Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 301748
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1248 PM CDT SAT AUG 30 2014

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 321 AM CDT SAT AUG 30 2014

MAIN FORECAST CONCERN IS WITH THE RAIN CHANCES TODAY AND FROM
SUNDAY NIGHT INTO MONDAY.

LOCAL AND REGIONAL RADARS SHOWING A LARGE AREA OF RAIN LIFTING
NORTHEAST ACROSS EASTERN MINNESOTA AND MUCH OF WISCONSIN. SOME
TRAILING RAIN STILL BACK ACROSS EASTERN IOWA.

EXPECT THE RAIN TO CONTINUE LIFTING NORTHEAST THIS MORNING AS THE
SURFACE LOW JUST ENTERING WESTERN WISCONSIN ALSO CONTINUES TO MOVE
NORTHEAST IN CONJUNCTION WITH THE UPPER LEVEL TROUGH. THE 30.04Z
HRRR SEEMS TO HAVE A DECENT HANDLE ON THE ONGOING RAIN AND SHOWS
THE BACK EDGE ALONG THE MISSISSIPPI RIVER BY 12Z WITH MOST OF THE
AREA DRY BY 18Z. THIS IS VERY SIMILAR TO WHAT THE 30.00Z HI-RES
ARW AND NMM SHOW AND WILL PLAN TO TREND THE RAIN CHANCES IN THIS
DIRECTION. THE QUESTION THEN BECOMES IF ADDITIONAL ACTIVITY WILL
DEVELOP THIS AFTERNOON. THE 30.00Z NAM AND GFS BOTH BRING A
TRAILING SHORT WAVE TROUGH ACROSS THE AREA THIS AFTERNOON. IT DOES
APPEAR IN THE WATER VAPOR IMAGERY THAT THIS WAVE DOES EXIST AND IS
OVER EASTERN SOUTH DAKOTA. HOWEVER...THE WATER VAPOR IMAGERY ALSO
SHOWS A LOT OF DRY AIR IN PLACE BEHIND THE DEPARTING SHORT WAVE
TROUGH AND THE CONCERN BECOMES WHETHER THIS SECONDARY SHORT WAVE
TROUGH WILL HAVE ENOUGH FORCING TO CAUSE SOME ADDITIONAL
DEVELOPMENT. THE HRRR IS SUGGESTING THAT SOME COULD START TO FORM
EARLY IN THE AFTERNOON WHICH IS SIMILAR TO THE NAM AND GFS WHILE
THE ARW AND NMM REMAIN DRY THROUGH THE AFTERNOON. WITH ALL THE DRY
AIR...TEND TO FEEL THE ARW AND NMM HAVE THE MORE CORRECT SOLUTION
BUT WILL HOLD ONTO A SMALL RAIN CHANCE JUST IN CASE SOMETHING DOES
POP UP.

AFTER SOME WEAK UPPER LEVEL RIDGING MOVES OVER THE UPPER MIDWEST
TONIGHT AND SUNDAY...THE NEXT SYSTEM WILL TAKE AIM AT THE REGION.
WATER VAPOR IMAGERY ALREADY SHOWS IT APPROACHING THE PACIFIC
NORTHWEST COAST AND IT IS EXPECTED TO MOVE QUICKLY ACROSS THE
NORTHERN ROCKIES AND ACROSS THE UPPER MIDWEST SUNDAY NIGHT AND
MONDAY. THE GFS AND 30.00Z ECMWF BOTH CONTINUE TO SHOW THIS SYSTEM
PRODUCING MODERATE TO STRONG PV ADVECTION IN THE 500-300 MB LAYER
LATE SUNDAY NIGHT INTO MONDAY MORNING. THE GFS SHOWS STRONG
ISENTROPIC UP GLIDE SHOULD SPREAD ACROSS THE AREA SUNDAY NIGHT
AHEAD OF THE SHORT WAVE TROUGH WITH UP TO 10 UBAR/S ON THE 305K
SURFACE. THE NOSE OF THE LOW LEVEL JET IS EXPECTED TO BECOME
ORIENTED INTO THE AREA SUNDAY EVENING WITH LITTLE MOVEMENT SUNDAY
NIGHT BEFORE VEERING OFF TO THE EAST MONDAY MORNING. WITH THE
AMPLE FORCING...WIDESPREAD SHOWERS AND STORMS ARE EXPECTED TO MOVE
IN SUNDAY EVENING AND WORK EAST ACROSS THE AREA BEFORE ENDING
MONDAY AFTERNOON. GOOD CAPE WILL BUILD SUNDAY AFTERNOON WEST OF
THE AREA AHEAD OF THE COLD FRONT ASSOCIATED WITH THIS SYSTEM. THE
GFS SUGGESTS THAT AN AXIS OF 1000-1500 J/KG OF ML CAPE WILL
PERSIST AHEAD OF THE FRONT THROUGH THE NIGHT AS THE SYSTEM WORKS
ACROSS THE AREA. GOOD SHEAR LOOKS TO OVERSPREAD THE REGION WITH 40
TO 50 KNOTS OF 0-6KM SHEAR...BUT MOST OF THIS LOOKS TO BE IN THE
0-3KM LAYER WITH 35 TO 40 KNOTS. EXPECT THAT THIS WILL BE
SUFFICIENT TO SUPPORT SOME STRONG TO SEVERE STORMS WITH HAIL AND
WIND THE MAIN THREATS.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 321 AM CDT SAT AUG 30 2014

SOME SMALL RAIN CHANCES WILL CONTINUE INTO TUESDAY AS A SECONDARY
SHORT WAVE TROUGH LOOKS TO SWEEP ACROSS THE UPPER MIDWEST.
AGAIN...THERE SHOULD BE GOOD DRYING SO THE QUESTION BECOMES IF THE
FORCING WILL BE ENOUGH TO GENERATE SOME ACTIVITY. AFTER
THAT...RIDGING LOOKS TO BUILD OVER THE REGION FOR A SHORT PERIOD
WEDNESDAY AND WEDNESDAY NIGHT. THE FLOW THEN SHOULD BECOME
SOUTHWEST ALLOWING A POSITIVE TILT LONG WAVE TROUGH TO APPROACH
FROM THE NORTHWEST. DIFFERENCES BETWEEN THE ECMWF AND GFS ON HOW
FAST THIS TROUGH MOVES THROUGH WITH THE ECMWF CONSIDERABLY FASTER.
WILL HAVE SOME RAIN CHANCES WITH THIS SYSTEM BUT WILL UNDERCUT THE
MODEL CONSENSUS GRIDS SOME THINKING THE RIDGE WILL BE THE DOMINANT
FEATURE THROUGH THE END OF THE PERIOD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1240 PM CDT SAT AUG 30 2014

MAIN STORM CIRCULATION NOW WELL EAST OF THE AREA...BUT LOW CLOUDS
AND SHOWERS STILL WRAPPING AROUND THE CYCLONIC CIRCULATION.
VISIBLE SATELLITE IMAGERY SHOWS SOME BREAKS IN THE CLOUD AND
INDEED MODEL SOUNDINGS SHOW THE MOISTURE LAYER IS SOMEWHAT THIN.
STILL...WHERE CLEARING TAKES PLACE THE SKY QUICKLY SELF-DESTRUCTS
WITH NEW CUMULUS DEVELOPMENT. RADAR IMAGERY WAS SHOWING SOME LIGHT
SHOWERS DEVELOPING IN THESE AREAS AS WELL. SO ANTICIPATE AN
AFTERNOON AND EARLY EVENING OF MVFR TO VFR CEILINGS BETWEEN 25-35
KFT WITH OCCASIONAL LIGHT SHOWERS. TONIGHT...MODELS SUGGEST LOW
CLOUDS WILL DIMINISH AS SUBSIDENCE SETS IN. FEEL IT WILL PROBABLY
HAPPEN...BUT NOT AS QUICKLY AS MODELS INDICATE. STILL...OPTED TO
CLEAR OUT THE MVFR CEILING FOR A TIME TONIGHT. THE PROBLEM WITH
THAT...THERE IS STILL A LOT OF BOUNDARY LAYER MOISTURE
AROUND...AND AS WINDS GO LIGHT...EXPECT FOG TO FORM. PREVIOUS
FORECAST INCLUDED LIGHT FOG BUT OPTED IN ENHANCE THAT
FURTHER...ESPECIALLY AT KLSE. MIXING PICKS UP SUNDAY MORNING AHEAD
OF THE NEXT SYSTEM...SO THE FOG SHOULD QUICKLY ERODE BY 14-15Z.

&&

.HYDROLOGY...
ISSUED AT 321 AM CDT SAT AUG 30 2014

ADDITIONAL RAINFALL TODAY WILL BE A QUARTER INCH OR LESS AND THIS
WILL NOT BE ENOUGH TO CAUSE ANY FLOODING PROBLEMS. WITH THE SYSTEM
THAT WILL AFFECT THE AREA SUNDAY NIGHT AND MONDAY...CURRENT
EXPECTATIONS ARE THAT THE RAIN TOTALS WILL BE AN INCH OR LESS. THE
PRECIPITABLE WATER IS NOT EXPECTED TO BE QUITE AS HIGH WITH THE
GFS SHOWING AROUND 1.75 INCHES BUT WARM CLOUD DEPTHS WILL STILL BE
IN THE 3.5 TO 4 KM RANGE. THE SHOWERS AND STORMS WILL HAVE THE
POTENTIAL TO PRODUCE SOME HIGHER RAIN RATES...BUT WITH THE
CONVECTION EXPECTED TO BE PROGRESSIVE...IT SHOULD NOT POSE ANY
LARGE SCALE FLOODING PROBLEMS AND PLAN TO ISSUE THE LAST ESF THIS
MORNING STATING THIS.

&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION...MW
HYDROLOGY...04


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