FXUS64 KJAN 220311
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
910 PM CST MON DEC 21 2009
.UPDATE...CLEAR SKIES PREVAIL ACROSS THE ARKLAMISS THIS EVENING BUT
THERE WILL BE AN INCREASE IN SOME HIGH CLOUDS THROUGH THE NIGHT.
OVERNIGHT LOWS WILL BE WARMER TONIGHT THAN IN PREVIOUS NIGHTS AS
WARM AIR ADVECTION CONTINUES TO INCREASE. THE CURRENT FORECAST LOOKS
ON TRACK...SO NO UPDATES ARE NEEDED AT THIS TIME./15/
.SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT...DRY CONDITIONS CAN
BE EXPECTED THROUGH THE DAY TOMORROW...ALTHOUGH THE REGION WILL BE
TRANSITIONING TO WARM/MOIST SOUTHERLY FLOW IN WAKE OF HIGH PRESSURE
MOVING OFF TO THE EAST. THE WARM ADVECTION WILL KEEP MORNING LOWS
TOMORROW WARMER THAN WE SAW TODAY...GENERALLY LOW 30S EAST TO UPPER
30S WEST WITH MAV GUIDANCE HANDLING THIS VERY WELL. TOMORROW WILL BE
A PLEASANT DAY ALTHOUGH CLOUD COVER WILL BE ON THE INCREASE AHEAD OF
A POTENT WEATHER SYSTEM TAKING SHAPE OVER THE PLAINS.
RAIN CHANCES WILL BE ON THE INCREASE OVER WESTERN ZONES STARTING
TUESDAY NIGHT AS WARM/MOIST AIR OVER THE GULF OF MEXICO IS LIFTED
AND TRANSPORTED NORTH AHEAD OF THE STRENGTHENING COLD FRONT.
MID/UPPER LEVEL LAPSE RATES REMAIN IN THE MEDIOCRE 5.5-6C/KM RANGE
WHILE MUCAPES INCREASE TO BETWEEN 100-200J/KG EARLY WED MORNING...BUT
COUPLED WITH 0-6KM SHEAR VALUES NEAR 50KTS WILL GO AHEAD AND INCLUDE
A SLIGHT CHANCE OF ELEVATED THUNDER OVER FAR WESTERN ZONES EARLY WED
MORNING. RAIN CHANCES WILL SPREAD TO AREAS FURTHER EAST THROUGH WED
AFTERNOON AS THE WARM UPSLOPE FLOW OVERTAKES MOST OF THE REGION
...ALTHOUGH GREATEST RAIN CHANCES REMAIN WEST OF I-55. MUCAPES REMAIN
LOW DUE TO THE WEAK LAPSE RATES THROUGH THE AFTERNOON HOURS...ON THE
ORDER OF 100-200J/KG...HOWEVER COVERAGE DOES SPREAD TO ALL AREAS WEST
OF THE I-55 CORRIDOR. BUT WITH SHOWALTER INDICES POINTING TO LIMITED
INSTABILITY...WILL LIMIT THE MENTION OF THUNDER TO THE DELTA REGION
AND ALONG AND WEST OF THE HIGHWAY 61 CORRIDOR WEDNESDAY AFTERNOON.
WITH ADDITIONAL WARM/MOIST AIR BEING FED INTO THE REGION WEDNESDAY
NIGHT AHEAD OF THE FRONT(850 THETA-E INCREASING IN EXCESS OF 320K)
FEEL THUNDER CHANCES WILL BE ON THE INCREASE INTO THE OVERNIGHT HOURS
AND HAVE INCLUDED CHANCE THUNDER AREAWIDE ACCORDINGLY. SEVERE
THUNDERSTORM POTENTIAL LOOKS LIMITED UNTIL THE STRONGER FORCING
ARRIVES EARLY THURSDAY HOWEVER A SEVERE STORM OR TWO IN ADVANCE OF
THE COLD FRONT CANNOT BE RULED OUT.
THE POTENTIAL FOR HEAVY RAINFALL WILL EXIST WITH THIS SYSTEM AS IT
TRAVERSES THE REGION. THE HIGHEST RAINFALL ACCUMULATIONS ARE
EXPECTED OVER WESTERN AREAS AND AS A RESULT...A FLASH FLOOD WATCH FOR
THESE AREAS WILL LIKELY BE NEEDED STARTING WEDNESDAY MORNING/EARLY
AFTERNOON. EXACT TIMING AND COVERAGE WILL BE ADDRESSED IN SUBSEQUENT
FORECASTS. SOME GUSTY WINDS WILL BE POSSIBLE WED AFTERNOON/NIGHT AS
THE PRESSURE GRADIENT TIGHTENS IN ADVANCE OF THE FRONT WITH BOTH GFS
AND EURO SHOW SUSTAINED SURFACE WINDS NEAR 20KTS. A LAKE WIND
ADVISORY MAY BE NEEDED DURING THIS TIME.
MAV GUIDANCE ACCEPTED THROUGH THE PERIOD ALTHOUGH DID BUMP HIGH TEMPS
A DEGREE OR TWO AT MOST SITES FOR TUESDAY AS GFS SEEMED A BIT
LOW...ESPECIALLY CONSIDERING HOW WARM WE GOT THIS AFTERNOON. /BK/
.PREVIOUS LONG TERM...THURSDAY THROUGH MONDAY...THE MODELS HAVE COME
INTO DECENT AGREEMENT ON THE TIMING OF THE COLD FRONT ACROSS THE AREA
ON THURSDAY...WITH THE EURO BEING THE SLOWER OF THE TWO. THE MODELS
HAVE BEEN FLUCTUATING ON THE NORTHWARD EXTENT OF THE INSTABILITY...
WITH THE GFS BEING MORE UNSTABLE. THE LATEST RUN OF THE GFS BRINGS
200 J/KG OF ML CAPE UP TO THE I-20 CORRIDOR...BUT PREVIOUS RUNS HAVE
BROUGHT THE INSTABILITY FURTHER TO THE NORTH. EXPECT THE MODELS TO
CONTINUE TO FLUCTUATE ON THIS OVER THE NEXT COUPLE OF DAYS AS THE
GULF BEGINS TO RECOVER. EITHER WAY THERE WILL BE VERY STRONG FORCING
AND THE SHEAR WILL BE THROUGH THE ROOF WITH AROUND 50KTS OF 0-6 BULK
SHEAR AND 0-3 HELICITIES OF 400 TO 600 M^2/S^2 THURSDAY MORNING INTO
THE AFTERNOON AHEAD OF THE BOUNDARY.
THE COLD FRONT WILL SWEEP ACROSS THE AREA THURSDAY AND WILL EXTEND
ACROSS ALABAMA BY THE EVENING HOURS. A FEW REMNANT SHOWERS WILL BE
POSSIBLE...BUT MOST OF THE ACTIVITY WILL SHIFT WELL TO THE EAST
DURING THE OVERNIGHT HOURS. SURFACE HIGH PRESSURE RIDGING WILL BUILD
IN FRIDAY WITH TEMPERATURES HOLDING IN THE 40S UNDER STRONG COLD AIR
ADVECTION. THE COOL CONDITIONS WILL CONTINUE THROUGH MUCH OF THE
WEEKEND...BUT THE GFS OPERATIONAL AND THE EURO DUE BEGIN TO DIVERGE
SIGNIFICANTLY SUNDAY AND MONDAY. THE GFS SHIFTS THE SURFACE HIGH TO
THE EAST MONDAY AND DEVELOPS WARM ADVECTION SHOWERS OVER THE AREA.
THE EURO KEEPS THE SURFACE HIGH OVER THE AREA...SO WILL JUST GO WITH
GUIDANCE FOR THIS PERIOD.
MADE A FEW ADJUSTMENTS TO GUIDANCE THROUGH THE PERIOD MAINLY WITH
TEMPERATURES. BUMPED SLIGHTLY ABOVE GUIDANCE POPS WEDNESDAY NIGHT IN
THE WEST AND OVER THE WHOLE AREA THURSDAY. ADJUSTED TEMPERATURES
WELL BELOW GUIDANCE HIGHS BOTH FRIDAY AND SATURDAY AS H925/H850
TEMPERATURES WOULD INDICATE MUCH COOLER HIGHS. ALSO WENT BELOW
GUIDANCE LOWS BOTH SATURDAY AND SUNDAY MORNING. STUCK PRETTY CLOSE
TO GUIDANCE FOR THE REMAINING PERIODS. /15/
&&
.AVIATION...VFR CONDS WILL PREVAIL THRU THE PERIOD AS HIGH PRES E
OF THE AREA KEEPS DRY CONDS IN PLACE. THERE IS POTENTIAL LATE
TONIGHT FOR A SOME MVFR/OCCSNL IFR CONDS NEAR MEI AND HBG ALTHOUGH
EXTENT AND DURATION OF SUCH WILL BE SHORT IN NATURE...GENERALLY
LIMITED TO NEAR SUNRISE. SOUTH/SOUTHEAST WINDS WILL BE ON THE
INCREASE DURING THE DAY TOMORROW AS THE PRES GRAD TIGHTENS IN ADVANCE
OF A POTENT FRONTAL SYSTEM APPROACHING THE REGION. UPPER LEVEL CLOUD
COVER WILL BE ON THE INCREASE AS WELL. /BK/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 35 65 51 61 / 0 0 40 83
MERIDIAN 30 63 45 61 / 0 0 17 59
VICKSBURG 38 65 53 64 / 0 3 63 92
HATTIESBURG 34 67 49 63 / 0 0 16 52
NATCHEZ 40 67 56 64 / 0 3 63 93
GREENVILLE 38 62 51 61 / 0 5 62 91
GREENWOOD 36 62 50 60 / 0 3 40 87
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
BK/15
