Prognostic Meteorological Discussion
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797
FXUS02 KWBC 230548
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
147 AM EDT THU MAR 23 2017

VALID 12Z SUN MAR 26 2017 - 12Z THU MAR 30 2017

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

THE MODELS AND ENSEMBLES CONTINUE TO SHOW A PARADE OF SYSTEM
EJECTING FROM THE EASTERN PACIFIC...WITH TROUGHS IN THE NORTHERN
STREAM CROSSING THE PACIFIC NORTHWEST AND DEAMPLIFYING AS THEY
CROSS THE NORTHERN ROCKIES.  THE SOUTHERN STREAM SYSTEMS MOVE
ACROSS THE SOUTHWEST AND SOUTHERN/CENTRAL PLAINS BEFORE EJECTING
NORTHEAST ACROSS THE MS VALLEY/OH VALLEY AND GREAT
LAKES/NORTHEAST.

TYPICAL TIMING DIFFERENCES PERSIST WITH THE INITIAL CLOSED LOW
EJECTING FROM THE MID MS VALLEY INTO THE OH VALLEY SUNDAY.  THE
OVERALL DISTRIBUTION REMAINS SIMILAR TO YESTERDAY...AND SHOWS THE
LOW WEAKENING AS IT CROSSES THE LAKES TOWARDS NEW YORK...WHILE A
RIDGE IS SLOW DEPART NEW ENGLAND.  MANUAL PROGS BLENDED THE 12Z
ECMWF/ECMWF ENSEMBLE MEAN/18Z GEFS MEAN/12Z CANADIAN/12Z CANADIAN
ENSEMBLE MEAN.

THE INITIAL TROUGH OVER THE SOUTHWEST SUN MORNING IS FORECAST TO
REACH THE CENTRAL PLAINS BY EARLY IN THE WEEK, AND WEAKENS IT
EJECTS NORTHEAST FROM THE PLAINS TOWARDS THE MID MS VALLEY ON MON
AND THEN
OH VALLEY ON TUE AND MID ATLANTIC STATES ON WED 29 MAR.

UPSTREAM ON  MON 27 MAR...THE MODELS/ENSEMBLES SHOW ANTICYCLONIC
WAVE BREAKING....AND DEVELOP A DOWNSTREAM TROUGH OVER THE
SOUTHWEST US.  THERE IS DIFFERENT CLUSTERING OF SOLUTIONS
DEPENDING ON
THE GEFS/ECMWF/CANADIAN ENSEMBLE CLUSTERING DIFFERENT ON THE
TROUGH TIMING/AMPLITUDE/PHASING.
SINCE THERE IS A LARGE SPREAD...CONFIDENCE DROPS...WITH LESS
WEIGHTING ON OPERATIONAL GFS/ECMWF MODELS USED GIVEN SIGNIFICANT
RUN TO RUN CHANGES AND DIFFERENCE BETWEEN MODELS AND THEIR
ENSEMBLE MEANS.
BY THIS POINT...LESS WEIGHT WAS USED ON THE OPERATIONAL RUNS AND
MORE WEIGHTING WAS GIVEN TO THE 18Z GEFS MEAN/12Z ECMWF ENSEMBLE
MEAN...AND 12Z CANADIAN/NAEFS ENSEMBLE MEAN.

WITH THE LARGE SPREAD DURING DAY 6 WED 29 MAR AND 7 THU 30 MAR,
FORECAST CONFIDENCE IS BELOW AVERAGE.


...SENSIBLE WEATHER/HIGHLIGHTS...

SHOWERS AND THUNDERSTORMS ARE LIKELY ON SUNDAY ACROSS THE OHIO
VALLEY TO THE CENTRAL APPALACHIANS, WITH STRATIFORM RAIN ACROSS
THE GREAT LAKES AND ALONG THE FRONTAL BOUNDARY IN NEW YORK AND NEW
ENGLAND. BY MONDAY, THE AREA OF PRECIPITATION IS FOCUSED IN NEW
ENGLAND.

THE NEXT TROUGH CROSSING THE SOUTHERN PLAINS TO THE LOWER
MISSISSIPPI VALLEY COMBINES WITH MOISTURE RETURN FROM THE GULF OF
MEXICO TO PRODUCE A ROUND OF CONVECTION ACROSS THE SOUTHERN AND
CENTRAL PLAINS INTO THE MID-LOWER MS VALLEY SUNDAY INTO
MONDAY...WHEN THE EJECTING LOW BRINGS A THREAT OF PRECIP INTO THE
OH VALLEY.  THE HEAVIEST RAINS FOR THE DAYS 3-7 PERIOD ARE
FORECAST OVER THE EASTERN HALF OF THE SOUTHERN PLAINS TOWARDS THE
LOWER MS VALLEY.

WIDESPREAD SHOWERS AND MOUNTAIN SNOW ARE EXPECTED TO ACCOMPANY THE
FRONTAL SYSTEM MOVING ONSHORE INTO THE PACIFIC NORTHWEST AND
NORTHERN ROCKIES FOR THE BEGINNING OF THE WORK WEEK.  THIS GETS
REPEATED FOR A FOLLOWING TROUGH AND WAVY SURFACE FRONT NEXT TUE
COMING INTO THE ROCKIES AND NORTHERN PLAINS WEE 29 MAR.  THE
SOUTHERN STREAM PORTION OF THIS WAVE COMES ACROSS THE SOUTHWEST
TUESDAY, WITH ADDITIONAL AREAS OF VALLEY RAIN AND MOUNTAIN SNOW
FROM THE GREAT BASIN TO THE CENTRAL AND SOUTHERN ROCKIES.  ONCE
THIS UPPER TROUGH EMERGES FROM THE SOUTHWEST...THE MODELS EXPAND
AMOUNTS AND COVERAGE OF PRECIP ACROSS THE CENTRAL TO SOUTHERN
PLAINS NEXT WED 29 MAR.

ABOVE NORMAL TEMPERATURES ARE EXPECTED TO PERSIST SUNDAY INTO
EARLY NEXT WEEK ACROSS THE OHIO AND TN VALLEYS EXTENDING SOUTHWARD
TO SOUTHEAST AND GULF COAST...AND TEXAS  A TIGHT TEMPERATURE
GRADIENT WILL LIKELY BECOME ESTABLISHED ACROSS THE MID-ATLANTIC
REGION AS A BACK DOOR COLD FRONT SWEEPS SOUTHWARD FROM NEW
ENGLAND.  THE PROGRESSION OF TROUGHS ACROSS THE PACIFIC NORTHWEST
AND THEIR ASSOCIATED SHOWERY CONDITIONS KEEPS TEMPERATURES BELOW
NORMAL FOR THESE AREAS.

PETERSEN

$$





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