FXUS64 KBMX 052339
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
539 PM CST SUN FEB 5 2012

.UPDATE...
FOR 00Z AVIATION.

 

.DISCUSSION...

COLD FRONT HAS NOW EXITED ALABAMA...LEAVING US WITH THE UPPER
LEVEL LOW/TROUGH ACROSS THE TENNESSEE VALLEY TO BE DEAL WITH.
BLOW OFF FROM EARLIER CONVECTIVE SYSTEM IN THE WESTERN GULF WILL
STREAM OVERHEAD LATE THIS AFTERNOON AND INTO THE OVERNIGHT WHICH
WILL CAUSE MINOR HEADACHES IN THE FORECAST. FORECAST LARGELY
UNCHANGED THROUGH THE MAINLY DRY WEEK. QUESTIONS COMING INTO THE
PICTURE IN THE EVOLUTION OF THINGS NEXT WEEKEND...WITH A DIFFICULT
PATTERN TO DISCERN.

.SHORT TERM...TONIGHT AND MONDAY.

EXTREMELY POSITIVELY TILTED BUT STRETCHED/SHEARED TROUGH IN THE
OHIO VALLEY WILL DRIFT SLIGHTLY SOUTHWARD AS THE REMNANT UPPER
LEVEL LOW EJECTS EASTWARD IN THE TROUGH. COLD ADVECTION AT THE
SURFACE WITH HIGH PRESSURE SYSTEM BUILDING EASTWARD OUT OF THE
ROCKIES...COMBINED WITH RICH LOW LEVEL MOISTURE TONIGHT WILL BRING
A FOG POTENTIAL TO THE AREA. HOWEVER...DEGREE OF EVAPORATIONAL
COOLING ALLOWED BY LOW CLOUDS ADVECTING SOUTHWARD AND HIGH CLOUDS
STREAMING FROM THE GULF WILL KEEP THE FOG THREAT FROM BEING
UNIFORM...SO WILL KEEP THE PATCHY FOG CONCEPT IN THE FORECAST.

NET RESULT WILL BE VARIABLE CLOUDS TONIGHT...WITH PATCHY FOG
DEPENDING ON WINDS AND CLOUD COVER WITH TEMPS NEAR NORMAL. AFTER
MORNING FOG AND LOW CLOUDS...EXPECT IMPROVING CONDITIONS AS
SURFACE HIGH BUILDS IN FROM THE WEST...WITH SEASONABLE TEMPS.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

NOT QUITE AS CONFIDENT WITH THE FORECAST THROUGH THE WEEK...BUT
CONFIDENCE IN A DRY FORECAST STILL REMAINS GOOD. ON THE OTHER
HAND...BY THE WEEKEND ALL BETS ARE OFF. OVERALL PATTERN REMAINS...
WITH ACTIVE SOUTHERN STREAM...AND A BIT OF A CONVOLUTED AND
EVOLVING NORTHERN BRANCH THROUGH THE WEEK.

LARGE UPPER LOW OVER THE FOR CORNERS AREA EJECTS AS A NEW UPPER
LOW UNDERCUTS THE UPPER RIDGE ON THE WEST COAST. THIS LEAD LOW
THEN OPENS UP AND PROGRESSES EASTWARD THROUGH THE WEEK...DRAGGING
A POORLY DEFINED...DRY COLD FRONT THROUGH THE AREA TUESDAY NIGHT
THROUGH WEDNESDAY MORNING. MAIN ENERGY WITH THIS SYSTEM SKIRTS BY
TO OUR NORTH...CENTERED OVER THE OHIO VALLEY. MODELS CONTINUE TO
KEEP ANY PRECIP JUUUST NORTH OF THE AREA...BRUSHING EXTREME
NORTHERN ALABAMA. STRONG 1030 HPA SURFACE HIGH SETTLES INTO THE
MID MISSISSIPPI VALLEY...WHICH SHOULD KEEP US IN A MORE OR LESS
CONTINUOUS NORTHERLY FLOW/WEAK CAA PATTERN WEDNESDAY AND THURSDAY.
DURING THIS TIME...KICKER LOW UNDERCUTTING WESTERN RIDGE SETTLES
NEAR BAJA.

BEYOND THURSDAY...MODELS QUITE DIVERGENT. THE MAIN BONE OF
CONTENTION COMES DOWN TO WHAT HAPPENS TO THE BAJA CUTOFF. THE GFS
RAPIDLY EJECTS THE CUTOFF FRIDAY/SATURDAY...COMING INTO PHASE
WITH LONG WAVE TROUGH EXTENDING FROM A HUDSONS BAY LOW...FORMING A
GULF LOW AND SHOOTING ACROSS THE FLORIDA PENINSULA...AND USHERING
IN SOME MUCH COOLER AIR. ON THE OTHER HAND...ECMWF IS STINGY WITH
THE BAJA LOW AND SLOW TO EJECT JUST A PIECE OF THAT ENERGY WHILE
MAINTAINING TROUGHINESS OVER WESTERN MEXICO. SHORTWAVE IN THE
NORTHERN BRANCH IS WELL OUT AHEAD OF THIS ENERGY...AND BRINGS A
DRY REINFORCING COLD FRONT THROUGH THE AREA LATE FRIDAY...WITH
HIGH PRESSURE DOMINATING THE WEEKEND. CANADIAN/CMC MORE OR LESS
IS A COMBINATION OF THE TWO...WITH A MUCH MORE VIGOROUS SHORTWAVE
DIVING SOUTH ACROSS THE PLAINS AND COMING INTO PHASE WITH EJECTING
ENERGY OUT OF THE BAJA TROUGH. GFS ENSEMBLES HAVE SEVERAL MEMBERS
WHICH HINT AT A SLOWER EJECTION OF THE BAJA LOW...WHICH JIVE MORE
WITH THE EUROPEAN AND THE OVERALL TENDENCY OF MODELS TO EJECT BAJA
SYSTEMS TOO QUICKLY...AND A PROPENSITY TO PHASE SYSTEMS TOO
FREQUENTLY. BELIEVE THE EURO HAS THE BETTER SOLUTION...BUT WITH
SUCH STARK DIFFERENCES IN POPS FOR THE WEEKEND...WILL GO AHEAD AND
SPLASH A 20 POP INTO FRIDAY NIGHT AND SATURDAY. ONE WAY OR THE
OTHER...FAIRLY CONFIDENT WE WILL HAVE SOME SORT OF FRONTAL PASSAGE
IN THAT GENERAL TIME FRAME...AND JUST A LITTLE MORE MOISTURE THAN
EURO IS ADVERTISING COULD SPRING SOME SHOWERS. 

AS IS TYPICAL...CONFIDENCE IN THE LONG TERM IN WINTER DOES NOT
STAY HIGH FOR LONG.

JD/02

.AVIATION...
00Z TAF DISCUSSION.

LOW CLOUDS HAVE DISSIPATED FROM CENTRAL ALABAMA THIS AFTERNOON DUE
TO MIXING AT THE LOW LEVELS. WITH A SURFACE TROUGH IN TENNESSEE
MOVING SOUTHWARD PROVIDING SOME UPLIFT... AND LOW CLOUDS IN
SURROUNDING STATES... COULD SEE SOME MVFR CEILINGS MAKE THEIR WAY
BACK INTO CENTRAL ALABAMA... GENERALLY FROM 08Z TO 11Z... BEFORE
BREAKING UP AFTER SUNRISE TOMORROW.

THERE IS A CHANCE FOR SOME PATCHY FOG DEVELOPMENT OVERNIGHT... AS
DEW POINTS REMAIN IN THE 40S. A LIMITING FACTOR WILL BE HIGH
CLOUDS STREAMING IN FROM THE WEST. DECIDED NOT TO PUT FOG IN AT
ANY SITES... BUT WILL CONTINUE TO MONITOR THE POSSIBILITY FOR 06Z
ISSUANCE.

77

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