Prognostic Meteorological Discussion
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FXUS02 KWBC 251639
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 PM EDT TUE APR 25 2017

VALID 12Z FRI APR 28 2017 - 12Z TUE MAY 02 2017

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

...THREAT FOR HEAVY RAINFALL WILL INCREASE OVER THE MIDDLE TO
LOWER MISSISSIPPI VALLEY THIS WEEKEND AND INTO EARLY NEXT WEEK...

...TEMPERATURES COULD APPROACH OR EXCEED RECORD HIGHS ACROSS THE
SOUTHEAST AND MID-ATLANTIC STATES THIS WEEKEND...


...PATTERN OVERVIEW AND GUIDANCE EVALUATION...

AN ACTIVE PATTERN IS IN STORE OVER THE CONUS DURING THE MEDIUM
RANGE PERIOD AS AN AMPLIFYING UPPER TROUGH SANDWICHED BETWEEN HIGH
AMPLITUDE RIDGES ANCHORED IN THE EASTERN PACIFIC AND WESTERN
ATLANTIC GRADUALLY PROGRESSES EAST/NORTHEASTWARD OUT OF THE
SOUTHERN ROCKIES/CENTRAL PLAINS THIS WEEKEND.  WHILE THE UPPER
TROUGH POSSIBLY CLOSES OFF AND LIFTS NORTHEASTWARD THROUGH THE
UPPER MIDWEST EARLY NEXT WEEK...UPSTREAM ENERGY STREAKING
SOUTHEASTWARD AROUND THE EASTERN PACIFIC RIDGE COULD BEGIN TO DIG
INTO THE NORTHWESTERN U.S..

MODELS REMAINED IN GOOD AGREEMENT WITH THE LARGE SCALE FLOW
PATTERN OVER THE LOWER 48...BUT THERE REMAINS SOME UNCERTAINTY
WITH THE DETAILS OF THE UPPER TROUGH SLOWLY PROGRESSING THROUGH
THE CENTRAL U.S....ESPECIALLY WITH THE ASSOCIATED DEEP SURFACE LOW
EXPECTED TO LIFT OUT OF THE MIDDLE MISSISSIPPI VALLEY LATE THIS
WEEKEND...DESPITE RELATIVELY GOOD AGREEMENT BETWEEN 00Z
DETERMINISTIC GUIDANCE WITH THE TRACK/STRENGTH OF THE LOW...A LACK
OF CLUSTERING AMONG 00Z ENSEMBLE MEMBER LOW PLOTS SUGGESTS THE
FORECAST IS NOT VERY STABLE.  THERE IS ALSO SOME MODEL SPREAD AND
FORECAST UNCERTAINTY WITH THE PROGRESSION OF A COLD FRONT POSSIBLY
PRESSING THROUGH THE NORTHEAST AND NORTHERN MID-ATLANTIC STATES
FRIDAY INTO SATURDAY...WHERE THE 00Z ECMWF SUGGESTS A BIT
FASTER/FARTHER SOUTH AND EAST SOLUTION THAN THE 00Z GFS AND
CONTINUITY.  A BLEND BETWEEN THE 06Z GFS/GEFS MEAN AND 00Z
ECMWF/ECWMF ENSEMBLE MEAN APPEARED TO OFFER A GOOD COMPROMISE
BETWEEN MODEL SPREAD AND MATCHED WELL WITH CONTINUITY...SO IT WAS
USED AS A STARTING POINT FOR THE WPC DAY 3-7 FORECAST


...WEATHER HIGHLIGHTS...

LATE SEASON SNOWFALL IS EXPECTED OVER THE HIGHER ELEVATIONS OF
COLORADO AND WYOMING AS AN UPPER TROUGH AMPLIFIES OVER THE
CENTRAL/SOUTHERN ROCKIES FRIDAY INTO SATURDAY...WITH SNOW POSSIBLY
EXPANDING INTO THE ADJACENT HIGH PLAINS ON SATURDAY.  WHILE THE
UPPER TROUGH CONTINUES TO AMPLIFY AND SLOWLY EDGE EASTWARD THROUGH
THE CENTRAL U.S. THIS WEEKEND...INCREASING MOISTURE ADVECTING
NORTHWARD OUT OF THE GULF OF MEXICO WILL HEIGHTEN THE RISK FOR
HEAVY RAINFALL ACROSS THE SOUTH CENTRAL U.S....ESPECIALLY OVER THE
MIDDLE TO LOWER MISSISSIPPI VALLEY.  PLEASE REFER TO THE STORM
PREDICTION CENTER (WWW.SPC.NCEP.NOAA.GOV) FOR INFORMATION ON THE
SEVERE WEATHER THREAT WITH THIS SYSTEM.  ALSO...ACCUMULATING SNOW
WILL BE POSSIBLE FOR PORTIONS OF THE UPPER MISSISSIPPI VALLEY AS
THE UPPER TROUGH/CLOSED LOW AND ASSOCIATED DEEP SURFACE CYCLONE
LIFT THROUGH THE UPPER MIDWEST EARLY NEXT WEEK...BUT THERE REMAINS
SOME UNCERTAINTY WITH THE DETAILS OF THE TRACK AND STRENGTH OF THE
SURFACE LOW.

AHEAD OF THE UPPER TROUGH IMPACTING THE CENTRAL U.S....AN UPPER
RIDGE EXPANDING 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
RETURN TO NEAR NORMAL AS A COLD FRONT CROSSES THE REGION EARLY
NEXT WEEK.


GERHARDT



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