National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS02 KWBC 221513
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1112 AM EDT TUE AUG 22 2017

VALID 12Z FRI AUG 25 2017 - 12Z TUE AUG 29 2017

GUIDANCE EVALUATION/PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE GUIDANCE SHOWS AN AMPLIFYING FLOW PATTERN ACROSS THE UNITED
STATES WITH RIDGING BUILDING ACROSS THE GREAT BASIN AND TROUGHING
DEVELOPING ACROSS THE MISSISSIPPI VALLEY, WHICH IS EXPECTED TO
SCOOP UP/MERGE WITH THE REMAINS OF THE REGENERATION OF TROPICAL
CYCLONE HARVEY.  TROUGHING ACROSS THE NORTHEAST DOWNSTREAM SHOULD
WEAKEN, THOUGH IT IS EXPECTED TO LURE A TROPICAL DISTURBANCE FROM
FL AS AN EXTRATROPICAL CYCLONE/POSSIBLE NOR`EASTER OFFSHORE THE
SOUTHEAST COAST.

THE GUIDANCE SHOWS RELATIVELY GOOD AGREEMENT, WITH THE LARGER
WRINKLES IN THE FORECAST RELATED TO HARVEY AND THE FL TROPICAL
DISTURBANCE.  USED A COMPROMISE OF 00Z UKMET/00Z CANADIAN/00Z
ECMWF/06Z GFS GUIDANCE FROM FRIDAY INTO SUNDAY BEFORE BLENDING IN
THE NAEFS AND ECMWF ENSEMBLE MEANS THEREAFTER FOR THE 500 HPA
HEIGHTS, PRESSURES, AND FRONTAL LOCATIONS.  THE REMAINDER OF THE
WEATHER GRIDS WERE BASED ON AN EVEN BLEND OF THE DETERMINISTIC AND
ENSEMBLE MEAN GUIDANCE.

THE DAYS 4-7 QPF IS TRICKY TODAY, BUT IS LIKELY TO INCREMENT
RAINFALL TOTALS UPWARDS BY A COUPLE INCHES ACROSS PORTIONS OF THE
MIDDLE AND UPPER TX COAST, IN THE NEIGHBORHOOD OF 7" ON DAYS 4-5
WITH LESSER, THOUGH HEAVY, AMOUNTS STREAKING NEAR AND LEFT OF ITS
TRACK ACROSS THE MID-MISSISSIPPI VALLEY INTO THE LOWER OHIO VALLEY
ONCE IT LINKS UP WITH A FRONTAL BOUNDARY.  WITH GUIDANCE TRENDING
NORTHEAST WITH HARVEY -- FITTING THE MULTI-DAY TREND OF RECURVING
HARVEY`S REMAINS FASTER -- DID NOT WISH TO GO OVERBOARD ON AMOUNTS
AS A PRECAUTION.  THERE IS TIME TO REFINE AMOUNTS AS UNCERTAINTY
CLEARS UP WITHIN THE SHORT RANGE PERIOD IN A COUPLE DAYS.  STAY
TUNED.


SENSIBLE WEATHER HIGHLIGHTS
~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE REMNANTS OF TROPICAL STORM HARVEY ARE EXPECTED TO REGENERATE
BACK INTO A TROPICAL CYCLONE PER THE LATEST OUTLOOK FROM THE
NATIONAL HURRICANE CENTER (NHC).  WITH TRENDS BRINGING THE
CIRCULATION IN THE VICINITY OF AND SOMEWHAT INLAND OF THE MIDDLE
AND UPPER TEXAS COAST...MULTIPLE MODELS PRODUCE A HEAVY RAIN EVENT
WITH THE CONVECTIVE CYCLONE.  SEE THE FORECASTS/TROPICAL WEATHER
OUTLOOKS FROM THE NHC ON THE CHANCES OF HARVEY REDEVELOPING.
MOISTURE INTERACTING WITH THE LINGERING FRONT ALONG THE GULF
COAST, THE LOW MOVING OFFSHORE THE SOUTHEAST EMANATING FROM A
TROPICAL DISTURBANCE MOVING AWAY FROM FL, AND UPSLOPE FLOW INTO
THE SOUTHERN APPALACHIANS COULD PRODUCE OTHER MODERATE TO HEAVY
RAINS OF CONCERN.

EXPECT SHOWERS AND THUNDERSTORMS TO FOCUS ACROSS THE SOUTHEAST AND
THE GULF COASTS ALONG A LINGERING STATIONARY FRONTAL BOUNDARY.
FLORIDA AND THE SOUTHEAST COAST SHOULD ALSO SEE AN INCREASE IN
RAINFALL AS A TROPICAL WAVE INTERACTS WITH THIS FRONTAL BOUNDARY
TO PRODUCE A WAVE THAT MOVES OFFSHORE THE SOUTHEAST AND MOISTURE
FROM THE FRINGE OF HARVEY ROTATE INTO THE REGION. TO THE
NORTH...SHOWERS AND THUNDERSTORMS WILL DEVELOP ACROSS THE CENTRAL
U.S. AND THE NORTHERN PLAINS/UPPER MIDWEST AHEAD OF UPPER
TROUGHING.  SHOWERS AND THUNDERSTORMS SHOULD ALSO DEVELOP ACROSS
THE SOUTHERN ROCKIES LATE IN THE WEEK WITH RETURN FLOW REACHING
THE SOUTHERN PLAINS BY THE WEEKEND.

REGARDING TEMPERATURES ACROSS THE COUNTRY...STRONG RIDGING OUT
WEST WILL ALSO LEAD TO WARMER THAN AVERAGE TEMPERATURES ACROSS
MUCH OF THE WESTERN U.S. AND THE GREAT BASIN/SOUTHWEST...EXPANDING
INTO THE NORTHERN ROCKIES EARLY NEXT WEEK.  NEAR THE SOUTHEASTERN
CYCLONE AND HARVEY, BELOW NORMAL TEMPERATURES ARE ALSO EXPECTED
WITH THE TYPICAL RECORD LOW MAXIMA POSSIBLE ALONG HARVEY`S TRACK.
WITH THE UPPER TROUGH ACROSS THE GREAT LAKES/OHIO
VALLEY/NORTHEAST...TEMPERATURES WILL BE SEVERAL DEGREES COOLER
THAN NORMAL LATER THIS WEEK AND THROUGH THE WEEKEND.

ROTH/PETERSEN
$$