Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 242323
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
623 PM CDT Wed May 24 2017

.SHORT TERM...(Tonight through Thursday Night)
Issued at 237 PM CDT Wed May 24 2017

Pesky closed low that has been responsible for the clouds and
scattered showers over the last couple days now centered over MO per
latest GOES Water Vapor/Visible loops/RAP 500mb analysis. Shower
activity has pretty much shut down and moved south of the area
closer to the low, but still plenty of stratus and perhaps a patch
or two of drizzle to contend with today. Clouds also holding
temperatures back with reading this afternoon in the 50s, or some 20
degrees below our normal highs for today.

For tonight the closed low finally budges east more into the Ohio
River Valley as a ridge of high pressure builds in from the Plains.
Clouds and areas of fog could become problematic tonight. Where
clouds do clear, fog will almost be a certainty late tonight into
Thursday morning. This looks most likely along and west of the
Mississippi River closer to the ridge axis. East of the river,
clouds look to hang on overnight limiting the extent of fog. Will
have to keep and eye on how dense this fog becomes along/west of the
Mississippi overnight into Thursday morning. Otherwise, plan on lows
tonight in the lower and middle 40s.

After some morning fog, mid-level ridge and surface warm air
advection will provide a nice Thursday for the area. Look for highs
topping off in the upper 60s to the lower 70s.

Increasing warm air advection/850-700mb moisture transport ahead of
a mid-level trough moving through the Northern Plains could produce
some elevated/high-based showers across the area Thursday night.
CAPE at this point looks very minimal, so will leave thunderstorm
mention out for now. Look for lows in the lower/middle 50s.

.LONG TERM...(Friday through Wednesday)
Issued at 237 PM CDT Wed May 24 2017

Friday/Friday evening will see a chance of showers/storms as a weak
mid-level trough/surface cold front pushes east across the area. NAM
builds a corridor of 1000-2000 J/kg across eastern MN/northwest WI
along the front but rapidly diminishes it with loss of heating
toward evening as it moves into our area. Therefore, severe threat
looks minimal at this time. Otherwise, temperatures pre-frontally
expected warm into the upper 60s to middle 70s.

A weak east/west frontal boundary hangs up across central southern
sections of the forecast area Saturday with weak mid-level
frontogenesis and incoming weak pv-advection. For this reason, will
carry a slight chance of showers in the morning and 20-40 pops in
the afternoon with daytime heating. Still warm though with highs
expected to be in the 70s.

For Sunday into Memorial Day...models in good agreement on dropping
a mid-level trough through the region from Canada. This will bring a
chance of showers and afternoon/early evening thunderstorms given
steepening lapse rates.

Tuesday looks like a return to cooler/showery weather a cyclonic
flow takes hold across the region. Plan on highs in the lower/middle
60s.

Latest ECMWF/GFS showing some differences for Wednesday with the GFS
building a ridge into the area while EC maintains cooler/cyclonic
flow and continued showers. Consensus has the day dry for now with
highs in the mid-upper 60s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 623 PM CDT Wed May 24 2017

Satellite imagery late this afternoon shows lots of clouds
covering a good share of the area, but there are some breaks in
the overcast. The concern becomes will the clouds or the breaks
win out overnight. A weak ridge of high pressure extends from
northeast Minnesota into eastern Nebraska with the clouds
extending into and through the ridge axis over Minnesota. This
ridge axis is expected to slide east and extend from northwest
Wisconsin into northern Missouri by 25.12Z. The 24.18Z NAM is
pretty pessimistic on the clouds remaining overnight as it keeps
the low level moisture high but looking at the forecast soundings,
it does thin out the moisture depth. The 24.21Z RAP is more
optimistic and suggest it will clear out overnight. For now, have
maintained forecast continuity and gone with the clearing
overnight, but have also hedged toward the NAM and not dropped the
sky coverage nearly as much as the previous forecast. This will
all have a big impact on whether or how much fog will form
overnight. If it does clear out, with all the moisture and light
winds, would expect to see fog form with IFR conditions for both
airports. Without the clearing, any fog would be minimal but
ceilings could come back down to MVFR. Again, have maintained
forecast continuity with fog forming and IFR conditions
developing. Expect this will burn off not long after sunrise
Thursday with VFR conditions the rest of the day.

&&

.HYDROLOGY...
Issued at 237 PM CDT Wed May 24 2017

Recent heavy rainfall will continue to cause minor flooding along
portions of the Mississippi River and also the Trempealeau River at
Dodge this week into early next week. Be sure to monitor river
levels closely if you have any plans or interests along these rivers.
You can access this information on our website at weather.gov/arx.

&&

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

$$

SHORT TERM...DAS
LONG TERM....DAS
AVIATION...04
HYDROLOGY....DAS



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