FXUS62 KJAX 231939
AFDJAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSONVILLE FL
239 PM EST WED DEC 23 2009
...STRONG TO SEVERE STORMS POSSIBLE CHRISTMAS EVE INTO EARLY
CHRISTMAS DAY...
...WIDE AREA OF 1 INCH RAINFALL TOTALS EXPECTED...
.SHORT TERM...LATEST MSAS ANALYSIS SHOWS STRONG HIGH PRESSURE
CENTERED NORTH OF THE US MAINLAND IN THE EASTERN PROVINCES OF
CANADA...BUT RIDGING EXISTS THROUGH THE OHIO VALLEY AND INTO THE
MID ATLANTIC AND DOWN THE REMAINDER OF THE SOUTHEAST COAST. THIS
CONTINUES TO PROMOTE A FAIR WX PATTERN ACROSS OUR AREA
CHARACTERIZED BY DRY AND GENERALLY PLEASANT CONDITIONS. TEMPS
HAVE BEEN KEPT DOWN SOMEWHAT BY CIRRUS STREAMING IN OFF THE GULF
WITH MERCURY BARELY BREAKING THE 60 DEGREE MARK AT MOST LOCATIONS.
FOR THE REMAINDER OF TONIGHT...EXPECT CIRRUS TO WANE SLIGHTLY
AFTER 06Z AND BE A MORE LIMITED INFLUENCE ON TEMPERATURES.
STILL...NOT AN OPTIMUM NIGHT FOR RADIATIONAL COOLING AND WILL KEEP
TEMPS A FEW DEGREES ABOVE SUGGESTED GUIDANCE. MODELS SHOWING
PATCHY FOG CONDITIONS POSSIBLE ALONG THE I10 CORRIDOR TONIGHT
WHERE BEST MOISTURE PROFILE EXISTS. WILL INCLUDE MENTION FOR
INLAND ZONES WHERE THIS COINCIDES WITH LIGHTER BOUNDARY LAYER WINDS.
THROUGH CHRISTMAS EVE...STRONG SOUTHERN STREAM DISTURBANCE EJECTS
OUT OF THE 4 CORNERS REGION AND INTO THE CENTRAL PLAINS BY THU
AFTERNOON ALLOWING FOR A DEEPENING SURFACE REFLECTION OVER
ARKANSAS AND OKLAHOMA. WARM FRONT LOOKS TO DEVELOP FROM THIS
FEATURE FROM THE PANHANDLE THROUGH THE EASTERN GULF AND OVER SOUTH
FLORIDA. AT THIS TIME...IT APPEARS THIS FEATURE WILL REMAIN SOUTH
AND WEST OF THE FORECAST THROUGH 22Z WITH JUST INCREASED CLOUD
COVER IN THE OFFING.
CONDITIONS WILL DETERIORATE VERY QUICKLY HOWEVER AS 40 TO 50 KT
ISENTROPIC ASCENT FLOW DEVELOPS BETWEEN 00Z AND 06Z...ALLOWING A
NARROW BUT INTENSE BAND OF SHOWERS AND EMBEDDED THUNDERSTORMS TO
TRAVERSE THE FORECAST AREA. MORE ELEVATED CAPE INDICATED ON THE
NAM BUFR SOUNDING THAN THE GFS BUT UPGLIDE FLOW SHOULD HELP
COMPENSATE FOR LACK OF INSTABILITY. HELICITIES LOOK MORE THAN
ADEQUATE FOR THE DEVELOPMENT OF ROTATING UPDRAFTS...ITS JUST A
QUESTION OF WILL UPDRAFTS BE ABLE TO SUSTAIN ROTATION TO THE
SURFACE TO PRODUCE ISOLATED TORNADOES. WILL BEEF UP GRIDS
SLIGHTLY TO ACCOUNT FOR THIS POSSIBILITY AND CONTINUE MENTION IN
HWO.
MODELS ACTUALLY SHOW MAIN LOW LEVEL WIND CORE SHIFTING WELL NORTH
OF THE AREA PRIOR TO ARRIVAL OF ACTUAL SQUALL LINE. STILL...ENOUGH
850MB FLOW EXISTS WITH INCREASING SURFACE INSTABILITY TO ALLOW FOR
STRONG THUNDERSTORM DEVELOPMENT INTO CHRISTMAS AFTERNOON.
.LONG TERM...HIGH MORE OR LESS BRIDGES ACROSS THE AREA IN THE WAKE
OF STRONG STORM SYSTEM FOR THE REMAINDER OF THE WEEKEND. THIS
SHOULD ALLOW FOR POP FREE CONDITIONS EVEN THOUGH MOISTURE DOES NOT
COMPLETELY SCOUR OUT. WILL SEE TEMPS RETURN TO CLIMO THROUGH EARLY
NEXT WEEK. CURRENT GRIDS HAVE A GOOD HANDLE ON THIS AND NO CHANGES
ARE PLANNED.
&&
.AVIATION...HIGH PRESSURE NORTH OF THE AREA WILL MAINTAIN NE TO E
WINDS THRU TONIGHT. HAVE KEPT 3-5SM VIS FOR TERMINALS AFTER 09Z
BUT CONFIDENCE IS LOW FOR FOG SINCE BOUNDARY LAYER WINDS WILL BE
INCREASING TONIGHT. THIS MAY MANIFEST AS LOW CIGS ESPECIALLY AT
GNV OR VQQ RATHER THAN REDUCED VIS. HAVE INCLUDED WIND GUSTS UP TO
20 KT AT SSI AFTER 16Z THURS ALTHO OTHER SITES COULD BEGIN GUSTING
THAT EARLY AS WELL.
&&
.MARINE...NO HEADLINES THROUGH TONIGHT. PRESSURE GRADIENT BETWEEN
A LOW PRESSURE MOVING INTO THE MS RIVER VALLEY AND HIGH PRESSURE
NORTH OF OUR AREA WILL INCREASE E WINDS TO 20KT BY THU AFTERNOON
AND POSSIBLY SOONER. ONSHORE FLOW WILL ALSO BUILD SEAS TO 5-7 FT
THU. WINDS WILL SHIFT TO SE THU NIGHT AS A COLD FRONT APPROACHES
THEN TO SW FRI FOLLOWING THE FRONTAL PASSAGE. AT THAT TIME WINDS
WILL DECREASE. HAVE ENDED THE SCA AT THAT TIME...BUT SCA FOR
HAZARDOUS SEAS MAY CONTINUE INTO SATURDAY.
&&
.PRELIMINARY POINT TEMPS/POPS...
AMG 44 67 52 66 / 10 20 80 60
SSI 52 68 59 69 / 0 10 90 60
JAX 50 71 60 71 / 10 20 80 50
SGJ 56 73 62 74 / 10 20 70 50
GNV 47 74 58 73 / 10 30 70 50
OCF 50 75 61 74 / 10 30 70 50
&&
.JAX WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
GA...NONE.
AM...SMALL CRAFT ADVISORY FROM 3 PM THURSDAY TO 1 PM EST FRIDAY FOR
ALTAMAHA SOUND GA TO FERNANDINA BEACH FL 20 NM TO 60 NM
OFFSHORE-FERNANDINA BEACH TO ST AUGUSTINE FL 20 NM TO 60 NM
OFFSHORE-ST AUGUSTINE TO FLAGLER BEACH FL 20 NM TO 60 NM
OFFSHORE.
&&
$$
DEESE/TRABERT/KEEGAN
