Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 220546
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 AM EDT WED MAR 22 2017

VALID 12Z SAT MAR 25 2017 - 12Z WED MAR 29 2017

...OVERVIEW/GUIDANCE EVALUATION/PREFERENCES...

THE MODELS AND ENSEMBLES CONTINUE TO SHOW A SERIES OF UPPER
TROUGHS PROGRESSING ONSHORE FROM THE EASTERN PACIFIC.  THE
SOUTHERN STREAM PORTION OF THE TROUGHS MOVE ACROSS THE
SOUTHWEST....SOUTHERN AND CENTRAL PLAINS...AND THEN DEAMPLIFY AS
THE MOVE NORTHEAST ACROSS THE MS VALLEY/OH VALLEY AND THE CENTRAL
APPALACHIANS/MID ATLANTIC.  THE NORTHERN STREAM PORTIONS CROSS THE
PACIFIC NORTHWEST AND DEAMPLIFY AS THE CROSS THE NORTHERN ROCKIES.

THE FIRST OF THE 3 UPPER TROUGH EMERGES FROM THE SOUTHERN PLAINS
AND CROSSES INTO THE MID MS VALLEY SUN AND CONTINUES TO WEAKEN
CROSSING THE OH VALLEY AND GREAT LAKES AND MID ATLANTIC MON.
THE MODE/ENSEMBLE SUITE IS QUITE SIMILAR TO YESTERDAY AS THE
ECMWF/ECMWF ENSEMBLES CLUSTER AS MOVING THE SYSTEM FORWARD FASTER
THAN THE GFS/GEFS ENSEMBLES AND THE OPERATIONAL 12Z CMC/UKMET
BEING THE SLOWEST OF THE BUNCH. A CONSENSUS APPROACH WAS TAKEN
UNTIL BETTER AGREEMENT DEVELOPS.

THE SECOND OF THE 3 SOUTHERN STREAM UPPER TROUGH COMES ASHORE IN
CA FRI NIGHT/SAT MORNING.
THE ECWMF/ECMWF ENSEMBLES CLUSTER FASTER THAN THE GFS/CANADIAN
GLOBAL/UKMET WITH THE SPEED OF THE 500 MB TROUGH.  THE UPSTREAM
FLOW OVER THE EASTERN PACIFIC IS CONFLUENT AND FAST...SO A FASTER
PROGRESSION IS POSSIBLE. A CONSENSUS APPROACH WAS USED GIVEN THE
MODEL CLUSTER HAVE BEEN CONSISTENT RUN TO RUN AND NOT CONVERGING
YET.  THE UPPER TROUGH PROGRESSES INTO THE SOUTHERN PLAINS SUNDAY
NIGHT...THEN LIFT INTO THE MO VALLEY BY EARLY NEXT WEEK WHERE IT
WILL DEAMPLIFY AND SHEAR.

LIKEWISE...THERE IS EVEN A TRAILING SYSTEM WHICH IS EXPECTED TO
MOVE THROUGH THE FOUR CORNERS REGION BY MONDAY/TUESDAY. WHILE
THERE IS SOME VARIABILITY IN PLACEMENT AND INTENSITY...GLOBAL
ENSEMBLE MEANS INDICATE THIS THIRD SYSTEM ENTERING THE FOUR
CORNERS REGION/SOUTHERN HIGH PLAINS.

SIMILAR ISSUES EXIST WITHIN THE NORTHERN STREAM TROUGH FORECAST TO
MOVE FROM THE NORTHEAST PACIFIC ONSHORE IN THE PACIFIC NORTHWEST
SAT NIGHT-SUN.  THE 18Z GFS WAS THE MOST AMPLIFIED OF THE
MODEL/ENSEMBLE SUITE...WITH BETTER AGREEMENT ON THE
TIMING/AMPLITUDE 12Z MON AMONG THE GEFS AND CANADIAN ENSEMBLE
MEANS.  LIKE WITH OTHER WAVES...THE ECMWF MEAN BOTH DEAMPLIFIES
THE WAVE SOONER AND MOVES THE SYSTEM INLAND FASTER.

MANUAL PROGS USED A CONSENSUS OF THE 18Z GFS/18Z GEFS MEAN ALONG
WITH THE 12Z ECMWF/ ECMWF ENSEMBLE MEAN FOR DAY3 TO 7.


...SENSIBLE WEATHER/HIGHLIGHTS...

SHOWERS AND THUNDERSTORMS CONCENTRATE SAT IN THE OH AND TN
VALLEYS...WITH MODERATE RAINFALL MOVING TOWARDS THE GREAT LAKES.
ON SUNDAY AND MONDAY THE AREA OF PRECIPITATION CROSSES FROM THE
LAKES ACROSS NEW YORK/MID ATLANTIC/NEW ENGLAND.  THE NEXT WAVE
CROSSING THE SOUTHERN PLAINS TO LOWER MS VALLEY COMBINES WITH
MOISTURE RETURN FROM THE GULF OF MEXICO TO PRODUCE A SECOND ROUND
OF CONVECTION ACROSS THE SOUTHERN/CENTRAL PLAINS INTO THE LOWER MS
VALLEY LATER SUN INTO MON 27 MAR. WIDESPREAD SHOWERS AND AREAS OF
RAIN ACCOMPANY THE PROMINENT WAVE MOVING ONSHORE INTO THE PACIFIC
NORTHWEST AND NORTHERN ROCKIES SUN INTO MON. THE SOUTHERN STREAM
PORTION OF THIS WAVE COMES ACROSS THE SOUTHWEST TUE AND RESULTS IN
THE DEVELOPMENT OF MORE VALLEY RAIN AND MOUNTAINS SNOW FROM THE
GREAT BASIN TO THE CENTRAL AND SOUTHERN ROCKIES.

ABOVE NORMAL TEMPERATURES ARE EXPECTED TO PERSIST THIS WEEKEND
INTO EARLY NEXT WEEK ACROSS
THE OH VALLEY TO THE THE CENTRAL AND SOUTHERN
APPALACHIANS...SOUTHEAST...LOWER MS VALLEY...AND SOUTH TEXAS.
OVER THE WEEKEND AND INTO EARLY NEXT WEEK...A TIGHT TEMPERATURE
GRADIENT SETS UP AS A BACK DOOR COLD FRONT SWEEPS SOUTHWARD FROM
NEW ENGLAND DOWN INTO THE MID-ATLANTIC.  THE PROGRESSION OF
TROUGHS ACROSS NORTHERN CA AND THE PACIFIC NORTHWEST AND THEIR
ASSOCIATED SHOWERY CONDITIONS KEEPS TEMPERATURES BELOW NORMAL FOR
THESE AREAS.

PETERSEN

$$





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