Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 260725

Area Forecast Discussion
National Weather Service La Crosse WI
225 AM CDT Sat May 26 2018

.SHORT TERM...(Today through Monday)
Issued at 225 AM CDT Sat May 26 2018

Water vapor satellite shows a short wave trough over southern
Saskatchewan this morning. This wave is expected to move
east across southern Ontario and far northern Lake Superior today,
which is farther north than what the previous model solutions had
been showing. With the forcing from this wave even farther north,
the showers and storms that form with it should stay to the north
with the area expected to be dry today. The exception to this
might be the far eastern parts of the area where the 26.00Z GFS
and a couple of the hi-res meso-scale models try to show some
development occurring in a ribbon of higher surface dew points.
However, confidence in this development is extremely low as the
GFS is trying to push the dew points to around 70 where it has
development and this seems way too high given there are no 70 dew
points anywhere close to the region.

The upper level ridge currently over the lee of the Rockies will
build east and over the region through the holiday weekend. This
will provide dry weather through Sunday with only a small chance
for some rain Sunday night and Monday. Several weak short wave
troughs are expected to ride up the back side of the ridge axis
and interact with a weak boundary extending out of the Dakotas
across Minnesota into northern Wisconsin. Convection should form
along and north of this boundary and move east with the question
being whether the southern edge of any of this activity will brush
the northern sections of the forecast area. With very low
confidence on how this will play out, will include just a small
rain chance across the northern and eastern for Sunday night into

The ridging will also bring the warmest air of the year so far.
925 mb temperatures are expected to warm 2 to 3C today and be in
the 25-27C range across the area. Some warming will continue into
Sunday with 27-28C expected across the area and then generally
around 27C for Monday. This is expected to push surface
temperatures into the upper 80s to middle 90s today and then into
the lower to upper 90s area wide for both Sunday and Monday.
Fortunately, dew points will not be excessively high and should
primarily be in the lower to middle 60s. This will help to keep
the heat indices below 100 for the most part with some of the
southern sections of the area possibly exceeding 100 for a couple
of hours Monday afternoon. The duration and areal coverage does
not look to be enough for an advisory at this point.

.LONG TERM...(Monday night through Friday)
Issued at 225 AM CDT Sat May 26 2018

This period will be dominated by the slow breakdown of the upper
level ridging with the remains of the current upper level low over
California working up and over the ridge axis. To further
complicate this pattern, Alberto will drift north across the Gulf
of Mexico with both the 26.00Z ECMWF and GFS continuing to bring
this system north into the mid-Mississippi River Valley before
turning it northeast through the Ohio River Valley. As can be
expected with this complicated flow, differences between the
models on the timing, although this is mainly with the remains of
Alberto. Differences also with the strength of the remains of
California upper level low where the ECMWF is weaker and brings
this up the back side of the ridge as a positive tilt trough. The
GFS keeps this stronger and with a neutral to slightly negative
tilt. With this pattern there will be on and off rain chances
through the entire period with the highest chances centered on
Wednesday which is when the forcing from the remains of the
California low should be the strongest.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1145 PM CDT Fri May 25 2018

Outside of some lingering light rain at KLSE over the next hour,
expect dry conditions at both TAF sites through at least Saturday
morning. There is a chance for some afternoon/early evening
showers and thunderstorms, but it looks like most activity will
remain north of I-94.

With lower dew point depressions from rainfall this evening, there
could be some patchy fog as skies clear and surface winds become
light. However, winds right off the surface will remain elevated
and this should help limit widespread development. Confidence not
high enough at this time to include in 06Z TAFs.

Winds will be light through the period from the west-southwest,
becoming variable Saturday evening.




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