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FXUS63 KARX 082323
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
623 PM CDT Wed Jul 8 2020

.SHORT TERM...(This evening through Thursday)
Issued at 313 PM CDT Wed Jul 8 2020

Forecast concerns in the short term will be the heat advisory
into early this evening and any convection that manages to develop
above the cap or with heating...thunderstorm evolution overnight
and Thursday and potential for severe storms and heavy rainfall.

By 18Z...LSE did reach 92 degrees with a heat index around 100...so
that makes a 9 day stretch of 90 degree plus days in a row. That
ties for 10th place for the longest stretch.

By early afternoon, the surface map and satellite imagery
highlighted an outflow boundary that had made it to Faribault, MN.
Behind the outflow, temperatures had cooled into the 70s and
dewpoints dropped back into the 60s. There is a mix of cumulus,
cirrus and convection. On the edge of the mid-level warming and with
a weak shortwave, convection continued and affected Taylor and Clark
counties, areas along that boundary and spotty locations outside
the cap. Early afternoon SPC mesographics have the 10 deg C h7
temperatures near LaCrosse, with the axis of higher precipitable
water still to the north. The thermal axis is over southeast MN
with There is a weak cap and it is forecast to remain weak, with
the 700mb 10 deg C temps building into southwest WI. So will need
to monitor during the afternoon for any convection with heating as
there may be some along boundaries and on the edge of the cap
where the 850mb moisture is around 18 deg C. and above the cap.

Water vapor satellite imagery highlights the mesoscale convective
complex traversing across the Upper Peninsula of Michigan and
spotty convection farther south over northern IL. The closed 500mb
low pressure system was noted over Saskatchewan with shortwave
trough energy in the flow across parts of Nebraska into the
Dakotas. As the closed low pushes east into Manitoba, the cold
front farther south and shortwave trough energy will tap into
precipitable water values around 1.5 inches. The low level jet
around 25kt across Minnesota will strengthen to 35 or
40kt...meanwhile, a 40kt low level jet develops across Kansas and
Nebraska, moving into Iowa by 12Z. The RAP MLCAPE/instability by
00Z along the cold front is 2500 J/kg and in parts of our area
with MUCAPE 4-5000J/Kg. 0-6km shear is around 45-55kts over the
Plains to our west. The deep layer shear is forecast to remain to
our west overnight, increasing to around 30kts for parts of the
northern WI ARX CWA by 12z and 25-35kts Thursday afternoon from MN
into parts of WI. Outside of the isolated storms locally, the
main attention will be from Nebraska toward MN where the organized
convection is expected and the storm prediction center has a
slight risk and an enhanced over Nebraska. Some of the CAMs have
the convection across Minnesota and northern WI with one area of
shortwave trough energy...spreading southward and weakening while
the convection over Nebraska drops southward. This seems
reasonable that some of the convection will drop south into the
instability, however the coverage should weaken as it moves into
the warm air. A 700mb circulation is forecast to move into Iowa
Thursday and this combined with the cold front should result in
more organized convection locally. Included pops for scattered
thunderstorms pushing south tonight and across much of the area
Thursday. With the moisture, instability, and steep lapse rate
environment along with focused wind maxes, some severe storms
possible late tonight into Thursday. Heavy rain is possible with
any of the storms that form. Precipitable water of 1.5 to 2
inches, warm cloud depth over 4Km and training of storms enough of
a concern for WPC to include parts of our area in the day 2
outlook for excessive rainfall.

Temperatures Thursday are only forecast to be in the 80s...so that
should end our streak of 90s.

.LONG TERM...(Thursday night through Wednesday)
Issued at 313 PM CDT Wed Jul 8 2020

Friday is currently looking dry with northwest winds and cooler.
A shortwave is forecast to develop over the Dakotas and drop
southeast in the northwest flow aloft sometime Friday night into
Saturday. Spotty rain is possible Sunday. Ridging is forecast for
Monday with a shortwave trough breaking down the ridge Monday
night into Tuesday. So...while locations to the south of the area
will be more on the hot and dry side, we will see periodic rain
chances with highs mostly in the 80s and more comfortable lows in
the 50s. and 60s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 623 PM CDT Wed Jul 8 2020

VFR conditions are expected with no visibility or weather impacts
through tonight. Shower and storm chances increase late morning and
last through the afternoon. Due to the uncertainty on the exact
timing of the storms, VCTS was kept in the TAFs. Winds will be
variable if any thunderstorms pass over. Otherwise, winds will be
mainly from the south around 5 to 10 knots.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Heat Advisory until 7 PM CDT this evening for WIZ029-032>034-
041>044-053>055-061.

MN...Heat Advisory until 7 PM CDT this evening for MNZ079-086>088-
094>096.

IA...Heat Advisory until 7 PM CDT this evening for IAZ008>011-018-019-
029-030.

&&

$$

SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...Peters
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