Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 191738
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1238 PM CDT TUE JUL 19 2016

.SHORT TERM...(Today and tonight)
Issued at 350 AM CDT Tue Jul 19 2016

Latest water vapor satellite imagery showing upper level ridge
building over the Northern Plains states. First impulse over topping
the ridge over central Nebraska is producing showers/thunderstorms
this area per latest mosaic radar.

Main forecast concerns today and tonight is flash flooding
potential. The 19.00z GFS/NAM/ECMWF are in good agreement in
building upper level ridge over the Northern Plains and Upper
Midwest through tonight. Impulse over central Nebraska overtopping
upper level ridge is expected to push into the western forecast area
around 00z Wednesday. Leading edge of moisture
transport/convergence/vertical motion in association with shortwave
trough is focused into southern Minnesota/northern Iowa by 18z
Today. Latest hi-resolution models suggest scattered convection will
be over the western forecast area around 18z...However confidence is
low this complex of showers/thunderstorms will move this far
east...based on better lift/moisture convergence is west of the
forecast area. For now...have chance of precipitation mainly along
and west of the Mississippi river during the daytime hours.

Next impulse overtops upper level ridge tonight and moves into
southern Minnesota/western Wisconsin tonight. The 19.00z
GFS/NAM/ECMWF indicate an increase in low level jet/moisture
transport by 06z over the western forecast area and move the better
axis of moisture transport/convergence/lift into much of the
forecast area around 06z. This would increase coverage of
convection over the forecast area. The 19.00z GFS/NAM show corfidi
vectors southeast movement with the convection and suggest the
convection may entrain over at any one particular location. This
would result in a flash flooding concern. At this
time...confidence is low with widespread flash flooding...however
potential is there given deep warm cloud depths and precipitation
waters up to 2 inches over the forecast area tonight. Some of the
storms could be strong with gusty winds and hail...for now severe
threat looks very low with any of the storms.

.LONG TERM...(Wednesday through Monday)
Issued at 350 AM CDT Tue Jul 19 2016

Complex of showers/thunderstorms weakens and pushes east of the
forecast area around 18z Wednesday...as the low level jet/moisture
convergence weakens over the area.

Then...upper level ridge builds into the Great Lakes Region
Wednesday night into Thursday. This allows warmer air to advect into
the forecast area. The 19.00z GFS/NAM/ECMWF continue to show plus 28
to around plus 30 degree celsius by 00z Friday. This will result in
high temperatures well into the 90s and heat indices of 100 to 115
across the forecast area Thursday. Friday...both the 19.00z
GFS/ECMWF suggest 925mb trough moves across the forecast area into
northern Iowa around 18z Friday. This cools the 925mb temperatures
slightly over forecast area around plus 25 degree celsius. This
produces heat indices of 100 to 105 over the southern forecast area.
Based on timing issues with the trough...will continue with
Excessive Heat Watch across the entire area Thursday into Friday.

Upper level trough/surface cold front flattens upper level ridge and
develop west to east zonal flow across the northern tier United
States Saturday into Sunday. The 19.00z GFS/ECMWF suggest weak
shortwave troughs embedded in the west to east zonal flow will
provide small shower/thunderstorm chances Saturday through Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1238 PM CDT Tue Jul 19 2016

Mainly vfr conditions expected through the period. Confidence is
low on how widespread storms will be tonight as there seems to be
a lack in a trigger mechanism to get the convection going. Seems,
as of now, the best time for storms would be in the 07-11z time
frame. These storms could produce some brief reduction in vsby
down to 4sm.

&&

.HYDROLOGY...
Issued at 350 AM CDT Tue Jul 19 2016

The combination of precipitable waters up to 2 inches/deep warm
cloud depths and possible 1 to 2 inches per hour rainfall
rates with the convection tonight will cause the potential for
flash flooding across much of the area. Entrainment of any storm
over any given location could produce up to 4 inches with total
rainfall amounts of 2 to 3 inches across parts of the forecast
area. Confidence on exact location where the heaviest
precipitation amounts is low at this time.

&&

.ARX Watches/Warnings/Advisories...
WI...Flash Flood Watch from 7 PM CDT this evening through Wednesday
     morning for WIZ032-033-041-053>055-061.

     Excessive Heat Watch from Thursday morning through Friday
     evening for WIZ017-029-032>034-041>044-053>055-061.

MN...Flash Flood Watch from 7 PM CDT this evening through Wednesday
     morning for MNZ079-086>088-094>096.

     Excessive Heat Watch from Thursday morning through Friday
     evening for MNZ079-086>088-094>096.

IA...Flash Flood Watch from 7 PM CDT this evening through Wednesday
     morning for IAZ008>011-018-019-029-030.

     Excessive Heat Watch from Thursday morning through Friday
     evening for IAZ008>011-018-019-029-030.

&&

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...DAS
HYDROLOGY...DTJ


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