Prognostic Meteorological Discussion
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000
FXUS02 KWBC 301600
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1200 PM EDT SUN APR 30 2017

VALID 12Z WED MAY 03 2017 - 12Z SUN MAY 07 2017

...PATTERN OVERVIEW AND GUIDANCE EVALUATION...

THE LATEST GUIDANCE CONTINUES TO SHOW AN EVOLUTION TOWARD AN
AMPLIFIED BLOCKY PATTERN BY THE WEEKEND...CONSISTING OF EAST AND
WEST COAST TROUGHS WITH A STRONG RIDGE OVER THE CENTRAL STATES. BY
MID-PERIOD...THE OPERATIONAL MODEL RUNS SHOW BIG DIFFERENCES WITH
RESPECT TO THE DETAILS...BUT THE ENSEMBLE MEANS CONTINUE TO
PROVIDE A MORE CONSISTENT FORECAST.

MODELS AND ENSEMBLES SHOW A TROUGH AMPLIFYING OVER THE MISSISSIPPI
VALLEY BY DAY 4/THURS WITH A POSSIBLE CUT-OFF LOW PROGRESSING
EAST-NORTHEAST THROUGH THE EASTERN U.S. BY THE WEEKEND. THE
OPERATIONAL GFS CONTINUES TO SHOW FAIRLY GOOD RUN-TO-RUN
CONTINUITY ON A LOW CUTTING OFF FROM THE BASE OF THE TROUGH AS IT
TRACKS TOWARDS THE SOUTHEAST AND MID-ATLANTIC...EVENTUALLY PHASING
WITH THE NORTHERN STREAM FLOW BY DAY 7/SUN. THE 00Z RUN OF THE
ECMWF WOULD ALSO SUPPORT THIS SAME GENERAL SOLUTION...BUT THIS IS
VASTLY DIFFERENT FROM ITS PREVIOUS RUN WHICH SHOWED A DISTINCT CUT
OFF LOW MEANDERING OVER THE SOUTHEAST. THE GEFS/NAEFS/EURO
ENSEMBLE MEAN WOULD ALSO SUPPORT THIS SAME PATTERN AND DESPITE
MINOR TIMING DIFFERENCES...ARE IN DECENT AGREEMENT WITH EACH OTHER
THROUGH THE ENTIRE MEDIUM RANGE PERIOD.

MEANWHILE OUT WEST...DIFFERENCES ARE APPARENT WITH RESPECT TO THE
EVOLUTION OF A SHORTWAVE APPROACHING THE NORTHWEST COAST ON DAY
5/FRI AND A POSSIBLE CLOSED LOW PUSHING INTO CENTRAL CALIFORNIA BY
THE END OF THE WEEKEND. THE LATEST RUN OF THE ECMWF HAS A VERY
DEEP LOW OFF THE NORTHWEST COAST 12Z SATURDAY (ALSO SUPPORTED BY
ITS ENSEMBLE MEAN) WHILE THE REMAINDER OF THE GUIDANCE AND
ENSEMBLES IS SLIGHTLY FASTER AND SHOWING MORE ELONGATED TROUGHING
ALONG THE WESTERN U.S. COASTLINE.


...WEATHER HIGHLIGHTS...

WITH SOME IMPORTANT DETAILS STILL IN DOUBT, GENERALLY EXPECT THE
SYSTEM ASSOC WITH THE AMPLIFYING CNTRL-ERN U.S. UPR TROUGH TO
GENERATE SOME LOCALLY MDT-HVY RNFL OVER PARTS OF THE CNTRL-SRN
PLAINS/W-CNTRL GULF COAST ON WED WITH ACTIVITY THEN SPREADING
EWD-NEWD TO THE EAST COAST BY LATE IN THE WEEK.  AMPLIFIED/BLOCKY
NATURE OF THE LARGE SCALE PATTERN COULD PROMOTE FAIRLY SLOW SYSTEM
MOTION AND LINGERING PRECIP OVER PARTS OF THE EAST INTO THE
WEEKEND.  COMBINING THE VARIOUS POSSIBILITIES FOR SYSTEM EVOLUTION
THE LWR MS VLY/CNTRL GULF COAST REGION APPEARS TO HAVE THE BEST
POTENTIAL FOR SEEING HIGHEST RNFL TOTALS WITH THIS SYSTEM.  SOME
LOCATIONS EXTENDING INTO THE MID ATLC/NORTHEAST, AND PERHAPS
WITHIN ANOTHER BAND FARTHER NW OF THIS AXIS, MAY SEE SIGNIFICANT
AMOUNTS AS WELL.  WARM SECTOR CONVECTION MAY BE STRONG TO SEVERE
WITH GUIDANCE DETAILS STILL TOO UNCERTAIN TO SPECIFY MOST LIKELY
AREAS TO BE AFFECTED.  THE COLD SECTOR OF THIS SYSTEM WILL BRING
BELOW NORMAL TEMPS FROM THE HIGH PLAINS INTO THE EAST WITH SOME
AREAS SEEING ONE OR MORE DAYS OF AT LEAST MINUS 10F ANOMALIES FOR
HIGHS.

AHEAD OF THE UPR TROUGH AMPLIFYING TOWARD THE WEST COAST, ABOVE TO
MUCH ABOVE NORMAL TEMPS WITH MANY ANOMALIES OF PLUS 10F OR GREATER
WILL PROGRESS FROM THE WEST COAST STATES THROUGH THE INTERIOR WEST
AND INTO THE ROCKIES/HIGH PLAINS.  BASED ON LATEST FCST FOR TEMPS
THERE STILL APPEARS TO BE A BETTER CHANCE FOR SCATTERED DAILY
RECORD WARM LOWS THAN RECORD HIGHS.  ARRIVAL OF THE UPR TROUGH
WILL BRING NEAR TO BELOW NORMAL READINGS TO THE WEST COAST FOR
NEXT WEEKEND.  MOST PRECIP SHOULD BE IN THE LGT-MDT RANGE OF
INTENSITY AND BE CONFINED MOSTLY TO THE NRN-CNTRL WEST COAST INTO
THE NRN ROCKIES, THOUGH SOME LGT/SCT ACTIVITY FARTHER S LATE IN
THE PERIOD CANNOT BE RULED OUT.

SANTORELLI

$$




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