Prognostic Meteorological Discussion
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FXUS02 KWBC 011608
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EST SUN MAR 01 2015

VALID 12Z WED MAR 04 2015 - 12Z SUN MAR 08 2015

...OVERVIEW...
AN ACTIVE MIGRATORY LONG-WAVE TROUGH MIGRATION ACROSS EASTERN
NORTH AMERICA PROVIDES THE MAJORITY OF THE SENSIBLE WEATHER FOR
THE LOWER 48---DURING THE FIRST HALF THIS MEDIUM RANGE PERIOD. THE
LATTER HALF OF THE MEDIUM RANGE---A SPLIT-FLOW PATTERN REAPPEARS
ALONG THE WEST COAST---AND EAST OF THE CONTINENTAL DIVIDE---A
FAST-MOVING WEST-NORTHWEST FLOW PATTERN PREVAILS ALONG THE
US/CANADIAN BORDER EASTWARD INTO THE CENTRAL GREAT LAKES AND NEW
ENGLAND.

.MODEL PREFERENCES...
THE MARCH 1/00Z NAEFS...ECENS AND GEFS MEANS CONTINUE TO
REASONABLY---PREDICT AND DEPICT---THE FLOW PATTERN ACROSS THE
LOWER 48. AND INTO THE LATTER PORTION OF DAY 5 (6/00Z-6/06Z)...THE
DETERMINISTIC 1/00Z ECMWF/GFS WERE DECENT PIECES OF
GUIDANCE---HANDLING THE DETAILS ALOFT---ACROSS THE SOUTHERN PLAINS
EASTWARD TO THE CAROLINAS...AND ACROSS BAJA CALIFORNIA. ACROSS
BRITISH COLUMBIA/SOUTHERN ALBERTA---AN EMERGING FAST-ZONAL
(WEST-NORTHWESTERLY FLOW)---A BY-PRODUCT OF A PATTERN SHIFT IN
ALASKA AND THE CUTOFF LOW INVOF 35N145W---THE DETERMINISTIC RUNS
(GFS/ECMWF) BEGIN TO BREAK DOWN AND DIFFER ENOUGH TO GO STRICTLY
WITH A ECENS/NAEFS BLEND.

...UNCERTAINTY ASSESSMENT...
ALONG THE WEST COAST ON NORTH AMERICA---
THE MARCH 1/00Z UKMET... GFS... CANADIAN... AND ECMWF---TO VARYING
DEGREES CARRY A SUBTLE SHORTWAVE INTO BRITISH COLUMBIA THAT
ENTRAINS INTO THE NORTHWESTERLIES AND REACHES MONTANA/ALBERTA
BORDER BY 6/12Z. BY THIS TIME FRAME THE UKMET...LOOKS TOO FAST
(ALREADY OVER MINNESOTA WITH IT) AND ATTEMPTS TO PHASE IT WITH
RESIDUAL SOUTHERN STREAM ENERGY. MIGHT NOT EVEN BE AN IMPORTANT
ITEM (WORTH TALKING ABOUT) IF IT WAS NOT FOR THIS WAVE DEPICTS THE
LEADING EDGE OF A PATTERN SHIFT---TO ZONAL FLOW---OVER ALASKA AND
THE YUKON. AND THE MAIN `FALLOUT` BEING---THE EMERGENCE OF A
CUTOFF LOW ALONG 140W-145W AROUND 6/12Z...OR IN THE CASE OF THE
CANADIAN...A DEEP MIGRATORY TROUGH IN THE GULF OF ALASKA. THOSE
WERE THE BIGGEST DEPARTURES FROM THE ENSEMBLES---AND BASED ON ALL
THE CURRENT GUIDANCE FOR THESE TIME FRAMES---THAT RULES OUT THE
CANADIAN AFTER 6/12Z IN THE EAST PACIFIC.

OVER THE CENTRAL...SOUTHERN AND EASTERN PORTIONS OF THE LOWER 48---
THE DAY 3 EASTERN NORTH AMERICAN LONG-WAVE TROUGH AND ST LAWRENCE
VALLEY CYCLONE MIGRATION---CONTINUES TO SHOW SIGNS OF GENERATING
AN `ANA-TYPE` FRONTAL STRUCTURE FROM NORTHEAST TEXAS TO THE
CAROLINAS (AND THE I-10 TO I-20 CORRIDOR FOR A TIME)...WITH THE
LEADING EDGE OF THE CANADIAN AIRMASS SPREADING OUT AND
`UNDERGLIDING`---TAKING PLACE IN ADVANCE OF THE UPPER-LEVEL JET
SUPPORT (AROUND THE 5/12Z TIME FRAME). THE DETERMINISTIC
GFS...CANADIAN AND ECMWF EXIT THE UPPER-LEVEL JET AXIS BETWEEN
CAPE HATTERAS AND CAPE MAY BY 7/00Z. HOWEVER...THERE IS JUST
ENOUGH LATITUDE DIFFERENCE IN THE JET-LEVEL WIND
FORECASTS---BETWEEN THESE 3 DETERMINISTIC SOLUTIONS---TO CREATE
UNCERTAINTY ON DAY 6 ALONG THE EASTERN SEABOARD AND ACROSS THE
SOUTHEAST.

LIKEWISE...THE LATITUDE OF THE RESIDUAL SURFACE RIDGE THAT SETTLES
OVER THE MID-ATLANTIC REGION AND NORTHEAST BEHIND THE EXITING JET
AXIS WILL BE A TRICKY TEMPERATURE FORECAST---WITH RESPECT TO THE
WIDENING SPREAD OF UPSTREAM NORTHERN STREAM ENERGY EXITING THE
SOUTHERN CANADIAN ROCKIES. THE TIMING/STRENGTH DIFFERENCES IN THE
EMERGING WEST-NORTHWEST SPLIT-FLOW (NORTHERN STREAM)---MAKES THE
TEMPERATURE PATTERN A VOLATILE ONE. OVERALL...THE FLOW LOOKS TO BE
RATHER DRY IN THE NORTHERN STREAM...WITH THE BROAD
DOWNSLOPING/ADIABATIC WARMING PROCESSES---OFFERED BY THE MOUNTAINS
OF WESTERN NORTH AMERICA...CREATING LOCALLY WARM
CONDITIONS...FOLLOWED BY DRY BUT COOLER WIND SHIFTS (BREEZY TO
WINDY AT TIMES) AND `ACCOMPANYING` SHALLOW SURGES OF MODIFIED
PACIFIC AIR.

...SENSIBLE WEATHER HIGHLIGHTS...
SHARP THERMAL CONTRASTS IN THE SOUTHERN PLAINS ON
WEDNESDAY...ALONG WITH A BROAD UPPER-LEVEL JET LOOK TO BRING A BIT
OF SPRING-LIKE CONVECTION AND DRASTIC SENSIBLE WEATHER CHANGES FOR
THE OZARK REGION...LOWER MISSOURI AND WESTERN OHIO VALLEYS. THESE
CHANGES MOVE DOWNSTREAM TO THE ATLANTIC COAST ON THURSDAY WITH
WINTER-LIKE CONDITIONS RETURNING TO THE NORTHEAST---GENERALLY
SPEAKING---NORTH OF THE MASON-DIXON WITH RESPECT TO PRECIPITATION.

TEMPERATURE CHALLENGES ALONG THE OHIO VALLEY...AND EAST OF THE
APPALACHIANS WEDNESDAY AND THURSDAY WITH BROAD WARM ADVECTION
FOLLOWED BY AN `ANA-TYPE` FRONTAL STRUCTURE---PRECEDING THE `VERY
COLD` AND DEEPER CORE OF THE MODIFIED-ARCTIC AIRMASS ON THE
BACKSIDE OF THE MIGRATORY LONG WAVE.

VOJTESAK

$$





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