Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 281726
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1226 PM CDT FRI AUG 28 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 354 AM CDT FRI AUG 28 2015

PRIMARY CHALLENGE TODAY WILL BE RAINFALL AMOUNTS AS A STRONG UPPER
TROUGH MOVES ACROSS THE UPPER MS RIVER VALLEY. STILL ON TRACK TO
SEE A BAND OF 1-2 INCHES...LOCALLY UP TO 3 INCHES...BUT THE AREA
HAS SHIFTED EVEN FURTHER SOUTH AS DEPICTED BY THE LATEST RAP/HRRR/
GFS/NAMNEST. STILL A FEW MODELS THAT ARE FARTHER NORTH...BUT
STRONGEST LIFT/CONVERGENCE/MOISTURE TRANSPORT LENDS SUPPORT TO THE
SOUTHERN SOLUTION.

28.08Z WATER VAPOR LOOP SHOWS A STRONG TROUGH MOVING INTO SOUTHWEST
MN WITH A LARGE MOISTURE PLUME EXTENDING FROM NORTHEAST KS INTO
SOUTH-CENTRAL MN. SURFACE LOW IS CURRENTLY NEAR GRAND ISLAND NE
AND WILL WEAKEN AS IT MOVES EASTWARD THROUGH THE DAY INTO SOUTH-
CENTRAL IA. STRONG LIFT ON THE 310 K ISENTROPIC SURFACE AND MID-
LEVEL CONVERGENCE...COMBINED WITH MODEST MOISTURE TRANSPORT AND
PWATS UP TO 1.5 INCHES WILL RESULT IN AN AREA OF LIGHT TO MODERATE
SHOWERS ACROSS THE FORECAST AREA TODAY. ALTHOUGH MUCAPE ONLY RISES
TO MAYBE A FEW HUNDRED J/KG...STILL EXPECT ISOLATED EMBEDDED
THUNDERSTORMS GIVEN STRENGTH OF WAVE/FORCING ALOFT. WARM CLOUD
DEPTHS INCREASE TO OVER 4 KM...SO POCKETS OF HEAVY RAIN ALSO
POSSIBLE.

RAINFALL AMOUNTS THROUGH TONIGHT UP TO AN INCH ARE EXPECTED ALONG
AND SOUTH OF THE I-90 CORRIDOR. HIGHER AMOUNTS UP TO 2 INCHES...
LOCALLY 3 INCHES...ARE POSSIBLE MAINLY ACROSS NORTHEAST IA INTO
FAR SOUTHWEST WI. MUCH OF THE AREA HAS SEEN LESS THAN 50 PERCENT
OF ITS NORMAL RAINFALL THE PAST MONTH AND WITH ONE-HOUR FLASH
FLOOD GUIDANCE VALUES GENERALLY 2.5 TO 3.0 INCHES...DO NOT THINK
RAIN RATES WILL BE HIGH ENOUGH/LONG ENOUGH TO CAUSE FLOODING
CONCERNS. DRY ANTECEDENT SOIL CONDITIONS SHOULD ALLOW RAIN TO
QUICKLY SOAK-IN. CLOUDS AND RAIN WILL KEEP TEMPERATURES IN THE
60S THROUGH THE DAY...COOLEST ACROSS NORTHEAST IA AND SOUTHWEST
WI.

MAJORITY OF RAINFALL SHOULD MOVE EAST OF THE AREA AFTER MIDNIGHT
TONIGHT...BUT CLOUD COVER WILL BE SLOW TO DISSIPATE...KEEPING
TEMPERATURES IN THE MID 50S TO LOWER 60S. LIGHT EASTERLY WINDS
WILL SLOWLY TURN TO THE NORTH AS THE SURFACE LOW MOVES INTO IL.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 354 AM CDT FRI AUG 28 2015

EXPECT ONE MORE COOL DAY ON SATURDAY IN THE WAKE OF THE LOW AS
CLOUDS DECREASE FROM WEST TO EAST. TEMPERATURES WILL RISE INTO THE
MID 70S WITH LIGHT NORTHERLY WINDS.

SUNDAY AND BEYOND...OVERALL SYNOPTIC REGIME CHANGES TO ONE WITH A
EASTERN CONUS RIDGE AND A WESTERN CONUS TROUGH. THE FORECAST AREA
WILL REMAIN ON THE WARM SIDE OF THE THERMAL GRADIENT...ALLOWING
TEMPERATURES TO CLIMB WELL ABOVE NORMAL BY EARLY NEXT WEEK. DAILY
AFTERNOON HIGHS MONDAY THROUGH THURSDAY WILL RISE INTO THE MID 80S
WITH SOME VALLEY FLOOR AREAS APPROACHING 90 DEGREES. NIGHTTIME
LOWS WILL GENERALLY BE IN THE 60S.

A FEW WEAK RIPPLES IN SOUTHWEST FLOW ALOFT COULD TRIGGER SOME
ISOLATED SHOWERS AND THUNDERSTORMS...BUT LOW-CONFIDENCE SET-UP
PRECLUDES ANY MORE THAN A 20 PERCENT MENTION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1226 PM CDT FRI AUG 28 2015

DESPITE THE FACT THAT IT HAS BEEN RAINING FOR A FEW HOURS AT BOTH
TAF SITES...THE CEILINGS HAVE YET TO START COMING DOWN AND REMAIN
VFR. THE MVFR CEILINGS HAVE REMAINED OVER WESTERN IOWA AND
SOUTHWEST MINNESOTA CLOSER TO THE SURFACE LOW. AS THE LOW MOVES
SLOWLY EAST...THESE CEILINGS SHOULD EVENTUALLY MAKE IT INTO BOTH
TAF SITES AND HAVE PUSHED THE TIMING BACK INTO THE MID TO LATE
AFTERNOON HOURS. EXPECTING THE RAIN TO PERSIST INTO THE EVENING
BEFORE MOVING OUT BUT PLENTY OF LOW LEVEL MOISTURE WILL REMAIN TO
KEEP THE MVFR CEILINGS IN PLACE. THE CONCERN THEN BECOMES WHAT THE
VISIBILITY WILL DO BEHIND THE RAIN. PLENTY OF MOISTURE AVAILABLE
FOR FOG BUT NO CLEARING WILL OCCUR AND THE BOUNDARY LAYER WILL
REMAIN SOMEWHAT MIXED WITH EAST TO SOUTHEAST WINDS OF 5 TO 10
KNOTS. CAN SEE MVFR VISIBILITIES FORMING WITH FOG BUT NOT
EXPECTING THESE TO GO DOWN TO IFR. ANY CLEARING THAT OCCURS SHOULD
BE RATHER SLOW TO DEVELOP SATURDAY MORNING SO PLAN TO SHOW THE
VISIBILITY IMPROVING TO VFR BUT KEEP THE CEILINGS IFR/MVFR.

&&

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

$$

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


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