Preliminary Forecasts
Issued by NWS

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000
FXUS02 KWNH 300508
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
107 AM EDT TUE MAY 30 2017

VALID 12Z FRI JUN 02 2017 - 12Z TUE JUN 06 2017

PATTERN OVERVIEW AND MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
TROUGHING ACROSS THE NORTHWEST AND GREAT LAKES ARE EXPECTED THIS
PERIOD, WITH SYSTEMS OCCASIONALLY MOVING THROUGH THE DESERT
SOUTHWEST INTO THE BASE OF THE GREAT LAKES TROUGH.  THE GUIDANCE
AGREES ON THESE GENERAL IDEAS.  IT`S THE SPECIFICS THAT ARE A
PROBLEM ACROSS THE MIDWEST, MID-SOUTH, AND GREAT LAKES AS THE
VARIOUS PIECES OF GUIDANCE ARE SHOWING OCCASIONAL TIMING ISSUES
AND SOME DEPTH ISSUES AS WELL WHICH LEAD TO A BIT OF SPREAD IN
SURFACE LOW TRACK ACROSS THE REGION.

TO DEAL WITH THE UNCERTAINTY IN THE PRESSURES, 500 HPA HEIGHTS,
AND WIND GRIDS, USED A COMPROMISE OF THE 12Z ECMWF/12Z UKMET/12Z
CANADIAN/18Z GFS FOR FRIDAY AND SATURDAY, BEFORE BLENDING IN
INCREASING PERCENTAGES OF THE 12Z NAEFS AND 12Z ECMWF ENSEMBLE
MEAN SOLUTIONS.  THIS CHOICE LED TO REASONABLE CONTINUITY.  WITH
THE TEMPERATURES, DEW POINTS, CLOUDS, WEATHER, AND PRECIPITATION
CHANCE GRIDS, USED AN EVEN SPLIT OF DETERMINISTIC (12Z
CANADIAN/12Z ECMWF/18Z GFS) AND ENSEMBLE MEAN (12Z ECMWF/12Z NAEFS
MEAN) GUIDANCE.  FOR THE DAYS 4-7 QPF, A ROUGH COMPROMISE OF THE
00Z GFS AND 12Z ECMWF WAS USED.


WEATHER HIGHLIGHTS
~~~~~~~~~~~~~~~~~~
IN THE WAKE OF A CYCLONE MOVING FROM THE CENTRAL PLAINS SATURDAY
INTO THE NORTHERN MID-ATLANTIC STATES EARLY NEXT WEEK, BELOW
NORMAL TEMPERATURES SHOULD SPREAD SOUTHWARD THROUGH THE
MIDWEST/MISSISSIPPI VALLEY.  ACROSS THE WEST, DESPITE THE PASSAGE
OF A WEAK FRONTAL ZONE, WARM CONDITIONS ARE EXPECTED ACROSS MUCH
OF THE REGION WEST OF THE CONTINENTAL DIVIDE.

THE HEAVIEST RAINFALL AND THUNDERSTORM ACTIVITY DURING THIS PERIOD
IS LIKELY FROM THE CENTRAL PLAINS TO THE MID-SOUTH INTO THE
CAROLINAS AND PORTIONS OF THE MID-ATLANTIC STATES WITH THE
DISTURBANCES MOVING EAST FROM THE SOUTHWEST U.S.  LOCALLY HEAVY
RAINS ARE ANTICIPATED IN AREAS THAT HAVE RECEIVED ABOVE NORMAL
RAINFALL THUS FAR THIS SPRING -- SUCH AS THE OZARKS, KY, WV, AND
VA -- AND THIS COULD LEAD TO FLOODING ISSUES FOR THOSE AREAS.

ROTH/HAMRICK
$$





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