FXUS63 KMKX 221721
AFDMKX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
1121 AM CST TUE DEC 22 2009
.UPDATE...
WENT WITH WINTER STORM WATCH...MAINLY FOR THE THREAT OF SLEET AND
FREEZING RAIN WEDNESDAY NIGHT INTO THURSDAY. MAINLY INLAND IN THE
SOUTHEAST LAKESHORE COUNTIES. 12Z NAM BRINGING IN PRECIPITATION
QUICKER...BUT GFS NOW NOT AS FAST. EITHER WAY THINK WATCH IS THE
WAY TO GO GIVEN BUFKIT SOUNDINGS AND POTENTIAL COLD SURFACE
TEMPERATURES.
&&
HENTZ
.PREV DISCUSSION... /ISSUED 336 AM CST TUE DEC 22 2009/
DISCUSSION...FORECAST FOCUS ON SNOW TODAY WITH CLIPPER AND LAKE
EFFECT. THEN FOCUS SHIFTS TO PRECIP TYPES WITH WARM CONVEYOR BELT
AHEAD OF EVOLVING STRONG LOW TO OUR SOUTHWEST. HEIGHT OF GREATEST
CONCERN...FREEZING RAIN ACCUMULATION...APPEARS TO BE SHAPING UP FOR
THURSDAY. NO HEADLINE FOR NOW...BUT FREEZING RAIN POTENTIAL IS
CLEARLY A CONCERN...ESPECIALLY FOR CHRISTMAS EVE.
TODAY- CONFIDENCE...MEDIUM 88D MOSAIC SHOWS LARGE AREA OF MAINLY
LIGHT SNOW BEING DRIVEN BY WARM AIR ADVECTION/ISENTROPIC UPGLIDE
AND VORTICITY CENTER IN NORTHERN IA/SOUTHERN MN. THE LOW LEVEL JET
IS PROGGD TO SLACKEN WHICH CONTRIBUTES TO A WEAKENING TREND IN THE
850 FRONTOGENESIS. 700-300 MILLIBAR Q-VECTOR CONVERGENCE WHICH
STARTS OFF MODERATE THIS MORNING ACROSS IA/MN ALSO SHOWS A
WEAKENING TREND. THERE IS A CONTINUATION OF LIGHT UPGLIDE
THROUGHOUT THE DAY. THE OTHER CONCERN IS LAKE EFFECT POTENTIAL.
THIS IS ALREADY BEING SEEN ON THE KGRB RADAR. NE FETCH IS BEST
THROUGH 15Z THEN THERE IS A SHIFT MORE TO THE EAST. DELTA T
BECOMES LESS FAVORABLE AFTER 18Z...AND EVEN THIS MORNING...ABOUT A
14C ISN/T OVERLY IMPRESSIVE. FAR SOUTHWEST CWA WILL BE CLOSEST TO
BETTER UPGLIDE/MOISTURE WHILE LOW LEVEL JET IS MOST ACTIVE...SO
HAVE HIGHEST AMOUNTS...3 INCHES SOUTHWEST OF MADISON.
TONIGHT- CONFIDENCE...MEDIUM
UPPER LEVEL RIDGE POPS UP AHEAD OF THE BIG STORM SYSTEM TO OUR
SOUTHWEST. IN THE LOW LEVELS SOME HINT OF WEAK 700 OMEGA CONTINUING.
OVERALL ISENTROPIC UPGLIDE LOOKS WEAK. BUFKIT SOUNDINGS SUGGESTING
LOSS OF SATURATION AT -10C...THUS LACK OF ICE COULD LEAD TO A
FREEZING DRIZZLE CONCERN. PLENTY OF LOW CLOUDS ACROSS THE UPPER
MIDWEST AND AS THE VORT CLOUDINESS DEPART THIS IDEA PLAYED OUT ON
BUFKIT SOUNDINGS DOES HAVE SOME MERIT. WILL THUS INTRODUCE FREEZING
DRIZZLE STARTING AFTER 6Z.
WEDNESDAY- CONFIDENCE...LOW TO MEDIUM
HIGH PRESSURE RIDGE ANCHORED NORTHEAST OF LAKE SUPERIOR WITH LOW
PRESSURE STARTING TO STRENGTHEN IN THE SOUTHERN PLAINS. 850 LOW
LEVEL JET WRAPPING AROUND THIS SYSTEM IS ORIENTED SE-NW WITH THE
AXIS TO OUR SOUTHWEST. WOULD APPEAR THAT THIS CONFIGURATION WOULD
SUPPORT THE BEST MOIST INFLUX TO OUR SOUTHWEST. THE NAM HAS A VERY
DRY LOOK WHILE THE GFS HAS LIGHT QPF GENERATED WITH SOME ISENTROPIC
UPGLIDE AND A MUCH MORE STATURATED LOOK TO THE COLUMN. AN AMALGAM OF
ALL QPF FIELDS SUGGEST A NE/SW GRADIENT IN POPS IS THE WAY TO GO.
HAVE ELECTED TO SCALE BACK CLOSER TO THE MAV MOS POPS. 850 TEMPS/TOP
DOWN AND THCIKNESSES SUGGEST ANY PRECIP AT THE OUTSET WILL BE SNOW.
WEDNESDAY NIGHT- CONFIDENCE...LOW
INCREASING ADIABATIC OMEGA ON ISENTROPIC PLOTS AS LOW LEVEL JET AXIS
SHIFTS MORE TO THE NORTHEAST WITH TIME. BUFKIT SOUNDINGS REVEAL THAT
COLUMN IS MOIST ENOUGH AND DEVOID OF ANY WARM LAYER TO DELAY
FREEZING RAIN POTENTIAL FOR A BIT. SOME SUGGESTION FROM THE NAM AND
ECMWF THAT WARM LAYER ARRIVES BY 12Z THURSDAY...BUT THAT IS ONLY
ABOUT 1-1.5 DEGREES C. WILL GO WITH ALL SNOW THROUGH 6Z...THEN
INTRODUCE SOME SLEET MIXED IN THE FAR SOUTH AFTER 6Z.
CHRISTMAS EVE- CONFIDENCE...LOW
TRICKIEST TIME FRAME FOR ICE POTENTIAL. ANY DURATION OF ICE
ACCUMULATION CAN BE A TRAVEL NIGHTMARE SO THIS WILL BE SOMETHING TO
MONITOR. WARM LAYER ARRIVES WITH EARNEST AND SOUNDINGS/2 METER TEMPS
CERTAINLY OFFER SOME CONCERN FOR FREEZING RAIN. SOUTHEAST 850 JET
INCREASES TO 50 KNOTS AND THINK MODIFICATION IN LOW LAYERS MAY TAKE
PLACE A LITTLE QUICKER THAN WHAT 2 METER TEMPS ARE SHOWING.
PRELIMINARY THINKING IS THAT GREATEST THREAT WILL BE INLAND DURING
THE MORNING AS WOULD EXPECT BOUNDARY LAYER TO WARM SUFFICIENTLY TO
GET TEMPS ABOVE CRITICAL LEVELS.
CHRISTMAS- CONFIDENCE...LOW
850 MILLIBAR AND SURFACE LOWS ACROSS IOWA WEAKEN AND COLD AIR
ADVECTION WRAPS INTO THE CWA FROM THE SOUTH. 850 TEMPS CRASH FROM
1-2C TO NEAR -12C BY 00Z SATURDAY. GFS AND ECMWF BOTH SHOW ANYWHERE
FROM 0.20 TO 0.40 INCH LIQUID THOUGH MUCH OF THIS ASSOCUIATED WITH
NORTHWARD MOVING PRECIP IN THE WARM CONVEYOR ZONE...850 WARM
PROD...SO HIGH UNCERTAINTY AS TO WHETHER ENOUGH OF THIS REMAINS WHEN
COLD AIR WRAPS IN AROUND THE LOW.
SATURDAY- CONFIDENCE...MEDIUM
STACKED LOW IN THE STATE SO SNOW SHOWER CHANCES REMAIN. WOULDN/T BE
SURPRISED TO SEE SOME LIGHT ACCUMULATIONS.
AVIATION...-SN SHOULD DECREASE IN INTENSITY THIS MRNG AS BETTER
ISENTROPIC LIFT WEAKENS AND SLIDES TO THE SOUTHEAST ALONG WITH UPPER
LEVEL SHORT WAVE. HOWEVER WEAK WARM AIR ADVECTION LINGERS THRU THE
DAY ALONG WITH HIGH LOW LEVEL RH. IN ADDITION...WEAK LAKE EFFECT
MAY PRODUCE -SNSH/FLURRIES AT TIMES NEAR THE LAKE. HOWEVER WITH
DRY AIR JUST TO THE NORTHEAST...MAY SEE CIGS RISE TO VFR AT TIMES AT
EASTERN TAF SITES...BUT THINKING PREDOMINANTLY MVFR OR LOWER THRU
THE PD. WL NEED TO WATCH FOR PATCHY -FZDZ TNGT.
MARINE...LIGHT NLY WNDS WL VEER TO THE EAST AND INCREASE AS PRES
GRADIENT TIGHTENS OVER SRN LAKE MI BTWN HIGH PRES TO THE NORTH OF LK
SUPERIOR AND DEVELOPING LOW PRESSURE IN THE SRN PLAINS. PRES GRAD
CONTINUES TO STRENGTHEN TONIGHT AND REMAINS TIGHT INTO FRI AS
WEAKENING LOW PRESSURE REMAINS IN THE AREA. ELY WNDS LIKELY TO
REACH SMALL CRAFT ADVY LEVELS LATE TNGT AND CONTINUE THRU WED NGT.
LAKE MI TEMP STILL AROUND 4C RESULTING IN STEEP LOW LEVEL LAPSE
RATES WHICH WILL ALLOW WINDSPEEDS TO NEAR GALE CRITERIA THU AND THU
NIGHT. FUTURE SHIFTS MAY BE ISSUING GALE WATCH FOR THIS PERIOD.
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY
AFTERNOON FOR WIZ062-067-068.
WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY
AFTERNOON FOR WIZ046-047-056>058-063-064-069-070.
WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY
MORNING FOR WIZ066-071-072.
WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY
AFTERNOON FOR WIZ051-052-059-060-065.
LM...SMALL CRAFT ADVISORY FROM 3 AM WEDNESDAY TO 6 AM CST THURSDAY
FOR LMZ643>646.
&&
$$
SHORT/LONG TERM...06/HENTZ
AVIATION/MARINE...08/WOOD
