Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 220655
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EDT FRI AUG 22 2014

VALID 12Z MON AUG 25 2014 - 12Z FRI AUG 29 2014

...FLOW PATTERN/WEATHER HIGHLIGHTS AND GUIDANCE/UNCERTAINTY
ASSESSMENT...

THE PERIOD BEGINNING NEXT WEEK WILL FEATURE A VERY AMPLIFIED
PATTERN WITH AN UPPER TROF DIGGING INTO THE PACIFIC
NORTHWEST/NORTHERN PLAINS WHILE A BROAD 588-DM RIDGE ENCOMPASSES
THE SOUTHERN PLAINS EASTWARD TO THE EAST COAST. THIS SYNOPTIC
PATTERN IS FORECAST TO GRADUALLY SLIDE EASTWARD CARRYING HEIGHT
FALLS INTO THE MS RIVER VALLEY BY MID-WEEK WITH THE RIDGE
ANCHORING THE EASTERN STATES. EVENTUALLY THE LONGWAVE TROF SHOULD
REACH THE EASTERN THIRD OF THE COUNTRY BY EARLY FRIDAY/AUG 29 WITH
THE GUIDANCE VARYING IN TIMING/AMPLITUDE OF THIS TROF. ONE
DIFFICULTY IN THE FORECAST IS RESOLVING THE POTENTIAL TROPICAL
DEVELOPMENT WITH THE AREA OF DISTURBED WEATHER AROUND 18N/62W. THE
NHC CURRENTLY INDICATES AN 80 PERCENT LIKELIHOOD OF DEVELOPMENT
INTO A TROPICAL CYCLONE DURING THE NEXT 5 DAYS BASED ON THE 06Z
OUTLOOK. THE GUIDANCE IS DEFINITELY AT ODDS WITH WHATEVER
MATERIALIZES WITH THE 12Z UKMET/CMC BOTH CARRYING THE AREA OF LOW
PRESSURE INTO THE GULF OF MEXICO. DEFINITELY DID NOT BUY THOSE
SOLUTIONS AND LEANED MORE CLOSELY ON THE MEDIUM RANGE COORDINATION
CALL WHICH FAVORED SOMETHING OVER THE WESTERN ATLANTIC.

WITH REGARD TO THE SYNOPTIC PATTERN ACROSS THE CONUS...THE MODELS
VARY WITH THE TIMING OF THE NORTHERN STREAM TROF SLIDING ACROSS
THE CENTER OF THE COUNTRY. THE 18Z GFS/GEFS MEAN WERE DECIDEDLY
SLOWER LATER IN THE FORECAST WHICH WAS WELL ADVERTISED BY THE
SPREAD NOTED IN THE 564-DM SPAGHETTI PLOTS. THIS GFS SUITE OF
SOLUTIONS WERE DEFINITELY SLOWER AND MORE AMPLIFIED WITH THE
PATTERN VERSUS THE MORE PROGRESSIVE 12Z ECMWF/ECMWF ENSEMBLE MEAN
SOLUTIONS. EVEN MORE EXTREME IS THE 12Z CMC WHICH CUTS-OFF ENERGY
OVER THE CENTRAL GREAT BASIN. THIS SEEMS UNLIKELY AS IT CARRIES
LONGWAVE ENERGY MUCH FARTHER SOUTHWEST THAN ANY PIECE OF GUIDANCE
ACROSS THE WESTERN U.S. FOR DAYS 3/4...FELT COMFORTABLE
INCORPORATING EQUAL CONTRIBUTIONS FROM THE 18Z GFS/12Z ECMWF WITH
A SMIDGE OF 12Z UKMET. DEFINITELY HAD TO TAKE 12Z UKMET OUT OF THE
EQUATION THEREAFTER GIVEN ITS HANDLING OF THE DISTURBANCE EAST OF
THE CARIBBEAN. BY DAY 5...ENDED UP DISREGARDING THE SLOWER 18Z GFS
ACROSS THE NORTHERN TIER AS IT WAS EVEN BECOMING SLOWER THAN ITS
OWN MEAN. THE REMAINING TWO DAYS WERE DOMINATED BY THE 18Z
GEFS/12Z ECMWF ENSEMBLE MEANS WITH A SLIGHT EDGE TO THE LATTER.
THE UPPER PATTERN DID NOT APPEAR TO SUPPORT SUCH A SLOW SOLUTION
AS THE GFS/GEFS MEAN BUT KEPT THE IDEA IN THE MODEL BLEND GIVEN
THE INCREASING FORECAST SPREAD.

IT SHOULD BE A RELATIVELY COOL PERIOD FOR THE NORTHERN U.S. WITH
HIGH TEMPERATURES ONLY IN THE 60S FROM THE UPPER INTERMOUNTAIN
WEST EASTWARD INTO THE UPPER GREAT LAKES. SUCH VALUES ARE ABOUT 15
TO 20 DEGREES BELOW NORMAL. MEANWHILE...FORECAST HIGHS SHOULD SOAR
OVER THE SOUTHERN/CENTRAL PLAINS AND INTO THE MS RIVER VALLEY WITH
TEMPERATURES WELL INTO THE 90S. THE SHARP BAROCLINIC ZONE BOUNDING
THESE TWO REGIONS WILL BE THE FOCUS FOR HEAVY RAINFALL MOVING FROM
WEST TO EAST. MEANWHILE...ACROSS THE EASTERN U.S...COOL CONDITIONS
SHOULD PREVAIL WITH A SURFACE HIGH ANCHORING THE REGION. THIS WILL
BE PARTICULARLY NOTED IN THE OVERNIGHT TEMPERATURES WITH LOWS IN
THE 50S ACROSS NEW ENGLAND AND DOWN INTO THE CENTRAL APPALACHIANS.
OF COURSE THE FLY IN THE OINTMENT IN THE MEDIUM RANGE PATTERN IS
THE POTENTIAL IMPACTS FROM THE AREA OF DISTURBED WEATHER EAST OF
PUERTO RICO.


RUBIN-OSTER

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