Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200356
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1056 PM CDT Sat Aug 19 2017

.SHORT TERM...(Tonight through Sunday Night)
Issued at 227 PM CDT Sat Aug 19 2017

After some morning fog, an absolutely beautiful Saturday afternoon
across the area with high pressure in control across the Upper
Mississippi River Valley Region. Under mostly sunny skies,
temperatures ranged from the middle 70s to near 80.

The area of high pressure will drift slowly east overnight as a mid-
level trough and surface cold front pushes in across the Northern
Plains into MN. NAM/GFS showing a decent amount of 850-700mb
lift/moisture transport which is expected to produce scattered to
broken altocumulus mainly west of the Mississippi River by daybreak.
With the clouds moving in and increasing southerly flow tonight, do
not think fog will be much of an issue like it was this morning in
most of the river valleys. Plan on overnight lows in the middle 50s
to near 60.

The mid-level trough/surface cold front will continue to push east
into northwest portions of the forecast area Sunday. With continued
moisture transport ahead of the front/heating of day/increasing mid-
level lapse rates expected to spark a few showers and storms. Bufkit
sounding shows decent elevated instability above 800mb of 1500-4000
J/kg with around 25kt of bulk shear by 18z. So, could see a storm or
two with stronger updrafts and potential for some hail. Otherwise,
plan on a warm and increasingly humid day with highs topping off in
the 80s.

Look for the front to continue pushing southward into the area,
hanging up from central WI into northeast IA by Monday morning.
Moisture transport looks like it actually wanes overnight but lift
and moisture convergence along the front still expected to produce
scattered shower/thunderstorms. Also, with 0-3km bulk shear
lacking in the 15 to 25 kt range, no severe storms are expected.

.LONG TERM...(Monday through Saturday)
Issued at 227 PM CDT Sat Aug 19 2017

Frontal boundary will be hung up across the area south of I-90
Monday with not a lot of moisture transport. So, not a lot of
impetus for widespread convection but scattered showers/storms still
expected with associated lift. Right now, it also appears we will be
mostly cloudy for the eclipse. Look for highs Monday in the upper
70s to the lower 80s.

For Monday night into early Tuesday morning, will be watching
another mid-level trough/weak surface low ripple along the hung up
boundary. This is expected to increase lift and moisture transport
over the boundary for more widespread showers and storms. NAM/GFS
indicating 1000-2500J/kg of MUCAPE along with increasing bulk shear
in the 20- 40kt range. So, could be a shot at some strong to
possibly severe storms Monday night into early Tuesday morning.
Localized heavy rainfall will also be a threat as precipitable
water values hover around 2 inches. Will have to keep an eye on
this.

A few lingering showers and storms expected from central/southwest
WI into far northeast IA Tuesday morning, but then strong push of
drier/cooler air takes over through the rest of the day as high
pressure builds in from the Northern Plains. Plan on highs in the
70s with dew points lowering into the 50s by afternoon.

Rest of the work week looks pleasant as high pressure dominates the
Upper Mississippi River Valley/Great Lakes regions. Look for slightly
below normal highs in the 70s with overnight lows in the
middle/upper 40s to the middle 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1056 PM CDT Sat Aug 19 2017

Surface high pressure will continue to move eastward through the
period, allowing for light southerly return flow at KRST/KLSE.
A drier air mass and stronger winds just off the surface tonight
will prohibit fog development.

Watching a convective complex across eastern NE/western IA late
this evening, but it should continue on its eastward trajectory,
passing south of TAF airfields by Sunday morning. Mostly clear
skies tonight give way to increasing VFR clouds on Sunday as a
cold front moves across the region. There is a 20-30 percent
chance for showers/thunderstorms prior to 00Z Monday, but
timing/coverage uncertainty precludes mention in 06Z TAFs. Rain
chances increase Sunday evening, but still too far out to pinpoint
favored periods for VCTS/VCSH.

Winds through the period will remain light from the south,
shifting to the northwest late at KRST behind the eastward
advancing cold front.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...DAS
LONG TERM...DAS
AVIATION...Rogers



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