Area Forecast Discussion
Issued by NWS La Crosse, WI

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307
FXUS63 KARX 210538
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1138 PM CST Fri Jan 20 2017

.UPDATE...
Issued at 1138 PM CST Fri Jan 20 2017

Based on WI DOT webcams along the I-90/I-94 corridors and
visibility reports of 1/4 mile in the vicinity of Tomah and Volk
Field, will extend the Dense Fog Advisory to cover Monroe, Juneau,
and Adams Counties. Widespread dense fog will continue elsewhere
across southeast MN, northeast IA, and southwest WI through the
night and into Saturday morning. Visibility reductions to 1/4 mile
or less could result in potentially hazardous travel.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 332 PM CST Fri Jan 20 2017

Little change in our weather pattern will occur in the short term
with a blocking upper ridge extending northward up into eastern Canada
not allowing for much progression of upstream features. Surface obs
and visible satellite imagery early this afternoon showed a broad area
of low stratus/fog has enveloped much of the Great Plains eastward into
the Great Lakes with light moist southeasterly surface flow ahead of
weak low pressure over SD. 20Z water vapor imagery showed one trough
slowly lifting northward across the Upper Midwest, with another upper
level shortwave trough currently across the central plains on track
to lift into our area tonight.

Modest isentropic lift through the lower to mid-levels and forcing from
the upper shortwave itself will help to break out some light rain again
later tonight with the approaching wave and with the downstream ridge
holding strong, this wave will be in no hurry to clear the region. As
a result, some light rain could linger into Saturday night, especially
north of I-94. Still could see a few icy spots north of I-94 due
to cold roads/temps near freezing, but temps have warmed several
degrees from yesterday at this time. In addition to the rain,
fog/drizzle will continue to be a concern during this time with
the weak low- level flow and depth of low- level saturation. Dense
fog is a good likelihood again tonight into Saturday. Have
initially gone with a Dense Fog Advisory from SE MN/NE IA into SW
WI late this afternoon through Saturday morning, and will continue
to monitor for adjustments.

With a warm front trying to briefly lift north into northeast Iowa into
southwest WI on Saturday, afternoon highs will be tricky. Widespread
low clouds may limit the diurnal temp rise, but depending on the progression
of the warm front and erosion of the low clouds into NE IA/SW WI, highs
could reach well into the 40s over parts of SW WI.

.LONG TERM...(Sunday through Friday)
Issued at 332 PM CST Fri Jan 20 2017

Sunday-Monday...Generally dry weather is expected Sunday into Monday
as weak surface/mid-level ridging gradually builds in from the west.
However with seasonably high atmospheric water content (precip water
> 0.50 inches) and continued weak boundary layer flow, low clouds
and/or fog will probably persist. GFS/NAM soundings do indicate some
drying on Monday and a shallower moist layer, but it may be tough to
completely scour out the low cloud cover. Temps will continue to be
mild with highs in the 30s to low 40s.

Tuesday-Friday...The main concern for this period is a strengthening
low pressure system moving from the Central High Plains northeastward
towards the Great Lakes region Tuesday into Wednesday. The GFS and ECMWF
have come into better agreement, but the GFS still remains slightly
farther north. The GEM is more in line with the ECMWF. Some details
in the forecast likely will change, but the general track of the
surface low is across central/southern Iowa into southern Wisconsin/northern
Illinois. Strong upper-level divergence near the left exit region of
a +120 kt jet should help aid in forcing for precipitation, perhaps
moderate to heavy at times. Precipitation types will likely be an issue
once again. Current forecast thermal profiles indicate precipitation
starting as rain or a rain/snow mix Tuesday afternoon then gradually
changing over to all snow from north to south by Wednesday morning.
There does appear to be a potential for a period of heavy, wet snow
across our area Tuesday night, with the GFS showing strong lift through
the DGZ and surface temperatures right around freezing. This will especially
be a concern if the forecast trends more towards the southern track
of the ECMWF. As the surface low passes off to our northeast, convective
flurries/snow showers will be possible Wednesday afternoon through at
least Thursday evening.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1138 PM CST Fri Jan 20 2017

LIFR/IFR ceilings will persist at KRST/KLSE through the period as
low stratus continues to hang tough across the region. Dense fog
with 1/4SM visibility at KRST may improve slightly overnight as an
area of light rain lifts northward. However, conditions should
tank back to 1/4SM once the rain moves north of the TAF airfield.
Visibility at KLSE has been slow to fall this evening, but should
eventually drop at least into the MVFR range overnight and
possibly IFR by daybreak Saturday morning. Some light rain is also
expected at KLSE overnight. Only slight improvements in visibility
are expected the latter half of the period. Light south-southeast
wind will be the rule, turning to the southwest at KRST late in
the period.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory until noon CST Saturday for WIZ042>044-
     053>055-061.

MN...Dense Fog Advisory until noon CST Saturday for MNZ079-086>088-
     094>096.

IA...Dense Fog Advisory until noon CST Saturday for IAZ008>011-018-
     019-029-030.

&&

$$

UPDATE...Rogers
SHORT TERM...Lawrence/JM
LONG TERM...JM/MH
AVIATION...Rogers



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