Weather Forecast Medium Range Outlook Aug 07

By: National Weather Service
By: National Weather Service


VALID 12Z TUE AUG 10 2010 - 12Z SAT AUG 14 2010

THE LONGWAVE PATTERN STARTS OFF WITH A FAR WRN NOAM TROF....A FLAT
CENTRAL NOAM RIDGE...AND A DEEP NEGATIVE HEIGHT ANOMALY OVER NERN
CANADA WITH A TROF EXTENDING SWD TO OFF THE NEW ENG COAST. THE
PATTERN ACROSS THE USA/CANADIAN BORDER IS EXPECTED TO FLATTEN BY
THE MIDDLE OF NEXT WEEK....BUT THE SMALLER SCALE SHORTWAVES WILL
BE BELOW AVERAGE CONFIDENCE.

AFTER AN INITIAL SURGE OF ANOMALOUS HEIGHT FALLS TUE INTO THE
PACIFIC NW....THE 00Z/07 GUIDANCE WAS IN GENERAL AGREEMENT THAT
THE TROFFING NEAR THE PACIFIC NW COAST TUESDAY WOULD SHEAR
APART...WITH A GOOD CHUNK OF HEIGHT FALLS GOING ENE INTO CENTRAL
CANADA BY NEXT WEEKEND. ALSO...A NUMBER OF GEFS AND ECMWF ENSEMBLE
MEMBERS TOOK A PORTION OF THE TROF/CLOSED LOW SW TO A POSITION
NEAR/W OF THE NRN CA COAST BY THU/FRI. NEW 12Z/07 MODEL GUIDANCE
BECOME QUITE INCONCLUSIVE BEYOND DAY 4 IN DETERMINING HOW MUCH
HEIGHT FALL MOVES ENE OUT OF THE PACIFIC NW TROF TOWARDS S CENTRAL
CANADA...VERSUS HOW MUCH GETS LEFT BEHIND OFF THE CA COAST...OR
SOMEWHERE IN BETWEEN! THE IN BETWEEN SOLUTIONS OF THE 12Z ECMWF
AND UKMET SHOW ALMOST A CLOSED LOW OVER NRN ID FOR FRI DAY 6!
TELECONNECTIONS ON THE STRONG RIDGE BUILDING INTO THE NE PACIFIC
GENERALLY FAVOR THE PATTERN OFFERED BY THE 00Z/07 ECMWF ENSEMBLE
MEAN...SO OUR ONLY CHANGE TO THE UPDATED PRELIM SURFACE WILL BE TO
WEAKEN THE GRADIENTS OVER THE NWRN PORTION OF THE CONUS FRI/SAT
DAYS 6-7 GIVEN THE UNCERTAINTY.

THE MOST RECENT 00Z/12Z ECMWF 850MB PROGS MOVE AN AREA OF VERY
HIGH PWS ACROSS FL IN THE NEXT TWO DAYS ALONG WITH A
CIRCULATION...LEAVING PLENTY OF LOW LEVEL MOISTURE BEHIND NEXT
WEEK. WE BELIEVE THAT ALL MODELS ARE DEFICIENT IN QPF OVER MOST OF
FL AND THE GULF COAST REGION AT LEAST INTO DAY 5 AND POSSIBLY
LONGER. ELSEWHERE...CONVECTION WILL BE DRIVEN BY FRONTAL ACTIVITY
AND OUTFLOW BOUNDARIES WITH THE MIDWEST LIKELY SEEING THE LIONS
SHARE OF THIS ACTIVITY. THE QPF FORECAST DAY 5 AND BEYOND WILL BE
LOW CONFIDENCE GIVEN SO MUCH SPREAD DEVELOPING IN THE NEW GUIDANCE
OVER THE NW QUADRANT OF THE CONUS.

FLOOD


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