Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2

000
FXUS02 KWBC 040457
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1255 AM EDT WED MAY 04 2016

VALID 12Z SAT MAY 07 2016 - 12Z WED MAY 11 2016

GENERAL FLOW PATTERN
~~~~~~~~~~~~~~~~~~~~
BLOCKY FLOW ACROSS THE COUNTRY (WITH TROUGHING IN THE SOUTHWEST
AND NORTHEAST) SIMPLIFIES THIS PERIOD AS A SYSTEM MOVING THROUGH
WESTERN CANADA MOVES THE WESTERN TROUGH INTO THE PLAINS, WHICH IN
TURN MOVES RIDGING FROM THE PLAINS INTO THE EAST.  THE PAIR OF
CLOSED CYCLONES IN EASTERN CANADA AND THE NORTHEAST JOIN FORCES,
FORMING A DEEP CYCLONE IN ATLANTIC CANADA WHICH THEN LIFTS
NORTHEASTWARD.


MODEL PREFERENCES
~~~~~~~~~~~~~~~~~
THE GUIDANCE IS MUCH MORE AGREEABLE THAN SEEN ON PAST DAYS.  AS
SUCH, FOR THE PRESSURES/500 HPA HEIGHTS/WIND GRIDS, USED A
COMPROMISE OF THE 12Z CANADIAN/12Z UKMET/12Z ECMWF/18Z GFS FOR
SATURDAY BEFORE ELIMINATING THE 12Z CANADIAN FROM CONSIDERATION
THEREAFTER AS IT STRAYS FROM THE PACK.  FOR SUNDAY INTO MONDAY,
USED A COMPROMISE OF THE 12Z UKMET/12Z ECMWF/18Z GFS.  FROM MONDAY
INTO NEXT WEDNESDAY, USED A COMBINATION OF THE 12Z ECMWF/18Z
GFS/12Z NAEFS MEAN/12Z ECMWF ENSEMBLE MEAN, WHICH INCREASINGLY
SHIFTS IN THE DIRECTION OF THE ENSEMBLE MEANS AND AWAY FROM THE
ECMWF WITH TIME DUE TO ITS ANOMALOUS UPPER LOW NEAR THE NORTHWEST
NEXT WEDNESDAY.  THIS KEPT GOOD CONTINUITY.  FOR TEMPERATURES/DEW
POINTS/CLOUDS/WEATHER/PRECIPITATION CHANCES, USED A 12Z NAEFS
MEAN/12Z ECMWF ENSEMBLE MEAN HEAVY BLEND.  HIGH TEMPERATURES IN
THE SOUTHEAST NEEDED TO BE TONED DOWN BY A CATEGORY OR TWO BASED
ON THE MODEL PREFERENCE -- CAPPED HIGHS IN NORTHEAST FL/EASTERN
GA/SOUTHERN AND CENTRAL SC AT 90F AFTER COORDINATION WITH THE
PEACHTREE CITY GA FORECAST OFFICE.  THE PRECIPITATION FORECAST FOR
DAYS 4-7 WAS DERIVED FROM A COMPROMISE OF THE 12Z ECMWF, 18Z GFS,
AND 00Z GFS.


WEATHER HIGHLIGHTS/THREATS
~~~~~~~~~~~~~~~~~~~~~~~~~~
THE NORTHWEST STAYS QUITE WARM AND DRY AS RIDGING ALOFT ATTEMPTS
TO PERSIST NEARBY THROUGH THE PERIOD.  A DEEP LOW/TROUGH WORKING
NORTHEASTWARD OUT OF THE SOUTHWEST WILL SPREAD A BROAD AREA OF
RAIN AND HIGHER ELEVATION SNOWS THROUGH THE GREAT BASIN INTO THE
ROCKIES... WITH LEAD RAINS DEVELOPING OVER THE CENTRAL US SUNDAY
INTO NEXT WEDNESDAY, INCLUDING THE RAIN-WEARY ARKLATEX. HIGHEST
TOTALS ARE EXPECTED ACROSS PORTIONS OF CO/WY THEN OUT OVER THE
PLAINS. SPC HAS A 15% RISK AREA OF SEVERE STORMS ON SATURDAY MAY 7
AHEAD OF THE COLD FRONT FROM W TEXAS NORTHWARD TO WESTERN KANSAS
AND EASTERN COLORADO. TEMPERATURES WITH THE SYSTEM ARE EXPECTED TO
BE 10-15F BELOW AVERAGE UNDER THE UPPER LOW. RIDGING ALOFT AHEAD
OF THIS SYSTEM IS EXPECTED TO SUPPORT LEAD WARMING SPREADING FROM
THE PLAINS SATURDAY INTO THE EAST WITH TIME.  PRECIPITATION ACROSS
THE NORTHEAST WILL BE SLOW TO CLEAR THIS PERIOD DUE TO A
PERSISTENT DEEP CYCLONE NEAR ATLANTIC CANADA WHICH WON`T PULL AWAY
FROM THE REGION UNTIL TUESDAY AND A FRONTAL ZONE MEANDERING ACROSS
THE SOUTHERN MID-ATLANTIC STATES.

ROTH
$$





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