Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 270831
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
331 AM CDT WED MAY 27 2015

.SYNOPSIS...

AN ACTIVE WEATHER PATTERN WILL PREVAIL OVER THE NEXT SEVERAL DAYS AS
SEVERAL IMPULSES MOVE ACROSS PORTIONS OF THE CONUS. THE FIRST
SHORTWAVE TROUGH THAT WILL IMPACT THE TN VALLEY HAS INDUCED MCS
ACTIVITY OVER THE ARKLATEX REGION AND WILL BE THE PRIMARY FOCUS FOR
THUNDERSTORM ACTIVITY OVER THE TN VALLEY THIS AFTERNOON. THEN,
ANOTHER MID-LEVEL SHORTWAVE TROUGH CROSSING THE DESERT SOUTHWEST WILL
PROVIDE ANOTHER FOCUS FOR THUNDERSTORM ACTIVITY ON THURSDAY ACROSS
THE SUPERSATURATED SOUTHERN PLAINS.

SL.77

&&

.DISCUSSION...

THE WEAKLY AMPLIFIED SHORTWAVE TROUGH THAT IS MOVING ACROSS OK INTO
AR WILL MOVE ACROSS THE TN VALLEY LATER THIS AFTERNOON. MCS ACTIVITY
ASSOCIATED WITH THIS TROUGH IS ALREADY IMPACTING THE ARKLATEX REGION
WITH BLOW OFF CIRRUS CROSSING OVER NW AL THIS MORNING. ADDITIONAL LOW
CLOUDS ARE MOVING ACROSS THE TN VALLEY. HOWEVER, THINNING OF THESE
CLOUDS IS LIKELY BUT IS DIFFICULT TO DETERMINE WHERE THE GREATEST
BREAKING IN THE CLOUDS WILL TAKE PLACE. IF THESE CLOUDS DO BREAK,
THEN INSOLATION ALONG WITH ALREADY WARM SFC TEMPERATURES WILL MEAN
DESTABILIZATION OF THE ENVIRONMENT SHOULD OCCUR. CURRENT MODEL
FORECAST SOUNDINGS SHOW MUCAPES BTWN 1000-2000 J/KG WITH THE NAM
MODEL THE MOST BULLISH WITH INSTABILITY. WEAK WIND SHEAR AND
ANTECEDENT SOUTHERLY FLOW COMBINED WITH THE INSTABILITY THAT IS
FORECAST MEAN THAT STRONG TO MARGINALLY SEVERE STORMS ARE LIKELY THIS
AFTERNOON. THERE IS UNCERTAINTY AS TO WHERE THE GREATEST INSTABILITY
WILL BE LOCATED GIVEN THE CLOUD COVER QUESTION. HOWEVER, THERE ARE
SOME INDICATIONS THAT NE AL MAY HAVE GREATER INSTABILITY WHERE HIGH
CLOUDS MAY NOT ENCROACH AS QUICKLY AS AREAS FURTHER WEST. SO, HAVE
INTRODUCED A GRADIENT IN POPS WITH HIGHER POPS OVER THAT AREA.
INVERTED V SOUNDINGS IN THE LOW LEVELS AND GENERALLY WEAK FLOW POINT
TOWARDS THE POSSIBILITY OF WET MICROBURSTS. THUS, THE PRIMARY THREAT
WITH THESE STORMS WILL BE GUSTY TO DAMAGING WIND GUSTS AND A LESSER
THREAT FOR SMALL HAIL. ONE LAST THING TO NOTE FOR TODAY`S FORECAST IS
THAT THERE MAY BE CONVECTIVE INDUCED MESOSCALE CONVECTIVE VORTICES
THAT MAY ACT TO ENHANCE REAR INFLOW JETS, PRODUCING HIGHER WIND GUSTS
ALONG ANY BOWING SEGMENTS.

AN ADDITIONAL SHORTWAVE TROUGH IS EXPECTED TO MOVE FROM THE SOUTHERN
PLAINS TOWARDS S MO/AR. AS IT DOES SO, IT WILL BE FURTHER REMOVED
FROM THE TN VALLEY (TO THE NW) WHICH WILL ACT TO LESSEN THE THREAT
FOR THUNDERSTORMS ON THURSDAY AFTERNOON/EVENING. THERE IS WEAK
INSTABILITY ON THURSDAY AFTERNOON WHICH WILL MAINLY TRANSLATE TO
ORDINARY THUNDERSTORMS ENDING LATE ON THURSDAY EVENING. MEANWHILE,
SHORTWAVE RIDGING WILL SPREAD NORTHWARD FROM THE GULF COAST. AS A
RESULT, BY FRIDAY, MORE ISOLATED TO SCATTERED THUNDERSTORMS WILL
PREVAIL DUE TO LACK OF LARGE SCALE LIFTING MECHANISM AND SUBSIDENCE.
IN ADDITION, DAYTIME HIGH TEMPERATURES SHOULD ALSO RISE INTO THE MID
80S (CLOSE TO NORMAL).

THEN, A CANADIAN UPPER LOW MOVING ALONG THE PREVAILING WESTERLIES OF
THE POLAR JET WILL EJECT A SHEARED TROUGH ACROSS THE N PLAINS, UPPER
MIDWEST, AND GREAT PLAINS ON FRIDAY INTO SATURDAY. A SFC COLD FRONT
WILL MOVE AHEAD OF THIS TROUGH AND ACT AS THE FOCUSING MECHANISM FOR
SHOWERS AND THUNDERSTORMS ACROSS THE OH AND MS RIVER VALLEYS. AS IT
SLOWLY PROGRESSES SOUTHEAST, IT IS EXPECTED TO BE THE FOCUSING
MECHANISM FOR DEEP CONVECTIVE UPDRAFTS OVER THE TN VALLEY ON SUNDAY
AFTERNOON. AS THE FRONT APPROACHES, IT LOOKS TO BECOME ILL-DEFINED OR
DISSIPATES ON MONDAY (TYPICAL FOR THIS TIME OF YEAR) BUT WILL STILL
KEEP CHC POPS IN THE FORECAST FOR THAT PERIOD. THE MID-UPPER FLOW
PATTERN THEN SHIFTS TO A SHORTWAVE TROUGH MEANDERING AROUND THE DEEP
SOUTH EARLY NEXT WEEK WHICH MAY ALSO AID IN STORM DEVELOPMENT OVER
THE TN VALLEY, DEPENDING ON ITS TRAJECTORY.

SL.77

&&

.AVIATION...
/ISSUED 1159 PM CDT TUE MAY 26 2015/
FOR 06Z TAFS...

SCATTERED MID AND HIGH LEVEL CLOUDS WILL CONTINUE TO FILTER ACROSS
THE FORECAST AREA THROUGH THE OVERNIGHT PERIOD. LOW LEVEL MOISTURE
REMAINS ELEVATED AND WITH BREAKS IN THE CLOUD COVER AND A LIGHT
WIND...MVFR BR IS EXPECTED TO DEVELOP AT THE KMSL AND KHSV TERMINALS
EARLY WEDNESDAY MORNING. THE FOG SHOULD MIX OUT AFTER
SUNRISE...HOWEVER A LOW STRATUS DECK WILL LIKELY MOVE ACROSS THE
AREA...WITH MVFR CIGS EXPECTED BY 16Z...WHICH WILL LIKELY BEGIN TO
LIFT BY THE AFTERNOON. WHILE A GREATER COVERAGE OF DIURNALLY DRIVEN
THUNDERSTORMS ARE EXPECTED DURING THE AFTERNOON TOMORROW...LOW
CONFIDENCE ON TIMING AND LOCATION OF INDIVIDUAL THUNDERSTORMS WILL
KEEP ONLY VCTS IN THE TAFS AT THIS TIME.

73

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    83  66  85  67 /  50  30  40  20
SHOALS        83  65  85  67 /  50  30  40  20
VINEMONT      81  65  83  66 /  50  30  40  20
FAYETTEVILLE  80  65  83  66 /  50  30  40  20
ALBERTVILLE   81  65  83  66 /  60  30  40  20
FORT PAYNE    80  65  82  65 /  60  40  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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