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Area Forecast Discussion

044
FXUS64 KHUN 192318
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
618 PM CDT SAT APR 19 2014

.UPDATE...
FOR 00Z TAFS

&&

.SYNOPSIS...
/ISSUED 303 PM CDT SAT APR 19 2014/

A SPLIT FLOW REGIME DOMINATES CENTRAL NORTH AMERICA FOR THE SHORT-
TERM WHILE A MORE PROGRESSIVE/DEEPER TROUGH PATTERN DEVELOPS DURING
THE EXTENDED PORTION OF THE FORECAST. CURRENTLY, A DEEP CYCLONE
CENTERED OVER S GA/N FL IS SLOWLY MOVING EAST WITH THE LAST VESTIGES
OF THIS SYSTEM (ACROSS THIS AREA) MOSTLY APPARENT VIA CIRRUS.
HOWEVER, LIGHT RAIN ON THE NORTHERN FLANK OF THIS VORTEX IS MOVING
WEST TOWARDS NE AL FROM S TN AND NW GA. THUS, SOME SPRINKLES AND
LIGHT RAIN MAY OCCUR OVER NE AL OVER NEXT COUPLE OF HOURS BEFORE
DISSIPATING.

SL.77

&&

.SHORT TERM (TONIGHT THROUGH MONDAY NIGHT)...
/ISSUED 303 PM CDT SAT APR 19 2014/

CLOUDS OVER NE AL WILL CONTINUE TO DECREASE TONIGHT AS THE DEEP
CYCLONE MOVES OFF TO THE EAST OFF THE ATLANTIC COASTLINE. NE AND E
SFC WINDS SHOULD DIMINISH WITH TEMPERATURES EXPECTED TO BE NEAR 50
DEGREES BY TOMORROW MORNING. WEAK COLD AIR DAMMING IS APPARENT AS
THIS SYSTEM MOVES OFF TO THE NORTHEAST, AND HAVE INCLUDED SOMEWHAT
COOLER DAYTIME HIGHS ON SUNDAY AFTERNOON OVER NE AL DUE TO THIS
POSSIBILITY.

MEANWHILE, A MID-LEVEL SHORTWAVE TROUGH CURRENTLY OVER THE DESERT
SOUTHWEST WILL CROSS OVER THE SOUTHERN PLAINS AND CORN BELT REGION
ON SUNDAY/SUNDAY NIGHT. AS IT DOES SO, THE WAVE APPEARS TO SPLIT
WITH THE SOUTHERN WAVE MOVING SE ACROSS THE SOUTHEAST ON MONDAY
AFTERNOON/EVENING. AFTER LOOKING AT FORECAST SOUNDINGS THERE IS WEAK
LIFT ON MONDAY AHEAD OF THE SHORTWAVE WITH CONDITIONAL INSTABILITY
AND A STRONG CAP. THUS, HAVE REMOVED THUNDERSTORMS FROM MONDAY`S
FORECAST. HOWEVER, THERE MAY BE ENOUGH FORCING FOR SHOWER ACTIVITY,
AND HAVE INSTEAD LEFT SHOWERS IN THE FORECAST. WARMER TEMPERATURES
ARE FORECAST FOR MONDAY NIGHT (NEAR 60) DUE TO THE INCREASED CLOUD
COVER AND SOUTHERLY FLOW. AS THE SOUTHERN SHORTWAVE WAVE APPROACHES
THE MS RIVER VALLEY MONDAY EVENING, THE PVA ASSOCIATED WITH THE WAVE
COMBINED WITH MUCAPES BTWN 500-800 J/KG, WILL BE ENOUGH TO ERODE THE
CAP AND SUPPORT WIDESPREAD THUNDERSTORMS ACROSS THE TN VALLEY
THROUGH MONDAY NIGHT. THERE MAY BE ENOUGH INSTABILITY TO SUPPORT
VERY SMALL HAIL WITH ANY OF THE STRONGER UPDRAFTS. OTHERWISE,
EXPECTING GUSTY WINDS AND HEAVY RAINFALL TO ALSO BE AN IMPACT WITH
ANY STORMS THAT FORM.

.LONG TERM (TUESDAY THROUGH SATURDAY)...

SHOWERS AND STORMS WILL CONTINUE AT TIMES DURING THE DAY ON TUESDAY
AS THE SHORTWAVE TROUGH MOVES OFF TO THE SOUTHEAST. MUCAPES RISE TO
1000-1500 J/KG BY TUESDAY AFTERNOON WITH THE POSSIBILITY OF SMALL
HAIL WITHIN THE STRONGER UPDRAFTS. CLOUD COVER MAY BE AN ISSUE IN
REALIZING INSTABILITY FROM SB PARCELS FROM DAYTIME HEATING. ANY OF
THE STRONGER UPDRAFTS COULD HAVE SMALL HAIL WITH THIS INSTABILITY
PROFILE ALONG WITH THE HEAVY DOWNPOURS. ONE THING TO NOTE WITH THESE
STORMS IS THE LACK OF APPRECIABLE WIND SHEAR (10-20KTS) WHICH WOULD
TRANSLATE TO SLOW MOVING STORMS THAT COULD TRAIN OVER THE SAME AREA.
THIS COULD TRANSLATE TO A FLASH FLOODING THREAT. NEVERTHELESS, WILL
STILL KEEP ANALYZING THE SETUP AS THERE IS STILL SOME UNCERTAINTY
WITH THE SPATIAL EXTENT OF THE RAINFALL. THE SHOWERS/STORMS SHOULD
DISSIPATE BY 00Z. THEN, A WEAK COLD FRONT IS EXPECTED TO PUSH SOUTH
BTWN 00-06Z BRINGING MAINLY A WIND DIRECTION CHANGE AND COOLER AIR.
THIS WILL MAINLY AFFECT THE OVERNIGHT LOWS FOR TUESDAY NIGHT-
SLIGHTLY COOLER THAN NORMAL IN THE UPPER 40S.

A RIDGE THEN BUILDS OVER THE SOUTHEAST AS A LONGWAVE TROUGH MOVES
EAST ACROSS THE CENTRAL ROCKIES. WE WILL BE IN THE MIDST OF NW FLOW
ON THE EASTERN FLANK OF THE RIDGE ON WEDNESDAY, BUT TEMPS ARE STILL
EXPECTED TO RISE INTO THE 70S FOR DAYTIME HIGHS. THEN, THE MODELS
DIVERGE ON THE STRENGTH OF THE BUILDING RIDGE STRETCHING FROM
WESTERN ONTARIO TO THE GULF COAST. THE GFS/CANADIAN SEND THE TROUGH
EAST ACROSS THE LOWER MS/OH RIVER VALLEYS WITH MORE WIDESPREAD
SHOWERS AND THUNDERSTORMS AFFECTING THE AREA ON FRIDAY. MEANWHILE,
THE ECMWF DEPICTS THE TROUGH MOVING NE ACROSS THE CORN BELT REGION
INTO THE GREAT LAKES WITH AN OCCLUDED SFC LOW AND WEAK SFC COLD
FRONT CROSSING THE TN VALLEY. FOR NOW, HAVE KEPT THE CHANCE OF
THUNDERSTORMS ON FRIDAY AND NEAR SEASONABLE DAYTIME HIGH
TEMPERATURES.

SL.77

&&

.AVIATION...
FOR 00Z TAFS...HIGH PRESSURE BUILDING OVER THE TN VALLEY ALONG WITH A
FAIRLY DRY ATMOSPHERE WILL KEEP VFR CONDITIONS THRU THE FCST PERIOD.

07

&&

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

$$

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



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