Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 090508
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1108 PM CST Mon Mar 8 2021

.SHORT TERM...(This afternoon through Tuesday)
Issued at 1224 PM CST Mon Mar 8 2021

At 18Z, temperatures were in the 50s across the area with clear
skies and a stalled frontal zone north of I-80 in Iowa into
southern WI. Ridging was dominating the weather locally, while
shortwave trough energy in a more southwesterly flow over
Colorado was bringing rain/snow there. This energy does move
across the area tonight with some mid-high cloud, but little in
the way of weather. Strong warm advection is also occurring
overnight in a fairly dry and stable airmass, warming 925mb
temperatures 4-5C by morning. Have bumped lows overnight with
clouds coming in and winds increasing...the lowest temperatures
should be around late evening or midnight.

Tuesday is still a breezy day with clouds clearing early, post
shortwave trough passage. 08.12Z NAM is really an outlier with
low-level temperature structure for Tuesday, possibly snow cover
impacted, and havent used it in any form for the forecast.
Latest HRRR, RAP, and GFS are indicating higher mixing depths and
warmer highs Tuesday /versus NAM/. Current forecast is about the
75th percentile for all model guidance and mixing depths to about
875mb support the forecast. Hitting 70F could happen if everything
goes right...full sun, warmer start in morning, mixing above 850
mb occurs, and model guidance is slightly low in the low-level
temperature forecast. But, certainly think that is an outlier
right now. Mixing depths would suggest wind gusts in the 30s /mph/
will be around Tuesday afternoon.

.LONG TERM...(Tuesday night through Monday)
Issued at 234 PM CST Mon Mar 8 2021

Southerly flow and warm air advection continues overnight Tuesday
with precipitation returning to the area. Widespread rainfall
chances last through Wednesday, persisting for some across the
southeast portions of the area into Thursday as a cold front dives
through the region. Plenty of moisture advecting into the region
from the south are driving this anonymously moist system. NAEFS
and ECMWF ENS are over 3 standard deviations above the
climatological mean with precipitable water values around 0.75"
across the northwestern counties of the area up to 1.00" towards
the southeastern part of the region. These amounts are in the
99.5th percentile with respect to climatology. Overall, total
rainfall accumulations ranging from 0.25" up to 1.0" are possible
across the region. Although this is still dependent on the track
of the system and where any potential deformation banding
develops.

There could be a few rumbles of thunder on Wednesday as model
guidance has been persistent with showing some instability
building into the afternoon. MU CAPE values nearing 750 J/kg are
possible for some, but this is highly dependent on where the low
pressure system tracks. Within the warm sector will have the
greatest chances for thunderstorm development. The further
northwest into cooler conditions a decent inversion above the
surface would greatly limit any surface based storms to develop as
shown by forecast soundings. With the potential convection,
precipitation accumulations would be impacted. Lower amounts could
be realized if there is a prolonged break in precipitation within
the warm sector of the low. Higher amounts are also possible as
potential storms pass over any given location.

After the cold front sweeps through the region, temperatures return
closer to near seasonable and high pressure builds in to the end
of the week. Kept with the blended model guidance through this
period into early next week as model guidance diverge from one
another.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1105 PM CST Mon Mar 8 2021

Considerable high cloudiness expected through Tuesday morning with
a shortwave over Nebraska tracking eastward across the forecast
area. A front to the south of the area will lift north with
southeast winds 5 to 15kts becoming south 15 to 20 kts gusting 25
to 30kts. Clouds deteriorate Tuesday afternoon and evening with
VFR mid clouds becoming MVFR. Mentioned low level wind shear
Tuesday evening.


&&

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

$$

SHORT TERM...Baumgardt
LONG TERM...Peters
AVIATION...Zapotocny



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