Tornadoes and Dust Storm in Texas, May 27, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE AMARILLO TX
1212 PM CDT WED MAY 27 2015

.AVIATION...
VFR CONDITIONS TO START THE 18Z TAF ISSUANCE BEFORE CONVECTION
DEVELOPS ACROSS THE TEXAS AND OKLAHOMA PANHANDLES. HAVE INSERTED
MENTION OF VICINITY THUNDER AROUND 20Z FOR KAMA AND KGUY WHICH HAVE
THE BETTER CHANCES FOR CONVECTION TO IMPACT THE TERMINALS BASED ON
ANTICIPATED INITIATION LOCATIONS. HAVE HELD OFF PREVAILING THUNDER AS
THERE IS SOME UNCERTAINTY IF CONVECTION WILL MOVE OVER THE TERMINALS.
SHOULD CONVECTION DIRECTLY IMPACT A TERMINAL KGUY HAS THE BEST CHANCE
FOLLOWED BY KAMA. KDHT SHOULD REMAIN MOSTLY CONVECTION FREE UNTIL
AFTER 00Z OR EVEN 06Z. CONVECTION INCREASES IN AREA COVERAGE
OVERNIGHT AND HAVE HAVE GONE WITH PREVAILING SHOWERS FOR KAMA WITH
VICINITY THUNDER AROUND 10Z. CEILINGS WILL LIKELY DEGRADE AS
CONVECTION APPROACHES THE TERMINALS AND HAVE STARTED A TREND OF LOWER
CEILINGS ESPECIALLY TOWARDS TOMORROW MORNING.

&&

.PREV DISCUSSION... /ISSUED 1133 AM CDT WED MAY 27 2015/

MESOSCALE UPDATE...
SEVERE THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AS INSTABILITY
BUILDS TO LEVELS NOT SEEN AROUND THE PANHANDLES IN MAYBE A FEW
YEARS. WIND SHEAR WILL BE A LIMITING FACTOR FOR SEVERE WEATHER,
BUT IN SPITE OF LACKING SPEED SHEAR, FAVORABLE DIRECTIONAL SHEAR
SHOULD PROVE ENOUGH TO PROMOTE STORM ORGANIZATION THIS AFTERNOON.

THERE WILL LIKELY BE MORE THAN ONE ROUND OF THUNDERSTORMS BETWEEN
NOW AND TOMORROW MORNING, BUT THIS DISCUSSION WILL FOCUS ON THE
THREAT FOR AFTERNOON CONVECTION. FORECAST SOUNDINGS FROM THE NAM/RAP
INDICATE UPWARDS OF 4500 J/KG MLCAPE BY EARLY THIS AFTERNOON IN THE
EASTERN HALF OF THE TX PANHANDLE, DRIVEN BY MID 60S SFC DEWPTS AND
RELATIVELY IMPRESSIVE MID LVL LAPSE RATES. EFFECTIVE SHEAR VALUES
WILL LIKELY REMAIN NEAR 30 KTS TODAY, WITH LIMITED LOW LVL SPEED
SHEAR. THIS COMBINATION OF CAPE/SHEAR PAIRED WITH ANVIL LEVEL SR
WINDS OF AROUND 30 KTS SHOULD PROVIDE AN ENVIRONMENT FAVORABLE FOR A
FEW SLOW, SOUTHEAST-MOVING HP SUPERCELLS MIXED IN WITH SOME
MULTICELL CONVECTION. GIVEN GENERALLY WEAK LOW LVL FLOW AND STORM
MOTIONS THAT WON'T ENHANCE STORM RELATIVE INFLOW, THINK THE TORNADO
THREAT SHOULD BE FAIRLY LIMITED. HOWEVER, GIVEN LOW LCL HEIGHTS AND
SIGNIFICANT CAPE IN THE LOWEST 3KM, A TORNADO CERTAINLY COULD NOT BE
COMPLETELY RULED OUT.  THE BIGGEST THREAT TODAY WILL BE LARGE HAIL
GIVEN THE IMPRESSIVE HAIL CAPE.  THINK HAIL TO THE SIZE OF GOLF
BALLS AND THE POSSIBILITY FOR AREAS WITH GROUND COVERING
ACCUMULATIONS OF SMALLER HAIL WILL BE THE MAIN THREATS, THOUGH THE
STRONGEST STORMS COULD SPIT OUT SLIGHTLY LARGER HAIL. AS A SIDE
NOTE, STORM TOPS SHOULD BE QUITE IMPRESSIVE TODAY, WITH 50,000+ FOOT
TOPS NOT OUT OF THE QUESTION.

THE MOST LIKELY TIMING FOR CONVECTIVE INITIATION WOULD BE EARLY
AFTERNOON (1-4PM) AS THE CAP WEAKENS AND A WEAK H5 WAVE CROSSES THE
PANHANDLES. THE BEST THREAT FOR SEVERE WEATHER THIS AFTERNOON SHOULD
REMAIN NORTH AND EAST OF A LINE FROM ROUGHLY STRATFORD DOWN TO
CLAUDE, MOST LIKELY NOT INCLUDING AMARILLO.

THOUGH FORECAST SOUNDINGS DON'T SCREAM FLASH FLOODING FROM A
TEXTBOOK STANDPOINT AS PRECIP EFFICIENCY WILL LIKELY BE LIMITED,
SLOW STORM MOTIONS AND ANTECEDENT SATURATED GROUND CONDITIONS COULD
CERTAINLY YIELD ISOLATED AREAS OF FLASH FLOODING IN THE ERN TX
PANHANDLE.

SIMPSON

PREV DISCUSSION... /ISSUED 1033 AM CDT WED MAY 27 2015/

UPDATE...

UPDATED HOURLY GRIDS TO MATCH TRENDS FOR THE DAY. THE REMAINDER OF
THE FORECAST LOOKS ON TRACK.

PREV DISCUSSION... /ISSUED 622 AM CDT WED MAY 27 2015/

AVIATION...
LOW CLOUDS IN THE IFR RANGE MAY MAKE IT TO THE AMA TAF SITE...SO HAVE
INSERTED A TEMPO GROUP THERE. THINKING RIGHT NOW IS THAT THE LOW
CLOUDS WILL NOT MAKE IT TO DHT OR GUY. SOUTHERLY WINDS WILL PICK INTO
THE 14 TO 17 KNOT RANGE BY EARLY THIS AFTERNOON...THEN THEY SHOULD
BACK SOME AND DECREASE DURING THE EVENING. THUNDERSTORMS WILL ALSO BE
POSSIBLE WITH THE GREATER CHANCES NEAR DHT AND GUY LATE THIS
AFTERNOON. HAVE NOT MENTIONED THEM IN THE TAFS AT THIS TIME AS
COVERAGE SHOULD BE PRETTY SCATTERED.

PREV DISCUSSION... /ISSUED 432 AM CDT WED MAY 27 2015/

DISCUSSION...

CHALLENGING FORECAST AHEAD WITH REGARDS TO TIMING OF PERIODS OF
HIGHEST PRECIPITATION CHANCES THROUGH THE END OF THE WEEK. EARLY
THIS MORNING CONVECTION WAS ONGOING IN A SMALL CLUSTER FROM THE
CENTRAL OKLAHOMA PANHANDLE NORTHWARD INTO EXTREME SOUTHWEST KANSAS.
OTHER ISOLATED/SCATTERED SHOWERS AND STORMS WERE MOVING EASTWARD
ACROSS NEW MEXICO. PRIMARY DRIVING FORCE FOR GREATER COVERAGE OF
CONVECTION THIS AFTERNOON ASIDE FROM DIABATIC
HEATING/DESTABILIZATION WILL BE A WEAK SHORTWAVE SEEN IN WATER VAPOR
NOW OVER SOUTH CENTRAL COLORADO. THIS IS THE MOST APPARENT OF A
SERIES OF WAVES EMBEDDED WITHIN RELATIVELY WEAK WESTERLY FLOW.
STORMS THAT OCCUR THIS AFTERNOON WILL BE IN AT LEAST A MODERATELY
UNSTABLE ENVIRONMENT WITH DEEP LAYER SHEAR AROUND 30-35 KNOTS
FAVORING STORM ORGANIZATION. ALL MODES OF SEVERE WEATHER ARE
POSSIBLE WITH HAIL BEING THE MOST COMMON TYPE. ROUGHLY THE NORTHEAST
HALF IS MOST FAVORED FOR DEVELOPMENT.

A MORE IMPACTFUL UPPER LEVEL FEATURE IN THE FORM OF A COMPACT CLOSED
LOW NOW OFF THE SOUTHERN CALIFORNIA COAST WILL MOVE TOWARD THE AREA
THROUGH TOMORROW. BY TOMORROW NIGHT MODELS ARE IN DECENT AGREEMENT
THAT THIS FEATURE WILL BECOME MORE OPEN AND PHASE SOMEWHAT WITH
NORTHERN STREAM SHORTWAVE. NET RESULT WILL BE MEAN HEIGHT FALLS AND
INCREASING LARGE SCALE ASCENT NECESSITATING HIGHER PRECIPITATION
PROBABILITIES LATE WEDNESDAY NIGHT INTO THURSDAY. WITH ANOMALOUS
MOISTURE STREAMING NORTHWARD LOCALLY HEAVY RAINFALL WILL BE
POSSIBLE...ESPECIALLY ACROSS THE SOUTHERN PORTION OF THE AREA FROM
ROUGHLY MID/LATE MORNING THURSDAY INTO THE AFTERNOON. DURING THIS
TIME SPATIAL AND TEMPORAL DETAILS BECOME INCREASINGLY BLURRY GIVEN
THE INHERENT NATURE OF DIFFICULT TO RESOLVE SMALL WAVES AND LARGER
SYNOPTIC SCALE DISCREPANCIES THAT EMERGE IN THE MODELS.
ADDITIONALLY...SMALLER SCALE DETAILS THAT ARE INFLUENCED BY THE
DEVELOPMENT OF CONVECTION INCLUDING BOUNDARY LAYER MOISTURE AND
MESOSCALE BOUNDARY FORCING WILL BE A FACTOR. ALL OF THIS WILL BE
RESOLVED BETTER WITH TIME. FOR NOW HAVE RELEGATED HIGHER
PRECIPITATION PROBABILITIES IN THE LIKELY CATEGORY TO THE SOUTHERN
PORTION OF THE AREA EARLY THURSDAY AND EXPANDED/INCREASED THIS
ACROSS ROUGHLY THE SOUTHEASTERN ONE THIRD OF THE TEXAS PANHANDLE
DURING THE AFTERNOON.

MODELS SHOW ONE MORE DISTINCT SHORTWAVE IN BROAD TROUGH THAT MAY LEAD
TO INCREASED PRECIPITATION PROBABILITIES FRIDAY EVENING AND FRIDAY
NIGHT FOLLOWED BY THE PASSAGE OF A COLD FRONT AND COOLER/DRIER
CONDITIONS FOR THE WEEKEND. MEDIUM RANGE GUIDANCE SHOWS A MORE
AMPLIFIED PATTERN EVOLVING EARLY NEXT WEEK WITH AT LEAST A BRIEF
PERIOD OF UPPER RIDGING AND WARMER TEMPERATURES. INTRODUCTION OF
ISOLATED-SCATTERED CONVECTION INTO THE FORECAST MAY BE NEEDED BY
TUESDAY IN LATER FORECAST ISSUENCES AS THE PATTERN DEAMPLIFIES AND A
TROUGH EVOLVES IN THE WEST. MEAN CROSS MOUNTAIN FLOW MAY BECOME
ESTABLISHED WITH A DEEPENING LEE SURFACE TROUGH AND SHARPENING
DRYLINE.

BRB

&&

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

&&

14/18

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE AMARILLO TX
1154 AM CDT WED MAY 27 2015

OKZ001>003-TXZ001>020-272200-
CIMARRON-TEXAS-BEAVER-DALLAM-SHERMAN-HANSFORD-OCHILTREE-LIPSCOMB-
HARTLEY-MOORE-HUTCHINSON-ROBERTS-HEMPHILL-OLDHAM-POTTER-CARSON-
GRAY-WHEELER-DEAF SMITH-RANDALL-ARMSTRONG-DONLEY-COLLINGSWORTH-
1154 AM CDT WED MAY 27 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE TEXAS AND OKLAHOMA
PANHANDLES.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND TONIGHT...MAINLY NORTH
AND EAST OF A STRATFORD TO CLAUDE LINE. SOME THUNDERSTORMS COULD
BECOME SEVERE WITH LARGE HAIL UP TO GOLF BALL SIZE AND DAMAGING WINDS
THE MAIN THREATS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

THUNDERSTORMS ARE LIKELY ON THURSDAY. A FEW SEVERE THUNDERSTORMS ARE
POSSIBLE. THUNDERSTORM CHANCES WILL CONTINUE FRIDAY AND FRIDAY NIGHT
BEFORE A DRIER PATTERN DEVELOPS THIS WEEKEND.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS MAY BE NEEDED THIS AFTERNOON AND TONIGHT AND AGAIN ON
THURSDAY.