Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 161723

Area Forecast Discussion
National Weather Service La Crosse WI
1223 PM CDT Sun Oct 16 2016

.SHORT TERM...(Today through Monday Night)
Issued at 305 AM CDT Sun Oct 16 2016

The active mid-October weather streak continues, with several
concerns of note...the first being fog/low cloud concerns through
the morning followed by several additional chances for convection,
some of which actually may have some potential to be on the stronger
side somewhere across the area (read more below). First and
foremost, the main topic first thing revolves around fog, with skies
clearing as expected with the passage of a weakish frontal boundary,
which has stalled across southeast WI down through central IA as of
06Z. Clearing skies, light flow, and moisture pooling near that
washed out feature has resulted in an expansion of dense fog across
parts of the area, which may eventually require a dense fog advisory at
some point before sunrise. However, at the moment, fog continues
to fight incoming much drier air across western areas (where skies
have been clear the longest), so unsure just how widespread it
will end up this morning. Regardless, if it does form, fog may
stick around for a few hours after sunrise, but the good news is
it appears drier air in the low levels will win the battle for
much of today with a bubble high pretty much directly overhead,
leading to quite the nice mid October Sunday afternoon with highs
soaring through the lower and middle 70s in many areas!

Things change quickly this evening and tonight as moisture comes
roaring back northward, with quite the strong low level moisture
transport signal into the region as our stalled boundary lifts back
north as a warm front. As discussed in this space yesterday, just an
impressive elevated mixed layer (EML) in place through the evening
and night across much of the area, with questions about how far
south we may erode a notable cap centered around 800mb. Confidence
in showers and storms is by far the highest along/north of I-94
where we will realize upwards of 1000 J/kg elevated CAPE per
forecast RAOBS but that confidence fades with southward extent
toward northeast IA and southwest WI given remnant stronger capping
in place. Effective shear of 40-45 knots does at least suggest the
potential for a stronger storm or two north of I-94 with hail the
main threat given a strongly stable sub-900mb layer. Downright balmy
by October standards, with lows only in the 60s expected (what month
is this again?).

Monday remains the final period of concern, with at least some risk
for potentially severe storms somewhere nearby. Per guidance trends,
still expecting the stronger shortwave expected to crash into
northern California this afternoon to rapidly work east into
southern Minnesota by Monday evening, with an attendant stronger
surface wave (nearing 990 mb) tracking somewhere just north of the I-
90 corridor. Effective shear during the late afternoon/early evening
period of simply off the charts, pushing 80+ knots thanks to an 80
knot 500mb and 110 knot 400mb jet core directly overhead. The big
question once again (especially given the time of year) is
instability, with another strong EML overhead and even stronger
capping than tonight centered around 700 mb. Still, given the
expected track of the surface wave and timing during late
afternoon/peak heating, we will really have to watch the area near
the warm front if we can break the cap for possible rapid-moving
supercells, though progged shear may prove to even be too much for
organized storms with relatively skinny CAPE profiles. A period
to watch very closely.

.LONG TERM...(Tuesday through Saturday)
Issued at 305 AM CDT Sun Oct 16 2016

Ready for a return to more typical October conditions? Looks like we
have that in store for mid and late week as the stronger Pacific jet
flow buckles with time into building West Coast ridging and
downstream falling heights through much of the central and eastern
CONUS. Still some details to be worked out regarding cloud trends
and the potential for a few showers at various times with maybe a
weaker wave or two embedded within the larger Midwest upper trough.
However, overall it appears we are in for a mainly dry stretch of
weather right on through next Saturday with temperatures cooling
back to more seasonable levels, especially by late week as notable
thermal troughing slides overhead. Given the buckling western flow
pattern, still can`t totally rule out the possibility for shortening
wave lengths to possibly carve out a closed low somewhere across
the central or eastern CONUS sometime by late week, but recent
guidance trends have steered farther away from that scenario.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1223 PM CDT Sun Oct 16 2016

Good VFR expected thru the afternoon hours as drier E-SE low level
flow prevails. MVFR/IFR cloud decks to then quickly return this
evening. This as shortwave energy comes across the plains and the
lower level flow turns southerly bringing abundant 925-850mb
moisture/clouds northward. These conditions, along with some MVFR
vsbys in BR then expected to persist across the area thru most if
not all of the late night/Mon morning hours as a stronger sfc low
and trough aloft move into the region. One stronger round of lift is
set to spread across the area tonight, producing sct SHRA and a few
TSRA. Given the sct coverage of SHRA and what looks to be more
isolated coverage of TSRA along I-90, for now only carried a VCSH
mention roughly 03z-09z at both KRST/KLSE.


Issued at 305 AM CDT Sun Oct 16 2016

Very mild conditions are expected today into Monday, with lows
tonight only expected to fall into the 60s. There is a chance that
both Rochester and La Crosse will set new record warm low
temperature readings for Monday, October 17th. Below is a look at
those records as they stand currently:

           Record Warmest Low   Year Established   Forecast Low
           ------------------   ----------------   ------------
La Crosse           64                 1994             66
Rochester           62                 1953             64




SHORT TERM...Lawrence
LONG TERM....Lawrence
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