Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 151732

Area Forecast Discussion
National Weather Service La Crosse WI
1231 PM CDT Sat Oct 15 2016

.SHORT TERM...(Today through Monday Night)
Issued at 305 AM CDT Sat Oct 15 2016

Quite the active/fast Pacific jet pattern impacting much of the
CONUS through the early work week period, with a series of jet
streaks and upper troughs crashing ashore along the West Coast and
some of that energy translating eastward in our direction. Still
some questions to be answered regarding the eventual impact on our
local sensible weather, as there is some chance we actually may not
end up seeing all that much in the way of precipitation locally
(more on that below). First things first, we must tackle the current
stratus field expanding northward and eastward across the area, with
thin but expansive moisture trapped beneath an impressive elevated
mixed layer emanating out of the central Plains states. Per
satellite trends, really don`t expect that stuff to go much of
anywhere today, with an overall cloudy flavor to the forecast
though quite mild with temps climbing through the 60s to lower
70s (`s still in the upper 50s/low 60s as of 2 am). Could
be even warmer if somehow we can manage to see a few peaks of
sunshine. The bigger question is drizzle potential in that
stratus, and honestly not seeing a big signal with a lack of lift
through the saturated sub-850mb layer and hints of an inverted-V
look to the lower levels. Of bigger question is convective
potential through the late afternoon and evening. Things remain
just crazy capped through much of the day with an impressive EML
intact, but with some cooling progged with the approach of a weak
upper wave/cold front, we may be able to release up to 1000 J/kg
elevated CAPE well east of the Mississippi River after 22Z. If
that does indeed occur over our eastern CWA (as opposed to more
into central/eastern Wisconsin), there is a small risk for a
stronger storm given effective shear of 40-45 knots.

Passage of the cold front should scour the stratus for western areas
late tonight into Sunday morning, with a drizzle threat initially
as we get into a light wind flow/moisture pooling along the
boundary. Should also see a fog threat wherever it does decide to
clear with quick cooling and light winds, with some potential for
widespread dense fog later tonight. As mentioned yesterday, low
stratus won`t be all that far away and with developing return
flow into Sunday afternoon, envision some stratus re-expanding
back northward though fighting a better mixed environment with
northward extent. Bigger story here is another quick uptick in low
level jet forcing and rather impressive moisture transport back
through the region, especially for areas along and north of the
I-94 corridor through late afternoon and especially overnight.
Similar to today, airmass is again very much capped through the
day, with forecast RAOBs showing a loss of capping to the north
after mainly 03Z. NAM profiles seem to be overdone with moisture
return into the area (surface dew points into the upper 60s don`t
seem likely), though elevated CAPE values around 1000 to maybe
1500 J/kg do appear doable in the presence of even stronger
effective shear (45-50+ knots), suggesting a few stronger storms
may be possible north of I-94. Farther south, looking like a
mainly dry and downright mild night for mid October, with lows
only ranging through the 60s!

Final period of interest lies in the Monday afternoon and night time
frame, with increased guidance agreement regarding the approach of a
stronger upper wave and surface reflection along a cold front
extending from western Kansas up through northern Michigan. Still
some timing differences (00Z GFS notably slower) but looking like
areas south of I-90 may remain capped through much of the period
while areas farther north by far stand the best risk for additional
precipitation. Not overly confident on the degree of available
instability at the moment with NAM boundary layer dew points into
the upper 60s again not very credible, though with enough signal for
an additional thunder threat.

.LONG TERM...(Tuesday through Friday)
Issued at 305 AM CDT Sat Oct 15 2016

Much of the mid and late week period continues to look much more
seasonable and mainly dry after our weekend and early week stretch
of downright balmy conditions for this time of year. Pretty good
agreement among medium range guidance for the Pacific "fire-hose"
jet pattern to buckle through midweek, with building ridging along
much of the West Coast and southwest Canada sending downstream
heights falling. That setup should favor some degree of central
CONUS troughing by late week, with associated thermal troughing
dropping our temperatures considerably closer to later October
normals, all while broad low level ridging works through southern
Canada. As alluded to by the previous shift, there are some
questions about how amplified that trough will become with time into
late week, with recent GFS runs much more amplified and actually
attempting to cut off an upper low to our south while the ECMWF
holds steadfast with a more progressive scenario. Given how much
energy will be digging through that trough, have to wonder if the
GFS scenario may be a little more correct (does have some ensemble
support), which could potentially impact our weather toward very
late week. Tough call one way or the other this far out, but lots of
time to watch it unfold.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1231 PM CDT Sat Oct 15 2016

Sfc thru mid level trough continues to move east across the Upper
Midwest early this afternoon. Some drier low level air working east
into the fcst area with this trough/front. This along with diurnal
warming/mixing, cigs rising into MVFR this afternoon, then expected
to rise into the 3k-4k ft range this evening. Moisture/clouds above
925mb moisture then expected to decrease overnight, with skies
becoming mostly clear after midnight. With lighter winds, this sets
the stage for radiational BR/FG formation at the TAF sites in the
08z-15z time period. For now, added 3SM BR at both KRST/KLSE for
this time period. Confidence not quite there yet to add a period of
IFR cigs/vsbys in BR/FG centered on 12z Sun.




SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...BOYNE is the U.S. government's official web portal to all federal, state and local government web resources and services.