Preliminary Forecasts
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FXUS02 KWNH 230624
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
224 AM EDT SAT SEP 23 2017

VALID 12Z TUE SEP 26 2017 - 12Z SAT SEP 30 2017

...HEAVY RAIN LIKELY FOR PORTIONS OF TEXAS AND OKLAHOMA NEXT
WEEK...


...OVERVIEW...

TROUGH/RIDGE SETUP OVER THE WEST/EAST TO START THE PERIOD ON
TUESDAY WILL TRANSITION TO A RIDGE/TROUGH BY FRIDAY. AN AXIS OF
HEAVY RAIN IS ANTICIPATED TO SET UP OVER TEXAS AS GULF MOISTURE
FEEDS NORTHWESTWARD INTO THE HILL COUNTRY AND POINTS NORTHWARD
INTO WESTERN OKLAHOMA. HURRICANE MARIA IS FORECAST TO MOVE
NORTHWARD JUST OFF THE EAST COAST BEFORE LIKELY TURNING
NORTHEASTWARD OUT TO SEA LATE NEXT WEEK, BUT MAY BE CLOSE ENOUGH
TO THE OUTER BANKS OF NORTH CAROLINA TO SPREAD RAINFALL OVER THE
AREA. PLEASE CONSULT THE NATIONAL HURRICANE CENTER FOR THE LATEST
FORECAST TRACK.


...GUIDANCE EVALUATION/PREFERENCES...

OVERALL/SYNOPTIC AGREEMENT REMAINS GOOD THROUGH ABOUT NEXT
WEDNESDAY, THOUGH THE DETERMINISTIC GFS/ECMWF WAVER ON HOW TO SORT
OUT THE FLOW ACROSS SOUTHERN CANADA IN ADDITION TO THE
SOUTHWESTERN PORTION OF THE TROUGH AXIS BACK INTO THE DESERT
SOUTHWEST. TREND HAS BEEN TO SPEED UP THE NORTHERN STREAM THROUGH
ONTARIO/QUEBEC VIA TWO SHORTWAVES WHILE LETTING THE UPPER LOW OVER
AZ/NV LINGER IN PLACE INSTEAD OF MOVING SLOWLY EASTWARD INTO NM
AND THE TX PANHANDLE. THIS LED TO A QUICKER FRONTAL PROGRESSION IN
THE CENTRAL/EASTERN STATES TUE-WED AS THE SFC LOW ZIPS THROUGH
QUEBEC. AT THAT TIME, HURRICANE MARIA IS FORECAST TO MOVE
NORTHWARD BETWEEN 72-73W PER THE 03Z NHC ADVISORY. THE ENSEMBLES
SHIFTED NOTABLE WESTWARD IN RECENT RUNS DUE TO SEVERAL FORCES;
NAMELY, STRENGTH/ORIENTATION OF THE UPPER RIDGE TO THE NORTH AND
THE SOUTHWARD EXTENT OF HEIGHT FALLS THROUGH THE NORTHEAST. HOW
FAR WESTWARD MARIA MAY TRACK WILL DEPEND ON ITS SHORT RANGE PATH
IN ADDITION TO THE FEATURES TO ITS NORTH. OFFICIAL POINTS PAIRED
WITH THE DAY SHIFT COORDINATION CALL MAINTAINED AN OFFSHORE PATH
BY A COUPLE HUNDRED MILES BUT ITS IMPACTS MAY BE FELT ALONG THE
COAST (AT LEAST IN THE FORM OF DANGEROUS SURF AND LIFE-THREATENING
RIP CURRENTS).

BLEND OF THE 12Z GFS/ECMWF OFFERED A GOOD STARTING POINT BEFORE
SMALLER SCALE DETAILS BECAME OUT OF SYNC BETWEEN THE MODELS. 12Z
NAEFS AND ECMWF ENSEMBLE MEAN BROUGHT IN SOME SMOOTHING TO THE
DETERMINISTIC DIFFERENCES THAT FIT WELL WITH CONTINUITY FOR NEXT
THU/FRI AS THE COLD FRONT MOVES OFF THE EAST COAST AND FINALLY
PUSHES MARIA OUT TO SEA. SECONDARY COLD FRONT THROUGH THE MIDWEST
AND OHIO/MS VALLEY WILL BRING IN COOLER AIR TO THE NORTHEASTERN
QUARTER OF THE CONUS. BY NEXT FRI/SAT, ENSEMBLES SHOW TROUGHING
EDGING INTO THE PAC NW BUT THE ECMWF ENSEMBLE MEAN HAS BEEN MUCH
MORE CONSISTENT THAN THE GEFS MEAN, SO USED A 70/30 BLEND BETWEEN
THE TWO AS THE DETERMINISTIC MODELS BECAME UNUSABLE DUE TO
SIGNIFICANT FEATURE DISPLACEMENTS FROM THE MEANS.


...WEATHER HIGHLIGHTS...

ONGOING HEAT IN THE GREAT LAKES AND NORTHEAST WILL END BY
WEDNESDAY AS THE COLD FRONT MOVES EASTWARD AND DROPS TEMPERATURES
BY ABOUT 20 DEGREES (BUT ONLY TO NEAR AVERAGE VALUES). MAIN AREA
OF PRECIPITATION WILL BE ASSOCIATED WITH THE SOUTHERN PORTION OF
THE COLD FRONT AS IT SINKS THROUGH TEXAS DURING THE WEEK.
SOUTHEAST FLOW AT LOW LEVELS WILL DRAW IN GULF MOISTURE FOR
SEVERAL DAYS BEFORE THE COLD FRONT PUSHES INTO MEXICO AND THE
WESTERN GULF, SETTING UP A MULTI-DAY RAINFALL EVENT. NEARLY ALL OF
THE GUIDANCE INDICATE THE POTENTIAL FOR SEVERAL INCHES OF RAIN
TUE-SAT FROM THE HILL COUNTRY NORTHWARD INTO OKLAHOMA (GENERALLY
WEST OF I-35). OTHER AREA TO WATCH WILL BE EASTERN NORTH CAROLINA
WITH MARIA JUST OFFSHORE. RAINFALL MAY BE LITTLE TO NONE IF MARIA
TRACKS FARTHER EAST OR AN INCH OR MORE IF IT TRACKS MUCH CLOSER TO
THE COAST.


FRACASSO


$$





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