000
FXUS63 KMKX 272127
AFDMKX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
327 PM CST MON DEC 27 2010
.VERY SHORT TERM...TONIGHT THROUGH TUESDAY...FORECAST CONFIDENCE
MEDIUM TO HIGH.
WE WILL START OFF WITH CLEAR SKIES THIS EVENING. HOWEVER...BOUNDARY
LAYER AIR...BELOW 1500 FEET...STILL HAS RELATIVE HUMIDITY VALUES OF
70 TO 90 PERCENT SINCE IT TOOK ALL OF THE MONDAY DAYLIGHT HOURS TO
BURN/MIX THE STRATUS CLOUDS/FOG. THERE IS STILL SOME LEFTOVER LOW
STRATUS AND LIGHT FOG IN PARTS OF IOWA...ILLINOIS AND NORTHERN
MISSOURI. SOME OF THIS MOISTURE SHOULD ADVECT INTO SOUTHERN
WISCONSIN TONIGHT.
RADIATIONAL COOLING OF THE BOUNDARY LAYER AIR WILL INITIATE THIS
EVENING...BUT ALL MODELS ALSO SHOW SOUTHWEST TO WEST WINDS IN THE 7
TO 12 MPH RANGE THROUGH TONIGHT. SO WE EXPECT ANOTHER STRATUS DECK
TO FORM OVER SOUTHERN WISCONSIN...WITH LIGHT FOG...UNDER THE
INVERSION WHICH IS PROGGED TO BE AT ABOUT 1000 FT AGL. THIS SHOULD
BURN/MIX BY MID-MORNING TUESDAY. BUFKIT SOUNDINGS FOR TONIGHT SHOW
THIS SCENARIO...WITH NAM SHOWING BEST RESOLUTION.
ALL MODELS HINT AT A WEAK SHORT-WAVE/VORTICITY MAX MOVING EAST ACROSS
IOWA THROUGH ILLINOIS BY LATE TONIGHT...BUT ONLY GENERATE SOME 60-80
PERCENT RELATIVE HUMIDIFIES IN THE MIDDLE ATMOSPHERE. SO NO EFFECT
AT THE SURFACE.
SUNSHINE FOR TUESDAY AFTERNOON WITH SUBSIDENCE MOST LEVELS.
.SHORT TERM...TUESDAY NIGHT THROUGH THURSDAY
.TUESDAY NIGHT AND WEDNESDAY...FORECAST CONFIDENCE MEDIUM TO HIGH.
ONE MORE COOL NIGHT TUESDAY NIGHT UNDER MOSTLY CLEAR SKIES BEFORE
WARM AIR ADVECTION REGIME AHEAD OF LATE WEEK SYSTEM BEGINS WEDNESDAY.
WENT WITH THE COOLER SIDE OF GUIDANCE FOR LOWS AS RIDGE OF SURFACE
HIGH PRESSURE NOSES OVER SOUTHERN WISCONSIN. BUFKIT FORECAST
SOUNDINGS INDICATING A STRONG INVERSION THAT WILL DECOUPLE SURFACE
WINDS FROM 15 TO 20 KNOT GRADIENT WINDS AT/ABOVE 950 MB.
DEVELOPING SOUTHERLY FLOW BRINGS +1C TO +2C 925MB TEMPERATURES INTO
SOUTHERN WISCONSIN BY 00Z THURSDAY. INVERSION OVER SNOW
COVER...INCREASING CLOUD COVER AND LOW-LEVEL MOISTURE WILL LIMIT
FULL BENEFIT OF THIS WARMING...BUT CONSENSUS HIGHS AROUND THE
FREEZING MARK IN LINE WITH FORECAST SOUNDINGS.
.WEDNESDAY NIGHT AND THURSDAY...FORECAST CONFIDENCE LOW TO MEDIUM.
ISENTROPIC LIFT INCREASES AND CONDENSATION PRESSURE DEFICITS LOWER
WEDNESDAY NIGHT INTO THURSDAY MORNING. EXPECT PATCHY FREEZING
DRIZZLE AND THEN LIGHT FREEZING RAIN BEFORE MIDNIGHT AS COLUMN
MOISTENS THROUGH AN EVER-INCREASING DEPTH...THEN A CHANCE OF RAIN
AFTER MIDNIGHT AS ENTIRE COLUMN BELOW 800 MB GOES ABOVE FREEZING.
BETTER FORCING OVER WESTERN CWA LATE WEDNESDAY NIGHT INTO THURSDAY
MORNING WITH LEAD SHORT WAVE PASSING OVER IOWA AND MINNESOTA...WITH
SOME HINTS AT A BREAK OR EASING OF THE PRECIPITATION TO PATCHY
DRIZZLE WITH SUBSIDENCE BEHIND WAVE DURING THE AFTERNOON.
HOWEVER...CONTINUED WARM ADVECTION OVER SNOW COVER WILL KEEP
WIDESPREAD FOG OVER THE AREA.
WEDNESDAY NIGHT LOWS WILL OCCUR EARLY IN THE EVENING AND THEREFORE BE
ONLY A FEW DEGREES LOWER THAN WEDNESDAY HIGHS...WITH STEADY OR
SLOWLY WARMING TEMPERATURES OVERNIGHT. RISE WILL CONTINUE THROUGH
THE DAY THURSDAY...BUT WILL BE HELD IN CHECK BY PRECIPITATION LOW
CLOUDS AND FOG.
.LONG TERM...THURSDAY NIGHT THROUGH MONDAY. FORECAST CONFIDENCE
LOW TO MEDIUM.
BETTER PRECIPITATION CHANCES COME THURSDAY NIGHT THROUGH FRIDAY AS
ISENTROPIC LIFT AND CONVERGENCE INCREASES ON NOSE OF LOW-LEVEL JET
INCREASING TO 40-50 KTS...THEN FORCING ASSOCIATED WITH DYNAMICS OF
MAIN WAVE AND COLD FRONT PASSAGE FRIDAY NIGHT INTO SATURDAY.
FLOODING STILL A CONCERN...THOUGH GFS IS NOW SHOWING ONLY 0.25 TO
0.50 INCH FOR THE EVENT...WHILE ECMWF TOTALS 0.75 TO 1.00 INCH.
AMOUNT OF SNOW MELT WILL BE CRITICAL...NOT ONLY FOR THE CONTRIBUTION
OF MELT WATER TO AREA RIVERS AND STREAMS...BUT THE ABILITY FOR SNOW
THAT DOES NOT MELT TO HOLD RAIN FALL AND KEEP IT FROM FLOWING INTO
RIVER SYSTEMS. WILL HAVE TO BE ALERT FOR POSSIBLE ICE JAMS AS
TEMPERATURES WARM AND ICE COVER WEAKENS...THEN AGAIN SATURDAY INTO
SUNDAY AS COLD TEMPERATURES RE-FREEZE RIVERS AND STREAMS.
WARM AIR ADVECTION REGIME WILL CONTINUE TO LEAD TO NON-DIURNAL
TEMPERATURE TRENDS THROUGH SATURDAY....WITH A SLOW STEADY WARM UP
THURSDAY NIGHT INTO FRIDAY...THEN STEADY INTO THE EVENING HOURS
FRIDAY...FALLING RAPIDLY WEST TO EAST AFTER MIDNIGHT WITH COLD FRONT
PASSAGE. ACTUAL VALUES WILL DEPEND ON THE AMOUNT OF SNOW COVER THAT
SURVIVES...AND COOLING AFFECTS OF RAIN...BUT USED A CONSENSUS BLEND
OF RAW MODEL TEMPERATURES THAT HAS PROVED FAIRLY ACCURATE IN THE
PAST WITH THESE ABNORMAL TEMPERATURE TRENDS.
ANY WET SURFACES...STANDING WATER...OR SATURATED SNOW COVER WILL
FREEZE OVER WITH THE COLD SURGE BEHIND THE LOW PROVIDING ANOTHER
TRAVEL HEADACHE.
&&
.AVIATION...VFR CONDS MOST LOCATIONS IN SOUTHERN WISCONSIN THIS EVENING.
COMBINATION OF RADIATIONAL COOLING OF BOUNDARY LAYER AIR PLUS SOME
LEFTOVER STRATUS AND FOG OVER IOWA AND ILLINOIS ADVECTING
NORTHEASTWARD WILL LEAD TO ANOTHER WIDESPREAD STRATUS DECK ABOUT 600
TO 900 FT AGL WITH VISIBILITIES OF 3 TO 5 MILES IN LIGHT FOG. THERE
COULD BE A FEW POCKETS OF VISIBILITY TO 1 TO 2 MILES. ALL OF THIS
SHOULD BURN OFF AND/OR MIX BY MID-MORNING TUESDAY TO VFR CONDITIONS.
GENERALLY SOUTHWEST SURFACE WINDS ARE EXPECTED TONIGHT THROUGH
TUESDAY.
&&
.MARINE...
SOUTHWEST WINDS EXPECTED TONIGHT THROUGH TUESDAY AHEAD OF A WEAK
LOW PRESSURE TROUGH WHICH WILL MOVE ACROSS THE NORTHERN PLAINS AND
THEN TROUGH THE GREAT LAKES REGION. SURFACE PRESSURE GRADIENT
SUPPORTS SUSTAINED WINDS OF 10 TO 15 KNOTS...WITH SOME GUSTS TO 20
KNOTS. SOME LOW STRATUS CLOUDS AND LIGHT FOG WITH VISIBILITIES OF 2
TO 5 MILES WILL OCCUR AFTER 3 AM TONIGHT AND THEN MIX OUT BY
MID-MORNING TUESDAY. NOTHING EXPECTED IN THE WAY OF PRECIPITATION.
A SURFACE LOW DEEPENS IN THE PLAINS WEDNESDAY NIGHT...AND THE
SURFACE PRESSURE GRADIENT WILL EVENTUALLY SUPPORT A SOUTH TO
SOUTHEAST WIND WHICH BECOMES FAIRLY STRONG THROUGH FRIDAY.
PERSISTENT SOUTH TO SOUTHEAST FETCH WILL BUILD WAVES OVER 4 FEET SO
ANOTHER EXTENDED PERIOD OF BRISK WINDS AND HIGH WAVES ON TAP LATER
THIS WEEK.
.HYDROLOGY...
MODELS IN EXCELLENT AGREEMENT IN SIGNIFICANT THAW WITH TEMPERATURES
ABOVE FREEZING FROM THURSDAY MORNING THROUGH FRIDAY EVENING...OR
ROUGHLY 36 HOURS. RAIN EXPECTED DURING THAT TIME PERIOD AS WELL.
TEMPERATURES COULD BE WELL INTO THE 40S ON FRIDAY. COMBINATION OF
FOG AND RAIN ALONG WITH ABOVE FREEZING TEMPERATURES WILL MELT A GOOD
DEAL OF THE SNOW PACK.
RECENT TRENDS ARE FOR THE GUIDANCE TO PREDICT LESS AND LESS RAIN.
EARLIER GUIDANCE WAS SHOWING 1-2" OF RAIN...AND IS NOW 0.25 TO 0.5
INCH OVER MOST OF SOUTHERN WISCONSIN. THUS...THERE IS THE
POTENTIAL FOR THE SNOW PACK TO ABSORB MUCH OF THE RAIN RATHER THEN
SIMPLY MELTING IN BULK. THIS WOULD BE GOOD NEWS AS IT WOULD REDUCE
THE THREAT OF FLOODING. HOWEVER...THAWS ARE ALWAYS TRICKY AS ICE
JAMS CAN DEVELOP.
COLDER WEATHER TO RETURN LATER FRIDAY NIGHT INTO THE WEEKEND...WITH
ANY STANDING WATER AND REMAINING SNOW PACK TURNING TO SHEETS OF
ICE.
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
LM...NONE.
&&
$$
SHORT/LONG TERM...09/REM
VERY SHORT TERM/AVIATION/MARINE...34/KAPELA
