Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 031118 AAA
AFDAMA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE AMARILLO TX
618 AM CDT SUN MAY 3 2015

.AVIATION...
MORE THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND EVENING ACROSS
MUCH OF THE PANHANDLES. BUT WILL NOT MENTION THUNDERSTORMS AT THE TAF
SITES AS THE COVERAGE WILL NOT BE WIDESPREAD ENOUGH TO MENTION AT
THIS TIME. SKIES WILL REMAIN VFR...UNLESS A TAF SITE TAKES A DIRECT
HIT FROM A THUNDERSTORM...THEN CONDITIONS WILL LIKELY DROP INTO THE
MVFR RANGE. GUSTY SOUTHERLY WINDS WILL GRADUALLY DECREASE WITH SUNSET.

&&

.PREV DISCUSSION... /ISSUED 520 AM CDT SUN MAY 3 2015/

DISCUSSION...

NO SIGNIFICANT CHANGES WERE NEEDED TO THE PREVIOUS FORECAST. CURRENT
WATER VAPOR AND RAP ANALYSIS SHOW AN UPPER LOW CURRENTLY OFF THE
CALIFORNIA COAST MOVING EASTWARD. THIS WILL BE THE IMPETUS FOR
WIDESPREAD POTENTIALLY HEAVY RAINFALL EARLY NEXT WEEK ACROSS THE
ENTIRE FORECAST AREA.

BROAD BUT WEAK UPPER LEVEL RIDGING IS PRESENT OVER THE SOUTH-CENTRAL
UNITED STATES AND WILL HAVE LESS INFLUENCE ON OUR WEATHER AS IT
CONTINUES TO WEAKEN AND SHIFT EASTWARD. INITIAL PRECIPITATION
CHANCES WILL BE TIED TO DIURNAL CYCLE AND OROGRAPHIC EFFECTS OF THE
HIGH TERRAIN IN NEW MEXICO WITH CONVECTION BECOMING FAIRLY NUMEROUS
THERE BY EARLY/MID AFTERNOON. MEAN WESTERLY FLOW WILL REMAIN RATHER
WEAK RESULTING IN SLOW EASTWARD PROGRESSION OF THIS CONVECTION.
FURTHER EAST ONTO THE NEW MEXICO PLAINS AND ACROSS AT LEAST THE
WESTERN PORTION OF THE PANHANDLES...DEEP MIXING DURING THE AFTERNOON
SHOULD BE SUFFICIENT FOR SCATTERED HIGH BASED CONVECTION TO DEVELOP.
DEEP DRY SUB-CLOUD LAYER WILL LIMIT PRECIPITATION AMOUNTS BUT COULD
RESULT IN STRONG WIND GUSTS WITH THE MOST ROBUST CONVECTION.
CONVECTION SHOULD SLOWLY WEAKEN DURING THE EVENING AND EARLY SUNDAY
NIGHT.

UPPER FLOW BECOMES INCREASINGLY DIFLUENT ON MONDAY AS THE UPPER LOW
APPROACHES. EVEN EARLY IN THE DAY SUFFICIENT LARGE SCALE FORCING
AND MOISTURE ADVECTION IS PRESENT TO JUSTIFY AT LEAST LOW
PRECIPITATION PROBABILITIES PRIMARILY ACROSS THE WESTERN HALF OF THE
AREA. 00Z RAOB FROM COASTAL TEXAS OFFICES STILL LACK DEEP MOISTURE
BUT LATEST SATELLITE DERIVED TPW SHOWS INCREASING MOISTURE ACROSS
THE WESTERN GULF. MODEL GUIDANCE IS INSISTENT ON A SURGE OF LOW
LEVEL MOISTURE AND ABOVE CLIMO PWAT VALUES INTO THE AREA BY LATE
MONDAY WITH STRENGTHENING LEE TROUGH AND SOUTHERLY WINDS. THIS
INCREASE IN MOISTURE COMBINED WITH THE ABOVE MENTIONED LARGE SCALE
FORCING SHOULD RESULT IN WIDESPREAD RAIN. SPATIAL AND TEMPORAL
DETAILS OF HEAVY RAIN AND POTENTIAL FLOODING ARE STILL A BIT UNCLEAR
BUT THE PATTERN FITS THESE THREATS. ONE TO THREE INCHES SEEMS LIKELY.
THE MAJORITY OF THE RAINFALL WILL OCCUR MONDAY NIGHT THROUGH THE
FIRST HALF OF TUESDAY.

SEVERE THUNDERSTORM POTENTIAL SHOULD BE MOST LIKELY...ALBEIT STILL
RELATIVELY LOW AND MARGINAL...MONDAY AFTERNOON AND EVENING
COINCIDENT WITH LOW LEVEL MOISTURE SURGE BENEATH STEEPENING MID
LEVEL LAPSE RATES. THIS SHOULD YIELD AT LEAST MARGINAL INSTABILITY
AND DEEPER/STRONGER CONVECTION THAN THE PREVIOUS DAY. EFFECTIVE
SHEAR MAY BE MARGINAL FOR STORM ORGANIZATION THOUGH. SIGNIFICANT
CONVECTIVE OVERTURNING SHOULD WEAKEN MID LEVEL LAPSE RATES ON
TUESDAY PRECLUDING A NOTEWORTHY SEVERE WEATHER THREAT ALTHOUGH
IF POCKETS OF INSTABILITY CAN DEVELOP SOME STRONG TO SEVERE
THUNDERSTORMS WOULD BE POSSIBLE. ONE OF THE FEW CHANGES THAT WERE
MADE TO THE FORECAST WAS TO LOWER HIGH TEMPERATURES ON TUESDAY TO
ACCOUNT FOR WIDESPREAD CLOUDS AND PRECIPITATION THAT WILL LIKELY
LIMIT THE MAGNITUDE OF DIURNAL HEATING.

AS UPPER LOW/OPENING WAVE DEPARTS...WEAK SHORTWAVE RIDGING WILL
BRIEFLY INFLUENCE THE AREA RESULTING IN A MOSTLY DRY DAY AND
TEMPERATURES RETURNING TO THE UPPER 70S AND LOWER 80S. A DEEP CLOSED
LOW WILL EVOLVE ALONG THE WEST COAST BY THURSDAY AND WITH
STRENGTHENING MEAN SOUTHWESTERLY FLOW LEE TROUGHING WILL
PERSIST/STRENGTHEN. MULTIPLE DAYS OF DRYLINE CONVECTION MAY OCCUR
FROM LATE WEEK THROUGH THE WEEKEND WITH HIGHEST PRECIPITATION
PROBABILITIES ACROSS THE EASTERN HALF OF THE AREA. SPREAD IN THE
ENSEMBLE AND UNCERTAINTY WITH TIMING OF SMALL LEAD WAVES AND
EASTWARD PROGRESSION OF UPPER LOW MAKES IT DIFFICULT TO DELINEATE
WHEN THE HIGHEST PROBABILITY OF PRECIPITATION WILL BE. SUBSEQUENT
FORECASTS WILL REFINE THESE DETAILS.

BRB

&&

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

&&

$$

15/17




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