Prognostic Meteorological Discussion
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FXUS02 KWBC 280629
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 AM EDT THU AUG 28 2014

VALID 12Z SUN AUG 31 2014 - 12Z THU SEP 04 2014

...OVERVIEW AND PREFERENCES...

RIDGING WILL PREVAIL OVER THE SOUTHEAST AND EVENTUALLY INTO THE
SRN PLAINS... AS A TROUGH INITIALLY OVER THE WRN HALF OF THE CONUS
FLATTENS IN THE PROCESS OF LIFTING NEWD THROUGH THE PERIOD AND NRN
PAC FLOW SETTLES INTO A TROUGH NEAR THE WEST COAST BY NEXT
WED-THU.  THE MOST PRONOUNCED TREND THIS CYCLE IS A FASTER
ADJUSTMENT IN NEARLY ALL GUIDANCE WITH THE LEADING HGT FALLS/SFC
FRONT CROSSING THE CNTRL-ERN STATES.  AT THE SAME TIME THE WEST
COAST TROUGH REMAINS THE MOST LIKELY SCENARIO LATE IN THE FCST BUT
WITH A FAIR AMOUNT OF UNCERTAINTY GIVEN THE FULL RANGE OF
OPERATIONAL MODEL/ENSEMBLE SOLNS.  LATEST CONSENSUS IS WELL
REPRESENTED BY AN AVG OF THE 12Z ECMWF/ECMWF MEAN AND 18Z GFS/GEFS
MEAN THROUGH AT LEAST DAY 4 MON... WHILE THE ENSEMBLE MEANS ARE
FAVORED EXCLUSIVELY BY DAYS 6-7 WED-THU AS OPERATIONAL FCSTS
DIVERGE.


...GUIDANCE EVALUATION...

THE FASTER TREND WITH THE FRONT CROSSING THE CNTRL-ERN STATES
ARISES AFTER DAY 3 SUN... WITH OPERATIONAL MODELS AND ENSEMBLE
MEANS ALL SHOWING THIS ADJUSTMENT.  THIS TREND IS ACCEPTED GIVEN
THE OVERWHELMING CLUSTERING.  THE 12Z GFS BROUGHT THE UPR LOW OVER
CANADA AND TROUGH TO ITS SE FARTHER SEWD THAN CONSENSUS SO ITS
SOLN WAS NOT INCLUDED IN THE FCST.  THE 00Z GFS/UKMET/CMC MAINTAIN
SIMILAR TIMING THROUGH MON AND ARE SLIGHTLY FASTER WITH THE NRN
PART OF THE FRONT BY TUE... SO THE FASTER TREND IN THE 12Z/18Z
CYCLE IS BEING CONFIRMED FOR THE TIME BEING.

ALTHOUGH NOT AS PRONOUNCED AS 24 HRS AGO... THERE IS STILL SOME
DIVERGENCE IN GUIDANCE ORIGINATING WITH FLOW SEPARATING FROM THE
SRN PART OF A NRN PAC/ALEUTIANS TROUGH EARLY IN THE PERIOD.  THUS
CONFIDENCE IS NO BETTER THAN AVG WITH THE DETAILS OF TROUGH ENERGY
REACHING THE NORTHWEST BY THE LATTER HALF OF THE FCST.  PREFER TO
MAINTAIN AN ENSEMBLE MEAN SOLN GIVEN THE CURRENT UNCERTAINTY BUT
ACKNOWLEDGE SOME OPERATIONAL MODEL HINTS AT A DEEPER AND/OR FASTER
SHRTWV ALOFT AND BETTER DEFINED SRN CANADA/NRN TIER SFC SYSTEM.

ON THE S SIDE OF THE RIDGE ALOFT THERE IS REASONABLE AGREEMENT
ASIDE FROM DIFFS IN AMPLITUDE WITH RESPECT TO A WEAKNESS
DEVELOPING OVER CUBA AND THE BAHAMAS THEN DRIFTING ACROSS THE FL
PENINSULA.  AN AVG OF THE 18Z GEFS/12Z ECMWF MEANS PROVIDES A GOOD
INTERMEDIATE DEPICTION OF THIS FEATURE.


...SENSIBLE WEATHER HIGHLIGHTS...

EXPECT THE FRONT PROGRESSING E/SE FROM THE NRN PLAINS TO SERVE AS
A CONVECTIVE FOCUS DURING THE PERIOD.  BEST AGREEMENT UPON HVY
RNFL/SEVERE THREAT IS OVER PARTS OF THE NRN HALF OF THE PLAINS/MS
VLY IN THE SUN-MON TIME FRAME.  CONSULT SPC OUTLOOKS FOR LATEST
INFO REGARDING SEVERE POTENTIAL.  COOLEST AIR BEHIND THE FRONT
SHOULD BE FROM THE NRN HALF OF THE WEST INTO THE NRN PLAINS WITH
HIGHS GENERALLY 5-15F BELOW NORMAL SUN-MON. ON THE OTHER HAND
QUITE WARM READINGS ARE FCST OVER PORTIONS OF THE SRN PLAINS INTO
EARLY NEXT WEEK.  LOCATIONS IN THE EAST MAY SEE AREAS OF
SHWRS/TSTMS EARLY IN THE PERIOD IN ASSOC WITH MSTR AHEAD OF THE
WEAKENING SHORT RANGE PLAINS SHRTWV REACHING THE GRTLKS/NEW
ENGLAND BY SUN-MON.  THE SOUTHEAST/MID ATLC SHOULD SEE WARMEST
TEMPS RELATIVE TO NORMAL BEFORE ARRIVAL OF THE PLAINS FRONT.  THE
FL PENINSULA AND EXTREME SRN TX MAY SEE SOME RNFL ENHANCEMENT...
FROM A WEAKNESS ALOFT AND THE NRN PERIPHERY OF A WAVE TRACKING
FROM THE NWRN CARIBBEAN INTO NERN MEXICO RESPECTIVELY.

RAUSCH

$$




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