Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 220800
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
300 AM CDT WED JUN 22 2016

.SHORT TERM...(Today and tonight)
Issued at 300 AM CDT Wed Jun 22 2016

Main focus is on the convective potential today, including heavy
rainfall this morning, and severe possibilities this afternoon.

Surface low center is over south-central SD at 07z with the warm
front reaching east across IA to central IL. Lots of elevated
convection north of the front from eastern SD all the way to IL.
The line is quasi-stationary, with individual cells moving east-
southeast across the same general area. So the position of the
Flash Flood Watch, and a few Warnings appear to be well placed for
the time being. Radar loops do show the back edge of the heaviest
activity will be passing through between 4 and 7 am. For now, will
leave the Flash Flood Watch in place through 10 am, but will
likely be able to be cancelled early if this present speed and
trajectory continue. There are additional showers and storms
further to the west...remnants of strong convection over the
Dakotas last evening. This is on a weakening trend and will
actually be key to how the afternoon convection may redevelop.

The main short wave trough was centered over far southern
Saskatchewan at 07z, and it is forecast to move to near Grand Forks
by 21z this afternoon. There is a pretty strong jet associated with
this wave, and it is resulting in rather strong bulk shear of
70-80 kts by afternoon. Moderate moisture transport into the the
warm front which will be located from eastern IA into northern IL by
afternoon. So the dynamic forcing is definitely there for a
significant event this afternoon/evening. But there are some caveats
as well. Current activity will leave behind a sizable cold pool that
will have to be overcome. Plus, if the trailing activity lingers, or
leaves behind enough remnant cloud cover, we may not be able to
realize as much instability. This will be especially true if the low
and warm front track further to the south. The cap will come into
play as well, with 700 mb temperatures expected to climb to +12
across northeast IA by afternoon. Model soundings do show incredible
shear and helicity, so strong to severe storms including supercells
with tornadic potential are indeed possible. But current thinking is
that the atmosphere will not be able to recover until after 21-22z,
or even later. By that time, the best focal area looks to be just
south and east of Dubuque...just south of the forecast area. SPC
initial Day 1 outlook paints the Dubuque area in a Moderate Risk for
much of the same reasoning as above. But we coordinated directly
with them, and there may be some south and eastward shift with the
13z update, depending on how things play out in the next few hours.

Outside of the severe potential, there may also be some convection
associated with the wave as it translates across MN into northern WI
tonight. Maintaining higher POPS over the northern portion of the
forecast area to account.

.LONG TERM...(Thursday through Tuesday)
Issued at 300 AM CDT Wed Jun 22 2016

A few showers could linter into early Thursday as the wave pulls
away. Beyond that, ridging builds in to provide a pleasant end to
the work week. But for the weekend, a strong closed circulation and
upper trough moves eastward along the international border toward
the dakotas. This will induce a strong return flow of moisture and
instability, and a resulting chance for showers and thunderstorms.
The highest likelihood will be Saturday night as a cold front
sweeps through. Given the timing, instability, and available shear,
there is a risk for severe weather with this. More on this
later...once we get through today`s event.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1216 AM CDT Wed Jun 22 2016

Line of heavy thunderstorms as of 22.05Z along the MN/IA border
and dropping southeastward towards KALO/KOLZ likely to remain
south of KLSE, but could clip KRST within the next few hours.
Better chance to see thunder at TAF airfields is from broken line
of thunderstorms moving into western MN from the Dakotas. Despite
occasional heavy rain, recent observations show high cloud bases
with limited restrictions to visibility. If stronger thunderstorm
moves over airfield, MVFR/brief IFR conditions are possible, but
the general rule through the period will be VFR. Best chance for
thunder at KRST is from 22.08Z to 22.14Z and from 22.10Z to 22.16Z
at KLSE. Low confidence in timing/coverage of thunderstorms later
in the period precludes mention at this time. Non-thunderstorm
winds will be light through the period from the southeast.

&&

.HYDROLOGY...
Issued at 300 AM CDT Wed Jun 22 2016

Storms quickly developed during the evening hours along a linear
band on the nose of the best moisture transport, running from
southwest MN across northern IA. With training cells moving
repeatedly over the same general area, went with a Flash Flood
Warning. But as the cold pool began to dominate, the cells weakened a
bit and shifted the training. So there have been no reports yet of
any flooding. With heavy rainfall shifting out of the area after 4
or 5 am, may be able to cancel the watch early.

There is some potential for heavy rainfall again this afternoon as
the new storms develop. But these are expected to be more
progressive, so do not anticipate them lingering in any one place
too long. Thus do not feel there is a need for any Watch for the
afternoon activity.


&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...Flash Flood Watch until 10 AM CDT this morning for IAZ008-009-
     018-019-029-030.

&&

$$

SHORT TERM...MW
LONG TERM...MW
AVIATION...ROGERS
HYDROLOGY...MW



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