246
FXUS63 KARX 250341
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1040 PM CDT MON SEP 24 2018
SHORT TERM
(THIS EVENING THROUGH TUESDAY)
ISSUED AT 244 PM CDT MON SEP 24 2018
AFTERNOON ANALYSIS SHOWED A SURFACE COLD FRONT STRETCHED FROM
NORTHERN MINNESOTA, SOUTHWESTWARD INTO FAR NORTHWEST IOWA AND INTO
NEBRASKA. PLENTY OF CLOUD COVER ASSOCIATED WITH THE FRONT, ALONG
WITH SOME SHOWERS AND AN ISOLATED STORM OR TWO. FARTHER WEST,
SATELLITE WATER VAPOR IMAGERY SHOWED A SHORTWAVE SLIDING THROUGH THE
IDAHO/MONTANA/WYOMING AREA. THIS WILL BECOME THE MAIN PLAYER IN
SHOWER AND STORM CHANCES ON TUESDAY.
FOR TONIGHT, THE COLD FRONT WILL MOVE INTO THE AREA AND PERHAPS
PRODUCE A FEW SHOWERS, BUT INSTABILITY LOOKS PRETTY MARGINAL (500
J/KG), SO NOT ANTICIPATING MUCH MORE THAN A COUPLE ISOLATED STORMS.
BETTER RAIN CHANCES WILL MOVE IN AS THE AFOREMENTIONED SHORTWAVE
WILL DIG ACROSS THE CENTRAL PLAINS AND APPROACH THE FORECAST AREA
FROM THE SOUTHWEST TUESDAY MORNING. THE COLD FRONT WILL BE DRAPED
NORTHEAST TO SOUTHWEST ACROSS WISCONSIN BY EARLY TUESDAY AFTERNOON.
MODELS PROG SOME DECENT MOISTURE ADVECTION AHEAD OF THE FRONT AND
BUILD IN AROUND 1500 J/KG OF MUCAPE, THOUGH CLOUD COVER COULD HINDER
DESTABILIZATION A BIT. STRONGEST DEEP LAYER SHEAR LOOKS TO BE BEHIND
THE COLD FRONT, BUT STILL LOOKING AT PERHAPS 40 KTS OF 0-6 KM SHEAR
ALONG WITH 30 KTS IN THE 0-3 KM LAYER. NOT A LOT OF LOW LEVEL SHEAR
UNTIL THE LOW LEVEL JET RAMPS UP LATER IN THE AFTERNOON OR TOWARD
EARLY EVENING, BUT THE COLD FRONT SHOULD BE WELL EAST OF THE
FORECAST AREA BY THEN. SO BOTTOM LINE, THINKING THERE COULD BE A
STRONG TO SEVERE STORM OR TWO POSSIBLE IN THE FORECAST AREA AHEAD OF
THE COLD FRONT WHERE THE BEST INSTABILITY CAN BUILD. AT THIS TIME,
THIS LOOKS TO BE CONFINED TO FAR SOUTHERN/SOUTHEASTERN PORTIONS, BUT
TRENDS HAVE BEEN PUSHING THE THREAT FARTHER NORTHWEST WITH TIME. AS
FAR AS HAZARDS, FORECAST SOUNDINGS SHOW RATHER "SKINNY" CAPE AND
GOOD MIXING TO 900 MB, SO THINKING THE MAIN SEVERE THREAT WOULD BE
DAMAGING WINDS.
OTHERWISE, TEMPERATURES BEHIND THE FRONT WILL TOP OUT IN THE UPPER
50S TO LOWER 60S ON TUESDAY, WHILE THOSE AREAS THAT STAY AHEAD OF
THE FRONT LONGER COULD GET INTO THE LOWER 70S.
LONG TERM
(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 244 PM CDT MON SEP 24 2018
FOR TUESDAY NIGHT THRU THURSDAY NIGHT: MAIN FCST CONCERNS THIS
PERIOD ARE COOLER TEMPS THRU THE PERIOD AND SHRA CHANCES WITH A
FRONT ON THU.
MODEL RUNS OF 24.12Z IN GOOD AGREEMENT ON LONGWAVE TROUGHING OVER
THE UPPER MIDWEST THRU THIS PERIOD. ONE SHORTWAVE IN THIS TROUGH TO
BE PUSHING EAST OF THE AREA TUE NIGHT, WITH ANOTHER STRONGER ONE TO
DROP INTO/ACROSS NORTHERN MN/NORTHERN GREAT LAKES THU/THU NIGHT.
FCST CONFIDENCE THIS PERIOD IS AVERAGE TO GOOD THIS CYCLE.
MID LEVEL TROUGH AXIS/SHORTWAVE TO PASS TUE NIGHT, BUT SFC-700MB
FRONT/TROUGH PROGGED TO ALREADY BE ON THE SE EDGE OF THE FCST AREA
BY 00Z WED. SOME LINGERING SHRA CHANCES ACROSS THE EAST SIDE OF THE
FCST AREA REASONABLE TUE EVENING, OTHERWISE HIGH PRESSURE WITH A
COOLER, DRIER AIRMASS TO BUILD IN FOR TUE NIGHT INTO WED NIGHT. NW
GRADIENT WINDS TO KEEP BL STIRRED TUE NIGHT AND LOWS FROM BOTTOMING
OUT TOO FAR. LOW LEVEL COLD ADVECTION SENDS 925MB TEMPS INTO THE 7-
10C RANGE FOR WED AFTERNOON, FOR WHAT IS PROMISING TO BE A COOL DAY.
THIS EVEN AS THE HIGH QUICKLY SLIPS OFF AND SW TO W WINDS/LOW LEVEL
WARM ADVECTION RETURNS BY LATE IN THE DAY. BLEND OF GUIDANCE HIGHS
MOSTLY IN THE UPPER 50S-LOW 60S REASONABLE. LOW LEVEL WARM ADVECTION
AND SW WINDS FOR BL MIXING SHOULD KEEP WED NIGHT LOWS MOSTLY IN THE
40S. NEXT SHORTWAVE INTO THE LONGWAVE TROUGH PUSHES ANOTHER SFC-
700MB TROUGH/FRONT WITH ITS ROUND OF LOWER LEVEL THERMO-DYNAMIC
FORCING INTO/ACROSS THE AREA LATER WED NIGHT/THU. MOISTURE RETURN
AHEAD OF THIS ONE APPEARS A BIT LIMITED, WITH DEEPER/STRONGER
FORCING MAINLY ACROSS THE NORTH 1/2 OF THE FCST AREA. CAPE APPEARS
QUITE LIMITED AS WELL. 30-60% SHRA CHANCES MAINLY ACROSS THE NORTH
HALF OF THE FCST AREA, CENTERED ON THU MORNING, OK FOR NOW.
FOR FRIDAY THRU MONDAY (DAYS 4-7): MAIN FCST CONCERNS THIS PERIOD
ARE BELOW NORMAL TEMPS AND PERIODIC RA/SHRA CHANCE.
MEDIUM RANGE MODELS OF 24.00Z/24.12Z IN REASONABLE AGREEMENT FOR
RIDGING/REX BLOCKING FLOW ALONG THE WEST COAST OF NOAM WITH
DOWNSTREAM TROUGHING OVER THE CENTRAL/EAST PARTS OF THE CONTINENT
THIS PERIOD. PLENTY OF DETAIL DIFFERENCES WITH SHORTWAVE THRU THE
TOUGHING FLOW OVER THE NORTH-CENTRAL CONUS FLOW THOUGH. FCST
CONFIDENCE THIS PERIOD IS GOOD ON BELOW NORMAL TEMPS AND AVERAGE FOR
SHRA CHANCES.
LOW LEVEL TROUGH/FRONT FROM THU USHERS ANOTHER SEASONABLY COOL
AIRMASS INTO THE AREA FOR FRI. NEXT WAVE THROUGH THE TROUGH QUICKLY
SPREAD SOME MOISTURE AND MID LEVEL ISENTROPIC UPGLIDE FLOW OVER THIS
COOL DOME, WITH RA/SHRA CHANCES INCREASING AND SPREADING NE ACROSS
THE AREA STARTING FRI AFTERNOON AND CONTINUING THRU SAT. PRESENT
TIMING WOULD GIVE THE AREA A BETWEEN-SYSTEMS BREAK FROM THE RA SAT
NIGHT, WITH A STRONGER WAVE LOOKING TO SPREAD INCREASING MOISTURE/
LIFT ACROSS THE AREA SUN THRU MON. AGAIN, PLENTY OF DETAIL/TIMING
DIFFERENCES WITH SHORTWAVES AND RESULTING LOWER LEVEL FEATURES/LIFT
IN THE FRI-MON PERIOD, SO TIMING OF HIGHER RAIN CHANCES THESE DAYS
IS SUBJECT TO CHANGE. EACH WAVE WILL BRING A SEASONABLY COOL AIRMASS
INTO THE REGION BEHIND IT. WHAT MAY WELL BE PLENTIFUL CLOUD COVER
AND ANY RA/SHRA WOULD ALSO HELP HOLD DAYTIME TEMPS DOWN AND
NIGHTTIME LOW UP. FOR NOW, THE BLEND OF GUIDANCE HIGHS MOSTLY IN THE
50S FRI/SAT, MODERATING TO THE 60S BY MON APPEARS REASONABLE.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1040 PM CDT MON SEP 24 2018
COLD FRONT TRACKS ACROSS THE REGION OVERNIGHT, BRINGING A FEW
SHOWERS. LOW CLOUDS WILL FOLLOW IN WAKE OF FRONT, WITH MORE
WIDESPREAD SHOWERS AS AN UPPER LEVEL SHORTWAVE TROUGH SPINS ACROSS
THE REGION TUE. ISOLD THUNDER THREAT, BUT NOT ENOUGH CONFIDENCE TO
INCLUDE IN FORECAST.
CIGS: EXPECT IFR/MVFR CIGS MOVING IN OVERNIGHT, IN THE WAKE OF A
PASSING COLD FRONT. LOW CIGS WILL HOLD THROUGH THE AFTERNOON TUE,
IMPROVING TUE NIGHT.
WX/VSBY: CURRENT RADAR POINTING TO SHOWERS AND ISOLD STORMS OVER
NORTHWEST WI - ALONG THE FRONT AND INCONCERT WITH THE LOW LEVEL JET.
FARTHER SOUTH THE SHOWERS HAVE DIMINISHED AS THE FRONTOGENETIC
FORCING WEAKENS AND THE PUSH OF THE LOW LEVEL JET STAYS NORTH. DON'T
SEE MUCH OF IMPACT FOR KRST (OR KLSE FOR THAT MATTER). SHOWERS
SHOULD BE MORE WIDESPREAD MID TO LATE TUE MORNING, EXITING EAST BY
LATER IN THE AFTERNOON. SOME VSBY RESTRICTIONS POSSIBLE, BUT WILL
HOLD VFR FOR NOW.
WINDS: SOUTH SWINGS TO WEST/NORTHWEST LATER TONIGHT, HOLDING THERE
INTO TUE NIGHT.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
SHORT TERM...CA
LONG TERM...RRS
AVIATION...RIECK
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