIVE EARLY MONDAY MORNING BRINGING NORTH WINDS WITH THE
ACTUAL FRONT ARRIVING JUST AFTER SUNRISE AND SWEEPING THROUGH TO
THE COAST BY MID AFTERNOON. TEMPERATURES WILL HOLD STEADY BEHIND
THE FRONT AND THEN SLOWLY FALL THROUGH TUESDAY MORNING WITH MOST
AREAS FALLING BELOW FREEZING ASIDE FROM THE IMMEDIATE COASTAL
AREAS. TEMPERATURES ACROSS OUR NORTHERN COUNTIES WILL LIKELY DROP
INTO THE MID 20S.

ON TUESDAY AN UPPER LEVEL DISTURBANCE WILL MOVE ACROSS NORTHERN
MEXICO AND BEGIN TO APPROACH OUR AREA FROM THE SOUTHWEST. THIS
FEATURE...COMBINED WITH FAVORABLE UPPER LEVEL SUPPORT FROM THE RRQ
OF AN UPPER JET...WILL PRODUCE LIGHT TO MODERATE PRECIPITATION
ACROSS SOUTHEAST TEXAS IN THE FORM OF A WINTRY MIX. AT THIS TIME
IT APPEARS THAT PRECIPITATION WILL BEGIN ACROSS OUR NORTHERN
COUNTIES EARLY TUESDAY AS A MIX OF SNOW AND SLEET WHICH WILL
GRADUALLY TRANSITION TO SNOW AS IT MOVES FROM NW TO SE ACROSS THE
REGION. ADDITIONAL PRECIPITATION WILL DEVELOP NEAR THE COAST BY
LATE MORNING AS A MIX OF FREEZING RAIN AND SLEET WHICH WILL
GRADUALLY TRANSITION TO SLEET AND SNOW THROUGH THE DAY BEFORE
MOVING EAST OF THE REGION LATE TUESDAY EVENING. WHILE THERE
REMAINS SOME UNCERTAINTY WITH REGARDS TO TIMING AND EXACT
PRECIPITATION AMOUNTS THERE IS GOOD CONSENSUS BETWEEN THE FORECAST
MODELS AND CONFIDENCE IS HIGH ENOUGH TO GO AHEAD AND ISSUE A
WINTER STORM WATCH FOR ALL OF SOUTHEAST TEXAS BEGINNING EARLY
TUESDAY MORNING THROUGH MIDNIGHT TUESDAY NIGHT/WEDNESDAY MORNING.
THIS COVERS THE EXPECTED TIME FOR PRECIPITATION ACROSS THE REGION
ALTHOUGH TRAVEL IMPACTS WILL LIKELY PERSIST INTO WEDNESDAY AS
TEMPERATURES WILL REMAIN BELOW FREEZING FOR MOST AREAS INTO MIDDAY
WEDNESDAY. GIVEN THAT WE ARE DEALING WITH WINTER WEATHER IN
SOUTHEAST TEXAS EXPECT TO SEE SOME ADJUSTMENTS TO THE FORECAST AS
WE GET CLOSER TO THE EVENT.

[DoctorMu]

Local KBTX rolling out their new forecast graphics...still buying in:

[Quixotic1]

I like the looks of this event for SE Texas. Looks even more promising than the last one.

Big pattern flip coming. We can finally be rid of this blasted NW flow and perhaps get some moisture in here. First year I remember where cold hasn't been a problem but moisture has.

[Ed Lizard]

Now that I know Armageddon can happen and my boss still thinks I should be at work, I am actually hoping nothing at all.  Would love an inch of snow, 2009 style, but any amount of ice, I'd just rather skip it.

 

Paid a small compliment to WxMX on KHOU thread.  I don't remember him much from before I was banned from OT anyway.

 

If there was an amateur of the year winner who would forever have a special colored tag, he'd be #3 or #4 in my book.  I think even (most) red taggers learn from Donald Sutherland.

 

 

We need more colorful tags of every color on this thread.  Also OT, but unable to post it, someone should at least nominate me for weenie of the year.  Except, sadly, tropical season 2013 may it hard to even weenie...

[Flexo]

Now that I know Armageddon can happen and my boss still thinks I should be at work, I am actually hoping nothing at all.  Would love an inch of snow, 2009 style, but any amount of ice, I'd just rather skip it.

 

Paid a small compliment to WxMX on KHOU thread.  I don't remember him much from before I was banned from OT anyway.

 

If there was an amateur of the year winner who would forever have a special colored tag, he'd be #3 or #4 in my book.  I think even (most) red taggers learn from Donald Sutherland.

 

 

We need more colorful tags of every color on this thread.  Also OT, but unable to post it, someone should at least nominate me for weenie of the year.  Except, sadly, tropical season 2013 may it hard to even weenie...

 

hey Ed!

 

looks like snow, huh?

[wxmx]

hey, thanks Ed! Looks like you in SE TX will cash in...at least some wintry precip will fall.

 

There are two mostly independent events...first one is from overrunning precipitation Tuesday...it appears that the area around College Station will be primed for this first batch. The second one is the one I'm monitoring for my area, and may affect anywhere from S to SE TX, especially close to the coastal area. This one is the one associated with the shortwave I have been talking about, and it has been a pain in the ass. It's showing up as a cute little mid/upper low in WV as of now approaching northern Baja

 

Time sensitive

 

[Ed Lizard]

hey Ed!

 

looks like snow, huh?

 

 

Snow only is cool.  1 inch or 1 foot.  Even my boss who lives 3 or 4 miles down Westheimer from the Galleria couldn't drive through a foot of snow.  Marginal temp ice event, if he can drive 3 or 4 miles down Westheimer, why is ~25 miles from Houston/Spring any different?

[wxmx]

0z NAM holds serve. Similar to 18z, slightly slower with the shortwave energy, so precip starts a little late around NE MX and the Rio Grande valley, but just in time for the coldest temps of the event.

[msp]

0z NAM holds serve. Similar to 18z, slightly slower with the shortwave energy, so precip starts a little late around NE MX and the Rio Grande valley, but just in time for the coldest temps of the event.

 

yeah, noticeably less precip across central TX with the stuff father north.  most of the nice totals across seTX are from IAH eastward.

[wxmx]

yeah, noticeably less precip across central TX with the stuff father north.  most of the nice totals across seTX are from IAH eastward.

For archiving purposes:

[DoctorMu]

GFS coming in colder and wetter so far than the NAM (but the run is just getting rolling).  NAM keeps to ULL more southerly - more snow for HOU, less for CLL

 

 

Looks more organized 27 hours from now on GFS > NAM  maybe 30-40 mi north a day away from cruising by SETX...we'll see if that makes a difference

 

 

Some like the Grammys, us weenies...

[DoctorMu]

That's a beautiful thing.  Hope it still happens.  My daughter was distraught about the limited snow in the last largely sleet and ice event.

 

 

Updated WPC Winter Weather Outlook Probabilities:

 

01262014 19Z Snow prb_24hsnow_ge01_2014012700f048.gif

 

 

[wxmx]

18z NAM is wintry precip heaven from here to lower Rio Grande valley. Not saying it was expected, but what I expected was the slowing down and strengthening of the s/w at the base of the trough, more in line with the rest of the guidance. I expect the same for the GFS...hopefully not by much.

 

 

Wrong...faster with the 18z run. Probably too fast.

But the 0z run did...well stronger and slower with the disturbance

[DoctorMu]

Party is ON for CLL and HOU and mountains S of Monterrey says GFS

 

 

[wxmx]

Party is ON for CLL and HOU says GFS

 

 

 

 

And MTY the 29th 12z

 

GGEM is not as far west as 12z...still rolling out, but looks like it will swing thru MX a la latest NAM/GFS...maybe a tad slower

 

Edit:

[1900hurricane]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
925 PM CST SUN JAN 26 2014

.UPDATE...
MAINLY CLEAR NIGHT WITH AN EARLY EVENING SPIKE IN DEW POINTS AS
SOUTHWEST BREEZES HAVE BACKED MORE SOUTHERLY. THIS MAY CREATE
MORE OPEN AREA PATCHY FOG (PRIMARILY OVER THE SOUTHERN HALF OF
THE FORECAST AREA) AS DEW POINT DEPRESSIONS FALL TO NEAR ZERO AND
THE BREEZE LAYS DOWN. THE RELATIVELY FAST-MOVING COLD FRONTAL
BOUNDARY CURRENTLY TRAVELING THROUGH NEBRASKA WILL BE PUSHING
ACROSS OUR NORTHERN FA JUST BEFORE SUNRISE...PROGRESSIVELY REACHING
THE COAST BY LATE MORNING.

THE AIR MASS BEHIND THIS FRONT WILL BE VERY COLD AND DRY...MID
TEEN AMBIENT AND NEGATIVE SINGLE DIGIT DEW POINTS IN THE DAKOTAS
EVIDENCE TO THE POTENCY OF THIS NEXT AIR MASS TO DESCEND INTO
TEXAS TOMORROW. NWP SUITE STILL FORECASTING AREAWIDE QPF IN THE
QUARTER (INTERIOR) TO NEAR HALF INCH (COAST) LIQUID PRECIP TUESDAY
THAT WOULD EQUATE TO SNOW MEASURED BY THE INCHES OVER A GOOD PART
OF THE NORTH AND CENTRAL FORECAST AREA. CONFIDENCE IS HIGHER WITH
AN EARLY DAY FROZEN MIX TRANSITIONING TO ALL SNOW (SANS THE IMMEDIATE
COAST...MAYBE) BY THE MID TO LATE AFTERNOON HOURS. THIS IS BECAUSE
OF THE COLD AIR ENTRENCHING ITSELF OVER THE AREA BEFORE AN ANTICIPATED
SHORTWAVE DISTURBANCE RIDING UP FROM THE WEST-SOUTHWEST INITIATES
THE LIFT NEEDED IN GENERATING PRECIPITATION. THIS WILL DEVELOP AS
EITHER UPPER LEVEL FALLING ICE CRYSTALS AND/OR SUPER-COOLED DROPLETS
EVAPORATIVELY-COOL THE LOWER COLUMN TOWARDS THE WET BULB TEMP THROUGH
THE DAY. RELATIVELY SHALLOW EARLY DAY 7-800MB WARM (ABOVE FREEZING)
LAYER IS ANTICIPATED TO SHRINK BACK TOWARDS 0 C INTO MID-DAY. WHILE
SNOW IS BECOMING NEARLY CERTAIN OVER THE FAR NORTHERN INTERIOR
COUNTIES...A LATE AFTERNOON INTO EVENING TURN OVER TO ALL SNOW
OVER (NEAR) COASTAL COUNTIES IS BECOMING A MENTIONABLE EVENT. OF
COURSE...THE REAL HAZARDS WILL COME WITH THE PRECURSOR FREEZING
RAIN AND SLEET THAT WILL COAT ROADWAYS AND POWER LINES WITH ICE.
THE BELOW REASONING STILL HOLDS TRUE ON HOW THIS WINTER WEATHER
EVENT WILL UNFOLD TUESDAY. OF COURSE...TEMPERATURES DURING THE
DAY TUESDAY WILL STRUGGLE TO RISE ABOVE FREEZING...ALL OF THIS
SOUND FAMILIAR? 31

[Ed Lizard]

It may not even end as all snow IMBY...

[DoctorMu]

Fingers crossed this one rolls as an equal opportunity event Ed.  Harder, Colder, Wetter.

 

 

[Quixotic1]

WS Watch for New Orleans. How rare is that?

[Ed Lizard]

WS Watch for New Orleans. How rare is that?

Happens every 4 days. 

 

Depending on the size of the sample...

 

(I do not actually know if they were under a watch or just went to a warning or advisory...)

[wxmx]

0z GGEM and 0z UKMET have abandoned the cutoff low nonsense. The GGEM still lags the shortwave disturbance a bit, and is way south with the precipitation associated to it, but the UKMET is very similar to the GFS/NAM with the evolution of the s/w, and has plenty moisture with it.

 

Let's see what happens with the Euro

[wxmx]

The Euro folded, and it appears very in line with the Ukie, GFS and NAM

[Srain]

Update from Jeff:

 

***High impact winter storm likely on Tuesday***

 

Discussion:

Arctic cold front is surging across TX the morning and is currently nearing College Station. Upstream temperatures over north TX have fallen below freezing with very strong N winds gusting to over 35mph. Even colder surge of air is currently pushing through OK with temperatures in the 10’s. Boundary will move off the coast around midday with strong N winds developing across the region. High temperatures near 60-65 in the next few hours will fall quickly into the 40’s this afternoon and 30’s by early to mid evening under strong cold air advection. A dry air mass will begin to moisten overnight into early Tuesday as lift increases within the cold arctic dome entrenching over the area. Lift appears to come from passing base of trough over the Midwest with precipitation breaking out along the I-35 corridor near Austin and spreading ESE into SE TX on Tuesday. From this I will go into the details.

 

Temperatures:

 

Upstream air mass is very cold and fairly dry. Expect temperatures to fall to freezing by around midnight tonight over our N and NW counties with the freezing line progressing southward early Tuesday and reaching the coast by mid morning on Tuesday. Combined effect of cold air advection and “wet bulbing” or falling precipitation cooling the air temperature toward the dewpoint looks effective in bringing much of the area below freezing in the 600am-1000am period on Tuesday. Onset of precipitation will likely help to enhance the cooling effect and drive temperatures lower during the day instead of upward. By mid afternoon temperatures could be in the mid to upper 20’s across much of the area. Very cold Wednesday morning…could be looking at hard freeze criteria with temperatures bottoming out in the upper 10’s north to low/mid 20’s elsewhere.

 

P-type:

 

Skip down for P-type, “is reasoning”

 

“I have spent a good deal of time pouring over the forecast model soundings this morning and analyzing various winter P-type techniques to attempt to nail down the P-type for this event. I focused on the snow aspect first using the 1000-850mb thickness values in the SREF ensemble guidance. Given a warm nose aloft I was looking for a value between roughly 1300m and 1275m. SREF guidance shows the 1300m line near HWY 105 around 600am Tuesday, but only sags it very slowly southward during the day reaching the I-10 corridor around 21Z (300pm). A fairly well defined and thick warm nose is noted on both the GFS and NAM forecast soundings roughly about 6,000ft thick. There is room within this warm nose for evaporative cooling, but it appears the mid levels do not cool much while it moistens. I have always been worried about that pesky warm nose in the mid levels and I am not sure it can be overcome to produce snow. The forecast soundings look very much like a freezing rain and sleet profile especially from HWY 105 southward to the coast. The warm nose does shrink and the entire temperature profile comes very close to freezing/sub-freezing in the 300-600pm time period Tuesday and this is when a changeover might occur further southward across the metro Houston area. However the soundings also show significant drying and precipitation ending in the 600-900pm time period so the window for snow production along and south of I-10 is fairly small.”

 

North of HWY 105: sleet and snow becoming all snow

North of US 59 (SW) and I-10 (E) of Houston: freezing rain mixed with sleet, possibly changing to all sleet and snow

Coast to US 59 (SW) and I-10 (E): freezing rain changing to freezing rain and sleet mix, possible light snow near end of event

 

Soundings and surface air temperatures really support a freezing rain and sleet event for the southern 2/3rds of SE TX. Northern counties could start as a very brief period of freezing rain, but will likely transition quickly over to snow and remain snow for most of the duration.

 

Timing:

 

Of great importance with this event is the onset timing of the precipitation as the area is facing some hard decisions today. Models are is fairly good agreement on the precipitation onset although some of the most recent guidance is trending just a touch faster so I have windowed out times instead of using hard points due to some uncertainty.

 

N of Hwy 105: 400-600am onset lasting until 300-600pm

N of US 59: 800-1000am onset lasting until 500-800pm

Coast northward: 1000am-noon onset lasting until 800-1000pm

 

Conditions will quickly deteriorate within about an hour or two of the onset of precipitation at a given location.

 

Accumulation:

 

Accumulation is strongly tied to P-type with snow producing more accumulation and sleet/freezing rain less. The major difference between this event and the event last week is that surface air temperatures appear to be about 2-3 degrees colder which will make for very effective ice formation. Additionally it appears temperatures will be at or below freezing the entire time the precipitation process is occurring helping to foster greater accumulation amounts.

 

Other item to keep in mind is the potential for some banding of the precipitation as is sometimes common is more snow situations which can generate locally heavy snowfall rates and localized higher amounts. This is nearly impossible to determine until it is underway, but the last 3 snow events in SE TX have all had meso scale snow bands which produced greater than expected accumulations. I see some of the shorter range guidance attempting to resolve some of this banding…but do not put much faith it their locations at this point.

 

Hwy 105 north: 1-3 inches of snow. A trace - .05 of an inch of ice

US 59 north: .10 to .20 inch of ice/sleet. .50 -1.5 inches snow

Coast to US 59: .10 to .30 inch of ice/sleet. Dusting of snow possible

Matagorda Bay area: .05-.10 inch of ice accumulation.

 

Impacts:

 

Expect some fairly significant impacts especially to travel starting Tuesday morning and lasting into at least midday Wednesday. Surface temperatures are colder with this event so much of the precipitation will freeze and not be “wasted”. Suspect the bridges and overpasses will go pretty quickly…even if they have been treated with the anti-ice agent. Could even see some problems with the surface streets by late Tuesday and especially Tuesday night with temperatures falling into the lower 20’s.

 

As for power outages…still think we are below the needed threshold to get widespread outages. Some of the more “wet” model guidance would push areas along and south of US 59 into the .30-.40 inch of ice accumulation range which could be enough to cause some issues…but this is likely the high end worst case with a more moderated ice accumulation of .10-.30 of an inch. N winds of 15-20mph could add some to the ice effect with additional pressure.  

 

Aviation travel is going to be affected with required de-icing procedures on departing aircraft. Expect ice accumulation on control surfaces prior to take-off and moderate to heavy icing through about 6,000 ft in mixed phase precipitation before breaking into the mid level warm nose.

 

Next update will be with the issuance of the Winter Storm Warning.