Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 182320
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
520 PM CST Sun Nov 18 2018

.SHORT TERM...(Tonight through Monday Night)
Issued at 152 PM CST Sun Nov 18 2018

Quiet out there for the moment with a nice sunny respite underway,
but we`re already eyeing out new player in the game in the form of a
shortwave diving southeastward out central Alberta. That feature
still on track to arrive here late tonight into Monday morning, with
a weak surface wave also progged to develop over western South
Dakota and jaunt east into northern Michigan by midday. Colder air
lurks in the wake of that passing low by Monday afternoon along with
likely widespread stratus (welcome back to the clouds!), but the
bigger story is the potential for some light wintry precip as the
upper wave arrives. Not a ton of overall forcing with the arrival of
the shortwave trough, but continued hints of a narrow axis of weak
but deeper layer sloped frontogenesis should do the trick to provide
enough saturation for some light snow generally north of I-94,
though with any accumulation into our area looking rather light with
maybe an inch up across Clark/Taylor Counties.

Will also have to watch the potential for ice nucleation issues at
times farther north with forecast soundings at times very close to
cloud-top temps around -12C, so can`t totally rule out some light
freezing drizzle, though confidence not overly high. Also can`t rule
out some lighter snow farther south, even toward and south of I-90
given the strength of the upper wave and a good push of lower level
convergence as a cold front swings through the area. All told,
looking continued chilly with cold advection through the afternoon
ensuring another day below freezing, while lower clouds into late
afternoon look to dwindle Monday evening/night as our low level flow
turns more westerly with high pressure just to the west. Could
potentially be another chilly night in some areas over the remaining
snow pack, though flow aloft looks a little stronger and pack will
have aged several days by that time, not to mention there are some
hints that stratus may linger longest across northeast Iowa.

.LONG TERM...(Tuesday through Sunday)
Issued at 152 PM CST Sun Nov 18 2018

Hard to believe it`s already Thanksgiving week, and thankfully our
overall weather looks pretty quiet into Wed-Thu for any travel.
However, still watching the onset of better warm advection aloft
later Tuesday into Tuesday evening. That warming should at a minimum
go into the production of more cloud cover, with some enhanced lower
level convergence/saturation likely along another cold front sagging
south through the area into Wednesday. Can`t rule out some
additional light snow near/north of I-94 as the boundary arrives,
with possibly some freezing drizzle tossed in as well with warmer
cloud top temperatures oscillating between -10 and -14C per forecast
soundings. Will also have to watch that drizzle/freezing drizzle
potential farther south as the boundary sinks toward the I-90
corridor, though much of the moisture looks rather shallow with
southward extent, such that we may fail to meet the 1km required
depth for drizzle production despite some shallow lift.

Clouds are then tricky into Wednesday-Thursday as we really start to
warm aloft. Guidance trends are rather pessimistic over the past few
days with an increasing signal for low level stratus to become stuck
beneath a stout inversion aloft. At the moment, not envisioning much
in the way of any precipitation threat given the shallow nature of
potential stratus, but it is a possible temperature "buster" heading
into Thanksgiving. Something to watch closely.

Otherwise, Friday still on track to bring widespread precipitation
chances back to the area with persistent hints of a stronger wave
advancing out of the central Plains in our direction and a solid
stripe of warm advection ascent/moisture transport pointed into the
region. Pretty decent warm nose aloft should ensure that much if not
all of that precip is of the liquid variety, though can`t rule out a
little snow far north with hints of isothermal profiles near 0C by
Friday evening. Otherwise, forecast confidence takes a big dive into
the weekend with guidance struggling in an active Pacific-driven
pattern but several pieces of energy from Canada also in the mix.
Suffice it to say a blend for some small precip chances (some
possibly of the wintry variety) is the way to go at this point until
we can sort out the details.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 508 PM CST Sun Nov 18 2018

Mid to high level clouds will increase this evening ahead of a
cold front. The front will pass through Monday morning with winds
quickly shifting to the north to northwest. In addition, MVFR
conditions are expected by mid to late Monday morning as a low
stratus deck sinks south behind the front. While a few
flurries/snow showers cannot be ruled out, the higher chances look
to be northeast of KLSE/KRST, so will not mention right now.

&&

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

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...JM



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