Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 020801
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
301 AM CDT TUE SEP 2 2014

.SYNOPSIS...

A SHORTWAVE TROUGH EMBEDDED WITHIN A BROAD AMPLITUDE TROUGH ACROSS
THE UPPER MS RIVER VALLEY IS BRINGING WIDESPREAD CONVECTIVE ACTIVITY
TO THE CORN BELT REGION AND E KS/N OK. A QUASI-ZONAL UPPER FLOW
PATTERN EXISTS OVER THE WESTERN HALF OF THE COUNTRY TO THE WEST OF
THIS FEATURE. MEANWHILE OVER THE ATLANTIC, AN AMPLIFIED RIDGE EXISTS
FROM MAINE/E ONTARIO TO EAST OF THE BAHAMAS.

IN ADDITION, TS DOLLY HAS FORMED OVER THE BAY OF CAMPECHE AND IS
EXPECTED TO IMPACT THE EASTERN MEXICAN COAST.

SL.77

&&

.DISCUSSION...

THE SHORTWAVE TROUGH MOVING ACROSS THE UPPER MS RIVER VALLEY WILL
CONTINUE TO DRIVE EASTWARD WITH THE ACCOMPANYING CONVECTIVE COMPLEX
EXPECTED TO MOVE SLOWLY SOUTH AND SOUTHEAST ACROSS THE OH RIVER
VALLEY TODAY. AS THIS FEATURE APPROACHES THE TN VALLEY, CLOUD COVER
WILL BEGIN TO INCREASE FROM NW TO SE. IN ADDITION, AN ANTECEDENT
TROPICAL AND UNSTABLE AIRMASS COULD TRANSLATE TO DIURNALLY DRIVEN
THUNDERSTORM ACTIVITY DURING THE AFTERNOON. THUS, HAVE INCLUDED
ISOLATED THUNDERSTORMS DURING THE AFTERNOON FOLLOWED BY HIGHER CHC
POPS FOR THIS EVENING AND LATE TONIGHT AS PORTIONS OF THE
THUNDERSTORM COMPLEX MOVE OVER MIDDLE TN TOWARDS N AL. HOWEVER, THE
COMPLEX DOES LOOK TO WEAKEN AS IT APPROACHES DUE TO THE LACK OF A
LARGE SCALE LIFTING MECHANISM. HOWEVER, OUTFLOW BOUNDARIES
ORIGINATING FROM THIS COMPLEX COULD PLAY A ROLE WITH MAINTAINING
DEEP CONVECTION INITIALLY, BUT INSTABILITY LOOKS TO DROP OFF
CONSIDERABLY WITH LOSS OF DAYTIME HEATING AND LITTLE IN THE WAY OF
MEAN FLOW.

THOUGH THERE DOES NOT APPEAR TO BE A SYNOPTIC FRONT ASSOCIATED WITH
THE PASSAGE OF THE MID-LEVEL SHORTWAVE TROUGH TO THE NORTHEAST, ANY
LINGERING OUTFLOW BOUNDARIES ON WEDNESDAY WILL LIKELY LEAD TO THE
DEVELOPMENT OF DIURNALLY DRIVEN, PULSE-LIKE THUNDERSTORMS.
FURTHERMORE, A WEAK 500-400 MB IMPULSE IS DEPICTED BY THE MODELS AS
MOVING ACROSS THE MID MS RIVER VALLEY AND OVER THE TN VALLEY ON
WEDNESDAY AFTERNOON--POSSIBLY PROVIDING ADDITIONAL LIFT FOR
THUNDERSTORMS.

SYNOPTICALLY, THE RIDGE OVER THE WESTERN ATLANTIC WILL BE BUILDING
WEST OVER THE SOUTH AND DEEP SOUTH/TN VALLEY SENDING THE QUASI-ZONAL
FLOW PATTERN TO THE NORTH OVER THE GREAT LAKES. THIS WILL ACT TO
BRING BACK SUMMER WITH VERY HOT AND HUMID CONDITIONS ON THURSDAY AND
FRIDAY. ISOLATED TO SCATTERED AFTERNOON THUNDERSTORMS WILL BE
POSSIBLE ON BOTH THURSDAY AND FRIDAY WITH DAYTIME HIGHS IN THE
MIDDLE 90S WITH LOWS IN THE LOW 70S. IN FACT, HEAT INDEX VALUES ARE
FORECAST TO RISE TO BETWEEN 100-104 ON THURSDAY AND MAY NEED A HEAT
ADVISORY IF DEWPOINTS OR TEMPERATURES ARE FORECAST TO BE HIGHER IN
LATER MODEL RUNS.

THEN FOR THE REST OF THE FORECAST, BY FRIDAY NIGHT A POSITIVELY
TILTED AXIS LOCATED FROM ALBERTA/SASKATCHEWAN TO THE PACIFIC
NORTHWEST WILL MOVE EAST ACTING TO DAMPEN THE RIDGE OVER THE SOUTH
AND SHIFT IT WEST. THIS TROUGH WILL THEN MOVE ACROSS THE NORTHERN
PLAINS AND OVER THE GREAT LAKES PUSHING A SFC COLD FRONT SE OVER THE
OH RIVER VALLEY BY FRIDAY NIGHT. THUNDERSTORM ACTIVITY IS EXPECTED
TO DEVELOP ALONG THIS FRONT ON SATURDAY INTO SATURDAY EVENING, BUT
IT LOOKS TO BE MORE PULSE-LIKE IN NATURE WITH MODERATELY UNSTABLE
SOUNDING PROFILE. THUS, HAVE KEPT THUNDERSTORMS IN THE FORECAST FOR
SATURDAY AND SUNDAY. HOWEVER, TAILORED POPS DOWNWARD WITH PASSAGE OF
FRONT ON SUNDAY EVENING/MONDAY. ALSO MADE MINOR ADJUSTMENTS TO THE
AIR TEMPERATURE AND DEWPOINT TEMPERATURE FORECAST (LOWERED SLIGHTLY)
DURING THAT TIME PERIOD GIVEN THE EXPECTED FRONTAL PASSAGE.

SL.77

&&

.AVIATION...
/ISSUED 1211 AM CDT TUE SEP 2 2014/
FOR 06Z TAFS... PATCHY BR MAY REDUCE VSBY INTO THE MVFR CATEGORY AT
KMSL AND KHSV FROM 09-12Z. OTHERWISE...VFR CONDITIONS ARE FORECAST
THRU THE PD. ISOLD-SCT TSRA ARE PSBL TUESDAY AFTN...BUT THE PROB
REMAINS TOO LOW TO INCLUDE IN THE PREVAILING FORECAST.

AK

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    92  70  92  70 /  20  30  40  20
SHOALS        93  71  93  71 /  20  40  40  20
VINEMONT      92  70  92  70 /  20  30  40  20
FAYETTEVILLE  90  68  90  69 /  20  40  40  20
ALBERTVILLE   89  70  90  70 /  20  30  40  20
FORT PAYNE    91  69  91  69 /  20  30  40  20

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE
AT WEATHER.GOV/HUNTSVILLE.


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