Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 160445
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1145 PM CDT Sun Oct 15 2017

.SHORT TERM...(Tonight through Monday)
Issued at 315 PM CDT Sun Oct 15 2017

Forecast focus for tonight is on the frost potential.

First though, upper level shortwave dropping across the northern
plains this afternoon, sliding it across the region tonight. Mostly
mid level saturation with the feature, but it has resulted in a
smattering of light pcpn - per sfc obs. HRRR/Hopwrf runs suggesting
this trend would continue into northern WI later this evening, and
looks reasonable. Not expecting measurable, and will hold north of I-
94.

The bigger, potentially widespread impact for the local area is
frost.

PRO`s:
* colder air in place: cold highs (mostly near 50) won`t have far to
  go to drop into the low to mid 30s.
* light sfc winds: bufkit soundings point to shallow decoupling
  (under 600ft)

CON`s:
* clouds: shortwave is bringing down a mid level deck that will
  cover at least the northern 2/3rds of the forecast area for a few
  hours this evening/overnight. Thus, cutting into radiational
  cooling time.
* near sfc winds: while soundings and guidance suggest decoupling
  and relatively light sfc winds, just off the deck (by 600 ft) its
  blowing +10 kts. How much decoupling really occurs and/or how much
  stirring/turning results isn`t certain.

Not a perfect scenario or "slam dunk" for widespread frost tonight.
If extent, time of coverage in the clouds...and winds do decouple
with little influence from a loft...areas of frost a lot more
likely. Conversely, if winds a bit higher and/or clouds linger...not
so much.

All that said, per coordination with surrounding offices will hoist
a Frost Advisory for a central/northern WI. Again, some
contingencies with that, but certainly low lying/shelter areas face
a pretty good risk for frost later tonight. Might need to expand the
adv into parts of southeast MN and northeast IA.

.LONG TERM...(Tuesday through Sunday)
Issued at 315 PM CDT Sun Oct 15 2017

After a spate of wet days, a stretch of dry and mild conditions is
on tap for next week - a nice break and a great opportunity to catch
some of those fall colors.

After the passage of the upper level trough east this evening, both
the GFS and EC have been insistent of moving to a zonal/ridging
upper level flow pattern for the better part of the new week. A
couple ripples in the flow around mid week, but hold mostly across
southern Canada and not much moisture to work with. Should stay dry
through Friday. Come Saturday, both the EC and GFS take an upper
level trough/sfc front combo east across the plains and through the
Upper Mississippi River Valley. Would see at least some scattered
showers (isolated storms?) in this scenario.

For temperatures - a return to above normal readings as the upper
level ridging becomes more pronounced. NAEFS 850 mb temp anomalies
generally +1/+2, with Friday looking like it would be the mildest
day. Highs in the mid 60s to low 70s looking likely for Tue into
Sat.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1145 PM CDT Sun Oct 15 2017

The mid level clouds continue to move east and will be past both
airports by or shortly after 16.06Z and plan to start both
forecast with just some remaining scattered clouds. Skies will
clear out by sunrise Monday with southwest wind under 10 knots for
much of the day with surface high pressure centered over Missouri
and Arkansas. As the high moves off to the east Monday evening as
a cold front advances onto the High Plains, forecast soundings
from the 16.00Z NAM suggest the potential for some low level wind
shear. Winds above the surface ahead of front look to increase
into the 40 to 45 knot range with surface winds of 10 knots or
less. This looks to be very late in the forecast period so will
not include it for now, but this will be needed if later model
runs continue to show this trend.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Frost Advisory until 9 AM CDT Monday for WIZ017-029-034-042>044.

MN...None.
IA...None.
&&

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...04


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