Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 182315 AAB
AFDAMA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE AMARILLO TX
615 PM CDT SAT APR 18 2015

.AVIATION...
A FEW SHOWERS AND THUNDERSTORMS HAVE DEVELOPED UNDER THE COLD CORE OF
THE LOW...SO HAVE ENTERED SOME GUSTY SHOWERS INTO THE TAFS FOR THIS
EVENING. NORTHWEST WINDS WILL GENERALLY REMAIN AT 10 KNOTS OR LESS
OUTSIDE OF THE SHOWERS. NORTHWEST TO NORTH WINDS WILL THEN PICK UP TO
25 TO 30 KNOTS WITH HIGHER GUSTS BY MID MORNING ON SUNDAY. SKIES
SHOULD REMAIN VFR.

&&

.PREV DISCUSSION... /ISSUED 521 PM CDT SAT APR 18 2015/

UPDATE...

WEST TEXAS MESONET AND SCHOOL NET OBSERVATIONS SHOW A CONTINUED
DECREASE IN SURFACE DEW POINTS AND VEERING OF SURFACE WINDS ACROSS
THE FAR EASTERN PORTION OF THE TEXAS PANHANDLE. SPC RAP MESOANALYSIS
HAS RESPONDED BY DEPICTING MUCH HIGHER LCL HEIGHTS THAT ARE LESS
FAVORABLE FOR TORNADOES. A MORE FAVORABLE ENVIRONMENT EXISTS FURTHER
EAST INTO OKLAHOMA WHERE SURFACE WINDS REMAINED BACKED AND AT LEAST
SHALLOW LOW LEVEL MOISTURE /DEW POINTS IN THE MID TO UPPER 50S/ IS
PRESENT. A FAIRLY POTENT VORT MAX IS MOVING ACROSS THE TEXAS
PANHANDLE NOW AS SEEN ON WATER VAPOR LOOP AND THIS MAY RESULT IN AN
UPTICK IN CONVECTION OVER THE NEXT COUPLE OF HOURS. HAIL AND WIND
ARE STILL POSSIBLE WITH THE STRONGEST STORMS AS ENOUGH INSTABILITY
REMAINS INTO EARLY EVENING. WILL CONTINUE TO MONITOR TRENDS IN THE
OBSERVATIONS...ESPECIALLY LATER THIS EVENING WHEN MIXING SUBSIDES
AND THE DRYLINE POSSIBLY SHIFTS WESTWARD SOME. THE BEST CHANCE OF
BETTER LOW LEVEL MOISTURE RETURNING TO THE FORECAST AREA WILL BE
ACROSS WHEELER AND COLLINGSWORTH COUNTIES.

BRB

PREV DISCUSSION... /ISSUED 221 PM CDT SAT APR 18 2015/

DISCUSSION...

EARLY THIS AFTERNOON A DEEP CLOSED LOW WAS SITUATED OVER EASTERN
COLORADO AND SLOWLY MOVING EAST. A BAND OF CLOUDS ASSOCIATED WITH A
RELATIVELY POTENT VORT LOBE ROTATING AROUND THE MID-UPPER LOW WAS
EVIDENT IN IR/VIS SATELLITE. SURFACE OBSERVATIONS SHOW LIGHT RAIN
BENEATH THIS BAND OF CLOUDS AT CLAYTON NEW MEXICO AND PRESUMABLY
FURTHER SOUTH-SOUTHWEST EAST OF TUCUMCARI INTO THE FAR WESTERN TEXAS
PANHANDLE WHERE LIGHT ECHOS WERE PRESENT ON REGIONAL RADAR MOSAIC.

FURTHER EAST ACROSS THE TEXAS AND OKLAHOMA PANHANDLE LOW CLOUDS HAVE
DIMINISHED AND/OR SHIFTED INTO OKLAHOMA AS SURFACE WINDS CONTINUE TO
VEER SLIGHTLY. SHALLOW LOW LEVEL MOISTURE SEEN ON 12Z KAMA SOUNDING
REMAINS ACROSS THE EASTERN PANHANDLES EAST OF A DIFFUSE DRYLINE.
THERE REMAINS SOME UNCERTAINTY ON THE POSITION OF THE DRYLINE THAT
IS EXPECTED TO SHARPEN THIS AFTERNOON AS DIABATIC HEATING/MIXING
COMMENCES. USING SHORT RANGE MODEL FORECAST SOUNDINGS AS GUIDANCE ON
THE DEPTH OF MOISTURE OFF THE CAPROCK AND ESPECIALLY FURTHER EAST
NEAR THE OKLAHOMA BORDER LEADS TO FAIRLY HIGH CONFIDENCE ON THE
PREVIOUS FORECAST WHICH RELEGATES ANY SUBSTANTIAL DEEP CONVECTION TO
NEAR OR JUST EAST OF THE OKLAHOMA STATE LINE LATER THIS AFTERNOON.
LOW LEVEL MOISTURE IS DEEPER FROM THERE EASTWARD INTO OKLAHOMA AND
THUS DRYLINE CIRCULATION THAT DEVELOPS STANDS A BETTER CHANCE AT
INITIATING CONVECTION THERE THAN WAS THE CASE FURTHER WEST
YESTERDAY. SO THROUGH THE LATE AFTERNOON AND EVENING THERE IS ONLY A
LOW PROBABILITY OF ISOLATED-SCATTERED CONVECTION ACROSS THE EXTREME
EASTERN PORTION OF THE PANHANDLES WITH BETTER CHANCES OUT OF THE
FORECAST AREA ACROSS WESTERN OKLAHOMA. IF THE ABOVE ASSESSMENT IS
MISPLACED SLIGHTLY EAST THAN ANY STORM THAT DOES DEVELOP ON OUR SIDE
OF THE STATE LINE WOULD HAVE THE POTENTIAL TO BECOME SEVERE DUE TO
MODERATE INSTABILITY AND SUFFICIENT DEEP LAYER SHEAR OF AROUND 30
KNOTS FOR STORM ORGANIZATION/PERSISTENCE. LARGE HAIL WOULD BE THE
PRIMARY THREAT INTO THE EVENING GIVEN STEEP MID LEVEL LAPSE RATES
OWING TO THE APPROACHING MID-UPPER LOW. WILL CONTINUE TO MONITOR
TRENDS IN SURFACE OBSERVATIONS AND DRYLINE EVOLUTION THROUGHOUT THE
AFTERNOON.

FURTHER WEST OF THE DRYLINE...DEEP MIXING WILL OCCUR GENERALLY EAST
OF THE AFOREMENTIONED BAND OF LOW-MID CLOUDS NOW ENTERING THE TEXAS
PANHANDLE. CU FIELD IS INCREASING IMMEDIATELY AHEAD OF THIS. BASES
SHOULD BECOME RELATIVELY HIGH AS MIXED LAYER DEEPENS THROUGH THE
AFTERNOON. WITH FORCING FROM PREVIOUSLY MENTIONED VORT LOBE
CONVECTION MAY BECOME DEEP ENOUGH FOR SHOWERS AND THUNDERSTORMS FOR
MUCH OF THE AREA LATER THIS AFTERNOON. IF CONVECTION BECOMES DEEP
ENOUGH FOR CHARGE SEPARATION AND LIGHTNING...LIMITED INSTABILITY
SHOULD PRECLUDE THE THREAT OF SEVERE THUNDERSTORMS. PROGNOSTICATIONS
FROM THE HI-RES CONVECTION ALLOWING GUIDANCE INCLUDING THE HRRR AND
TTU WRF SEEM TO LINE UP WELL WITH THE ABOVE THINKING.

AS THE MID-UPPER LOW CONTINUES TO SHIFT EAST A COLD FRONT WILL MOVE
THROUGH THE AREA TONIGHT. MODEL GUIDANCE IS IN AGREEMENT IN AN
EVOLUTION OF THE LOW INTO A MORE OPEN AND PROGRESSIVE WAVE THAT WILL
BE EAST OF THE AREA BY TOMORROW AFTERNOON. AN AREA OF MOISTURE ON
THE BACK SIDE OF THIS EVOLVING SHORTWAVE TROUGH FAVORABLY TIMED WITH
PEAK HEATING SHOULD BE ENOUGH FOR EXTENSIVE CUMULUS DEVELOPMENT
DURING THE AFTERNOON POSSIBLY ENOUGH FOR BROKEN SKY CONDITIONS
ESPECIALLY ACROSS THE EASTERN PORTION OF THE AREA. DEPTH OF
CONVECTION IN ROUGHLY THE NORTHEAST THIRD WILL NEED TO BE MONITORED
AS IT MAY BECOME SUFFICIENT FOR A FEW SHOWERS GIVEN RESIDUAL COOL MID
LEVEL TEMPERATURES AND RELATIVELY HIGH TQ INDEX VALUES. ADJUSTED LOW
POPS ON SUNDAY AFTERNOON TO EXTEND A BIT FURTHER SOUTH AND WEST TO
ACCOUNT FOR THIS.

EARLY NEXT WEEK A SPLIT UPPER FLOW PATTERN WILL EXIST WITH STRONG
PERIODICALLY PERTURBED WESTERLY SOUTHERN BRANCH JUST SOUTH OF US AND
NORTHWESTERLY NORTHERN BRANCH ACROSS THE CENTRAL PLAINS. MEAN
RIDGING WILL BE PRESENT OVER THE WESTERN STATES. GRADUALLY
INCREASING 500 MB HEIGHTS AND A SLIGHTLY MORE AMPLIFIED PATTERN WILL
EVOLVE THROUGH THE WEEK ESPECIALLY AS ANOTHER CLOSED LOW DEVELOPS
AND DEEPENS OVER THE SOUTHWESTERN CONUS BY THURSDAY. AS THIS MOVES
EAST THIS WILL PROBABLY RESULT IN ANOTHER CONVECTIVELY ACTIVE
PATTERN FOR THE LATTER HALF OF THE WEEK. AS IS TYPICALLY THE CASE AT
THAT TIME RANGE MODEL GUIDANCE DIFFERS IN TIMING AND AMPLITUDE BUT
THE SIGNAL IS THERE FOR A SCENARIO FAVORING A NORTH/WEST SURGE OF
LOW LEVEL MOISTURE AND FORCING FOR ASCENT RESULTING IN ABOVE CLIMO
PRECIPITATION PROBABILITIES AND THE POSSIBILITY OF SEVERE
THUNDERSTORMS BY MID AND ESPECIALLY LATE WEEK. EVEN BEFORE THEN
THERE WILL BE A FEW OPPORTUNITIES FOR PRECIPITATION EARLIER IN THE
WEEK AS DIFFICULT TO RESOLVE SMALL SHORTWAVE TROUGHS WITHIN MEAN
WEST-NORTHWESTERLY FLOW CROSS THE AREA. CONVECTION MAY EMANATE FROM
THE HIGHER TERRAIN OF COLORADO AND NEW MEXICO AND MOVE INTO THE
PANHANDLES LATE MONDAY AND AGAIN LATE TUESDAY...ALTHOUGH THIS
FORECAST WILL BE LESS DETERMINISTIC WITH TIMING OF HIGHER
PROBABILITIES OF PRECIPITATION AND MORE BROAD BRUSH GIVEN INHERENT
UNCERTAINTIES OF THIS TYPE PATTERN.

BRB

&&

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

&&

$$

15/06





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