Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 302324
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
624 PM CDT TUE SEP 30 2014

.SHORT TERM...(THIS EVENING THROUGH THURSDAY NIGHT)
ISSUED AT 312 PM CDT TUE SEP 30 2014

FOCUS OF THE FORECAST IS ON THE RAIN CHANCES TONIGHT THROUGH
THURSDAY NIGHT.

THE 30.12Z MODELS FOR NOW HAVE COME INTO A BETTER CONSENSUS ON HOW
THIS PERIOD IS EXPECTED TO PLAY OUT. THE UPPER LEVEL LOW OVER
SOUTH DAKOTA WILL CONTINUE TO LIFT NORTH TONIGHT INTO CANADA AND
WITH THE UPPER LEVEL RIDGE CURRENTLY OVER THE UPPER MIDWEST
SHIFTING EAST...THIS WILL ALLOW A SOUTHWEST FLOW ALOFT TO DEVELOP
OVER THE REGION. A COUPLE OF SHORT WAVE TROUGHS ARE EXPECTED TO
COME OUT OF THE CENTRAL ROCKIES AND APPROACH THE AREA LATE TONIGHT
BEFORE PASSING ACROSS WEDNESDAY MORNING. THIS WAVE IS EXPECTED TO
PRODUCE A ROUND OF WEAK TO MODERATE PV ADVECTION IN THE 500-300 MB
LAYER ALONG WITH WEAK TO MODERATE QG CONVERGENCE IN A DEEP LAYER
BETWEEN 1000 AND 300 MB. THIS FORCING LOOKS TO BE AIDED BY SOME
UPPER LEVEL JET DYNAMICS WITH THE 30.12Z NAM SHOWING THE AREA
GETTING UNDER THE RIGHT ENTRANCE REGION OF THE 300 MB LEVEL JET.
THE WHOLE EASTWARD MOVEMENT OF THIS SYSTEM WILL BE RATHER SLOW
TONIGHT WHICH WILL ALSO ALLOW FOR A SLOW EASTWARD PROGRESSION OF
THE RAIN...ESPECIALLY SINCE IT WILL BE ATTEMPTING TO MOVE INTO THE
DRIER AIR IN PLACE FROM THE SURFACE HIGH THAT WILL BE RETREATING
ACROSS THE EASTERN GREAT LAKES. HAVE GONE WITH THIS SLOWER
APPROACH OF THE RAIN KEEPING THE ENTIRE AREA DRY EARLY THIS
EVENING BUT THEN ADVANCING IT PART WAY ACROSS SOUTHEAST MINNESOTA
AND NORTHEAST IOWA THROUGH THE LATE EVENING BRINGING IN UP TO 80
PERCENT CHANCES ACROSS THE FAR WEST. THE SLOW EASTWARD ADVANCE
WILL CONTINUE THROUGH THE OVERNIGHT AND HAVE KEPT 40 TO 80 PERCENT
CHANCES ALONG AND WEST OF THE MISSISSIPPI RIVER WHILE KEEPING
CENTRAL AND SOUTHWEST WISCONSIN DRY. AS THIS SHORT WAVE TROUGH
LIFTS ACROSS THE AREA WEDNESDAY...EXPECT TO SEE THE BAND OF MOST
WIDESPREAD RAINS LIFT FROM ABOUT THE I35 CORRIDOR NORTHEAST TOWARD
NORTH CENTRAL WISCONSIN BY LATE WEDNESDAY AFTERNOON AND WILL HAVE
A CORRIDOR OF 80 TO 90 PERCENT RAIN CHANCES IN THIS PATTERN.

EXPECTING SOME WHAT OF A LULL IN THE RAIN CHANCES WEDNESDAY NIGHT
AS THE AREA GETS IN BETWEEN SHORT WAVE TROUGHS. THE RAIN MAY NOT
END COMPLETELY AS THE AXIS OF MOISTURE TRANSPORT WILL BE ACROSS
THE AREA...BUT WOULD EXPECT IT TO BECOME PRETTY LIGHT OR COULD
EVEN GO TO DRIZZLE FOR A WHILE. DROPPED THE RAIN CHANCES BACK TO
ABOUT 60 PERCENT ACROSS THE EAST FOR THE EVENING AND THEN CONFINED
THESE HIGHER AMOUNTS TO THE SOUTHEAST SECTIONS OVERNIGHT WHILE
GOING DOWN TO ABOUT 30 PERCENT ACROSS THE WEST. THE FORCING WILL
THEN INCREASE AGAIN FOR THURSDAY INTO THURSDAY NIGHT AS THE MEAN
LONG WAVE TROUGH APPROACHES WITH A SHORT WAVE TROUGH IN THE
SOUTHERN PART OF THE TROUGH ALONG WITH A STRONG NORTHERN STREAM
SYSTEM. THE PV ADVECTION IN THE 500-300 MB LAYER WILL INITIALLY
START OUT WEAK THURSDAY BUT CONTINUALLY INCREASE AND BECOME STRONG
BY LATE THURSDAY NIGHT. THE DEEPEST QG CONVERGENCE WILL BE
THURSDAY AFTERNOON AND EVENING AND THEN WILL BECOME CONFINED TO
ABOVE 500 MB THURSDAY NIGHT BUT IS EXPECTED TO BE VERY STRONG. A
DECENT SHOT OF ISENTROPIC UP GLIDE WILL OCCUR THURSDAY AFTERNOON
AND EVENING WITH UP TO 3 UBAR/S EXPECTED TO OCCUR AHEAD OF THE
NORTHWARD ADVANCING SURFACE LOW. THIS LOW SHOULD MOVE PAST THE
AREA THURSDAY EVENING WITH A GOOD SIGNAL FOR A LARGE AREA OF WRAP
AROUND PRECIPITATION ON THE BACK SIDE OF THE LOW AHEAD OF THE
STRONG NORTHERN SHORT WAVE TROUGH. STARTED TO INCREASE THE RAIN
CHANCES AGAIN THURSDAY MORNING AND BY AFTERNOON WENT BACK TO 70
PERCENT ACROSS THE ENTIRE AREA AND THESE LIKELY WILL NEED TO GO
HIGHER BASED ON THE CURRENT FORCING SIGNALS. REALLY UPPED THE RAIN
CHANCES THURSDAY EVENING IN THE WRAP AROUND WITH 60 TO 80 PERCENT
CHANCES ALONG AND EAST OF THE MISSISSIPPI RIVER.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 312 PM CDT TUE SEP 30 2014

FRIDAY LOOKS TO BE THE LAST DAY OF HIGHER RAIN CHANCES WITH THIS
SYSTEM UNTIL THE UPPER LEVEL LOW AND SHORT WAVE TROUGH MOVE PAST
THE AREA. INCREASED THE RAIN CHANCES TO 50 PERCENT ALONG AND NORTH
OF INTERSTATE 90 WITH A COOL RAW DAY EXPECTED. HIGH TEMPERATURES
MAY NOT CRACK 50 FOR PORTIONS OF THE AREA WITH NORTHWEST WINDS OF
15 TO 20 MPH. SOME LINGERING PRECIPITATION CHANCES TO CONTINUE
INTO FRIDAY NIGHT AND SATURDAY AND IT COULD EVEN GET COLD ENOUGH
FOR SOME SNOW TO MIX IN FRIDAY NIGHT ALONG AND NORTH OF INTERSTATE
94. ANOTHER SMALL CHANCE FOR SOME PRECIPITATION SUNDAY AS A
SHORT WAVE TROUGH COMES ACROSS IN THE NORTHWEST FLOW ALOFT. SOME
SUGGESTIONS BY THE LONGER RANGE MODELS THAT THERE WILL THEN BE A
PARADE OF WEAKER SHORT WAVE TROUGH IN THIS NORTHWEST FLOW THAT
COULD BRING SOME LIGHT PRECIPITATION INTO EARLY NEXT WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 624 PM CDT TUE SEP 30 2014

BAND OF SHOWERS AND ISOLATED THUNDERSTORMS FROM SOUTH CENTRAL
MINNESOTA THROUGH WESTERN IOWA WILL MOVE SLOWLY TO THE NORTH-
NORTHEAST THIS EVENING AND OVERNIGHT. RAIN ONSET AT KRST/KLSE
STILL REASONABLE GIVEN SLOW FORWARD PROPAGATION AND INITIAL LOW-
LEVEL DRY EASTERLY FLOW. CURRENT ACTIVITY MAY ALSO DISSIPATE
SOMEWHAT OVERNIGHT AS PRIMARY FORCING MECHANISM AND MID-LEVEL
MOISTURE TRANSPORT LIFTS INTO THE DAKOTAS. EXPECT PREDOMINANT
RAIN AT BOTH TAF SITES AFTER 01.12Z AND CONTINUING THROUGH THE
DAY. MVFR/IFR CEILINGS AND VISIBILITY FROM 2 TO 5 SM IN MIST
POSSIBLE WITH THE HEAVIER SHOWERS. SURFACE WINDS TO REMAIN AT OR
BELOW 10 KTS...VERY SLOWLY TURNING TO A MORE SOUTHERLY DIRECTION.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...04
LONG TERM...04
AVIATION...ROGERS


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