Prognostic Meteorological Discussion
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FXUS02 KWBC 051603
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1202 PM EDT THU MAY 05 2016

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

...PATTERN OVERVIEW...

LARGE-SCALE UPPER-LEVEL VORTICES ON BOTH THE WESTERN AND EASTERN
U.S. ARE EXPECTED TO DEAMPLIFY AND LIFTS NORTHEASTWARD THROUGH
EARLY NEXT WEEK.  THIS WILL THEN EVOLVE INTO A REX BLOCK/SPLIT
FLOW PATTERN AS A DEEP-LEVEL RIDGE OR CUTOFF HIGH FORMS INTO
CENTRAL CANADA WHILE AN UPPER-LEVEL SHORTWAVE DIGS DOWN INTO THE
NORTHERN ROCKIES THROUGH EARLY TO MIDDLE OF NEXT WEEK.  A LOW
PRESSURE WAVE MAY DEVELOP AS IT SWINGS ACROSS IN THE GREAT LAKES
REGION BY NEXT THURSDAY BUT THE UNCERTAINTY REMAINS RELATIVELY
HIGH IN THIS AREA.


...GUIDANCE EVALUATION/MODEL PREFERENCES...

MODELS ARE IN BEST AGREEMENT HANDLING THE INITIAL UPPER LOW SLOWLY
OPENING UP AND MOVING TOWARD THE PLAINS AND MID-MS VALLEY THROUGH
THE MIDDLE OF NEXT WEEK.  AS FOR THE EAST COAST LOW...THE ECMWF
SOLUTION APPEARS A BIT TOO WEAK WHEREAS THE GFS SOLUTION APPEARS A
BIT TOO STRONG AND TOO FAR SOUTH.  THEREAFTER...OPERATIONAL MODELS
ARE STILL TRYING TO RESOLVE THE DEGREE OF DEVELOPMENT REGARDING
THE SHORTWAVE DIGGING DOWN FROM WESTERN CANADA AND EVENTUALLY
SWINGING EASTWARD INTO THE NORTHERN PLAINS.  EVEN THE ENSEMBLE
MEANS HAVE NOT QUITE SETTLED INTO A STEADY SOLUTION REGARDING THIS
FEATURE.  NEVERTHELESS...IN A BROADER SCALE...A LOW PRESSURE
WAVE/SYSTEM SHOULD CONTINUE TO MOVE ACROSS THE MIDWEST INTO THE
GREAT LAKES THROUGH THE MIDDLE OF NEXT WEEK.  THE DETERMINISTIC
00Z ECMWF IS TAKEN OUT OF CONSIDERATION FROM DAY 5/TUE AND BEYOND
AS IT SHOWS AN ANOMALOUS UPPER LOW ROTATING SOUTH FROM
CANADA...RESULTING IN ANOMALOUS DEVELOPMENT OF THE LOW PRESSURE
WAVE.  THE 06Z GFS IS TAKEN OUT OF CONSIDERATION BY DAY 5 AS
WELL...AS THE POSITION OF THE LOW IN THE PLAINS APPEARS TO FAR
NORTH. THUS THE WPC BLEND BEGINS WITH THE 00Z ECMWF...AND 06Z GFS
MIXING IN WITH THE RESPECTIVE ENSEMBLE MEANS FOR DAYS 3 AND 4
FOLLOWED BY TRENDING HEAVILY TOWARD THE EC MEANS THROUGH DAY 7.


...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.


KONG/RUBIN-OSTER

$$





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