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Area Forecast Discussion

171
FXUS64 KHUN 260809
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
309 AM CDT TUE MAY 26 2015

.SYNOPSIS...

A WET SUMMER LIKE PATTERN PREVAILS FOR THIS FORECAST AS WEAK
IMPULSES ENVELOPED WITHIN THE PREVAILING SOUTHWEST TO SOUTHERLY FLOW
IMPACT THE TN VALLEY. A MEAN TROUGH PREVAILS ACROSS THE SOUTHERN
PLAINS/OZARKS/MS RIVER VALLEY WHILE BROAD RIDGING EXISTS JUST OFF THE
GA/SC/E FL COAST. THIS MEAN TROUGHING HAS RESULTED IN SEVERAL ROUNDS
OF RAINFALL AND SIGNIFICANT HISTORIC FLASH FLOODING OVER TX/OK.
MEANWHILE, A SPLIT FLOW REGIME WITH A COUPLE OF SHORTWAVE TROUGHS
PREVAILS FROM THE INTERMOUNTAIN WEST TO JUST OFF THE WEST COAST.

SL.77

&&

.DISCUSSION...

THE FIRST ONE IN THE SERIES OF WEAK MID-LEVEL SHORTWAVE TROUGHS
MOVING ACROSS AN UNSTABLE AND SATURATED ENVIRONMENT HAS KEPT A
SEVERE QLCS MOVING ACROSS THE LOWER MS RIVER VALLEY. THE NORTHERN
HALF OF THIS QLCS HAS ACTUALLY DIMINISHED IN INTENSITY DUE TO THE
MOISTURE ADVECTION CUTOFF BY THE STRONGER PORTIONS OF THE QLCS OVER
CENTRAL MS TO CENTRAL LA AND NW GULF COAST LINE. AS A RESULT OF THE
PREVAILING SW TO S FLOW ALOFT, MUCH OF THE TRAILING STRATIFORM AND
DEBRIS CIRRUS CLOUDS ARE MAINLY MOVING NORTHWARD ACROSS THE CORN
BELT REGION. HIGH CLOUDS ARE GRADUALLY SHIFTING NE TOWARDS THE TN
VALLEY BUT THIS CLOUD COVER MAY NOT ARRIVE IN TIME TO INHIBIT
DESTABILIZATION ESPECIALLY OVER NE AL LATE THIS MORNING AND
AFTERNOON. CURRENTLY, MODEL OUTPUT IS SUGGESTING THAT THE REGION
WILL REALIZE ~1000-2000 J/KG OF SBCAPE. HOWEVER, THOUGH THIS WILL
LARGELY DEPEND ON THE EXTENT/THICKNESS OF THE CLOUD COVER ANOTHER
QUESTION MARK IS THAT THE WIND SHEAR PARAMETERS ARE WEAK WITH 0-3 KM
BULK SHEAR VALUES BTWN 20-25KTS (JUST TO SPECIFY ONE PARAMETER). DUE
TO DAYTIME HEATING, DEWPOINT DEPRESSIONS SHOULD RISE WITHIN THE
MIXED LAYER ACTING TO INCREASE THE POTENTIAL FOR WET MICROBURSTS
GIVEN THE SATURATED COLUMN ABOVE ~900 MB. THE TIMING FOR ANY STORM
DEVELOPMENT APPEARS TO BE BETWEEN LATE MORNING AND EARLY AFTERNOON
WITH A STORM MODE OF DISCRETE TO MULTI-CELL CLUSTERS. AT THIS POINT,
THERE COULD BE STRONG TO MARGINALLY SEVERE THUNDERSTORMS WITH MAINLY
DAMAGING WINDS (FROM THE WET MICROBURST POTENTIAL), VERY HEAVY
RAINFALL, AND SMALL HAIL. THOUGH NOT EXPECTING A WIDESPREAD FLASH
FLOODING EVENT, GIVEN THE 1-2.5 INCHES OF RAINFALL THAT FELL
YESTERDAY ESPECIALLY OVER NW AL, THIS WILL BE MONITORED FOR A
POSSIBLE FLASH FLOOD WATCH.

THE SLOW MOVING MID-LEVEL SHORTWAVE TROUGH SHOULD THEN EXIT THE TN
VALLEY LATER THIS EVENING (BTWN 00Z-06Z) WHICH SHOULD MARK THE END
OF WIDESPREAD DEEP CONVECTION. DID KEEP CHC POPS IN FOR ANY ACTIVITY
THAT DEVELOPS FROM ANY LINGERING OUTFLOW BOUNDARIES AND/OR ANY WEAK
IMPULSES THAT MOVE ACROSS THE TN VALLEY WITHIN THE SATURATED
ENVIRONMENT. THEN, ON WEDNESDAY, ANOTHER WEAKLY AMPLIFIED SHORTWAVE
TROUGH MOVES ACROSS FROM THE ARKLATEX REGION BRINGING THE
POSSIBILITY FOR THUNDERSTORM ACTIVITY AGAIN. MODERATE INSTABILITY
COMBINED WITH WEAK WIND SHEAR WILL MEAN YET ANOTHER DAY OF
POTENTIALLY STRONG TO MARGINALLY SEVERE THUNDERSTORMS WITH SIMILAR
IMPACTS AS TUESDAY: DAMAGING WIND GUSTS FROM WET MICROBURSTS, VERY
HEAVY RAINFALL, AND SMALL HAIL.

FURTHER WEST, SHORTWAVE RIDGING WILL BEGIN OVER THE SOUTHERN PLAINS
ON WEDNESDAY WHICH MAY AFFORD TX AND OK AT LEAST A BRIEF BREAK FROM
WIDESPREAD RAINFALL. THIS SHORTWAVE RIDGE WILL SHIFT EASTWARD AND
AMPLIFY OVER THE SOUTHEAST ON THURSDAY INTO FRIDAY TRANSLATING TO
MORE DIURNALLY DRIVEN ISOLATED TO SCATTERED THUNDERSTORM ACTIVITY
DURING BOTH DAYS. SIMILAR CONDITIONS MAY PREVAIL ON SATURDAY BEFORE
A MEAN TROUGH MOVES OVER THE PLAINS AGAIN LATER THIS WEEKEND TOWARDS
THE TN VALLEY. THOUGH MED RANGE MODELS SOLUTIONS VARY WITH THIS
UPPER FLOW PATTERN, HAVE KEPT CHANCE FOR THUNDERSTORMS IN THE
FORECAST THROUGH THE REST OF THE EXTENDED. HAVE ALSO KEPT MORE
SEASONABLE MID 80S DAYTIME HIGHS AND OVERNIGHT LOWS IN THE MID 60S
PREVAILING THROUGH THE WEEKEND GIVEN THE POTENTIAL FOR BROKEN CLOUD
COVER AND DEEP WAA.

SL.77

&&

.AVIATION...
/ISSUED 1238 AM CDT TUE MAY 26 2015/
FOR 06Z TAFS...
VERY MOIST AIRMASS AND SOUTHERLY FLOW WILL LEAD TO LOW CLOUD
DEVELOPMENT IN AREAS THIS MORNING INCLUDING TEMPO IFR CIGS AT BOTH
KMSL AND KHSV. A LINE OF SHRA AND TSRA IS EXPECTED TO ARRIVE SLOWER
THAN PREVIOUSLY FORECAST. GIVEN THIS UNCERTAINTY, CONTINUE TO
FORECAST VCTS ATTM. REDEVELOPMENT DURING THE AFTERNOON IS ALSO
CONTINGENT ON MORNING PRECIP TRENDS, SO MAINTAINED VCTS AT BOTH KMSL
AND KHSV THRU THE DAY. SOUTHERLY WINDS WILL BE GUSTING AT 15-20KT
THRU THE DAY.

AK

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    79  67  84  67 /  90  50  50  30
SHOALS        79  67  84  67 /  90  50  50  30
VINEMONT      78  67  81  66 /  90  50  50  30
FAYETTEVILLE  78  66  81  66 /  90  50  50  30
ALBERTVILLE   79  66  81  65 /  90  50  60  30
FORT PAYNE    78  66  80  64 /  90  50  60  40

&&

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

$$

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



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