FXUS64 KMOB 081756
AFDMOB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOBILE AL
1154 AM CST TUE DEC 8 2009
.AVIATION (18Z ISSUANCE)...DIFFICULT CEILING FORECAST FOR TAFS.
WARM FRONT CURRENTLY IN THE PROCESS OF MOVING INLAND THROUGH THE
COASTAL COUNTIES BUT CEILINGS HAVE BEEN SLOW TO RISE. HAVE GONE
WITH PREVAILING MVFR CONDITIONS THROUGH MUCH OF THE PERIOD WITH
TEMPO GROUPS FOR SHOWERS GRADUALLY TRANSITIONING TO IFR CONDITIONS
IN THUNDERSTORMS FROM ABOUT 6-10Z AS A WEAKENING SQUALL LINE IS
EXPECTED TO MOVE THROUGH THE AREA. VFR CONDITIONS FOLLOW IN THE
WAKE A COLD FRONT WHICH MOVES THROUGH AROUND 14-16Z WEDNESDAY. /29
** PREVIOUS DISCUSSION **
.SHORT TERM...(TODAY AND TONIGHT) A MCS WHICH DEVELOPED OVER SOUTH
CENTRAL LOUISIANA LAST NIGHT CONTINUES TO SPREAD EAST...TRACKING
ALONG THE IMMEDIATE COOL SIDE OF A DEVELOPING WARM FRONT OVER THE
NORTHERN GULF OF MEXICO. THIS COMPLEX HAS ALSO BEEN AIDED BY STRONG
UPPER LEVEL DIVERGENCE ASSOCIATED WITH A 100 KT 200 MB JET WHICH HAS
TRACKED ACROSS THE CENTRAL GULF OVERNIGHT. WHILE THE DIVERGENCE
ASSOCIATED WITH THE UPPER JET WILL DIMINISH THIS MORNING AS THE JET
MAX SHIFTS EAST...ISENTROPIC LIFT WILL INCREASE AS A LOW LEVEL JET
CONTINUES TO INCREASE IN RESPONSE TO THE DEVELOPING STORM SYSTEM
OVER THE SOUTHERN PLAINS. THEREFORE...EXPECT PERIODS OF RAIN TO
CONTINUE ACROSS THE AREA THROUGH THE MORNING HOURS WITH ISOLATED
THUNDER POSSIBLE ALONG THE CLOSE WHICH IS IN CLOSE PROXIMITY OF THE
WARM FRONT.
THE LATEST OBS ACTUALLY SUGGEST THE WARM FRONT IS VERY CLOSE TO THE
COAST WITH WINDS AT THE BUOY JUST SOUTH OF ORANGE BEACH HAVING GONE
SOUTHEAST WITH A DEWPOINT OF 60. MEANWHILE...WINDS ALONG THE COASTAL
COUNTIES ARE STILL OUT OF THE EAST AND NORTHEAST WITH DEWPOINTS IN
THE LOWER 50S. THE WIDESPREAD PRECIP THIS MORNING WILL LIKELY DELAY
THE FRONT FROM SURGING NORTH AS THE COOL STABLE LAYER INLAND IS
FURTHER REINFORCED. HOWEVER...AS 850 MB WINDS INCREASE TO NEAR 50
KTS THIS AFTERNOON...THE BOUNDARY SHOULD BEGIN TO SPEED UP ITS
NORTHWARD PROGRESSION WITH THE ENTIRE CWA EXPECTED TO BE IN THE WARM
SECTOR BY EARLY THIS EVENING. AS THE WARM FRONT SHIFTS NORTH...THE
CORRESPONDING ISENTROPIC LIFT WILL SHIFT NORTH AS WELL. THEREFORE...
PRECIP IN THE WARM SECTOR WILL LIKELY BECOME MORE SCATTERED IN
NATURE...ESPECIALLY CONSIDERING THE LACK OF ANY LARGE SCALE UPPER
LEVEL FORCING.
THE BIG QUESTION FOR LATE THIS AFTERNOON AND TONIGHT IS HOW MUCH OF
A SEVERE WEATHER THREAT WILL WE HAVE. AS PREVIOUSLY STATED...WE
EXPECT MOST IF NOT ALL OF THE AREA TO BE WARM SECTORED BY EARLY THIS
EVENING WITH DEWPOINTS CLIMBING INTO THE LOW AND MID 60S. EVEN WITH
THIS MOIST AIRMASS...INSTABILITY STILL LOOKS HARD TO COME BY GIVEN
850-500 MB LAPSE RATES OF ONLY 5.5 C/KM. MLCAPES LOOK TO STRUGGLE TO
REACH 500 J/KG ACROSS THE AREA. SREF PROBS HAVE INCREASED SINCE
YESTERDAY REGARDING CHANCES FOR CAPES OF 500 J/KG...BUT THEY ARE
STILL ONLY 30-50%...WHICH IS NOT VERY HIGH FOR A SHORT TERM
FORECAST. ANOTHER CONCERN IS THE LACK OF LARGE SCALE LIFT IN
VICINITY OF THE WARM SECTOR. ALL GUIDANCE IS IN GOOD AGREEMENT ON
KEEPING THE BEST FORCING WELL TO OUR NORTHWEST AS THE SHORTWAVE
ENERGY BECOMES NEGATIVELY TITLED OVER THE SOUTHERN PLAINS AND LIFTS
INTO THE MIDWEST TONIGHT. SO FOR A GOOD PART OF THE EVENING...THERE
IS SOME QUESTION AS TO HOW MUCH CONVECTION WE WILL EVEN HAVE. AN
850-700MB CONFLUENCE AXIS DOES SHIFT EAST OVERNIGHT...AND THIS MAY
HELP TO SUPPORT A BROKEN LINE OF STORMS INTO THE REGION. BY THIS
TIME...THE LOW LEVEL WIND FIELD IS VEERING AND WE LOSE A GOOD
PORTION OF THE 0-1KM SRH. STILL...0-6KM BULK SHEAR WILL BE ON THE
ORDER OF 50-60 KT AND 0-1KM SRH STILL MORE THAN SUFFICIENT AT
200-250 M2/S2. SO IF WE CAN REALIZE ENOUGH INSTABILITY
OVERNIGHT...THEN THERE WILL BE THE CHANCE FOR A FEW SEVERE STORMS
WITH THE POTENTIAL FOR DAMAGING WINDS AND ISOLATED TORNADOES.
HOWEVER...AT THIS JUNCTURE IT STILL APPEARS THAT THE INGREDIENTS ARE
STILL OUT OF PHASE...WHICH WOULD PREVENT A MORE WIDESPREAD THREAT.
WE WILL CONTINUE TO MONITOR THE EVOLUTION OF THIS SYSTEM VERY
CAREFULLY.
STAYED CLOSE TO MOS FOR HIGHS TODAY...BUT WENT WARMER FOR TONIGHT
GIVEN THE DELAY OF COLD AIR ADVECTION UNTIL WEDNESDAY. ONCE WE ARE
WARM SECTORED...IT WILL BECOME BREEZY WITH SUSTAINED WINDS NEAR 15
MPH AND GUSTS TO 25 MPH. IF THE BOUNDARY LAYER BECOMES MORE UNSTABLE
THAN CURRENTLY EXPECTED...WINDS MAY REACH CLOSE TO WIND ADVISORY
CRITERIA. SOMETHING ELSE WE WILL WATCH THROUGH THE DAY. 34/JFB
.MARINE...A WARM FRONT WILL MOVE NORTH OVER THE MARINE AREA THIS
MORNING WITH SOUTH TO SOUTHEASTERLY WINDS INCREASING THROUGH THE
DAY. DECIDED TO COMBINE THE START TIMES OF THE SMALL CRAFT ADVISORY
FOR THE OFFSHORE WATERS AND START IT AT 15Z. MOBILE BAY WILL GO INTO
ADVISORY AT 21Z. WINDS VEER TO THE SOUTHWEST AND INCREASE FURTHER
TONIGHT AS A DEEPENING LOW PRESSURE SYSTEM MOVES ACROSS THE SOUTHERN
PLAINS INTO THE MIDWEST. SEAS WILL RESPOND TO THE INCREASED
SOUTHERLY FLOW WITH SIGNIFICANT WAVE HEIGHTS BUILDING TO 5 TO 8
FEET. A COLD FRONT MOVES ACROSS THE NORTHERN GULF DURING THE DAY
WEDNESDAY WITH A STRONG OFFSHORE FLOW DEVELOPING WEDNESDAY NIGHT.
WINDS STAY STRONG AND BECOME EASTERLY BY FRIDAY AS HIGH PRESSURE
MOVES TOWARD THE CAROLINAS AND A SURFACE LOW BEGINS TO DEVELOP OVER
THE WESTERN GULF. THE LOW IS FORECAST TO TRACK ACROSS THE NORTHERN
GULF LATE FRIDAY INTO SATURDAY...MAINTAINING A STRONG WIND FIELD AND
BRINGING ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS TO THE AREA.
34/JFB
.LONG TERM..BY 12Z WED MAIN UPPER SHORT WAVE /SFC LOW MOVES NORTH TO
THE UPPER MS RIVER VALLEY AND GREAT LAKES REGION WITH TRAILING COLD
FRONT JUST WEST OR NEAR THE SE MS/SW AL BORDER PROGGED TO MOVE JUST
EAST OF THE CWFA BY AROUND 18Z. AHEAD OF THE FRONT LIGHT RAIN WITH A
FEW SCATTERED SHOWERS CAN BE EXPECTED WITH THE BETTER RAIN CHANCES
OCCURRING OVER EASTERN AND COASTAL SECTIONS OF CWFA WED MORNING. DUE
TO LIMITED FORCING IN THE MID LEVELS AND MARGINAL INSTABILITY ACROSS
THE REGION BY THIS TIME WED WILL MENTION PRECIP AS MAINLY SHOWERS
THROUGH 18Z. FOR WED AFTERNOON GOOD CLEARING IS NOTED IN THE LOWER
LEVELS FROM WEST TO EAST BY MOST OF THE MODEL GUIDANCE WITH SOME LOW
STATUS LINGERING ALONG THE COAST AND OFFSHORE THROUGH 00Z.
ALOFT...FAVORABLE REGION OF UPPER JET STRETCHING FROM THE GREAT
PLAINS TO THE MID ATLANTIC REGION GIVES WAY TO INCREASED LIFT ACROSS
MUCH OF THE CENTRAL GULF COAST REGION LATE WED INTO THU RESULTING IN
SOME HIGH TO MID CLOUDINESS TO REFORM OVER MUCH OF THE CENTRAL GULF
COAST REGION WED NIGHT INTO THU. THE EXTRA CLOUDS WILL LIKELY HAVE
AN EFFECT ON TEMPS WED NIGHT LEADING ME TO GO SLIGHTLY WARMER THEN
MAV GUIDANCE FOR MINS EARLY THU MORNING BUT NOT AS WARM AS THE MET
GUIDANCE...WHICH SHOWS MUCH WARMER CONDITIONS BY THU MORNING MOST
LIKELY FROM BETTER HIGH CLOUDINESS FORMING AND MOVING IN FROM THE
NORTH. FOR THU INTO FRI SFC RIDGE SETTLES OVER MUCH OF THE SE CONUS
AND TN RIVER VALLEY EVENTUALLY SETTING THE STAGE FOR GOOD
OVERRUNNING OR LAYER LIFT EVENT DEVELOPING FROM WEST TO EAST LATE
FRI INTO SAT IN RESPONSE TO NEXT SHORT WAVE/SFC LOW APPROACHING FROM
THE WEST AND GOOD MOISTURE STILL PRESENT IN THE MID TO UPPER
LEVELS. BOTH GFS AND ECMWF SHOW REMNANT FRONTAL BOUNDARY WELL
OFFSHORE RETROGRADING NORTHWARD AS A WARM FRONT FRI NIGHT INTO
SAT...REACHING TO THE IMMEDIATE COAST OR MOVING JUST INLAND SAT
MORNING THEN SHIFTING SE OR EAST OF THE CWFA BY 00Z SUN. DUE TO
WIDESPREAD RAIN DEVELOPING WELL AHEAD OF THIS NEXT SYSTEM DURING THE
DAY ON FRI AND PLENTY OF WET GROUND SURFACE ACROSS THE REGION
CONDITIONS WILL HAVE TO BE CLOSELY MONITORED FOR POSSIBLE FLOODING
OR FLASH FLOODING MOSTLY FRI NIGHT AND EARLY SAT MORNING. FOR LATER
IN THE PD UPPER FLOW REMAINS MOSTLY ZONAL AND PROGRESSIVE IN NATURE
GIVING WAY TO ANOTHER ROUND OF WET WEATHER BY EARLY NEXT WEEK. AS
FOR TEMPS AS MENTIONED ABOVE WILL GO SLIGHTLY WARMER THAN THE MEX
GUIDANCE FOR WED NIGHT THEN STAY CLOSE TO THE CURRENT 00Z GUIDANCE
THROUGH THE REMAIN OF THE FORECAST PD.
&&
.AVIATION....(12Z TAF CYCLE) WIDESPREAD RAIN AND MVFR CIGS CURRENTLY
AFFECTING ALL TAF SITES AND THIS LOOKS TO CONTINUE FOR THE NEXT
SEVERAL HOURS. ALSO CANNOT RULE OUT ISOLATED THUNDER THIS MORNING
ESPECIALLY AS DEEPER CONVECTION MOVES EAST OUT OF LOUISIANA. A WARM
FRONT WILL SURGE NORTH LATER TODAY WITH WINDS BECOMING INCREASINGLY
STRONG OUT OF THE SOUTH AND SOUTHEAST. WILL SEE PERIODS OF SHOWERS
AND THUNDERSTORMS THROUGH THE PERIOD...SOME OF WHICH COULD BE
STRONG...ESPECIALLY TONIGHT. CIGS WILL BE PREDOMINATE MVFR BUT MAY
SEE OCCASIONAL IFR. 34/JFB
&&
.FIRE WEATHER...AFTERNOON RELATIVE HUMIDITIES WILL LIKELY FALL BELOW
35 PERCENT OVER SOME INLAND AREAS OF NWFL ON THU BUT LESS THAN 4
HOURS. FOR NOW...WILL CONTINUE TO MONITORED THIS SITUATION CLOSELY
FOR POSSIBLE WATCHES OR WARNINGS FOR THU AFTERNOON. /32
&&
.PRELIMINARY POINT TEMPS/POPS...
MOBILE 70 63 69 37 / 100 80 30 00
PENSACOLA 69 64 72 43 / 90 70 40 00
DESTIN 68 65 73 45 / 80 60 50 00
EVERGREEN 68 62 67 35 / 90 90 30 00
WAYNESBORO 68 56 63 32 / 100 90 20 00
CAMDEN 66 60 65 34 / 100 90 20 00
CRESTVIEW 69 65 74 38 / 80 70 40 00
&&
.MOB WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
FL...NONE.
MS...NONE.
GM...SMALL CRAFT ADVISORY FROM 9 AM TUESDAY TO NOON WEDNESDAY FOR
THE FOLLOWING ZONES: COASTAL WATERS FROM DESTIN TO PENSACOLA
FL OUT 20 NM...COASTAL WATERS FROM PENSACOLA FL TO
PASCAGOULA MS OUT 20 NM...WATERS FROM DESTIN TO PENSACOLA FL
FROM 20 TO 60 NM...AND WATERS FROM PENSACOLA FL TO PASCAGOULA
MS FROM 20 TO 60 NM.
SMALL CRAFT ADVISORY FROM 3 PM TUESDAY TO NOON WEDNESDAY FOR
THE FOLLOWING ZONES: MOBILE BAY.
&&
$$
