Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 190317

Area Forecast Discussion
National Weather Service La Crosse WI
1017 PM CDT Fri May 18 2018

.SHORT TERM...(This evening through Saturday)
Issued at 313 PM CDT Fri May 18 2018

At 3 PM, east winds on the southern periphery of a Canadian high
pressure system continued to bring dry air into the Upper
Mississippi River Valley. While the radar and some of the meso
models (ARW, NMM, and HRRR) are trying to produce rain, the air
mass below 600 mb remains rather dry, so we have not been seeing
any of this rain reaching the ground. This trend should continue
for the remainder of the afternoon.

For tonight, we will remain in between low pressure systems. One
low pressure system, currently located over the Mid Mississippi
River Valley, will move northeast into the southern Great Lakes.
Meanwhile, a cold front will remain off to our northwest.

On Saturday, a cold front will move southeast through the area.
As low level moisture pools along and north of this front, there
may be enough instability for scattered showers and isolated
storms to develop across southeast Minnesota and in west-central
and north-central Wisconsin.

.LONG TERM...(Saturday night through Friday)
Issued at 313 PM CDT Fri May 18 2018

From Saturday night through Sunday, the models are in general
agreement that the precipitation will be found along and south of
Interstate 94. With limited instability, only expecting periodic
showers with this wave.

From Sunday night into Monday night, the models continue to differ
on the northern extent of showers. Both the GFS and GEM are
further northwest with the upper level short wave, so showers end
up occurring across much of the area. Meanwhile, the NAM and
ECMWF are further southeast with their upper level short wave and
also have the Canadian high a bit further south, so as a result
they have their rain remaining mainly south of Interstate 90.

From Wednesday through Friday, the models are in general agreement
that a short wave trough will slowly move from the Northern Plains
into the Great Lakes. This system will provide a chance of showers
and storms. With weak 0-3 and 0-6 km shear, not anticipating any
severe weather from these storms.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1017 PM CDT Fri May 18 2018

A tricky forecast heading into Saturday with regard to low cloud
potential, but first we`ll deal with continued VFR conditions the
next few hours. Will have to watch RST for some potential of light
fog development through sunrise within a lighter wind regime ahead
of an approaching cold front, and there are also some small hints
that lower stratus could blossom across northeast Iowa into
southeast Minnesota as well as parts of western Wisconsin as low
pressure passes by to the east. Still, confidence just isn`t very
high, nor is it regarding additional low stratus behind the cold
front currently in place over the Dakotas. Model guidance to
varying degrees hints that said stratus will either envelop the
area tomorrow morning/early afternoon or simply erode as it
approaches. Gut feeling is RST will end up with MVFR ceilings
under some of that stratus, but may see the cloud deck "stall"
with eastward extent after the sun rises, suggesting LSE may end
up mainly VFR with some cumulus development by midday. Given such
weak flow, will have to watch trends closely, but of higher
confidence is that winds will shift from the southeast now to the
northwest and north 10-15 knots on Saturday.




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