Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 250305
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
905 PM CST SAT JAN 24 2015

.UPDATE...
LOWERED TEMPS A FEW DEGREES OVER NE AL AND TWEAKED SKY COVER.

&&

.DISCUSSION...
UNDER CLR SKIES TEMPS WERE RANGING FROM 41 AT MSL TO 30 AT FT PAYNE.
THUS HAD TO LOWER TEMPS A FEW DEGREES IN NE AL TO ACCOUNT FOR TEMPS
ALREADY BELOW FCST VALUES. ALSO MADE SOME MINOR TWEAKS TO SKY COVER
OVERNIGHT. OTHERWISE CDFNT/TROF OVER CENTRAL PLAINS WILL CONTINUE TO
HEAD TOWARDS THE TN VALLEY TONIGHT. NO RAIN EXPECTED ONLY AN INCREASE
IN MID/HIGH CLOUDS. FOR NOW WILL LEAVE IN PATCHY FOG WORDING BUT DONT
THINK THE FOG WILL BECOME DENSE OR WIDESPREAD DUE TO THE INCREASING
CLOUDS. NEW NAM DATA STILL SHOWS RAIN DEVELOPING ALONG THE TN/AL
BORDER BY 00Z SUNDAY.

07

&&

.AVIATION...
/ISSUED 611 PM CST SAT JAN 24 2015/
FOR 00Z TAFS...THE NEXT WX MAKER IS NOW OVER THE NRN/CENTRAL PLAINS.
AS THIS SYSTEM APPROACHES THE CWA THE CHC OF RAIN WILL INCREASE
ESPECIALLY AFTER 00Z SUNDAY. OTHERWISE EXCEPT FOR SOME PATCHY MVFR
FOG BETWEEN 10Z AND 14Z...VFR CONDITIONS ARE EXPECTED THRU THE FCST
PERIOD.

07

&&

.PREV DISCUSSION...
/ISSUED 305 PM CST SAT JAN 24 2015/
THE SYSTEM THAT PROVIDED THE RAIN/SNOW FRI NIGHT IS MOVING WELL TO
THE NORTHEAST LEAVING MOSTLY CLEAR SKIES AND WEST-SOUTHWEST FLOW AT
THE SURFACE. WINDS WILL START TO DIMINISH OVERNIGHT SO TEMPS WILL BE
ABLE TO COOL INTO THE LOWER TO MIDDLE 30S. WITH THE COOLING TAKING
PLACE...PATCHY FOG WITH VISIBILITIES BELOW 3 MILES IS POSSIBLE. IN
ELEVATED AREAS WHERE TEMPS WILL REACH 32 OR BELOW...FREEZING FOG IS
POSSIBLE.

THE NEXT SYSTEM STARTS TO TAKE SHAPE OVERNIGHT AS AN UPPER TROUGH
DEEPENS AND WILL DIG INTO THE MID MISSISSIPPI VALLEY AND EVENTUALLY
DIG SOUTH INTO THE SOUTHEASTERN STATES. IN RESPONSE...A SURFACE LOW
WILL TRACK SE FROM SE MISSOURI SUNDAY AFTERNOON TO THE CAROLINAS BY
MONDAY AFTERNOON. WARM ADVECTION AND SOUTHERLY FLOW AHEAD OF THE
SYSTEM WILL ALLOW HIGH TEMPS TO RAISE INTO THE LOWER 50S. AS
WELL...SOME GUSTY WINDS WILL BE POSSIBLE AS THE SYSTEM APPROACHES.
LIGHT RAIN SHOULD START ACROSS THE AREA FROM NW TO SE AFTER NOON ON
SUNDAY. PRECIP SHOULD STAY ALL RAIN THROUGH THE DAY SUNDAY AND WHAT
HAPPENS AFTER MIDNIGHT IS WHERE THE QUESTION IS.

THERE ARE BASICALLY TWO SCENARIOS FOR SUNDAY NIGHT. THE FIRST IS THE
CURRENT FORECAST AND THE MOST PROBABLE AT THIS TIME. THERE IS QUITE
A BIT OF DISCREPANCY WITH TEMPS SUNDAY NIGHT...RANGING FROM BELOW
FREEZING TO WELL INTO THE UPPER 30S WHICH WILL HAVE A SIGNIFICANT
IMPACT ON PRECIP TYPE. ONLY GUIDANCE SHOWING LOWS FREEZING OR BELOW
IS MOSGUIDE WITH EVERYTHING WELL ABOVE FREEZING AND ABOVE PREVIOUS
FORECASTS. WITH THE UPPER LOW PROGGED TO PASS RIGHT OVER THE
AREA...WILL UNDERCUT GUIDANCE A DEGREE OR TWO. THIS BRINGS LOWS DOWN
TO 32-35 DEGREES. AS WELL...AS THE LOW MOVES OVERHEAD...DYNAMIC
COOLING COULD LOWER TEMPS MORE THAN MODELS ARE FORECASTING. THIS
SITUATION WILL LEND TO RAIN CHANGING OVER TO RAIN/SNOW OR ALL SNOW
BY 10-12Z MONDAY. HAVE INCLUDED A DUSTING OF SNOW ACCUMULATION AT
HIGHER ELEVATIONS FOR 6-12Z MONDAY TO ACCOUNT FOR THIS. ONCE THE LOW
MOVES OFF THE NORTHEAST...MID/HIGH LEVEL MOISTURE IS QUICKLY GONE
WHICH WILL ALLOW PRECIP TO TAPER OFF AS FLURRIES OR DRIZZLE
DEPENDING ON THE TEMP AFTER 12Z MONDAY.

SCENARIO 2 IS IF THE TEMPERATURE NEVER COOLS ENOUGH TO ALLOW SNOW
OVERNIGHT SUNDAY NIGHT. THIS MEANS THAT THE COLUMN AND THE SURFACE
TEMP WOULD COOL TO FREEZING MORE TOWARDS MONDAY MORNING INSTEAD OF
SUNDAY NIGHT. WITH THE UPPER LEVEL MOISTURE GONE AT THAT
POINT...PRECIP COULD END AS FREEZING DRIZZLE. AGAIN...THIS IS NOT
THE CURRENT FORECAST BUT IT WAS WORTH MENTIONING.

THE LOCAL AREA REMAINS ON THE BACKSIDE OF THE UPPER LOW THEN THROUGH
THURSDAY. WITH A FEW SHORTWAVES ROTATING AROUND THE BASE...CLOUDS
WILL FILTER IN AN OUT THROUGH THE TIME FRAME. HIGHS WILL BE NEAR
NORMAL...LOWER 50S TUE-THU WITH LOWS WARMING INTO THE MIDDLE 50S BY
WED NIGHT.

ANOTHER WEAK TROUGH DEVELOPS ALOFT OVER THE MIDWEST THURSDAY
DRAGGING A COLD FRONT THROUGH THURSDAY THROUGH THURSDAY NIGHT. THIS
WILL BE WARM ENOUGH FOR ALL RAIN AND DROP HIGH TEMPS FOR FRIDAY INTO
THE MIDDLE 40S. HIGH PRESSURE RETURNS FOR THE WEEKEND WITH HIGH
CLOUDS STREAMING OVER THE UPPER RIDGE.

LN

&&

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

$$

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



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