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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1557Z Apr 19, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EDT SAT APR 19 2014

VALID 12Z TUE APR 22 2014 - 12Z SAT APR 26 2014

...OVERVIEW...
A RELATIVELY-STABLE WAVE PATTERN AT MID-LATITUDES WILL PRODUCE A
SERIES OF MIGRATORY SYSTEMS FOR THE LOWER 48.

...MODEL PREFERENCES/UNCERTAINTY ASSESSMENTS/SENSIBLE WEATHER
HIGHLIGHTS......
THE 19/00Z MODEL CYCLE...EXCLUDING THE DETERMINISTIC
CANADIAN...SEEMED TO REASONABLY DEPICT THE SERIES OF MIGRATORY
SYSTEMS TRAVERSING THE EASTERN PACIFIC...WEST COAST ...MIDWEST
...AND NORTHEAST THROUGH DAY 6. FOR THE PAST 2 to 3 DAYS...THE
MODEL GUIDANCE HAS DONE A NICE JOB OF TIMING THE PATTERN AND ITS
REPLACEMENT--EAST OF THE ROCKIES. IE...FROM A
MULTI-WAVE...SPLIT-FLOW TYPE PATTERN EXITING THE EASTERN CONUS
(DAY 3-4)...TO ONE THAT GIVES THE APPEARANCE OF A SERIES OF
HIGHER-AMPLITUDE TROUGHS ACCOMPANIED BY BROAD SHORTWAVE RIDGES.

THE 19/00Z ENSEMBLE SPREAD IS A RATHER TIGHTLY-CLUSTERED SET OF
SOLUTIONS. THE 19/00Z GEFS/ECENS MEANS AND THEIR DETERMINISTIC
RUNS COULD EASILY BE BLENDED INTO DAY 6 (26/00Z) ACROSS THE GREAT
LAKES...INVOF HAIDA GWAII (QUEEN CHARLOTTE ISLAND) AND SOUTH OF
PRINCE EDWARD ISLAND.

A NEGATIVE-TILT TROUGH AXIS SOLUTION INVOF 50N LAT 130W LONG...IS
THE ACCEPTED SOURCE REGION AND ENTRY POINT FOR A STORM TRACK THAT
WILL MAINTAIN A SPRING RAIN/HIGH ELEVATION SNOW PATTERN IN THE
NORTHWEST AFTER DAY 5. ASIDE FROM THE EARLY DAY 3 SYSTEM TRACKING
THROUGH THE NORTHERN ROCKIES...THE SOUTHERN EXTENSIONS OF THE
PACIFIC COLD FRONTS...WILL BE ESSENTIALLY DRY--(EXCEPT AT HIGH
ELEVATION)--AND BREEZY/WINDY EVENTS FOR THE I-80 CORRIDOR FROM THE
BAY AREA TO THE GREAT BASIN AND THROUGH THE CENTRAL ROCKIES.

DOWNSTREAM...ALONG AND EAST OF THE CONTINENTAL DIVIDE (ALONG THIS
I-80 CORRIDOR)...THE HIGHER-AMPLITUDE FLOW ALLOWS SHORTWAVE RIDGES
TO BROADEN WARM ADVECTION AND EXPAND BREEZY CONDITIONS NORTHWARD
FROM THE SOUTHERN PLAINS TO THE MIDWEST/OHIO VALLEY. AND ALTHOUGH
THIS PATTERN DOES NOT FAVOR AN OPEN-GULF LOW-LEVEL MOISTURE FEED
INTO THE MISSOURI VALLEY BASIN...A DRYLINE-TYPE CONVECTIVE PATTERN
DOES BODE WELL FOR WEST TEXAS...EASTERN NEW MEXICO...WESTERN
OKLAHOMA...EASTERN COLORADO AND WESTERN KANSAS. HIT-N-MISS
CONVECTION AND ISOLATED HEAVY RAINFALL POTENTIAL...INCLUDING
NOCTURNAL SHOWERS...ARE ANTICIPATED AHEAD OF THE DRY LINE. 

DAYS 3-4...AND ALONG THE DRYLINE...THE CHALLENGE APPEARS TO BE HOW
EXPANSIVE THE DRY-ADIABATIC WARMING WILL BE...FOR THE SOUTHERN AND
CENTRAL HIGH PLAINS. THE DRY AIR INTRUSION AND RAPIDLY-SOARING
TEMPERATURES COULD EASILY BEGIN TO TRANSLATE NORTHEASTWARD INTO
THE LOWER MISSOURI VALLEY...OZARKS AND WESTERN OHIO VALLEY INTO
DAY 5...AS A SLOWLY-AMPLIFYING SURFACE WAVE TAKES SHAPE OVER THE
NORTHERN PLAINS AND GREAT LAKES. THE DETERMINISTIC 19/00Z
GFS/ECMWF GENERALLY DEPICT A SUB 994MB SURFACE LOW INVOF
SOUTHEAST/SOUTH CENTRAL SOUTH DAKOTA AROUND 24/12Z. THERE ARE SOME
SLIGHT DIFFERENCES BEYOND DAY 5 WITH THE CYCLONE TRACK AND DEPTH
THROUGH THE NORTHEAST...BUT A BLEND OF THE ECENS/GEFS MEANS
APPEARED A GOOD MIDDLE GROUND FOR NOW.

VOJTESAK