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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1558Z Mar 31, 2015)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1158 AM EDT TUE MAR 31 2015

VALID 12Z FRI APR 03 2015 - 12Z TUE APR 07 2015

...OVERVIEW...
THROUGH SUNDAY (APRIL 5TH)...THE NORTHEAST AND GREAT LAKES REMAIN
IN A RATHER COOL SPRING FLOW PATTERN AS ANOTHER COLD FRONT SURGES
EASTWARD AND UPPER-LEVEL TROUGHING ANCHORS ACROSS HUDSON BAY. IN
THE WEST...AN ONSHORE FLOW AND COOLER...WETTER WEATHER RETURNS TO
THE PACIFIC NORTHWEST NEXT WEEKEND. THIS LATEST PACIFIC TROUGH
MIGRATES THROUGH THE GREAT BASIN AND ROCKIES BY THE END OF THE
WEEKEND. ITS EXITING ENERGY PRODUCES A MORE 'SPRING-LIKE'
CONVECTIVE WEATHER PATTERN AND LARGE TEMPERATURE SWINGS  TO THE
PLAINS STATES/MIDWEST---AND GENERATES A BROAD AREA OF WARM
ADVECTION THAT MIGRATES NORTHEASTWARD TOWARDS THE OHIO VALLEY AND
MID-ATLANTIC REGION.

THE PACIFIC TROUGH SHOULD BEGIN TO LIFT THE HUDSON BAY TROUGH
EASTWARD INTO LABRADOR EARLY NEXT WEEK AND A MILDER BUT MODIFIED
PACIFIC AIRMASS GRADUALLY SPREADS EASTWARD ACROSS THE NORTHEASTERN
QUARTER OF THE LOWER 48.

...MODEL PREFERENCES...
THE 31/00Z MODEL GUIDANCE ACCEPTS A DEEP UPPER-LEVEL LOW IN
WESTERN HUDSON BAY AT THE START OF DAY 3...AND TRANSITORY
MID-LEVEL ENERGY ENTRAINMENT INTO THE BASE OF THE UPPER FEATURE.
ONE ENTITY EMBEDDED ALONG THE ST LAWRENCE VALLEY...A SECOND
ENTITY---LESS OBVIOUS---INVOF THE COLORADO-KANSAS BORDER. SOLUTION
STRENGTH AND ENSEMBLE AGREEMENT (BETWEEN THE 31/00Z
ECENS/NAEFS/GEFS) ARE WELL ABOVE AVERAGE (IN MY ESTIMATION) WITH
RESPECT TO THE ST LAWRENCE 'ENTITY' GENERATING APPRECIABLE
TEMPERATURE ADVECTION VARIATIONS FOR THE GREAT LAKES (TO COOL THEN
VERY COLD) AND THE NORTHEAST/MID-ATLANTIC REGION (FROM WARM TO
COLD) ON SATURDAY (DAY 3).

WITH RESPECT TO THE SECOND 'ENTITY' OVER THE WEST CENTRAL HIGH
PLAINS---THE MASS FIELD CONTINUITY ALOFT DISPLAYED BY THE
ENSEMBLES AND THEIR MEANS ARE---ABOVE AVERAGE. THE 31/00Z
DETERMINISTIC GUIDANCE DID A NICE JOB HANDLING THE 250MB JET
STREAK AND FLOW AXIS (AT 4/12Z)---'STRADDLING' THE OHIO VALLEY AND
GENERALLY SUGGESTING A POSSIBLE 'ANA-FRONT' QUALITY TO THE FRONTAL
STRUCTURE AND PRECIPITATION FOR SUNDAY (5/12Z TIME FRAME) BEHIND
THE LEADING EDGE OF THE COLD FRONT PROGRESSION THROUGH THE
SOUTHEAST/MID-ATLANTIC'S 'PORTION' OF THE COLD ADVECTION PATTERN.
BY DAY 5...THIS DETERMINISTIC 250MB JET STREAK SOLUTION AND ITS
OVERALL CHARACTER/DEPICTION LOSES CONTINUITY FAIRLY QUICKLY ALONG
75W LONGITUDE BETWEEN 40N-45N. BELIEVE PART OF THIS 'LOSS IN
CONTINUITY' IS MERELY THE LEADING EDGE OF A WEAK MID-LEVEL SYSTEM
MIGRATING INTO THE BASE OF THE UPPER-LEVEL---ORIGINATING IN THE
NORTHERN HIGH PLAINS (MID-TO UPPER-LEVEL PACIFIC INFLUENCES).
THOUGHT THE 31/00Z UKMET...GFS AND ECMWF DETERMINISTIC RUNS WERE
"EQUALLY-USEFUL" MODEL GUIDANCE THROUGH DAY 4 FROM WEST TO EAST
ACROSS THE LOWER 48.    

...UNCERTAINTY ASSESSMENT...
THE POST-FRONTAL PRECIPITATION PATTERN FOR SUNDAY INTO
MONDAY---ACROSS THE EAST AND APPALACHIA SEEMS TO BE WHERE THE
DETERMINISTIC GUIDANCE TENDS TO BREAK DOWN AND THE 'ADDED VALUE'
LOST. AND IN THE NORTHWEST...THE GUIDANCE HAS YET TO TRULY
'LOCK-IN' WITH THE TRANSITION (DAYS 4-6) WHEN THE PACIFIC
INFLUENCE SPREADS---IN EARNEST---EAST OF THE ROCKIES AND 100W
LONGITUDE.

THE 31/00Z CANADIAN DETERMINISTIC SOLUTION WOULD BE THE AGGRESSIVE
(AND FASTER) SOLUTION OVER THE NORTHERN DIVIDE AND
DOWNSTREAM---WITH RESPECT TO THE LEAD PACIFIC WAVE MIGRATING INTO
THE PLAINS (DAY 5-6). THIS WOULD LEAD TO A STRONGER WARM ADVECTION
PATTERN OVER THE CENTRAL ROCKIES EASTWARD INTO THE MIDDLE HALF OF
THE MISSISSIPPI VALLEY (AROUND 6/12Z) AND AN ACTIVE 250MB JET
STREAK EJECTING OUT ACROSS NORTHERN COLORADO/SOUTHEAST WYOMING.
CERTAINLY THE PATTERN (A MIGRATORY PACIFIC TROUGH) WOULD SUGGEST
THE FLOW PATTERN WILL CHANGE IN THE CENTRAL AND NORTHERN
PLAINS---THE CHALLENGE IS WITH THE ACCURACY OF THE DRASTIC CHANGE
IN SENSIBLE WEATHER...PRIMARILY ON THE TEMPERATURE AND CONVECTIVE
SIDE. WITH IT BEING DAY 6-7...WOULD RECOMMENDED A GEFS...NAEFS AND
ECENS BLEND FOR THE MOMENT. THIS SHOULD WORK FROM SOUTHWEST-TO-
NORTHEAST ACROSS THE LOWER 48...WITH EXCEPTION. THE EXCEPTION IS
THE MUCH SLOWER ECENS APPROACH OFF THE WEST COAST AT DAY 7. AND
WITH THE POSSIBILITY OF ONE OR MORE ROUNDS OF 'DRY-LINE STYLE'
ACROSS THE SOUTHERN AND WEST CENTRAL HIGH PLAINS. BELIEVE THAT
USING TOO MUCH ECENS---THIS FORECAST--- MIGHT 'MISS OUT' WITH SOME
OF THE PROGRESSIVENESS IN THE DOWNSTREAM PATTERN---AND POTENTIAL
MID-LEVEL ENERGY EXITING THE ROCKIES DURING THE DAY 4-6 TRANSITION
PERIOD. TO HANDLE THIS WEST-TO-EAST TRANSITION...USED MORE OF A
60/20 BLEND OF THE NAEFS/ECENS RESPECTIVELY FOR DAY 5 AND 80/20
BLEND AT DAY 7.
VOJTESAK

...SENSIBLE WEATHER HIGHLIGHTS...

MILD TEMPERATURES AHEAD OF THE COLD FRONT STRETCHED FROM THE GREAT
LAKES BACK TOWARD THE SOUTHERN PLAINS ON FRIDAY WILL BE REPLACED
BY COOLER THAN AVERAGE AIR FOR THE WEEKEND. TEMPERATURES IN THE
WEST SHOULD TREND COOLER WITH INCOMING LOWER HEIGHTS... BUT HARD
TO SAY TO WHAT DEGREE AND HOW FAR SOUTH ITS INFLUENCE WILL BE...
THUS THE HESITATION TO EXTEND BELOW AVERAGE TEMPS MUCH PAST THE
GREAT BASIN  AND CENTRAL ROCKIES. THE CENTRAL PLAINS AND SOUTHWEST
SHOULD HAVE ABOVE AVERAGE TEMPS. PRECIPITATION IS FORECAST TO
EXPAND THROUGH THE OHIO/MISSISSIPPI VALLEYS BY NEXT WEEK AS THE
UPPER TROUGH MOVES SLOWLY EASTWARD IN THE WEST.
FRACASSO