Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 070835
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
335 AM CDT Tue Apr 7 2020

.UPDATE...
Issued at 335 AM CDT Tue Apr 7 2020

Skies have cleared out early this morning generally along and
south of Interstate 90. With light winds and plenty of low level
boundary moisture in place, fog has formed with some of this being
dense. Quite a few spots already reporting visibilities of a half
mile or less and not expecting much change until after sunrise.
Have issued a dense fog advisory where it appears the dense fog
will be the most widespread and last the longest.

&&

.SHORT TERM...(Today through Tonight)
Issued at 209 AM CDT Tue Apr 7 2020

Water vapor satellite this morning shows an upper level trough was
moving across Saskatchewan this morning with a short wave in the
southern end of the trough working across the northern High Plains.
With some weak downstream ridging, these two features are expected
to continue moving east/northeast through the day with the short
wave trough passing by to the north of the area this morning. A
second short wave trough cutting under the mean long wave trough
looks to come out of the northern Rockies and quickly move across
the Upper Midwest this afternoon and evening. This wave looks to be
oriented pretty parallel to the upper level flow, which will limit
it`s overall forcing. Only some weak pv advection in the 500-300 mb
layer is expected today from the two short wave troughs. An area of
low pressure at the surface over South Dakota will move
east/northeast with the short wave troughs and track across central
Minnesota early this morning and be over northern Lake Michigan by
late afternoon. This will push a cold front across the area late
this morning into the early afternoon with a band of weak
frontogenesis in the 1000 to 500 mb layer. Warm advection this
morning has created a strong low level cap that forecast soundings
from both the 07.00Z NAM and several runs of the RAP indicate will
remain in place until the cold front moves through. This should
limit most of the rain chances today to across the northern sections
of the area closer to the slightly stronger forcing from the long
wave trough and where the cap will not be quite a strong. Will
maintain some small chances along the front during the afternoon
across the eastern sections in case some elevated activity gets
going above the cap.

A weak area of high pressure slides in behind the departing low/cold
front tonight for clearing conditions this evening. Increasing
clouds will take then place after midnight ahead of a mid-level
trough pushing toward the area from the Northern Plains. Plan on
lows tonight in the mid 30s to the lower 40s.

.LONG TERM...(Wednesday through Monday)
Issued at 209 AM CDT Tue Apr 7 2020

A cold front drops into the region Wednesday with strong mid-level
frontogenesis. Forcing from this looks to generate a band of light
to moderate rainfall. With the thickening clouds/rain moving in,
plan on temperatures to top off by noon in the lower 50s to
lower 60s then slowly falling through the afternoon.

There will be another chance of showers Thursday, mainly north of I-
94, as a secondary mid-level trough/surface cold front rolls
through. Otherwise, a rather chilly/raw day on tap with highs only
in the upper 30s to middle 40s. Brisk northwest winds in the 15 to
25 mph range will add to the chill.

High pressure slides into the region Friday for mostly sunny but
continued cooler than normal with highs in the 40s to near 50.

Northwest flow aloft ushers in another cold front Friday night/
Saturday for shower chances.

Cold mid-level trough then carves out over the central CONUS/Upper
Mississippi River Valley Region Sunday into Monday for continued
cooler than normal temperatures and smaller-end shower chances
(possibly mixing with snow at times). Look for lows in the 20s/30s
and highs mainly in the 40s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 1000 PM CDT Mon Apr 6 2020

Cigs: IFR/LIFR expected into Tue morning with improvement as a cold
front passes east in the afternoon. That said, there are some hints
in the meso models that improvement could occur for a few hours at
KRST overnight, but likely fill back in with low clouds/fog before
front sweeps that away. Satellite imagery has raggedy western edge of
the low clouds just west of KRST. Confidence not high in timing out
this potential period of VFR, so will hold with the low cigs for
now. Will monitor and update if needed.

WX/vsby: warm front to the south will continue to be a focus for
showers through the night, the bulk staying south of the TAF sites.
That said, models are a bit more bullish on fog formation north of
the front, with lower vsbys at KRST. Will continue to trend the
forecast this way. Look for improvement by mid morning Tue.

Winds: southeast through the night, becoming west/northwest late
morning/early afternoon with passage of a cold front.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory until 9 AM CDT this morning for WIZ053>055-
     061.

MN...Dense Fog Advisory until 9 AM CDT this morning for MNZ086>088-
     094>096.

IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ008>011-
     018-019-029-030.

&&

$$

UPDATE...04
SHORT TERM...04/DAS
LONG TERM...DAS
AVIATION...Rieck



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