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Some interesting runs occurred tonight by both the GFS and NAM in regards to this weeks arctic front. We should continue to see rising temperatures through Wednesday as we see some nice Warm Air Advection from the Gulf Coast. This should push temps into the 80's over the next couple of days with morning fog being an issue for most of the area. Calm winds and higher temps paired with cooler offshore waters should allow for some dense fog to develop throughout most of the area for the next couple of days. This will all change on Thursday though, as we see the progression of a very strong but shallow surface front. Models have been struggling with the forward motion of the front and I expect this to continue for the next couple of days. This synoptic setup looks similar to that of last weeks and models are probably underestimating the density/ speed of the cold air. Right now my thinking is that any delay/temporary stall of the front will be minimal and we will see FROPA passage throughout the northern counties before Noon on Thursday. Temps should begin to drop pretty rapidly behind the shallow front leading to a cold and wet Friday with temps in the 40 to 50's throughout most of the area. Things get interesting on Saturday, especially for our northern counties as we begin to see moisture override the front. With an active jet to the north upper level divergence could allow for some decent overrunning of precip across the area spreading all the way north to North Texas. On top of that models have begun to sniff out a coastal low developing S-SE of Brownsville on Saturday morning. This should help to increase moisture levels especially at the lower levels. Looking at temps, the 00z runs have come in quite a bit colder with temps in our northern counties in the upper 20's/lower 30's for Saturday and in the upper 30's for the Houston Metro Area. This could create problems to the north with freezing rain/sleet. Due to the shallow nature of this front freezing levels look to only extend up to 900mb which means if you want any hope of wintry precipitation, below freezing temps are going to be crucial at the ground. There is a strong inversion (lack of frontal passage) after 900mb where temps get close to 10 C which would completely liquefy anything falling. The key here is while we see FROPA (Frontal Passage) at the ground, the upper levels show no passage of the cold air. This is pretty obvious if you check out the skew-t I have posted below (notice the Northern winds at the ground and the SW winds above indicating the lack of FROPA). While models are indicating dry air at the 500mb level I suspect with saturation throughout the rest of the column, it won't take much to eat through that dry level and could even allow for a little bit of evaporative cooling (but I doubt that will make its way to the surface). Overall I feel like models are heading in the right direction with this one and with the source region (Alaska/NW Canada) being colder than the last event, this event has a better chance of being confirmed. Beginning Thursday night Northern Texas could begin to see Wintry precip and I suspect that some of our northern counties will join in Saturday. As always though with any wintry precip possibilities the details will make or break this event so we will have to keep an eye on the TRENDS throughout the next couple of days and we should get a better idea as the colder air begins moving south.


KCLL 108H Sounding:
GFS 120H 10m Wind/temps:
NAM 84H 10m Wind/Temps:

Wow, nice comprehensive write-up Andrew! Plenty here for us laypeople to understand but also you included some good technical, rule-of-thumb meteorological information.

The coastal low/trough issue is obviously huge for us in South Central and Southeast Texas in the possibility of freezing precip down the road.

Hey all, is there anywhere to find a future radar forecast, hourly, for Thursday? We have a parade that night and need to play it by ear, need to finish the float in the afternoon, and get the kids on board. parade starts at 7. wondering exactly how much rain we will face and if it will be cold for the kids that night. thank you!

Andrew wrote:
The NAM isn't "TERRIBLE" at 24-48 hours out but is definitely one, that if an outlier, I will disregard. Interesting to note though that the 00z GFS is coming in faster and colder and is comparable to the 00z NAM

NAM has been right in the past. I do like their Doppler radar forecast for what the storm would look like.

hlewis wrote:Hey all, is there anywhere to find a future radar forecast, hourly, for Thursday? We have a parade that night and need to play it by ear, need to finish the float in the afternoon, and get the kids on board. parade starts at 7. wondering exactly how much rain we will face and if it will be cold for the kids that night. thank you!

Here's the high-resolution NAM model that has a simulated radar reflectivity product that goes out to 60 hours in the future. It is usually a pretty accurate model in my opinion.
http://mag.ncep.noaa.gov/model-guidance ... imageSize=

I feel the models are underestimating the level of cold air near the surface. They're not reflecting the snow/ice cover which will be laid down to our immediate north and I think that will end up placing surface temps several degrees lower in parts of south central and east Texas than what we are currently seeing in the model depictions. Just my two pesos.

Think this system might be a little colder than the pre-Thanksgiving one but will feature less quantitative precip. Regardless, I do think Friday morning in areas like Aggieland and Bevoland may be more dicey than what the models currently suggest.

Made a couple of meteograms for Houston & Dallas from the 12Z GFS. Neither indicates any pleasant weather after tomorrow. No ice down here, but there may be problems up north of Houston.

hlewis wrote:Hey all, is there anywhere to find a future radar forecast, hourly, for Thursday? We have a parade that night and need to play it by ear, need to finish the float in the afternoon, and get the kids on board. parade starts at 7. wondering exactly how much rain we will face and if it will be cold for the kids that night. thank you!

It would help to know what city the parade is in. For the general Houston area, I'd say light to moderate showers are a high probability Thursday evening - with temperatures in the 40s. Very cold and miserable.

Ed, I do agree with you that a wintry weather event for folks in our part of the world is useless if it happens on a weekend. South Texas winter events are hard enough to come by as is, but when they do occur you'd like to see school/work get impacted!

Worst case scenario is when we all go to work/school and while we're there, the weather bottoms out and the powers-that-be say "ok, everyone go home!" Seen that too many times here in Austin and every time it's a nightmare.

GFS continues to remain quite chilly but the key here is the strong gradient being depicted by these models. To give you an idea the gfs has a low of 27 Saturday morning in College Station but only has a low of 36 in Houston. Where and how far that gradient setups will be key. Pretty impressive to say the least for early December.

KCLL MOS (N/X represents min and max for that day):

KCLL GFSX MOS GUIDANCE 12/03/2013 1200 UTC
FHR 24 36| 48 60| 72 84| 96 108|120 132|144 156|168 180|192
WED 04| THU 05| FRI 06| SAT 07| SUN 08| MON 09| TUE 10|WED CLIMO
N/X 61 78| 63 63| 33 39| 27 38| 32 46| 35 46| 32 49| 33 43 65
TMP 63 72| 67 43| 35 33| 28 34| 34 42| 37 40| 34 43| 35


KHOU MOS:

KHOU GFSX MOS GUIDANCE 12/03/2013 1200 UTC
FHR 24 36| 48 60| 72 84| 96 108|120 132|144 156|168 180|192
WED 04| THU 05| FRI 06| SAT 07| SUN 08| MON 09| TUE 10|WED CLIMO
N/X 67 77| 69 75| 47 47| 36 41| 36 52| 42 52| 40 54| 40 48 66
TMP 69 71| 71 63| 48 40| 38 40| 38 48| 44 47| 43 48| 41

Ah, thank you all for the information as to what is happening on thursday. you are so very helpful.

Jeff's Latest:

Near record warmth the next few days followed by a strong arctic blast.

Upper air pattern is currently undergoing amplification along the US west coast with high pressure building deep into Alaska which will develop and deepen a downstream trough over the western and central US over the next 24-48 hours. Large 1058mb arctic high pressure cell currently over NW Canada is already starting to move southward this morning and will cross the US border via Montana later today. Boundary will plunge southward across the Rockies and down the front range of the Rockies with significant temperature falls.

Locally warm moist southerly flow will continue to advect moisture into the region. Clear skies and temperatures cooling toward the dewpoints is resulting in radiation fog development and this will be possible again tonight if winds are light. High temperatures will push into the lower 80’s this afternoon and again on Wednesday afternoon which is just short of records for the dates. Rain chances will remain low until Thursday.

Big news continues to be the arrival of the upstream arctic boundary into the region on Thursday and the impacts of this boundary. Front will make good progress into TX and then slow across SE TX as upstream energy digs into the western US. Expect the powerful cold front to reach our NW counties early Thursday and slowly cross the area during the day…not reaching the coast until the evening. This will setup a strong temperature gradient across the area with our NW counties likely having temperatures falling into the 40’s on Thursday while areas south of the front reach near 80. There could be a thin light of showers or even a thunderstorm with the front, but widespread heavy rainfall is not expected.

Thursday night into Friday the arctic boundary pushes offshore with a cold air mass enveloping the entire region. Temperatures will hold in the 40’s all day on Friday under gusty north winds and cold air advection along with periods of post frontal rain. Similar to the weekend before Thanksgiving, the shallow cold surface dome will be overrun by warm moist southerly flow just above the surface producing widespread clouds, drizzle, and light to moderate rainfall. Friday morning appears to be a favored period for good lift as a jet stream disturbance moves across the area producing lift. Will likely see widespread light to moderate rainfall Friday morning. Will hold all temperatures above freezing into Friday evening for all areas and keep all precipitation liquid.

Next disturbance looks to move across the area Saturday afternoon into Sunday with another round of light rainfall. Surface temperatures at this time period may approach the freezing mark from College Station to Huntsville to Lufkin suggesting the potential for some light freezing rainfall early Sunday morning across our far northern counties. Given the extremely warm weather today-early Thursday, ground temperatures will remain warm into the weekend and suspect any freezing rain and ice will be limited to elevated surfaces such as trees and power lines. Precipitation amounts will be on the light side. Still a lot of time to watch temperature and moisture trends over the next few days for this weekend. Temperatures will be cold both Saturday and Sunday with lows in the 30’s and highs in the upper 30’s to low 40’s.

Any update on next weekend's (Dec 14) weather? Are we still looking at bitter cold, and what about precip?

vci_guy2003 wrote:Any update on next weekend's (Dec 14) weather? Are we still looking at bitter cold, and what about precip?

GFS is making wild swings back and forth for that weekend (15-20 deg). Too early to get a firm handle on it. Maybe by next Monday.

Euro is starting to agree with the operational GFS on the second blast of colder air 168 or so hours out:

The plot thickens for south central and southeast Texas ... relevant snippets from afternoon forecast discussions just issued below:

EWX:
.LONG TERM (THURSDAY THROUGH TUESDAY)...
THE NEXT ARCTIC BLAST ARRIVES EARLY THURSDAY AND WILL PROVIDE
ANOTHER DAY OF RAPIDLY DESCENDING TEMPERATURES AND UNCERTAINTIES
ON MAX TEMPS FOR THE DAY. MODEL GUIDANCE TRENDS SUGGEST THE
NORTHERN HILL COUNTRY COULD DROP TO NEAR FREEZING BY EARLY IN THE
EVENING. NO WINTER MIX IS EXPECTED TO AFFECT THE AREA THROUGH
THURSDAY AFTERNOON...BUT THERE IS A CHANCE THAT THE SHALLOW AIR
MASS COULD PROMOTE FREEZING RAIN AS EARLY AS LATE THURSDAY
EVENING. IN A SIMILAR FASHION TO THE PAST WINTER WEATHER SYSTEM A
WEEK AGO. THERE WILL BE A PROLONGED PERIOD OF OVERRUNNING
INSTABILITY THAT IS EXPECTED TO PROVIDE A THREAT OF A MAINLY
FREEZING RAIN AND A LITTLE SLEET...WITH HIGHER PRECIPITATION
TOTALS EXPECTED TO FOCUS OVER THE NORTHEASTERN TWO-THIRDS OF SOUTH
CENTRAL TEXAS FROM LATE THURSDAY EVENING THROUGH FRIDAY AFTERNOON.
DYNAMICS ARE MUCH WEAKER...AND MOST OF THE RAINFALL AND FREEZING
RAINFALL RATES ARE EXPECTED TO BE LIGHT. HOWEVER...THIS SYSTEM
LOOKS TO BE COOLER AND THE LIGHT ICING THAT MAY DEVELOP HAS A
CHANCE TO AFFECT MORE AREAS. WITH UNCERTAINTIES IN TEMPERATURES
NOTED IN THE MODEL TRENDS...AND LOW AMOUNTS OF ICING EXPECTED...
WILL HOLD OFF ISSUING A WATCH AND KEEP WITH THE SPS. SOME
INCREASES IN SLEET POTENTIAL ARE ADDED IN THIS FORECAST PACKAGE
OVER THE WEEKEND AS MODEL SOUNDINGS SHOW A FREEZING LAYER DEPTH TO
4000 FT IN NORTHERN COUNTIES. THE SLEET COULD ENHANCE
ACCUMULATION POTENTIAL...BUT THE OVERRUNNING PATTERN SHOULD BE
WEAKER THAN WHAT IS TO BE EXPECTED ON FRIDAY.

A SECONDARY SURGE OF COLD AIR IS FORECAST FOR MONDAY TO PROLONG
THE COLD PERIOD. HOWEVER...THIS SURGE SHOULD BE FOLLOWED BY DRIER
AIR ALOFT AND A BROADER DIURNAL TEMPERATURE RANGE.

HGX:
WINTER WEATHER POTENTIAL...LETS JUST SAY THERE IS SUBSTANTIAL
UNCERTAINTY. RIGHT NOW THERE LOOKS TO BE THE POTENTIAL FOR
FREEZING RAIN/DRIZZLE FRIDAY INTO SATURDAY. MAIN AREAS WILL BE
FROM COLLEGE STATION TO HUNTSVILLE TO GROVETON NORTHWARD. COLD
AIRMASS GETS COLDER ON FRI AND WITH MOISTURE TRAPPED OVER THE
FRONTAL SURFACE...COULD LEAD TO RAIN/DRIZZLE. POSSIBLE THAT THESE
AREAS COULD BECOME COLD ENOUGH LATE FRIDAY TO SUPPORT FREEZING
RAIN/DRIZZLE. THE MORE LIKELY TIME FRAME APPEARS TO BE SATURDAY
MORNING. GFS HAS TRENDED COLDER WITH THE AIRMASS WITH TEMPS BELOW
FREEZING. ECMWF SEEMS TO BE JUST AS COLD BUT ENDS PRECIP FRI
NIGHT. ISENTROPIC LIFT IS EXPECTED TO INCREASE SATURDAY WITH THE
APPROACH OF THE NEXT JET STREAK. GFS RAMPS UP PRECIP SAT MORNING
AND THEN THROUGH THE AFTERNOON. ECMWF IS SLOWER TO DO SO AND HAS
MUCH DRIER AIR AT THE SURFACE WHICH WOULD HAVE TO SATURATE THROUGH
WET-BULB THERMODYNAMIC PROCESSES. SO IF THERE IS PRECIP FALLING
FROM 09Z-18Z SATURDAY...CHANCES ARE THERE WILL BE ENOUGH OF A SUB-
FREEZING LAYER NEAR THE SURFACE FOR PRECIP TO FREEZE. MODEL
SOUNDINGS SHOW A SIGNIFICANT WARM LAYER ABOVE WHICH MAY BE TOO
MUCH FOR PRECIP TO OVERCOME AND FREEZE. SOUNDINGS MAY SUPPORT MORE
DRIZZLE WHICH MAY NOT TAKE AS MUCH OF A SUB-FREEZING LAYER TO
CAUSE FREEZING. SO IF THE AIRMASS FRI NIGHT IS NOT AS DRY AS THE
ECMWF INDICATES THEN ANY PRECIP THAT DEVELOPS DUE TO ISENTROPIC
LIFT WILL LIKELY FALL AS FREEZING RAIN/DRIZZLE. STILL QUITE A BIT
OF UNCERTAINTY IN THIS BUT WORTH MONITORING.

Portastorm wrote:The plot thickens for south central and southeast Texas ... relevant snippets from afternoon forecast discussions just issued below:



HGX:
WINTER WEATHER POTENTIAL...LETS JUST SAY THERE IS SUBSTANTIAL
UNCERTAINTY. RIGHT NOW THERE LOOKS TO BE THE POTENTIAL FOR
FREEZING RAIN/DRIZZLE FRIDAY INTO SATURDAY. MAIN AREAS WILL BE
FROM COLLEGE STATION TO HUNTSVILLE TO GROVETON NORTHWARD. COLD
AIRMASS GETS COLDER ON FRI AND WITH MOISTURE TRAPPED OVER THE
FRONTAL SURFACE...COULD LEAD TO RAIN/DRIZZLE. POSSIBLE THAT THESE
AREAS COULD BECOME COLD ENOUGH LATE FRIDAY TO SUPPORT FREEZING
RAIN/DRIZZLE. THE MORE LIKELY TIME FRAME APPEARS TO BE SATURDAY
MORNING. GFS HAS TRENDED COLDER WITH THE AIRMASS WITH TEMPS BELOW
FREEZING. ECMWF SEEMS TO BE JUST AS COLD BUT ENDS PRECIP FRI
NIGHT. ISENTROPIC LIFT IS EXPECTED TO INCREASE SATURDAY WITH THE
APPROACH OF THE NEXT JET STREAK. GFS RAMPS UP PRECIP SAT MORNING
AND THEN THROUGH THE AFTERNOON. ECMWF IS SLOWER TO DO SO AND HAS
MUCH DRIER AIR AT THE SURFACE WHICH WOULD HAVE TO SATURATE THROUGH
WET-BULB THERMODYNAMIC PROCESSES. SO IF THERE IS PRECIP FALLING
FROM 09Z-18Z SATURDAY...CHANCES ARE THERE WILL BE ENOUGH OF A SUB-
FREEZING LAYER NEAR THE SURFACE FOR PRECIP TO FREEZE. MODEL
SOUNDINGS SHOW A SIGNIFICANT WARM LAYER ABOVE WHICH MAY BE TOO
MUCH FOR PRECIP TO OVERCOME AND FREEZE. SOUNDINGS MAY SUPPORT MORE
DRIZZLE WHICH MAY NOT TAKE AS MUCH OF A SUB-FREEZING LAYER TO
CAUSE FREEZING. SO IF THE AIRMASS FRI NIGHT IS NOT AS DRY AS THE
ECMWF INDICATES THEN ANY PRECIP THAT DEVELOPS DUE TO ISENTROPIC
LIFT WILL LIKELY FALL AS FREEZING RAIN/DRIZZLE. STILL QUITE A BIT
OF UNCERTAINTY IN THIS BUT WORTH MONITORING.

Didn't they rule our winter precip a day or two ago? I can't...

Well, remember what Michael Corleone said in The Godfather: Part III?

"Just when I thought I was out, they pull me back in."

Eric Berger posted this on Facebook 3 hours ago


all we need is moisture around this time....

Are those temps highs or lows.