Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 280251

Area Forecast Discussion
National Weather Service La Crosse WI
951 PM CDT Tue Sep 27 2016

Issued at 925 PM CDT Tue Sep 27 2016

Yep...definitely feels like fall. Temps here at the office
sitting around 47 degrees with a steady light rain the past few
hours, with those showers pivoting southward across a good chunk
of the CWA the past few hours. Those come courtesy of a decent
shortwave diving south through the area, on the westward flank of
quite the closed low spinning over Lake Superior. Per radar and
near term guidance trends, looking like all of the showers will
exit the region by around 06Z with loss of forcing, leaving a
good deal of lower stratus in their wake as thicker sub-900mb
moisture seen just to our north oozes southward within broad low
level cyclonic flow. The current forecast has this trend well in
hand, with only cosmetic changes required heading into the night.
We will have to watch these clouds carefully, as there is a good
shot much of tomorrow may end up just plain cloudy.


.SHORT TERM...(Tonight through Wednesday)
Issued at 230 PM CDT Tue Sep 27 2016

Closed 500 mb low/trough sinking southward across the northern Great
Lakes early this afternoon...with models in lock-step taking it
south/southeast to across the oh river valley by 00z tonight. Area
of showers firing in response to the closed/stacked low pressure
system, with a strong bit of upper level energy having a large hand
in its production. The area of showers/forcing has reached the I-94
corridor later this afternoon, sinking south of I-90 by late
afternoon/early evening. The bulk of the rain looks to drop south
between 06-08z. The showers will be widespread east of the
Mississippi river, more scattered west of there. Amounts will be on
the light side, mostly 1/10 of an inch or less.

A few showers remain possible Wed, mostly east of the Mississippi
river. Despite the bulk of the forcing mechanisms having vacated the
local area, the low level lapse remain favorable, there hints in the
GFS/NAM of weak (~50 J/kg) of instability, and the proximity of the
low (still close by) also support the small chances.

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 230 PM CDT Tue Sep 27 2016

The main concern for the beginning of this period is if the closed
low will retrograde and affect the forecast area. The ECMWF has
retrograded the system consistently over several runs, while the GFS
only recently came into agreement with this pattern. Assuming this
happens, the next issue is how far west the associated precipitation
will make it. The 27.00Z ECMWF has showers throughout the forecast
area on Saturday, while the 27.06Z GFS keeps everything just to the
east. However, the 27.12Z GFS came into a bit more agreement with
the ECMWF, with rain in the area east of the Mississippi River. The
focus then shifts to a trough and moving into the area early next
week bringing another chance of showers and storms, though some
model timing differences still exist with this system.


.AVIATION...(For the 06Z TAFS through 06Z Thursday morning)
Issued at 951 PM CDT Tue Sep 27 2016

Showers are exiting the area but lower stratus is quickly
following, expected to overtake LSE/RST the next couple of hours.
Overall MVFR to higher end IFR ceilings are expected (lowest for
RST), with stratus slowly mixing up into more of a broken cumulus
cloud deck into the afternoon hours on Wednesday. Winds will also
become a bit gusty from the north Wednesday afternoon, with gusts
of 20-25 knots expected, highest for RST.




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