Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 030547
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
146 AM EDT WED SEP 03 2014

VALID 12Z SAT SEP 06 2014 - 12Z WED SEP 10 2014

...MULTI-DAY RAIN THREAT FOR ARIZONA...


...OVERVIEW AND GUIDANCE PREFERENCES...

SUBTROPICAL RIDGING IN THE LOWER CONUS LATITUDES AT THE START OF
THE MEDIUM RANGE PERIOD WILL CONDENSE ALONG 30N AND ALSO BUILD TO
THE NW AND NE OF THE MID-LATITUDES NEAR 45-50N. THIS SHOULD LEAVE
TROUGHING DIGGING INTO THE PLAINS BY MIDWEEK NEXT WEEK. SYNOPTIC
PATTERN REMAINS FAIRLY PREDICTABLE WITH WELL-DEFINED AND
SEMI-PROGRESSIVE TROUGH/RIDGE COUPLETS EXTENDING UPSTREAM THROUGH
THE NORTH PACIFIC. THE DEVIL IS IN THE DETAILS. ASIDE FROM THE OUT
OF SYNC 18Z GFS/GEFS MEAN... THE 12Z GFS/ECMWF AND THEIR MEANS
FORM A GOOD CONSENSUS AGAIN THOUGH THAT ONGOING CLUSTER PREFERENCE
DOES NOT NECESSARILY SHOW THE BEST CONTINUITY... ESPECIALLY IN THE
WEST AND SOUTHERN CANADA. HOWEVER... THE DECREASING LEAD TIMES
SHOULD... IN THEORY... LEAD US CLOSER TO THE TRUTH. IF I COULD
TURN BACK TIME... I WOULD PROBABLY PUT MORE WEIGHT IN SOME OF THE
ECMWF RUNS DESPITE THEIR MARGINALLY EXTREME APPEARANCE TO THE REST
OF THE ENSEMBLES. AFTER ALL THE MODELS WERE CONSIDERED... A BLEND
OF THE GFS/ECMWF/ECENS MEAN WAS USED THROUGH MON/D5 BEFORE A
SIMPLE 50/50 12Z GEFS/ECENS MEAN BLEND WAS USED FOR NEXT TUE/WED.
EVEN JUST A BLEND OF THE MEANS YIELDS ABOUT A 1-1.5 STD DEVIATION
BELOW AVG HEIGHTS FOR THE HIGH PLAINS /ECENS WAS DEEPER THAN THE
GEFS/.


...SENSIBLE WEATHER HIGHLIGHTS...

INITIAL WARM TEMPERATURES IN THE NORTHEAST AND WEST COASTS WILL
FADE IN TIME... BEHIND THE FRONT IN THE EAST AND AS THE UPPER
TROUGH SWINGS THROUGH THE PAC NW MON/D5. PRECIPITATION WILL FOCUS
MOST IN THE EAST ALONG/AHEAD OF THE COLD FRONT AND ALSO IN THE SW
AS MOISTURE SURGES UP THE GULF OF CALIFORNIA WELL AHEAD AND TO THE
NORTHEAST OF TROPICAL STORM NORBERT. PW ANOMALIES SHOULD CLIMB TO
+2 OR EVEN +3 STD DEVIATIONS PER THE ENSEMBLES... INCREASING THE
CHANCE FOR AT LEAST ISOLATED HEAVY RAIN OF 1-3 INCHES. SEE THE NHC
WEBSITE FOR THE LATEST TRACK INFORMATION AS THE ENSEMBLES HAVE NOT
BEEN CONSISTENT IN RECENT CYCLES. AS THE TROUGH PROGRESSES/DIGS
INTO THE HIGH PLAINS BY THE END OF THE PERIOD... PRECIPITATION
SHOULD EXPAND THROUGH THE PLAINS INTO THE UPPER MIDWEST AHEAD OF
THE COLD FRONT. IN THE SOUTHWEST.. CONTINUED MOISTURE SHOULD
REMAIN IN PLACE OVER ARIZONA ESPECIALLY BUT ALSO INTO COLORADO...
KEEPING TEMPERATURES A BIT BELOW AVERAGE.


FRACASSO

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