Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 170143

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

Issued at 843 PM CDT Sun Oct 16 2016

We are finally starting to see some ACCAS (elevated showers/storms)
develop west of Mankato,MN moving east northeast. This activity is
occurring in the axis of 1000 MUCAPE and is being driven by a
weak shortwave lifting northeast across southern
Minnesota/northern Iowa. 850mb moisture transport will really ramp
up and focus into the Forecast Area over the next 1-3 hours.
Showers and thunderstorms should become more widespread north of
Interstate 90 in response to this increasing 850 mb moisture
transport. We continue to see the potential for a strong storm or
two capable of producing hail, given the elevated CAPE and strong
effective shear.


.SHORT TERM...(Tonight through Monday Night)
Issued at 210 PM CDT Sun Oct 16 2016

Water vapor imagery showing a strong storm system over the Pacific
Northwest/Intermountain West. RAP analysis showing strong 300mb jet
energy of 110-160kt blowing through northern CA into WY. This energy
will have an impact on our weather here tonight into Monday.

For the time being...high pressure was providing the area with a
glorious Mid-October day. Under mostly sunny skies across most of
the area, temperatures as of 2 pm were in the 60s with even a few
lower 70s across far southwest WI.

Rapid changes expected late this evening/overnight as that
aforementioned energy starts to impact us. A warm frontal boundary
will surge northeast into the area this evening as surface
cyclogenesis takes place on the leeside of the Northern Rockies.
Strong 925-850mb moisture transport/isentropic lift over the front
expected to fire convection mainly along/north of I-90. RAP showing
MUCAPE around 1500J/KG and effective bulk shear in the 60-70kt.
This begs the question of whether the shear will be too strong to
sustain a strong core updraft. Believe there will be a few that will
be able to sustain some larger hailstones but remaining sub-severe.
Appears highest hail threat will be along and north of the I-94
corridor. Otherwise...a very mild night on tap in warm air advection
with overnight lows only dropping back into the upper 50s/middle
60s. In fact, new records may be established for highest lows for
the 17th. See climate section below for details.

Monday afternoon into Monday evening is a concern as models show a
deepening surface low moving northeast into the region from the
Central Plains. This wave will be moving along a boundary in place.
This sets up a very dynamic high helicity/strongly curved hodograph
environment across our area. Fly in the ointment will be amount of
stratus and even some patchy drizzle which is forecast to be in
place, which in turn, will limit CAPE. NAM soundings also show a
fairly strong cap in place across the area, centered 700-750mb. This
would limit surface based storms. On the other hand...if cap is not
as strong and more CAPE is realized, we could be looking at an
increased severe potential including the potential for a few
tornadoes. We will continue to watch this environment very closely.
Otherwise, temperatures on Monday will be much above normal, topping
off in the 70s.

.LONG TERM...(Tuesday through Sunday)
Issued at 210 PM CDT Sun Oct 16 2016

Tuesday through Wednesday...

Looks cooler and dry Tuesday through Wednesday as a weak surface
ridge of high pressure drifts across the region. Look for highs in
the upper 50s to the middle 60s, which is still some 3-5 degrees
above normal.

Wednesday night through Sunday...

The GFS and ECMWF continue to slide a longwave trough through the
area, bringing cooler temperatures with highs in the 50s and lows in
the 30s and 40s into the weekend. The models have also come into
better agreement with timing of this trough moving through, though
the 16.12Z GFS continues to cut off a low over the southern US, but
is much less aggressive in doing so and farther east than previous
runs. The region will mostly remain dry through the period, but it`s
difficult to rule out a shortwave or two working through and giving
the area a couple chances for showers.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 649 PM CDT Sun Oct 16 2016

MVFR stratus will move into the TAF sites this evening with
conditions possibly falling to IFR by late evening into the
overnight. A few showers and thunderstorms are possible tonight
but the bulk of this activity looks to develop north of the TAF
sites. LIFR conditions  in dense fog is possible at KRST by
Monday morning as a moist airmass settles in. Otherwise conditions look
to improve to MVFR by mid morning Monday and remain there through
much of the day.


Issued at 210 PM CDT Sun Oct 16 2016

Very mild conditions are expected through Monday with overnight lows
tonight in the 60s. These overnight lows will be some 20 to 25
degrees above normal. In fact, there is a chance that both Rochester
and La Crosse will set new record warm low temperature readings for
October 17th. Below is a look at those records as they stand

           Record Warmest Low   Year Established   Forecast Low
           ------------------   ----------------   ------------

La Crosse           64                 1994             65
Rochester           62                 1953             64




LONG TERM...DAS/Aegerter
CLIMATE...DAS is the U.S. government's official web portal to all federal, state and local government web resources and services.