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 13 14
000
FXUS02 KWNH 240608
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
207 AM EDT SUN MAY 24 2015

VALID 12Z WED MAY 27 2015 - 12Z SUN MAY 31 2015

...OVERVIEW...
SUMMER-LIKE CONDITIONS WILL PREVAIL ACROSS THE EASTERN PORTION OF
THE NATION ---BENEATH A DEEP-LAYERED RIDGE ANCHORING ACROSS THE
SOUTHEAST MOST OF THIS MEDIUM RANGE PERIOD. SPLIT-FLOW PATTERN IN
THE EASTERN PACIFIC --- DIRECTS THE MAJORITY OF THE SENSIBLE
WEATHER AND PRECIPITATION TOWARDS THE PACIFIC NORTHWEST AND
NORTHERN ROCKIES.

...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT...
GENERALLY ACCEPT THE ECENS/NAEFS VERSION OF THE SYNOPTIC-SCALE
PATTERN THIS MEDIUM RANGE PERIOD. THE KEY FEATURES OF THE PATTERN
REMAIN CONSISTENT --- WITH AMPLIFICATION OF THE SOUTHEAST RIDGE
SHUNTING FRONTS INTO THE ST LAWRENCE VALLEY AND NEW ENGLAND. AND
ALONG THE WEST COAST OF NORTH AMERICA --- A SPLIT-FLOW PATTERN ---
WITH HIGH LATITUDE PACIFIC FLOW `UNDERCUTTING` A QUASI-STATIONARY
RIDGE DRAPED ACROSS INTERIOR ALASKA AND THE YUKON.

THE 23/12Z AND 23/18Z DETERMINISTIC GFS/GEFS MEAN ARE THE
SOLUTIONS THAT WOULD BE TROUBLESOME FOR BOTH COASTS--- THIS MEDIUM
RANGE PERIOD. IN THAT --- THEIR SOLUTIONS WERE QUICKER TO
`SUPPRESS` THE RIDGE ALONG THE EAST COAST AND FARTHEST SOUTH ALONG
THE WEST COAST --- WITH THE ENTRY POINT FOR UNDERCUTTING PACIFIC
ENERGY.

OVER THE CENTRAL PORTION OF THE COUNTRY --- INCLUDING CENTRAL
ROCKIES --- THE GFS/GEFS SOLUTIONS WERE NOT BAD AT ALL. BUT ITS
THE WED-THU FRONTAL PASSAGE ACROSS THE APPALACHIANS --- AND
INSISTENCE ON A MUCH DEEPER SOLUTION ALOFT ALONG THE
ONTARIO/QUEBEC BORDER --- THAT ALLOWS THE SOUTHEAST RIDGE TO BE
FLATTENED SUBSTANTIALLY AND CREATES MORE WESTERLY FLOW ALOFT FROM
THE OHIO VALLEY TO THE DELMARVA FOR THE LATTER HALF OF THE
FORECAST PERIOD.

TO MAINTAIN BETTER CONTINUITY WITH THE PREVIOUS WPC GRAPHICS ---
USED THE 23/12Z ECENS/NAEFS AND BLENDED (FOR DETAIL) THE 23/12Z
DETERMINISTIC ECMWF THROUGH FRIDAY AFTERNOON/EVENING (30/00Z).

...SENSIBLE WEATHER HIGHLIGHTS...
SUMMER-LIKE PATTERN FOR THE EAST...WITH HIT-N-MISS AFTERNOON AND
EVENING AIRMASS POP-UP SHOWERS/THUNDERSTORM ACTIVITY. THE MORE
ORGANIZED AREAS OF PRECIPITATION WILL FOLLOW THE WEST THROUGH
NORTHWEST FLANKS OF THE MID-LEVEL RIDGE --- INCLUDING THE SOUTH
CENTRAL PLAINS...OZARKS...MID-MS & WESTERN OHIO VALLEYS AND
EASTERN LAKES/NORTHERN NEW ENGLAND---WHERE THE MID-CONTINENT FRONT
HAS A PATHWAY TO MIGRATE ---IN NORTHEASTWARD FASHION TOWARDS THE
ST LAWRENCE VALLEY AND NORTHERN NEW ENGLAND.

CONVECTION SHOULD BE ON THE INCREASE ACROSS THE OKANAGAN REGION OF
BC/WA...THE NORTHERN DIVIDE AND ADJACENT NORTHERN HIGH PLAINS THIS
MEDIUM RANGE PERIOD AS MID-LEVEL ENERGY MIGRATES SOUTHEASTWARD
FROM THE MOUNTAINS OF SOUTHWEST CANADA AND SOUTHERN ALASKA
PANHANDLE.

ALONG THE WEST COAST --- THE SPLIT-FLOW PATTERN WILL PROVIDE A
GRADUAL WARMING/DRYING TREND ACROSS THE SOUTHWEST DESERTS AND
INTERIOR CALIFORNIA. AN AMPLIFYING SURFACE RIDGE OVER THE GULF OF
ALASKA WILL PRODUCE AN ONSHORE NORTHWESTERLY FLOW ACROSS THE
PACIFIC NORTHWEST.

VOJTESAK

$$




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