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FXUS63 KARX 171218
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
715 AM CDT Wed Jul 17 2019

.SHORT TERM...(Today and tonight)
Issued at 310 AM CDT Wed Jul 17 2019

Severe weather threat late this afternoon into tonight including the
potential for flash flooding (possibly significant), damaging winds,
and cannot rule out an isolated tornado or two in the late afternoon
and early evening.

A weakening complex of thunderstorms is expected to push east out of
eastern South Dakota and southwest Minnesota early this morning,
impacting the local area late this morning into early this
afternoon. Now this will add some uncertainty into how the late
afternoon and early evening thunderstorms will evolve. Initially,
depending on where an outflow boundary, if this complex produces
one, and a surface warm front set up, there may be the potential for
Supercell structures near a warm front and potential tornado threat
mainly in the 4 PM to 8 PM timeframe. Damaging winds and maybe some
large hail could also accompany this activity. At this time, it
appears the areas that may see this would be across northeast Iowa
and possibly over southeast Minnesota, closer the boundaries. This
area could be further south and west too will have to keep a close
eye on this. The threat then quickly transitions over to flash
flooding and possibly damaging winds as the low level jet
intensifies into the elevated warm frontal boundary. Thinking the
storms should be elevated at this point, but if not, there could be
a few hours where an isolated tornado threat may exist. Intense
moisture transport into the boundary, precipitable water values of 2
to 2.5 inches. and warm cloud depth of 4 to 4.5 km, will set the
stage for potential flash flooding tonight. There is uncertainty on
exactly where the heaviest rain will fall given various
convective allowing model solutions. Given the environment and
recent heavy rainfall in some areas, decided to issue a Flash
Flood Watch, with refinements to the watch likely during the day
today once it becomes more clear on where the heaviest rain will
fall. The watch will include all of southeast Minnesota, northeast
Iowa, and portions of west central into southwest Wisconsin. Some
of the 06Z CAMs suggest the watch may need to include areas along
and north of Interstate 94. Rainfall amounts of 2 to 4 inches are
possible and if training occurs there could be some areas that
receive 6 inches plus. Thunderstorms will then taper off by
sunrise Thursday morning.


.LONG TERM...(Thursday through Tuesday)
Issued at 310 AM CDT Wed Jul 17 2019

Main forecast concerns are the heat and humidity Thursday and Friday
with a heat advisory likely. There will also be periodic chances for
thunderstorms late this week into the weekend.

Hot and humid conditions are expected Thursday and Friday with high
temperatures climbing into the 90s and dew points in the mid to
upper 70s. This will produce heat index values of 95 t 110.
Headlines will likely be needed for this potentially dangerous
heat. A frontal boundary then looks to slide through the area late
in the day on Friday into Friday night bringing chances for
showers and storms to the area. This front will cool temperatures
a bit for Saturday and drop dew points a bit to so heat index
values will be less, mainly in the 85 to 99 range. The front then
looks to stall over Iowa Saturday night into Sunday with continued
chances for thunderstorms, possibly producing some heavy rain. A
broad upper trough then looks to drop into the region for early
next week with much more comfortable temperatures and drier
weather too.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 715 AM CDT Wed Jul 17 2019

Some morning IFR/LIFR conditions around the region due to fog which
will impact flights for a few more hours, then burn off. Should
return to VFR later this morning, but then focus shifts to next
convective threat.

Timing and location of convective evolution a bit troubling but will
have to watch possibility of some afternoon development, and more
importantly, how things transpire tonight. Could see a period this
evening and into the overnight of occasional IFR conditions due to
heavy rain and lower ceilings until storms clear the area on
Thursday.

&&

.HYDROLOGY...Tonight
Issued at 310 AM CDT Wed Jul 17 2019

Potential for Flash Flooding and some river flooding tonight into
Thursday morning. Thunderstorms will be capable of producing very
heavy rainfall tonight and may repeat over areas. Confidence is
lower on exactly where the heaviest rain will fall but given the
very favorable environment for heavy rain and a strong low level
jet focused into an elevated warm front, felt a Flash Flood Watch
was necessary. The watch may need to be adjusted once it becomes
more clear on where the heaviest rain will fall. Current thinking
is that 2 to 4 inches of rainfall is likely in the heavy rain axis
with localized higher amounts possible. Monitor forecasts closely
today and be ready for potential flooding.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Flash Flood Watch from this evening through Thursday morning for
WIZ032-033-041-042-053>055-061.

Excessive Heat Watch from Thursday afternoon through Saturday
evening for WIZ054-055-061.

MN...Flash Flood Watch from this evening through Thursday morning for
MNZ079-086>088-094>096.

IA...Flash Flood Watch from this evening through Thursday morning for
IAZ008>011-018-019-029-030.

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

&&

$$

SHORT TERM...Wetenkamp
LONG TERM...Wetenkamp
AVIATION...DAS/Shea
HYDROLOGY...Wetenkamp
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