Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 222329 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
629 PM CDT FRI AUG 22 2014

.UPDATE...
FOR 00Z TAFS

&&

.DISCUSSION...
/ISSUED 219 PM CDT FRI AUG 22 2014/
A HOT AND STEAMY DAY EXISTS ACROSS THE TENNESSEE VALLEY WITH THE
COMBINATION OF AIR TEMPERATURES /IN THE LWR 90S/ AND HUMIDITY
RESULTING IN HEAT INDICES BTWN 95-100F AS OF 19Z. A WEST-NORTHWEST
SFC WIND APPEARS TO BE MIXING BOUNDARY LAYER JUST ENOUGH TO LOWER
DEWPTS SEVERAL DEGREES /MID TO UPR 60S/...ESPECIALLY ACROSS NE
ALABAMA. AT THE UPR LVLS...A BROAD AREA OF HIGH PRESSURE EXTENDS
FROM THE SOUTHERN PLAINS TO THE SOUTHEAST REGION. CONVECTION CAN BE
SEEN DEFINING THE OUTER EDGES OF THIS UPR HIGH AS A SERIES OF UPR LVL
DISTURBANCES/WAVES MOVE CLOCKWISE AROUND THE UPR HIGH.

THROUGH MONDAY...THE MAIN STORY WILL CONTINUE TO BE THE HEAT AND
HUMIDITY WHICH WILL RESULT IN AT LEAST ONE MORE DAY /SATURDAY/ OF
HEAT INDEX VALUES APPROACHING OR EXCEEDING 105F. THIS IS WHAT
PROMPTED THE HEAT ADVISORY FOR THE AREA -- WHICH WILL CONTINUE
THROUGH SATURDAY AFTERNOON. ASIDE FROM THE HEAT...UPR LVL ENERGY
CURRENTLY SLIDING SOUTHEAST ACROSS THE OHIO VALLEY /NRN PERIPHERY OF
UPR RIDGE/ WILL HEAD TOWARD THE SOUTHERN APPALACHIANS AND EVENTUALLY
TURN BACK TO THE SOUTHWEST ON SUNDAY AS THE UPR RIDGE RE-POSITIONS
ITSELF ALONG THE MS RIVER. THE RESULT WILL BE ISOLATED AFTN
SHRA/TSRA MAINLY EAST OF I-65 SATURDAY.

COVERAGE OF CONVECTION IS EXPECTED TO INCREASE SUNDAY INTO MONDAY AS
UPR LVL S/W ENERGY INTERACTS WITH A BACK DOOR "FRONT" FCST TO ENTER
EASTERN ALABAMA BTWN 06Z-12Z MONDAY. LOSS OF HEATING SUNDAY NIGHT
COULD QUELL CONVECTION BEFORE IT FIRES BACK UP ALONG THE LEADING
EDGE OF THE FRONTAL BOUNDARY /DRIFTING WEST/ ACROSS THE AREA MONDAY.
HIGH INSTABILITY BUT RELATIVELY LOW SHEAR SUGGESTS POTENTIAL FOR A
FEW STRONG BUT POORLY ORGANIZED STORMS CAPABLE OF GUSTY WINDS AND
HEAVY RAIN...GIVEN PWATS LIKELY BETWEEN 1.8 AND 2.0 INCHES. STORM
MOVEMENT WILL BE NORTH-TO-SOUTH OR NORTHEAST-TO-SOUTHWEST BY SUNDAY.
DUE TO EXPECTED INCREASE IN CLOUDS AND PRECIP...FEEL THE AREA WILL
NOT SEE `HEAT ADVISORY` CRITERIA ON SUNDAY OR MONDAY.

TUESDAY THROUGH FRIDAY...
BEHIND THE PASSING SHORTWAVE TRAVERSING THE SOUTHERN EDGE OF THE UPR
HIGH...THE RIDGE WILL BRIEFLY BUILD BACK OVER THE SOUTHEAST REGION
TUESDAY AND WEDNESDAY. THEN THINGS GET A LITTLE MESSY AS THE MEDIUM
RANGE MODELS DIVERGE. THE 22/12Z GFS SHOWS A MORE PROGRESSIVE OPEN
WAVE TROUGH APPROACHING AND CROSSING THE AREA THURSDAY AND FRIDAY.
THE 12Z ECMWF IS SLOWER AND DOESN`T REALLY BRING THE TROUGH ACROSS
THE AREA UNTIL NEXT WEEKEND. AT THIS TIME...MAINTAINED JUST A SLIGHT
CHANCE /20%/ POP GOING THURSDAY AND FRIDAY TO ACCOUNT FOR
DISCREPANCIES. TEMPS WILL REMAIN WARM...AT OR A FEW DEGREES ABOVE
NORMAL THROUGH MID WEEK. TEMPS WILL THEN BE DEPENDENT ON WHAT THE
ABOVE MENTIONED UPR TROUGH DECIDES TO DO. USED A BLEND BETWEEN THE
EXTENDED GFS MOS AND ECMWF MOS GUIDANCE FOR TEMPS WED-FRI.

DJN.83

&&

.AVIATION...
FOR 00Z TAFS...

VFR CONDITIONS ARE EXPECTED ACROSS N AL/S MIDDLE TN FOR THE NEXT 24
HOURS WITH THE EXCEPTION OF FOG FORMATION EXPECTED BTWN 08-12Z THAT
MAY LOWER CAT TO MVFR/IFR.

SL.77

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...HEAT ADVISORY UNTIL 9 PM CDT SATURDAY FOR ALZ001>010-016.

TN...HEAT ADVISORY UNTIL 9 PM CDT SATURDAY FOR TNZ076-096-097.

&&

$$

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


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