Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200530
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1130 PM CST Thu Jan 19 2017

.UPDATE...
Issued at 559 PM CST Thu Jan 19 2017

Based on current observations across north-central IA and good
agreement between the RAP/HRRR short-term visibility plots, will
adjust the start time to the Dense Fog Advisory to begin at 8 PM
CST. Also added all southeast MN counties. Still looks like the
thickest fog will remain west of the MS River through the night,
but will monitor observations throughout the evening for possible
extension into portions of WI.

&&

.SHORT TERM...(This evening through Friday)
Issued at 310 PM CST Thu Jan 19 2017

The widespread fog has gradually lifted through the late morning and
early afternoon. Meanwhile, low clouds along with light rain have been
spreading northward across eastern Iowa within region of enhanced low-
level moisture transport ahead of an upper low slowly lifting northeastward
out of the central Plains. The light rain will continue to spread northward
into the area late this afternoon and evening. While most areas are
expected to be above freezing, areas north of I-94 stand the best chance
for some freezing rain/icy roads with temps near freezing and
cold roads. Have issued a Freezing Rain Advisory this evening into
Friday morning for Clark/Taylor counties to account for this. Will
have to watch surface/road temps closely this evening for any
possible adjustments to this area.

In addition, outside of the precip, there will likely be fog again and
some drizzle as well into Friday with NAM soundings indicating deep
saturation to around 1.5 km in depth along with some weak warm advection
and light boundary layer flow. As a start, have included northeast Iowa
counties in a Dense Fog Advisory from midnight tonight until noon Friday,
where precip is expected to be lighter and confidence is highest. This
could need to be expanded through the evening or overnight. Areas of
Clark/Taylor counties that have been slow to clear, and thus have warmed
little today, may see fog return quickly this evening, even before the
precip arrives, so that will be another area to watch.

.LONG TERM...(Friday night through Thursday)
Issued at 310 PM CST Thu Jan 19 2017

Another upper shortwave trough will lift northeastward into the Upper
MS Valley Fri night in response to amplified upper level ridging/blocking
downstream into eastern Canada. The strongest mid-level forcing/Q vector
convergence will shift from Iowa into northwestern WI bringing some
light rain into the region, with boundary layer temps largely above
freezing. With the relatively weak forcing based on the placement
of the upper wave via the GFS/ECMWF, it may be a very light rain/drizzle
scenario. Also, with plenty of boundary layer moisture and modest
low-level warm advection, may still have some fog issues to deal
with as well. Not much change is expected into Saturday with low
stratus persisting along with some residual light rain/drizzle
from the slowly moving upper wave. Temps on Saturday will be mild,
but how warm we get likely will be impacted by the degree of low
stratus/fog across the area.

The disjointed blocking upper level flow pattern will continue into
early next week with little change in air mass. As a result, temps
will remain seasonably mild with generally cloudy under weak surface
ridging.

The next time frame to watch will be later Tues/Wed with both the 19.12Z
GFS/ECMWF indicating an upper shortwave trough/surface low ejecting
out of the Rockies towards the Upper MS Valley. It`s too early to have
confidence in the track, amounts, and thermal profiles/precip types
yet, but this will be a time to watch. For now based precip types
on surface temps as a start.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1130 PM CST Thu Jan 19 2017

IFR/LIFR conditions to dominate both KLSE/KRST through the period.
At KRST, ceilings not likely to budge above 300 ft agl, dropping
as low as 100 ft agl in dense fog tonight into Friday morning with
prolonged reductions in visibility to 1/4SM or less. Only slightly
better conditions expected at KLSE with ceilings in the 500 to
1000 ft agl range through 20.10Z, dropping to around 300 ft agl
thereafter. That said, dense fog may not quite make it to KLSE,
so will keep visibility reductions at 3SM. However, amendments to
go lower are certainly a possibility. Expect little to no
improvement Friday afternoon before conditions tank once again
Friday evening. Winds through the period will be light and
variable with a slight southeast directional preference.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Freezing Rain Advisory until 9 AM CST Friday for WIZ017-029.

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

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

&&

$$

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



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