Prognostic Meteorological Discussion
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FXUS02 KWBC 241556
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1155 AM EDT FRI MAR 24 2017

VALID 12Z MON MAR 27 2017 - 12Z FRI MAR 31 2017

WEATHER PATTERN OVERVIEW:

THE LATEST GUIDANCE CONTINUES THE TREND OF AN ACTIVE WEATHER
PATTERN ACROSS MOST OF THE CONTINENTAL U.S. FEATURING A SERIES OF
EASTERN PACIFIC SHORTWAVES ARRIVING INTO AND THEN EJECTING FROM A
SYNOPTIC SCALE TROUGH CENTERED OVER THE WESTERN STATES.  A
SEPARATE NORTHERN STREAM ACROSS THE NORTHERN PLAINS AND UPPER
MIDWEST AND ALSO SOUTHERN CANADA SHOULD HAVE SOME INFLUENCE ON
SYSTEM PROGRESSION FARTHER TO THE SOUTH.  THE MAIN FEATURES OF
INTEREST NATIONWIDE WILL BE A COUPLE OF WEAKENING SHORTWAVE
TROUGHS OVER THE CENTRAL AND EASTERN U.S. AT THE BEGINNING OF THE
FORECAST PERIOD, A CLOSED LOW DEVELOPING OVER THE DESERT SOUTHWEST
AND TRACKING TOWARDS THE CENTRAL PLAINS, AND YET ANOTHER CLOSED
LOW BECOMING MORE LIKELY BY THE END OF THE FORECAST PERIOD NEAR
THE FOUR CORNERS REGION.


MODEL EVALUATION AND PREFERENCES:

THE ENSEMBLE MEANS AND THE OPERATIONAL GFS/ECMWF/UKMET ARE IN
DECENT AGREEMENT AT THE BEGINNING OF THE FORECAST PERIOD WITH
RESPECT TO THE WESTERN U.S. LARGE SCALE TROUGH AND THE SHORTWAVES
CROSSING THE CENTRAL PLAINS AND OHIO VALLEY.  THE 00Z CMC BEGINS
DIFFERING EARLY IN THE PERIOD AND INDICATES MORE IN THE WAY OF
MID-LEVEL RIDGING OVER THE OHIO VALLEY AND GREAT LAKES REGION,
WHEREAS THE MODEL CONSENSUS AGREES ON THE IDEA OF A WEAKENING
TROUGH.  IT IS ALSO FARTHER SOUTH WITH THE CLOSED LOW TRACKING
EASTWARD FROM THE SOUTHERN ROCKIES.  BY THURSDAY MORNING, THE
ENSEMBLE MEANS ARE FARTHER WEST THAN THE GFS/ECMWF DETERMINISTIC
RUNS, WITH THE 6Z GFS WELL AHEAD OF THE CONSENSUS BY THAT TIME.
BY FRIDAY MORNING, MORE SIGNIFICANT MODEL SPREAD IS APPARENT WITH
THE LATEST SPAGHETTI PLOTS SHOWING A WIDE RANGE OF POSSIBLE
SOLUTIONS WITH RESPECT TO THE SECOND CLOSED LOW DEVELOPING OVER
THE FOUR CORNERS REGION.  THE EC MEAN SHOWS GREATER DEFINITION TO
THIS FEATURE COMPARED TO THE GEFS MEAN, WHICH INDICATES ONLY BROAD
TROUGHING.  THE FORMER ALSO IS CLOSER TO THE DETERMINISTIC ECMWF
COMPARED TO THE GFS, WHICH IS FARTHER NORTH.  AS A RESULT, THE
FORECAST BLEND WAS BASED ON ROUGHLY HALF DETERMINISTIC AND HALF
MEANS FOR THE FIRST 2 DAYS, AND THEN TRENDING MORE TOWARDS THE
ENSEMBLE MEANS FOR THE LAST 3 DAYS, WITH GREATER EMPHASIS ON THE
EC MEAN.  SOME PREVIOUS WPC CONTINUITY WAS ALSO MAINTAINED FOR
THIS FORECAST.


SENSIBLE WEATHER HIGHLIGHTS AND POTENTIAL HAZARDS:

A STORMY WEATHER PATTERN IS LOOKING INCREASINGLY LIKELY ACROSS
MUCH OF THE SOUTHERN TIER STATES FOR NEXT WEEK.  THIS ESPECIALLY
HOLDS TRUE FOR THE CLOSED LOW TRACKING EASTWARD FROM THE SOUTHWEST
TO THE CENTRAL PLAINS ALONG WITH ITS OCCLUDED SURFACE LOW.  THERE
IS A GOOD CHANCE OF SEVERE WEATHER DEVELOPING ACROSS THE CENTRAL
AND SOUTHERN PLAINS BY THE MIDDLE OF THE WEEK, AND THE STORM
PREDICTION CENTER HAS ADDITIONAL INFORMATION REGARDING THAT.  IT
IS ALSO IMPORTANT TO NOTE THAT MOST OF THE MODEL GUIDANCE,
ESPECIALLY THE 6Z GFS, IS INDICATING THE INCREASING LIKELIHOOD OF
EXCESSIVE RAINFALL ACROSS PARTS OF TEXAS AND OKLAHOMA ON WEDNESDAY
AND POSSIBLY EXTENDING INTO THURSDAY.  SOME OF THE STORMS THAT
DEVELOP WILL LIKELY BE SLOW MOVING AND TRAIN OVER THE SAME AREAS,
AND COULD BE CAPABLE OF CAUSING FLASH FLOODING.  FUTURE EXCESSIVE
RAINFALL OUTLOOKS WILL LIKELY COVER THIS POTENTIAL AS THE EVENT
ENTERS THE SHORT RANGE FORECAST PERIOD.

IN TERMS OF TEMPERATURES, MOST AREAS EAST OF THE ROCKIES WILL
LIKELY HAVE TEMPERATURES ABOVE NORMAL BY LATE MARCH STANDARDS,
WITH THE GREATEST ANOMALIES LIKELY FROM TEXAS TO THE DEEP SOUTH.
THIS WILL BE EVEN MORE APPARENT WITH THE WARM OVERNIGHT LOWS
EXPECTED SOUTH OF THE FRONTAL BOUNDARY.  HIGH DEWPOINTS AND CLOUD
COVER WILL LIMIT THE AMOUNT OF OVERNIGHT COOLING FOR MANY AREAS,
MAKING IT FEEL MORE LIKE THE MONTH OF MAY.  COOLER THAN AVERAGE
TEMPERATURES ARE LIKELY UNDER THE UPPER LOW OVER THE SOUTHWESTERN
U.S. AND ALSO FOR NORTHERN NEW ENGLAND, WHICH WILL CONTINUE TO BE
INFLUENCED BY THE CANADIAN HIGH TO ITS NORTH.


D. HAMRICK

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