Preliminary Forecasts
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FXUS02 KWNH 250618
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
212 AM EDT THU AUG 25 2016

VALID 12Z SUN AUG 28 2016 - 12Z THU SEP 01 2016

THE SYNOPTIC-SCALE PATTERN SEEMED STRAIGHT FORWARD ENOUGH ACROSS
MID-LATITUDE NORTH AMERICA TO GO WITH A BLEND OF THE 24/12Z
DETERMINISTIC GFS/ECMWF RUNS AND THE 3 ENSEMBLE MEANS THROUGH DAY
5. AND THIS WOULD SEEM TO WORK FOR THE LOWER 48 FORECAST WITH A
SW-TO-NE ORIENTATION OF THE UPPER-LEVEL TROUGH AXIS WEST OF THE
DIVIDE AND THE CONFIGURATION OF THE DOWNSTREAM RIDGE AXIS NESTLED
IN ACROSS THE EAST CENTRAL STATES.

WHAT DIFFERENCES THERE WERE OVER ARCTIC CANADA HAVE SETTLED INTO
BETTER AGREEMENT NOW. AT LEAST THROUGH DAY 7 --- THE
ECENS/CANADIAN MEANS KEEPS THE FLOW IN A PROGRESSIVE WESTERLY
ZONAL CONFIGURATION ACROSS NORTHERN CANADA --- RATHER THAN WHAT
THE GEFS CARRIED --- A LONGWAVE TROUGH EAST OF THE CONTINENTAL
DIVIDE ALONG 105W. MIND YOU --- THE GEFS STILL WANTS TO RETROGRADE
COLD AIR WESTWARD OVER NORTHWEST CANADA AND RELOAD THE COLD POOL
INVOF 55N 130W --- BUT THAT `TREND` IF IT SHOULD VERIFY --- SHOULD
NOT IMPACT THE ZONAL FLOW AND PROGRESSIVE NATURE OF THE SHORTWAVES
ALONG THE US/CANADA BORDER FOR THE REMAINDER OF THIS MEDIUM RANGE
PERIOD.

THINGS BEGIN TO `CHANGE` AFTER DAY 5 --- WITH THE SMALLER-SCALE
DETAILS EMBEDDED WITHIN THE UPPER-LEVEL TROUGH ALONG THE WEST
COAST --- IF YOU BELIEVE THE GFS/GEFS AND THE TROUGH OVER THE
ALASKA PANHANDLE FILLING WITH ANOTHER SHOT OF COLD ARCTIC AIR.
SUGGEST A BLEND OF THE ECENS/NAEFS MEANS TO HOLD THE PATTERN ALOFT
IN PLACE BETWEEN DAYS 6-8 AND USE CAUTION WITH ANY OF THE
DETERMINISTIC GUIDANCE --- THAT WANTS TO PHASE A DEEP 500MB TROUGH
ACROSS THE OLYMPIC PENINSULA AND TRACK THIS PHASED ENERGY EASTWARD.

THE ONLY PLACE THAT LOOKED LIKE IT STILL REQUIRED A BIT OF `MANUAL
INTERVENTION` --- WAS ACROSS THE EASTERN HALF OF THE GULF OF
MEXICO AND FLORIDA. UNFORTUNATELY, NOT USING A SPECIFIC
DETERMINISTIC MODEL RUN (FOR OBVIOUS REASONS) WASHES OUT THE WIND
GRIDS. THE `APPEARANCE` OF A SURFACE CYCLONE DOES HAVE SOME FORM
FOR DAY 3-4 ACROSS THE EVERGLADES --- WITH LIMITED SUCCESS. THIS
AFTER MANUALLY INSERTING A CLOSED LOW AT 500MB AND AT THE SURFACE
IN THE WPC GRAPHICS. LIKEWISE...THOUGHT THE DAYTIME TEMPERATURES
SEEM A TAD TOO HIGH --- ESPECIALLY IN ANTICIPATION OF A RATHER
BROAD CLOUD SHIELD TO MIGRATE ACROSS THE SOUTHERN HALF OF FLORIDA
AND GRADUALLY SETTLE IN ACROSS THE NORTHEAST QUARTER OF THE GULF
OF MEXICO DURING THIS PARTICULAR MEDIUM RANGE PERIOD.

AS HAS BEEN THE CASE THE PREVIOUS TWO MID SHIFTS --- THE CHALLENGE
IS TO DECIDE WHICH DETERMINISTIC RUN TO FEATURE IN THE D4-5 AND
D6-7 QPFS WITHIN THE `BIG PICTURE` SYNOPTIC-SCALE ENVIRONMENT
DEPICTED FROM THE NAEFS/ECENS MEAN PRECIPITATION OUTPUT. GENERALLY
HAVE LIKED THE 27KM HI-RES ECMWF FOR THIS SCENARIO --- SO I WILL
KEEP THIS IN MIND AGAIN TONIGHT.

VOJTESAK







$$





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