Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4

000
FXUS02 KWBC 181556
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1156 AM EDT THU SEP 18 2014

VALID 12Z SUN SEP 21 2014 - 12Z THU SEP 25 2014

...BIG PATTERN CHANGE FOR THE PACIFIC NORTHWEST NEXT WEEK...


...OVERVIEW...

MUCH OF THE NORTHERN HEMISPHERE SHOULD UNDERGO A PATTERN CHANGE
OVER THE NEXT WEEK AS A STRONG PACIFIC JET /170KTS OR SO/ MOVES
EASTWARD ACROSS THE DATELINE. THE AMPLIFIED RIDGE/TROUGH PATTERN
ACROSS THE WEST/EAST AT THE START OF THE MEDIUM RANGE IS FORECAST
TO PUSH EASTWARD... WHICH WILL ESSENTIALLY FLIP THE PATTERN ACROSS
THE CONUS. INITIAL TROUGHING IN THE EAST WILL SUPPORT A SFC COLD
FRONT THAT WILL PUSH OFFSHORE THE EAST COAST BY EARLY NEXT WEEK
AND INTO THE GULF BY TUE/D5 WITH HIGH PRESSURE IN ITS WAKE. A LEAD
COLD FRONT IN THE PACIFIC SHOULD APPROACH WA/OR EARLY IN THE WEEK
BUT DISSIPATE AS STRONGER UPSTREAM MID-LEVEL ENERGY SWINGS THROUGH
BEHIND IT... WHICH SHOULD MAINTAIN ITSELF INTO THE PAC NW BY THE
END OF THE PERIOD.


...GUIDANCE/UNCERTAINTY ASSESSMENT AND PREFERENCES...

THE MODELS/ENSEMBLES HAVE HAD A WORLD OF TROUBLE RESOLVING THE
PATTERN ACROSS THE PACIFIC -- THE FORECASTS FROM TWO DAYS AGO ARE
BASICALLY 180 DEGREES OUT OF PHASE -- BUT HAVE COME INTO MUCH
BETTER AGREEMENT IN THEIR RECENT CYCLE. THE AREAS OF CONTENTION
LIE IN THE NORTHEAST AROUND TUE/D5 WHERE THE 06Z GFS AND MANY
00Z-06Z GEFS MEMBERS LINGER ENERGY IN NEW ENGLAND WHEREAS THE
CONSENSUS IS TO KEEP IT PROGRESSIVE AND MOVE IT OUT OF THE AREA.
WAVELENGTH SPACING DIFFERENCES BETWEEN THE ECMWF AND GFS ENSEMBLES
SEEM TO BE CONTRADICTORY -- THE GEFS ARE QUICKER IN THE WEST BUT
SLOWER IN THE EAST -- BUT THE FLOW IS COMPLICATED BY THE NORTHERN
STREAM IN EASTERN CANADA. PREFER TO STICK WITH CONTINUITY AND THE
LARGER AGREEMENT NEAR THE ECMWF... BUT INCLUDED A VERY MINOR
GFS/GEFS WEIGHTING GIVEN THE POSSIBILITY OF A SLOWER EXIT OF THE
TROUGH MIDWEEK NEXT WEEK.

IN THE WEST... THE GFS AND GEFS MEMBERS ARE LIKELY SHOWING THEIR
TYPICAL BIAS OF BEING TOO QUICK BY WED-THU/D6-7 TO BRING TROUGHING
INTO THE WEST... AS THE TREND IN THE ECMWF ENSEMBLES -- AND EVEN
THE GEFS -- HAS BEEN SLOWER. IN ADDITION... THE EXTRATROPICAL
TRANSITION OF CURRENT TROPICAL STORM FUNG-WONG LATE IN THE PERIOD
EAST OF JAPAN SHOULD ACT TO AMPLIFY/SLOW THE PATTERN AT LEAST
SOMEWHAT ACROSS THE PACIFIC. 00Z ECMWF/ECENS MEAN WERE THE
PREFERENCE FOR MIDWEEK NEXT WEEK IN THE WEST.


...SENSIBLE WEATHER HIGHLIGHTS...

COOLER/WARMER THAN AVERAGE TEMPERATURES WILL FOLLOW THE UPPER
RIDGE/TROUGH PATTERN FROM WEST TO EAST THOUGH THE PAC NW SHOULD
SEE THE LARGEST SWING FROM WARM TO COOL DURING THE PERIOD.
PRECIPITATION SHOULD FOCUS ALONG THE EXITING COLD FRONT IN THE
EAST AND THROUGH FLORIDA AS IT STALLS IN THE GULF. THE REMNANTS OF
ODILE WILL PUSH THROUGH OK AND MERGE WITH THE FRONTAL BOUNDARY...
LIKELY ENHANCING THE PRECIPITATION OVER THE SOUTHERN PLAINS AT
LEAST AT THE START OF THE MEDIUM RANGE. THEREAFTER... AN UPPER LOW
INITIALLY OVER CALIFORNIA WILL SLOWLY MOVE THROUGH ID/WY TOWARD
THE DAKOTAS WHICH SHOULD BE A PROGRESSIVE FOCUS FOR PRECIP THROUGH
THE PERIOD. FINALLY... WITH THE APPROACH OF A BONA FIDE COLD FRONT
INTO WA/OR AND NORTHERN CALIFORNIA... AND PW VALUES PERHAPS RISING
TO +2 TO +3 STANDARD DEVIATIONS... THE WA/OR COASTS SHOULD SEE
THEIR FARE SHARE OF RAIN WED-THU/D6-7.


FRACASSO

$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.