Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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000
FXUS63 KMKX 290918
AFDMKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
318 AM CST THU JAN 29 2015

.TODAY AND TONIGHT...FORECAST CONFIDENCE IS MEDIUM.

AN UPPER LEVEL SHORTWAVE WILL EXIT EASTERN WISCONSIN JUST AFTER
SUNRISE...WHILE ANOTHER MUCH WEAKER SHORTWAVE DROPS IN FROM THE
NORTHWEST TAKING THE MAIN TROUGH AXIS OFF TO THE EAST THIS
AFTERNOON. WEAK UPPER DIVERGENCE EXITS THE FAR EAST WITH THE FIRST
SHORTWAVE...THEN GOING NEUTRAL...WITH WEAK UPPER CONVERGENCE LATER
THIS AFTERNOON BEHIND THE TROUGH AXIS. THE 700 MB UPWARD MOTION
MOVES OUT OVER LAKE MICHIGAN AFTER SUNRISE...WITH ANOTHER VERY
WEAK AREA OF UPWARD MOTION WITH THE SECOND SHORTWAVE. DOWNWARD
MOTION WILL OCCUR TONIGHT.

850/700 MB COOLING OCCURS TODAY. HOWEVER THE 700 MB RH IS RATHER
DRY OVER SOUTH CENTRAL WISCONSIN AND DRIES THIS MORNING OVER THE
SOUTHEAST. DESPITE THE COOLING...WE DO NOT HAVE MUCH MOISTURE IN
THE DENDRITE ZONE...SO PRECIPITATION TYPE WILL BE MAINLY PATCHY
DRIZZLE/FREEZING DRIZZLE AND FLURRIES AFTER THE TROUGH PASSES THIS
MORNING.

925 MB RH REMAINS HIGH TODAY AND INTO TONIGHT...SO LOW CLOUD
CLEARING WILL LIKELY BE SLOW.

THE SURFACE TROUGH IS NEAR LAKE MICHIGAN JUST AFTER
SUNRISE...WITH BRISK NORTHWEST WINDS DEVELOPING LATER THIS MORNING
AND THIS AFTERNOON BEHIND THE TROUGH.

.SHORT TERM...

.FRIDAY THROUGH SATURDAY...FORECAST CONFIDENCE IS MEDIUM.

SYNOPTIC MODELS ARE IN GOOD AGREEMENT WITH WEAK HIGH PRESSURE
SLIDING SOUTHEAST ACROSS THE AREA FRIDAY. QUIET WEATHER IS
EXPECTED...WITH TEMPERATURES BELOW SEASONAL NORMALS.

WARM AIR ADVECTION DEVELOPS OVER THE AREA FRIDAY NIGHT INTO
SATURDAY MORNING...WITH A COLD FRONT THEN SLIDING SOUTHEAST
THROUGH THE AREA IN THE AFTERNOON. A 500 MB VORTICITY MAXIMUM
SLIDES SOUTHEAST AND CLIPS THE AREA FRIDAY NIGHT AS WELL. NAM AND
GFS FORECAST SOUNDINGS DIFFER WITH THE AMOUNT OF LOW LEVEL
MOISTURE...WITH THE NAM MORE MOIST AND THE GFS LESS SO. UPWARD
VERTICAL MOTION IS WEAK.

CANADIAN MODEL HAS LIGHT QPF IN THE NORTHEAST COUNTIES LATE
FRIDAY NIGHT...WITH THE NAM KEEPING MOST OF IT JUST SOUTH OF THE
AREA SATURDAY. THE ECMWF AND GFS ARE DRY. GIVEN SOME UNCERTAINTY
HERE...WILL MAINTAIN THE DRY FORECAST FRIDAY NIGHT INTO SATURDAY.
TEMPERATURES SHOULD REMAIN STEADY FRIDAY NIGHT...WITH HIGHS AROUND
30 ON SATURDAY.

.SATURDAY NIGHT THROUGH SUNDAY NIGHT...FORECAST CONFIDENCE IS
LOW.

THE ECMWF/GFS HAVE CHANGED QUITE A BIT SINCE YESTERDAY WITH THE
TRACK OF THE SURFACE LOW AND 500 MB SHORTWAVE TROUGH AMPLITUDE FOR
SATURDAY NIGHT INTO SUNDAY NIGHT. THEY HAVE SHIFTED TO A MORE
SOUTHERN TRACK WITH THE SURFACE LOW...FROM TEXAS INTO THE
SOUTHEASTERN STATES. THE MAIN 500 MB SHORTWAVE TROUGH SHIFTED TO
THE SOUTH AS WELL.

THUS...MOST OF THE QPF WITH THIS SYSTEM ARE SOUTH OF THE AREA IN
THESE MODELS. THEY DO INDICATE SOME LAKE EFFECT SNOW POTENTIAL FOR
SUNDAY INTO SUNDAY NIGHT...AS LOW LEVEL WINDS ARE NORTHEAST WITH
VERY FAVORABLE DELTA T VALUES AND A MOIST DENDRITE ZONE IN THE LOW
LEVELS. THERE IS DRY AIR ABOVE THE INVERSION...WHICH WOULD BE A
NEGATIVE.

THE NAM/CANADIAN MODELS CONTINUE TO SHOW A MORE NORTHERLY TRACK
WITH THE SURFACE LOW...AND CONTINUE TO BRING A SWATH OF QPF ACROSS
THE AREA SATURDAY NIGHT INTO SUNDAY EVENING. THERE WOULD BE SOME
LAKE ENHANCEMENT POTENTIAL IN THE EASTERN COUNTIES...GIVEN THE
CONDITIONS DESCRIBED ABOVE. AS COLDER AIR IS ABSORBED INTO THE
AREA...WOULD EXPECT SNOW TO LIQUID RATIOS TO INCREASE. SEVERAL
INCHES OF SNOW WOULD RESULT IF THESE MODELS ARE CORRECT.

FOR NOW...WILL USE A CONSENSUS BLEND OF THE MODELS WITH
POPS...WHICH BRINGS DOWN THE POPS A BIT FROM THE PREVIOUS COUPLE
OF FORECASTS. ALSO REDUCED QPF/SNOW AMOUNTS A FAIR AMOUNT...GIVEN
THE DRIER LOOK OF THE GFS/ECMWF MODELS. NOT A LOT OF CONFIDENCE IN
THIS FORECAST PERIOD.

.LONG TERM...

.MONDAY THROUGH WEDNESDAY...FORECAST CONFIDENCE IS MEDIUM.

GFS/ECMWF ARE SHOWING DIFFERENCES WITH TIMING OF FEATURES FOR THIS
PERIOD. THE GFS BRINGS A WEAKENING SURFACE LOW THROUGH THE AREA
MONDAY NIGHT INTO TUESDAY...ACCOMPANIED BY A 500 MB SHORTWAVE
TROUGH. A DECENT AMOUNT OF QPF IS SEEN WITH THIS
SYSTEM...SUPPORTED BY SATURATION AND DECENT UPWARD VERTICAL MOTION
IN THE DENDRITE ZONE PER GFS FORECAST SOUNDINGS.

THE ECMWF BRINGS SOME WARM AIR ADVECTION LIGHT QPF THROUGH THE
AREA MONDAY NIGHT...WITH MORE QPF WITH THE COLD FRONTAL PASSAGE
LATER TUESDAY INTO TUESDAY EVENING. GIVEN THE TIMING AND PLACEMENT
DIFFERENCES MONDAY NIGHT INTO TUESDAY NIGHT...WENT WITH THE
CONSENSUS BLEND OF MODELS WITH POPS.

BOTH MODELS DO SHOW A TREND TOWARD COLD TEMPERATURES MONDAY INTO
WEDNESDAY...WITH WINDS HIGH ENOUGH TO BRING SOME COLD WIND CHILLS
IN THE TEENS BELOW ZERO EARLY MONDAY.

&&

.AVIATION/12Z TAFS/...

LOOK FOR AN AREA OF LIGHT DRIZZLE/FREEZING BEHIND A SURFACE
TROUGH THAT WILL EXIT THE SOUTHEAST EARLY THIS MORNING. SOME
FLURRIES ALSO POSSIBLE LATER THIS MORNING.

EXPECT MVFR/IFR CIGS MUCH OF THE MORNING...THEN BECOMING MAINLY
MVFR THIS AFTERNOON. 925 MB RH REMAINS HIGH TODAY AND INTO
TONIGHT...SO CLEARING WILL LIKELY BE SLOW THIS EVENING.

&&

.MARINE...

WINDS WILL BRIEFLY DECREASE THIS MORNING AS A SURFACE TROUGH
MOVES ACROSS LAKE MICHIGAN. WINDS THEN TURN NORTHWEST AND INCREASE
AROUND 9 AM CST BACK TO SMALL CRAFT ADVISORY LEVELS...WITH A FEW
GALE FORCE GUSTS POSSIBLE. NO CHANGES TO CURRENT SMALL CRAFT
ADVISORY.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 6 AM CST FRIDAY FOR LMZ643>646.

&&

$$

TODAY/TONIGHT AND AVIATION/MARINE...HENTZ
FRIDAY THROUGH WEDNESDAY...WOOD



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