Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 021204
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
604 AM CST MON MAR 2 2015

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 500 AM CST MON MAR 2 2015/

WATER VAPOR IMAGERY SHOWS MUCH OF THE AREA UNDER ZONAL FLOW
ALOFT. AT THE SURFACE...LIGHT RAIN CONTINUES TO MOVE EAST ACROSS THE
FORECAST AREA...BEHIND A SURFACE COLD FRONT THAT HAS PUSHED TO THE
EAST OF THE AREA. THIS FRONT IS EXPECTED TO STALL TO THE SOUTH...WITH
SHOWERS CONTINUING THROUGH THE MORNING IN RESPONSE TO SEVERAL WEAK
SHORTWAVES MOVING EAST IN THE UPPER LEVEL ZONAL FLOW. COVERAGE WILL
LIKELY DECREASE THIS AFTERNOON...AS DRIER AIR FILTERS INTO THE
REGION. HIGH PRESSURE AT THE SURFACE WILL MOVE EAST ACROSS THE GREAT
LAKES...WITH NORTHERLY WINDS SHIFTING TO THE EAST THIS EVENING. THE
AFOREMENTIONED COLD FRONT IS EXPECTED TO LIFT NORTHWARD
OVERNIGHT...WITH SHOWERS...WITH AN ISOLATED THUNDERSTORM...POSSIBLE
AFTER 06Z. ALTHOUGH SHOWERS WILL LIKELY BE ONGOING TUESDAY
MORNING...TEMPERATURES ARE EXPECTED TO WARM UP QUITE A BIT...DUE TO
THE STRONG WAA AT THE SURFACE AND A DECREASE IN RAIN COVERAGE BY THE
AFTERNOON.

THE MAIN FOCUS FOR THE FORECAST THIS MORNING CONTINUES TO BE THE
SETUP ON TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. AN UPPER LEVEL
CLOSED LOW OFF OF THE SOUTHERN CALIFORNIA COAST WILL PUSH ASHORE
LATER TODAY...AS AN UPPER LEVEL TROUGH BEGINS TO DIG SOUTHWARD OUT
OF CANADA. SURFACE CYCLOGENESIS WILL OCCUR OVER CANADA...WITH A
DEEPENING SURFACE LOW EXPECTED TO MOVE EAST ACROSS THE GREAT LAKES. A
STRONG COLD FRONT WILL DEVELOP AND DRAG SOUTHWARD FROM THE SURFACE
LOW AND MOVE THROUGH THE FORECAST AREA WEDNESDAY INTO THURSDAY.
WHILE MODEL GUIDANCE IS STILL IN GOOD AGREEMENT WITH THE OVERALL
SETUP...THE TIMING DIFFERENCES ARE STILL GLARING...WITH EACH TIMING
SCENARIO POSING A DIFFERENT SET OF THREATS FOR THE FORECAST AREA.
THIS MAKES THINGS QUITE UNCERTAIN...HOWEVER FOR NOW...HAVE GONE WITH
A BLEND OF THE GFS AND ECMWF...WITH AN EMPHASIS ON THE GFS.

AHEAD OF THE COLD FRONT...A 50-60KT LLJ WILL MOVE JUST TO THE NORTH
OF THE FORECAST AREA. SOUTHERLY FLOW AT THE SURFACE CONTINUES...WITH
HIGHS ON TUESDAY IN THE UPPER 60S...AND DEWPOINTS REACHING INTO THE
UPPER 50S. SHOWERS...WITH ISOLATED THUNDERSTORMS ARE POSSIBLE
OVERNIGHT TUESDAY AND INTO EARLY WEDNESDAY MORNING. INSTABILITY DOES
APPEAR TO BE LIMITED...GIVEN A FAIRLY STRONG CAPPING INVERSION
ADVERTISED BY MODEL SOUNDINGS. WIND SHEAR WILL BE DECENT TO SUPPORT A
FEW ORGANIZED THUNDERSTORMS...BUT GIVEN THE CURRENT SOLUTION...THERE
LOOKS TO BE ONLY A SMALL WINDOW WHERE STRONG TO SEVERE THUNDERSTORMS
WILL BE POSSIBLE...JUST AHEAD OF THE COLD FRONT. IF THE SLOWER NAM
SOLUTION PANS OUT...WE MAY HAVE MORE TIME TO WARM UP ON WEDNESDAY
AFTERNOON AND THERE WOULD BE MORE OF AN OPPORTUNITY FOR THE INVERSION
TO DIMINISH. HOWEVER...THE NAM SEEMS TO BE A BIT TOO SLOW...GIVEN THE
STRONG AIRMASS BEHIND THE FRONT.

THE COLD FRONT IS EXPECTED TO ENTER THE NORTHWEST PORTION OF THE
FORECAST AREA BY 18Z ON WEDNESDAY...AND MOVE TO THE EAST OF THE AREA
BY 00Z THURSDAY. BEHIND THE FRONT...TEMPERATURES WILL DROP
QUICKLY...WITH MUCH OF THE AREA NEAR OR BELOW FREEZING BY 00Z. THE
UPPER LOW CURRENTLY OVER SOUTHERN CALIFORNIA WILL PHASE WITH THE
UPPER TROUGH OVER CANADA AND THE UPPER LEVEL JET IS EXPECTED TO
INTENSIFY SIGNIFICANTLY. THE FORECAST AREA WILL BE LOCATED IN THE
AREA OF ENHANCED LIFT...WITH AN ABUNDANCE OF MOISTURE LAGGING BEHIND
THE FRONT AS WELL. THIS SETS THE STAGE FOR ONGOING MODERATE
PRECIPITATION ACROSS THE AREA. AS TEMPERATURES FALL DURING THE
AFTERNOON...RAIN WILL TRANSITION TO FREEZING RAIN ACROSS THE
NORTHWEST...AND THEN CONTINUE TO TRANSITION ACROSS THE REST OF THE
AREA. MODEL SOUNDINGS INDICATE A PROLONGED PERIOD OF FREEZING RAIN
ACROSS MUCH OF THE AREA...WITH A BRIEF CHANGE OVER TO SLEET BY
06Z...AND THEN TO LIGHT SNOW BY 12Z. FAIRLY SIGNIFICANT ICE
ACCUMULATIONS ARE POSSIBLE...WITH MUCH OF THE AREA EXPECTED TO
RECEIVE AROUND A QUARTER OF INCH...WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. THE WARM NOSE ALOFT WILL COOL FASTER ACROSS THE
NORTHWEST...WHERE A TRANSITION TO SLEET AND SNOW WILL OCCUR SOONER.
THEREFORE...IN THESE LOCATIONS...UP TO 2 INCHES OF SNOW/SLEET
ACCUMULATIONS ARE POSSIBLE. IF THE TRENDS CONTINUE...THESE AMOUNTS
MAY HAVE TO BE ADJUSTED. AGAIN...IT SHOULD BE NOTED THAT EVEN WITH
THE SLOWER MODEL SOLUTIONS...THERE WILL STILL BE THE THREAT FOR
FROZEN PRECIPITATION BEHIND THE FRONT...HOWEVER THE DURATION MAY BE
LESS.

BEYOND 12Z THURSDAY...PRECIPITATION WILL COME TO AN END FROM WEST TO
EAST AS HIGH PRESSURE BUILDS IN. TEMPERATURES WILL NOT WARM UP VERY
MUCH ON THURSDAY...WITH MOST LOCATIONS REMAINING BELOW FREEZING.
TEMPS ON FRIDAY WILL BOTTOM OUT IN THE TEENS...BEFORE WARMING INTO
THE LOWER 40S. A LIGHT WARMING TREND WILL CONTINUE THROUGH THE
EXTENDED...WITH ONLY A SLIGHT CHANCE OF RAIN EXPECTED TOWARDS THE
LATTER PART OF THE PERIOD.

73

&&

.AVIATION...
FOR 12Z TAFS...COLD FRONT HAS PUSHED SOUTH OF BOTH HSV/MSL WITH NNE
FLOW OF 10G18 KTS EXPECTED TO PERSIST THROUGH 02/15Z...ALONG WITH
IFR CIGS AND MVFR VSBY REDUCTIONS IN -DZ/BR. WEAK MIXING IN WAKE OF
FRONT AND DRIER AIRMASS MOVING INTO THE REGION SHOULD ALLOW VSBY TO
IMPROVE AND CIGS TO LIFT INTO THE 1500-2500 FT RANGE BY 15Z...AS
WINDS DIMINISH AND VEER TO ENE. THREAT FOR SHRA MAY INCREASE ONCE
AGAIN BY 21Z AS A WEAK UPPER AIR DISTURBANCE APPROACHES...ALTHOUGH
GIVEN SCT COVERAGE EXPECT CIGS TO REMAIN MVFR UNTIL LOW-LEVEL FLOW
VEERS TO ESE ARND 03/03Z. WINDS WILL INCREASE AND SHIFT TO SSE BY 08Z
AS WARM FRONT MOVES NWD...WITH MVFR VSBY REDUCTIONS IN BR PSBL BEYOND
THIS POINT. THREAT FOR SCT SHRA WILL CONTINUE OVERNIGHT... WITH A FEW
STORMS ALSO PSBL. HOWEVER...THREAT FOR TSRA IS TOO LOW TO MENTION IN
TAF ATTM.

70/DD

&&

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

&&

$$

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


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