FXUS63 KLMK 080820
AFDLMK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
320 AM EST TUE DEC 8 2009
.SHORT TERM (TODAY AND TONIGHT)...
VERY DRY AIR ON THE 290K ISENTROPIC SURFACE THIS MORNING WILL
QUICKLY BECOME SATURATED WITH WINDS INCREASING TO GREATER THAN 50KTS
THIS AFTERNOON SO IT LOOKS AS IF PRECIPITATION WILL ARRIVE SOMETIME
AFTER 12Z ACROSS THE LOWER OHIO VALLEY. WITH THAT IN MIND VERY FEW
CHANGES HAVE BEEN MADE TO THE ONGOING FORECAST FOR TODAY AND
TONIGHT. NO CONCERNS ABOUT PRECIPITATION BEGINNING AS A PERIOD OF
SNOW OVER THE NORTH AS TEMPERATURES HAVE ALREADY BEEN RISING THIS
MORNING. AFTERNOON READINGS WILL BE SOMEWHAT OF AN ISSUE WITH THE
EXPECTED CLOUD COVER AND RAINFALL. WE WILL HOLD HIGHS IN THE MID TO
UPPER 40S ACROSS THE NORTH TO AROUND 50 ACROSS THE SOUTH.
TEMPERATURES WILL NOT FALL MUCH IF ANY OVERNIGHT WITH THE STRONG
WARM AIR ADVECTION CONTINUING ACROSS THE AREA.
WE WILL ALSO CONTINUE TO MENTION ISOLATED THUNDERSTORMS TONIGHT.
BASED ON THE LATEST FORECAST SOUNDINGS THERE IS SOME INSTABILITY
ABOVE 850MB SO THE ONLY ISSUE FROM THUNDERSTORM DEVELOPMENT WOULD
BE THE POSSIBILITY OF SOME HAIL. A VERY STABLE LAYER WILL EXIST NEAR
THE SURFACE SO I DON'T EXPECT THE VERY STRONG (50KTS+) 800MB WINDS
TO REACH THE SURFACE, STILL EXPECT ENOUGH LOW-LEVEL MOMENTUM
TRANSFER TO PRODUCE A WINDY NIGHT.
RAINFALL WILL BE FAIRLY SUBSTANTIAL WITH AMOUNTS UP TO 1 INCH COMMON
ACROSS THE FORECAST AREA BY 12Z WEDNESDAY MORNING.
.LONG TERM (WEDNESDAY - MONDAY)...
...STRONG WINDS LIKELY FOR WEDNESDAY...
WEDNESDAY THROUGH FRIDAY...
POTENT WEATHER SYSTEM CLEARLY ON TRACK TO TAKE A GOOD SWIPE AT US
EARLY IN THIS PORTION OF THE FORECAST PERIOD. STRONG SFC LOW OVER
SE MO EARLY IN THE PD WILL RACE NORTHEAST AND BOMB OUT OVER LOWER MI
DURING THE DAY ON WEDNESDAY. MAIN PRECIPITATION SHIELD AT THE START
OF THIS TIME FRAME WILL BE LOCATED TO OUR NORTHEAST AND EAST AS SFC
COLD FRONT WILL BE PUSHING THROUGH THE REGION DURING THE EARLY PART
OF THE DAY ON WED. STRONG GRADIENT WINDS ARE EXPECTED THROUGHOUT
THE DAY AS THE PRESSURE GRADIENT WILL BE EXCEPTIONALLY STRONG WITH
THIS SYSTEM AS IT DEEPENS TO OUR NORTH. LATEST 08/00Z GFS AND GFSX
RUNS STILL ARE SUGGESTING A BIT OF A DRY SLOT PUSHING INTO SOUTHERN
KY BY THE AFTERNOON. STRONG MIXED LAYER WINDS IN THE BOUNDARY LAYER
ARE STILL FORECAST TO BE IN THE 40-58 KT RANGE. IF WE GET SOME SUN
TO PEEK OUT...THEN THESE WINDS COULD EASILY BE TRANSPORTED TO THE
SFC. GRADIENT WINDS WILL BE HIGH WITH SFC WINDS OF 25-35 MPH
SUSTAINED DURING THE DAY...AND GUSTS UP TO 50-55 MPH WILL BE
POSSIBLE IF THE SOME CLEARING TAKES PLACE. THE HIGH WIND WATCH WILL
REMAIN IN EFFECT AT THIS TIME. AN UPGRADE WILL BE POSSIBLE DURING
THE DAY BASED ON THE LATEST WEATHER DATA. AS IF THE WINDS WILL BE
ENOUGH TO DEAL WITH...TEMPERATURES WILL CRASH THROUGH THE DAY.
HIGHS WED WILL BE EARLY WED MORNING WITH TEMPS FALLING QUICKLY AFTER
14Z OR SO. SOME WRAP AROUND PRECIPITATION SEEMS LIKELY WED
AFTERNOON IN THE FORM OF SNOW SHOWERS OR SNOW SQUALLS GIVEN THE
ANTICIPATED WINDS. PRECIPITATION AND WINDS WILL DIE DOWN QUICKLY
WED NIGHT AS THE GRADIENT RELAXES AND AN INFLUX OF DRIER AIR GETS
INTO THE REGION. GENERALLY STUCK CLOSE TO THE RAW 2M TEMPS FROM THE
GFS HERE EARLY MORNING HIGHS WED IN THE UPPER 40S TO THE LOWER WITH
LOWS THU MORNING DROPPING INTO THE LOWER 20S.
SFC HIGH PRESSURE WILL PUSH INTO THE REGION FOR THU AND FRIDAY
RESULTING IN MOSTLY SUNNY CONDITIONS AND DRY WEATHER. WHILE THE SUN
MAY BE OUT...IT WILL BE QUITE COLD THROUGH THE PERIOD. WE STUCK
CLOSE TO THE 08/00Z RAW GFS TEMPS THROUGH THE PD WITH HIGHS THU
WARMING INTO THE UPPER 20S TO AROUND 30 IN THE NORTH AND LOWER 30S
ACROSS THE SOUTH. VERY COLD CONDITIONS ARE EXPECTED FRI MORNING AS
GOOD RADIATIONAL COOLING SHOULD COMMENCE. LOWS ARE EXPECTED TO DROP
INTO THE 10-15 DEG RANGE IN THE NORTH WITH UPPER TEENS ACROSS THE
SOUTH. COLD WEATHER WILL STILL BE WITH US FOR FRIDAY WITH HIGHS
ONLY WARMING INTO THE LOWER 30S IN THE NORTH AND MID 30S IN THE
SOUTH.
FRIDAY NIGHT THROUGH MONDAY...
...WINTERY WEATHER POSSIBLE ON SATURDAY...
LONGER RANGE MODELS CONTINUE TO BE IN DECENT AGREEMENT THROUGH THIS
TIME FRAME. FCST PERIOD LOOKS TO START OFF WITH A FAST WSW FLOW
ALOFT IN THE MID-LEVELS WITH AN ACTIVE SOUTHERN STREAM. A VERY
HEALTHY MID-LEVEL WAVE IS FCST TO MOVE THROUGH THE SOUTHERN STREAM
AND ACROSS THE SOUTHEAST U.S. BEGINNING LATE FRIDAY NIGHT AND
EXITING THE SE COAST BY SUNDAY MORNING. ON THIS TRACK...WE'LL BE IN
THE NORTHERN/COLD SIDE WITH A GOOD SHOT AT SOME WINTRY WEATHER.
STRONG INFLUX OF MOISTURE ALONG WITH ISENTROPIC LIFT IS EXPECTED TO
BRING PRECIPITATION BACK INTO THE REGION EARLY SATURDAY MORNING.
WITH COLD AIRMASS ALREADY IN PLACE...PRECIPITATION WILL BE THE FORM
OF SNOW DURING THIS TIME FRAME.
FORECAST THEN BECOMES VERY CHALLENGING DURING THE DAY ON SATURDAY AS
THE LOW-LEVEL JET BRINGS IN A WARM LAYER OF AIR ALOFT...OVER THE
PRE-EXISTING COLD AIRMASS THAT IS ALREADY IN PLACE. TAKEN
VERBATIM...THE 08/00Z GFS SOLUTIONS START PRECIPITATION OFF AS SNOW
ACROSS THE ENTIRE AREA SATURDAY MORNING AND THEN QUICKLY CHANGES
THINGS OVER TO A MIX OF FREEZING RAIN/SNOW FROM SOUTH TO NORTH
DURING THE DAY. WHILE THIS SEEMS REASONABLE...GIVEN THE SYNOPTIC
SETUP...THE MODELS HAVE ALWAYS BEEN NOTORIOUS FOR TRYING TO RID THE
ATMOSPHERE OF LOW-LEVEL COLD AIRMASSES.
SO THERE SEEMS TO BE TWO SCENARIOS THAT COULD PLAY OUT. IF THE COLD
AIRMASS HANGS TOUGH THEN WE COULD BE LOOKING AT ACCUMULATING SNOWS
FOR SAT/SAT NIGHT AS FRONTOGENETICAL FORCING LOOKS DECENT FOR
MDT/HVY BANDED PRECIP SAT AFTERNOON/EVE. ON THE OTHER HAND...IF WE
DO GET SOME WARMING IN THE PBL ABOVE THE COLD SFC LAYER...WE COULD
BE LOOKING AT A SIGNIFICANT ICING PROBLEM SATURDAY AFTERNOON/EVE.
CERTAINLY SOMETHING TO WATCH OVER THE COMING DAYS...ESPECIALLY AS
THE SYSTEM GETS INTO THE NAM-WRF'S FORECAST WINDOW...AS IT USUALLY
HANDLES LOW-LEVEL COLD AIR BETTER THAN THE GFS.
BY SAT NIGHT...THERMAL PROFILES COOL BACK OFF RESULTING IN MORE OF A
SNOW SOLUTION THAN A WINTRY MIX. PRECIPITATION WILL WIND DOWN FROM
WEST TO EAST SAT NIGHT WITH DRY/COLD CONDITIONS EXPECTED FOR SUN.
ANOTHER SYSTEM LOOKS TO TAKE AIM AT OUR REGION BY LATE SUN/MON.
QUITE A BIT OF UNCERTAINTY IN THERMAL PROFILES BETWEEN THE 08/00Z
EURO AND GFS SOLUTIONS HERE AS THE EURO IS QUITE A BIT WARMER THAN
THE GFS. FOR NOW WILL LEAVE A MIX OF RAIN/SNOW IN THE FCST FOR NOW.
FOR TEMPS...AGAIN STUCK CLOSE THE 08/00Z RAW 2M TEMPS FROM THE GFS.
LOWS FRIDAY NIGHT WILL DROP INTO THE MID-UPPER 20S WITH HIGHS SAT IN
THE 30-35 DEG RANGE. LOWS SAT NIGHT LOOK TO DROP BACK INTO THE
MID-UPPER 20S IN THE NORTH AND LOWER 30S IN THE SOUTH. HIGHS FOR
SUN HAVE BEEN TRIMMED BACK INTO THE UPPER 30S...AND MON HIGHS IN THE
UPPER 30S IN THE NORTH AND MID-UPPER 40S ACROSS THE FAR SOUTH.
OVERNIGHT LOWS LOOK TO DROP INTO THE UPPER 20S TO THE LOWER 30S.
&&
.AVIATION (06Z TAF ISSUANCE)...
A FOUR CORNERS LOW WILL QUICKLY MOVE ACROSS THE COUNTY AND INTO THE
MID MISSISSIPPI VALLEY BY 06Z WEDNESDAY. FOR THE LOWER OHIO VALLEY A
SOUTHERLY FLOW WILL DEVELOP AND INTENSIFY WITH RAIN OVERSPREADING
THE TAF SITES AFTER 15Z. FOR THE OVERNIGHT PERIOD WE EXPECT MAINLY
MVFR CIGS WITH SOME IFR CIGS POSSIBLE BY 12Z. MVFR CIGS AND VSBYS
EXPECTED ONCE THE RAIN BEGINS.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...HIGH WIND WATCH FROM LATE TONIGHT THROUGH WEDNESDAY AFTERNOON
FOR KYZ023>025-028>043-045>049-053>057-065>067.
IN...HIGH WIND WATCH FROM LATE TONIGHT THROUGH WEDNESDAY AFTERNOON
FOR INZ076>079-083-084-089>092.
&&
$$
SHORT TERM........JA
LONG TERM.........MJ
AVIATION..........JA
