Prognostic Meteorological Discussion
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FXUS02 KWBC 190458
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1258 AM EDT SAT AUG 19 2017

VALID 12Z TUE AUG 22 2017 - 12Z SAT AUG 26 2017

...OVERVIEW...

NORTHERN HEMISPHERE WILL DO A LITTLE ATMOSPHERIC SHUFFLING NEXT
WEEK WHICH WILL BE FORCED BY STRONG BLOCKING IN THE NORTH ATLANTIC
AND INCREASED TROUGHING INTO THE NORTHEAST. RIDGING IN THE PAC NW
WILL ONLY TEMPORARILY YIELD AS TROUGHING FROM THE GULF OF ALASKA
TRIES TO DIP INTO SOUTHERN BRITISH COLUMBIA. THIS WILL BRING A
COLD FRONT EASTWARD AND SOUTHWARD, USHERING IN COOLER AIR (NEAR TO
A FEW DEGREES BELOW AVERAGE) BY NEXT WEEKEND IN THE GREAT LAKES
AND NORTHEAST.



...GUIDANCE EVALUATION/PREFERENCES...

MODELS/ENSEMBLES SHOW BETTER AGREEMENT WITH THE SFC LOW EXITING
OUT OF THE GREAT LAKES ON TUESDAY THROUGH ONTARIO AND QUEBEC
THOUGH THE 12Z GFS WAS SLOWER/DEEPER THAN THE OTHER 12Z MODELS AND
ENSEMBLE MEANS. A BLEND OF THE 18Z GFS/GEFS MEAN AND THE 12Z
ECMWF/ECENS MEAN OFFERED A GOOD STARTING POINT FOR NEXT WED-FRI.
QUESTION REMAINS HOW TO HANDLE THE UPPER LOW EXITING THE GULF OF
ALASKA -- STRONGER/DEEPER AND FARTHER SOUTH INTO SOUTHERN BRITISH
COLUMBIA (GFS AND PERHAPS THE UKMET IF EXTRAPOLATING, AS WELL AS
PREVIOUS ECMWF RUNS) OR FARTHER NORTH (ECMWF/CANADIAN AND PREVIOUS
GFS RUNS). GIVEN THE FLIP FLOPPING, OPTED TO SPLIT THE DIFFERENCE
BETWEEN THE TWO CAMPS WHICH ONLY MODIFIED THE FRONTAL TIMING
THROUGH THE PAC NW INTO IDAHO/MONTANA A BIT. FARTHER EAST, STILL
EXPECT THE COLD FRONT TO DROP ALL THE WAY TO THE GULF COAST NEXT
FRI/SAT WITH AT LEAST SOME MODEST COOLING/DRYING INTO THE DEEP
SOUTH.


...WEATHER HIGHLIGHTS...

TUE-THU - FRONT WILL PUSH EASTWARD AND DROP SOUTHWARD AS THE SFC
LOW LIFTS INTO SOUTHERN CANADA. TEMPERATURES WILL WARM AHEAD OF
THE BOUNDARY WELL INTO THE 80S OR NEAR 90 INTO NEW ENGLAND (WITHIN
A FEW DEGREES OF RECORD HIGHS) AND STAYING IN THE 90S AND LOW 100S
OVER TEXAS. PRECIPITATION COULD BE HEAVIEST THROUGH THE
LOWER/EASTERN LAKES AS THE SFC LOW LIFTS NORTHEASTWARD. FLORIDA
SHOULD ALSO SEE AN INCREASE IN RAINFALL AS A TROPICAL WAVE MOVES
THROUGH THE STATE WED/THU.

THU-SAT - PAC NW WILL SEE AN INCREASE IN SHOWERS AS THE COLD FRONT
PUSHES INLAND BUT AMOUNTS SHOULD BE GENERALLY LIGHT. COOLER
TEMPERATURES ARE EXPECTED WITH THE INCREASE IN CLOUD COVER BUT
ONLY BRIEFLY. FARTHER SOUTH, COMBINATION OF THE WEAKENING UPPER
LOW/TROUGH PUSHING INTO SOUTHERN CALIFORNIA AND THE UPPER RIDGE
FOCUSING OVER TEXAS SHOULD SUPPORT INCREASED SHOWERS/CONVECTION
OVER THE FOUR CORNERS REGION, MOSTLY OVER NEW MEXICO AND SOUTHERN
COLORADO PER THE ENSEMBLES.


FRACASSO


$$





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