Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 280736
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
230 AM CDT Fri Apr 28 2017

.SHORT TERM...(Today through Monday)
Issued at 230 AM CDT Fri Apr 28 2017

Cold...wet. The only two words you`ll need to remember for the
weekend.

Very active pattern for the region as a parade of shortwaves spin
across southern portions of the region today-sat, with a
trough/closed 500 mb lifting northeast through the region Sun night-
Monday.

1) Today: shortwave trough currently across the southern plains (per
latest watervapor satellite imagery) will shift northeast across IA
into WI later today. Decent shot of low level warming (850-700 mb)
leads the shortwave into the area, with a west-east run of 600-700
mb frontogenetic forcing around the ia-mn border this
afternoon/evening.

North-south running x-section keeps the deeper saturation south of I-
90, with mostly mid level clouds across the north. Models generally
favoring keeping rain chances from around I-90 southward, with
perhaps some sprinkles from the mid level frontogenetic forcing
north of there. This looks reasonable given the setup.

2) Saturday: another piece of shortwave energy slated to round a
west coast trough and lift northeast to across southern mn/wi sat
afternoon-evening.  The west-east elevated frontogenetic boundary
still lingers across the region at this time, and the lift enhances
along it as the shortwave approaches. There is also another shot of
low level warm air advection. Similar to what is expected for later
today, but with a bit more forcing and a more northward extent of
deeper moisture. Better rain chances will still lie to the south,
but threat will extend farther north - especially later Sat night.

3) Sunday-Monday: 500 mb trough/closed low moving from the desert
southwest northeast through the plains to across WI by 00z Tue. The
system is vertically stacked by this time, and developing a bit of a
negative tilt as it moves in. Good push of low level warming ahead
of the low.

Nice fetch of moisture leading the system with the nose of the 850
mb moisture transport/jet nosing into southwest WI by 00z Mon, but
quickly shifting into eastern WI as the whole system continues its
northeast track. The moisture does wrap well north/west of the low,
helping to feed its` deformation region.

As it sits right now, there looks to be two main focuses for pcpn
with this storm system. The first will be move convective in nature,
located ahead of the system`s cold front, with some help from the
low level jet/moisture and bits of upper level energy. The bulk of
this would fall over ill-eastern WI. The second would be in the
deformation region of the low, mostly impacting western
ia/mn/northwest wi.

In between, where the local forecast area sits, still expect pcpn -
especially with the initial thermodynamics/approach of the low. But
there is a mid level/600:700 mb dry punch wrapping into the
south/southeast of the low pressure system, providing a limiting
factor to spread/amounts - more so late Sun night/Mon morning.

Pcpn chances continue Mon night into Tue morning as the exiting low
drags its westward hanging pcpn shield through WI. Should be fairly
light, diminishing by this time.

As for type, should be rain predominately, but snow looks likely in
parts of that deformation region. Could see some accumulations,
although given the track of the storm, that threat looks greater
over central MN into northwest WI.

All in all, its going to be wet, but the higher rainfall amounts
look to be east of the local area, while the great snow threat lies
west and north.

.LONG TERM...(Tuesday through Thursday)
Issued at 230 AM CDT Fri Apr 28 2017

GFS/EC drop another upper level shortwave trough across the Upper
Mississippi River Valley Wed night. Not packing the kind of punch as
the Sun-Tue system, and moisture isn`t as prevalent.  That said,
could be enough lift/saturation to spark scattered showers.

Some hope in temperatures for the later part of the new week with
upper level ridge building starting Friday. Could get back to the
seasonable normals.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1153 PM CDT Thu Apr 27 2017

Low clouds are finally starting to erode from the west, and should
clear RST toward or just after 06Z and LSE around 08Z, leaving some
increasing mid and higher clouds into Friday. There could also be a
period of some cumulus development during the morning hours of
Friday, with westerly winds becoming north but overall holding under
10 knots.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Frost Advisory til 8 AM CDT this morning for WIZ041-053>055-
     061.

MN...Frost Advisory til 8 AM CDT this morning for MNZ088-096.

IA...Frost Advisory til 8 AM CDT this morning for IAZ011-030.

&&

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Lawrence


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