Prognostic Meteorological Discussion
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FXUS02 KWBC 050633
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
233 AM EDT THU MAY 05 2016

VALID 12Z SUN MAY 08 2016 - 12Z THU MAY 12 2016

...PATTERN OVERVIEW...

SPLIT FLOW WILL CONTINUE TO DOMINATE THE COUNTRY MARKED BY RATHER
HIGH AMPLITUDE. THE PATTERN SHOULD REMAIN BLOCKY IN NATURE WITH A
SLOW-MOVING BROAD UPPER LOW EXTENDING ACROSS THE FOUR CORNERS
REGION ON SUNDAY. THIS FEATURE WILL GRADUALLY WEAKEN AS IT MOVES
THROUGH THE CENTRAL PLAINS AND INTO THE MIDDLE MS VALLEY BY EARLY
NEXT WEEK. WITHIN THE ACTIVE NORTHERN STREAM...NEGATIVE HEIGHT
ANOMALIES WILL INITIALLY EXIST ACROSS WESTERN CANADA AS WELL AS
OVER THE GREAT LAKES/NORTHEASTERN U.S. THE LATTER AREA CAN EXPECT
LOWER HEIGHTS OVERHEAD THROUGH TUESDAY BEFORE SHORTWAVE RIDGING
BUILDS AS THE PATTERN BEGINS TO DEAMPLIFY. MEANWHILE...ENERGY
ACROSS WESTERN CANADA IS FORECAST TO DIP DOWN THROUGH THE NORTHERN
TIER OF THE COUNTRY ESTABLISHING SOME SORT OF LONGWAVE TROUGH
ACROSS THE REGION INTO THE MIDDLE OF NEXT WEEK. THIS WILL ALLOW
POSITIVE HEIGHT ANOMALIES TO EXTEND ALONG THE WEST COAST FAVORING
TRANQUIL CONDITIONS.


...GUIDANCE EVALUATION/MODEL PREFERENCES...

MODELS ARE IN GENERAL AGREEMENT HANDLING THE INITIAL UPPER LOW
MIGRATING FROM THE SOUTHWESTERN U.S. TOWARD THE CENTRAL
PLAINS/MIDDLE MS VALLEY. WHERE THEY SEEM TO VARY IS WITH STRENGTH
AS THE PAST FEW GFS SOLUTIONS HAVE FAVORED A DEEPER/MORE PROLONGED
WAVE OF LOW PRESSURE. SUCH FORECASTS MAINTAIN A MORE DEFINED UPPER
LOW MOVING INTO THE UPPER GREAT LAKES BY LATE TUESDAY WHICH HAS
SOME ENSEMBLE SUPPORT...ALBEIT FROM THE GEFS MEMBERS. WHERE THE
MODELS HAVE EXHIBITED THE LARGEST ISSUES ARE WITH THE DIGGING
TROUGH FROM WESTERN CANADA DOWN INTO THE NORTH-CENTRAL STATES. IN
PARTICULAR...THE LEAD SHORTWAVE TRACKING ALONG THE INTERNATIONAL
BORDER INTO THE DAKOTAS BY MID-WEEK IS THE MOST NEBULOUS OF THE
BUNCH WITH THE PAST FEW ECMWF SOLUTIONS DEPICTING A COMPACT UPPER
LOW SHIFTING EASTWARD. THE 12Z CMC SHOWS THIS BUT WELL TO THE
NORTH WHILE THE RECENT GFS CYCLES FAVOR A BIT MORE PROGRESSION IN
THE FLOW.

REGARDING PREFERENCES...A MIX AND MATCH OF THE 18Z GFS/12Z ECMWF
APPEARED REASONABLE THROUGH 10/0000Z WITH SLIGHTLY HIGHER
CONTRIBUTIONS FROM THE ECMWF GIVEN THE UNCERTAINTY IN THE INITIAL
UPPER LOW TRACK IN THE CENTRAL PLAINS. EVENTUALLY ADDED SOME OF
THE 18Z GEFS/12Z ECMWF ENSEMBLE MEAN SOLUTIONS INTO THE DAY 5
BEFORE RESORTING TO ALL ENSEMBLE MEANS FOR THE FINAL COUPLE OF
DAYS. WEIGHTED THE FORECAST ABOUT 70 PERCENT TOWARD THE 12Z ECMWF
ENSEMBLE MEAN GIVEN ITS BEEN MORE STABLE WHEN COMPARING RECENT
MODEL CYCLES.


...WEATHER HIGHLIGHTS/THREATS...

AHEAD OF THE UPPER LOW BARRELING THROUGH THE SOUTHERN HIGH
PLAINS...EXPECT A ROBUST AREA OF CONVECTION EXTENDING ACROSS THE
SOUTHERN/CENTRAL PLAINS WITH SEVERE WEATHER POSSIBLE GIVEN THE
LATEST SPC OUTLOOKS. UNDERNEATH THE CLOSED LOW ITSELF...STEEP
MID-LEVEL LAPSE RATES WILL FAVOR ABUNDANT SHOWERS ACCOMPANIED BY
BELOW NORMAL TEMPERATURES ON THE ORDER OF THE 5 TO 10 DEGREE
DEPARTURES FROM CLIMATOLOGY. ADDITIONALLY...A WEST-EAST AXIS OF
PRECIPITATION IS LIKELY FROM THE CENTRAL PLAINS BACK TOWARD THE OH
VALLEY AS A FRONTAL ZONE MEANDERS ACROSS THE REGION.

WITHIN THE AMPLIFIED NORTHERN STREAM...COOL AND UNSETTLED
CONDITIONS ARE LIKELY UNDERNEATH THE INFLUENCE OF LOWER HEIGHTS
ALOFT ACROSS NEW ENGLAND. FARTHER UPSTREAM...THE AFOREMENTIONED
UNCERTAINTIES ACROSS THE NORTH-CENTRAL U.S. MAKES THE FORECAST
CHALLENGING BUT MODELS DO SUPPORT A MARKED INCREASE IN
PRECIPITATION THREATS FOR MUCH OF EARLY/MID NEXT WEEK.
MEANWHILE...ACROSS THE WEST COAST...TRANQUIL CONDITIONS WILL BE
FAVORED GIVEN THE BUILDING MID-LEVEL HEIGHTS.


RUBIN-OSTER

$$




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