Area Forecast Discussion
Issued by NWS La Crosse, WI

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685
FXUS63 KARX 241718
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1218 PM CDT Sun Sep 24 2017

.SHORT TERM...(Today through Tuesday)
Issued at 202 AM CDT Sun Sep 24 2017

The main concern for today will once again be the temperatures.
925 mb temperatures Saturday were between 25 and 26C and the model
consensus is that these only cool about 1 degree for today.
Forecast soundings show the mixing will be plenty deep enough
again to bring this warm air down to the surface. Will bump up
temperatures again for today to be as warm as or within a degree
of Saturday.

The attention then turns to the slow transition in the upper air
pattern allowing the surface front to ooze into the area. The
24.00Z models remain consistent in showing the upper level ridge
moving slowly east and eventually to the northeast side of Maria
by Tuesday. This will allow the upper level trough to also start
moving slowly east and to also begin filling in with time. As the
trough starts to lift and fill, several short wave troughs should
move over or near the area starting late tonight and continuing
right through Tuesday when the remains of the trough will be
lifting out of the Dakotas and into Manitoba and Ontario. None of
these short wave troughs will produce much forcing with just
several periods of very weak to weak pv advection expected in the
500-300 mb layer. As the long wave trough fills in, the low level
moisture transport will be affected and is expected to weaken as
well. This will be the strongest over the area tonight but with no
forcing to speak of, it is not expected to generate any
convection. The moisture transport will then really weaken for
Monday through Tuesday and be through the area and focused well
to the north ahead of the remains of the upper level trough. The
front is expected to slide into the area Monday and remain through
much of Tuesday before moving off to the east. Only weak
frontogenesis will accompany the front with this primarily limited
to the 1000-850 mb layer. Generally expecting scattered showers
and some storms to move across the area with the front. The
deepest moisture to support this activity will be behind the
front, so this gives very little opportunity for the deep layer
shear, that will also be behind the front, to overlap the CAPE
ahead of the front. Not expecting severe weather to occur with
this system.

.LONG TERM...(Tuesday night through Saturday)
Issued at 202 AM CDT Sun Sep 24 2017

Other than some lingering shower chances across the eastern
sections Tuesday night, this period will start out dry and cooler
as high pressure builds in from the northwest. A short wave trough
in the northern stream should drop across the Great Lakes Thursday
to provide a small chance for some showers over Wisconsin during
the afternoon. It then looks to generally be dry with seasonable
temperatures for Friday and Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1153 AM CDT Sun Sep 24 2017

VFR conditions expected through the period, with afternoon
cumulus and southerly winds around 10-12 kts. Could also see some
gusts up to 20 kts at RST. A broken 10 kft ceiling will move into
both sites by the end of the period as a cold front approaches.
Some showers will be present along the front and could impact RST
toward the end of the period, but timing and coverage differences
in guidance do not provide enough confidence to include a mention
at this time.

&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION...CA



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