Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 191736
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1236 PM CDT Sun Mar 19 2017

.SHORT TERM...(Today and tonight)
Issued at 225 AM CDT Sun Mar 19 2017

Main forecast concerns today are on whether any showers or isolated
thunderstorms will develop this afternoon into this evening and
breezy southerly winds late this morning through around mid
afternoon.

High pressure exits the region today as a cold front and
shortwave approach from the Northern Plains. A tight pressure
gradient develops across the area today ahead of the front. Plan
on southerly winds of 15 to 20 mph with gusts to around 30 mph at
times in open areas. The cold front then slides in mid afternoon
through mid evening possibly bringing some showers or perhaps
isolated thunderstorms to the area. Atmospheric moisture is a
problem with this feature and there isn`t much to work with. 850
mb moisture transport noses into the area from the west this
afternoon and if we are going to see any shower activity it should
be developing along this feature. Forecast models really struggle
to saturate and the shortwave moving through is pretty weak.
Looking at the NAM and RAP forecast soundings across the area an
air parcel would have to be lifted from around 800 mb to get any
convection/thunderstorms to develop. With only weak forcing moving
through it probably won`t be enough for thunderstorms to develop
but cannot rule it out. Will confine thunderstorms changes to
portions of northeast Iowa and far southwest Wisconsin where
stronger moisture transport is in place this evening and some
mesoscale models are also developing convection in this area.
There is a better signal in the mesoscale models for the
thunderstorms to develop just south of the area. Will have to keep
a close eye on moisture return today, especially in the 850 to
800 mb level. If its stronger, a line of showers and embedded
thunderstorms would move through the area. Any showers and storms
that develop should quickly exit the area by mid to late evening.

.LONG TERM...(Monday through Saturday)
Issued at 225 AM CDT Sun Mar 19 2017

Dry high pressure builds into the region Monday through Wednesday
with dry weather expected with the potential for some lower
relative humidity values at times possibly leading to fire weather
concerns. See Fire Weather Discussion for details. A fast moving
shortwave just clips northeast Iowa and far southwest Wisconsin
late Monday night into Tuesday possibly bringing some light rain
or snow to northeast Iowa. Will keep a low precipitation chance
over this area but if model trend further south, this will not be
needed.

The high departs the region late Wednesday as a deep trough develops
over the southwest conus and lifts northeast towards the Upper
Mississippi River Valley. The first wave of precipitation looks to
arrive late Wednesday night into Thursday morning and with some
colder air near the surface and a warm layer aloft, we could see
some mixed precipitation type concerns across portion of central
into north-central Wisconsin. Confidence wasn`t high enough to
include exact details on precipitation types but will have to keep a
close eye on this timeframe. Precipitation chances continue through
Saturday as the low looks to continue impacting the region.
Depending on the low track, we may see some precipitation type
concerns again.  The the Thursday-Saturday timeframe will be a
period that bears close watching the next few days.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1236 PM CDT Sun Mar 19 2017

Gusty southerly winds will persist this afternoon, especially at
KRST, where gusts to 30 kts are expected. Winds will weaken
towards sunset ahead of an approaching cold front. Winds will
become northerly during the predawn hours behind the cold front,
although there may be a period of light/variable winds in advance
of the front overnight. While a shower could not be ruled out late
today and this evening, confidence is low that any showers will
impact KLSE/KRST, so will not mention at this time. If winds do
become light late tonight, some fog could not be ruled out before
northerly winds bring in drier air, but timing of the front
suggests higher chances will be south of the terminals. Otherwise,
VFR conditions should prevail most of this period.

&&

.FIRE WEATHER...Monday through Wednesday
Issued at 225 AM CDT Sun Mar 19 2017

Dry Canadian high pressure builds into the region Monday through
Wednesday bringing low relative humidity values to the area. Winds
look to be fairly light through this period so not expecting Red
Flag conditions at this time. Monday: Areas north of Interstate 90
across much of western into northern Wisconsin will have the lowest
relative humidity values in the 20 to 30 percent range. Tuesday:
Much of western into central Wisconsin will see afternoon relative
humidity values fall into the 20 to 30 percent range again. It`s
possible they will go even lower across central Wisconsin. Tuesday
will have a little more wind to contend with. Expect northwest winds
of 12 to 13 mph with gusts up to 20 mph possible during peak
heating. Wednesday looks to have the lowest relative humidity
values, ranging from 20 to 30 percent for areas along and east of
the Mississippi River, including central Wisconsin. Again central
Wisconsin could see values drop into the teens. Winds will be fairly
light on Wednesday as the high settles overhead.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM.....Wetenkamp
LONG TERM......Wetenkamp
AVIATION...JM
FIRE WEATHER...Wetenkamp


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