Area Forecast Discussion
Issued by NWS Amarillo, TX

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000
FXUS64 KAMA 021118 AAA
AFDAMA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE AMARILLO TX
618 AM CDT SAT MAY 2 2015

.AVIATION...
HIGH CLOUDS WILL THIN LATER THIS MORNING. MORE THUNDERSTORMS WILL
DEVELOP OVER THE MOUNTAINS OF NEW MEXICO AND COLORADO AND THE UPPER
FLOW WILL SEND THEM THIS WAY. A FEW THUNDERSTORMS MAY AFFECT THE DHT
TAF SITE THIS EVENING...BUT COVERAGE WILL BE TOO ISOLATED TO MENTION
IN THE CURRENT FORECAST. SOUTHERLY WINDS WILL GET GUSTY BY MID TO
LATE MORNING...THEN THEY WILL DECREASE WITH SUNSET.

&&

.PREV DISCUSSION... /ISSUED 443 AM CDT SAT MAY 2 2015/

DISCUSSION...

BROAD BUT FAIRLY WEAK UPPER LEVEL RIDGING EXTENDS FROM THE SOUTHWEST
THROUGH THE SOUTHERN PLAINS. ELEVATED HEATING IN THE MOUNTAINS OF
NEW MEXICO AND COLORADO RESULTED IN CONVECTION THAT HAS DRIFTED
SLOWLY EAST-SOUTHEASTWARD ONTO THE PLAINS LAST EVENING. WITH
STRONGEST MEAN FLOW FURTHER NORTH ALONG THE PERIPHERY OF UPPER RIDGE
ACROSS THE CENTRAL AND NORTHERN ROCKIES...BOTH ORGANIZATION AND
EASTWARD PROGRESS OF CONVECTION HAS BEEN LIMITED ACROSS EASTERN NEW
MEXICO AND OFF THE RATON MESA. FURTHERMORE...FAIRLY DRY AIR MASS AS
EVIDENT BY REGIONAL OBSERVED SOUNDINGS HAS LIMITED PRECIPITATION
AMOUNTS WITH THIS CONVECTION. EARLY TONIGHT...ONLY A FEW LINGERING
LIGHT RAIN SHOWERS REMAINED ACROSS THE OKLAHOMA AND FAR NORTHERN
TEXAS PANHANDLES. ONLY A HUNDREDTH OF AN INCH OCCURRED AT CLAYTON
ASOS EARLIER IN THE EVENING WITH NO OTHER OBSERVATIONS INDICATING
MEASURABLE PRECIPITATION.

NOT A LOT OF CHANGE IS EVIDENT IN SHORT RANGE MODEL GUIDANCE FOR
TOMORROW. THE RIDGE WEAKENS SLIGHTLY. WEAK PERTURBATIONS WITHIN
WESTERLY FLOW ALOFT ACROSS THE CENTRAL PLAINS ARE PROBABLY AT LEAST
AUGMENTED SOME BY LATENT HEAT RELEASE FROM DIURNAL HIGH TERRAIN
CONVECTION. THESE SMALL WAVES SHOULD STILL BE COINCIDENT WITH SOME
CONVECTION INTO THE EVENING THAT WOULD IMPACT MAINLY THE NORTHERN AND
WESTERN PORTIONS OF THE AREA. WITHOUT SIGNIFICANT FORCING...CONTINUED
WEAK FLOW ALOFT...AND NOT MUCH OF AN UPWARD TREND IN MOISTURE IN THE
SHORT TERM...PRECIPITATION AMOUNTS AND COVERAGE SHOULD AGAIN BE QUITE
LIMITED.

WESTERLY MOMENTUM ALOFT FROM STRENGTHENING SUBTROPICAL JET HAS BEEN
EVIDENT IN MODEL GUIDANCE FOR SEVERAL DAYS AND WILL REACH BAJA BY
SUNDAY SPREADING EASTWARD ACROSS DEEP SOUTH TEXAS THROUGH EARLY
MONDAY. MEANWHILE A MID/UPPER CLOSED LOW EVOLVES IN THE VICINITY OF
THE SOUTHERN CALIFORNIA COAST. MODELS AGREE ON A FAIRLY SIGNIFICANT
RESPONSE OF SURFACE PRESSURE FIELDS AS RIDGE BREAKS DOWN AND THE
SYSTEM IN THE SOUTHWEST APPROACHES. THIS WILL RESULT IN
STRENGTHENING SOUTHERLY LOW LEVEL FLOW THIS AFTERNOON. LOW LEVEL
TRAJECTORIES FROM THE WESTERN GULF SHOULD RESULT IN FAIRLY ROBUST
MOISTURE ARRIVAL BY LATE MONDAY. THIS SCENARIO SEEMS TO EVOLVE IN
SUCH A WAY THAT WOULD FAVOR RELATIVELY DEEP MOIST MERIDIONAL FLOW AND
PROBABLY MORE OF A HEAVY RAIN/POTENTIAL FLOODING THREAT THAN SEVERE
WEATHER THREAT. ALTHOUGH FAIRLY WIDESPREAD CONVECTION GENERATED IN
THE MODELS SEEMS TO CONTAMINATE THE FORECAST SOUNDINGS LATE MONDAY
AND ESPECIALLY TUESDAY SHOWING SATURATED ADIABATIC PROFILES AND
MINIMAL INSTABILITY...THERE WILL PROBABLY BE PERIODS/POCKETS OF
HIGHER CAPE AND CORRESPONDING MORE ROBUST POTENTIAL FOR SEVERE
CONVECTION. FOR THIS REASON FEEL COMFORTABLE CONTINUING TO MENTION
THE POTENTIAL FOR MARGINALLY SEVERE THUNDERSTORMS IN PUBLIC PRODUCTS.
THE PREVIOUS FORECAST HAD A GOOD HANDLE ON THIS SCENARIO AS IT
MENTIONS BOTH THREATS IN THE HAZARDOUS WEATHER OUTLOOK WITH MORE OF A
FOCUS ON HEAVY RAIN IN THE PUBLIC FORECAST. KEPT STORM TOTAL QPF
AROUND ONE TO TWO INCHES BUT WITH PWAT VALUES PEAKING ABOVE THE 90TH
PERCENTILE EARLY TUESDAY THERE IS POTENTIAL FOR HIGHER AMOUNTS. LATER
FORECASTS MAY ADJUST UPWARD DEPENDING ON QUALITY OF MOISTURE RETURN
AND AT LEAST SOME POTENTIAL FOR UPSTREAM CONVECTION OVER DEEP SOUTH
TEXAS TO LIMIT QUALITY OF MOISTURE RETURN.

BEYOND TUESDAY AS THE SHORTWAVE DEPARTS AND DEEP MOISTURE SHIFTS
EAST...SHORTWAVE RIDGING WILL BUILD RESULTING IN DRIER CONDITIONS.
AT THE SAME TIME...PACIFIC UPPER LOW WILL DEEPEN AND BROADEN AS IT
DROPS SOUTHWARD ALONG THE PACIFIC COAST. AN ACTIVE PATTERN WILL
CONTINUE IN THE EXTENDED PERIOD ALTHOUGH CONSIDERABLE UNCERTAINTY
EXISTS. ANOTHER IN A SERIES OF SHORTWAVES WILL ROTATE AROUND THE
UPPER LOW AND IMPACT THE AREA THURSDAY FOLLOWED BY STRONGER LARGE
SCALE FORCING FROM THE APPROACHING UPPER LOW BY FRIDAY AND SATURDAY.
DESPITE UNCERTAINTIES THE GENERAL PATTERN WOULD SUGGEST MORE OF A
DIFFERENTIAL ADVECTION SCENARIO WITH A DRYLINE POSITIONED ACROSS THE
FORECAST AREA AND SOME POTENTIAL FOR IT TO MIX EASTWARD LIMITING
THUNDERSTORM CHANCES FURTHER WEST. THIS IS ESPECIALLY TRUE TOWARD
SATURDAY AS MEAN SOUTHWESTERLY FLOW STRENGTHENS WITH THE APPROACH OF
THE MAIN UPPER LOW. HAVE KEPT HIGHER PRECIPITATION PROBABILITIES IN
ROUGHLY THE EASTERN HALF OF THE PANHANDLES FOR THE LATE WEEK PERIOD
INTO THE FIRST PART OF NEXT WEEKEND.

BRB

&&

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

&&

$$

15/17




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