December 2014: New Year's Eve Wintry Mix Possible

[brooksgarner]

Waiting for 12z GFS to finish... so interesting 9-10 days out to see our first real wintry precip event potentially shaping up. While it's totally insane to talk "precip type" this far out, it seems to me that an all snow event in Houston is unlikely due to the relatively shallow nature of the arctic air associated with that giant 1050+mb ridge next week... It looks like warmer air will overrun the low-level arctic push producing isentropic lift and associated freezing drizzle ... if enough hydrostatic cooling can happen, maybe sleet (ice pellets.) My gut says freezing rain and sleet with a few flakes once you get into the Hill Country and north TX... I'm getting a bit giddy in anticipation of it all -- just glad we don't have a "10-day outlook" on our TV graphics. Even attempting a 7-day forecast can feel a bit -- ostentatious.

[Heat Miser]

I think you're safe predicting freezing drizzle and or an ice pellet or two, Brooks. All of us would rather see snow for a number of reasons. But many here, like me, have lived in this sub-tropical climate all our lives and know the scenario you painted is the more likely scenario.

[ronyan]

The 12z GFS is colder for SE TX, drives the arctic high straight down the Rockies into TX.

[srainhoutx]

2 meter temperatures are disgustingly cold all the way to Coastal Texas and Louisiana on the 2nd of January via the long range GFS.

[TexasBreeze]

Much colder, but dry too.

[srainhoutx]

The 12Z Parallel GFS now has a Winter Storm near New Years Eve into New Years Day across S Central Texas.

[brooksgarner]

Here's as close as the 12z GFS brings the wintry mix to Houston: Washington County -- Brenham. New Year's morning. This will change as the models get a better grasp on how cold that shallow arctic air mass becomes... I'd expect (loosely) that the ZR line sets up along and north of I-10...

I'll bring this to my facebook page after the holidays... --> http://fb.com/khouBrooksGarner

[srainhoutx]

The afternoon Updated CPC Analogs and Prognostic Discussions to end 2014...

PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EST TUE DECEMBER 23 2014

6-10 DAY OUTLOOK FOR DEC 29, 2014 - JAN 02, 2015

TODAYS MODEL SOLUTIONS REMAIN IN GOOD AGREEMENT ACROSS THE WESTERN CONUS AND
ALASKA. THE 0Z/6Z GFS AND 0Z ECMWF ENSEMBLE MEANS FEATURE A TROUGH OVER THE
BERING SEA, A RIDGE ACROSS THE NORTHEAST PACIFIC, AND A 500-HPA TROUGH
EXTENDING FROM HUDSON BAY SOUTHWEST TO THE SOUTHERN ROCKIES. THE HIGH
RESOLUTION MODEL RUNS ARE INCLUDED IN THE 500-HPA MANUAL BLEND AS THESE
SOLUTIONS CONSISTENTLY INDICATE A CLOSED 500-HPA LOW OVER THE DESERT SOUTHWEST.
HOWEVER, THE 12Z GFS IS MORE PROGRESSIVE WITH THE TROUGH. THE 0Z CANADIAN
ENSEMBLE MEAN IS LIKELY AN OUTLIER SINCE ITS SOLUTION DOES NOT DEPICT THE
POSITIVELY TROUGH OVER THE LOWER 48. MODEL AGREEMENT IMPROVED AMONG TODAY'S
ODEL SOLUTIONS ACROSS THE EASTERN CONUS.

THE HIGH RESOLUTION 6Z GFS AND 0Z ECMWF MODEL RUNS INDICATE A 1048 TO 1052-HPA
SURFACE HIGH BUILDING SOUTH FROM THE CANADIAN PRAIRIES INTO THE ROCKIES EARLY
IN THE PERIOD. TEMPERATURES ARE FORECAST TO AVERAGE AS MUCH AS 20 DEGREES F
BELOW-NORMAL ACROSS THE ROCKIES AND HIGH PLAINS ON DAYS 6 AND 7. BELOW-NORMAL
TEMPERATURES ARE LIKELY FOR MUCH OF THE WESTERN AND CENTRAL CONUS DUE TO THE
ANOMALOUS TROUGH. TEMPERATURE GUIDANCE IS IN BETTER AGREEMENT TODAY WITH NEAR
TO BELOW-NORMAL TEMPERATURES FAVORED FOR THE NORTHEAST, WHILE A SUBTROPICAL
RIDGE FAVORS ABOVE-NORMAL TEMPERATURES ACROSS THE FLORIDA PENINSULA.

SOUTHWEST FLOW ALOFT INCREASES CHANCES FOR ABOVE-MEDIAN PRECIPITATION ACROSS
THE GULF COAST STATES NORTHEAST TO SOUTHERN NEW ENGLAND. THE HIGH RESOLUTION
MODELS ARE IN GOOD AGREEMENT WITH MORE THAN ONE INCH OF RAINFALL OCCURRING
ALONG THE CENTRAL GULF COAST WHERE THE HIGHEST PROBABILITIES FOR ABOVE-MEDIAN
PRECIPITATION ARE FORECAST. UPSLOPE FLOW TILTS THE ODDS TOWARDS ABOVE-MEDIAN
PRECIPITATION ACROSS THE SOUTHERN HIGH PLAINS. LITTLE OR NO RAINFALL IS
EXPECTED ACROSS SOUTH FLORIDA WHERE BELOW-MEDIAN PRECIPITATION IS FAVORED. A
DRY SIGNAL AMONG PRECIPITATION IS STRONGEST ACROSS THE PACIFIC NORTHWEST AND
NORTHERN CALIFORNIA, ASSOCIATED WITH THE RIDGE OVER THE NORTHEAST PACIFIC AND
ANOMALOUS OFFSHORE FLOW.

SURFACE LOW PRESSURE OVER THE BERING SEA COUPLED WITH RIDGING OVER THE
NORTHEAST PACIFIC ENHANCE ODDS FOR ABOVE-NORMAL TEMPERATURES AND ABOVE-MEDIAN
PRECIPITATION ACROSS ALASKA.

TODAY'S OFFICIAL 500-HPA BLEND CONSISTS OF 15% OF TODAY'S 0Z GFS ENSEMBLE MEAN
CENTERED ON DAY 8, 15% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED ON DAY 8, 10%
OF TODAY'S OPERATIONAL 0Z GFS CENTERED ON DAY 8, 10% OF TODAY'S OPERATIONAL 6Z
GFS CENTERED ON DAY 8, 40% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY
8, AND 10% OF TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8


MODEL OF THE DAY: 0Z ECMWF ENSEMBLE MEAN

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: AVERAGE, 4 OUT OF 5, DUE TO
IMPROVED MODEL AGREEMENT ACROSS THE EASTERN CONUS AMONG THE 0Z/6Z GFS AND 0Z
ECMWF ENSEMBLE MEANS AND TEMPERATURE GUIDANCE.

[Katdaddy]

Only received .10" today in League City. Gusty winds this afternoon especially along the coastal regions today.

[Paul Robison]

Waiting for 12z GFS to finish... so interesting 9-10 days out to see our first real wintry precip event potentially shaping up. While it's totally insane to talk "precip type" this far out, it seems to me that an all snow event in Houston is unlikely due to the relatively shallow nature of the arctic air associated with that giant 1050+mb ridge next week... It looks like warmer air will overrun the low-level arctic push producing isentropic lift and associated freezing drizzle ... if enough hydrostatic cooling can happen, maybe sleet (ice pellets.) My gut says freezing rain and sleet with a few flakes once you get into the Hill Country and north TX... I'm getting a bit giddy in anticipation of it all -- just glad we don't have a "10-day outlook" on our TV graphics. Even attempting a 7-day forecast can feel a bit -- ostentatious.

Are we looking at a particularly damaging winter wx similar to what happened back in March 2014 occurring around New Year's Eve/Day, Brooks? Ya got me kinda worried.

[jeff]

Dont think we are looking at anything record breaking or historic with respect to the cold air. Not sure we are looking at a repeat of March 2014 ice storm either. Too many variables at play over a week a away to even attempt to forecast P-type. However the pattern and upper flow due suggest both cold and moisture could be at hand late next week. Forget the run to run of the models and focus on the upper air pattern, the details will work themselves out in time.

[Paul Robison]

Dont think we are looking at anything record breaking or historic with respect to the cold air. Not sure we are looking at a repeat of March 2014 ice storm either. Too many variables at play over a week a away to even attempt to forecast P-type. However the pattern and upper flow due suggest both cold and moisture could be at hand late next week. Forget the run to run of the models and focus on the upper air pattern, the details will work themselves out in time.

Oh, I forgot about those variables. I just hope the upper air flow doesn't cause H-town any serious harm, that's all. Thank you very much for your response, Jeff.

[Ptarmigan]

Dont think we are looking at anything record breaking or historic with respect to the cold air. Not sure we are looking at a repeat of March 2014 ice storm either. Too many variables at play over a week a away to even attempt to forecast P-type. However the pattern and upper flow due suggest both cold and moisture could be at hand late next week. Forget the run to run of the models and focus on the upper air pattern, the details will work themselves out in time.

Forecasting winter weather events and freezes is about as challenging as forecasting hurricanes will go.

[Ptarmigan]

The afternoon Updated CPC Analogs and Prognostic Discussions to end 2014...

12232014 CPC Day 8+ Analogs 610analog_off.gif

PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EST TUE DECEMBER 23 2014

6-10 DAY OUTLOOK FOR DEC 29, 2014 - JAN 02, 2015

TODAYS MODEL SOLUTIONS REMAIN IN GOOD AGREEMENT ACROSS THE WESTERN CONUS AND
ALASKA. THE 0Z/6Z GFS AND 0Z ECMWF ENSEMBLE MEANS FEATURE A TROUGH OVER THE
BERING SEA, A RIDGE ACROSS THE NORTHEAST PACIFIC, AND A 500-HPA TROUGH
EXTENDING FROM HUDSON BAY SOUTHWEST TO THE SOUTHERN ROCKIES. THE HIGH
RESOLUTION MODEL RUNS ARE INCLUDED IN THE 500-HPA MANUAL BLEND AS THESE
SOLUTIONS CONSISTENTLY INDICATE A CLOSED 500-HPA LOW OVER THE DESERT SOUTHWEST.
HOWEVER, THE 12Z GFS IS MORE PROGRESSIVE WITH THE TROUGH. THE 0Z CANADIAN
ENSEMBLE MEAN IS LIKELY AN OUTLIER SINCE ITS SOLUTION DOES NOT DEPICT THE
POSITIVELY TROUGH OVER THE LOWER 48. MODEL AGREEMENT IMPROVED AMONG TODAY'S
ODEL SOLUTIONS ACROSS THE EASTERN CONUS.

THE HIGH RESOLUTION 6Z GFS AND 0Z ECMWF MODEL RUNS INDICATE A 1048 TO 1052-HPA
SURFACE HIGH BUILDING SOUTH FROM THE CANADIAN PRAIRIES INTO THE ROCKIES EARLY
IN THE PERIOD. TEMPERATURES ARE FORECAST TO AVERAGE AS MUCH AS 20 DEGREES F
BELOW-NORMAL ACROSS THE ROCKIES AND HIGH PLAINS ON DAYS 6 AND 7. BELOW-NORMAL
TEMPERATURES ARE LIKELY FOR MUCH OF THE WESTERN AND CENTRAL CONUS DUE TO THE
ANOMALOUS TROUGH. TEMPERATURE GUIDANCE IS IN BETTER AGREEMENT TODAY WITH NEAR
TO BELOW-NORMAL TEMPERATURES FAVORED FOR THE NORTHEAST, WHILE A SUBTROPICAL
RIDGE FAVORS ABOVE-NORMAL TEMPERATURES ACROSS THE FLORIDA PENINSULA.

SOUTHWEST FLOW ALOFT INCREASES CHANCES FOR ABOVE-MEDIAN PRECIPITATION ACROSS
THE GULF COAST STATES NORTHEAST TO SOUTHERN NEW ENGLAND. THE HIGH RESOLUTION
MODELS ARE IN GOOD AGREEMENT WITH MORE THAN ONE INCH OF RAINFALL OCCURRING
ALONG THE CENTRAL GULF COAST WHERE THE HIGHEST PROBABILITIES FOR ABOVE-MEDIAN
PRECIPITATION ARE FORECAST. UPSLOPE FLOW TILTS THE ODDS TOWARDS ABOVE-MEDIAN
PRECIPITATION ACROSS THE SOUTHERN HIGH PLAINS. LITTLE OR NO RAINFALL IS
EXPECTED ACROSS SOUTH FLORIDA WHERE BELOW-MEDIAN PRECIPITATION IS FAVORED. A
DRY SIGNAL AMONG PRECIPITATION IS STRONGEST ACROSS THE PACIFIC NORTHWEST AND
NORTHERN CALIFORNIA, ASSOCIATED WITH THE RIDGE OVER THE NORTHEAST PACIFIC AND
ANOMALOUS OFFSHORE FLOW.

SURFACE LOW PRESSURE OVER THE BERING SEA COUPLED WITH RIDGING OVER THE
NORTHEAST PACIFIC ENHANCE ODDS FOR ABOVE-NORMAL TEMPERATURES AND ABOVE-MEDIAN
PRECIPITATION ACROSS ALASKA.

TODAY'S OFFICIAL 500-HPA BLEND CONSISTS OF 15% OF TODAY'S 0Z GFS ENSEMBLE MEAN
CENTERED ON DAY 8, 15% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED ON DAY 8, 10%
OF TODAY'S OPERATIONAL 0Z GFS CENTERED ON DAY 8, 10% OF TODAY'S OPERATIONAL 6Z
GFS CENTERED ON DAY 8, 40% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY
8, AND 10% OF TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8


MODEL OF THE DAY: 0Z ECMWF ENSEMBLE MEAN

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: AVERAGE, 4 OUT OF 5, DUE TO
IMPROVED MODEL AGREEMENT ACROSS THE EASTERN CONUS AMONG THE 0Z/6Z GFS AND 0Z
ECMWF ENSEMBLE MEANS AND TEMPERATURE GUIDANCE.

12232014 CPC Day 6 to 10 Temps 610temp_new.gif

12232014 CPC Day 6 to 10 Precip 610prcp_new.gif

One of the analog, the one in January 1962, had a strong surface high. It set many high pressure record as it went down into the Lower 48. It caused a freeze in Houston area. It froze for 68 hours!

1/9/1962 56/22
1/10/1962 27/20
1/11/1962 30/20
1/12/1962 48/23

Number of Hours in Houston below freezing
http://www.wxresearch.com/almanac/frezhour.htm

On the topic of freeze, it has been 25 years we had that epic freeze from December 22-25, 1989. It snowed on December 22 and reached a low of 7°F on December 23.

[srainhoutx]

Evening briefing from Jeff:

Clear but cool Christmas…arctic outbreak and possible winter storm looms in the extended.

Potent storm system moved across the region this morning with a quick round of showers and even a few thunderstorms. Cold air advection continues this evening and on into Wednesday with clearing skies. Winds will keep temperatures from bottoming out tonight…mainly in the 40’s with highs only in the mid 50’s on Wednesday. Coldest night comes Wednesday into Christmas morning with mid 30’s and likely some lower 30’s over portions of the area under clear skies and light winds.

Christmas Day:
Surface high responsible for the current intrusion of cold air begins to move eastward on Thursday allowing onshore flow to resume. Cold start under clear skies will feature a good warm up into the lower 60’s for highs helped by sun and southerly flow.

Friday:
Probably the best day of the week temperature wise with lows in the 40’s and highs near 70 under increasing southerly flow. Clouds will start to increase ahead of a storm system for the weekend.

Weekend:
Next storm system will move across in the fast progressive flow aloft. Cold surface dome will only slowly modify and expect clouds and light rain to increase Saturday with the old surface front from today remaining offshore. A round of fog, drizzle, light rain seems likely Saturday and Sunday as the next system moves across and the surface cold pool hangs tough over the area. Models have been trending wetter and wetter with this system especially on Sunday so rain chances may need to be increased into the 60-70% range. Temperatures will be cool with both highs and lows regulated by clouds and rainfall to the 50’s and 40’s.

Next Week:
Upper air flow undergoes significant amplification with strong ridging building deep into Alaska resulting in the formation of a deep downstream longwave trough over the western and central US. Extremely cold air mass now of Siberia and northern Russia (-70 F wind chill today) will become entrained into the flow aloft and progress into NW Canada (the favored source region for US arctic air outbreaks) featuring temperatures in the -30 to -40F by the early to middle part of next week. With the trough in place over the western and central US, the arctic air begins to roar southward under the influence of a 1045-1055mb arctic surface ridge entering the US via Montana. The dense very cold air dams against the Rockies and spills southward straight down the front range into TX at a very rapid pace. True shallow arctic air masses almost always outrun model guidance and I think this event will be no different. Models are also almost always too warm with the air mass and undergo run to run temperature decreases as the event nears in the 48 hour time period. Don’t think we are looking at anything historic or record breaking with respect to the cold air, but a period of freezing and sub freezing temperatures is looking increasingly likely from as early as the 31st through the 2nd or even 3rd of Jan and this could include near freezing daytime highs. Intensity of the cold air is still subject of model disagreement, but once arctic air starts moving southward it is hard to stop it and the pattern certainly supports this.

Next and perhaps the bigger question is will there be any moisture in the post frontal arctic air. Forecast models have been off and on suggesting a portion of the upper trough hangs back over the SW US with a upper level flow out of the SW over the surface arctic air mass in place over TX. This would produce an overrunning pattern with warm air flow up and over the surface cold dome. Upper disturbances in this upper flow would help to enhance lift from time to time producing periods of precipitation. Long range forecast soundings show mostly a surface freezing layer with temperatures above freezing in the mid levels. P-type could be a potential issue from late on the 31st into the 2nd with the mostly likely precipitation being rain or freezing rain with the current suggested profiles. A fairly significant winter storm pattern is being suggested by the forecast models for the state of TX during this time period, but given how far out in time we are the fine details are beyond the limits of any forecasting certainty and more speculation. Much attention to be paid to this part of the forecast over the next several days.

[unome]

I'm hoping for no precip of any type for the New Year's Eve/Day time period - really don't need another factor to make more accidents

Interactive Interface for viewing Day 3-7 WPC and MOS forecasts

http://www.wpc.ncep.noaa.gov/medium/

[srainhoutx]

The overnight guidance continues to advertise a rollercoaster pattern into the weekend and early next week. The 00Z European suggests a very strong Arctic front arrives on the 30th with a lot of troughiness extending to our West. That tends to spell over running moisture with a cold air mass at the surface. The GFS paints a freezing rain sleet storm on day 8 in Metro Houston and the parallel GFS spit out some impressive snow totals across Central Texas. This wintry mess extends into Louisiana as well.

[snowman65]

SRAIN do you have any graphics for Dec 31-Jan 2 time frame?

[srainhoutx]

SRAIN do you have any graphics for Dec 31-Jan 2 time frame?

I do, but figured I'd wait and see how much the 12Z runs flip flop as the computer models struggle with the upper air disturbances beyond day 6-7. I have little doubt the cold air is coming. This weekend begins that pattern shift to a very active period next week. The finer details will be worked out. Meanwhile, Merry Christmas Everyone and may the New Year bring peace and prosperity to you and yours.

[snowman65]

Thanks!....Same to you and everyone else in here...BE SAFE!