Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 250839

Area Forecast Discussion
National Weather Service La Crosse WI
339 AM CDT Tue Jun 25 2019

.SHORT TERM...(Today and tonight)
Issued at 338 AM CDT Tue Jun 25 2019

500mb heights were rising early this morning as shortwave troughing
departs over the Upper Great Lakes. A subtle mid-level ridge was
dampening as it moved into the Upper Mississippi Valley, but weak
warm air advection was ongoing at 850mb and 925mb out ahead of a
cold front advancing into Minnesota and northwest Iowa. Regional
radar revealed mostly isolated convection tied to this area of WAA
as well as weak shortwave energy in the vicinity of the front.
Activity has been repressed by lower PWATs (less than 1 inch) and
hence less instability.

WAA will be ongoing through the morning with somewhat stronger
isentropic ascent targeting portions of northeast Iowa and southwest
Wisconsin after daybreak. The front and weak energy aloft will drive
some additional ascent as they push through the forecast area from
mid-morning through late afternoon. PWs will recover somewhat after
daybreak, rising just above 1 inch mainly across the southeastern
half of the CWA. Some guidance is overdoing dewpoints, and forecast
soundings show a well mixed (inverted-V profile) boundary layer
developing this afternoon which would further knock down surface
dewpoints. Will go with the conservative range of MLCAPEs for today,
generally 1500-2000 J/kg across northeast Iowa and southwest
Wisconsin. Shear will be decent but largely unidirectional and
mostly tied to the lowest 3 km at ~30-40 knots. HREF paints some
weak updraft helicity across our far south in the late afternoon to
early evening. Overall a low expectation for any stronger/severe
storms, but if they develop, highest potential for anything stronger
within our area would mainly be across far southwest WI and
northeast IA. Isolated gusty winds and hail would be the main
threats. Shortwave energy passing by farther north may trigger
scattered showers and perhaps a few storms up in our northern
counties this afternoon and early evening. Rain chances then
diminish this evening as the front and shortwave energy depart and a
surface ridge builds into the region. Decent chance of valley fog
development again tonight.

Temperatures today will experience a noticeable bump given this
morning`s WAA and considerably more sunshine than yesterday. Highs
will range from near 80 to the middle 80s. Lows in the 50s to lower
60s tonight.

.LONG TERM...(Wednesday through Monday)
Issued at 338 AM CDT Tue Jun 25 2019

Surface ridge axis traverses the Upper Mississippi Valley on
Wednesday, but models are now hinting rather strongly at perhaps
some rain chances arriving during the day. This will be tied to some
ripples of mid-level energy riding around an amplifying upstream
ridge. Due to uncertainty in the location and timing of this
potential activity, have kept present forecast dry for the daytime
hours, but the day shift today may well need to introduce some PoPs
across a portion of the forecast area. Greater potential will arrive
in the evening as a warm front lifts toward the area with stronger
moisture transport taking aim at our area. There will be increased
instability as the airmass becomes juicier out ahead of that
building mid-level ridge just upstream. Decent shear will also be
found on the cold side of the boundary, so will need to monitor
the potential for some stronger storms.

That warm front will stall out over the area towards the end of the
week, stretching from North Dakota down through southern Wisconsin.
This will place us in a favorable spot near/within the warm sector
for juicy dewpoints pooling in the upper 60s to lower 70s, with heat
building through the weekend as 850mb temperatures approach +20C.
Highs in the upper 80s to lower 90s are expected by the weekend.
This warm and unstable environment will favor additional storm
chances at times. Thursday afternoon/evening looks to be the period
of greatest interest as a more robust shortwave slides through the
region, and our current chance PoPs may well need to be increased as
we get closer in time. Additional periodic shower/storm chances will
linger through the period with that boundary draped over the region.
Looks like the upper ridge begins to break down early next week with
the heat slowly subsiding (somewhat) Monday into Tuesday.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1205 AM CDT Tue Jun 25 2019

Besides some very local ground fog threat early this morning, VFR
conditions prevail across the region. Only real threat in this
forecast is risk of any convection as weak impulses move through.
Coverage seems like it will be quite spotty so confidence not high
enough to include risk at TAF sites. Will keep occasional passage of
mid/high level clouds going, along with subtle wind shifts as waves
move through. Otherwise pretty quiet in offing.




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