Prognostic Meteorological Discussion
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FXUS02 KWBC 281439
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1039 AM EDT SUN MAY 28 2017

VALID 12Z WED MAY 31 2017 - 12Z SUN JUN 04 2017


...PATTERN OVERVIEW AND MODEL PREFERENCES...

TROUGHING IS EXPECTED IN THE NORTHWEST AND NORTHEAST THIS PERIOD
WITH RIDGING IN BETWEEN CENTERED ON THE NORTHERN PLAINS.  SYSTEMS
ORIGINATING IN THE SOUTHWEST MOVE ACROSS THE SOUTHERN ROCKIES AND
PLAINS...EVENTUALLY REACHING THE LOWER-MID MS VALLEY NEXT WEEKEND.


THE MODEL GUIDANCE DIFFERS ON THE TIMING/PHASING/AMPLITUDE OF THE
DEEP CYCLONE IN SOUTHEAST CANADA AND A REINFORCING SECONDARY WAVE
THAT FORMS NEAR HUDSON BAY OR JAMES BAY AND POTENTIALLY DEVELOPS
INTO THE GREAT LAKES DAY 7 SUN 04 JUN. THE 00Z ECMWF COMPLETELY
FLIPPED THE TREATMENT OF THE GREAT LAKES NEXT WEEKEND...CHANGING
FROM A DEVELOPING RIDGE IN THE 12Z SAT RUN TO DEVELOPING CLOSED
LOW ON THE 00Z SUN RUN.  THIS PLACES LOW CONFIDENCE IN THE
OPERATIONAL RUN.  TELECONNECTIONS DO SUPPORT PERSISTENCE OF A
NORTHEAST TROUGH AND THE GFS/CANADIAN DO SHOW A SECONDARY WAVE
FORMING IN ONTARIO...JUST FURTHER NORTH AND WEAKER THAN THE 00Z
ECMWF.

THE MODELS SHOW DIFFERENCES IN THE TROUGH AMPLITUDE ACROSS THE
PACIFIC NORTHWEST FRI-SUN AND EVOLUTION OF THE TROUGH.  THE 00Z
ECMWF CONTINUES TO HAVE A HIGHER AMPLITUDE TROUGH THAN MOST OF ITS
ENSEMBLE MEMBERS...SO THE MEAN IS NOT AS AMPLIFIED.
THE 06Z GFS ALSO TRIES TO TAKE A PIECE OF SHORTWAVE ENERGY AND
MOVE IT EAST ACROSS THE NORTHERN ROCKIES AND PLAINS...MAINTAINING
A SYSTEM THROUGH THE HEART OF THE DEEP LAYER RIDGE SHOWN IN THE
MEAN AND TELECONNECTIONS THAT SUPPORT A CONTINUING MID LEVEL RIDGE
IN THE NORTHERN PLAINS.

TO ACCOUNT FOR UNCERTAINTY, THE PRESSURES/500 HPA HEIGHTS/WIND
GRIDS STARTED OUT WITH AN EVEN SPLIT OF THE 00Z ECMWF/06Z GFS AND
00Z ECMWF/06 GEFS ENSEMBLE MEANS...AND USED ONLY THE ECMWF/GEFS
ENSEMBLE MEANS FOR DAYS 6 AND 7 GIVEN THE OPERATIONAL MODEL RUN TO
RUN CHANGES AND DIFFERENCES WITH THEIR MEANS AND TELECONNECTIONS.


...WEATHER HIGHLIGHTS...

COOLER THAN NORMAL TEMPERATURES ARE EXPECTED TO CONTINUE INTO NEXT
WEEK ACROSS THE GREAT LAKES AND NORTHEAST DUE TO LINGERING UPPER
LEVEL TROUGHING.  MEANWHILE, WARM CONDITIONS ARE EXPECTED ACROSS
MUCH OF INTERMOUNTAIN WEST...WITH AN APPROACHING COLD FRONT
BRINGING SOME ASSOCIATED LATE-SEASON PRECIPITATION.

THE MOST WIDESPREAD RAINS THU AND FRI ARE FORECAST ACROSS THE
CENTRAL AND SOUTHERN PLAINS WITH THE WAVE(S) MOVING EAST FROM THE
SOUTHWEST US. LOCALLY HEAVY RAINS ARE POSSIBLE ACROSS PORTIONS OF
THE SOUTHERN PLAINS AND MID-MISSISSIPPI VALLEY.

WARM ADVECTION HELPS SHOWERS DEVELOP DOWNSTREAM INTO THE MID MS
VALLEY. NEXT WEEKEND RAINS IN THE SOUTHERN PLAINS MOVE EAST INTO
THE LOWER-MID MS VALLEY AND OH VALLEY TO THE NORTHEAST.  RAINS IN
THE NORTHERN PLAINS TO THE GREAT LAKES DEPEND ON THE STRENGTH OF
UPPER TROUGH IN THESE REGIONS WITH SIGNIFICANT MODEL/ENSEMBLE
VARIABILITY THAT HAS TO BE RESOLVED LATER.

SHOWERS AND STORMS DEVELOP AND ACROSS FL AND SOUTHEAST COASTAL
AREAS DUE TO LOW-LEVEL MOISTURE AVAILABILITY AND DAYTIME HEATING
WITH LIFT INITIATED BY SEA BREEZES AND AN AGING STATIONARY FRONT.
THE MODELS SHOW THEIR BEST AGREEMENT IN THESE AREAS FROM A QPF
PERSPECTIVE.

PETERSEN/ROTH

$$




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