Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 272334

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

.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 00Z TAFS through 00Z Wednesday evening)
Issued at 635 PM CDT Tue Sep 27 2016

Quite the upper level low continues to spin over Lake Superior
this evening, with another wave of deeper moisture sliding south
through the area and resulting in a band of showers crossing much
of the region through late evening. Per upstream trends, MVFR
conditions appear much slower to develop as we initially have
quite the dry airmass to overcome, though can`t rule out a brief
period of MVFR conditions during the showers at LSE. Still looking
like we will see a better shot at some lower stratus arriving late
tonight into Wednesday morning, with IFR ceilings possible at RST.
Heading into the afternoon, do expect to see ceilings gradually
lift with some scattering out of clouds late in the day. Winds
will become a little gusty from the north to northwest through the
night and especially from midday Wednesday onward through the
early evening hours.




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.