Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 050804
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
304 AM CDT WED AUG 5 2015

.SYNOPSIS...

THE UNUSUAL UPPER FLOW PATTERN CHANGES SLIGHTLY FOR THIS FORECAST
WITH MEAN TROUGHING OFF EITHER COAST AND RIDGING OVER THE
CENTRAL/SOUTHERN PART OF THE COUNTRY. A SHEARED VORTICITY CONVERGENCE
ZONE, WITH AT LEAST TWO EMBEDDED SHORTWAVE TROUGHS, OVER THE MO RIVER
VALLEY WILL SLOWLY AMPLIFY OVER THE NEXT 24 HOURS AS IT MOVES CLOSER
TO THE TN VALLEY. MEANWHILE, THE SYNOPTIC SCALE RIDGE CURRENTLY
LOCATED OVER THE DESERT SOUTHWEST WILL BEGIN TO BUILD EAST OVER THE
SOUTHERN PLAINS LATER THIS WEEKEND. AS A RESULT OF THE APPROACH OF
THE SLOWLY AMPLIFYING SHEARED TROUGH, STRONG TO MARGINALLY SEVERE
THUNDERSTORMS WILL PREVAIL ON THU/FRI AND A RETURN TO HOT CONDITIONS
ON SUN/MON.

SL.77

&&

.DISCUSSION...

HOT AND HUMID CONDITIONS WILL PREVAIL AGAIN TODAY WITH AN ADDED
BONUS POTENTIAL FOR SHOWERS AND THUNDERSTORMS. THE CLOUD COVER AND
THUNDERSTORM ACTIVITY WILL ACT TO LOWER DAYTIME HIGHS FOR TODAY
COMPARED TO YESTERDAY, BUT STILL EXPECTING TEMPERATURES TO RISE CLOSE
TO OR EXCEED 90 DEGREES. DRY AIR ALOFT AND WEAK SHEAR WILL ACT TO
LIMIT UPDRAFT STRENGTH TODAY WITH INSTABILITY PROFILES SHOWING
SBCAPES OF 1000-2000 J/KG. THE PRIMARY LIFTING MECHANISM FOR THIS
AFTERNOON WILL PRIMARILY CENTER AROUND A WEAK EDDY ROTATING WITHIN A
BELT OF PREVAILING WESTERLIES OVER THE CENTRAL PLAINS. IN ADDITION TO
THIS FEATURE, SEVERAL OUTFLOW BOUNDARIES FROM EARLY CONVECTIVE
ACTIVITY MAY ALSO BE THE FOCUS FOR PULSE-LIKE CONVECTIVE CELLS. WITH
THE WEAK SHEAR AND STEERING FLOW, ANTICIPATING SCATTERED
THUNDERSTORMS POSSIBLY MERGING INTO CLUSTERS.

THEN, AS THE AFOREMENTIONED SHEARED TROUGH AMPLIFIES AND MOVES
CLOSER TO THE TN VALLEY TONIGHT, MORE WIDESPREAD SHOWERS AND
THUNDERSTORMS SHOULD DEVELOP AND MOVE SOUTHEAST THIS EVENING. A
MARKED INCREASE IN BULK SHEAR IS NOTED (LIKELY DUE TO THE ENHANCEMENT
OF SHEAR WITH THE TROUGH ITSELF). ADDITIONAL SATURATION OF THE MID TO
UPPER LEVELS WILL ACT TO ENHANCE CLOUD PHYSICS (LARGER RAIN DROPS),
UPDRAFT LONGEVITY, AND--WITH DRY LOW-LEVELS--MICROBURST POTENTIAL. A
BREAK IN THE CONVECTIVE ACTIVITY SHOULD OCCUR ON EARLY THURSDAY
MORNING BEFORE DISCRETE CELLS FORM AHEAD OF WHAT APPEARS TO BE A VORT
MAX AHEAD OF THE TROUGH AXIS. THOUGH CHALLENGING TO ASCERTAIN THE
MODEL HANDLING THE INSTABILITY PROFILE DURING THIS PARTICULAR
EPISODE, THERE SHOULD BE AT LEAST IMPACTFUL HEAVY RAINFALL AND
PERHAPS GUSTY WINDS UP TO 40 MPH WITH ANY STORMS THAT DEVELOP. AS THE
SHORTWAVE TROUGH AXIS SWINGS OVER MS/CENTRAL TN AN ENHANCEMENT OF
WIND SHEAR AND VEERING OF THE MID-LEVEL WINDS LOOKS TO SUPPORT WEAK
ROTATING UPDRAFTS AND DISCRETE CELLS. THOUGH, AGAIN, CHALLENGING TO
PREDICT THE MESOSCALE INSTABILITY PROFILES MODEL OUTPUT SUGGESTS THE
POTENTIAL FOR 0-3 KM BULK SHEAR VALUES BTWN 30- 45 KTS ALONG WITH
SBCAPES AROUND 600-1000 J/KG. BECAUSE OF THE INCREASE IN WIND SHEAR
AND PWATS CLOSE TO 2.0 INCHES, ANTICIPATE A THREAT FOR GUSTY TO
DAMAGING WIND GUSTS AND VERY HEAVY RAINFALL UNTIL THURSDAY EVENING.

SHOWERS AND THUNDERSTORMS WILL LIKELY LINGER INTO FRIDAY AS ANOTHER
WEAK EDDY WITHIN THE PREVAILING NW FLOW ENTERS THE TN VALLEY UPSTREAM
OF THE EXITING SHORTWAVE TROUGH. DRIER WEATHER SHOULD THEN PREVAIL ON
SATURDAY THROUGH MONDAY AS THE TROUGH EXITS OFF THE COAST. HOWEVER,
WITH RIDGE BUILDING TAKING PLACE FROM THE DESERT SOUTHWEST TO THE
SOUTHERN PLAINS ON THURSDAY INTO FRIDAY, IT IS PLAUSIBLE (AND AT
LEAST 1 MODEL IS HINTING AT THIS SCENARIO) THAT A COUPLE OF MID-LEVEL
SHORTWAVE TROUGHS ROTATING AROUND THE NORTHERN FLANK OF THE RIDGE
COULD IMPACT US. THE TIMING OF THESE WAVES IS CHAOTIC IN THE MED
RANGE MODELS, BUT IT DOES LOOK PROBABLE AND HAVE LEFT A SCHC-CHC OF
POPS IN THE FORECAST ON MONDAY/TUESDAY. MEANWHILE, DAYTIME HIGH
TEMPERATURES WILL BE BACK IN THE LOW TO MID 90S ON SUNDAY AND PERHAPS
MONDAY DEPENDING ON THE TIMING OF THESE SHORTWAVE TROUGHS FOR THESE
THUNDERSTORMS. THIS WILL MEAN A RETURN TO HEAT INDEX VALUES BTWN
100-105!

SL.77

&&

.AVIATION...
/ISSUED 1200 AM CDT WED AUG 5 2015/
FOR 06Z TAFS...CURRENT RADAR DATA SUGGESTS SCT SHRA/ISOLD TSRA WILL
PASS SUFFICIENTLY CLOSE TO HSV WITHIN THE NEXT COUPLE OF HRS TO
WARRANT VCSH. IN THE WAKE OF THIS PCPN...LGT/VRBL FLOW WILL PROMOTE
DEVELOPMENT OF PATCHY BR/FG BTWN 05/09-14Z. OTHERWISE...VFR CONDS ARE
EXPECTED -- WITH SCT AC BENEATH BKN/OVC CS. MID/HIGH-LEVEL CIGS WILL
CONTINUE THICKEN/LOWER TOMORROW MORNING AND EARLY AFTN...WITH WINDS
INCREASING TO ARND 5-10 KTS FROM THE WSW. THREAT FOR ADDITIONAL
SHRA/TSRA WILL INCREASE AT BOTH TERMINALS BY 22Z...AS A STRONGER
UPPER AIR DISTURBANCE BEGINS TO MOVE SEWD FROM THE MID-MISSISSIPPI
VALLEY REGION. THIS ACTIVITY WILL LIKELY REMAIN A THREAT THRU AT
LEAST END OF THE CURRENT TAF PERIOD -- AND POSSIBLE BEYOND. SFC WINDS
TOMORROW EVENING WILL BACK TO THE SE AND DECREASE TO ARND 5 KTS OR
LESS.

70/DD

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    94  72  88  72 /  30  40  70  50
SHOALS        93  72  89  73 /  30  40  80  40
VINEMONT      91  70  86  70 /  30  40  70  50
FAYETTEVILLE  90  71  85  70 /  30  40  70  50
ALBERTVILLE   92  71  86  71 /  30  40  70  50
FORT PAYNE    91  70  85  68 /  30  40  70  50

&&

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

$$

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


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