Area Forecast Discussion
Issued by NWS Birmingham, AL

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000
FXUS64 KBMX 282359
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
559 PM CST SAT FEB 28 2015

.UPDATE...
FOR 00Z AVIATION.

&&

.DISCUSSION...

LOOKING AT OBSERVATIONS ACROSS CENTRAL ALABAMA TEMPERATURES HAVE
RISEN QUICKLY TODAY WITH READINGS IN THE UPPER 50S TO LOW 60S. PLENTY
ON INSOLATION AND INCREASING UPPER LEVEL HEIGHTS HAVE BEEN THE MAIN
REASON FOR THE HIGHER TEMPERATURES. CURRENT WATER VAPOR IMAGERY AND
RUC UPPER AIR ANALYSIS INDICATES RATHER ZONAL FLOW ACROSS THE CONUS.
A COUPLE OF WEAK SHORTWAVE TROUGHS CAN BE NOTED IN THE ZONAL FLOW
BUT NOTHING OVERLY IMPRESSIVE. AT THE SURFACE...A HIGH PRESSURE
CENTER IS LOCATED ACROSS THE NORTHEAST WITH EASTERLY FLOW AT THE
SURFACE ACROSS CENTRAL ALABAMA. EASTERLY FLOW IS TRYING TO SET UP A
WEDGE OF COOLER AIR MOVING IN FROM THE EAST BUT HAS BEEN OUTDONE SO
FAR BY THE HIGHER HEIGHTS ALOFT AND INSOLATION. VISIBLE SATELLITE
INDICATES EXPANSIVE LOW LEVEL CLOUD COVER ACROSS SOUTHEAST
ALABAMA...SOUTHERN GEORGIA AND THE FLORIDA PANHANDLE. THE LIFT IS
SUFFICIENT ENOUGH TO SEE A FEW REPORTS OF LIGHT RAIN IN THIS REGION.
MODELS INDICATE THIS LOW LEVEL LIFT WILL SHIFT NORTHWARD THROUGHOUT
THE OVERNIGHT HOURS AND SPREAD INTO CENTRAL ALABAMA. THE LATEST
MODEL RUNS ARE A BIT MORE AGGRESSIVE WITH THE LOW LEVEL LIFT AND HAVE
INCREASED POPS SLIGHTLY TONIGHT BUT EXPECT ANY RAINFALL AMOUNTS WILL
BE LIGHT. IN ADDITION...EXPECT DRIZZLE WILL BE POSSIBLE DUE TO THE
LOW LEVEL SATURATION. MODEL SOUNDINGS INDICATE THAT THE ATMOSPHERE IS
RATHER DRY ABOVE 800 MB. DUE TO THE EXPANSIVE CLOUD COVER EXPECTED
TONIGHT...LOWS SHOULD ONLY DROP OFF INTO THE UPPER 30S TO MID 40S.
THIS LOW LEVEL LIFT SHIFTS TO THE NORTH DURING THE DAY ON SUNDAY AND
EXPECT THE BEST CHANCE FOR LIGHT PRECIPITATION WILL BE ACROSS THE
NORTHERN COUNTIES. HAVE CONTINUED AT LEAST A SLIGHT CHANCE ACROSS
THE ENTIRE FORECAST AREA BUT FURTHER SOUTH...CONDITIONS COULD REMAIN
DRY MOST OF THE DAY.

NEXT WEEKS FORECAST WILL BE CHARACTERIZED BY WEATHER EXTREMES.
EXPECT CENTRAL ALABAMA WILL GO FROM TEMPERATURES IN THE UPPER 70S TO
LOW 80S EARLY IN THE WEEK TO THE POTENTIAL FOR A WINTER STORM LATE
WEDNESDAY INTO EARLY THURSDAY. SO...HOW DO WE SET THE STAGE FOR SUCH
A DRAMATIC SWING. ON MONDAY...A CUT OFF LOW ACROSS THE DESERT
SOUTHWEST BEGINS TO KICK OUT TO THE EAST...AT THE SAME TIME AN UPPER
LEVEL TROUGH WILL DIVE OUT OF CANADA INTO THE NORTHERN PLAINS.
CLOSER TO HOME...UPPER LEVEL HEIGHTS WILL BEGIN TO RISE IN RESPONSE
TO THE LOW ACROSS THE DESERT SOUTHWEST EJECTING TO THE EAST.
SOUTHWESTERLY FLOW AROUND AN 850MB RIDGE LOCATED ALONG THE FLORIDA
PENINSULA WILL ADVECT IN WARM AIR AND MOISTURE WITH RAIN CHANCES
INCREASING ACROSS THE NORTHWESTERN COUNTIES. A LEE LOW DEVELOPS LATE
MONDAY INTO TUESDAY AS THE TROUGHS APPROACH FROM THE NORTHWEST AND
SOUTHEAST. CLOSER TO HOME...A WARM FRONT IS EXPECTED TO SURGE
NORTHWARD ON TUESDAY AS THE SURFACE LOW TRACKS ACROSS THE CENTRAL
PLAINS. UPPER LEVEL HEIGHTS WILL CONTINUE TO INCREASE IN RESPONSE TO
THE DEEPENING TROUGH TO THE WEST. SOUTHERLY LOW LEVEL WINDS AND WARM
AIR ADVECTION WILL PUSH TEMPERATURES INTO THE 70S AREAWIDE ON
TUESDAY WITH LOW 80S POSSIBLE ACROSS THE SOUTHERN COUNTIES. A FEW OF
THE MODELS INDICATE SOME ELEVATED INSTABILITY AS THE WARM FRONT
LIFTS TO THE NORTH AND EXPECT THERE COULD BE SOME THUNDERSTORMS AS
CENTRAL ALABAMA TRANSITIONS TO THE WARM SECTOR.

THE TROUGH COMING IN FROM THE NORTHERN PLAINS PHASES WITH THE
SOUTHERN TROUGH ON WEDNESDAY AS THE COLD FRONT PUSHES THROUGH
CENTRAL ALABAMA. THE ATMOSPHERE BECOMES RATHER SATURATED AHEAD OF
THE APPROACHING FRONT WITH PW VALUES OVER 1.5 INCHES WHICH IS AROUND
THE 99TH PERCENTILE FOR EARLY MARCH. WITH THE SATURATED
ATMOSPHERE...LAPSE RATES WILL BE NEAR MOIST ADIABATIC PRODUCING
LIMITED INSTABILITY. THE LOW LEVEL WINDS AHEAD OF THE SYSTEM BECOME
SOUTHWESTERLY AND EXPECT THIS WILL ALSO LIMIT THE LOW LEVEL SHEAR
SOMEWHAT. THE 850MB JET INCREASES TO AROUND 50KTS. GIVEN THE
COMBINATION OF PARAMETERS EXPECT A FEW STRONG STORMS WILL BE POSSIBLE
AND EXPECT THE SEVERE WEATHER THREAT IS TOO LIMITED TO MENTION IN
THE HWO AT THIS TIME.

THE MAJOR IMPACTS FROM THIS FORECAST WILL BE THE POTENTIAL WINTER
STORM LATE WEDNESDAY INTO EARLY THURSDAY. THE GFS...ECMWF AND GEM
HAVE COME INTO MUCH BETTER AGREEMENT WITH THE TIMING OF THE SYSTEM
AND THE LOW LEVEL COLD AIR MOVING IN BEHIND THE FRONT. THE COLD
FRONT SHOULD MOVE INTO NORTHWESTERN PORTIONS OF CENTRAL ALABAMA
WEDNESDAY AFTERNOON WITH TEMPERATURES DECREASING RAPIDLY WEDNESDAY
EVENING INTO THE OVERNIGHT HOURS. AS THE UPPER LEVEL TROUGHS PHASE
AN INCREDIBLE UPPER LEVEL JET IN EXCESS OF 180 KTS DEVELOPS ACROSS
THE OHIO RIVER VALLEY INTO THE NORTHEAST. THIS WILL PUT ALABAMA IN
THE RIGHT ENTRANCE REGION OF AN INCREDIBLE JET. THIS MEANS THERE
WILL BE AMPLE SYNOPTIC SUPPORT FOR POST-FRONTAL PRECIPITATION TO
CONTINUE. MODEL SOUNDINGS INDICATES PW VALUES OVER 1 INCH WITH
SURFACE TEMPERATURES FALLING INTO THE 20S. A WARM NOSE IS PRESENT ON
THE SOUNDINGS OF AROUND 5 DEGREES CELSIUS. THEREFORE...EXPECT THE
MAIN PRECIPITATION TYPE WILL BE FREEZING RAIN. THE WARM NOSE BEGINS
TO COOL SOME EARLY THURSDAY AND THERE COULD BE A BRIEF MIXTURE OF
SNOW AND SLEET BEFORE PRECIPITATION ENDS BUT EXPECT THE MAJORITY OF
THE POST-FRONTAL PRECIPITATION WILL BE FREEZING RAIN. ALL OF THESE
PARAMETERS ARE BEGINNING TO COME IN LINE FOR ANOTHER WINTER STORM.
EXPECT THE MAIN IMPACTS WILL BE ALONG AND NORTH OF THE I-59 CORRIDOR
ALTHOUGH SOME OF THE LATEST MODELS SUGGEST WINTRY PRECIPITATION
COULD BE A LITTLE BIT FURTHER TO THE SOUTH. EXPECT THIS EVENT WILL
HAVE MORE IMPACTS THAN THE PREVIOUS EVENT DUE TO THE PRECIPITATION
TYPE. IN ADDITION...WINDS WILL BE AROUND 10-20 MPH AND COULD CAUSE
MORE ISSUES WITH TREES AND POWER-LINES IF THE EVENT UNFOLDS AS THE
CURRENT MODELS INDICATE. PLEASE CHECK BACK FOR THE LATEST UPDATES
WITH THE EVENT STILL BEING OVER 4 DAYS AWAY. MODELS INDICATE THAT
TEMPERATURES WILL REMAIN NEAR TO BELOW FREEZING ACROSS AREAS ALONG
AND NORTH OF I-59 THROUGHOUT THE DAY THURSDAY AND SOME LOCATIONS MAY
NOT GO ABOVE FREEZING UNTIL FRIDAY AFTERNOON.

05/MA

&&

.AVIATION...
00Z TAF DISCUSSION.

SAME THINKING AS PREVIOUS FORECAST BUT BROUGHT CIGS DOWN A BIT
QUICKER IN THE SOUTH. 4-5K FT CLOUD DECK IS QUICKLY SPREADING
NORTHWARD AND HAS ALREADY REACHED EET. CIGS HAVE NOW FALLEN TO
MVFR AT TOI. STILL EXPECT THE LOWER CIGS TO MOVE FROM SOUTH TO
NORTH THIS EVENING WITH CIGS LOWERING TO MVFR THEN IFR AREAWIDE BY
09Z-10Z. SOME DRIZZLE AND/OR PATCHY FOG IS LIKELY WITH THE LOWER
CIGS. IFR CONDITIONS MAY PERSIST THRU MUCH OF THE DAY ON SUNDAY.

19

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     39  53  44  54  47 /  20  30  60  60  50
ANNISTON    40  57  45  58  50 /  30  30  40  60  50
BIRMINGHAM  42  57  48  56  51 /  20  30  60  70  50
TUSCALOOSA  44  57  49  57  50 /  10  20  60  60  50
CALERA      44  59  49  58  53 /  20  20  40  60  50
AUBURN      41  56  46  64  54 /  40  30  30  40  40
MONTGOMERY  44  62  50  66  56 /  30  20  30  50  30
TROY        43  62  49  68  56 /  40  20  20  30  20

&&

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

&&

$$






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