Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 141801
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
101 PM CDT Sat Apr 14 2018

.UPDATE...
Issued at 1257 PM CDT Sat Apr 14 2018

Have opted to upgrade some more counties across southeast
Minnesota into northeast Iowa to a winter storm warning. The main
concern will be with the strong winds producing blowing snow and
significantly reducing the visibility. Near white-out conditions
will be possible at times once the wintry precipitation completely
changes over to snow. These conditions will primarily be tonight
into early Sunday morning as this will be the period with the
strongest winds. Wind speeds will start to diminish Sunday morning
with a corresponding reduction in the amount of blowing snow.

&&

.SHORT TERM...(Today through Sunday)
Issued at 300 AM CDT Sat Apr 14 2018

>>> Nuts and Bolts <<< : without getting too long winded/overly
verbose...current convection/pcpn tying directly into the low level
jet/moisture transport, piece of upper level energy kicking ahead of
the main trough, and south-north sloping frontogenetic region with
tight thermal profile north of the system`s warm front. Shortwave
and branch of low level jet shifts east early this morning while the
frontogenetic region and north east-west running 850 mb jet holds
across the local. Main pcpn band will shift east, but there will
still be areas/intermittent pcpn to content with.

The parent upper level trough/500mb closed low moves east/northeast
across the local area by late this afternoon/night - with its
leading edge serving as another focus for more widespread/higher
intensity pcpn. Pcpn bands will also persist in the deformation
region northwest of the low.

The shortwave lifts northeast early Sunday morning. Enough wrap
around moisture/upper level support to continue areas of pcpn
although qpf/intensity will be much lighter.

>>> Pcpn types and amounts <<<: max wet bulb temps still coldest in
the EC, but not as big of spread between that and the GFS/NAM as in
previous days. By 00z this evening the 0 tw line shifts into central
WI down into northeast IA, then mostly southeast of the local area
12z Sun.

North-south running x-sections via the NAM/GFS/EC all point to a
loss of ice today continuing into tonight. The saturation gradually
taps into the colder air a loft on Sunday. That said, by this
evening cold air is already pushing in northwest of the low - with
the soundings suggesting that while there may not be ice in the top
of the cloud, ice would be introduced into the cloud layer toward
850 mb. Interesting feature. In addition, any convective-type
element would certainly stretch the saturation into the ice bearing
layer. Models are having a hard time here, not capturing the
convective elements - thus producing more freezing rain when sleet
or a sleet/freezing rain/etc mix would be more appropriate. Will add
more sleet and reduce freezing rain threat a bit to account for
this.

For types, mainly snow north of I-90, with a wintry mix of
sleet/freezing rain/snow in that corridor today into tonight.
Farther south rain will become more of a wintry mix late this
afternoon/evening. Most can expect snow on Sunday.

Snow/sleet accumulation generally 6 to 12 inches north of I-90, with
localized amounts approaching 14 north of highway 29 in Wisconsin.
About 1 to 4 for northeast IA/southwest WI. Icing from a glaze to
around 1/4" along I-90 possible.

All amounts still hold a fair amount of uncertainty as ptype can
fluctuate quite a bit today and tonight.

>>> Wind <<< : wind is going to remain a factor through the weekend
with the tight pressure gradient not showing much relaxing until
later in the day Monday. Strongest winds will be today into this
evening.

.LONG TERM...(Monday through Friday)
Issued at 300 AM CDT Sat Apr 14 2018

Consistent signal in the models with driving a shortwave trough from
the desert southwest on Tue to across the local areas late tue
evening through Wed. Both the GFS and EC take the associated sfc low
through IA and into southern WI, dragging the main deformation
region across southern MN into northern WI. Some differences with
how much cold air will be in place and wrapped into the system -
obvious impacts on pcpn type and potential amounts. As it sits now
accumulating snows would be possible mostly north of interstate 94
(several inches) with mainly rain south of there. Plenty of time for
shifts in location/timing along with the thermal profile. It`s a
system that bears a close watch as winter keeps us firmly in its
grasp.

Taking a quick look at next weekend - the GFS and EC suggest another
storm system could bring widespread precipitation to the region. At
this time, temperatures would favor mainly rain.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1151 AM CDT Sat Apr 14 2018

With the main area of surface low pressure still to the southwest
of the region, still primarily be impacted by waves of
precipitation riding north over the warm front on the isentropic
up glide. These continue to be a wide variety of precipitation
types but should gradually transition to more snow as the low
moves slowly east allowing for more cloud ice to be introduced.
Until then, will hold with the wintry mix this afternoon for both
airports with primarily snow expected tonight into Sunday
morning. With the strong northeast winds, blowing snow will also
be a concern for KRST once there is enough snow to move around.
With the slow movement of the storm system, conditions will be
slow to improve with IFR for most if not all of the period, with
maybe some slight improvement in the visibility for KRST Sunday
morning.


&&

.HYDROLOGY...(Today through Sunday)
Issued at 300 AM CDT Sat Apr 14 2018

Rainfall totals from Friday and Friday night have been in the 1/2 to
1 1/2 inch range across the area, with precipitation from Wabasha to
Jackson county and northward mainly falling in the frozen form.
Rises on area rivers and stream from this rainfall so far have been
within bank rises.

Additional precipitation amounts of around an 1 inch are expected
today through Sunday. There will be a lull in the precipitation
across much of the area through mid morning. By the time the heavier
precipitation returns later this morning into this afternoon,
temperatures aloft across much of the fcst area trend cold enough
for the precip to mainly be wintry types. Much of the additional
precipitation from noon today thru Sunday is expected to fall as
freezing rain, sleet or snow, which would run off at a later time,
reducing the threat of flooding in the near-term.

Please continue to monitor forecasts closely, especially if you have
interests along or live near a river or stream.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 7 PM CDT Sunday for WIZ061.

     Wind Advisory until 1 PM CDT this afternoon for WIZ061.

     Winter Storm Warning until 7 PM CDT Sunday for WIZ017-029-
     032>034.

     Winter Weather Advisory until 7 PM CDT Sunday for WIZ041>044-
     053>055.

     Winter Weather Advisory until 1 PM CDT this afternoon for WIZ017-
     029-032>034.

MN...Winter Storm Warning until 7 PM CDT Sunday for MNZ079-086>088-
     094-095.

     Winter Weather Advisory until 7 PM CDT Sunday for MNZ096.

     Winter Weather Advisory until 1 PM CDT this afternoon for MNZ079-
     086>088-094-095.

IA...Winter Weather Advisory until 7 PM CDT Sunday for IAZ019-029-030.

     Wind Advisory until 1 PM CDT this afternoon for IAZ018-019-029-
     030.

     Winter Storm Warning until 7 PM CDT Sunday for IAZ008-009-018.

     Winter Weather Advisory until 7 PM CDT Sunday for IAZ010-011.

     Winter Weather Advisory until 1 PM CDT this afternoon for IAZ008-
     009.

&&

$$

UPDATE...04
SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...04
HYDROLOGY...RRS



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