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000
FXUS63 KARX 132359
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
659 PM CDT Sat Apr 13 2024

.KEY MESSAGES...

- Another warm day Sunday with elevated fire weather conditions.

- Spring storm system to bring widespread rain (75 to 100% probability
  of 0.25"+) and potential for severe weather (15%+ to parts of
  northeast IA and southern WI) to the region.

- After the above normal warmth early in the week, should cold
  temperatures materialize Friday or Saturday mornings, local
  vegetation could see damage.

&&

.DISCUSSION...
Issued at 230 PM CDT Sat Apr 13 2024

Overview:

Water vapor satellite imagery and heights show a ridge of 500mb
high pressure over the area with a closed low off near/over
parts of the West Coast and a long wave trough moving through
the East Coast. Surface low pressure was noted over the Dakotas
with south flow and much warmer temperatures locally in the 60s
and 70s. Strongest 19Z gusts were at RST with a gust to 37 mph
with 15 to 30 mph wind gusts elsewhere.

Tonight and Monday:

A shortwave trough will track to our north tonight with
increasing clouds and a few showers/storms generally north of
the forecast area. We do have some showers mentioned for parts
of Taylor Co. This weather system will bring a wind shift
through. Temperatures will Monday are still forecast to be
above normal in the 60s and 70s with northwest winds. See below
for Fire Weather concerns.

Showers/Thunderstorm Chances Increase This Week:

Sunday night, we will be under the influence of surface high
pressure, however as we move into the Monday-Wednesday period, a
more active weather pattern develops.  Closed 500mb low pressure
over the Great Basin area tracks eastward through the Four Corners
region into the Central Plains and then the Mid-Mississippi Valley.
Broad moisture transport develops across the Plains Monday afternoon
and Monday night and shifts eastward into the Mississippi Valley as
the vertically stacked area of low pressure moves east. The NAEFS
integrated water vapor transport (IVT) is 2 to as high as 5 standard
deviations above normal from the Gulf of Mexico...across Arkansas
northward through the Mississippi Tuesday.  The NAEFS mean
precipitable water increases to 99.5% of climate normals by 18Z
Tuesday. There is good general agreement on the track of the
closed 500mb low and the track of the stacked surface low, with
some differences in latitude that will help determine how far
north the severe weather will occur.

Severe weather potential:

Monday night, as broad synoptic lift increases with the approaching
low pressure system, upper level support increases with strong warm
air and deep moisture advection, we should see showers and
thunderstorms become more widespread across the region. Through
the day Tuesday the warm front lifts north across Iowa into
southern Wisconsin. In the short term we will be looking at the
warm frontal location and mesoscale features to assess the
potential for severe weather. This far out, the SPC/CSU
probabilities are 15% to less than 30% across northeast Iowa
and southern Wisconsin with CSU a little farther north into
southeast MN and central WI. 13.00Z Mean GFS/EC/Canadian
ensembles show 200-500J/kg of SBCAPE for this area Tuesday
afternoon. Freezing levels are somewhat low to average from
9500 to 11,000 ft. AGL Mean deep layer shear values of 40 to
45kts are present, increasing to the south of the forecast area,
thus sufficient for severe storms.

Heavy rain potential:

Even though is has been dry, if rainfall rates are high enough or
rain/storms persist over an area long enough, it can cause ponding
on roads and rises in ditches along with local flooding in poor
drainage areas. The mean GFS/EC/Canadian ensembles show a 30 to
55% probability of 1" or more of rainfall for 24hrs by 7am
Wednesday. Flash flood guidance is in the 1.5" to 2" range per
hour and 2.25" to 3" inch range over six hours. Some isolated
local hydro issues could occur with the EC/GFS showing 25 to 30%
probabilities of 1.5" or more and at times 200-275% normal of
precipitable water. Forecast soundings are saturated with a warm
cloud depth of 3km with a storm movement of 20 to 30kts. The
storm system appears progressive enough and the rainfall amounts
not high enough to cause general hydro concerns.

Warmth to Start the Week with Potential Freeze to End the Week:

The warmth from Sunday continues into Monday with 50-70% of the EC
ensemble members showing maximum temperatures above the mean climate
max. However, these probabilities increase across Iowa toward the
Kansas City area.  Above normal temperatures continue through mid-
week with a cooling trend to end the week.  We should have a good
assessment by mid-week as to how vulnerable vegetation is due to the
several days of highs in the 60s and 70s for potential frost/freeze
headlines if the cold temperatures are realized Friday and Saturday
mornings. The typical last freeze of the year at LSE/REST are
May 1 and May 6, but vary quite a bit from year to year.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 659 PM CDT Sat Apr 13 2024

VFR conditions are expected to remain through the TAF period
with the main concerns revolving around winds. Winds look to ease
some late overnight and will shift northwest behind a passing
frontal boundary. Low level wind shear may develop (KLSE) for a
time tonight before diminishing as the front moves through the
area. Northwest winds then look to increase to around 10-12
kts again into the daytime Sunday.


&&

.FIRE WEATHER...
Issued at 230 PM CDT Sat Apr 13 2024

Another warm day is forecast for Sunday with highs in the 60s
and 70s. Afternoon minimum relative humidity forecasts drop to
around 25 percent area wide. The winds are forecast to not be as
strong, but still gust 10 to 20 mph. Fuel levels using FFMC
values for the area are forecast to range from 89 to 91. After
collaboration with surrounding offices, conditions do not favor
Red Flag conditions, but a Special Weather Statement may be
needed for elevated fire weather conditions Sunday.

&&

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

&&

$$

DISCUSSION...Zapotocny
AVIATION...EMS
FIRE WEATHER...Zapotocny