FXUS63 KMKX 212109
AFDMKX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
309 PM CST MON DEC 21 2009
.SHORT TERM...
TONIGHT AND AND TUESDAY...CONFIDENCE: MEDIUM
WATER VAPOR IMAGERY SHOWS SHORTWAVE OVER SOUTH DAKOTA/NEBRASKA AREA.
MODELS MOVE THE SHORTWAVE ACROSS NORTHERN ILLINOIS TUESDAY
MORNING AND WEAKENS IT SOMEWHAT. MAINLY AN INCH OR TWO OF SNOW EXPECTED
WITH ISOLATED 3 INCH AMOUNTS IN AREAS SOUTHWEST OF MADISON. LESSER
AMOUNTS NORTH TOWARD SHEBOYGAN AND FOND DU LAC.
EAST WIND OFF LAKE MICHIGAN WITH DELTA T APPROACHING CONDITIONAL
CATEGORY FAVORABLE FOR SOME LIGHT SNOW SHOWERS OR FLURRIES. EAST
WIND FETCH IS MINIMAL...BUT STEEP LAPSE RATES BELOW 875 MB INDICATE
SOME SNOW SHOWER POTENTIAL.
.WEDNESDAY...CONFIDENCE: MEDIUM
FOCUS IS ON STRONG SHORTWAVE THAT WILL REACH THE FAR WESTERN U.S.
BY TUESDAY MORNING...AND BE WELL OVER THE SOUTHWEST U.S. BY
WEDNESDAY MORNING. UPPER RIDGE OVER WISCONSIN SHOULD KEEP MUCH OF
THE PRECIPITATION SOUTH. PERSISTENT EAST FLOW OFF LAKE MICHIGAN
CONTINUES. INVERSION LOWERS BUT A FEW FLURRIES STILL POSSIBLE NEAR
THE LAKE. GFS AND ECMWF PUSH PRECIP NORTH RATHER QUICK IN
DEVELOPING LOW LEVEL JET. PREFER THE NAM A BIT WITH STRONGER
RECEDING SURFACE HIGH...KEEPING DRY AIR IN LONGER...AND DELAYING
ONSET OF PRECIPITATION. AS SUCH WILL NOT GO WITH ANY WINTER STORM
WATCH...SINCE MAIN MIXED PRECIPITATION EXPECTED WEDNESDAY NIGHT.
THICKNESS/850MB TEMPS INDICATE A MIX OF PRECIPITATION TYPES.
INITIALLY SURFACE TEMPERATURES INLAND WILL BE BELOW FREEZING.
TEMPERATURES ARE CLOSE TO ISOTHERMAL OVER A LARGE PORTION OF THE
ATMOSPHERIC COLUMN. ALSO SNOW CRYSTAL REGION IS NEAR 600 MB AND
ABOVE. SATURATION EXISTS THROUGHOUT...BUT TEMPERATURES BEGIN TO
NUDGE TOWARD FREEZING FROM 850 TO 750MB. EXPECT A MIX OF
PRECIPITATION TYPES...BEGINNING AS SNOW BUT QUICKLY BECOMING MIXED
WITH SLEET AND FREEZING RAIN. STRONG WINDS OFF LAKE MICHIGAN
SHOULD KEEP SURFACE TEMPERATURES ABOVE FREEZING NEAR THE LAKE.
.LONG TERM...
THURSDAY AND CHRISTMAS...CONFIDENCE: MEDIUM
MODELS HAVE BEEN HAVING DIFFICULTIES ON TRACK AND TIMING OF
RESULTANT SURFACE LOW BUT APPEAR TO BE FOCUSING ON A TRACK FROM
DUBUQUE TO GREEN BAY. CONFIDENCE ON THE TRACK IS MEDIUM...BUT
CONFIDENCE RATHER HIGH THAT THE STRONG LOW WILL BE AFFECTING THE
MIDWEST CHRISTMAS EVE AND CHRISTMAS DAY.
BOTH MODELS SHOW A STRONG LOW BECOMING WELL OCCLUDED AND WEAKENING BY
THE TIME IT REACHES WISCONSIN FRIDAY NIGHT. APPEARS GREATEST QPF
WILL FALL THURSDAY NIGHT BUT BY THIS TIME MUCH OF THE PRECIPITATION
WILL HAVE CHANGED TO RAIN ESPECIALLY THURSDAY NIGHT.
EXPECT MOST OF THE SNOW EARLY WITH ISENTROPIC LIFT...THEN MAINLY
A MIX BECOMING MAINLY RAIN ESPECIALLY SOUTHEAST THURSDAY NIGHT. AS
UPPER LOW APPROACHES DYNAMIC COOLING WILL AGAIN CHANGE THE
PRECIPITATION TO SNOW DURING THE DAY FRIDAY. BUT BY THIS TIME THE
HEAVIEST PRECIPITATION WILL BE TO THE NORTH AND NORTHEAST...AND IN
THE DEFORMATION ZONE TO THE WEST. BEST CHANGE OF WARNING CRITERIA
WILL BE WITH A FREEZING RAIN AND SLEET EVENT. HOWEVER WITH 50 KNOT
850 MB LOW LEVEL JET...AND LACK OF VERY COLD AIR NORTHEAST...THINK
ENOUGH SURFACE WARMING MAY LIMIT THE ICING POTENTIAL. EXPECT
ADVISORIES WILL EVENTUALLY BE NEEDED OVER MUCH OF THE FORECAST
AREA...BUT A WINTER STORM WATCH MAY BE NEEDED FOR PORTIONS OF
SOUTH CENTRAL WISCONSIN.
SATURDAY...CONFIDENCE: MEDIUM
SURFACE LOW MOVES OFF TO THE NORTHEAST AND LINGERING LIGHT SNOW
DIMINISHES TO FLURRIES UNDER WESTERN SECTION OF UPPER TROUGH.
SUNDAY...CONFIDENCE: MEDIUM
SURFACE HIGH BUILDS INTO THE NORTHERN PLAINS AND UPPER MISSISSIPPI
VALLEY WITH COLD AIR ADVECTION CONTINUING ON THE BACK SIDE OF THE
DEPARTING LOW.
&&
.AVIATION...
WEAK WAVE THAT BROUGHT LIGHT SNOW TO PORTIONS OF SRN WI
EARLIER HAS MOVED ON...BUT LOW LEVEL MOISTURE AND MVFR CIGS REMAIN.
THERE IS NOT A LONG PERIOD FOR CIGS TO IMPROVE BEFORE NEXT SHORTWAVE
MOVES THROUGH TONIGHT AND EARLY TOMORROW. STILL THINK THERE IS A
CHANCE CIGS COULD BRIEFLY IMPROVE TO VFR LATE THIS EVENING AND EARLY
TONIGHT...MAINLY NORTH AND EAST OF KMSN. MODEL LOW LEVEL RH FIELDS
SUGGEST KMKE AND KUES RIGHT ON THE BORDER OF THIS DRIER AIR...SO
WILL HAVE TO CONTINUE TO MONITOR OBS/SATELLITE AND UPDATE TAFS IF
NEEDED. OTHERWISE...EXPECT MVFR CIGS TO PREVAIL THROUGH THE FORECAST
PERIOD.
SHORTWAVE WILL BRING A DECENT SHOT FOR SNOW TO SRN WI TONIGHT AND
INTO TOMORROW MORNING...WITH THE BEST CHANCE ALONG AND SOUTH OF A
LINE FROM KDLL TO KRAC...WHERE 1 TO 3 INCHES IS POSSIBLE. EXPECT IFR
CONDITIONS AT TIMES DURING THE BEST PERIOD OF SNOWFALL LATE IN THE
NIGHT THROUGH AT LEAST MID MORNING.
&&
.MARINE...LARGE LOW PRESSURE SYSTEM BEGINS TO FORM OVER THE SOUTHERN
PLAINS TUESDAY NIGHT WHILE STRONG HIGH PRESSURE RESIDES OVER THE
NORTHERN GREAT LAKES INTO SOUTHERN CANADA. THE TIGHTENING PRESSURE
GRADIENT WILL BRING BRISK EASTERLY WINDS TUESDAY NIGHT WITH BUILDING
WAVES. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED. THE LOW WILL BE
VERY SLOW TO MOVE NORTH INTO THE UPPER MIDWEST...BRINGING A
PROLONGED PERIOD OF MODERATE TO STRONG ON SHORE WINDS AND LARGE
WAVES THROUGH FRIDAY.
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
LM...NONE.
&&
$$
SHORT/LONG TERM...06/HENTZ
AVIATION/MARINE...07/DDV
