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Area Forecast Discussion

217
FXUS64 KHUN 021926
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
226 PM CDT THU JUL 2 2015

.SYNOPSIS...

A WET, MEAN TROUGH PATTERN WILL PREVAIL ACROSS THE TN VALLEY OVER
THE NEXT 4-5 DAYS. CURRENTLY, A MEAN TROUGH REMAINS ACROSS THE
EASTERN HALF OF THE CONUS WHILE THE WESTERN CONUS REMAINS WITHIN AN
ELONGATED RIDGE STRETCHING NORTH TO BRITISH COLUMBIA. COMPRESSED BTWN
THE MEAN TROUGH AND RIDGE ARE SEVERAL MID LEVEL SHORTWAVE TROUGHS
MOVING SOUTHEAST FROM THE DAKOTAS TOWARDS THE TN/MS RIVER VALLEYS.
THE TRAJECTORY OF THESE MID-LEVEL SHORTWAVE TROUGHS AND MCS INDUCED
OUTFLOW BOUNDARIES WILL BE THE PRIMARY IMPETUS FOR SHOWERS AND
THUNDERSTORMS FOR THE FORECAST.

SL.77

&&

.DISCUSSION...

STRONG TO SEVERE THUNDERSTORMS THAT HAVE BEEN MOVING ACROSS NE AL
AND S MIDDLE TN WILL GRADUALLY MOVE OFF TO NORTH GA AS A WEAK
CONVERGENCE AXIS OVER S TN WILL SHIFTS EAST. A MID-LEVEL SHORTWAVE
TROUGH CURRENTLY MOVING ACROSS CENTRAL KY/TN MAY CAUSE THE
DEVELOPMENT OF ADDITIONAL SHOWERS AND THUNDERSTORMS LATE TONIGHT INTO
EARLY TOMORROW MORNING ESPECIALLY OVER S TN/NE AL. THE THUNDERSTORM
COMPLEX THAT ARRIVES (OVER S TN AND NE AL) MAY BE A COMBINATION OF AN
ONGOING CLUSTER OF THUNDERSTORMS AND OUTFLOW BOUNDARY OUTRUNNING THE
CLUSTER PRODUCING ADDITIONAL ACTIVITY. THESE THUNDERSTORMS MAY
ACTUALLY COLLAPSE UPON ARRIVAL DUE TO THE LACK OF INSTABILITY AND
EASTERLY BULK SHEAR VALUES EARLY FRIDAY MORNING WHICH WILL BE THE
PRIMARY IMPACT (STRONG TO MARGINALLY SEVERE WIND GUSTS).

THEN, FOR THE INDEPENDENCE DAY HOLIDAY WEEKEND, AS MENTIONED EARLY
IN THE DISCUSSION, THERE ARE A SERIES OF MID-LEVEL SHORTWAVE TROUGHS
AND MCS INDUCED OUTFLOW BOUNDARIES THAT ARE OF PARTICULAR CONCERN FOR
THE HOLIDAY WEEKEND. FRIDAY`S EARLY MORNING ACTIVITY MAY RESULT IN
SOME INHIBITION AT LEAST FOR PART OF THE DAY UNTIL DAYTIME HEATING
GRADUALLY DESTABILIZES THE TN VALLEY AGAIN. THEN, ADDITIONAL STRONG
TO SEVERE THUNDERSTORMS ARE POSSIBLE ALONG ANOTHER CONVERGENCE
BOUNDARY OVER S TN AND WEAKLY AMPLIFIED SHORTWAVE TROUGH.
FURTHERMORE, A STRONG LLJ STRETCHING FROM THE NW GULF TO THE TN/MID
MS RIVER VALLEY ALREADY WILL HAVE CREATED AN ENVIRONMENT WITH HIGH
PWATS CLOSE TO 2.0 INCHES AND LOW DEWPOINT DEPRESSIONS THROUGHOUT THE
COLUMN. SO, ANY STORMS THAT DEVELOP ON FRIDAY AFTERNOON WILL BE
EFFICIENT RAINFALL PRODUCERS ALONG WITH THE POTENTIAL FOR WET
MICROBURSTS AND STRAIGHT-LINE WIND GUSTS. THE FORECAST FOR FRIDAY
NIGHT AND SATURDAY MORNING WILL MAINLY CENTER OVER THE PROGRESSION OF
A SHEARED TROUGH PUSHING ACROSS THE APPALACHIANS TO THE TN VALLEY
WHICH COULD SEND A LINE OF SHOWERS AND THUNDERSTORMS FROM THE OH
RIVER VALLEY SOUTHWARD. THEN, AFTER A BRIEF BREAK DURING THE DAY, YET
ANOTHER MID-LEVEL SHORTWAVE TROUGH FROM THE CENTRAL/SOUTHERN PLAINS
WILL MOVE ACROSS AR/N MS ON SATURDAY AFTERNOON/EVENING WITH MORE
THUNDERSTORMS DEVELOPING FROM N MS/W TN. THESE STORMS WOULD THEN PUSH
OVER THE TN VALLEY ON SATURDAY EVENING. ONE THING TO KEEP IN MIND IS
THAT THE TIMING OF THESE THUNDERSTORM "EPISODES" HAS BEEN CHANGING
(AND WILL LIKELY CHANGE AGAIN) FROM ONE MODEL RUN TO THE NEXT. SO,
THOSE ENJOYING OUTDOOR ACTIVITIES THIS WEEKEND SHOULD MONITOR THE
LATEST FORECASTS EACH DAY AS THIS SCENARIO PROGRESSES. BY SUNDAY
MORNING, MODELS ARE SHOWING THE MAIN TROUGH AXIS SHIFTING EAST
UNDERNEATH A RIDGE. THIS COULD TRANSLATE TO A BREAK IN THE
THUNDERSTORM ACTIVITY ON SUNDAY AFTERNOON AND EVENING.

DAYTIME HIGH TEMPERATURES DURING THE WEEKEND WILL BE HIGHLY
DEPENDENT ON THE SPATIAL COVERAGE AND TIMING OF THE THUNDERSTORM
ACTIVITY. SO, DESPITE THE DAYTIME HIGH TEMPERATURE FORECAST IN THE
LOW 80S, THERE COULD BE HIGHER DAYTIME HIGHS IN BETWEEN ANY
BREAKS/QUICK CLEARINGS THAT OCCUR.

THEN, WITH THE UPPER FLOW PATTERN CHANGING TO A MORE ZONAL FLOW
PATTERN, MONDAY MAY BE THE TRANSITION DAY WHERE POPS MAY NEED TO BE
TAILORED DOWNWARD. FOR NOW, HAVE KEPT HIGH END POPS DUE TO THE
COMPLEX PATTERN TRANSITION AND THE POSSIBILITY FOR OTHER MID-LEVEL
SHORTWAVE TROUGHS ROTATING AROUND THE BUILDING RIDGE TO THE WEST AND
EXITING TROUGH. SPEAKING OF THE BUILDING RIDGE, TUESDAY AND WEDNESDAY
MAY YIELD MORE ISOLATED TO SCATTERED THUNDERSTORMS DUE THE RIDGE THAT
HAD BEEN RELEGATED TO THE CARIBBEAN AND BERMUDA FINALLY BUILDING
NORTH ACROSS THE PLAINS/SOUTHEAST. THIS WILL LIKELY MEAN THE RETURN
OF HOTTER TEMPERATURES (IN THE UPPER 80S/LOW 90S) AND LOWER POPS BY
THE END OF NEXT WEEK.

SL.77

&&

.AVIATION...
/ISSUED 1244 PM CDT THU JUL 2 2015/
FOR 18Z TAFS...THE UNSETTLED WEATHER PATTERN WILL PERSIST ACROSS THE
REGION OVER THE NEXT 24 HOURS. A SERIES OF UPPER LEVEL DISTURBANCES
WILL TRAVERSE THE REGION COMBINING WITH A WARM AND UNSTABLE AIRMASS
TO BRING PERIODIC SHOWER AND THUNDERSTORM ACTIVITY. GIVEN THE
CHALLENGES WITH TIMING THE INDIVIDUAL FEATURES...HAVE INCLUDED VCSH
THROUGH A RATHER LARGE PORTION OF THE PERIOD WITH GENERALLY VFR
CONDITIONS. EXPECT A SLIGHTLY HIGHER POTENTIAL FOR THUNDERSTORMS
THROUGH AFTN AT BOTH TAF SITES AND INCLUDED TEMPO GROUPS
ACCORDINGLY. PROBABILTIIES INCREASE AGAIN IN A WINDOW LATE
TONIGHT/EARLY FRIDAY AND INTRODUCED ANOTHER THREAT PERIOD THEN AS
WELL.

15

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    70  85  69  82 /  80  60  50  60
SHOALS        70  84  70  82 /  70  60  50  60
VINEMONT      69  84  69  81 /  70  60  50  60
FAYETTEVILLE  69  83  68  81 /  80  60  50  60
ALBERTVILLE   69  82  69  82 /  80  60  50  60
FORT PAYNE    68  83  68  81 /  80  60  50  60

&&

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

$$

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



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