FXUS64 KMOB 071041
AFDMOB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOBILE AL
441 AM CST MON DEC 7 2009
.SHORT TERM...[TODAY AND TONIGHT] REGIONAL RADAR THIS MORNING SHOWS
RAIN BEGINNING TO INCREASE IN COVERAGE ACROSS LOUISIANA AND
MISSISSIPPI. THIS IS IN RESPONSE TO STRENGTHENING ISENTROPIC
LIFT...MAINLY IN THE 295-300K LAYER...AS AN 120-130 KT UPPER LEVEL
JET IS CURRENTLY TRAVERSING THE ARKLATEX. EXPECT THE ISENTROPIC
LIFT AND RESULTANT RAIN TO GRADUALLY SPREAD EAST TODAY AS THE UPPER
JET MOVES ACROSS THE TN VALLEY. MODE GUIDANCE IN GOOD AGREEMENT ON
CONFINING THE STRONGEST LIFT ACROSS THE SOUTHEAST MISSISSIPPI COUNTIES
WITH VERY LITTLE OCCURRING OVER THE FAR EASTERN ZONES. WILL ALIGN
POPS ACCORDINGLY...SHOWING LOW LIKELY IN THE FAR WESTERN ZONES TO NO
CHANCE IN THE FAR EAST. EVEN IN THE WEST WHERE HIGH CHANCE OR LOW
LIKELY POPS ARE LOCATED...THIS IS EXPECTED TO BE A LIGHT EVENT GIVEN
THE SHALLOW NATURE OF THE ISENTROPIC UPGLIDE. HIGHS 58-64.
THE UPGLIDE WANES THIS EVENING AS THE UPPER LEVEL JET PULLS AWAY
FROM THE REGION...SO RAIN SHOULD BEGIN TO TAPER OFF. THE FOCUS FOR
RAIN WILL BEGIN TO SHIFT WELL TO THE WEST AS ABUNDANT ENERGY BEGINS
TO EJECT EAST OUT OF THE INTER-MOUNTAIN WEST. THE LOW LEVEL JET (LLJ)
WILL BEGIN TO INTENSIFY OVERNIGHT...ESPECIALLY TO OUR
WEST...INCREASING TO NEAR 45 KT OVER LOUISIANA...BUT ONLY NEAR 20 KT
ACROSS THE FL PANHANDLE. THIS LLJ AND INCREASING WARM AIR ADVECTION
WILL AID IN THE DEVELOPMENT AND NORTHWARD MOVEMENT OF A WARM FRONT
THAT SHOULD BE NEARING THE COASTAL ZONES BY 12Z TUESDAY. HIGHEST RAIN
CHANCES WILL BE CONFINED TO THE FAR WESTERN ZONES GIVEN THE LIKELY
NW/SE ORIENTATION OF THE SFC BOUNDARY AND THE LOCATION OF THE STRONGEST
LOW LEVEL CONVERGENCE. HOWEVER...POPS WILL BE KEPT IN THE CHANCE
RANGE FOR NOW GIVEN THAT THE STRONGEST FORCING STAYS WEST OF OUR
AREA THROUGH THE NIGHT. LOWS DEPENDENT ON PROGRESS OF THE WARM FRONT.
WILL NOT DEVIATE MUCH FROM MOS WITH LOWS UPPER 40S FAR INLAND TO
UPPER 50S ALONG THE COAST. SOUTHERN SECTIONS OF THE AREA MAY ACTUALLY
SEE TEMPS BEGIN TO RISE IN THE EARLY MORNING HOURS WITH THE APPROACH
OF THE WARM FRONT. 34/JFB
.SHORT TERM [TUESDAY THROUGH THURSDAY]....MODEL OUTPUTS IN FAIR
AGREEMENT ON ANOTHER VIGOROUS SHORTWAVE MOVING ACROSS THE SOUTHEAST
STATES AND BRINGING STRONG DEEP LAYER ISENTROPIC FORCING TUESDAY.
STRONG COLD FRONT WILL BE MOVING IN FROM THE WEST BRINGING PERIODS
OF RAIN WITH ISOLATED SHOWERS AND THUNDERSTORMS DEVELOP MAINLY
ACROSS THE NORTHWESTERN HALF OF THE FORECAST AREA TAPERING EASTWARD
AND WILL HAVE CATEGORICAL POPS IN THIS AREA WITH LIKELY ELSEWHERE.
LATEST SREF SHOWS OF ALL 21 MEMBERS OF THE ENSEMBLE, ALL SHOW MINIMAL
PROBABILITY OF CAPE EXCEEDING 500 J/KG, AND LOCAL STATISTICAL
STUDIES STRONGLY INDICATE THAT THE 25TH PERCENTILE OF STORM CASES
ARE NON SUPERCELL WITH CAPES BELOW 325 J/KG IN THIS AREA. THE LIFTED
INDEX DOES NOT GET NEGATIVE UNTIL TUESDAY EVENING. IT IS THE SEASON
FOR TORNADOES BUT DOUBT IS CREEPING THROUGH OUR MINDS THAT TUESDAY
WILL BE ONE OF THOSE BANNER DAYS. WE DO EXPECT WE COULD SEE A BAND
OF HEAVY PRECIPITATION FORMING UPSTREAM MOVING THROUGH THE FORECAST
AREA LATE TUESDAY WITH POPS CATEGORICAL TO NEAR CATEGORICAL
CONTINUING. OPEN GULF AIR SURGES INTO THE SOUTHEAST THROUGH TUESDAY
WITH PRECIPITABLE WATER CLOSE TO 2 INCHES BUT DAYTIME INSTABILITY
WILL BE LIMITED BY 850-500 MB LAYER WARMING BRINGING WEAK LAPSE RATES
AND DAYTIME POSITIVE LI. ALTHOUGH FAVORABLE SHEAR WILL ENHANCE BY A
50 KNOT WIND AT 850 MB...AND A BREEZY SOUTHEAST SURFACE FLOW IT IS
THE LIMIT OF INSTABILITY WHICH STEERS US TO A MORE BENIGN EVENT
HAPPENING. IF A CLOSER PHASING OF INGREDIENTS HAPPENS ESPECIALLY
DURING THE DAY AND INSTABILITY PROVES ADEQUATE THEN SUPERCELL
DEVELOPMENT IS MORE LIKELY. BUT FOR NOW WE ARE SEEING ONLY A
WEAKENING LINE OF CONVECTION MOVING THROUGH THE AREA TUESDAY NIGHT TO
BRING GUSTY WINDS. WE ARE THEREFORE SAYING IT IS A MINIMAL RISK
DURING THIS PERIOD BUT WILL CONTINUE TO MONITOR DUE TO CONCERNS WITH
CHANGES IN TIMING AND INSTABILITY. THE COLD FRONT WILL MOVE THROUGH
WEDNESDAY WITH A BRIEF CLEARING AND POST FRONTAL CLOUDS THAT
AFTERNOON. DRY CONDITIONS FOLLOWING FOR WEDNESDAY NIGHT, AND THURSDAY
AS WELL WILL BE CLEAR AND BREEZY UNDER A STEEP GRADIENT PRESENTED BY
THE ANTICYCLONE PUSHING IN.
.LONG TERM [THURSDAY NIGHT THROUGH SUNDAY]...MINOR CHANGES TO GRIDS.
DRY WEATHER TO CONTINUE FOR THE FORECAST AREA THROUGH THURSDAY NIGHT
AS A HIGH MOVES ACROSS THE REGION. AS THAT PASSES A CHANCE FOR RAIN
WILL RETURNS FRIDAY CONTINUING THROUGH SUNDAY AS A STREAM OF
VORTICITY MAXIMA IN THE SUBTROPICAL JET STREAM MOVE ACROSS THE
REGION. TEMPERATURE RETURNING TO SEASONABLE THROUGH NEXT WEEKEND. 77/BD
&&
.AVIATION...INCREASED ISENTROPIC LIFT OVER LA/MS WILL TRY TO SPREAD EAST
TODAY...WITH THE FRINGES OF THE STRONGEST LIFT NEARING BFM/MOB. THIS MAKES
THE CLOUD FORECAST FOR THESE TERMINALS RATHER TRICKY. AT THIS
POINT...EXPECT GENERAL VFR CIGS WITH OCCASIONALLY LOWERING TO MVFR
LEVELS WITH PERHAPS SOME LIGHT RAIN THROUGH THE EARLY AFTERNOON.
FURTHER EAST TOWARD PNS...EXPECTING MAINLY A VFR DAY. VFR CONDITIONS
FOR ALL TERMINALS THIS EVENING...WITH PERHAPS A RETURN TO MVFR CIGS
TOWARD DAYBREAK TUESDAY AS A WARM FRONT BEGINS TO APPROACH THE
COAST. A LIGHT EASTERLY FLOW BEGINS TO INCREASE OUT OF THE
SOUTH/SOUTHEAST AROUND 12Z TUE IN RESPONSE TO THE APPROACHING WARM
FRONT. 34/JFB
&&
.MARINE...BUOY OBS AROUND MIDNIGHT AT 42012 AND 42007 SHOWED WINDS
VERY CLOSE TO SMALL CRAFT ADVISORY LEVELS AND WELL ABOVE ANY MODEL
GUIDANCE. OVER THE PAST FEW HOURS...WINDS OFFSHORE HAVE SETTLED INTO
THE 15-20 KT RANGE AND EXPECT THIS TO CONTINUE THROUGH THE EARLY
MORNING...SO WILL LEAVE SMALL CRAFT EXERCISE CAUTION IN FOR THE
MORNING. THE GRADIENT RELAXES A LITTLE TODAY...SO EXPECT WINDS TO
SETTLE INTO THE 10-15 KT RANGE FOR MUCH OF THE DAY. THE LIGHTER
WINDS WILL BE SHORT LIVED AS WINDS SHIFT TO THE SOUTHEAST AND SOUTH
OVERNIGHT AND INCREASE IN RESPONSE TO A WARM FRONT MOVING ONSHORE.
BY TUESDAY...A STRONG ONSHORE FLOW WILL APPROACH SMALL CRAFT
ADVISORY LEVELS AND PERSIST INTO TUESDAY NIGHT...BECOMING SOUTHWEST
AND INCREASING A LITTLE FURTHER LATE AS A COLD FRONT APPROACHES FROM
THE WEST. A LONG FETCH AND DURATION OF THE WINDS WILL RESULT IN SEAS
BUILDING TO 6-8 FEET DURING THIS TIME. THE FRONT PASSES THROUGH THE
MARINE AREA ON WEDNESDAY...WITH A STRONG OFFSHORE DEVELOPING IN THE
FRONT'S WAKE WEDNESDAY NIGHT AND PERSISTING THROUGH THURSDAY. THE
FLOW BECOMES EASTERLY BY FRIDAY IN RESPONSE TO LOWER PRESSURES OVER
THE WESTERN GULF. 34/JFB
&&
.FIRE WEATHER...NO CONCERNS. GULF RETURN FLOW THROUGH MONDAY WITH
RAIN CHANCES INCREASING. A LOW WILL MOVE ALONG THE NORTHWESTERN GULF
COAST ACCOMPANIED BY A SERIES OF STRONG UPPER DISTURBANCES BRINGING
PERIODS OF RAIN. ISOLATED HEAVIER SHOWERS AND THUNDERSTORMS REGION-
WIDE TUESDAY AND TUESDAY NIGHT. A COLD FRONT WILL MOVE THROUGH THE
REGION WEDNESDAY WITH DRY WEATHER FOLLOWING WEDNESDAY NIGHT. HUMIDITY
WILL REMAIN WELL ABOVE RED FLAG CRITERIA THROUGH WEDNESDAY AND
LIKELY THROUGH THE WEEKEND. 77/BD
&&
.PRELIMINARY POINT TEMPS/POPS...
MOBILE 61 56 70 60 / 40 30 90 80
PENSACOLA 64 54 71 64 / 20 20 90 80
DESTIN 64 58 69 66 / 10 10 80 70
EVERGREEN 60 49 69 57 / 20 20 90 90
WAYNESBORO 58 50 68 54 / 60 50 90 90
CAMDEN 58 48 66 55 / 40 30 90 90
CRESTVIEW 63 52 68 61 / 10 10 90 80
&&
.MOB WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
FL...NONE.
MS...NONE.
GM...NONE.
&&
$$
