Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 271120

Area Forecast Discussion
National Weather Service La Crosse WI
520 AM CST Sun Nov 27 2016

.SHORT TERM...(Today and tonight)
Issued at 300 AM CST Sun Nov 27 2016

Most immediate concern early this morning is areas of dense fog
across much of MN into northeast IA and central/northern WI. Many
surface observations in these areas already reporting visibility
restrictions to 1/2 mile or less and with weak flow/several hours
before sunrise, expect dense fog to persist through mid-morning. A
Dense Fog Advisory is in effect for these areas through 9 am.
Further expansion of the advisory appears unlikely, but will
continue to monitor observational trends for that possibility.

Once fog dissipates later this morning, attention turns to the
strong Eastern Pacific trough now moving into the intermountain
west. A lee surface cyclone will develop across northeast CO by
18Z today in response to this wave and then lift to near the
Dakotas/MN border region by 12Z Monday. Dry/warm conditions will
be the rule through 21Z this afternoon with temperatures once
again rising into the 40s to near 50 degrees. Then expect a band
of rain showers to move quickly northward late this afternoon into
the evening along the mid-level warm front. Although model
instability is still only a couple hundred J/kg of MUCAPE
throughout the atmospheric column, cannot completely rule out
thunder chances, especially given strong forcing. As such, will
keep isolated thunder mention.

Copious moisture with this system with PWATS approaching one inch
will result in rainfall amounts overnight around a half inch,
possibly nearing three quarters of an inch in some places that see
periods of moderate rain. In addition to the rainfall, expect
strong southerly winds overnight, gusting at times to between 30
and 35 mph. Cloud cover and wind will keep low temperatures
tonight elevated in the upper 30s to lower 40s.

.LONG TERM...(Monday through Saturday)
Issued at 300 AM CST Sun Nov 27 2016

Warm advective rainfall band will be north of the forecast area by
daybreak Monday morning with just scattered lingering showers
through the morning. Then, re-development of showers/isolated
thunderstorms are possible Monday afternoon, especially east of
the MS River, as the cold front swings across the region. An
additional tenth of an inch of rain is possible for these areas.
Prior to the cold frontal passage, expect a very warm day with 925
hPa temperatures peaking between +7 and +10 Celsius, resulting in
afternoon highs well into the 50s for most areas.

The low pressure system then stalls across MN as it occludes
on Tuesday, although most of the area should remain in the dry
slot. Wrap around precipitation chances then return Wednesday
into Thursday as the surface low moves quickly into the Great
Lakes region in response to a kicker short-wave dropping south
from the Pacific Northwest and into the Great Basin. With 925 hPa
temperatures dropping below freezing, precipitation type will be
dependent on surface temperatures. Therefore, best chances for a
rain/snow mix or all snow will be in the overnight hours. Little
to no snow accumulation is expected at this time.

Expect a return to dry conditions Friday into Saturday as broad
surface high pressure builds across the region. Temperatures will
be cooler with daily highs in the 30s, which is closer to early
December normals.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 520 AM CST Sun Nov 27 2016

MVFR/IFR fog across portions of the area will lift/dissipate through
the mid morning hours and diurnal warming and increasing mixing with
increased gradient winds in the sfc-850mb layer spread across the
area. A period of VFR then expected at both TAF sites for the late
morning thru mid afternoon hours. SE winds will increase across the
area during this time as the pressure gradient continues to tighten.

Deeper moisture and increasing lift then spread into/across the area
late this afternoon/evening, with vsbys becoming MVFR in SHRA/BR and
cigs dropping to MVFR/IFR for tonight as the deeper moisture spreads
across the area. Isolated TSRA also possible across the area
tonight, but given the expected isolated coverage and some timing
uncertainties, left this mention out of both KRST/KLSE TAFs for now.
Pressure gradient to continue to tighten for tonight, with SE winds
15-20kts G20-30kts expected much of tonight into Mon morning.


WI...Dense Fog Advisory until 9 AM CST this morning for WIZ017-029-

MN...Dense Fog Advisory until 9 AM CST this morning for MNZ079-

IA...Dense Fog Advisory until 9 AM CST this morning for IAZ008-009-



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