Preliminary Forecasts
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FXUS02 KWNH 030517
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
117 AM EDT TUE MAY 03 2016

VALID 12Z FRI MAY 06 2016 - 12Z TUE MAY 10 2016

GENERAL FLOW PATTERN
~~~~~~~~~~~~~~~~~~~~
A MID-LATITUDE OMEGA STYLE BLOCK BREAKS DOWN THIS WEEKEND AS A
LARGE CLOSED LOW DEVELOPS ACROSS EASTERN CANADA...ENGULFING THE
EASTERN US DEEP CYCLONE.  MEANWHILE...THE WESTERN UPPER LOW
BRIEFLY BECOMES ORIENTED IN A REX BLOCK MANNER SATURDAY AND SUNDAY
WHILE A RIDGE MOVES ACROSS WESTERN CANADA BEFORE A SYSTEM FLATTENS
THE WESTERN CANADIAN RIDGE WHICH ESCORTS THE WESTERN CYCLONE
EASTWARD INTO THE PLAINS BY EARLY NEXT WEEK.


MODEL PREFERENCES
~~~~~~~~~~~~~~~~~
THE ENSEMBLE MEAN SOLUTIONS SHOW BETTER AGREEMENT THAN THIS TIME
YESTERDAY, ADDING CONFIDENCE IN THE EXPECTED FLOW PATTERN.
PRESSURE/500 HPA/WIND-WISE, A COMBINATION OF THE 12Z ECMWF/12Z
UKMET/12Z CANADIAN/18Z GFS WORKED FOR FRIDAY.  BY SATURDAY, THE
12Z CANADIAN BECAME A SOUTHERN OUTLIER WITH THE DEEP CYCLONE IN
EASTERN CANADA AND WAS EXCLUDED FROM THE MIX, LEAVING THE 12Z
UKMET/12Z ECMWF/18Z GFS AS CONTENDERS.  FROM LATE SUNDAY ONWARD,
THE 18Z/00Z GFS SOLUTIONS WERE MOST ALIGNED WITH THE ENSEMBLE MEAN
SOLUTIONS -- USED A 50/30/20 COMPROMISE OF THE 18Z GFS/12Z NAEFS
MEAN/12Z ECMWF ENSEMBLE MEAN DURING THIS TIME FRAME.  AS USUAL,
THE OTHER MEDIUM RANGE GRIDS (TEMPERATURES, DEW POINTS, CLOUDS,
WEATHER, RAIN CHANCES) UTILIZED HIGHER ENSEMBLE MEAN PERCENTAGES.
PRECIPITATION-WISE, USED A COMPROMISE OF THE 12Z ECMWF/18Z GFS/00Z
GFS FOR THE DAY 4-5 QPF, BEFORE USING A 40/40/20 BLEND OF THE 18Z
GFS/00Z GFS/12Z ECMWF FOR DAYS 6-7 QPF.  THIS KEPT REASONABLE
PROGRESSION WITH THE PRECIPITATION PATTERN PUT FORTH FROM MONDAY`S
DAY SHIFT.


WEATHER HIGHLIGHTS/THREATS
~~~~~~~~~~~~~~~~~~~~~~~~~~
A DEEP LOW/TROUGH WORKING GRADUALLY OVER THE WEST WILL SPREAD A
BROAD AREA OF RAIN AND HIGHER ELEVATION SNOWS FROM THE WEST COAST
INTO THE ROCKIES...WITH LEAD RAINS DEVELOPING OVER THE CENTRAL US
THIS WEEKEND INTO NEXT MONDAY. HIGHEST TOTALS ARE EXPECTED FROM
FAVORED SIERRA NEVADA AND INTERMOUNTAIN WEST TERRAIN INTO PORTIONS
OF CO/WY THEN OUT OVER THE PLAINS. TEMPERATURES WITH THE SYSTEM
ARE EXPECTED TO BE UPWARDS OF 10F BELOW NORMAL. RIDGING ALOFT
AHEAD OF THIS SYSTEM IS EXPECTED TO MEANWHILE SUPPORT LEAD WARMING
SPREADING FROM THE ROCKIES THURSDAY TO THE CENTRAL THEN EASTERN US
SATURDAY INTO TUESDAY.

AMPLIFIED MEAN UPPER TROUGHING AND INDIVIDUALLY UNCERTAIN FOCUS
WITH MULTIPLE EAST COAST/WRN ATLANTIC SURFACE LOWS WILL GENERALLY
SUPPORT COOL AND UNSETTLED WEATHER OVER THE EAST FRIDAY INTO
SATURDAY MORNING. MUCH OF THE PRECIPITATION IS EXPECTED OVER THE
MID-ATLANTIC/SOUTHERN NEW ENGLAND STATES FRIDAY INTO SATURDAY IN
CLOSEST PROXIMITY TO LOW SUPPORT.

ROTH
$$





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