Area Forecast Discussion
Issued by NWS La Crosse, WI

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326
FXUS63 KARX 270804
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
304 AM CDT Fri Apr 27 2018

.SHORT TERM...(Today through Sunday)
Issued at 304 AM CDT Fri Apr 27 2018

A bit of an active weather day potentially to wrap up the work week,
with the focus on both fire weather concerns for areas farther west
while eastern areas see an increasing risk for mainly afternoon
showers and storms (it`s the season for such things, of course).
Early morning analysis places a departing shortwave into eastern
Wisconsin, while a second notable wave is dropping south out of
Manitoba, on its way also into central Wisconsin later this
afternoon, as a surface wave tracks to the southeast, just east of
the Mississippi River. That setup places areas west of the Miss
River in the warmer air through the day, with a modest gradient and
deep mixing (not to mention westerly wind component) promoting
warmer temps and lowered dew points as well as surface gusts likely
into the 30-ish knot range. That in turn gives us continued fire
weather concerns given the ongoing drier conditions and history of
fires, especially with the expected stronger winds, though
conditions look to fall just shy of Red Flag Warning criteria for
the moment.

Farther east is a different story, with an axis of 250-500 J/kg
surface-based CAPE progged to develop in the vicinity of the surface
low track by early afternoon. With increased forcing arriving after
18Z (greatest toward central Wisconsin), envision a smattering of
showers and some thunder developing in many areas, with deep
inverted-V profiles likely supporting some gusty winds in the
vicinity of any convection. That could also pose a fire weather
concern, though added clouds should keep overall fire weather
conditions somewhat tempered through the day. With rather chilly
thermal profiles aloft as well (freezing levels only 6-8kft), can`t
rule out some smaller hail with any cells, though would like to
maybe see a little better CAPE profiles to support more robust
updrafts.

Showers could stick around for a bit into late evening within
lingering weaker frontogenetic forcing, and interestingly there are
even a few hints that some snow (gulp!) could possibly mix in north
of I-94 briefly before ending, provided that a) we still have precip
to work with and b) that moisture depth remains sufficient as much
colder air works south. Regardless, very quiet weather looks to
arrive into Saturday with broad low level ridging pretty much
directly overhead, and a cooler start Saturday afternoon beneath
thermal troughing leading to some chilly overnight lows by Sunday
morning. With those cooler temps, fire weather concerns are a bit
lower for Saturday afternoon but return by Sunday with a tighter
gradient/warmer airmass working back into the region.

.LONG TERM...(Sunday Night through Thursday)
Issued at 304 AM CDT Fri Apr 27 2018

Return to a potentially much more active weather regime looks on tap
through much of next work week with upper troughing over the western
CONUS spitting pieces of energy in our direction at times.
Broad/deep southerly return flow through the early work week should
help us achieve an increasingly moist airmass this far north,
potentially helping alleviate overall fire weather issues but with
several chances for some needed rainfall as we welcome the first few
days of May. Exact timing still somewhat questionable but the first
shots come Monday and Tuesday, mainly over the western half of the
area with lead shortwaves lifting north through Minnesota with
another (maybe better?) chance later Wednesday/Wednesday night with
a stronger wave arriving locally. Plenty of time for things to
change, but right now it appears that while we have sufficient shear
for organized convection, we may struggle with instability issues at
times. Definitely something to watch, with daily temperature trends
strongly dictated by clouds each afternoon.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1147 PM CDT Thu Apr 26 2018

VFR conditions are expected through the TAF period, with the main
aviation concerns being strong and gusty northwest winds Friday
afternoon. A quick moving low pressure system dives southward
across Wisconsin on Friday bringing increasing northwest winds to
the TAF sites with the potential for a shower or two at KLSE. Plan
on winds increasing to around 17 kts with gusts of 25 to 35 kts
possible. The strongest winds will be at KRST. Also, winds gusts
of 35 kts are possible near any showers or isolated thunderstorms
across central Wisconsin during the day on Friday.

&&

.FIRE WEATHER...
Issued at 304 AM CDT Fri Apr 27 2018

Plenty of fire weather issues the past few days, and those continue
today and into the weekend. Will be closely watching areas mainly
near and west of the Mississippi River today with the combination of
wind gusts of 25-30 knots, minimum RH values in the 25-30% range,
and highs back into the 60s. Areas farther east will deal with some
scattered showers and storms through the afternoon, with any of
those capable of producing gusty and erratic winds though added
clouds should help keep fire weather parameters a little more in
check, though given better mixing, we may still see lower RH values
nearing 30% at times. Could potentially be near Red Flag Warning
criteria for parts of northeast Iowa later this afternoon based on
current GFDI forecast, but for the moment, RH values appear just a
little too high for issuance at this time.

Thankfully, a brief period of cooler weather for Saturday should
help lower fire weather concerns (still some lower RH values of 25-
30%), but breezy and warmer conditions should make a return by later
Sunday. Some question at the moment about how low relative humidity
values will end up by Sunday afternoon, but right now, looking like
moisture return will be sufficiently slow to support another day of
lower RH values, especially near/west of the Mississippi River where
afternoon highs end up the warmest. Thereafter, increasing moisture
should aid in holding up afternoon RH values Monday through much of
the work week, with several chances for rainfall as well, though
will need to monitor closely just how fast moisture in fact returns
over the next few days.

&&

.HYDROLOGY...
Issued at 304 AM CDT Fri Apr 27 2018

Flood warnings remain (or are likely to be issued over the next day
or two) for portions of the Mississippi River and the Yellow River
at Necedah. Minor to possibly moderate flooding is expected into the
first week of May as water from melting snow to our north works down
into the area. Please see the latest flood statements or
water.weather.gov for more detailed information.

&&

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

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...Wetenkamp
FIRE WEATHER...Lawrence
HYDROLOGY...Lawrence/DAS



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