Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 191054
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
554 AM CDT SUN APR 19 2015

.DISCUSSION...
MAJORITY OF THE NEAR TERM FORECAST WILL CONTINUE TO BE INFLUENCED BY
A LARGE UPPER LOW -- CURRENTLY CENTERED NEAR THE COLORADO-KANSAS
BORDER. THIS FEATURE IS EXPECTED TO SHIFT EAST-SOUTHEASTWARD INTO THE
WESTERN OZARKS BY EARLY THIS EVENING AND OPEN INTO A NEUTRALLY-TILTED
TROUGH AS IT INTERACTS WITH A MORE INTENSE NORTHERN STREAM WAVE
DIGGING SOUTHEASTWARD ACROSS SASKATCHEWAN/MANITOBA. A LEAD MID-LEVEL
VORTICITY MAXIMA LARGELY RESPONSIBLE FOR WIDESPREAD EARLY MORNING
RAINFALL WILL EJECT RAPIDLY NORTH-NORTHEASTWARD INTO THE SOUTHERN
GREAT LAKES BY 00Z MONDAY...WITH ASSOCIATED SURFACE LOW FORECAST TO
DEEPEN AND LIFT NORTHEASTWARD FROM WESTERN TN INTO CENTRAL INDIANA.
BASED ON SIMPLE EXTRAPOLATION OF THE SOUTHWESTERN EDGE OF THE CURRENT
PRECIP REGION...WE WILL CARRY FAIRLY HIGH POPS FOR THE NORTHEASTERN
HALF OF THE REGION THIS MORNING. EXPECT SKIES TO AT LEAST PARTIALLY
CLEAR IN WAKE OF MORNING PRECIP...WITH A GUSTY SOUTHWEST FLOW WITHIN
THE WARM SECTOR HELPING TO BOOST TEMPERATURES INTO THE MID/UPPER 70S.

ATTENTION THIS AFTERNOON WILL FOCUS ON MCS CURRENTLY SHIFTING
NORTHEASTWARD ACROSS THE LOWER MISSISSIPPI VALLEY. THIS FEATURE --
OR ITS REMNANTS PERHAPS IN THE FORM OF A CONVECTIVELY GENERATED VORT
MAX ALOFT -- WILL LIKELY ARRIVE IN THE REGION AROUND THE TIME OF PEAK
HEATING THIS AFTERNOON. ALTHOUGH LOW-LEVEL FORCING FOR ASCENT WILL BE
GENERALLY WEAK...SEVERAL HIGHLY ORGANIZED MULTICELL CLUSTERS --
INCLUDING THE POTENTIAL FOR BOWS/LEWPS -- ARE EXPECTED TO DEVELOP AND
TRACK RAPIDLY NORTHEASTWARD OVER THE REGION. FORECAST SOUNDINGS
DEPICT A VERY UNSTABLE AIRMASS CHARACTERIZED BY LOW-LEVEL DEWPOINTS
IN THE MID/UPPER 60S AND STEEP LAPSE RATES ALOFT -- YIELDING ML CAPE
VALUES OF 1500-2000 J/KG. ALTHOUGH WEAKENING/VEERING LOW-LEVEL JET
AND CORRESPONDING REDUCTION IN 0-3 KM SRH WILL LEAD TO LITTLE THREAT
FOR TORNADOES...THE THERMODYNAMIC ENVIRONMENT WILL SUPPORT DAMAGING
WINDS (PERHAPS IN EXCESS OF 70 MPH) AND DAMAGING HAIL (PERHAPS LARGER
THAN GOLF BALL SIZE).

SHORT RANGE NWP GUIDANCE REMAINS IN EXCELLENT AGREEMENT THIS MORNING
IN FORECASTING THE WESTERN OZARKS MID-LEVEL TROUGH TO BECOME
NEGATIVELY- TILTED AS IT LIFTS NORTHEASTWARD INTO THE LOWER OHIO
VALLEY BY 12Z MONDAY AND BECOMES ABSORBED IN CIRCULATION AROUND A
DEEPENING LONGWAVE TROUGH CENTERED ACROSS SOUTHERN ONTARIO/NORTHERN
MINNESOTA. AS THIS OCCURS A DEEPENING SURFACE WAVE WILL SPREAD
EASTWARD INTO THE MID-MISSISSIPPI VALLEY BY 06Z MONDAY AND INTO
SOUTHWESTERN INDIANA BY 12Z. A BROKEN QLCS WILL LIKELY EVOLVE ACROSS
THE LOWER MISSISSIPPI VALLEY LATE THIS AFTERNOON/EARLY THIS EVENING
AS SUBTLE PREFRONTAL TROUGH SHIFTS EASTWARD...WITH REMNANTS OF THIS
ACTIVITY APPROACHING NW ALABAMA AROUND MIDNIGHT. INSTABILITY WILL
REMAIN ELEVATED OVERNIGHT...WITH 500-1000 J/KG CAPE AVAILABLE FOR
SURFACE PARCELS AND THIS ACTIVITY WILL ALSO POSE A RISK OF SEVERE
WIND/HAIL. AS STRONGEST MID-LEVEL FORCING FOR ASCENT BEGINS TO LIFT
NORTHEASTWARD AND AWAY FROM REGION AFTER MIDNIGHT...EXPECT REMNANTS
OF THIS QLCS TO WEAKEN FURTHER AS IT TRACKS EASTWARD INTO THE REGION.
DESPITE THIS...IT SHOULD BE NOTED THAT THE LOW-LEVEL JET WILL
INCREASE AFTER 06Z AS MID-LEVEL SYSTEM APPROACHES THE LOWER OHIO
VALLEY AND THIS MAY SUPPORT AN INCREASING THREAT FOR
MESOCYCLONES/TORNADOES WITH REMNANTS OF QLCS. STORM THREAT WILL
DIMINISH BY 12Z MONDAY AS PREFRONTAL TROUGH WILL BE EAST OF THE
REGION...BUT CLOUDS WILL PERSIST AND LINGERING SHOWERS MAY OCCUR
ALONG SYNOPTIC COLD FRONT AS IT PUSHES EASTWARD BETWEEN 12-18Z. CLEAR
SKIES AND LIGHT FLOW ON MONDAY NIGHT WILL LEAD TO A GOOD RADIATIONAL
COOLING EVENT WITH PATCHY FOG POSSIBLE AS LOWS FALL INTO THE MID 40S.

A WEST-NORTHWEST FLOW ALOFT WILL CONTINUE FOR FIRST HALF OF EXTENDED
PERIOD...AS UPPER LOW SHIFTS SLOWLY EAST-SOUTHEASTWARD OVER
SOUTHERN ONTARIO/NORTHERN GREAT LAKES REGION. AT THE SURFACE...RIDGE
AXIS WILL TRANSLATE EASTWARD OFF THE SOUTHEAST ATLANTIC COAST TUESDAY
NIGHT...ALLOWING RETURN FLOW OF WARM AND MOIST AIR BY WEDNESDAY.
MEANWHILE...A REINFORCING COLD FRONT IS STILL EXPECTED TO DROP
SOUTHWARD INTO THE REGION SOMETIME LATE WEDNESDAY NIGHT/EARLY
THURSDAY...AND HAVE INCREASED POPS FOR THIS PERIOD AND INCLUDED
SLIGHT CHANCE OF THUNDERSTORMS BASED ON FORECAST SOUNDINGS. ANOTHER
SHOT OF COOL/DRY CANADIAN AIR WILL SPREAD ACROSS THE REGION THURSDAY-
FRIDAY. HOWEVER...EXTENDED RANGE GUIDANCE CONTINUES TO SUGGEST A
RATHER WET/STORMY PATTERN EVOLVING BY FRIDAY NIGHT/SATURDAY AS NEXT
UPPER TROUGH DIGS SOUTHEASTWARD FROM THE CENTRAL PLAINS. ALTHOUGH
MUCH OF THE CONVECTION WILL REMAIN ELEVATED ON FRIDAY NIGHT...A
PORTION OF THE REGION MAY BE IN THE UNSTABLE WARM SECTOR OF THE
CYCLONE ON SATURDAY.

70/DD

&&

.AVIATION...
/ISSUED 1258 AM CDT SUN APR 19 2015/
FOR 06Z TAFS...A BAND OF SHRA IN ASSOC/W A WARM FRONT WILL MOVE
ACROSS TAF LOCATIONS OVERNIGHT. CIG/VIS WILL GRADUALLY DECREASE
FROM VFR CONDITIONS AT 06Z TO MVFR BY 08-09Z. SOME INDICATIONS THAT
CIGS COULD LOWER INTO IFR RANGE BY 12Z...BUT NOT ENOUGH CONFIDENCE TO
INCLUDE IMPACT IN TAFS AT THIS TIME. A BREAK IN THE PCPN MAY OCCUR
FOR A FEW HOURS BEGINNING ARND 18Z SUNDAY. HOWEVER...SCT TSRA MAY
REDEVELOP BETWEEN 20Z AND 01Z ACROSS THE TAF SITES. AFTER
01Z...ANOTHER BREAK IN THE PCPN MAY OCCUR THRU THE END OF THE TAF
PERIOD. OTHERWISE MAINLY MVFR CONDITIONS THRU 20Z...AFTER 20Z VFR
CONDITIONS ARE EXPECTED EXCEPT MVFR IN TSRA.

07/KDW

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    76  61  70  47 /  70  50  30  10
SHOALS        78  60  69  45 /  60  70  30  10
VINEMONT      75  61  69  46 /  70  50  30  10
FAYETTEVILLE  74  61  68  44 /  70  50  40  10
ALBERTVILLE   75  61  69  46 /  80  40  30  10
FORT PAYNE    75  60  70  44 /  80  30  30  10

&&

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

&&

$$

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


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