Prognostic Meteorological Discussion
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FXUS02 KWBC 281525
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1125 AM EDT FRI APR 28 2017

VALID 12Z MON MAY 01 2017 - 12Z FRI MAY 05 2017

...PATTERN OVERVIEW AND GUIDANCE EVALUATION...

THE ESTABLISHED LONGWAVE PATTERN OF A TROUGH OVER THE CENTRAL U.S.
AND RIDGE NEAR OR JUST OFF THE WEST COAST WILL LIKELY BEGIN TO
PROGRESS EWD BY THE LATTER HALF OF THE PERIOD, WITH THE TROUGH
HEADING INTO THE EAST AND THE RIDGE CROSSING THE WEST. BEHIND THE
RIDGE A SHRTWV TROUGH SHOULD APPROACH THE WEST COAST LATE NEXT
WEEK. EMBEDDED WITHIN THE MEAN TROUGH THE TWO DOMINANT SYSTEMS OF
INTEREST DURING THE PERIOD WILL BE LEADING DEEP LOW PRESSURE
CROSSING THE MIDWEST/UPR GRTLKS MON-TUE, FOLLOWED BY A SYSTEM THAT
WILL DEVELOP OVER THE ERN HALF OF THE COUNTRY IN RESPONSE TO
INCOMING PACIFIC ENERGY THAT WILL RELOAD THE OVERALL TROUGH.

WPC KEPT CONTINUITY FROM OVERNIGHT IN MAINTAINING MAJORITY
WEIGHTING OF 00Z-06Z GFS/00Z ECMWF SOLNS RELATIVE TO 06Z GEFS/00Z
ECMWF MEANS FOR THE EARLY PART OF THE EXTENDED FCST. THIS DRIVES A
LARGE DEEP CYCLONE FROM THE UPPER/MID MS VALLEY THROUGH THE GREAT
LAKES, WHILE A SURFACE COLD FRONT SWEEPS THROUGH THE EAST. BASED
ON THE FULL SPREAD OF GUIDANCE FOR THE SECOND SYSTEM, MOST LIKELY
DEVELOPING FROM A SRN PLAINS WAVE ON TUES/WED AND REACHING NEAR
THE MID-ATL COAST BY NEXT FRI, CONFIDENCE IN EXISTENCE IS MUCH
HIGHER THAN FOR DETAILS. THIS IS DUE TO THE SENSITIVITY OF THE SFC
EVOLUTION TO SPECIFICS OF THE AMPLIFYING ENERGY ALOFT NOT
TYPICALLY WELL RESOLVED 6-7 DAYS OUT IN TIME. THE 00Z
GEFS/ECMWF/NAEFS ENSEMBLE LOW ENVELOPE HAS QUITE BROAD EXPANSIVE
OCCLUDED SYSTEM AND RECENT OPERATIONAL MODEL RUNS HAVE LIKEWISE
VARIED WITH TRACK AND DEGREE OF DEVELOPMENT. THE 00Z/06Z GFS RUNS
SUGGEST A FULLY PHASED AND LARGE DEEP CLOSED LOW, WHILE THE 00Z
ECMWF ADJUSTED TO A PLAUSIBLE SOLN OF SPLIT FLOW ALOFT TO LEAVE
BEHIND A GULF COAST WAVE INSTEAD OF A SYSTEM REACHING THE VICINITY
OF THE MID ATLC. EVEN WITH THE ENSEMBLE MEMBER SPREAD THE
RESULTING MEANS HAVE PROVIDED BETTER STABILITY THAN THE
OPERATIONAL MODELS THUS FAR, FAVORING GREATER WEIGHTING OF THE
MEANS TOWARD THE LATTER PORTION OF NEXT WEEK. THE MEANS HAVE ALSO
BEEN MORE AGREEABLE/CONSISTENT FOR THE UPR TROUGH/LEADING FRONT
REACHING THE NORTHWEST LATE IN THE PERIOD.

...WEATHER HIGHLIGHTS...

THE STRONG STORM TRACKING OUT OF THE MIDWEST WILL BRING VARIOUS
TYPES OF SIGNIFICANT WEATHER ACROSS THE ERN HALF OF THE COUNTRY
INCLUDING LOCALLY STRONG WINDS. JUST NW OF THE LOW TRACK EXPECT A
BAND OF ENHANCED PRECIP WITH SOME POTENTIALLY FALLING AS SNOW OR
FROZEN PRECIP. MEANWHILE THE LEADING COLD FRONT MAY BRING A BAND
OF LOCALLY MDT-HVY RAIN BUT LIKELY WITH LESS EXTREME TOTALS THAN
IN THE SHORTER RANGE TIME FRAME AND SOME CONVECTION MAY BE STRONG
TO SEVERE.

PRECIPITATION WITH THE SECOND SYSTEM WILL START OFF ON TUES WILL
START OFF AS A STREAK OF RAIN/CONVECTION FROM LIKELY SATURATED
OK/SRN KS INTO NRN AR/SRN MO, WITH PERHAPS A BLOWUP OF CONVECTIVE
ACTIVITY NEAR SERN TX/WRN LA GULF COAST NEAR A DEVELOPING DEWPOINT
WARM FRONT. THEN ON WED, THE STREAK OF PRECIP WILL SHIFT TOWARD
THE OH RIVER INTO THE TN VALLEY, WHILE CONVECTIVE HEAVY RAIN
FLOURISHES IN THE CENTRAL GULF COAST STATES. THEN ON THURS,
ANYWHERE FROM COASTAL NORTHEAST AND PARTS OF THE MID-ATL INTO THE
SOUTHEAST AND SOUTH EXPECT THE POTENTIAL FOR PRECIP AND CONVECTIVE
HEAVY RAINS WITH LIGHTER MOISTURE POSSIBLY EXTENDING BACK UP INTO
THE OH VALLEY TO THE UPPER LOW CENTER. THEN DUE TO THE LARGE
OPERATIONAL SPREAD BY NEXT FRI, EXPECT PRECIP POTENTIAL FROM THE
NORTHEAST/MID-ATL TO THE SOUTHEAST/FL.

FOR TEMPS DURING THE PERIOD VIA THE WPC MEAN MAX TEMP ANOMALY, THE
MOST ABOVE AVG TEMPS WILL BE OUT WEST FROM OR/NV/AZ TO CA WITH
LARGE SCALE OFFSHORE FLOW, AS MUCH AS 5 TO 10 DEG ABOVE AVG. ALSO
SPOT ABOVE AVG TEMPS WILL BE POSSIBLE IN SOUTH TX, FL PENINSULA
AND COASTAL NC/VA. MEANWHILE BELOW AVG TEMPS WILL BE HIGHLIGHTED
FROM THE FRONT RANGE OF THE ROCKIES THROUGH THE ENTIRE MIDWEST
INTO THE OH/TN VALLEYS AND SOUTH/LOWER MS VALLEY, WITH COLDEST
ANOMALIES OF 5 TO 10 DEG BELOW AVG STRETCHING FROM THE UPPER TO
MID MS VALLEY.

MUSHER/RAUSCH

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