Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 281719
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1218 PM 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 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1218 PM CDT TUE JUL 28 2015

VSBYS IMPROVING/GOOD AT BOTH TAF SITES FOR THE AFTERNOON AS THE
FIRST BAND OF SHRA/TSRA WEAKENS/EXITS. LOW LEVEL MOISTURE AND
OUTFLOW BEHIND THE DISSIPATING BAND OF SHRA/TSRA PRODUCING SOME MVFR
STRATO-CU ACROSS THE AREA THRU THE EARLY AFTERNOON HOURS. WITH
DIURNAL WARMING/MIXING THIS SHOULD MIX/LIFT TO A SCT VFR DECK BY MID
AFTERNOON...WITH SOME BRISK SOUTHEAST TO SOUTH WINDS. CONSIDERABLE
UNCERTAINTY REMAINS WITH THE CHANCES OF MORE SHRA/TSRA AT THE TAF
SITES THIS EVENING. TIMING OF 01-04Z AT KRST AND 03-06Z AT KLSE
APPEARS REASONABLE. HOWEVER...LOOKING LIKE THIS MAY COME ACROSS THE
AREA AS MORE OF A LINE OF SCT SHRA/TSRA AND LEFT MENTION OF IT AS
VCTS/CB IN BOTH TAFS. DRIER PUSHES IN BEHIND THE COLD FRONT LATER
THIS EVENING/OVERNIGHT...WITH GENERALLY GOOD VFR EXPECTED ONCE ANY
SHRA/TSRA IN THE LINE/NEAR THE FRONT WOULD EXIT THE AREA.

TIGHTER PRESSURE GRADIENT OVER THE AREA WED. WITH MODEL SOUNDINGS
SHOWING MIXING TO 800MB WED AFTERNOON...BRISK/GUSTY WEST TO
NORTHWEST WINDS 15-20KT G25-30KTS EXPECTED BY LATE WED MORNING AND
FOR WED AFTERNOON.

&&

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

$$

SHORT TERM...BOYNE
LONG TERM....BOYNE
AVIATION.....RRS



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