Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 281142
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
642 AM CDT TUE JUL 28 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 342 AM CDT TUE JUL 28 2015

AT 3 AM...A COLD FRONT WAS LOCATED OVER THE WESTERN DAKOTAS. A
SQUALL LINE HAS DEVELOPED ALONG A PRE-FRONTAL TROUGH AHEAD OF THIS
COLD FRONT. THIS SQUALL LINE IS CURRENTLY MOVING INTO SOUTHWEST
MINNESOTA AND NORTHWEST IOWA. AHEAD OF THIS TROUGH... THERE IS A
700 TO 500 MB WARM FRONT WHICH EXTENDS FROM SIOUX FALLS SOUTH
DAKOTA TO OTTUMWA IOWA. WITH WEAK TO MODERATE MOISTURE TRANSPORT
INTO THIS BOUNDARY...SCATTERED SHOWERS AND STORMS ARE DEVELOPING
ALONG THIS BOUNDARY.

FOR THIS MORNING...MANY OF THE MESO MODELS ARE CURRENTLY DOING
WELL WITH THE DEVELOPMENT OF THIS MESOSCALE CONVECTIVE COMPLEX.
THE ARW...NMM...HRRR...CR HRRR...AND SPC WRF ARE SHOWING THAT THIS
SYSTEM WILL MOVE INTO SOUTHEAST MINNESOTA AND NORTHEAST IOWA
BETWEEN 28.11Z...AND REACHES THE MISSISSIPPI RIVER AROUND 28.15Z.
THIS LINE THEN WEAKENS AS THE UPPER FORCING OUTRUNS THIS LINE AND
THE FORCING MOVES NORTHEAST INTO THE MINNESOTA ARROWHEAD AND
WESTERN UPPER MICHIGAN. PRECIPITABLE WATER VALUES CLIMB
DRAMATICALLY THIS MORNING FROM 1.3 INCHES TO 2.3 INCHES. THIS
ALONG WITH 4 TO 4.5 KM WARM CLOUD LAYER DEPTHS...THESE STORMS WILL
BE VERY EFFICIENT RAIN PRODUCERS. WOULD NOT BE OVERLY SHOCKED SEE
RAIN TOTALS OF 1 TO 3 INCHES WITH A FEW LOCATIONS EVEN HIGHER THAN
THAT. WITH THE 0-3 KM AND 0-6 KM SHEAR LESS THAN 20 KNOTS WITH
THIS LINE AND DONOVAN VALUES OF 40 TO 45K FEET...NOT
ANTICIPATION ANY SEVERE WEATHER WITH THIS LINE. HOWEVER WITH THIS
SAID THERE WILL BE GUSTY WINDS AND THE POTENTIAL FOR FLOOD PRONE
URBAN AREAS TO SEE SOME FLOODING. THIS WILL BE ESPECIALLY THE CASE
WEST OF THE MISSISSIPPI RIVER.

FOR THIS AFTERNOON...THE CONVECTIVE SYSTEM WILL CONTINUE TO WANE
ACROSS WESTERN WISCONSIN AND EASTERN NORTHEAST IOWA. THERE IS SOME
CONCERN THAT THE OUTFLOW BOUNDARY FROM THIS SYSTEM TO PUSH SOUTH
INTO IOWA. IN ADDITION...THE RAIN COOLED AIR WILL LIKELY SLOW THE
DEVELOPMENT OF INSTABILITY ACROSS THE REGION. THE 0-1 KM CAPES
FROM MANY OF THE MESO MODELS ONLY RECOVER INTO THE 1 TO 2K RANGE.
THIS COULD RESULT IN LITTLE CONVECTION DEVELOPING ACROSS THE
DURING THE MIDDLE AND LATTER PARTS OF THE AFTERNOON. AS A
RESULT...LOWERED THE RAIN CHANCES FOR THIS TIME PERIOD.

FOR THIS EVENING AND EARLY OVERNIGHT...THERE CONTINUES TO BE
CONCERN ON HOW MUCH CONVECTIVE DEVELOPMENT THERE WILL BE ALONG THE
COLD FRONT. MANY OF THE MESO MODELS ARE ONLY SHOWING SCATTERED
SHOWERS AND STORMS TO DEVELOP ALONG THIS FRONT...SO LOWERED THE
RAIN CHANCES. WITH THIS SAID... MAY NOT HAVE BEEN LOW ENOUGH YET.
WITH THE BEST SHEAR REMAINING BELOW 3 KM...EXPECT ANY CONVECTION
TO BECOME LINEAR...SO WILL HAVE WATCH OUT FOR DAMAGING WINDS AND
MAYBE SOME LARGE HAIL. IN ADDITION TO THIS...THE STORMS WILL BE
VERY EFFICIENT RAIN PRODUCERS DUE TO PRECIPITABLE WATER VALUE
AROUND 2.1 INCHES AND WARM CLOUD LAYER DEPTHS OF 4.5 KM.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 342 AM CDT TUE JUL 28 2015

THE NEXT CHANCE FOR RAIN LOOKS TO BE FROM SATURDAY THROUGH MONDAY
AS A SERIES OF SHORT WAVES ROUND THE WESTERN UPPER LEVEL RIDGE.
WITH THE MODELS CONTINUING TO STRUGGLE WITH THE TIMING OF THESE
WAVES...SO JUST WENT WITH THE MODEL BLEND FOR NOW.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 642 AM CDT TUE JUL 28 2015

PERIODS OF SHOWERS AND THUNDERSTORMS WILL MOVE ACROSS BOTH
KRST/KLSE THIS MORNING. MVFR/IFR CEILINGS AND VISIBILITY POSSIBLE
WITH THE STRONGEST STORMS...ESPECIALLY AT KRST. FOR NOW...WILL
KEEP LIGHT SOUTHEAST WINDS AT BOTH AIRFIELDS WITH AN OCCASIONAL
AFTERNOON GUST INTO THE MID 20 KT RANGE...ALTHOUGH CANNOT RULE OUT
A THUNDERSTORM INDUCED GUST OF 30 PLUS KTS. MULTIPLE UPDATES MAY
BE NECESSARY THROUGH 28.18Z.

WILL SEE A BREAK IN PRECIPITATION THIS AFTERNOON BEFORE A COLD
FRONT SWEEPS THROUGH THE REGION THIS EVENING. SCATTERED
THUNDERSTORMS POSSIBLE ALONG AND AHEAD OF THE FRONT...BUT TIMING
AND COVERAGE UNCERTAINTY PRECLUDES ANYTHING BEYOND VCTS/CB MENTION
AT THIS TIME. WILL ADD DETAIL AS FRONT APPROACHES LATER TODAY.
AFTER FRONTAL PASSAGE...EXPECT A RETURN TO VFR CONDITIONS AND A
WIND SHIFT TO THE WEST-SOUTHWEST.

&&

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

$$

SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION...ROGERS



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