Prognostic Meteorological Discussion
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FXUS02 KWBC 240509
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
109 AM EDT TUE MAY 24 2016

VALID 12Z FRI MAY 27 2016 - 12Z TUE MAY 31 2016

...OVERVIEW AND GUIDANCE ASSESSMENT...

LARGE SCALE PATTERN ACROSS NORTH AMERICA LATE THIS WEEK INTO NEXT
WEEK FEATURES UPPER RIDGING BUILDING INTO ALASKA AND AN UPPER LOW
INITIALLY IN NORTHEASTERN CANADA REFORMING IN THE NORTH ATLANTIC.
THESE TWO ANOMALY CENTERS BOTH SUPPORT TROUGHING NEAR/IN THE
WESTERN CONUS AS WELL AS IN THE SOUTHEAST, WITH RELATIVELY HIGHER
HEIGHTS IN THE GREAT LAKES/NORTHEAST/MID-ATLANTIC. MODELS AND
ENSEMBLES REMAIN IN GOOD AGREEMENT OVERALL WITH TYPICAL
TIMING/DEPTH DIFFERENCES. BLEND OF THE RECENT GFS/GEFS AND
ECMWF/ECENS MEAN OFFERED A REASONABLE STARTING POINT FOR FRI-MON
BEFORE A SHIFT TOWARD AN ENSEMBLE MEAN BLEND FOR NEXT TUESDAY.

AREAS OF CONTENTION IN THE GUIDANCE LIE IN THE WEST AND SOUTHEAST.
FOR THE FORMER, THE DETERMINISTIC MODELS HAVE WAVERED ON HOW TO
MAINTAIN TROUGHING GENERALLY WEST OF THE DIVIDE -- WITH A CUTOFF
LOW OR WITH SEVERAL SMALLER SHORTWAVES SLIDING THROUGH A MEAN
TROUGH AXIS NEAR 120W. TREND SEEMS TO BE TOWARD A MORE FRACTURED
APPROACH BUT THE OVERALL THEME SHOULD STICK. A BIT FARTHER
DOWNSTREAM, THE BROAD SW FLOW THROUGH THE PLAINS SHOULD CONTINUE
WITH EMBEDDED SHORTWAVES EJECTING TOWARD THE NORTHEAST. OVER TIME
THE SFC BOUNDARY MAY BECOME LESS DEFINED ABSENT ANY LARGER SCALE
CHANGE/REINFORCEMENT.

FOR THE LATTER, THE GFS WAS FIRST TO SHOW POSSIBLE
TROPICAL/SUBTROPICAL DEVELOPMENT UNDERNEATH THE MID-LEVEL WEAKNESS
OVER THE BAHAMAS LATER THIS WEEK, AND THE 00Z AND ESPECIALLY 12Z
MODELS ON MONDAY FOLLOWED SUIT (THOUGH VERIFICATION MAY PROVE TO
BE SOMETHING ELSE). STILL, THE GFS-BASED GUIDANCE (I.E., THE GEFS)
REMAIN STRONGER WITH THIS POSSIBLE SYSTEM THAN THE CANADIAN/ECMWF
ENSEMBLES. WILL CONTINUE TO SHOW AN INVERTED TROUGH AND PERHAPS A
WEAK SFC LOW MOVING TOWARD THE GA/SC COAST THIS WEEKEND GIVEN THE
INCREASE IN MODELS SHOWING AT LEAST SOMETHING REFLECTED AT THE
SURFACE.


...SENSIBLE WEATHER HIGHLIGHTS...

TROUGHING IN THE WEST WILL MAINTAIN BELOW AVERAGE TEMPERATURES
(ESPECIALLY DAYTIME MAX TEMPERATURES) AND FAIRLY WIDESPREAD BUT
GENERALLY LIGHT RAIN OR HIGHER ELEVATION SNOW. FLOW THROUGH THE
PLAINS SUPPORTS A DAILY THREAT OF RAIN AND STORMS, POSSIBLY
SEVERE, THOUGH PLACEMENT IS UNCLEAR. PLEASE CONSULT THE SPC
OUTLOOKS FOR THE LATEST INFORMATION ON SEVERE THREATS.

FRONTAL BOUNDARY THROUGH THE NORTHERN TIER REMAINS A CHALLENGE TO
TEMPERATURE FORECASTING, ESPECIALLY IN COASTAL AREAS OF THE
NORTHEAST WHERE OCEAN TEMPERATURES ARE STILL COLD AND ONSHORE FLOW
WOULD KEEP THESE AREAS QUITE CHILLY. AREAS SOUTH OF THE FRONT
WOULD FEEL RATHER SUMMER-LIKE -- 70S/80S AND MAYBE NEAR 90F. THE
SOUTHEAST MAY TURN MORE UNSETTLED AS THE INVERTED TROUGH OR WEAK
SFC LOW APPROACH THE REGION. AT THE LEAST, THIS MAY KNOCK DOWN
AFTERNOON MAX TEMPS A BIT THANKS TO MORE CLOUD COVER AND
SHOWERS/STORMS. RAINFALL AMOUNTS VARY QUITE A BIT AMONG THE
ENSEMBLES BUT THE TREND HAS BEEN MORE EVEN PER THE RELATIVELY
DRIER ECMWF ENSEMBLES.


FRACASSO

$$




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