Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 130425
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1125 PM CDT Thu Oct 12 2017

.SHORT TERM...(This evening through Friday)
Issued at 238 PM CDT Thu Oct 12 2017

Afternoon upper air analysis showed a ridge axis moving through
lower Michigan with surface analysis showing a surface trough and
cold front extending north to south across the Dakotas. Low clouds
remained in the area throughout the day, but continue to slowly
decay from from west to east from central Minnesota into north-
central Missouri. May see a brief break in the clouds by late
Thursday afternoon/early evening, but additional clouds will quickly
move in/develop as the cold front approaches the area from the west.
RAP BUFKIT soundings have consistently shown saturating low levels
after midnight, especially east of the Mississippi River, coupled
with decent negative omega and some isentropic lift, so have added
drizzle mention for these areas.

For Friday, 12Z guidance shows the surface cold front moving into
the northwest part of the forecast area by Friday morning, with
frontogenesis increasing across the southern part of the forecast
area during the afternoon. The best moisture transport does not
reach the area until Friday evening, so have delayed the highest
PoPs a bit, but rain still appears likely for much of the southern
half of the forecast area by late Friday afternoon. Any instability
looks to remain to the south during this time period, so have left
out thunder mention.

.LONG TERM...(Friday night through Thursday)
Issued at 238 PM CDT Thu Oct 12 2017

Wave of low pressure rides up along the baroclinic boundary laid
up across eastern IA into northern IL Friday night into Saturday
morning. Increasing moisture transport/isentropic lift over this
frontal boundary will produce more showers and a few
thunderstorms, mainly across far northeast IA/southwest WI.

Will continue to keep a close eye on Saturday afternoon/evening as
our far southeastern forecast area will be on the cusp of being in the
warm sector. Right now, looks like better CAPE stays just to our
southeast. However, if we can get a bit deeper into the warm
sector/better CAPE, we will have more than plenty Bulk Shear and
impressive hodographs for a severe storm threat. Will maintain
mention of a few stronger storms in the Hazardous Weather Outlook.
Another aspect to consider will be heavy rain threat as
precipitable water values creep up into the 1.5-2 inch range.

Attention then turns to strong/deepening low pressure coming
through the area later Saturday night into Sunday. Most models
have central pressure dropping 15-20mb in 12 hr (Sun 00-12z) as
the low lifts from northeast IA into eastern Lake MI...impressive!
Models drive a dry slot into the area as the low pulls into
northeast WI/southern Upper MI. At the same time, expecting winds
to pick up significantly from the west as the low rapidly deepens.
Could see winds sustained in the 20-30 mph range with some gusts
over 40 mph through Sunday morning, then tapering through the
afternoon as the low pulls into eastern Ontario. Cooler air also
filters in on these gusty winds with highs only in the upper 40s
to the middle 50s.

Clear/cold conditions set up for Sunday night/Monday morning as
high pressure settles in across the region. Lows will be in the
30s and looks like it will produce frost for the majority of the
area.

Looks like quiet conditions then through Thursday as a ridge of
high pressure builds over the central CONUS. Temperatures are
expected to be at or a couple degrees above seasonal normals.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1125 PM CDT Thu Oct 12 2017

A cold front continues its approach late this evening, and will
cross the area through the morning hours. Stratus has redeveloped
ahead of said front, mainly in MVFR range, but appears somewhat
transient per current satellite trends. As such, barring
additional redevelopment, should see a return to VFR conditions
toward or before sunrise, as mid clouds thicken through the late
morning and afternoon hours, followed by some showers later in the
day. At the moment, there remain questions about how widespread
showers may become, but regardless it appears both LSE and RST
will see a period of some showers with ceilings holding VFR right
on into Friday evening.

&&

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

$$

SHORT TERM...CA
LONG TERM...DAS
AVIATION...Lawrence



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