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000
FXUS63 KARX 141121
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
621 AM CDT Sun Apr 14 2024

.KEY MESSAGES...

- Dry, breezy, and mild today with elevated fire weather
  concerns.

- Robust spring storm system Monday night - Wednesday will bring
  widespread substantial rainfall (70-90% chance for greater
  than 1" across most of the area) and a severe weather threat
  late Tuesday afternoon-evening to parts of northeast IA and
  southwest WI.

- Turning cooler than normal for second half of week into next
  weekend; some nights may bring a chance of frost/freeze.

&&

.DISCUSSION...
Issued at 319 AM CDT Sun Apr 14 2024

Dry and mild again today: elevated fire weather concerns

A weak cold front is dropping through the area early this morning,
with winds swinging around to the northwest behind it. Earlier
convection across north-central Wisconsin managed to clear out
rather quickly, and lingering isolated showers have diminished
across southern Minnesota and northeast Iowa. Clearing skies and
weak cold air advection will be in place today as surface high
pressure builds in from Manitoba/Saskatchewan. Similar to yesterday,
a very dry airmass will be in place with deep mixing this afternoon.
Despite the cold air advection, this robust mixing should yield yet
another unseasonably warm day with highs from around 70 to near 80.
Unlike yesterday, winds will be a smidge lighter with gusts mostly
on the order of 20-25 mph. Overall, another day posing elevated fire
weather concerns, but lighter winds today should keep things in
check (see fire wx discussion below).

Tonight into Monday the surface high drifts into Ontario with
increasing heights aloft as an upper level ridge axis drifts
overhead by evening. Looks like a continued influx of dry Canadian
air with dry low level mixing, though not quite as deep as over the
weekend. Increasing mid to high clouds along and north of I-94 in
the afternoon will lead to highs in the 60s north to mid 70s south.

Widespread rainfall Mon Night - Wed; Severe Weather Threat Tue

Focus Monday night will quickly turn to a robust upper low over the
Rockies that is progged to make quick headway toward the area on
Tuesday with an abundance of moisture. This dynamic system will be
preceded by the arrival of a warm front Tuesday afternoon lifting
into northern Iowa and southern Wisconsin. Strong upper divergence
overhead will increase through the day as the system approaches,
with strong low level moisture transport. This will bring steadily
increasing rain chances from late Monday night through Tuesday. A
lot of moisture to work with, as GEFS/ENS/CMC ensembles all show
precipitable water increasing to 250% of normal on Tuesday. Still
some slight differences in timing and track of the low, but for
being a few days out there is good overall ensemble member agreement
for the surface low to be near the Nebraska/Iowa border by late
Tuesday, with the warm sector making it up into our far southern
counties by late afternoon or early evening.

While it will depend on the exact low track, the highest instability
in the region will likely reside just south of our area over
southern Iowa. That`s where ensemble probability for CAPE > 500 J/kg
has been highest, given it will have the greatest chance for
recovery after a morning round of showers/storms. Severe potential
will depend on the degree to which the atmosphere over northeast
Iowa and southwest Wisconsin can destabilize by late afternoon and
early evening. There will be ample deep layer shear for some
supercell thunderstorms, but there may also be some capping. If
storms struggle to become surface based, the greatest threat may end
up being some large hail. SPC has introduced Day 3 marginal to
slight risks south of I-90, with a localized enhanced risk spanning
central to southeast Iowa.

The surface low will begin to depart Wednesday afternoon with
continued shower/storm chances. There has been a consistent signal
among ensemble families for a high probability (70-90% chance) of
greater than 1" of total rainfall through Wednesday, especially
south of I-94. Not out of the question that some spots could see
localized 2" or greater.

General Late Week Outlook

A pattern shift for the second half of the week with temperatures
running cooler than normal into next weekend. Looking very likely
there will be some nights with a frost and/or freeze threat by late
in the week. Overall a much drier airmass, so not much opportunity
for any additional widespread rain chances beyond Wednesday.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 619 AM CDT Sun Apr 14 2024

VFR prevails across the forecast area in the Upper Mississippi
River Valley for the 14.12Z TAF period. Increased winds with
gusts of 20 to 30 mph out of the northwest today lighten tonight
and turn counter clockwise, becoming east after the 14.12Z TAF.

&&

.FIRE WEATHER...
Issued at 319 AM CDT Sun Apr 14 2024

Another day of elevated fire weather concerns with Canadian
surface high pressure ushering in another shot of dry air.
Deep, dry mixing and sunny skies should again yield high
temperatures from around 70 north to near 80 in the far south
with minimum afternoon RH in the 20-30% range. Similar to
yesterday, can`t rule out the potential for mixing to overachieve
and yield warmer highs and slightly lower RH, except today`s
northwest winds and weak cold air advection should keep things
more in check. Winds will be a tad lighter than yesterday but
still with potential to gust 20-25 mph. Fuels are approaching
critical dryness, but FFMC values will again hold below 92.
After collaborating with neighboring offices, will issue an
area-wide Special Weather Statement for elevated fire weather
conditions.

Monday will be another mild, dry mixing day with afternoon
minimum RH around 25-30%. Winds look to be even lighter.

&&

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

&&

$$

DISCUSSION...Kurz
AVIATION...JAR
FIRE WEATHER...Kurz