Prognostic Meteorological Discussion
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FXUS02 KWBC 261641
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1240 PM EDT WED APR 26 2017

VALID 12Z SAT APR 29 2017 - 12Z WED MAY 03 2017

...LATE SEASON WINTER STORM EXPECTED TO BRING SNOW TO THE
SOUTHERN/CENTRAL ROCKIES AND PORTIONS OF THE ADJACENT HIGH PLAINS
THIS WEEKEND...WITH SNOW ALSO POSSIBLE ACROSS THE UPPER
MISSISSIPPI VALLEY EARLY NEXT WEEK...

...THREAT FOR HEAVY AND EXCESSIVE RAINFALL OVER SOUTHERN PORTIONS
OF THE PLAINS AND MISSISSIPPI VALLEY THIS WEEKEND...ESPECIALLY
FROM OKLAHOMA INTO ARKANSAS AND MISSOURI...


...PATTERN OVERVIEW AND GUIDANCE EVALUATION...

MODEL GUIDANCE REMAINED IN GOOD AGREEMENT WITH THE LARGE SCALE
FLOW PATTERN OVER THE LOWER 48 THIS WEEKEND AND INTO THE EARLY
HALF OF NEXT WEEK WHICH WILL FEATURE A MEAN CENTRAL U.S. TROUGH
SANDWICHED BETWEEN UPPER RIDGING OVER THE EASTERN PACIFIC AND
WESTERN ATLANTIC.  WITHIN THE MEAN FLOW...A CLOSED UPPER LOW OVER
THE FOUR CORNERS REGION ON SATURDAY WILL SLOWLY EDGE
EAST/NORTHEASTWARD TOWARDS THE CENTRAL PLAINS THIS WEEKEND.  ON
MONDAY...THE DYNAMIC SYSTEM...INCLUDING A DEEPENING SURFACE
LOW...WILL LIFT THROUGH THE UPPER MISSISSIPPI VALLEY WHILE
UPSTREAM ENERGY STREAKS SOUTHEASTWARD INTO THE PACIFIC NORTHWEST
AND POTENTIALLY AMPLIFIES OVER THE INTERMOUNTAIN WEST AND ROCKIES.

MODELS HAVE REMAINED FAIRLY STABLE WITH THE LONG WAVE PATTERN AND
EVEN ARE STARTING TO COME INTO GOOD AGREEMENT WITH THE SMALLER
SCALE FEATURES OF THE UPPER LOW EXITING THE FOUR CORNERS
REGION...SO THE WPC FORECAST WAS LARGELY BASED ON A BLEND BETWEEN
THE 00Z ECMWF AND 00Z/06Z GFS.  HOWEVER...THE GEFS/ECMWF ENSEMBLE
MEAN WERE ALSO INCORPORATED INTO THE FORECAST BLEND...ESPECIALLY
NEXT MONDAY-WEDNESDAY...IN ORDER TO ACCOUNT FOR SOME OF THE SPREAD
THAT DEVELOPS WITH THE DEEP SURFACE LOW EXITING THE UPPER
MISSISSIPPI VALLEY AS WELL AS SOME OF THE UNCERTAINTY WITH THE
AMPLITUDE AND TIMING OF THE ENERGY STREAKING INTO THE PACIFIC
NORTHWEST.


...WEATHER HIGHLIGHTS...

MULTIPLE WEATHER HAZARDS ARE EXPECTED WITH A DYNAMIC CLOSED LOW
WHILE IT EDGES OUT OF THE FOUR CORNERS REGION AND LIFTS
NORTHEASTWARD THROUGH THE CENTRAL U.S. THIS WEEKEND.  INCREASING
MOISTURE ADVECTION AHEAD OF THE SYSTEM WILL HEIGHTEN THE RISK FOR
HEAVY AND EXCESSIVE RAINFALL OVER PORTIONS OF THE PLAINS AND
MISSISSIPPI VALLEY THIS WEEKEND...ESPECIALLY OVER EASTERN OKLAHOMA
AND INTO ARKANSAS AND MISSOURI.  LATE SEASON SNOWFALL WILL ALSO BE
POSSIBLE WITH THIS SYSTEM...INITIALLY OVER THE CENTRAL/SOUTHERN
ROCKIES AND INTO PORTIONS OF THE ADJACENT HIGH PLAINS WHILE THE
UPPER LOW CLOSES OFF OVER THE FOUR CORNERS REGION EARLY
SATURDAY...FOLLOWED BY LOCATIONS OVER THE UPPER MISSISSIPPI VALLEY
AS A DEEPENING SURFACE LOW LIFTS THROUGH THE REGION SUNDAY NIGHT
INTO MONDAY.  PLEASE REFER TO THE STORM PREDICTION CENTER
(WWW.SPC.NCEP.NOAA.GOV) FOR INFORMATION ON THE SEVERE WEATHER
THREAT WITH THIS SYSTEM.

IN TERMS OF TEMPERATURES ACROSS THE NATION...A HIGH AMPLITUDE
UPPER RIDGE OVER THE SOUTHEASTERN U.S. COULD BRING WIDESPREAD
RECORD HIGH OR NEAR RECORD HIGH TEMPERATURES TO THE SOUTHEAST AND
MID-ATLANTIC STATES THIS WEEKEND...BUT THEN TEMPERATURES SHOULD
DECLINE TO NEAR NORMAL AFTER A COLD FRONT CROSSES THE REGION EARLY
NEXT WEEK.  WELL ABOVE NORMAL TEMPERATURES ARE FORECAST ACROSS
SOUTHERN CA INTO THE DESERT SOUTHWEST EARLY TO MIDDLE PORTIONS OF
NEXT WEEK AS WARM AIR ALOFT PROGRESSES DOWNSTREAM FROM THE
ANTICYCLONE IN THE EASTERN PACIFIC.


GERHARDT



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