Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 010007
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
607 PM CST SAT JAN 31 2015

.UPDATE...
FOR 00Z TAFS

&&

.DISCUSSION...
/ISSUED 225 PM CST SAT JAN 31 2015/
THE 20Z SURFACE ANALYSIS INDICATED THAT THE LARGE AREA OF HIGH
PRESSURE WAS CENTERED OVER THE MID ATLANTIC REGION...WITH THE BACK
EDGE OF THE RIDGE AXIS NEARING THE FORECAST AREA. TEMPS ACROSS THE
FORECAST AREA WERE IN THE MID TO UPPER 40S ACROSS SOUTHERN MIDDLE
TENNESSEE AND INTO THE LOWER TO MID 50S ELSEWHERE ACROSS NORTH
ALABAMA. MID AND HIGH CLOUDS WERE CONTINUING TO SHIFT EAST-NORTHEAST
ACROSS THE OHIO AND TENNESSEE VALLEY REGION AHEAD OF A DEVELOPING
STORM SYSTEM IN THE SOUTHERN PLAINS STATES.

MID AND HIGH CLOUDS WILL CONTINUE TO THICKEN ACROSS THE FORECAST AREA
TONIGHT IN ADVANCE OF THE STORM SYSTEM. HAVE FOLLOWED CLOSE TO
FORECAST GUIDANCE TEMPS FOR TONIGHT DUE TO EXPECTED WARM ADVECTION
AND CLOUD COVER. THE SHORT TERM MODELS ARE CONSISTENT AGAIN TODAY IN
DEVELOPING A SURFACE LOW ACROSS WESTERN MISSOURI BY 12Z SUNDAY WITH
QUITE A BIT OF LOW LEVEL MOISTURE EXPECTED TO RAPIDLY MOVE NORTH-
NORTHEAST INTO THE REGION OUT OF THE SOUTHERN PLAINS. EXPECT
RAIN...MAINLY LIGHT...TO OVERTAKE THE FORECAST AREA BY AROUND 18Z ON
SUNDAY...WITH CATEGORICAL POPS ACCEPTED.

THE SURFACE LOW IS EXPECTED TO MOVE PROGRESSIVELY EASTWARD THROUGH
SUNDAY AFTERNOON...AND IS PROGGED TO BE OVER EAST CENTRAL ILLINOIS-
WEST CENTRAL INDIANA BY 00Z SUNDAY. A TRAILING COLD FRONT IS EXPECTED
TO MAKE IT INTO SOUTHWEST KENTUCKY...EXTENDING SOUTHWARD INTO
NORTHERN MISSISSIPPI DURING THIS SAME TIME PERIOD. CURRENT
INDICATIONS ARE THAT THE COLD FRONT SHOULD MOVE THROUGH NORTHWEST
ALABAMA BY AROUND THE 03Z MONDAY TIME PERIOD...AND THROUGH SOUTHERN
MIDDLE TENNESSEE AND INTO NORTHEAST ALABAMA BY 06Z MONDAY. STRONG
COLD ADVECTION WILL SHIFT SOUTHEAST INTO THE FORECAST AREA
OVERNIGHT...WITH TEMPS EXPECTED TO MAKE IT TO THE FREEZING MARK
ACROSS MUCH OF THE FORECAST AREA BY AROUND 12Z. FORECAST SOUNDING
DATA AND CRITICAL LOW LEVEL TEMP PROFILES INDICATE THAT A CHANGE
OVER FROM LIGHT RAIN TO LIGHT SNOW WILL STILL BE POSSIBLE FOR A BRIEF
TIME PERIOD SHORTLY AFTER 06Z TOWARD NORTHWEST ALABAMA...AND
ELSEWHERE BEFORE 12Z MONDAY. EXPECT LIGHT SNOW/FLURRY AMOUNTS TO BE
GENERALLY UP TO A DUSTING AT THIS TIME.

WILL CONTINUE WITH A BRIEF MENTION OF LIGHT SNOW/FLURRIES ON MONDAY
MORNING ESPECIALLY IN NORTHEAST ALABAMA AND BACK INTO SOUTHERN MIDDLE
TENNESSEE. STRONG COLD ADVECTION ON MONDAY WILL KEEP TEMPS GENERALLY
IN THE 30S ACROSS THE FORECAST AREA...WHICH IS IN LINE WITH TEMP
GUIDANCE. THE FAST UPPER LEVEL FLOW WILL TRANSPORT THE TRAILING AREA
OF HIGH PRESSURE INTO THE OHIO/TENNESSEE VALLEY REGION BETWEEN MONDAY
AFTERNOON AND THROUGH TUESDAY.

THE ECMWF AND GFS MODELS THEN DIFFER INVOLVING THE NEXT STORM SYSTEM
IN THE SOUTHERN STREAM AND ANOTHER TRAILING COLD FRONT DROPPING
SOUTHEAST OUT OF THE NORTHERN PLAINS. THE GFS MODEL MOVES THE LOW
PRESSURE AREA EAST-NORTHEAST THROUGH THE NORTHERN GULF OF MEXICO
THROUGH 12Z THURSDAY. THE GFS MODEL SHIFTS MORE LOW LEVEL
MOISTURE/LIGHT PRECIP NORTHWARD TOWARD AND INTO PORTIONS OF THE
FORECAST AREA BETWEEN WEDNESDAY NIGHT AND INTO THURSDAY. THE ECMWF
MODEL KEEPS THE SURFACE LOW WELL SOUTH OF THE AREA...AND DRY
CONDITIONS ACROSS MUCH OF THE SOUTHEAST. THE GFS MODEL IS SLOWER WITH
THE SOUTHEAST MOVEMENT OF A COLD FRONT INTO THE TENNESSEE VALLEY
REGION BY 12Z THURSDAY...COMPARED TO THE DRIER AND FASTER MOVEMENT OF
THE COLD FRONT THROUGH THE REGION BY THE ECMWF MODEL DURING THE SAME
TIME PERIOD. BOTH THE GFS AND ECMWF MODELS REMAIN GENERALLY
CONSISTENT IN THEIR DEPICTION OF THIS SCENARIO COMPARED TO THE PAST
2-3 MODEL RUNS.

FOR NOW...WILL KEEP IN A CHANCE TO SLIGHT CHANCE MENTION OF LIGHT
RAIN FOR THE FORECAST AREA FROM WEDNESDAY AFTERNOON THROUGH MUCH OF
THURSDAY. THE GFS MODEL KEEPS MUCH MORE LOW MOISTURE OVERRUNNING THE
COLD FRONT...COMPARED TO THE ECMWF MODEL DURING THIS TIME FRAME. WILL
GO WITH A COMPROMISE BETWEEN THE MODELS FOR NOW AND SEE HOW THE NEXT
MODEL RUN OR TWO DEVELOPS BEFORE MAKING WIDESPREAD CHANGES TO THE
EXTENDED FORECAST PERIODS. AS COLD ADVECTION CONTINUES TO PUSH INTO
THE REGION ON THE HEELS OF THE COLD FRONT BY 06Z FRIDAY...WILL KEEP
IN AT LEAST A SLIGHT CHANCE OF LIGHT SNOW FROM THE 06Z TO 12Z FRIDAY
TIME PERIOD. HIGH PRESSURE WILL THEN BUILD INTO THE REGION FROM NEXT
FRIDAY THROUGH SATURDAY. WILL FOLLOW WITH A COMPROMISE INVOLVING
TEMPS BETWEEN THE COOLER ECMWF AND WARMER GFS TEMP GUIDANCE THROUGH
THE EXTENDED FORECAST PERIODS.

TT

&&

.AVIATION...
FOR 00Z TAFS...BKN/OVC CS AND AS CIGS ARE CURRENTLY IN PLACE AT BOTH
TERMINALS...WITH A LIGHT ESE WIND. THESE GENERAL CONDS SHOULD
PERSIST FOR ROUGHLY FIRST HALF OF VALID TAF PERIOD...WITH CIGS
GRADUALLY FALLING TO ARND 12 KFT AND WINDS INCREASING FROM THE SE IN
ADVANCE OF APPROACHING STORM SYSTEM. CIGS WILL CONTINUE TO FALL FROM
W-TO-E BTWN 01/11-13Z AS STRENGTHENING SE FLOW ADVECTS RICH MOISTURE
NWD INTO THE REGION. SHRA THREAT WILL INCREASE BTWN 14-16Z...WITH
MVFR STRATUS BCMG ESTABLISHED DURING THIS PERIOD AS WELL. COVERAGE OF
SHRA WILL INITIALLY BE SCT AND HAVE ONLY INDICATED VCSH THRU LATE
MORNING/EARLY AFTN. SHRA WILL BE MOST WIDESPREAD BTWN 01/17Z-02/00Z
AND HAVE INDICATED THIS AS PREVAILING WX COND ALONG WITH BKN/OVC MVFR
CIGS. WINDS WILL REMAIN ARND 12 KTS BUT VEER TO SSW TOMORROW AFTN AS
COLD FRONT APPROACHES FROM THE WEST.

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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