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000
FXUS64 KHUN 162003
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
303 PM CDT THU MAY 16 2013

.DISCUSSION...
THE POLAR WESTERLIES REMAIN TO THE NORTH, OVER THE CANADA/US BORDER,
WHILE AN OPEN SHORTWAVE TROUGH (FORMERLY CUTOFF LOW) MOVES ACROSS THE
OZARKS INTO THE MS RIVER VALLEY. A COMPLEX SCENARIO WILL UNFOLD AS
THIS OPEN WAVE SHIFTS EASTWARD, AND IT WILL BE THE MAIN PLAYER FOR
IMPACTS IN THE SHORT TERM. MEANWHILE, AN APPROACHING LONGWAVE UPPER
TROUGH JUST OFF THE WEST COAST WILL BECOME IMPORTANT BY THE MIDDLE
PART OF NEXT WEEK. THEN, WELL TO THE SOUTH IS A WEAK SUBTROPICAL JET
STRETCHING ACROSS NORTHERN MEXICO.

THE AFOREMENTIONED WEAKENING MID-LEVEL SHORTWAVE TROUGH WILL
GRADUALLY MOVE EASTWARD OVERNIGHT OVER THE LOW TO MID MS RIVER
VALLEY. AS IT DOES SO, MID TO HIGH LEVEL CLOUDS WILL INCREASE WHILE
STORMS DEVELOP WITHIN A MODERATELY UNSTABLE (MAINLY ELEVATED)
ENVIRONMENT OVER MS/W TN (AT LEAST THIS EVENING). INSTABILITY THEN
DECREASES AFTER SUNSET AND WITH THE OVERALL WEAK STEERING FLOW,
THESE STORMS WILL LIKELY BE MORE PULSE-LIKE IN NATURE. ADJUSTMENTS
MAY BE NEEDED FOR LATE TONIGHT WHERE SCATTERED SHOWERS MAY BE MORE
PREVALENT, BUT AM NOT COMPLETELY SURE THAT WILL OCCUR DUE TO THE
TRAJECTORY OF THE WAVE AND THE EMBEDDED WAVES ROTATING AROUND THE
MAIN SHORTWAVE TROUGH. OVERNIGHT LOWS SHOULD HOLD IN THE LOW TO MID
60S.

AS THE OPEN SHORTWAVE TROUGH EDGES CLOSER ON FRIDAY INTO THE OH/MS
RIVER VALLEYS, ADDITIONAL SHOWER AND THUNDERSTORM DEVELOPMENT IS
EXPECTED INTO THE MORNING. ELEVATED INSTABILITY WILL ACTUALLY BE
SOMEWHAT HIGHER WITH SOMEWHAT STEEPER MID-LEVEL LAPSE RATES.
FREEZING LEVELS ALSO LOOK TO DROP CLOSE TO 10-12 KFT BY FRIDAY
MORNING. THUS, HAVE INCREASED POPS TO LIKELY MAINLY OVER NW AL
(CLOSER TO THE MID-LEVEL SHORTWAVE TROUGH AXIS). THERE WILL LIKELY
BE A BREAK DURING THE MIDDLE OF THE DAY BEFORE A WEAK VORT MAX
ROTATES AROUND THE WAVE AS IT MOVES ACROSS S IL ON FRIDAY
AFTERNOON/EVENING POSSIBLY SPARKING OFF ADDITIONAL SHOWERS/STORMS.
HAVE KEPT THUNDERSTORMS IN THE FORECAST ON FRIDAY NIGHT TO ACCOUNT
FOR ANY LINGERING CONVECTION AND DUE TO THE POSSIBILITY OF COLD POOL
INDUCED CONVECTION. DID KEEP DAYTIME HIGHS MAINLY IN THE UPPER 70S
TO LOW 80S ON FRIDAY DESPITE CONVECTION AND CLOUD COVER. WITH THE
PREVAILING NW FLOW OVER THE TN VALLEY, AN ADDITIONAL VORT MAX
ROTATING AROUND THE SHORTWAVE TROUGH MAY SPARK OFF AN MCS OVER THE
EASTERN CORN BELT THAT MAY DROP OVER THE TN VALLEY LATE FRIDAY NIGHT
INTO SATURDAY MORNING. THOUGH MODELS HAVE DIFFICULTY DEPICTING THESE
FEATURES THIS FAR IN ADVANCE, WILL KEEP CHC POPS. AS THE SHORTWAVE
OR REMNANT WEAK LIFT EXITS THE REGION ON SATURDAY, THERE MAY BE
ADDITIONAL DEVELOPMENT MAINLY OVER NORTHEAST AL/S MIDDLE TN THROUGH
SATURDAY EVENING.

MEANWHILE, MODEL DEPICTIONS OF THE PREVIOUSLY MENTIONED LONGWAVE
TROUGH OVER THE WEST COAST SHOW IT MOVING INTO THE ROCKIES BY SUNDAY
WHILE RIDGE BUILDING BEGINS OVER EASTERN NORTH AMERICA. THIS WILL
TRANSLATE TO EVEN WARMER CONDITIONS ON SUNDAY THROUGH TUESDAY OVER
THE TN VALLEY WITH DAYTIME HIGHS IN THE LOW 90S, AND DEEP SW WARM
FLOW. AS THE UPPER TROUGH MOVES EASTWARD, EACH MODEL HAS A SLIGHTLY
DIFFERENT PROGRESSION OF THE UPPER TROUGH. HOWEVER, IT DOES APPEAR
THAT NEGATIVELY TILTED SHORTWAVE TROUGHS EMBEDDED AND ROTATING
WITHIN THE PRIMARY BROAD UPPER TROUGH WILL ENHANCE A LLJ (INCREASING
MOISTURE), STEEPEN LAPSE RATES, AND INCREASE WIND SHEAR, BRINGING
THE POSSIBILITY OF SEVERE WEATHER OVER THE CENTRAL AND SOUTHERN
PLAINS ON SUNDAY NIGHT THROUGH MONDAY NIGHT. AN ACCOMPANYING COLD
FRONT WILL LIKELY TRANSLATE TO A LINE OF SHOWERS AND THUNDERSTORMS
SHIFTING SOUTHEAST AND SLOWING (AS IT APPROACHES THE MS RIVER) AS
THE UPPER TROUGH LIFTS NORTHEAST ATOP THE BUILDING RIDGE. THE MODEL
DEPICTIONS OF THE PROGRESSION OF THIS TROUGH IS DIFFERENT WITH ONE
PARTICULAR MODEL RUN (ECMWF 16/12Z) SHOWING THE TROUGH CLOSING OFF
INTO A LOW AND ROTATING OVER THE NORTHERN PLAINS FOR A COUPLE OF
DAYS. THIS COULD MEAN THAT THE SHOWERS AND STORMS MAY NOT IMPACT THE
TN VALLEY UNTIL LATER ON WEDNESDAY. HOWEVER, WILL KEEP THE CURRENT
TIMING FOR NOW WITH FURTHER ADJUSTMENTS LIKELY, ESPECIALLY WITH
TYPICALLY SLOWER MOVEMENT OF TROUGHS THIS TIME OF YEAR AS RIDGES
BEGIN TO STRENGTHEN.

SL.77

&&

.AVIATION...
/ISSUED 1151 AM CDT THU MAY 16 2013/
FOR 18Z TAFS... VFR CONDITIONS SHOULD PREVAIL DURING MOST OF THIS
PERIOD. ISOLATED TO SCATTERED -SHRA REMAIN PSBL THIS AFTN DURING PEAK
HEATING. THESE SHOULD DIMINISH EARLY THIS EVENING. AN APPROACHING
UPPER LEVEL DISTURBANCE LATE TONIGHT WILL RESULT IN SCT SHRA AND TSRA
DEVELOPMENT, SO HAVE INCLUDED A VCTS AT BOTH KHSV (AFT 06Z) AND KMSL
(AFT 10Z). VSBY AND CIG RESTRICTIONS COULD OCCUR IF SHRA OR TSRA
IMPACT THE TERMINALS MORE DIRECTLY, SO STAY ABREAST OF FUTURE AMDS.

KULA

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    63  82  67  83 /  30  50  50  40
SHOALS        61  78  68  83 /  30  60  50  40
VINEMONT      62  81  67  83 /  20  50  50  40
FAYETTEVILLE  61  81  65  81 /  30  50  50  50
ALBERTVILLE   63  81  66  80 /  20  50  50  50
FORT PAYNE    59  80  63  79 /  20  50  50  50

&&

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

$$

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