Preliminary Forecasts
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FXUS02 KWNH 060627
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
225 AM EDT FRI MAY 06 2016

VALID 12Z MON MAY 09 2016 - 12Z FRI MAY 13 2016

...OVERVIEW...
SPLIT-FLOW PATTERN RETURNS TO THE WEST COAST OF NORTH AMERICA AND
EAST OF THE DIVIDE --- THE FLOW GRADUALLY TRANSITIONS TO THIS
SPLIT-FLOW PATTERN AFTER DAY 6.

...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT...
FOR THE MOST PART...A BLEND OF THE 5/12Z ECENS...NAEFS AND GEFS
MEANS (40/30/30) SEEMED TO BE IN ORDER --- AFTER 11/12Z (BEGINNING
OF DAY 5) --- TO HANDLE THE SPLIT-FLOW PATTERN DETAILS DEVELOPING
EAST OF THE CONTINENTAL DIVIDE.

THE POINT OF DETERMINISTIC MODEL CONTENTION (LONGER TERM) REMAINS
--- IN THE NORTHERN BRANCH OF THE SPLIT-FLOW --- AND TIED TO THE
ENERGY ENTERING CANADA`S WEST COAST ON/AFTER 10/12Z. EARLY IN THE
PERIOD --- THE ENERGY MOVING SOUTHEASTWARD OUT OF ALBERTA APPEARS
TO DISLODGE THE SOUTHWEST US CUTOFF LOW --- AND SEND THE BULK OF
ITS ENERGY NORTHEASTWARD INTO THE GREAT LAKES/OHIO VALLEY. BUT
WHAT THE DETERMINISTIC GUIDANCE DIFFERS WITH --- IS RELATED TO THE
DETAILS OF THIS NORTHERN STREAM ENTITY`S MIGRATORY STORM TRACK.
AND ULTIMATELY ---ITS SENSIBLE WEATHER AND `LIFE-SPAN` ON/AFTER
DAY 5. UPSTREAM NORTHERN STREAM PACIFIC FLOW EITHER FEEDS MORE
NORTHERN STREAM ENERGY AND `INVIGORATES` THE MID-LEVEL SYSTEM INTO
A WELL-DEFINED CYCLONE THAT MARCHES VERY SLOWLY ACROSS THE
NORTHERN PLAINS AND UPPER MIDWEST --- OR SHEARS IT OUT RATHER
UNCEREMONIOUSLY DOWNSTREAM ACROSS ONTARIO AND THE ST LAWRENCE
VALLEY.

ALTHOUGH THE SPLIT-FLOW PATTERN`S SOUTHERN BRANCH (THE SOUTHERN
PLAINS TO THE MID-ATLANTIC REGION) SEEMED TO BE `WELL-MODELED` ---
THE EMBEDDED `DETAILS` IN THE WEST-SOUTHWESTERLY FLOW ALOFT
PRODUCES SOME SPACING CONCERNS DOWNSTREAM OF THE 5/5 0713Z SPC
DAY3 OUTLOOK. THE ORIGIN POINT FOR THE MID-LEVEL ENERGY SEEMS TO
BE A GREAT STARTING POINT AND THE MEDIUM RANGE FORECAST CHALLENGE
--- WHERE TO `TRACK` THE SHORTWAVE ENERGY DOWNSTREAM AND FOR HOW
LONG? TO THE MISSISSIPPI VALLEY, TO THE CENTRAL APPALACHIANS? OR
CARRY THE WAVE OUT TO SEA BETWEEN LONG ISLAND AND THE DELMARVA?
FOR THE MOST PART --- THE 5/12Z DETERMINISTIC GFS/ECMWF APPEARED
TO BE REASONABLE SOLUTIONS THROUGH DAY 4 WITH THE DEPTH OF A
POTENTIAL SURFACE WAVE --- TEEMING WITH --- RESIDUAL NORTHERN
STREAM MID-LEVEL ENERGY OVER CENTRAL QUEBEC. THESE TWO SOLUTIONS
OFFER ENOUGH FRONTAL WAVE `VARIANCE` AND TEMPERATURE
DISCONTINUITIES OVER THE EASTERN STATES AND ACROSS THE SOUTHERN
PLAINS --- TO LEAN TO THE ENSEMBLE APPROACH (60 PCT OF THE BLEND
---20 PCT OF EACH MEAN) THIS MORNING. --- FOR THE DAY 3-4 ENERGY
EXITING THE LOWER 48.

...SENSIBLE WEATHER HIGHLIGHTS...
THE DAY 3-4 SYSTEM EXITING THE SOUTH CENTRAL PLAINS IS EXPECTED TO
GENERATE DEEP CONVECTION --- WITH STEEP MID-LEVEL LAPSE RATES ---
PRODUCING SCATTERED TO NUMEROUS SHOWERS AND BELOW NORMAL
TEMPERATURES BENEATH THE COLD CORE MID-LEVEL CYCLONE. A
WEST-TO-EAST ORIENTATION OF THE PRECIPITATION AXIS (DOWNSTREAM) IS
ANTICIPATED FOR DAY 4 --- BETWEEN THE CENTRAL PLAINS AND THE OHIO
VALLEY --- BEFORE THE CYCLONE EXITS THE EAST COAST --- AND SPREADS
OUT A `NEW FRONTAL BOUNDARY` CONFIGURATION ACROSS THE SOUTHEAST
QUARTER OF THE COUNTRY.

ACROSS THE WEST...SPLIT-FLOW GENERATES A PERIOD OF OFFSHORE FLOW
AND MILD...TRANQUIL CONDITIONS ALONG THE COASTLINE --- AND ABOVE
NORMAL TEMPERATURES AND GENERALLY DRY WEATHER --- FOR THE INTERIOR
(WEST OF THE DIVIDE).

VOJTESAK

$$





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