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000
FXUS64 KBMX 181132
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
532 AM CST WED DEC 18 2013

.UPDATE...
FOR 12Z AVIATION.

&&

.DISCUSSION...

THE NICE WEATHER WILL CONTINUE TODAY WITH RELATIVELY DRY AIR IN
PLACE AND SURFACE HIGH PRESSURE IN CONTROL. TEMPERATURES WILL RISE
INTO THE 50S DURING THE AFTERNOON. THE SURFACE HIGH WILL BEGIN TO
SHIFT TO THE EAST TONIGHT BUT ANOTHER COLD NIGHT IS EXPECTED. A
WARMING TREND WILL BEGIN ON THURSDAY AS SOUTHERLY FLOW DEVELOPS
AROUND THE DEPARTING SURFACE HIGH.

A MAJOR PATTERN SHIFT WILL BEGIN THURSDAY ACROSS THE WESTERN
UNITED STATES AS AN UPPER-LEVEL RIDGE OVER THE NORTHEAST PACIFIC
CAUSES A STRONG JET STREAM TO DIVE SOUTHWARD OVER THE WEST
COAST...CARVING OUT A DEEP TROUGH OVER SOUTHERN ARIZONA BY FRIDAY.
IN RESPONSE A SUBTROPICAL RIDGE WILL STRENGTHEN OVER THE BAHAMAS
CAUSING THE DEVELOPMENT OF A DEEP MOISTURE FETCH FROM THE
CARIBBEAN INTO THE GULF COAST STATES. SHOWERS AND MAYBE EVEN A
FEW THUNDERSTORMS ARE POSSIBLE BEGINNING ON FRIDAY ESPECIALLY
ACROSS THE NORTHWESTERN HALF OF THE CWA.

THE SITUATION BECOMES MUCH MORE COMPLEX AS THE TROUGH BEGINS TO
SWING TO A NEUTRAL AND THEN NEGATIVE TILT BY SATURDAY EVENING. IT
HAS BEEN DIFFICULT TO DIAGNOSE THE MOST PROBABLE EVOLUTION OF THIS
WEATHER EVENT DUE TO MODEL DISAGREEMENT...BUT I BELIEVE WE ARE
FINALLY GETTING A HANDLE ON THIS. THE 00Z GFS APPEARS TO BE AN
OUTLIER FROM THE MORE TIGHTLY CLUSTERED GEM/UKMET/ECMWF GROUP.
THE 00Z GFS HAS A RATHER PITIFUL DEPICTION OF THE SURFACE
FEATURES...SHOWING A WEAK AND ELONGATED FRONTAL ZONE AND LACKING A
WELL-DEFINED SURFACE LOW...LIKELY DUE TO THE MODEL SHEARING OUT
THE 500 MB VORT MAX AT 00Z SUNDAY. THE 06Z GFS IS IN MUCH BETTER
AGREEMENT WITH THE OTHER MODELS...SLOWER WITH THE EJECTION OF THE
UPPER TROUGH AND ATTENDANT MORE WELL-DEFINED SURFACE LOW.

THE SEVERE WEATHER RISK ON SATURDAY AFTERNOON AND EVENING WILL
LIKELY EXTEND ACROSS A RATHER LARGE AREA TO OUR WEST WITH AN
EXPANSIVE AND HIGH-QUALITY WARM SECTOR IN PLACE. WHILE A QLCS IS
LIKELY TO DEVELOP CLOSER TO THE STRONGER FORCING ADJACENT TO A
HYBRID DRYLINE/FRONT NEAR THE ARKLATEX AT 00Z SUNDAY...IT APPEARS
THAT PREFRONTAL SEVERE THUNDERSTORMS COULD DEVELOP ACROSS
LOUISIANA AND MISSISSIPPI AROUND 21Z SATURDAY AND MOVE NORTHEAST.
MOST OF THIS ACTIVITY SHOULD STAY TO THE WEST OF OUR CWA THROUGH
06Z SUNDAY BUT A FEW STORMS COULD CLIP THE NORTHWEST COUNTIES. THE
MAIN RISK WILL COME AFTER 06Z AS THE QLCS MERGES WITH THE
PREFRONTAL ACTIVITY. DEWPOINTS RISING INTO THE UPPER 60S WILL
ALLOW FOR CAPE VALUES OF 500-700 J/KG OVERNIGHT...AND VERY STRONG
0-1 KM SHEAR BE SUFFICIENT FOR DAMAGING WINDS AND TORNADOES AS THE
QLCS TRAVERSES THE CWA SUNDAY MORNING. WE SHOULD BE ABLE NARROW
DOWN THE DETAILS OF THE THREAT LEVEL AND TIMING OVER THE NEXT
COUPLE OF DAYS...BUT I WOULD DEFINITELY TAKE THIS EVENT SERIOUSLY.

MUCH COOLER AND DRIER AIR SHOULD MOVE INTO THE REGION ON MONDAY AND
TUESDAY BEHIND THE FRONT.

87/GRANTHAM

&&

.AVIATION...
12Z TAF DISCUSSION.

VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD. A WEAK COLD FRONT
PASSED OVER CENTRAL ALABAMA OVERNIGHT...WITH LIGHT NORTHERLY WINDS
RESULTING. A SURFACE HIGH PRESSURE AREA WILL BE CENTERED OVER
ALABAMA TODAY...WHICH WILL SHIFT THE WINDS FROM LIGHT NORTHERLY IN
THE MORNING TO LIGHT EASTERLY/SOUTHEASTERLY IN THE AFTERNOON.

77/GLEASON

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     54  27  61  36  63 /   0   0   0  10  60
ANNISTON    55  30  63  42  65 /   0   0   0  10  50
BIRMINGHAM  56  35  63  49  66 /   0   0   0  10  60
TUSCALOOSA  59  32  66  50  68 /   0   0   0  20  60
CALERA      56  34  64  45  66 /   0   0   0  10  50
AUBURN      56  35  61  45  66 /   0   0   0  10  20
MONTGOMERY  59  32  65  45  70 /   0   0   0  10  20
TROY        59  30  65  45  69 /   0   0   0  10  20

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$