Area Forecast Discussion
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022
FXUS64 KLUB 211031
AFDLUB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LUBBOCK TX
431 AM CST WED JAN 21 2015

...CONFIDENCE CONTINUES TO INCREASE THAT A MAJOR WINTER STORM WILL
IMPACT THE REGION STARTING TONIGHT AND LASTING THROUGH THURSDAY...

.SHORT TERM...
00Z UPPER-AIR ANALYSIS SHOWS ZONAL TO WEAK NORTHWESTERLY FLOW ALOFT
ACROSS THE SOUTHWESTERN U.S. AHEAD OF A DEEPENING TROUGH PUSHING
ACROSS SOUTHERN CALIFORNIA.  MID AND UPPER LEVEL MOISTURE CONTINUES
TO INCREASE AHEAD OF THE TROUGH WHICH IS PRODUCING A DECK OF HIGH
CLOUDS THAT WILL CONTINUE TO INCREASE IN COVERAGE AND THICKNESS.
CLOSER TO THE SURFACE...WEAK NORTH TO NORTHEASTERLY SURFACE WIND IS
HELPING TO KEEP LOW 30 DEWPOINTS IN PLACE ACROSS THE REGION.  MODELS
INITIALIZED THE TROUGH DECENTLY ENOUGH BUT ARE ALREADY STRUGGLING
WITH WHETHER THIS FEATURE IS STILL AN OPEN WAVE OR HAS STARTED TO
CLOSE OFF.  MODELS ALSO CONTINUE TO QUICKLY BRING A SHORTWAVE OUT OF
THE NORTHERN ROCKIES WHICH WILL HELP TO SLOW DOWN THE EASTWARD
PROGRESSION OF THE TROUGH AND EVENTUALLY/POSSIBLY DEVELOP ANOTHER
CLOSED LOW CENTER WEST OF THE FORECAST AREA.

BASED ON THE TRACK AND TIMING OF THE WAVE...PREVIOUS FORECAST HAD A
GOOD HANDLE ON THINGS AND ONLY HAD TO MAKE MINOR ADJUSTMENTS TO THE
TIMING OF PRECIPITATION AND ONSET TIMES OF SNOW IN THE GRIDS.
EXPECT TO SEE PRECIPITATION START OFF NORTH OF THE AREA ACROSS
NORTHEAST NEW MEXICO INTO THE TEXAS PANHANDLE THIS AFTERNOON.  THIS
WILL GRADUALLY START TO SPREAD SOUTHWARD THROUGH THE LATE AFTERNOON
INTO THE EARLY EVENING.  DEPENDING ON HOW THICK THE CLOUD COVER IS
THIS AFTERNOON...HIGH TEMPERATURES WILL BE DIFFICULT TO FORECAST AND
COOLER HIGHS THAN WHAT ARE CURRENTLY FORECAST WILL ALLOW FOR A
QUICKER TRANSITION TO SNOW THIS EVENING.  A COLD FRONT WILL ALSO
PUSH ACROSS THE REGION LATE THIS EVENING THROUGH THE OVERNIGHT HOURS
HELPING TO COOL THE BOUNDARY LAYER AS THE EVENT PROGRESSES.  AN
INITIAL ROUND OF LIFT WILL PUSH ACROSS THE AREA THIS EVENING WHICH
WILL HELP TO INITIATE PRECIPITATION BUT THE HEAVIER AMOUNTS WILL
HOLD OFF UNTIL AFTER MIDNIGHT ONCE STRONG ISENTROPIC LIFT DEVELOPS
THROUGH A THICK LAYER ACROSS THE REGION.  THE LAYERS BETWEEN 285K
AND 300K /OR ROUGHLY FROM 850HPA TO 600HPA/ ALL SHOW STRONG LIFT AND
SATURATION SIGNALS WHICH WOULD FAVOR MODERATE TO OCCASIONALLY HEAVY
PRECIPITATION.  THE EXACT TRANSITION TIME FROM LIQUID...TO A MIX OF
RAIN AND SNOW...TO ALL SNOW REMAINS TRICKY AS ANY CHANGES IN SPEED
OF THE APPROACHING TROUGH...HOW FAST THE BOUNDARY LAYER COOLS FROM
THE FRONT...OR DRY/MOIST ADIABATIC COOLING FROM LIFT/PRECIPITATION
RESPECTIVELY ALL CONTRIBUTE TO COOLING THE COLUMN.

THE BIGGEST QUESTION IS NOT HOW HIGH OF POPS TO CARRY AS WE ARE
PRETTY MUCH INCREASING TO 100 PERCENT ACROSS THE ENTIRE AREA BY
MIDNIGHT.  THE MILLION DOLLAR QUESTION IS HOW MUCH SNOW AND WHERE
THE HEAVIEST SNOW WILL FALL.  CURRENT THINKING AND FORECAST WILL
START OFF WITH ALL LIQUID PRECIPITATION TODAY THROUGH 6 PM AS
TEMPERATURES REMAIN ABOVE FREEZING IN THE BOUNDARY LAYER.
TRANSITION TO RAIN/SNOW MIX WILL START AFTER SUNSET ACROSS THE
NORTHWESTERN COUNTIES AS PRECIPITATION COVERAGE STARTS TO EXPAND.
MODELS HAVE COME INTO GOOD AGREEMENT WITH TWO HEAVIER AREAS OF
PRECIPITATION...ONE DEVELOPING ACROSS NORTHEAST NEW MEXICO INTO THE
TEXAS PANHANDLE THAT WILL PUSH SOUTH WITH TIME.  THE SECOND AREA
DEVELOPS ACROSS THE SOUTHERN ROLLING PLAINS AND SPREADS TOWARDS THE
BIG COUNTRY AND CONCHO VALLEY.  AS THE COLUMN RAPIDLY COOLS ACROSS
THE NORTHWESTERN SOUTH PLAINS...ALL SNOW COULD DEVELOP AS EARLY AS
9 PM.  RAIN/SNOW MIX LINE WILL SPREAD SOUTHEAST THROUGH THE EVENING
AND REACH THE EDGE OF THE CAPROCK BY MIDNIGHT WITH THE TRANSITION TO
ALL SNOW CLOSELY BEHIND.  HEAVIEST SNOWFALL RATES SHOULD START TO
DEVELOP AROUND MIDNIGHT AS THE STRONGEST ISENTROPIC LIFT SETS UP
ACROSS THAT REGION WHILE A SLIGHTLY WARMER BOUNDARY LAYER ACROSS THE
ROLLING PLAINS KEEPS THE SECOND AREA OF PRECIPITATION ALL LIQUID
THROUGH MOST OF THE NIGHT.  BY SUNRISE THURSDAY MORNING...THE ONLY
AREA THAT COULD STILL SEE ALL RAIN COULD BE THE SOUTHERN ROLLING
PLAINS AROUND ASPERMONT AS THE REST OF THE AREA WILL HAVE TRANSITION
TO ALL SNOW OR A RAIN/SNOW MIX.

ALTHOUGH THE STRONGEST LIFT WILL BE BELOW THE FAVORED DENDRITIC
GROWTH ZONE...AMPLE MOISTURE THROUGHOUT THE COLUMN WILL RESULT IN
SOME PRETTY SIGNIFICANT SNOW AMOUNTS FOR PORTIONS OF THE AREA.
BETWEEN 6 PM TONIGHT/00Z THURSDAY AND 6 AM/12Z THURSDAY...PORTIONS OF
THE NORTHWESTERN SOUTH PLAINS COULD RECEIVE UP TO 5-7 INCHES OF
SNOW.  BECAUSE SNOWFALL WILL START ACROSS THE NORTHWESTERN SOUTH
PLAINS FIRST...OPTED TO GO AHEAD AND UPGRADE PARMER...CASTRO...AND
BAILEY COUNTIES TO A WINTER STORM WARNING THAT GOES INTO EFFECT AT
6 PM TONIGHT.  WINTER STORM WATCH FOR ALL BUT THE ROLLING PLAINS WILL
REMAIN IN EFFECT WITH THE ADDITION OF GARZA COUNTY.  OPTED TO HOLD
OFF UPGRADING THE REST OF THE AREA TO GET A BETTER FEEL FOR HOW THE
INCOMING STORM SYSTEM WILL DEVELOP AND MOVE ACROSS THE AREA.
SNOWFALL TOTALS FOR THE ENTIRE EVENT WILL BE DISCUSSED BELOW AS IT
HEADS INTO THE FIRST PART OF THE EXTENDED FORECAST.

JORDAN

&&

.LONG TERM...
THE EFFORTS IN THE EXTENDED WERE CENTERED STRICTLY AROUND THE
IMPENDING WINTER STORM...WITH THE REMAINDER OF THE LONG TERM GRIDS
LARGELY UNTOUCHED.

THE CENTER OF THE PRIMARY UPPER LOW IS PROGGED TO BE NEAR OR JUST
SOUTH OF THE FOUR CORNERS AT 12Z THURSDAY. THE LOW SHOULD DIG SLOWLY
SOUTHEASTWARD THROUGH THE DAY BEFORE GRADUALLY OPENING AND EJECTING
EASTWARD LATE THURSDAY OR EARLY FRIDAY. THE SLOWER AND DEEPER
EVOLUTION OF THE STORM SYSTEM WILL MEAN AN EXTENDED PERIOD OF LARGE
SCALE LIFT FOR MOST THE SOUTH PLAINS REGION ON THURSDAY...PERHAPS
LINGERING WELL INTO THURSDAY NIGHT OR EARLY FRIDAY IF THE
SLOWEST/DEEPEST SOLUTIONS ARE CORRECT. THIS MEANS A PROLONGED PERIOD
OF LIGHT TO MODERATE PRECIPITATION FOR THE REGION.

AT 12Z THURSDAY...IT SHOULD BE COLD ENOUGH THAT ALL THE
PRECIPITATION FALLING ON THE CAPROCK WILL BE IN THE FORM OF SNOW.
HOWEVER...IT MAY REMAIN JUST WARM ENOUGH IN THE LOWEST LEVELS OF
THE ATMOSPHERE ACROSS THE EASTERN ZONES...FROM CHILDRESS THROUGH
JAYTON AND ASPERMONT...THAT THEY MAY SEE SOME MIX OF RAIN AND
SNOW. THE THREAT OF A RAIN/SNOW WINTRY MIX MAY PERSIST MUCH OF
THE DAY ACROSS THE EASTERN MOST ZONES...THOUGH THE REMAINDER OF
THE FA SHOULD REMAIN COLD ENOUGH FOR ALL SNOW. SEVERAL MORE INCHES
OF SNOW ARE EXPECTED TO FALL OVER THE CAPROCK THROUGH THE DAY
THURSDAY...WITH THE HIGHEST TOTALS CURRENTLY EXPECTED ACROSS THE
WESTERN ZONES. OUT EAST...WHERE THE P-TYPE IS LESS CERTAIN...SNOW
TOTALS ARE ALSO MORE IFFY...BUT WE CURRENTLY HAVE AN ADDITIONAL
INCH OR TWO FOR MOST SPOTS. THE SNOW MAY LINGER WELL INTO THURSDAY
EVENING/NIGHT...PARTICULARLY ACROSS THE SOUTHERN ZONES...CLOSEST
TO WHAT REMAINS OF THE UPPER LOW. A LITTLE SNOW COULD EVEN PERSIST
AFTER MIDNIGHT OVER THE SOUTHERN SECTIONS...BUT WHATEVER FALLS
SHOULD BE LIGHT WITH LITTLE IN THE WAY OF ADDITIONAL
ACCUMULATIONS. THUS...WE HAVE DECIDED TO KEEP THE EXPIRATION TIME
OF THE WINTER STORM WATCH AS 06Z FRIDAY. IN ADDITION TO THE
SNOW...GUSTY NORTHEASTERLY WINDS OF 15-25 MPH COULD RESULT IN
AREAS OF BLOWING AND DRIFTING SNOW AND LIMITED VISIBILITIES
THROUGH THE DAY THURSDAY BEFORE THEY GRADUALLY DIMINISH THURSDAY
NIGHT.

BY THE TIME ALL IS SAID AND DONE...SNOW TOTALS OF A HALF A FOOT OR
MORE APPEAR A GOOD BET FOR OUR NORTHWESTERN MOST ZONES...WITH 8 TO
10 INCHES OR MORE NOT OUT OF THE QUESTION. OUT IN THE ROLLING
PLAINS...SNOW TOTALS OF 1 TO 3 INCHES SEEM POSSIBLE...THOUGH THE
TIMING OF THE TRANSITION FROM RAIN TO SNOW WILL HAVE AN IMPACT ON
THIS. BETWEEN THE TWO AREA...INCLUDING IN LUBBOCK...A GENERAL 3 TO
6 INCHES ARE EXPECTED...WITH LOCALLY HIGHER AMOUNTS.

AFTER THE STORM SYSTEM DEPARTS...WE SHOULD SEE A RETURN OF ABUNDANT
SUNSHINE BY FRIDAY AFTERNOON...BUT TEMPERATURES WILL BE SLOW TO
RECOVER...ESPECIALLY WHERE THE HEAVIER SNOW PACK IS IN PLACE. BEYOND
FRIDAY...A MODERATING TREND WILL ENSUE UNDER DRY NORTHWEST FLOW
ALOFT THROUGH EARLY NEXT WEEK...THOUGH ANY RESIDUAL SNOW PACK
COULD TEMPER THIS WARMING TREND.

&&

.PRELIMINARY POINT TEMPS/POPS...
FRIONA        40  25  27   8  33 /  40 100  90  30   0
TULIA         43  28  29  12  36 /  40 100  90  30  10
PLAINVIEW     45  28  30  15  35 /  20 100  90  30  10
LEVELLAND     45  29  30  15  37 /  20 100  90  50  10
LUBBOCK       47  30  31  17  36 /  20 100  90  50  10
DENVER CITY   44  29  32  18  36 /  20 100  90  50  10
BROWNFIELD    45  29  33  19  36 /  20 100  90  50  10
CHILDRESS     51  32  34  23  44 /  20 100  90  20  10
SPUR          50  31  34  23  43 /  20 100  90  50  10
ASPERMONT     52  33  38  27  46 /  20 100  90  50  10

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM THIS EVENING THROUGH THURSDAY EVENING
FOR THE FOLLOWING ZONES: TXZ023-024-028>030-033>036-039>042.

WINTER STORM WARNING FROM 6 PM THIS EVENING TO MIDNIGHT CST
THURSDAY NIGHT FOR THE FOLLOWING ZONES: TXZ021-022-027.

&&

$$

14/23

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