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Area Forecast Discussion

588
FXUS64 KHUN 051109 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
509 AM CST FRI FEB 5 2016

.UPDATE...
FOR 12Z TAFS

&&

.SYNOPSIS...
/ISSUED 301 AM CST FRI FEB 5 2016/

THE UPPER FLOW PATTERN REMAINS CHARACTERISTICALLY ACTIVE FOR THIS
TIME OF YEAR AS SEVERAL MID-LEVEL SHORTWAVE TROUGHS/RIDGES MOVE
ACROSS THE CENTRAL AND EASTERN PORTIONS OF NORTH AMERICA. FURTHER
WEST, A LARGE SCALE RIDGE WILL BEGIN TO AMPLIFY, RESULTING IN GRADUAL
DEEPENING OF THE TROUGH PATTERN OVER THE EASTERN HALF OF NORTH
AMERICA.

COLD BUT SEASONABLE AND DRY CONDITIONS WILL PREVAIL FOR THE SHORT-
TERM (THROUGH SUNDAY) WHILE THE EXTENDED FORECAST WILL BE VERY COLD
WITH THE POSSIBILITY FOR WINTRY PRECIPITATION.

SL.77

&&

.DISCUSSION...
/ISSUED 301 AM CST FRI FEB 5 2016/

AFTER A COLD START TO THE MORNING TODAY WITH LOWS GENERALLY IN THE
MID TO UPPER 20S, A MID-LEVEL SHORTWAVE RIDGE WILL BRING SOMEWHAT
WARMER CONDITIONS TODAY WITH DAYTIME HIGHS IN THE LOW 50S. THEN, A
MID-LEVEL SHORTWAVE TROUGH TRAVERSING THE EASTERN PORTIONS OF THE
INTERMOUNTAIN WEST WILL GRADUALLY DEEPEN OVER TX INTO THE GULF COAST
ON FRIDAY NIGHT. AS A RESULT, `WARM` AIR ADVECTION WILL CAUSE DAYTIME
HIGHS TO RISE INTO THE MID 50S ON SATURDAY WHILE CLOUD COVER
GRADUALLY INCREASES. AS THIS SHORTWAVE TROUGH MOVES ESE, MOISTURE
ADVECTION WILL NOT BE STRONG ENOUGH TO PRODUCE PRECIPITATION WITH THE
ONCOMING LIFTING MECHANISM. HOWEVER, CLOUDS WILL INCREASE TO MOSTLY
CLOUDY ON SATURDAY EVENING.

WHILE THIS MID-LEVEL SHORTWAVE TROUGH IS MOVING ACROSS THE GULF
COAST AND SOUTHEAST, AN ADDITIONAL MID-LEVEL SHORTWAVE TROUGH FROM
THE NORTHWEST TERRITORIES OF CANADA WILL BE DEEPENING OVER THE
PLAINS. IT WILL BE PUSHING A VERY COLD ARCTIC AIRMASS SOUTHEAST OVER
THE PLAINS AND EVENTUALLY TO THE SOUTHEAST. HOWEVER, FIRST, A MID-
LEVEL SHORTWAVE RIDGE WILL KEEP TEMPERATURES MODERATED ON SUNDAY INTO
THE LOW TO MID 50S AND OVERNIGHT LOWS IN THE MID 30S. AS A RESULT OF
THE BRIEF MOISTURE ADVECTION ON SUNDAY, ANTICIPATING THAT JUST ENOUGH
SATURATION OF THE ENVIRONMENTAL PROFILE WILL TAKE PLACE TO PRODUCE
RAINFALL ON SUNDAY NIGHT. THIS WILL OCCUR AS THE COLD FRONT PASSES
FROM THE MS RIVER VALLEY TO THE TN VALLEY. MODELS DO VARY SOMEWHAT ON
THE TIMING OF THIS FRONT, BUT IT APPEARS THAT IT SHOULD PASS OVER THE
REGION ON MONDAY MORNING BETWEEN 06Z-12Z (1AM- 6AM). COOLING ALOFT
MAY YIELD A MIX OF SNOW/RAIN DURING THE TIME FRAME OF THE FROPA ON
MONDAY.

THEN, EXPECT THAT THE MIX OF RAIN/SNOW WILL GRADUALLY CHANGE BACK TO
RAIN ON MONDAY DUE TO LIMITED DAYTIME HEATING. HOWEVER, THIS WILL
RAPIDLY CHANGE AS THE COLD AIRMASS CONTINUES TO ADVECT SOUTHWARD OVER
THE SOUTHEAST DURING THE DAY ON MONDAY. THE RAIN/SNOW MIX SHOULD
RETURN ON MONDAY AFTERNOON AND BY LATE EVENING INTO THE OVERNIGHT
CHANGING TO ALL SNOW. THE FORECAST SOUNDINGS WILL LIKELY CHANGE OVER
THE COMING DAYS AS MODELS CHANGE TRAJECTORY, TIMING, AND EVOLUTION OF
COLD AIRMASS. THE THERMAL PROFILE SUPPORTS SNOW, BUT STILL LOOKS TO
BE LIGHT SNOW AND LIKELY LITTLE IN THE WAY OF ACCUMULATION. THIS IS
MAINLY DUE TO THE LACK OF STRONG LIFT AT THE CRITICAL -10C/-20C
LEVELS, THE NATURE OF THE MOISTURE ADVECTION AHEAD OF/DURING THE
TROUGH PASSAGE (BEHIND THE FRONT), TRAJECTORY OF MID- LEVEL
SHORTWAVES MOVING WITHIN THE MEAN TROUGH OVER THE EASTERN HALF OF THE
COUNTRY, AND SOURCE REGION OF THE COLD AIRMASS. SO, GIVEN THESE
VARIABLES, ADJUSTMENTS TO THE FORECAST OVER THE COMING DAYS IS
LIKELY.

THE PRECIPITATION LOOKS TO END SOMETIME ON LATE TUESDAY AFTERNOON AS
SNOW (POSSIBLY MIXED WITH RAIN), AS THE LAST COUPLE OF SHORTWAVE
TROUGHS ROTATE AROUND THE PRIMARY TROUGH PROVIDE ADDITIONAL
PRECIPITATION. VERY COLD DAYTIME HIGH TEMPERATURES ARE ALSO EXPECTED
ON TUESDAY. THIS IS MAINLY DUE TO THE FACT THAT CLOUDS ASSOCIATED
WITH THE PRIMARY TROUGH ARE NOT EXPECTED TO BREAK UNTIL LATER ON
TUESDAY NIGHT, AND BREEZY NORTHERLY WINDS OF 10-15 MPH WILL
CONTRIBUTE TO THE COLD/RAW CONDITIONS. ONCE THE CLOUDS BREAK AND
ANTECEDENT VERY COLD HIGHS ON TUESDAY, TEMPERATURES SHOULD DROP
RAPIDLY BELOW FREEZING ON TUESDAY NIGHT AND ANTICIPATE MORNING LOWS
TO BE IN THE LOW TO MID 20S. WITH THOSE COLD TEMPERATURES AND
CONTINUED BREEZY CONDITIONS, WIND CHILLS WILL BE IN THE TEENS AND
POSSIBLY SINGLE DIGITS OVER THE HIGHER ELEVATIONS OF NORTHEAST AL AND
SOUTHERN MIDDLE TN.

MOSTLY SUNNY TO PARTLY CLOUDY CONDITIONS ARE EXPECTED ON WEDNESDAY,
BUT NOT MUCH MODIFICATION TO THE COLD AIRMASS WILL OCCUR AS DAYTIME
HIGHS STRUGGLE TO REACH 40. WARMER AND DRY CONDITIONS SHOULD RETURN
BY THURSDAY AS THE AMPLIFIED PATTERN BEGINS TO DAMPEN OVER THE
EASTERN HALF OF THE COUNTRY AND MODIFICATION OF THE AIRMASS PREVAILS.

SL.77

&&

.AVIATION...
FOR 12Z TAFS...

VFR CONDITIONS ARE FORECAST DURING THE NEXT 24 HOURS. HIGH PRESSURE
WILL PRODUCE LIGHT WIND FLOW TODAY INTO TONIGHT.

&&

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

$$

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



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