January: Seasonal Temps To End The Month

[srainhoutx]

Winter Storm Watches have been hoisted for El Paso to Presidio into the Big Bend Region on E into Alpine for 4-6 inches of snow. NWS San Angelo has issued a SPS regarding a rain/snow mix extending E as far as Brownwood. NWS San Antonio/Austin now talking about the first snow of the season for the Edwards Plateau and Hill Country. NWS Houston/Galveston does mention a 20% chance of light rain on Saturday. Depending on timing and just how much the dry air at the surface can moisten up, I guess a stray ice pellet or two may not be out of the question. As always, these type events are also difficult to forecast and often come as a surprise. We'll see what the next 24 hours or so holds and just how strong the upper level low is as it ejects across W Texas.

HPC:

SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
351 AM EST WED JAN 02 2013

VALID 12Z WED JAN 02 2013 - 12Z FRI JAN 04 2013

...RATHER QUIESCENT CONDITIONS SHOULD PERSIST OVER MUCH OF THE
REMAINDER OF THE CONUS...

...ACCUMULATING SNOWS WILL FOCUS OVER THE GREAT LAKES REGION AS
WELL AS ACROSS SOUTHWEST TEXAS...

MOISTURE AS A WHOLE SHOULD REMAIN RATHER LIMITED AS A FRONTAL
BOUNDARY SINKS SOUTHWARD INTO THE GULF OF MEXICO. MUCH OF THE
MOISTURE FROM THE GULF WILL POOL NORTHWARD FOCUSING AN AXIS OF
SCATTERED RAIN SHOWERS ALONG THE IMMEDIATE GULF COAST.
HOWEVER...THE MID-LEVEL PATTERN WILL NOT BE VERY SUPPORTIVE FOR
MORE WIDESPREAD PRECIPITATION EXCEPT FOR THE FEW WEAK IMPULSES
EMERGING WITHIN THE BROADER SCALE SOUTHWESTERLY FLOW. WHILE IT
WILL NOT BE A SOAKER ALONG THE GULF COAST...SCATTERED SHOWERS ARE
FORECAST TO IMPACT THE REGION THE NEXT COUPLE OF DAYS GIVEN THE
PRESENCE OF THE STALLED BOUNDARY OVER THE CENTRAL GULF. LOOKING
FURTHER UPSTREAM...A CLOSED UPPER LOW DROPPING SOUTH TO
SOUTHEASTWARD INTO NORTHERN BAJA CALIFORNIA WILL BE THE NEXT
PRECIPITATION MAKER TO SECTIONS OF SOUTHERN NEW MEXICO AND INTO
WEST TEXAS. LOW-LEVEL TEMPERATURES ARE FORECAST TO BE AROUND
FREEZING WHICH WILL ALLOW SNOW TO FALL OVER THIS REGION BY
THURSDAY AFTERNOON. THROUGH FRIDAY MORNING...THE HPC WINTER
WEATHER DESK IS ADVERTISING A FEW INCHES OF SNOW WITH POCKETS OF
SLIGHTLY HEAVIER AMOUNTS CLOSER TO THE RIO GRANDE RIVER.

LOOKING TO THE NORTH...AN UPPER RIDGE ANCHORING THE NORTHWESTERN
STATES WILL ALLOW AN EXPANSIVE TROUGH TO DEVELOP OVER THE
NORTH-CENTRAL CONUS AND OUT TOWARD THE NORTHEASTERN U.S. THE
SPARSE MOISTURE PROFILES WILL LIMIT PRECIPITATION FROM THESE
IMPULSES TRACKING THROUGH THE REGION. HOWEVER...LIGHT TO MODERATE
SNOW SHOWERS ARE EXPECTED TO DEVELOP OVER THE NORTHERN GREAT LAKES
AS A FRONTAL BOUNDARY SETS UP ORIENTED WEST-TO-EAST ALONG THE
LAKES. LOW-LEVEL LIFT AIDED BY THIS FRONT COMBINED WITH FAVORABLE
WIND TRAJECTORIES ALONG THE LAKE SURFACE WILL HELP INITIATE SNOW
SHOWERS THROUGHOUT THE PERIOD. 2 TO 4 INCHES OF SNOW WILL BE
POSSIBLE THROUGH FRIDAY MORNING WITH ISOLATED HEAVIER AMOUNTS
DOWNWIND OF LAKE ONTARIO.

THE INTERMOUNTAIN WEST WILL BE DOMINATED BY A SURFACE/UPPER RIDGE
WHICH SHOULD KEEP CONDITIONS RATHER QUIET THROUGHOUT MUCH OF THE
WEEK. IDEAL RADIATIONAL COOLING EFFECTS WILL LEAD TO SUB-ZERO
OVERNIGHT LOWS ACROSS CERTAIN AREAS WHILE HIGHS ONLY REBOUND INTO
THE TEENS AND 20S. THIS SETUP WILL ALSO ALLOW OFFSHORE FLOW TO
DOMINATE THE STATE OF CALIFORNIA. HOWEVER...THE PRESSURE GRADIENT
DOES NOT APPEAR TO BE SIGNIFICANT ENOUGH TO RESULT IN A STRONG
WIND EVENT.


RUBIN-OSTER


PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
417 AM EST WED JAN 02 2013

VALID 12Z WED JAN 02 2013 - 12Z SAT JAN 05 2013

DAY 1...

THE PROBABILITY OF SIGNIFICANT SNOW AND/OR ICING IS LESS THAN 10
PERCENT.


DAY 2...

...WEST TEXAS / TRANS PECOS REGION...

A CLOSED LOW SEEN ON WV IMAGERY OFF THE SRN CA COAST THIS MORNING
WILL TRACK EWD ACROSS NWRN MEXICO TONIGHT...WHILE A NRN STREAM
TROUGH AXIS BEARS DOWN ACROSS THE SWRN U.S. FROM THE NORTH. THE
TWO WILL INTERACT THU INTO FRI RESULTING IN A CLOSED LOW OVER THE
SOUTHWEST. THE MODELS CONTINUE TO COME INTO BETTER AGREEMENT THIS
THIS SCENARIO AND INDICATE A SIGNIFICANT SNOW STORM FOR PORTIONS
OF WEST TEXAS / NRN MEXICO. ALTHOUGH THE UKMET IS DELAYED IN
CLOSING OFF A LOW...THERE IS GOOD CONSENSUS AMONG THE 00Z
NAM/GFS/ECMWF/CMC AND SREF/GEFS/EC ENSEMBLE MEANS AS WELL AS
RUN-TO-RUN AGREEMENT TO DISCOUNT THE 00Z UKMET. USED ROUGHLY EQUAL
WEIGHTING IN A BLEND OF THE NAM/GFS/ECMWF/SREF...NOT PUTTING TOO
MUCH WEIGHT ON THE NAM AS IT TENDS TO HAVE A COLD/WET BIAS.

DESPITE AN INITIALLY DRY ATMOSPHERE TO BATTLE...SNOW LOOKS TO
OVERSPREAD SWRN TEXAS WITH PERHAPS RAIN FOR THE LOWER ELEVATIONS
OF THE RIO GRANDE VALLEY THU MORNING...AS STRONG...DIFLUENT LIFT
ALOFT COMBINES WITH LOW LEVEL UPSLOPE FLOW IN CONNECTION TO
STRONG/COLD HIGH PRESSURE ANCHORED OVER THE PLAINS. MODEL FORECAST
SOUNDINGS INDICATE WARMING TO NEAR...BUT STILL BELOW 0 C...AT AND
BELOW 700 MB...WHICH COULD BE A TREND TOWARD SLEET MIXING IN. IN
ADDITION...THE LOWEST 10-15 KFT OF THE SOUNDING IS FCST ABOVE -10
C...INDICATIVE OF A HEAVY/HIGH DENSITY SNOW. SLR VALUES MAY
AVERAGE CLOSE TO 10:1 BUT PERHAPS A LITTLE GREATER IN THE HIGHER
ELEVATIONS. A SLIGHT RISK OF 4 INCHES WAS DRAWN FOR MUCH OF WEST
TEXAS INTO FAR SRN NEW MEXICO. A MODERATE RISK OF 4 WITH A SLIGHT
RISK OF 8 WAS DRAWN FOR THE HIGHER ELEVATIONS...ESPECIALLY INTO
THE DAVIS...GLASS AND CHINATI MOUNTAINS.

AS THE UPPER LOW BEGINS TO EJECT OUT TOWARD THE END OF DAY 2...FRI
MORNING...THE MID LEVEL JET COMING AROUND THE BASE OF THE LOW MAY
BRING IN ENOUGH DRY AIR ALOFT TO CAUSE ANY REMAINING PCPN TO FALL
AS FZDZ AS MODEL FCST SOUNDINGS INDICATE TO THE TOP OF THE
SATURATED LAYER NEAR OR ABOVE -10 C.

[oleander]

Light sleet falling at my house in Oak Forest right now.

[tireman4]

Light sleet falling at my house in Oak Forest right now.

Oak Forest, as in Houston, Texas? As in Oak Forest Subdivision?

[oleander]

Yes, 290 @ Antoine. Just a brief sprinkle with sleet. Gone now. That I why I love weather, you never know what you will see.

[srainhoutx]

Just had a couple of sleet pellets up here in NW Harris County as well with the sprinkles of very light rain.

[harpman]

What is you air temp?

[srainhoutx]

What is you air temp?

41F. The colder air aloft is where this is coming from. Too warm at the surface for anything but a novelty...

[harpman]

Send it east, srain!!!

[jeff]

Yep...light IP with light rain at US 290 and 610

[harpman]

What is you air temp?

41F. The colder air aloft is where this is coming from. Too warm at the surface for anything but a novelty...

I didn't think this airmasss had the right thickness for anything frozen.

[srainhoutx]

Morning update from Jeff:

Classic winter weather pattern in place over TX this week with cold air flowing southward from the north being overrun by moist SW flow aloft.

Cloudy, cold, and at times wet pattern will remain in place through the weekend as an active sub-tropical jet stream on the south side of a mean southwestern US trough overtops a cold surface air mass over TX. A cold front crossed the region early Tuesday morning producing a period of very heavy rainfall of 3-5 inches right along the coast from Brazoria County to Jefferson County. Galveston recorded at record 4.01 inches of rainfall making it the wettest New Years Day ever for that location. Most of the rest of the area saw much less rainfall with totals averaging in the .5 to 1.0 inch range. Cold front has made steady progress off the coast and well into the Gulf waters however a warm and moist upper level flow is pouring NNE over the surface cold dome resulting in a large stream of clouds from the eastern Pacific across much of TX. A review of the morning soundings from BRO, CRP, LCH, and FWD shows much wetter profiles from Corpus southward with significant amounts of dry air located just north of SE TX in the N TX and N LA soundings. The LCH sounding had a dry layer from roughly 850 to 700mb. While the radar is highly active only small amounts of rainfall are able to pass through the dry layer and reach the ground. Surface observations indicate rain is reaching the ground mainly southwest of a line from High Island to Hobby Airport to Columbus. Given the upstream look at the radar (widespread coverage), suspect the mid level dry layer will shrink some today allowing a few more locations to pick up measurable rainfall…especially near the coast where the column is already saturating. Do not think any location will see more than .25 of an inch.

With thick clouds and drizzle/light rain temperatures will warm very little and many locations will not make 50.

Forecast models show the main area of light rainfall and lift shifting eastward tonight while the next short wave rotates through the western side of the trough over the SW US and prepares to move into TX Thursday night. Expect the dry layer to deepen some over SE TX on Thursday and this will shut down rainfall chances, but keep clouds in place. Increasing lift spreads from N MX into SW/W TX Thursday night with precipitation developing. Once again moisture will be limited, but more importantly the air column will be near or slightly below freezing west of a line from Waco to Del Rio suggesting light rain mixed with or changing to snow. Some significant snowfall will be possible over the Big Bend of TX into the Hill County region Thursday night and Friday morning. Think the snow may reach as far east as I-35 north of Austin into the Waco area. Locally, profiles are too warm for snow and moisture is very limited until later on Friday. Would not rule out a snow flurry or two over our western counties if they can penetrate that mid level dry layer.

Rain chances increase slightly Friday night and Saturday as the above mentioned short wave moves across TX. Main lift is aimed at N TX, but the combination of increasing isentropic lift over the surface cold dome will support at least a 30-40% chance of showers….best period for rainfall seems to be Saturday morning, but I am concerned that dry low levels from a re-enforcing shot of cold air on Thursday may have to be overcome before rainfall will reach the ground.

Cloudy and at time periods of rainfall will keep temperatures nearly uniform throughout the entire period with lows in the 40’s (maybe the upper 30’s) and highs in the lower 50’s.

May begin to see more warmer weather under sunnier conditions by early next week.

[srainhoutx]

Another Update from Jeff:

A few reports of light sleet mixed with light rain over the area in the past 30 minutes.

It appears that the mid levels are saturating enough to allow precipitation to reach the ground mainly in the form of light rain…however onset of light rain has been mixed with light sleet across Harris County. Surface temperatures have cooled into the upper 30’s and low 40’s, but this is still well above freezing. Even with evaporative cooling due to the precipitation process cooling the air temperature toward the dewpoint, the dewpoints are mainly at or above freezing.

May continue to see light sleet mix with the light rain for the next few hours especially at the onset of any precipitation, but all areas should transition over to pure rain by noon as the dry layer aloft shrinks and any evaporative processes end. With surface temperatures above freezing there will be no accumulations.

[Portastorm]

The 12z GFS suggests that frozen precip may end up quite close to the Austin metro area later this week. We shall see.

[Kludge]

The 12z GFS suggests that frozen precip may end up quite close to the Austin metro area later this week. We shall see.

Yep... looks like you and I will be just inside the magic blue line on Friday morning. A few flakes would be nice...

[srainhoutx]

Getting a bit more sleet than light rain at this time in NW Harris County.

[Portastorm]

A few flakes is about all that looks to happen West of I-35 into the Hill Country/Big Country per 12Z GFS.


Nothing mind-blowing. Look at GFS surface high, cold air is taking quite the indirect route, plenty of time to modify. Looks like the Permian Basin is where cold and moisture might line up. Might be some upsloping flow at work as well, MAF is about a kilometer above sea level.

Think I'll have to respectfully disagree. The 12z GFS snowfall map below suggests more than "a few flakes."

[wxman666]

Had some light sleet mixed in here off 290 & Mason Rd.

[srainhoutx]

Looking a bit further out in model world, there continues to be growing interest in the mid/late January time frame. In fact the 12Z operational GFS and to some extent the long range Euro and their ensembles have been suggesting a rather cold period developing as the pattern reloads after a brief warm up next week. A fairly classic looking McFarland signature if you ask me. We will see...

[MontgomeryCoWx]

Full latitude trough!

[srainhoutx]

The 12Z Euro continues to advertise wintry weather for West & Central Texas. The next couple of days could prove rather interesting to say the least.