Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 241145

Area Forecast Discussion
National Weather Service La Crosse WI
645 AM CDT Fri Mar 24 2017

Issued at 645 AM CDT Fri Mar 24 2017

The band of precipitation lifting northeast across the region has
been waning early this morning in conjunction with weakening 850
mb frontogenesis. Have made some adjustments to pops this morning
to better match trends and high res model output, focusing the
highest rain chances north of I-90 through much of the day.


.SHORT TERM...(Today through Sunday)
Issued at 240 AM CDT Fri Mar 24 2017

On going banded convection running from northern iowa into central
wi associated with a west-east running warm front (sloping
northward), low level jet and ribbon of elevated instability. Meso
models point to the bands shifting north and weakening as the
morning wears on, with hints of this already via radar trends. South
of I-90 could be mostly "dry" this morning through mid afternoon.
Pcpn chances ramp backup in the south as the trough/sfc low approach
and the low level jet kicks back in. North of I-90 then has a better
chance to be dry - or at least small rain amounts.

The nuts and bolts: 500 mb trough moves out of the desert southwest
today, weakening as it lifts across the oh river valley/eastern
great lakes Sat night/Sun. At the sfc, west-east running warm front
sitting around I-90 slowly sinks south over the next couple days,
getting a little push from a high tracking east across southern
Canada. The upper level trough`s accompanying sfc low lifts into
northern IL by 18z Sun. Decent sloping frontogenetic lift along and
north of the front, evidenced by north-south running x-sections,
with the 850 mb jet impinging on this boundary through today
(especially this morning) and into Sat. Aloft, right entrance region
of 300 mb jet streak with enhance the available lift today.

Forcing suggests somewhat narrow bands with the mod/heavier bands of
pcpn. An inch, locally 2 inches still possible over the next couple
days. More on rain amounts and impacts in the HYDRO section below.

Thunder chances look low at this time. Not much instability
indicated (outside of the ongoing convection now) via the GFS and
NAM. What instability is shown is small, skinny and across the far
south. Will continue some small thunder mention today into tonight.
No severe weather anticipated.

Could see a brief wintry mix (freezing rain) later tonight and sat
night north of I-94...mostly a loss of ice in cloud issue. Doesn/t
look like a high probability, but enough of a chance to
hold the mention in the forecast.

.LONG TERM...(Monday through Thursday)
Issued at 240 AM CDT Thu Mar 23 2017

Quasi-zonal (split?) flow anticipated via the GFS and EC for the
better part of next week, although could probably call it non-
nondescript for the local area. Fairly active to the south with a
series of 500 mb shortwave troughs progged to rotate out of the
desert southwest, lifting across the mid mississippi river valley,
headed toward the eastern great lakes. Mostly just south of the
local area. Meanwhile, ripples in the northern portion of the upper
level flow look to hold across southern Canada. Overall, this would
keep the local area "dry", although some glancing blows both north
and south certainly are possible. And, small shifts in the track
could change the forecast from dry to wet, especially if the lows
moving out of the southwest trend a bit more northeast. Will let
forecast blend dictate any pcpn chances for next week for now.

For temperatures, pattern favors temps at or above the late March


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 645 AM CDT Fri Mar 24 2017

Predominantly LIFR/IFR to MVFR conditions expected through the
period. Widespread low stratus will impact KLSE/KRST through the
period as the area remains north of a warm front associated with
low pressure passing to the south. In addition, IFR/MVFR
visibilities are possible within the moist low-level air mass.
Periods of showers will also impact the terminals, which may also
contribute to IFR/MVFR visibilities. At this point, expect the
higher chances for any thunder to remain south of KRST/KLSE.


.HYDROLOGY...Today through Saturday
Issued at 240 AM CDT Fri Mar 24 2017

PWs from 1 to 1 1/4 inches through Sat night with NAEFS pw anomalies
hovering around +2. SREF QPF plumes vary quite a bit, from 1/2 to 2
inches - means around 1 inch. Much of the variability likely stems
from the expected narrow banding of the heavier rains. As is stands,
1 to locally 2 inches still look possibly/probable. Models currently
favoring the higher amounts around the I-90 corridor.

Most of what falls will runoff into the area waterways. Expect some
impact to rivers and streams, obviously dependent on where the rain
bands ultimately setup. Within bank rises likely, but can`t




LONG TERM....Rieck
HYDROLOGY...Rieck is the U.S. government's official web portal to all federal, state and local government web resources and services.