000
FXUS64 KHUN 180309 AAB
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
1009 PM CDT FRI MAY 17 2013

.UPDATE...
TRIMMED BACK RAIN CHANCES FROM CATEGORICAL TO LIKELY FOR THE
OVERNIGHT. ALSO ADDED PATCHY FOG LATE IN THE NIGHT.

&&

.DISCUSSION...
SHOWERS ASSOCIATED WITH A CONVECTIVE COMPLEX (WITH A MCS LIKE
APPEARANCE FROM A SATELLITE PERSPECTIVE) WERE EXITING FAR NE
ALABAMA. THROUGHOUT THE EVENT (ACROSS THE TENNESSEE VALLEY)...
LIGHTNING ACTIVITY WAS AT BEST SPORADIC AND MAINLY AFFECTED AREAS
SOUTH OF THE TENNESSEE RIVER. RAINFALL WITH THIS SYSTEM RANGED FROM
1/2 TO ABOUT 1.5 INCHES. AS THEN HEAVIER CONVECTION IN THE SYSTEM
CROSSED THE I-65 CORRIDOR...PRODUCED TWO SHORT LIVED EF-0 TORNADOES.
ONE PRODUCED SPOTTY DAMAGE ON THE EAST SIDE OF ATHENS...AND THE OTHER
NEAR ELKMONT. SEE OUR LATEST PUBLIC INFORMATION STATEMENT FOR MORE
INFORMATION. MORE INFORMATION ABOUT THIS STORM WILL BE POSTED ON OUR
WEBSITE VERY SHORTLY.

IN THE MEANWHILE...A WEAK SOUTHERLY FLOW WAS BRINGING A SUPPLY OF
MOISTURE INLAND FROM THE GULF. THIS MOISTURE AND LIFT PROVIDED BY
PASSING UPPER DISTURBANCES HELPED TO CREATE THE RECENT CONVECTION THE
AREA EXPERIENCED. THE DISTURBANCE...NOW OVER NE AL...AND ITS LOWER
REFLECTION HAD CREATED RATHER HIGH (300-500 M/S) HELICITY VALUES
ACROSS THE REGION EARLIER. SHORT TERM MODEL OUTPUT WAS IN GENERAL
AGREEMENT OF MORE SHOWER/THUNDERSTORM DEVELOPMENT DURING THE
OVERNIGHT...DUE TO MANY INTERACTING BOUNDARIES AND CONTINUED
INSTABILITY. DUE TO A GOOD CHANCE OF MORE SHOWER ACTIVITY...STAYED
WITH LIKELY RAIN CHANCES FOR THE NIGHT TIME. NOT CERTAIN ENOUGH FOR
CATEGORICAL CHANCES...SO TRIMMED THEM DOWN A CATEGORY. HAVE ALSO
ADDED A MENTION OF PATCHY FOG IN FOR THE LATE NIGHT...GIVEN LEFTOVER
MOISTURE FROM THE RECENT RAINS. LOW TEMPERATURE FORECASTS...WINDS...
AND CLOUD COVER LOOK FINE...WITH ONLY A MINOR TWEAK HERE/THERE IN
THOSE AREAS. UPDATED FORECASTS HAVE BEEN ALREADY SENT.

RSB

&&

.AVIATION...
/ISSUED 647 PM CDT FRI MAY 17 2013/
FOR 00Z TAFS...AS SHRA CONTINUE TO MOVE ACROSS THE AREA THRU THE
PERIOD...CIGS WILL REMAIN A PROBLEM AT BOTH TERMINALS. OVERALL
PREDOMINANT CONDITIONS THRU LATE TOMORROW MORNING SHOULD BE AT LEAST
BELOW ALT REQ...BUT HIGHLY VARIABLE CIGS SHOULD BE EXPECTED.

AFTER THE MAIN AREA OF SHRA PUSHES EAST OF KHSV OVER THE NEXT COUPLE
OF HRS...WE SHOULD SEE A DROP TO IFR CIGS (AS HAS BEEN OCCURRING AT
KMSL). PERIODIC LIFTING TO VFR CIGS MAY OCCUR THROUGH 04Z AT BOTH
SITES...WITH A SHORT PERIOD OF PREVAILING MVFR/ALT REQ CIGS POSSIBLE
NEARING 06Z. AFTER 10Z CONDITIONS SHOULD AGAIN WORSEN (PERHAPS TO
NEAR ALT MINS) WITH IMPROVEMENT EXPECTED TOWARD 18Z. VFR CIGS COULD
RETURN BY THE AFTN HRS BUT CONFIDENCE IN THAT IS LOW ATTM.

CCC

&&

.PREV DISCUSSION...
/ISSUED 305 PM CDT FRI MAY 17 2013/
A TRICKY FCST SHAPING UP WITH TIMING/COVERAGE OF PCPN FOR THIS
WEEKEND...NOT TO MENTION TEMPS AND TIMING OF A CDFNT FOR THE MIDDLE
OF NEXT WEEK. FOR NOW WILL GO WITH A BLEND OF NAM/GFS FOR THIS FCST.

FOR THE REST OF THIS AFTN/EVENING...A SLOW MOVING UPPER TROF WILL
HAVE ENOUGH LOW LEVEL SHEAR/INSTABILITY FOR SOME STRONG TO SVR STORMS
WITH DAMAGING WINDS THE MAIN THREAT. HOWEVER CANT RULE OUT LARGE
HAIL...LOCALIZED HVY RAIN/FLOODING AND A FEW WEAK TORNADOES. THE SVR
WX THREAT SHOULD BEGIN TO DIMINISH LATER THIS EVENING...ESPECIALLY
AFTER THE LOSS OF DAYTIME HEATING. OTHERWISE ANOTHER MUGGY NIGHT WITH
OVERNIGHT LOWS IN THE MID 60S. WILL KEEP HIGH POPS TONIGHT ACROSS THE
TN VALLEY DUE TO THE SLOW MOVING UPPER TROF.

SATURDAY...THE AXIS OF THE UPPER TROF WILL BE ALONG THE AL/GA LINE
ARND 12Z. HOWEVER MODELS SHOW A WEAK WAVE ARND 8H WHICH WILL KEEP THE
CHC OF SHRA/TSRA THRU THE AFTN. HOWEVER BY LATE AFTN/EVENING THE
SHRA/TSRA ACTIVITY SHOULD BEGIN TO TAPER OFF.

SUNDAY...THINKING THAT MODELS MAY BE OVER DOING THE CHC OF PCPN SINCE
RIDGING WILL BEGIN TO BUILD ACROSS THE AREA. ANYHOW WILL KEEP LOW
POPS FOR THE MRNG/AFTN HOURS ONLY. RIDGING SHOULD BE STRONG ENOUGH BY
THE NIGHT TO REMOVE THE CHC OF PCPN.

MONDAY/TUESDAY...CONFIDENCE BEGINS TO DROP OFF BY THE BEGINNING OF
NEXT WEEK BUT FOR NOW...THINKING THAT UPPER RIDGING WILL CONTINUE
THE DRY CONDITIONS WITH VERY WARM TEMPS...HIGHS NEAR 90.

WEDNESDAY/THURSDAY...ANOTHER UPPER TROF/CDFNT WILL BEGIN TO AFFECT
THE CWA WITH MORE SHRA/TSRA. ATTM THE GFS HAS THE CDFNT MOVING THRU
THE CWA BY THURSDAY NIGHT.

FRIDAY...THE CDFNT IS PROGGED BY GFS TO BE WELL SOUTH OF THE TN
VALLEY WITH A LITTLE COOLER/DRIER AIR MASS.

07

&&

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

$$

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