Prognostic Meteorological Discussion
Issued by NWS

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FXUS02 KWBC 220650
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 AM EDT FRI SEP 22 2017

VALID 12Z MON SEP 25 2017 - 12Z FRI SEP 29 2017

HEAVY RAIN LIKELY FOR THE TEXAS HILL COUNTRY INTO OKLAHOMA NEXT
WEEK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~


OVERVIEW
~~~~~~~~

BIG PATTERN CHANGE FOR THE LOWER 48 NEXT WEEK -- INITIAL
TROUGH/RIDGE SETUP WILL FLIP AS RIDGING ENTERS THE WEST COAST
WED-THU AND TROUGHING DIGS INTO THE EAST ON FRIDAY. THIS WILL PUT
AN END TO THE RECORD HEAT FOR THE NORTHEAST MON-WED AS
TEMPERATURES FALL BACK TO MORE TYPICAL LEVELS FOR LATE SEPTEMBER.
TROUGH PROGRESSION TO THE EAST WILL ALSO SET UP AN AXIS OF HEAVY
RAIN OVER TEXAS AS GULF MOISTURE FEEDS NORTHWESTWARD INTO THE HILL
COUNTRY AND POINTS NORTHWARD INTO WESTERN OKLAHOMA. HURRICANE
MARIA IS FORECAST TO MOVE NORTHWARD BETWEEN THE EAST COAST AND
BERMUDA BEFORE LIKELY TURNING NORTHEASTWARD OUT TO SEA LATE NEXT
WEEK. PLEASE CONSULT THE NATIONAL HURRICANE CENTER FOR THE LATEST
FORECAST TRACK.


GUIDANCE EVALUATION/PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

THE GFS AND ECMWF ENSEMBLES SHOWED GOOD AGREEMENT AND RELATIVELY
LOW SPREAD THROUGH NEXT WEEK WITH A TREND TOWARD A BIT MORE
AMPLIFIED PATTERN. THE 18Z GFS AND 12Z ECMWF ALIGNED WELL WITHIN
THE ENSEMBLE SPREAD THROUGH MOST OF THE PERIOD AND A BLEND OF THE
TWO OFFERED A REASONABLE STARTING POINT. ADDED MORE ENSEMBLE MEAN
WEIGHTING THROUGH THE PERIOD TO ADDRESS UNCERTAINTIES IN HOW
QUICKLY THE NORTHERN VORT MAX LIFTS INTO AND THROUGH SOUTHERN
CANADA WEDNESDAY AND ALSO HOW THE SOUTHERN VORT MAX OF THE WESTERN
TROUGH SAUNTERS OUT OF THE FOUR CORNERS REGION AND INTO THE TX/OK
PANHANDLES BY FRIDAY. THESE BOTH AFFECT THE PACE OF THE COLD FRONT
FROM WEST TO EAST WHICH TRANSLATED INTO ABOVE AVERAGE SPREAD IN
ENSEMBLE RANGE OF ESPECIALLY MAX TEMPS. GAVE A BIT MORE WEIGHT TO
THE ECMWF GIVEN ITS BETTER CONTINUITY. WITH MARIA, A MIDDLE GROUND
SOLUTION FIT WELL WITH THE 03Z UPDATE AND THE VAST MAJORITY OF
ENSEMBLES TAKE IT OUT TO SEA NEXT THU/FRI AHEAD OF THE COLD FRONT.



WEATHER HIGHLIGHTS
~~~~~~~~~~~~~~~~~~

ONGOING LATE SUMMER/EARLY FALL HEAT IN THE GREAT LAKES AND
NORTHEAST WILL END BY WEDNESDAY AS THE COLD FRONT MOVES EASTWARD.
TEMPERATURES WILL DROP ABOUT 20 DEGREES BACK TO NEAR AVERAGE
VALUES BEHIND THE LEAD FRONT, WITH A REINFORCING COLD FRONT BEHIND
IT. MAIN AREA OF PRECIPITATION WILL BE ASSOCIATED WITH THE
SOUTHERN PORTION OF THE COLD FRONT AS IT SINKS THROUGH TEXAS.
SOUTHEAST FLOW AT LOW LEVELS WILL DRAW IN GULF MOISTURE FOR
SEVERAL DAYS BEFORE THE COLD FRONT PUSHES INTO MEXICO AND THE
WESTERN GULF. NEARLY ALL OF THE GUIDANCE INDICATE THE POTENTIAL
FOR SEVERAL INCHES OF RAIN MON-FRI FROM THE HILL COUNTRY NORTHWARD
INTO OKLAHOMA (GENERALLY WEST OF I-35). THIS MAY SPREAD
SOUTHEASTWARD TOWARD THE NW GULF COAST LATER NEXT WEEK.


FRACASSO


$$





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