Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 251710 AAA
AFDAMA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE AMARILLO TX
1110 AM CST WED FEB 25 2015

.AVIATION...
FOR 18Z TAFS...NORTHWEST WINDS WILL BE ON THE INCREASE THIS
AFTERNOON AND WINDS WILL GRADUALLY VEER TO A MORE NORTHERLY
DIRECTION. AN ARCTIC COLD FRONT IS STILL EXPECTED TO PUSH INTO THE
PANHANDLES OVERNIGHT...MORE LIKELY BETWEEN 04Z AND 06Z. WINDS WILL
SHIFT TO THE NORTHEAST WITH GUSTS OF 30KTS TO 40KTS. THE FRONT WILL
ALSO BRING MVFR CEILINGS AND A CHANCE OF SNOW. CEILINGS COULD FALL TO
IFR CATEGORY AT KAMA AND KDHT AFTER 06Z. WILL LIKELY HOIST AN AVIATION
WEATHER WARNING FOR KAMA AND TRADEWIND AIRPORT FOR WINDS GUSTS.

GARCIA

&&

.PREV DISCUSSION... /ISSUED 533 AM CST WED FEB 25 2015/

AVIATION...
VFR CONDITIONS EXPECTED TODAY AND INTO THE EARLY EVENING WITH ONLY
MID- AND HIGH-LEVEL CLOUDS EXPECTED.  LIGHT NORTHWEST SURFACE WINDS
THIS MORNING EXPECTED TO BECOME MORE NORTHERLY BY 18Z TODAY...WITH
GUSTS TO AROUND 25 KT.  ARCTIC COLD FRONT EXPECTED TO PASS TERMINALS
BETWEEN 02Z AND 04Z THURSDAY...WITH MVFR CEILINGS AND NORTHEAST
SURFACE WINDS GUSTING TO AROUND 35 KT.  CHANCES FOR SNOW INCREASE
MARKEDLY LATE TONIGHT...ESPECIALLY AT KDHT...WHERE OCCASIONAL IFR
CEILINGS AND VISIBILITIES ARE FORECAST.

COCKRELL

PREV DISCUSSION... /ISSUED 441 AM CST WED FEB 25 2015/

DISCUSSION...

EARLY THIS MORNING AN UPPER LEVEL TROUGH WAS EVIDENT IN SATELLITE/WV
LOOP AND UPPER AIR ANALYSIS FROM THE EASTERN TEXAS PANHANDLE
EXTENDING INTO SOUTHEAST TEXAS. REGIONAL RADAR COMPOSITE AND SURFACE
OBSERVATIONS SHOW THAT PRECIPITATION WAS MOSTLY CONFINED TO CENTRAL
TEXAS IN AN AREA WHERE ISENTROPIC UPGLIDE AND MOISTURE ADVECTION WAS
MAXIMIZED. KAMA RADAR HAD LIGHT ECHOS ACROSS THE EASTERN PORTION OF
THE AREA BUT NONE OF THE MESONET SITES INDICATED MEASURABLE
PRECIPITATION OWING TO EXTENSIVE DRY SUB-CLOUD LAYER.

UPPER TROUGH WILL CONTINUE TO SHIFT EASTWARD WITH A BRIEF PERIOD OF
MID LEVEL HEIGHT RISES OCCURRING TODAY IN ITS WAKE WHICH WILL
BRING ONE MORE DAY OF REASONABLE TEMPERATURES. GIVEN THE MAGNITUDE
OF SHORTWAVE RIDGING AND VISIBLE SATELLITE SHOWING THAT MOST OF THE
SNOW COVER HAS MELTED DECIDED TO RAISE HIGH TEMPERATURES SLIGHTLY.
WITH THE DEPARTURE OF THIS SYSTEM MID LEVEL STRATUS DECK SHOULD EXIT
THE ENTIRE AREA DURING THE EARLY MORNING LEAVING MOSTLY CLEAR
CONDITIONS FOR A SHORT PERIOD PRIOR TO THE ARRIVAL OF EXTENSIVE
CIRRUS PRECEDING THE NEXT SYSTEM. THROUGH THE MORNING WINDS WILL
VEER TO MORE OF A NORTHERLY DIRECTION BEHIND A WEAKLY BUT INCREASINGLY
BAROCLINIC SURFACE TROUGH/FRONT BY LATE MORNING AND PERSIST INTO THE
AFTERNOON.

PRIMARY SHORT TERM CHALLENGE IS TIMING OF COLD FRONT THAT WILL BE
COINCIDENT WITH WITH RATHER SUBSTANTIAL HEIGHT FALLS ASSOCIATED WITH
THE FIRST IN A SERIES OF SHORTWAVES THAT WILL PASS THROUGH. USED THE
WRF-ARW TO POPULATE THE GRIDS AS A STARTING POINT AND NUDGED SPEEDS
TOWARD STATISTICAL GUIDANCE WHICH IS OFTEN MORE REPRESENTATIVE IN
THESE SCENARIOS WITH 3 HOUR MSLP RISES OF NEARLY 10 MB. AS IS OFTEN
THE CASE IN THIS AREA WITH ARCTIC AIR MASS INTRUSIONS WE WILL NEED
TO WATCH THE MAGNITUDE AND DEPTH OF LOW LEVEL MOISTURE AND POTENTIAL
FOR SATURATION IN THE SUB-DENDRITIC GROWTH ZONE THAT COULD LEAD TO
PATCHY FREEZING DRIZZLE. CONFIDENCE IS NOT PARTICULARLY HIGH IN
SUFFICIENT MID LEVEL/DGZ SATURATION INITIALLY TO INTRODUCE ICE
CRYSTALS SINCE DEEPEST ASCENT ARRIVES AFTER 06Z AND CLOSER TO 12Z.
CONFIDENCE IS ALSO NOT VERY HIGH THAT LOW LEVELS WILL SATURATE
ENOUGH FOR ANY CONCERN BEYOND LOW STRATUS FOR AVIATION INTERESTS BUT
WILL NEED TO MONITOR TRENDS CLOSELY.

THE COMBINATION OF MOIST UPSLOPE FLOW...DEEP MOISTENING...AND
INCREASING ASCENT LATE WEDNESDAY NIGHT INTO EARLY THURSDAY MORNING
SHOULD RESULT IN QUITE AN EXPANSIVE AREA OF SNOW DEVELOPING OVER NEW
MEXICO. MODEL QPF SIGNALS ARE GENERALLY CONFINED TO THE WESTERN
THIRD OF THE FORECAST AREA DURING THIS PERIOD. THESE UPSLOPE REGIMES
CAN SOMETIMES YIELD EXAGGERATED QPF IN THE MODELS PARTICULARLY IF
DEEP SATURATION AND LARGE SCALE ASCENT IS DELAYED. THUS THE BEST
CHANCE OF SNOW APPEARS TO BE LATER IN THE NIGHT WITH ADVISORY LEVEL
AMOUNTS SEEMING INCREASINGLY LIKELY ACROSS MAINLY THE FAR WEST AND
SOUTHWESTERN PORTIONS OF THE PANHANDLES. THERE WILL BE A LULL IN THE
HIGHEST PROBABILITIES OF SNOW DURING THE DAY ON THURSDAY AS THE
FIRST SHORTWAVE SHIFTS EAST. BY LATE IN THE DAY MOISTURE DEEPENS
ONCE AGAIN AND THE SECOND ROUND OF SNOW SHOULD BEGIN IN THE FAR WEST
AND ESPECIALLY NORTHWEST. PROBABILITIES INCREASE OVERNIGHT THURSDAY
NIGHT THROUGH FRIDAY MORNING AS ISENTROPIC UPGLIDE AND MOISTURE
DEPTH IS MAXIMIZED. THIS IS WHEN THE GREATEST SNOWFALL ACCUMULATIONS
COULD OCCUR WITH A FIRST GUESS OF TWO TO FOUR INCHES ACROSS MAINLY
THE SOUTHERN TWO THIRDS OF THE TEXAS PANHANDLE AND LIGHTER AMOUNTS
ACROSS THE FAR NORTHERN TEXAS PANHANDLE AND THE OKLAHOMA PANHANDLE.

AFTER THIS SECOND SHORTWAVE DEPARTS LATE FRIDAY MODELS AGREE ON A
PERIOD OF SUBTLE HEIGHT RISES AND BACKING OF UPPER FLOW IN RESPONSE
TO DEEPENING TROUGH IN THE WEST. TRANSIENT SMALL DIFFICULT TO
RESOLVE PERTURBATIONS IN WESTERLIES WILL RESULT IN RELATIVELY LOW
PROBABILITY PRECIPITATION CHANCES THROUGH THE WEEKEND. BETTER
CHANCES RETURN MONDAY AS THE SOUTHWESTERN TROUGH APPROACHES. BEYOND
THIS GENERALIZATION THERE IS A MYRIAD OF UNCERTAINTIES IN THE
EXTENDED RANGING FROM TEMPERATURES AND PRECIPITATION TO TIMING OF
THE UPPER TROUGH. GFS IS FASTER THAN BOTH ITS ENSEMBLE MEAN AND THE
EUROPEAN AND THIS MAY DELAY THE BEST PRECIPITATION CHANCES. ADJUSTED
PROBABILITIES MONDAY NIGHT UPWARD FROM PREVIOUS FORECAST TO ACCOUNT
FOR THIS. ANOTHER RATHER ROBUST COLD SURGE COULD MAKE IT INTO AT
LEAST THE NORTHERN PART OF THE AREA LATE SUNDAY FORCED BY A NORTHERN
STREAM SHORTWAVE. WITH AMPLIFYING TROUGH TO THE WEST AND BUILDING
RIDGING TO THE EAST THIS COLD FRONT PROBABLY WILL NOT PROGRESS THROUGH
THE AREA. QUITE AN INTENSE BAROCLINIC ZONE LOOKS TO DEVELOP WITH A
FAIRLY STRONG LEE LOW SPAWNING ALONG THIS ON MONDAY...PERHAPS LATER
IF THE LESS PROGRESSIVE MEDIUM RANGE MODELS PROVE TO BE CORRECT.
THIS HAS TREMENDOUS IMPLICATIONS FOR PRECIPITATION TYPE WITH SNOW
AND FREEZING RAIN POSSIBLE NORTH OF THE COLD FRONT IF IT CAN MAKE IT
INTO THE AREA. THUNDER IS POSSIBLE FURTHER SOUTH IF LOW LEVEL
WARM/MOIST ADVECTION PROVES TO BE SUFFICIENT.

BRB

&&

.AMA WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
OK...NONE.

&&

$$






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