Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 272328
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
628 PM CDT Thu Apr 27 2017

.UPDATE...
Issued at 628 PM CDT Thu Apr 27 2017

Stratus - the bane of a forecaster`s existence sometimes. Per
satellite trends, clouds have gone nowhere today, courtesy of both
low level chilly air (for some diurnal component) and pronounced
low level cyclonic flow with low pressure departing into southeast
Ontario. Given recent trends, have pushed back the clearing time
for many areas (save for the far south) by a few hours, and may
need to go a big longer. However, recent RAP runs seem to have a
good handle on the situation, with increasingly anticyclonic flow
south of I-90 through the night likely helping erode the stratus,
though am intrigued to see what happens farther north where
cyclonic flow remains intact overnight. Can envision some low
clouds hanging tight for much of the night north of I-90.
Regardless, clouds will obviously impact overnight lows but
planning no changes to current Frost Advisory as current temps are
already in the mid 30s to lower 40s, and it won`t take but a few
hours of clearing for readings to dip.

&&

.SHORT TERM...(Tonight through Friday night)
Issued at 247 PM CDT Thu Apr 27 2017

GOES Water Vapor imagery this afternoon showing the mid-level wave
responsible for snow burst east of the Mississippi River this
morning now exiting into northeast WI. Radar still showing some
lingering rain/snow shower activity across the area in steep low
level lapse rate/cold cyclonic flow. Temperatures this afternoon
were chilly with readings in the 30s. West winds 10-20 mph were
adding a bite to the chilly air.

For tonight, a ridge of high pressure builds in from southwest to
northeast for clearing skies allowing for good radiational cooling
given light airflow. Depending on how much decoupling takes place,
will likely see some freezing temperatures across the area. And,
given the advanced blooming of vegetation across some of the area,
concerned for some plant/bloom damage. As such, have frost headlines
posted for areas along the Mississippi/Wisconsin Rivers where
progression of Spring/blooming has advanced.

Models continue to show a mid-level wave/weak surface low rippling
northeast across IA/IL Friday afternoon into Friday night. Fairly
strong frontogenesis noted by the NAM/GFS centered around 700mb
sliding through the region. This should be sufficient for isolated
to scattered showers south of I-94, more numerous south of I-90.
Otherwise, looks a bit warmer for highs with readings in the upper
40s/lower 50s. Friday night may need frost headlines again for
portions of the area as temperatures dip into upper 20s to the
middle 30s.

.LONG TERM...(Saturday through Thursday)
Issued at 247 PM CDT Thu Apr 27 2017

Looks like a dry start to Saturday but then rain chances spread south
to north into the area through the day ahead of cyclogenesis over
the southern Plains. Otherwise, plan on increasing clouds with highs
in the upper 40s to the middle 50s.

Strengthening low pressure moves out of the Southern Plains toward
the region Saturday night through Monday for an increasingly wet
period. GFS and NAM still showing precipitable water values in the 1-
1.25 inch with a wide-open gulf tap. Right now, looking at rainfall
from Saturday night through Sunday in the 1/3 to 1 inch range with
potentially another 1/2 to 1 inch through Monday. See hydrology
section below for impact on area rivers. Otherwise, looks like a
cold rain with highs Sunday and Monday mainly in the 40s. Look for
mixing of the rain with snow later Monday night as column cools with
low becoming vertically stacked.

Cool cyclonic flow aloft continues through Tuesday for a chance of
showers as highs top off in the upper 40s to the upper 50s.

Temperatures slowly rebound Wednesday and Thursday with that closed
low filling/moving off to the east. Still a couple weak waves
rippling through we`ll have to keep an eye on for slight shower
chances. Right now, they don`t look too impactful.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 628 PM CDT Thu Apr 27 2017

Stubborn and widespread stratus remains draped across the region,
but is gradually thinning on its western and southern fringes the
past few hours. Ceilings are MVFR just about everywhere and should
remain that way through late evening and early overnight, as
clouds very slowly continue to erode eastward. At the present
time, it appears RST will see some clearing toward 06Z while LSE
will likely wait until 07-08Z per current trends. However, there
is a chance that clouds could take even longer to clear,
especially given plenty of remaining low level cyclonic flow near
and north of I-90 overnight, and it`s not impossible that MVFR
stratus could sneak back southward later tonight for a time. Even
if that does occur, a return to VFR conditions is still expected
everywhere on Friday, as mid and high clouds thicken through the
day. Westerly winds 10-15 knots this evening will diminish
overnight and then become light from mainly the north on Friday.

&&

.HYDROLOGY...(Concerning rainfall this weekend)
Issued at 247 PM CDT Thu Apr 27 2017

Looking at another very wet weather system moving through the region
Saturday night through Monday. Right now looking at 1 to 2 inch of
rainfall through the period. Plan on river rises but not
anticipating any flooding at this time.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Frost Advisory from 1 AM to 8 AM CDT Friday for WIZ041-053>055-
     061.

MN...Frost Advisory from 1 AM to 8 AM CDT Friday for MNZ088-096.

IA...Frost Advisory from 1 AM to 8 AM CDT Friday for IAZ011-030.

&&

$$

UPDATE...Lawrence
SHORT TERM...DAS
LONG TERM....DAS
AVIATION...Lawrence
HYDROLOGY....DAS


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