Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 090947

Area Forecast Discussion
National Weather Service La Crosse WI
445 AM CDT Fri Jun 9 2023

.DISCUSSION...(Today through Thursday)
Issued at 223 AM CDT Fri Jun 9 2023

Key Messages:

 - Widespread Precipitation Chances Likely Early Saturday Morning,
   Initially Delayed by Dry Air Lingering Through Today

 - Cool End to the Weekend, Gusty Through Monday Providing Potential
   Fire Weather Concerns

 - Above Normal Temperatures Through New Work Week


Dry, warm conditions continue today from a slight building in
upper level heights, evident on water vapor satellite imagery
early this morning near the Minnesota-Canada border, extending
temporal residency locally of surface high pressure. Upstream
RAOBs and AMDAR observations exhibit this dry air, evident on high
resolution RAP & HRRR (09.03/06Z) soundings just off the deck.
From slightly bumping up maximum high temperatures today, there is
increased ability to tap into this drier air, further reducing
dewpoints today.

Incoming Precipitation:

Given the drier conditions in most high resolution models, initial
precipitation chances have been delayed compared to previous
forecasts, now during early Saturday morning from northwest to
southeast. Upper level trough digs through Minnesota through
Saturday while phasing towards neutral providing sufficient
quasigeostrophic forcing and advecting a low level increased
theta e wave over the forecast area. Lobes of positive mid level
vorticity advection will also also increase precipitation chances
through Saturday into Saturday night.

Precipitation Impacts:

Stronger storm chances shift from north to south through the
afternoon as a MLCAPE axis above 1000 J/kg slides south-southeast
to Interstate 90 with increased low level theta e axis and
surface frontal boundary. Low level shear is minimal, with
increased mid to upper level speed shear potentially providing
sufficient tilting, preventing storms from crashing on themselves
as well as potential hazard of small hail. Highest confidence in
high resolution ensemble forecasts (09.00Z) suggest a widespread
local probability matched mean of a half an inch of rainfall with
above an inch in maxima possible in heavier downpours and storms.
Current forecast window limited to near precipitation onset for
the 09.00Z HREF however.

Cool, Dry, Gusty Conditions Sunday and Monday:

Upper level trough expected to close over the forecast area through
Sunday, advecting over the Great Lakes through Monday. Local
forecast area remains in the drier, cold air advection regime with a
tight surface pressure gradient. Resultant northeast to northwest
winds Sunday to Monday expected at 15 gusting to 30 mph.
Continued with National Blend guidance, keeping surface dewpoint
temperatures in the high 30s to low 40s and maximum daytime
temperatures in the 70s. Forecast hour keeps increased weights on
longer term global models which have been more moist than higher
resolution models as of late, so will be something to keep an eye
on for fire weather concerns to wrap up the weekend into the new
week. Also, areas that receive higher rainfall amounts will help
maintain more surface moisture and abate fire weather concerns,
resulting in patchy lower RHs likely. Lots of spread in model
certainty violin plots at this time, with National Blend along the
bottom quartile. In summary, many specifics to solidify yet but
something to keep an eye on incoming forecasts.

Above Seasonable Temperatures Through New Work Week:

Through the new work week an amplified upper level ridge and upper
level diffluent flow abates increased precipitation chances.
Compared to the previous week, ridge is weaker in magnitude and more
progressive (actually progressive rather than regressive), keeping
maximum daytime temperatures in the 80s, only a few degrees above
normal. Ensemble and deterministic guidance for maximum daytime
high temperatures are in closer agreement than in previous
pattern as well, eliminating need for forecaster intervention at
this time.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 445 AM CDT Fri Jun 9 2023

CIGS: a few high thin clouds today, with increasing high/mid deck
later tonight. Cigs should continue to lower on Sat as a cold front
pushes in from the northwest. Could drop into MVFR for a few hours
Sat night.

WX/vsby: no impact through tonight. SHRA/TS will accompany the cold
front for Sat, which will linger into Sat night. Some vsby
restrictions from time to time in the rain. Storms look more
scattered in nature.

WINDS: light for speeds with a swing west by the afternoon then more
southerly tonight. Cold front looks to ease southeast of the TAF
sites Sat evening, swinging winds to the northeast.




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