Area Forecast Discussion
Issued by NWS Amarillo, TX

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000
FXUS64 KAMA 291200 AAA
AFDAMA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE AMARILLO TX
600 AM CST THU JAN 29 2015

.AVIATION...
MID AND HIGH LEVEL CLOUDS WILL PREVAIL ACROSS THE TAF SITES THROUGH
THIS FORECAST...SO CONDITIONS WILL BE VFR. NORTHEAST WINDS WILL
INCREASE TODAY TO AROUND 20 KNOTS WITH HIGHER GUSTS. WINDS WILL THEN
DECREASE AND VEER TONIGHT.

&&

.PREV DISCUSSION... /ISSUED 441 AM CST THU JAN 29 2015/

DISCUSSION...

PRIMARY CHALLENGES ARE TIMING OF THE ONSET OF PRECIPITATION FRIDAY
MORNING AND PRECIPITATION TYPE THROUGHOUT THE DURATION OF THE EVENT.

CURRENT WATER VAPOR LOOP SHOWS PLUME OF SUBTROPICAL MOISTURE
STREAMING EASTWARD FROM THE PACIFIC ACROSS THE SOUTHWEST INTO THE
SOUTHERN PLAINS AHEAD OF A FAIRLY DEEP TROUGH OFF THE WEST COAST
MOVING SLOWLY EAST. SATELLITE-DERIVED CLOUD PRODUCT CONFIRMS A
RATHER EXPANSIVE AREA OF CIRRUS IS PRESENT OVER THE AREA ASSOCIATED
WITH THIS PACIFIC MOIST PLUME. UPPER FLOW WAS PROGRESSIVE BUT FAIRLY
AMPLIFIED ACROSS THE CONUS. A TRANSIENT SHORTWAVE NOW OVER THE UPPER
MIDWEST HAS FORCED A COLD FRONT SOUTH WHICH SHOULD CLEAR THE AREA
THIS MORNING BRINGING AN END TO THE UNSEASONABLY WARM WEATHER. FOCUS
THEN SHIFTS TO THE MAGNITUDE/DEPTH AND PERSISTENCE OF SECOND COLD
SURGE THAT WILL ARRIVE AHEAD OF THE NEXT SYSTEM AND IMPLICATIONS
THAT WILL HAVE ON PRECIPITATION TYPE.

MODEL CONSENSUS IS FOR A CLOSED UPPER LOW TO EVOLVE OVER THE
SOUTHWEST CONUS AND RATHER EXPANSIVE BUT WEAK ISENTROPIC ASCENT
BENEATH INCREASINGLY DIFFLUENT FLOW ALOFT. BY 12Z FRIDAY MODELS
SATURATE THROUGH A RELATIVELY DEEP LAYER WITH SOME RESIDUAL DRY AIR
AT THE SURFACE LEADING TO THE AFOREMENTIONED UNCERTAINTY ON
PRECIPITATION ONSET. HELD THE ONSET BACK SLIGHTLY IN THE EAST FROM
PREVIOUS FORECAST AND INCREASED POPS IN THE WEST FOR EARLY FRIDAY.
BUFKIT SOUNDINGS SHOW NEARLY ISOTHERMAL WET BULB PROFILES NEAR 0
DEGREES CELSIUS ALL DAY. HOWEVER...GIVEN THE MAGNITUDE OF VEERING
WITH HEIGHT IN THE LOW LEVELS AM CONCERNED THAT THERE WILL BE A MORE
PRONOUNCED WARM LAYER ALOFT SUFFICIENT FOR A NOT SO CLEAR
DIFFERENTIATION SPATIALLY BETWEEN RAIN AND SNOW. IN FACT MODELS HAVE
TRENDED WARMER AND HAVE FOLLOWED THIS TREND BY BEING LESS
DETERMINISTIC WITH SNOW IN THE WEST INTRODUCING RAIN AND SNOW WORDING
AND ALSO EXPANDING THE ALL RAIN AREA FURTHER WEST. LOWERED SNOW
AMOUNTS SLIGHTLY AS WELL. CONFIDENCE IN OVERALL SCENARIO REMAINS LOW
GIVEN THE INHERENT NATURE OF CLOSED UPPER LOWS IN THE
SOUTHWEST...PARTICULARLY WHEN STILL OFF SHORE. CONFIDENCE WILL
INCREASE AT CLOSER TIME RANGE.

BY SUNDAY THE CLOSED LOW MOVES SOUTHEASTWARD INTO MEXICO AND A
NORTHERN STREAM SHORTWAVE DIVES SOUTHEASTWARD SWEEPING MOISTURE
EASTWARD AND ENDING PRECIPITATION CHANCES. OUR AREA WILL REMAIN IN
NORTHWESTERLY FLOW ON THE PERIPHERY OF MEAN WESTERN CONUS RIDGING
DURING THE EXTENDED PERIOD. THIS WILL RESULT IN A RETURN TO NEAR OR
SLIGHTLY ABOVE NORMAL TEMPERATURES AND GENERALLY DRY CONDITIONS FOR
THE FIRST PART OF NEXT WEEK. THE EXCEPTION MIGHT BE AROUND WEDNESDAY
NIGHT WHEN A WEAK SYSTEM BRINGS A SLIGHT CHANCE OF RAIN OR SNOW TO
THE AREA.

BRB

&&

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

&&

$$

15/17





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