Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 220756

Area Forecast Discussion
National Weather Service La Crosse WI
256 AM CDT Tue May 22 2018

.SHORT TERM...(Today through Wednesday)
Issued at 256 AM CDT Tue May 22 2018

A mid level trough will continue to move east of the area this
morning with weak surface ridging remaining in place over the area.
Extensive low stratus/fog encompassing much of eastern Minnesota
through Wisconsin is expected to gradually scatter out through the
day. Despite the strong late May sun, weak mixing could impact how
quickly skies clear today. Temps should be closer to seasonal norms
in the upper 60s to mid 70s.

Tonight into Wednesday, surface ridging remains centered across
eastern WI/IL while southerly flow/warm advection begins to
develop west of the Mississippi. Some elevated showers/storms may
reach areas primarily west of the Mississippi late tonight, but
with the low-level jet and axis of stronger moisture transport
remaining farther west and little in the way of instability east
of the MS River, expect these to be on the decline as they
progress eastward on Wednesday. Will have to watch for additional
fog development later tonight, especially closer to the surface
high east of the Mississippi River with light boundary layer flow
and relatively clear skies. The warming trend continues tomorrow
with highs well into the 70s or low 80s for most areas.

.LONG TERM...(Wednesday night through Monday)
Issued at 256 AM CDT Tue May 22 2018

A very summer-like stretch of weather is expected through the
Memorial Day weekend. Seasonally weak synoptic flow fields will
dominate late this week within a gradually warming and moistening
airmass. Mid-level and surface ridging will translate eastward into
Thursday with southerly boundary layer flow helping advect a more
moist airmass into the area with precip water values approaching
1.50 inches. Some showers/storms are possible Wed night into
Thursday within broad low/mid level warm advective regime, with
models hinting at convective development along the edge of the
stronger moisture transport/elevated instability axis over the
area. Assuming clouds/convection don`t limit the diurnal temp
rise, a very warm day with highs in the 80s is expected Thursday
as 925 mb temps climb to 21-23C.

Heading into Friday, the 22.00Z GFS/ECMWF both indicate a bit
better defined shortwave trough crossing the area. This may lead
to increasing chances for storms as 850 mb flow/moisture transport
focuses over the area ahead of the upper wave and diffuse surface
trough. CAPE values should increase Thursday and Friday as low-
level moisture continues to increase. Deep layer shear looks to
remain on the weaker side, though.

Little change in the pattern is expected through the weekend with
guidance suggesting a continuation of a somewhat stagnant, weak flow
pattern along with warm temps. Given the low predictability of
subtle features in this pattern, will retain some very low end
shower/storm chances into the weekend at times although no strong
convective signal is apparent. Well above average highs in the
80s are expected although some areas could hit 90 in this
pattern. Lows will be in the 50s and 60s.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1135 PM CDT Mon May 21 2018

A soupy airmass across the area tonight will result in continued
widespread stratus and likely some fog development through the mid
morning hours. IFR conditions are prevalent right now and will
remain in place through mid to late morning, with ceilings likely
dipping to LIFR or even VLIFR levels at RST and potentially even
LSE as clouds gradually lower overnight. With that occurring,
won`t be shocked to see some fog develop either at RST, with the
potential for at least a few hour period of dense fog there, while
LSE likely sits closer to the 1 mile range but with nearby ridges
obscured due to very low ceilings. We should see gradual
improvement through the morning hours with ceilings lifting back
to MVFR before eventually scattering out completely for the
afternoon as winds remain 5 knots or less the next 24 hours. Could
also see some additional fog development later Tuesday night with
light winds again in place, but most of that appears it would
develop toward or after 06Z.




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