AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1124 AM CST WED FEB 2 2011
...WINTER STORM WATCH ISSUED FOR ALL OF SE TX...
.DISCUSSION...
COLD AIRMASS SETTLING INTO SE TX THIS MORNING WITH A 1045 MB HIGH
BUILDING SOUTH THROUGH THE PLAINS. VISIBLE SATELLITE IMAGERY
SHOWS SOME CLEARING ACROSS THE CENTRAL THIRD OF THE AREA. DESPITE
THE CLEARING...TEMPS HAVE WARMED VERY LITTLE SO FAR THIS
MORNING...STILL RUNNING IN THE LOW/MID 20S IN MOST LOCATIONS. HAVE
LOWERED MAX TEMPS ACROSS THE AREA. THE NORTHERN 2/3 OF SE TX WILL
LIKELY STAY BELOW FREEZING ALL AFTN...WITH TEMPS ONLY RISING ABOVE
FREEZING FOR A COUPLE OF HOURS OVER THE SOUTH. AS A RESULT...HAVE
RECONFIGURED THE HARD FREEZE WARNING TO JUST CONTINUE FROM NOW
THROUGH NOON ON THURSDAY.
DUE TO INCREASING CONFIDENCE IN THE FORECAST...HAVE DECIDED TO
ISSUE A WINTER STORM WATCH FOR ALL OF THE CWA FROM 18Z THURSDAY
THROUGH 18Z FRIDAY. TWO PRIMARY CHANGES HAVE BEEN NOTED IN THE
LAST FEW MODEL RUNS. THE MODELS ARE TRENDING FASTER WITH THE
MOVEMENT OF THE APPROACHING UPPER LOW...NOW SHOWING THE ONSET OF
PRECIP ON THURSDAY AFTN. THE SECOND CHANGE IS A WARM LAYER ALOFT
THAT IS PRESENT IN THE RECENT MODEL FORECAST SOUNDINGS...WHICH
SUGGESTS A THREAT OF FREEZING RAIN OVER THE SE THIRD OF THE AREA.
CURRENT THINKING IS AN ALL SNOW EVENT FOR THE NW HALF OF THE
CWA...WITH A MIX OF SNOW AND SLEET FURTHER SOUTH AND EAST. WE ARE
PLACING THE WESTERN EDGE OF THE THREAT OF FREEZING RAIN FROM
MATAGORDA TO DOWNTOWN HOUSTON TO RYE IN LIBERTY COUNTY. FOR THE
COASTAL SECTIONS OF BRAZORIA COUNTY...THROUGH GALVESTON...
CHAMBERS...AND LIBERTY COUNTIES THIS IS LOOKING LIKE PRIMARILY AN
ICE EVENT AS THE WARM LAYER ALOFT INTENSIFIES WITH TIME. QPF
AMOUNTS LOOK PLENTY SUFFICIENT TO SATISFY OUR CRITERIA FOR WINTER
HEADLINES...ESPECIALLY OVER THE ICE THREAT AREA WHERE PWS WILL BE
AROUND AN INCH. HAVE CHOSEN TO START THE WATCH AT NOON ON THURSDAY
SINCE MODELS SHOW THE ONSET OF PRECIP THU AFTN AND UNCERTAINTY
EXISTS ON WHETHER TEMPS WILL BE ABLE TO CLIMB ABOVE FREEZING THU
AFTN.
THE ONE THING THAT WILL DIFFERENTIATE THIS EVENT WITH THE WINTRY
PRECIP EVENTS WE SAW LAST YEAR IS THE HIGHER THREAT OF ICING
DEVELOPING ON THE ROADWAYS. SFC DEWPOINTS ARE NOW IN THE SINGLE
DIGITS AND TEENS...SO EVAPORATIVE COOLING WILL EASILY RESULT IN A
TEMPERATURE DROP AT THE SFC WHEN THE PRECIP BEINGS. SFC TEMPS WILL
BE SEVERAL DEGREES COLDER THAN THE EVENTS LAST YEAR...SO EVEN IF
QPF TOTALS ARE LIGHT THE ROADWAYS WILL LIKELY BECOME ICY AND
HAZARDOUS.