386 FXUS64 KBMX 091004 AFDBMX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BIRMINGHAM AL 404 AM CST SUN DEC 9 2012 .DISCUSSION... ANOTHER CLOUDY START TO THE DAY ACROSS CENTRAL ALABAMA. A DENSE FOG ADVISORY IS CURRENTLY IN EFFECT ACROSS ALL OF CENTRAL ALABAMA WITH MANY LOCATIONS REPORTING REDUCED VISIBILITIES. DUE TO THE FOG AND LOW CLOUDS...4 AM TEMPERATURES ARE STILL IN THE UPPER 50S AND LOW 60S ACROSS THE AREA. THE FOG AND LOW CLOUDS ARE DUE TO THE CONTINUED LOW LEVEL SOUTHERLY FLOW AND ISENTROPIC UPLIFT. AT UPPER LEVELS...A BROAD SCALE TROUGH STRETCHES ACROSS A MAJORITY OF THE CONUS WITH A SHORTWAVE TROUGH PIVOTING ACROSS THE ROCKY MOUNTAIN REGION. AT THE SURFACE...A FRONT TO THE NORTH ACROSS TENNESSEE STRETCHES WESTWARD TOWARDS A SURFACE LOW THAT HAS DEVELOPED ACROSS THE TEXAS PANHANDLE. THIS UPPER LEVEL SHORTWAVE AND SURFACE FRONT WILL BE THE MAIN WEATHER FEATURES OVER THE NEXT COUPLE OF DAYS. TODAY...CLOUDS AND FOG WILL LINGER FOR MUCH OF THE MORNING. MODELS ARE SHOWING THAT THE CLOUDS WILL EVENTUALLY LIFT AND SOME BREAKS WILL BE POSSIBLE. THE MOISTURE IS NOT FORECAST TO BE AS DEEP AS IT WAS YESTERDAY WITH SHALLOWER MOISTURE ACROSS THE SOUTH. THEREFORE... EXPECT CLOUDS ACROSS THE SOUTH WILL BREAK UP MID LATE MORNING WITH SOME BREAKS IN THE CLOUDS FURTHER TO THE NORTH BY LATE MORNING TO EARLY AFTERNOON. MIXING WILL ALSO HELP CLOUDS BREAK UP AS SOUTHERLY WINDS WILL INCREASE THROUGHOUT THE DAY TODAY. NOT EXPECTING ANY THUNDERSTORMS TODAY AS UPPER LEVEL LAPSE RATES REMAIN RATHER WEAK AND MODEL SOUNDINGS ARE INDICATING A WEAK CAP SHOULD KEEP CONVECTION FROM FORMING. A STRAY SHOWER WILL BE POSSIBLE ACROSS THE NORTH LATE THIS MORNING WITH A BIT DEEPER MOISTURE AS NOTED EARLIER. TONIGHT...THE FOCUS SHIFTS TO THE COLD FRONT AND THE SHORTWAVE TROUGH APPROACHING FROM THE WEST. ONE OF THE MAIN FORECAST CHALLENGES IS WILL THERE BE ANY RAIN AHEAD OF THE FRONT DURING THE OVERNIGHT PERIOD. THE GFS IS THE MOST AGGRESSIVE WITH PRECIPITATION AHEAD OF THE FRONT WITH PW VALUES INCREASING TO 1.5 INCHES AROUND 06Z. THE NAM IS MUCH DRIER DURING THE OVERNIGHT PERIOD WITH MAXIMUM PW VALUES AT 06Z AROUND 1.25 INCHES. THEREFORE...THERE IS STILL A LOT OF UNCERTAINTY WITH THE EVOLUTION OF THIS SYSTEM. ADDITIONALLY...THE GFS IS SHOWING A WEAK BUT MORE ROBUST SHORTWAVE TROUGH MOVING ACROSS THE FORECAST AREA DURING THE OVERNIGHT PERIOD. AT 12Z MONDAY...THE FRONT WILL BEGIN TO NUDGE INTO NORTHWESTERN PORTIONS OF THE FORECAST AREA. THEREFORE...INCLUDED DEFINITE POPS ACROSS THE WEST LATE TONIGHT WITH DECREASING POPS TOWARDS THE SOUTHEAST. THERE IS AN OUTSIDE CHANCE THAT STRONG TO SEVERE STORMS DEVELOP IN MISSISSIPPI AND MAKE IT INTO FAR NORTHWEST ALABAMA...NEAR THE FRONT...AFTER 4 AM...BUT HWO WILL KEEP THE CONFIDENCE FAIRLY LOW. ON MONDAY...THE COLD FRONT WILL MOVE ACROSS THE FORECAST AREA AS THE MAIN UPPER LEVEL TROUGH LIFTS TO THE NORTHEAST. THE LOW LEVEL JET LOOKS TO STRENGTHEN EARLY IN THE DAY TO AROUND 45-50 KTS AND SHOULD PROVIDE ENOUGH FORCING FOR A LINE OF SHOWERS AND THUNDERSTORMS TO MOVE ACROSS THE FORECAST AREA DURING THE DAY MONDAY. THE FOCUS OF THE JET WILL BE ACROSS THE NORTH WHERE THE BETTER SHEAR LOOKS TO EXIST BASED ON THE MODELS. THE REAL QUESTION REMAINS HOW MUCH INSTABILITY WILL BE AVAILABLE. THE NAM REMAINS THE MOST AGGRESSIVE MODEL WITH INSTABILITY WITH SBCAPE VALUES RANGING FROM 300-500 J/KG. THE GFS AND ECMWF ARE NOT AS IMPRESSIVE WITH THE INSTABILITY WITH SBCAPE VALUES OF ONLY 100-300 J/KG AT BEST. ADDITIONALLY...THESE VALUES SHOW THAT THE CAPE IS GENERALLY LIMITED TO THE SOUTH WITH THE BETTER SHEAR TO THE NORTH. THEREFORE...THERE IS NOT A LOCATION OF A GOOD BALANCE BETWEEN THE INSTABILITY AND SHEAR. HOWEVER...BASED ON THE NAM FORECAST WILL CONTINUE A LOW END THREAT FOR STRONG TO SEVERE STORMS ON MONDAY. THE SHEAR WILL BE RATHER IMPRESSIVE...ESPECIALLY ACROSS THE NORTH...AND IF ANY CAPE CAN BE REALIZED THEN SEVERE STORMS WILL BE POSSIBLE. MODELS SHOW THAT SEVERE WEATHER PARAMETERS WILL ACTUALLY DECREASE THROUGHOUT THE AFTERNOON AND EVENING AND THE THE LINE OF SHOWERS AND THUNDERSTORMS SHOULD BE WEAKENING AS IT PUSHES ACROSS SOUTHEAST. THE MAIN THREATS WITH ANY STRONG TO SEVERE STORMS WILL BE DAMAGING WINDS AND HEAVY RAINFALL. SOME LOCATIONS COULD SEE RAINFALL AMOUNTS OF 1-2 INCHES. THE FRONT IS FORECAST TO EXIT THE AREA MONDAY NIGHT AND RAIN CHANCES WILL END AFTER 06Z TUESDAY ACROSS THE SOUTHEAST. COLDER AIR WILL MOVE IN BEHIND THE FRONT. TEMPERATURES ACROSS THE NORTHWEST ON TUESDAY MORNING WILL BE NEAR FREEZING. MODELS ARE INDICATING THAT THE FRONT MAY STALL OUT JUST TO THE SOUTHEAST OF THE FORECAST AREA. THEREFORE...NOT AS CONFIDENT THAT TEMPERATURES ACROSS THE SOUTHEAST WILL DROP OFF AS MUCH. ADDITIONALLY...MODELS ARE INDICATING A RATHER ROBUST TROUGH THAT WILL MOVE ACROSS THE AREA TUESDAY NIGHT INTO WEDNESDAY. DUE TO THIS ROBUST TROUGH AND LINGERING BOUNDARY...INTRODUCED POPS TO THE FORECAST ACROSS THE SOUTHEAST ON TUESDAY NIGHT INTO EARLY WEDNESDAY. SURFACE HIGH PRESSURE WILL BE LOCATED TO THE NORTHEAST OF THE FORECAST AREA LATE IN THE WORK WEEK SETTING UP A WEDGE ADVECTING IN COOLER TEMPERATURES ACROSS THE EAST. EVENTUALLY...THE SURFACE HIGH MOVES OFF TO THE EAST OVER THE WEEKEND AS THE NEXT SYSTEM APPROACHES FROM THE WEST WITH CHANCES FOR PRECIPITATION RETURNING TO THE FORECAST NEXT WEEKEND. MA && .AVIATION... 06Z TAF DISCUSSION. IFR CIGS CONTINUE TO SPREAD ACROSS CENTRAL ALABAMA LATE THIS EVENING...AND TERMINALS THAT HAVE YET TO OBSERVE LOW CLOUDS AND FOG SHOULD CONTINUE TO DETERIORATE OVER THE NEXT COUPLE OF HOURS. THE LOW STRATUS HAS ACTUALLY BEGUN TO LOWER TO THE SURFACE CREATING LIFR CIGS AND LIFR TO IFR VISIBILITIES AS WELL. UNFORTUNATELY...THESE TRENDS WILL CONTINUE THROUGH 15Z AT THE LATEST. A FEW FLUCTUATIONS IN CIGS AND VIS CAN BE EXPECTED...BUT PREVAILING CONDITIONS WILL CONTINUE LIFR TO IFR FOR ALL TERMINALS. AFTER 15Z...CIGS AND VIS WILL GRADUALLY IMPROVE ACROSS THE BOARD WITH VFR CONDITIONS EVENTUALLY EXPECTED FOR ALL TERMINALS BY 21Z. THE SOUTHERN SITES OF KMGM AND KTOI SHOULD CLEAR FIRST WITH A STRONG SOUTHERLY FLOW EXPECTED THAT SHOULD MIX OUT A MAJORITY OF THE LOWER CLOUD COVER. SOUTHERLY WINDS WILL PREVAIL THROUGH THE AFTERNOON HOURS AROUND 8-10 KNOTS. 56/GDG && .PRELIMINARY POINT TEMPS/POPS... GADSDEN 70 57 64 33 50 / 20 60 100 30 10 ANNISTON 71 58 68 36 52 / 10 30 100 40 10 BIRMINGHAM 70 61 65 34 51 / 10 60 100 30 10 TUSCALOOSA 72 61 65 35 52 / 10 80 100 30 10 CALERA 71 59 67 37 52 / 10 60 100 40 10 AUBURN 71 57 71 43 54 / 10 20 80 50 10 MONTGOMERY 75 59 74 42 56 / 10 30 100 50 10 TROY 73 57 73 43 54 / 10 20 70 60 10 && .BMX WATCHES/WARNINGS/ADVISORIES... DENSE FOG ADVISORY UNTIL 9 AM CST THIS MORNING FOR THE FOLLOWING COUNTIES: AUTAUGA...BARBOUR...BIBB...BLOUNT...BULLOCK... CALHOUN...CHAMBERS...CHEROKEE...CHILTON...CLAY...CLEBURNE... COOSA...DALLAS...ELMORE...ETOWAH...FAYETTE...GREENE...HALE... JEFFERSON...LAMAR...LEE...LOWNDES...MACON...MARENGO...MARION... MONTGOMERY...PERRY...PICKENS...PIKE...RANDOLPH...RUSSELL... SHELBY...ST. CLAIR...SUMTER...TALLADEGA...TALLAPOOSA... TUSCALOOSA...WALKER...WINSTON. && $$