FXUS64 KJAN 031040
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
440 AM CST THU DEC 3 2009
...EARLY SEASON SNOW EXPECTED FRIDAY NIGHT...
.SHORT TERM...WELL...FORECAST IS NOT ANY EASIER THAN LAST NIGHT AS
FOCUS FOR THE NEXT 48 HRS REMAINS ON THE POTENTIAL SNOW EVENT FRI
NIGHT. THE QUESTION WITH THE PREV FORECASTS WAS: WILL IT SNOW? IF
SO...THEN THE AMOUNTS WERE GOING TO BE LIGHT. NOW...CONFIDENCE IS
MUCH HIGHER ON THE FACT THAT IT WILL SNOW. THE CHALLENGE NOW IS HOW
MUCH. MORE ON THE POTENTIAL SNOW EVENT BELOW.
CURRENTLY...WE HAVE SFC HIGH PRESSURE STEADILY BUILDING INTO THE
AREA AS YESTERDAYS STORM SYSTEM CONTINUES TO LIFT ACROSS THE NE.
WHAT IS LEFT IN THE WAKE OF THAT SYSTEM IS A QUITE LARGE AND DEEP
CENTRAL CONUS TROF WITH MEAN MID LEVEL HEIGHTS SOME 2-3 STANDARD DEV
BELOW NORMAL VALUES WHICH EXTENDS FROM THE DAKOTAS DOWN THROUGH S
TX. WITH COOLER/DRIER AIR STEADILY BUILDING INTO THE REGION AND NO
APPRECIABLE LIFT OCCURRING ACROSS THE AREA...LOOK FOR TODAY INTO THE
FIRST 1/2 OR 1/3 OF FRI TO BE PRECIP FREE. CONDITIONS WILL BE ON THE
CHILLY SIDE AND RUN SOME 10-13 DEGREES BELOW THE NORMS. CLOUDS TODAY
WILL BE A BIT TRICKY. A GOOD PORTION OF THE REGION CONTINUES TO HAVE
A STRATUS DECK BETWEEN 1700-3000 FT. HOWEVER...THERE ARE MULTIPLE
BREAKS IN THAT DECK AS IT IS FAR FROM CONTINUOUS. THIS VARIABLE
NATURE WILL MAKE IT DIFFICULT TO PINPOINT THE BKN/OVC AREAS. WHAT I
EXPECT TODAY IS A MORE HOMOGENEOUS CLOUD DECK TO DEVELOP AS SFC
HEATING OCCURS AND MIXING ALLOWS FOR SOME SORT OF SCT/BKN DECK.
VARIATIONS ON PARTLY TO MO CLOUDY SKY CONDITION LOOKS TO FIT BEST.
GUID HIGH TEMPS LOOKED GOOD AND HAVE FOLLOWED.
FOR TONIGHT...THE LOW CLOUDS LOOK TO DISSIPATE WITH JUST SOME HIGH
STUFF SPREADING OVER AND BECOMING THICKER FRI MORNING. GUID TEMPS
WERE GENERALLY IN THE MID 30S. THE GFS ENSEMBLE AND NAM HAVE BEEN
OFFERING COOLER LOWS AND I HAVE DECIDED TO CUT THE GFS TEMPS SOME
2-3 DEGREES.
FOR FRI...WE WILL BEGIN TO SEE THE EFFECTS OF THE STRONG S/W TROF
WHICH WILL ROUND THE BASE OF THE LONG WAVE FEATURE. AS THIS
OCCURS...DECENT LIFT WILL OCCUR ALOFT AND DEVELOP...THEN SPREAD
QUITE A BIT OF MID/HIGH CLOUDS OVER THE REGION. AT THE SAME
TIME...THE SFC LOW OVER THE NW/N GULF WILL BEGIN TO TAKE SHAPE AS
HEIGHT FALLS OCCUR ACROSS TX. DUE TO THICKENING CLOUD COVER...STEADY
CAA FROM N/NE LOW LEVELS WINDS RESPONDING TO THE DEVELOPING SFC
LOW...I EXPECT TEMPS TO REMAIN ON THE COOL SIDE AND STAY SOME 3-6
DEGREES BELOW GFS MOS GUID. AS FOR ANY ONSET OF PRECIP...I HAVE
LOWERED POPS FROM THE MOST RECENT GUID FOR FRI AFTERNOON AND STAYED
WITH THE PREV FORECAST. IT APPEARS THERE WILL BE A GOOD DEAL OF
VIRGA FALLING BUT THAT WILL MAINLY SERVE TO COOL THE LOWER LEVELS
DUE TO EVAPORATION AND SET THE STAGE FOR THE WINTRY WX LATER FRI
NIGHT.
AS FOR THE POTENTIAL SNOW EVENT FRI NIGHT. THE LATEST GUID HAS
STRONG SUPPORT AND CONTINUITY FROM ALL MODELS IN DEVELOPING SNOW
ACROSS THE CWA. THE MAIN QUESTION NOW IS...HOW MUCH? THE VARIOUS
MEMBERS OF THE SREF AND GFS ENSEMBLE ALL POINT TO SOLID POTENTIAL
FOR A 1/2 TO 1 INCH TYPE ACCUMULATIONS WITH SOME MEMBERS OFFERING
2-4 INCHES. WHILE THERE DOES EXIST THE POTENTIAL FOR SOME STRIPE OF
THE CWA TO SEE >2 INCHES...NOT ENOUGH CONFIDENCE EXISTS IN THAT AT
THE MOMENT TO RUN WITH SUCH A SOLUTION. THAT WILL HAVE TO BE WATCHED
CLOSELY AS 2 INCHES IS OUR LOCAL THRESHOLD FOR ISSUING HEAVY SNOW
WATCHES/WARNINGS. RIGHT NOW...CONFIDENCE IS HIGH IN IT SNOWING WITH
LIGHT 1 INCH OR LESS ACCUMULATIONS FOR AREAS ALONG I-20 AND SOUTH.
ACTUALLY THE BEST AREA FOR ACCUMULATING SNOW APPEARS TO EXTEND SW TO
NE ALONG A LINE FROM NATCHEZ TO NEWTON WITH IN A SWATH SOME 30-40
MILES EITHER SIDE OF THE DEFINED AXIS. THAT AREA OFFERS THE BEST
COMBINATION OF MOISTURE...DYNAMIC COOLING AND ASCENT. RECENT EVENTS
OVER THE PAST TWO YRS HAVE GIVEN US TROUBLE IN PINPOINTING THE
HEAVIEST LOCATIONS B/C THEY HAVE OCCURRED IN WHAT APPEARED TO BE THE
WARMER AREAS. HOWEVER...DYNAMIC COOLING HAS ALWAYS WON OUT AND THE
GREATEST SNOW AMOUNTS HAVE FALLEN S/SE OF THE INITIAL AXIS...CLOSER
TO THE MOISTURE SOURCE. TAKING ALL THAT INTO ACCOUNT...I AM LEANING
MORE TO THE S THIS GO ROUND FOR THE PRIMARY ACCUMULATION AXIS. AS
FOR NOW...NO WATCHES WILL BE ISSUED DUE TO THE UNCERTAINTY IN
GETTING TO THAT 2 INCH THRESHOLD. HOWEVER...AS MORE MODEL DATA
ARRIVES AND CONFIDENCE INCREASES IN LOCATION/AMOUNTS...WE WILL HAVE
TO DECIDE ON IF WE NEED A ADVISORY/WATCH AND ULTIMATELY A WARNING.
AT THIS TIME...A ADVISORY WOULD FIT THIS SITUATION AND WOULD LIKELY
BE NEED BY THIS SHIFT TOMORROW NIGHT. HOWEVER...THE DAY SHIFT MAY
DECIDE TO GET THINGS GOING IF CONFIDENCE INCREASES WITH RESPECT TO
AMOUNTS.
AS FOR THE TIMING...FRI NIGHT IS THE TIME WITH SOME ONSET STARTING
DURING THE EVENING. LIGHT SNOW WILL BE THE DOMINATE TYPE WITH SOME
LIGHT RAIN MIXING IN AT THE START. HOWEVER...ONCE COOLING GET THE
BOUNDARY LAYER TEMP CLOSE TO 34/35 DEGREES THEN IT WILL BECOME ALL
SNOW. I LEFT LIGHT SNOW WORDING FOR THE ONSET AND THEN FOR AREAS N
OF I-20. BETWEEN 04-12Z...AREAS ALONG AND S OF I-20 I WENT WITH MOD
SNOW TO COVER THE POTENTIAL FOR THE 1 INCH TYPE ACCUMULATION. /CME/
.LONG TERM...SATURDAY THROUGH NEXT THURSDAY...SOME LIGHT SNOW COULD
LINGER ACROSS FAR EASTERN PORTIONS OF THE FORECAST AREA EARLY
SATURDAY MORNING...BUT WILL QUICKLY TAPER OFF AND SHIFT EAST AS
TEMPERATURES RISE AND HIGH PRESSURE BUILDS EAST INTO THE REGION.
CLOUDS WILL ALSO GRADUALLY CLEAR THROUGH THE DAY FROM WEST TO EAST
AS TEMPERATURES REMAIN ON THE COOL SIDE AND ONLY CLIMB INTO THE MID
40S. CLOUDS WILL LIKELY HANG ON A LITTLE LATER INTO THE AFTERNOON
IN THE EAST...THUS TEMPERATURES WILL BE A LITTLE COOLER IN THIS
AREA. THEN WITH MOSTLY CLEAR SKIES EXPECTED SATURDAY NIGHT WITH A
DOWN RIGHT COLD AND DRY AIRMASS OVER THE REGION...LOWS TEMPERATURES
WILL BOTTOM OUT IN THE MID 20S AREA WIDE.
THE ACTIVE/WET PATTERN LOOKS TO CONTINUE FROM SUNDAY EVENING RIGHT
ON THROUGH INTO THE MIDDLE OF THE UPCOMING WORK WEEK. CLOUDS WILL
BUILD BACK INTO THE FORECAST AREA THROUGH THE DAY SUNDAY AND RAIN
CHANCES INCREASE SUNDAY NIGHT AS A WEAK COLD FRONT APPROACHES THE
REGION FROM THE WEST. TEMPERATURES ALSO MODERATE UP DURING THIS
TIME...AS WELL AS THROUGH THE REST OF THE PERIOD...WITH HIGHS SUNDAY
AFTERNOON GENERALLY CLIMBING BACK UP INTO THE LOW TO MID 50S AND
LOWS SUNDAY NIGHT RANGING FROM THE MID 30S TO THE MID 40S.
THE FRONT LOOKS TO BRIEFLY MEANDER ACROSS THE SOUTHEAST HALF OF THE
CWA MONDAY NIGHT. AS THIS HAPPENS...AN UPPER LEVEL SHORTWAVE WILL
SWING EAST ACROSS THE NATION'S MID-SECTION ON TUESDAY. THIS WILL
CAUSE THE FRONT TO LIFT BACK TO THE NORTH WHILE A SURFACE LOW
DEVELOPS WEST OF THE REGION AND APPROACHES THE FORECAST ON
WEDNESDAY. DECENT RAIN CHANCES WILL EXIST ACROSS THE ENTIRE CWA
DURING THIS TIME...BEFORE FINALLY COMING TO AN END THURSDAY. AS THE
LOW PRESSURE SYSTEM EXITS THE REGION TO THE EAST...STRONG HIGH
PRESSURE BUILDS SOUTHEAST INTO THE LOWER MISSISSIPPI RIVER VALLEY
THURSDAY FILTERING IN YET ANOTHER COLDER DRIER AIRMASS INTO THE
FORECAST AREA. /19/
&&
.AVIATION...DISCUSSION WILL BE OUT AFTER TAF ISSUANCE.
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 51 33 46 30 / 0 0 19 79
MERIDIAN 53 33 47 30 / 0 0 9 78
VICKSBURG 50 32 45 30 / 0 0 30 77
HATTIESBURG 54 37 48 32 / 0 0 17 82
NATCHEZ 50 33 46 29 / 0 0 34 82
GREENVILLE 47 30 43 29 / 0 0 18 49
GREENWOOD 49 30 44 30 / 0 0 11 52
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
CME/19/
