Prognostic Meteorological Discussion
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FXUS02 KWBC 301539
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1138 AM EDT TUE AUG 30 2016

VALID 12Z FRI SEP 02 2016 - 12Z TUE SEP 06 2016

...OVERVIEW...

GUIDANCE CONFIDENTLY SHOWS THE MEAN PATTERN SETTLING INTO AN ERN
PAC RIDGE/WRN U.S. TROUGH/ERN RIDGE AND WEAKNESS OFF THE EAST
COAST CONFIGURATION BUT WITH SOME DEFINITE UNCERTAINTIES FOR THE
MEDIUM RANGE PERIOD. THE DIFFERENCES INCLUDE SHRTWV DETAILS WITHIN
THE WRN TROUGH BEFORE THESE IMPULSES EMERGE ACROSS THE MIDWEST AND
THE ENTIRE WEAKNESS OFFSHORE OF THE EAST COAST... WHETHER IT
INCLUDES TD 9. AS FOR THE TROPICS... THE NATIONAL HURRICANE CENTER
IS ISSUING ADVISORIES ON TD 8 WHICH SHOULD BE EXTRA-TROPICAL BY
FRI AND OUT OF THE PICTURE. HOWEVER TD 9... WHICH IS FCST TO CROSS
NRN FLORIDA IN THE LATTER PART OF THE SHORT RANGE PERIOD AND
EMERGE OVER THE WRN ATLANTIC... A LARGE AMOUNT OF SPREAD DEVELOPS
ON WHETHER THE INITIAL EAST COAST TROUGH ACCELERATES 9 INTO THE
OPEN WATERS OF THE ATLANTIC OR 9 GET LEFT BEHIND OFF THE EAST
COAST WITH A WEAKNESS.


...GUIDANCE/UNCERTAINTY ASSESSMENT...

WPC WENT WITH A 50/50 OPERATIONAL GFS/ECMWF ON FRI... TRANSITION
TO A 60 EC/EC MEAN 40 GFS/GEFS MEAN OVER THE WEEKEND AND FOR LABOR
DAY AND NEXT TUES A 90 EC/EC MEAN/GEFS MEAN AND 10 GFS BLEND.

THE GUIDANCE IS VERY SIMILAR EARLY ON WITH THE WRN MEAN TROUGH...
AS A STRONG EMBEDDED SHORT WAVE LIFTS FROM THE PAC NW TO THE NRN
PLAINS/CENTRAL CANADA. SOME SLIGHT SPREAD ON THE PROGRESSION OF
THE SHORT WAVE... AS GFS APPEARS TO BE A SLOWER OUTLIER. AS THIS
DEEPENING SYSTEM GOES THROUGH COMPLETE CYCLOGENESIS OVER CANADA
AND WEST/SW OF HUDSON BAY OVER THE WEEKEND... ADDITIONAL PAC
DYNAMICS DIVE INTO THE WRN TROUGH. THE GFS HERE IS STILL A BIT
MORE BULLISH WITH THIS IMPULSE ARRIVING INTO THE PAC NW/NRN
ROCKIES AND ADVANCING DOWNSTREAM. BY LATE IN THE FCST PERIOD...
THE MEAN TROUGH BECOMES LESS AMPLIFIED AND BROADEN... STRETCHING
FROM THE PAC NW COAST TO THE WRN GREAT LAKES.

THE FCST OVER THE EAST SEEMS PRETTY STRAIGHT FORWARD AT THE
BEGINNING OF THE PERIOD... AS POSITIVE TILTED TROUGH OVER THE EAST
SHOULD PICK UP TD 9... WHICH WILL BE JUST OFFSHORE OF THE
SOUTHEAST. THE TROPICAL SYSTEM ADVANCES NORTH AND EAST ON FRI
AHEAD OF THE UPPER TROUGH/SURFACE FRONT BUT BY SAT... TREMENDOUS
SPREAD DEVELOPS. THE EC/EC MEAN ALLOW THE TROUGH TO ADVANCE TD 9
INTO THE OPEN WATERS OF THE ATLANTIC AND EXTEND THE WEAKNESS FROM
THE DEEP SYSTEM TO THE SOUTHEAST COAST. THE GFS/CANADIAN/GEFS MEAN
ALLOW THE WESTERLIES AND TROUGH TO ADVANCE DOWNSTREAM... A PIECE
OF UPPER DYNAMICS TO DIG TOWARD THE CAROLINAS AND THIS LEAVES TD 9
HOVERING JUST OFFSHORE OF THE MID-ATL/NORTHEAST THROUGH THE
HOLIDAY WEEKEND. THE UKMET APPEARS TO BE THE MORE MIDDLE OF THE
ROAD SOLUTION.


...WEATHER HIGHLIGHTS/THREATS...

THOSE NEAR THE EAST COAST... AND THE SOUTHEAST/SRN MID ATLC COAST
IN PARTICULAR... SHOULD CONTINUE TO MONITOR FCSTS FOR T.D. NINE
WHICH WILL LIKELY BE ACCOMPANIED BY HVY RAIN/STRONG WINDS. THE
EXTENT TO WHICH THE REST OF THE EAST COAST SEES ANY EFFECTS FROM
T.D. NINE IS VERY UNCERTAIN AT THIS TIME. FROM THE NORTHWEST INTO
THE PLAINS... MAJORITY OF PAC NW AND NRN ROCKIES PRECIP SHOULD
OCCUR AT THE BEGINNING OF THE FCST PERIOD. THE SURFACE COLD FRONT
WILL SURGE OUT INTO THE PLAINS BUT MOVE EXTREMELY SLOWLY AND
SHOULD BE A FOCUS FOR CONVECTIVE HEAVY RAINFALL FROM THE CENTRAL
PLAINS/MID MS VALLEY TO THE UPPER MIDWEST/UPPER MS VALLEY AND WRN
GREAT LAKES. ELSEWHERE EXPECT SOME LINGERING DIURNAL RNFL OVER FL
AND NEAR THE GULF COAST.

THE NRN PLAINS WILL SEE THE MOST DRAMATIC CHANGE IN TEMPS DURING
THE FCST PERIOD AS ADVANCING COOL AIR OVER THE WEST DISPLACES LATE
WEEK HEAT. NRN PLAINS HIGHS SHOULD BE 10-20F ABOVE NORMAL FRI BUT
THEN FALL TO 5-15F BELOW NORMAL BY SUN-MON. HIGH PRESSURE BUILDING
INTO THE EAST WILL BRING NEAR TO SLIGHTLY BELOW NORMAL TEMPS
DURING THE FIRST HALF OF THE PERIOD BUT WARM FLOW ON THE WRN SIDE
OF THE HIGH WILL LIKELY PUSH HIGHS 10-15F ABOVE NORMAL FROM THE OH
VLY/GRTLKS INTO NORTHEAST BY EARLY NEXT WEEK.

MUSHER/RAUSCH

$$





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