Prognostic Meteorological Discussion
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000
FXUS02 KWBC 231556
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1156 AM EDT SAT JUL 23 2016

VALID 12Z TUE JUL 26 2016 - 12Z SAT JUL 30 2016

...OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT...

MODELS AND ENSEMBLES ARE IN GOOD AGREEMENT THROUGH AROUND DAY
5/THURSDAY BEYOND WHICH THE MOST RECENT OPERATIONAL RUNS OF THE
06Z GFS AND 00Z ECMWF APPEAR TO BE ON THE DEEPER SIDE OF THE
AMPLIFICATION OF THE MEAN TROUGH OVER THE CENTER OF THE
COUNTRY...WHILE THE ECMWF ENSEMBLES ARE CLEARLY MORE PROGRESSIVE
WITH THE TROUGH SPEED THAN THE GEFS/NAEFS ENSEMBLES.  THESE
DIFFERENCES AT DAYS 6 AND 7 WERE SMOOTHED BY A MULTIMODEL BLEND
SINCE IT IS TOO EARLY TO SEE ANY TRENDS .

THE LARGE SCALE EVOLUTION SHOWS A PERSISTENT GREAT BASIN/FOUR
CORNERS RIDGE AND A SLOWLY AMPLIFYING/SHARPENING MEAN TROUGH OVER
THE VICINITY OF THE MISSISSIPPI VALLEY.  HOWEVER THE DIFFERENCES
NOTED ABOVE AND THE RELATIVELY SMALL SCALE OF IMPORTANT EMBEDDED
DETAIL DIFFERENCES LATE IN THE FORECAST MEANS LOW PREDICTABILITY
FOR SPECIFICS THAT WILL IMPACT SENSIBLE WEATHER..

THE EVOLVING AMPLIFICATION OF A MEAN TROUGH SHOULD BEGIN TO TAKE
SHAPE WITHIN FLOW TO THE SOUTHWEST OF A CLOSED LOW CROSSING
EASTERN CANADA WHILE WEAK SHORTWAVE ENERGY PASSES FROM THE EASTERN
PACIFIC/WESTERN CANADA ENERGY CROSSING A MODEST MEAN RIDGE OVER
WESTERN CANADA.  THERE IS RELATIVE AGREEMENT THAT FLOW ALOFT WILL
REFLECT AT THE SFC AS A COUPLE OF WEAK MEANDERING SURFACE FRONTS
FOR MUCH OF THE FORECAST PERIOD WITH A POSSIBLE TREND TOWARD A
BETTER DEFINED FRONT WITH COOLER AIR MOVING INTO THE NORTH CENTRAL
US LATE IN THE FORECAST LATE IN THE COMING WEEK AND WEEKEND.

ONE WEAK FRONTAL BOUNDARY EXTENDS WESTWARD FROM THE MID ATLANTIC
STATES INTO THE PLAINS AND A SECOND THAT BEGINS TO DRIFT SOUTHWARD
INTO THE NORTHERN TIER OF STATES BY WEDNESDAY INTO THURSDAY.  WEAK
IMPULSES ALONG THESE FRONTS ARE DIFFICULT TO PREDICT WITH ANY
DETAIL AT THIS POINT PROBABLY UNTIL BECOMING HOPEFULLY MORE CLEAR
OVER THE NEXT COUPLE DAYS.

THE FORECAST USED THE 00Z ECMWF AND 06Z GFS AS WELL AS THE 06Z
GEFS AND  00Z ECMWF ENSEMBLE MEANS.

...WEATHER HIGHLIGHTS/THREATS...

EXPECT EVOLVING FLOW ALOFT AND IMPULSES ALONG THE WEAK SURFACE
FRONTS TO SUPPORT AREAS OF ORGANIZED CONVECTION FROM THE NORTHERN
AND CENTRAL PLAINS INTO THE OHIO/TENNESSEE VALLEYS AND EASTWARD
TOWARD THE APPALACHIANS AND MIDDLE ATLANTIC STATES.  UNCERTAINTY
OF LOCATION OF HEAVIEST RAINFALL WITHIN THIS AREA IS HIGH BUT
THERE IS A GOOD CHANCE THAT SOME OF THE AREAS CLOSE TO THESE
SEPARATE BOUNDARIES COULD SEE LOCALLY HEAVY RAINFALL ASSOCIATED
WITH DEVELOPING CONVECTIVE COMPLEXES.

ELSEWHERE... THE SOUTHWEST AND ROCKIES SHOULD SEE DIURNAL EPISODES
OF CONVECTION WITHIN A BAND OF MONSOONAL MOISTURE WHILE MOSTLY
DIURNAL CONVECTION OVER THE GULF COAST AND SOUTHEAST US MAY BE
ENHANCED BY ONE OR MORE MID LVL IMPULSES RETROGRADING AROUND THE
SRN SIDE OF THE SRN TIER RIDGE ALOFT.

THE MOST EXTREME TEMPS RELATIVE TO NORMAL SHOULD BE FROM THE WEST
COAST STATES INTO THE NORTHERN ROCKIES WITH SOME HIGHS REACHING
10-20F ABOVE NORMAL ON ONE OR MORE DAYS.  ISOLATED RECORD HIGHS
AND/OR RECORD WARM MINIMA MAY BE POSSIBLE WITHIN THIS AREA.  THE
LESSER ANOMALIES THE EAST COAST STATES WILL LIKELY REMAIN VERY
WARM AHEAD OF THE DEVELOPING MISSISSIPPI VALLEY MEAN TROUGH ALOFT.
 THE NRN PLAINS/UPPER MISSISSIPPI SHOULD  BELOW NORMAL WITH SOME
MINUS 5-10F ANOMALIES FOR HIGHS.

KOCIN

$$





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