Preliminary Forecasts
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12
000
FXUS02 KWNH 260603
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
202 AM 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 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...

...PATTERN OVERVIEW AND GUIDANCE EVALUATION...

AN UPPER TROUGH PERSISTS MUCH OF THIS PERIOD FROM THE SOUTHERN
ROCKIES AND CENTRAL PLAINS TO THE UPPER MS VALLEY.  AN EMBEDDED
CLOSED LOW PROGRESSES NORTHEASTWARD THIS WEEKEND...WITH A SURFACE
LOW DEVELOPING IN THE SOUTHERN PLAINS BY 12Z SAT AND MOVING TO THE
MID MS VALLEY BY 12Z SUN 30 APR AND THEN THE UPPER MS VALLEY/UPPER
GREAT LAKES 12Z MON BEFORE MOVING ON INTO CANADA THEREAFTER.

THE 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. THE GFS AND ECMWF AND THEIR RESPECTIVE ENSEMBLES CONTINUE
TO HAVE MODEL TO MODEL AND RUN TO RUN DIFFERENCE SON THE
TIMING/PHASING OF THE UPPER TROUGH AND ASSOCIATED SFC REFLECTION
AND EVOLUTION OF THE FRONTS.

THE OVERALL ENVELOPE OF SOLUTIONS REMAINS FAIRLY STABLE SO THIS
LEADS TO
GOOD CONTINUITY DUE TO THE PREFERENCE TO USE A BLEND BETWEEN THE
18Z AND 12Z GFS AND 12Z ECMWF/ECWMF ENSEMBLE MEAN.

ONCE THE AFOREMENTIONED CLOSED LOW EJECTS NORTHEAST INTO
CANADA..THE NEXT UPPER TROUGH DEVELOPS WITH A WAVE MOVING
SOUTHEAST FROM THE ROCKIES ONTO THE PLAINS WED 03 MAY.  THE 18-00Z
GFS WERE HIGH IN AMPLITUDE AND SLOWER IN TIMING VS THE 12Z ECMWF
AND ITS ENSEMBLE MEAN.  A COMPROMISE WAS USED FOR THE DAYS 6-7
FORECAST...AS THE 18Z GEFS MEAN FORGED A MIDDLE GROUND BETWEEN THE
2 CAMPS.

...WEATHER HIGHLIGHTS...

MODERATE TO HEAVY ON SNOWFALL IS EXPECTED OVER THE FRONT RANGE OF
THE COLORADO AND WYOMING ROCKIES AS AN UPPER TROUGH AMPLIFIES OVER
THE CENTRAL/SOUTHERN ROCKIES FRIDAY INTO SATURDAY...WITH SNOW
POSSIBLY EXPANDING INTO THE ADJACENT HIGH PLAINS ON SATURDAY.

INCREASING MOISTURE ADVECTING NORTHWARD OUT OF THE GULF OF MEXICO
WILL HEIGHTEN THE RISK FOR HEAVY RAINFALL ACROSS THE MIDDLE TO
LOWER MISSISSIPPI VALLEY.
MULTIPLE FORECASTS SEEM TO BE TARGETING HEAVIER AMOUNTS IN
ARKANSAS AND ADJACENT PORTIONS OF SURROUNDING STATES
MO/OK/TX/LA/MS.  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 SUN/MON...BUT THERE REMAINS SOME UNCERTAINTY
WITH THE DETAILS OF THE TRACK AND STRENGTH OF THE LOW AND
RESULTANT TEMPERATURE PROFILES AND DURATION OF EACH PRECIPITATION
TYPE.

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.


PETERSEN



$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.