Preliminary Forecasts
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12
000
FXUS02 KWNH 230622
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 AM EDT SAT AUG 23 2014

VALID 12Z TUE AUG 26 2014 - 12Z SAT AUG 30 2014

...PATTERN/MODEL EVALUATION...

THE PERIOD WILL BEGIN TUESDAY MORNING...26/1200Z...WITH A RATHER
AMPLIFIED MID-LEVEL PATTERN AS A BROAD TROF SLIDES THROUGH THE
INTERMOUNTAIN WEST/ROCKY MOUNTAIN REGION. FURTHER DOWNSTREAM AN
EXPANSIVE RIDGE WILL SET UP EXTENDING FROM THE MS RIVER VALLEY
EASTWARD TO THE EASTERN SEABOARD. OVER THE COURSE OF THE NEXT FEW
DAYS THE UPPER TROF WILL MIGRATE EASTWARD WHILE ADDITIONAL HEIGHT
FALLS TRAIL IN TO THE PACIFIC NORTHWEST BY DAYS 6/7. TWO OF THE
BIGGER UNCERTAINTIES IN THE FORECAST ARE HOW MUCH ENERGY PEELS OFF
THE UPPER TROF TOWARD THE CENTRAL PLAINS AND THE PROSPECTS FOR
TROPICAL DEVELOPMENT OVER HISPANIOLA. THE OVERNIGHT ASSESSMENT
FROM NHC SUGGEST TROPICAL CYCLONE FORMATION IS LIKELY WITHIN THE
NEXT 48 HOURS. OVERALL...THE MODELS ARE IN HALF DECENT AGREEMENT
ON DAY 3 WITH THE UPPER TROF ALTHOUGH THE 12Z UKMET CUTS OFF TOO
MUCH ENERGY ACROSS THE DESERT SOUTHWEST EARLY ON. THERE ARE A FEW
ENSEMBLE MEMBERS IN THE 576-DM SPAGHETTI PLOT SIGNIFYING WHAT THE
12Z UKMET SHOWS BUT IT LOOKS LIKE A MINORITY SOLUTION.
LIKEWISE...THE 18Z GFS TENDED TO LOOK TOO PROGRESSIVE WITH THE
NORTHERN STREAM WITH LITTLE INDICATION OF ENERGY SPLITTING OFF.
THE 12Z GFS AT LEAST WAS SUPPORTED BY THE 12Z ECMWF ALONG WITH THE
18Z GEFS/12Z ECMWF ENSEMBLE MEANS. BY DAY 4 ONWARD THE 12Z GFS
STARTS TO SPEED UP LIKE THE 18Z GFS WHICH TAKES IT AWAY FROM THE
SLOWER BUT MORE CLUSTERED ENSEMBLE MEANS. THE 12Z ECMWF ACTUALLY
FOLLOWS THE MEANS QUITE WELL UNTIL ABOUT DAY 5/6 WHEN THE MODELS
VARY ON THE AMPLITUDE/SPEED OF THE MID-LEVEL FLOW. BY DAY 7...AUG
30...IT APPEARS CERTAIN THAT ANOTHER UPPER TROF WILL CARVE ITS WAY
INTO THE PACIFIC NORTHWEST WITH HEIGHTS BUILDING OVER THE CENTER
OF THE U.S.

WITH REGARD TO THE POSSIBLE TROPICAL DEVELOPMENT AFFECTING
U.S...CONTINUED TO FOLLOW THE TRACK SUGGESTED BY THE AFTERNOON
MEDIUM RANGE COORDINATION CALL. THE 18Z GFS AND 12Z CMC/UKMET
DEFINITELY STRAYED AWAY FROM THIS AGREED UPON TRACK AS THESE
MODELS CARRIED THE AREA OF LOW PRESSURE INTO FL AND/OR ACROSS THE
GULF OF MEXICO. THE 12Z GFS/ECMWF AND 18Z GEFS/12Z ECMWF ENSEMBLE
MEANS WERE CLOSEST TO THE COORDINATED POINTS WHICH KEPT THE
SURFACE LOW SOMEWHERE BETWEEN THE EASTERN U.S. AND BERMUDA.


...WPC PREFERENCE...

AS ALLUDED TO...STAYED AWAY FROM THE 18Z GFS GIVEN ITS MORE
PROGRESSIVE SOLUTION WITH THE CENTRAL U.S. UPPER TROF WHILE ALSO
DISREGARDING ITS MORE WESTERN TROPICAL SOLUTION. UTILIZED A
COMBINATION OF THE 12Z GFS/ECMWF FOR DAY 3 BUT QUICKLY REMOVED THE
12Z GFS BY DAY 4 AS IT BECAME QUICKER WITH THE SYNOPTIC SCALE
TROF. FOR DAYS 4 THROUGH 6 FAVORED A BLEND OF THE 12Z ECMWF WITH
THE 18Z GEFS/12Z ECMWF ENSEMBLE MEAN WITH INCREASED PERCENTAGES OF
THE MEANS TOWARD DAY 6. BY DAY 7 STAYED ENTIRELY WITH THE ENSEMBLE
MEANS...50/50 18Z GEFS/12Z ECMWF ENSEMBLE MEANS GIVEN INCREASING
SPREAD NOTED IN ALL RELEVANT SPAGHETTI PLOTS.


...SENSIBLE WEATHER HIGHLIGHTS...

ONE OF THE BIG STORIES DURING THE MEDIUM RANGE WILL BE THE COOL
CONDITIONS AFFECTING A SIGNIFICANT PORTION OF THE NORTHERN
TIER...ESPECIALLY ON DAYS 3/4. HIGHS ARE EXPECTED TO ONLY BE IN
THE LOW/MID 60S WHICH IS APPROXIMATELY 15 TO 20 DEGREES BELOW
NORMAL. THIS STRETCHES FROM THE NORTHERN ROCKIES EASTWARD TO THE
UPPER GREAT LAKES. MEANWHILE...TEMPERATURES SHOULD SOAR OVER THE
SOUTHERN PLAINS AS HIGH TEMPERATURES APPROACH AND LOCALLY EXCEED
THE CENTURY MARK. THE SHARP BAROCLINIC ZONE SEPARATING THESE TWO
DISTINCT AIR MASSES WILL BE A SITE FOR HEAVY RAINFALL OVER THE
CENTER OF THE COUNTRY. THIS THREAT WILL EVENTUALLY SHIFT EASTWARD
IN TIME TOWARD THE END OF THE MEDIUM RANGE PERIOD. OF
COURSE...INTERESTED PARTIES ACROSS THE U.S. WILL HAVE TO FOLLOW
THE TROPICAL DEVELOPMENT ACROSS HISPANIOLA AS SOME MODELS HAVE
TRACKS APPROACHING THE EASTERN U.S.


RUBIN-OSTER

$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.