Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 240429

Area Forecast Discussion
National Weather Service Green Bay WI
1129 PM CDT Sun Apr 23 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 309 PM CDT Sun Apr 23 2017

The latest rap analysis and satellite/radar imagery show a cold
front dropping southeast from Merrill to Oshkosh early this
afternoon.  As winds turned to the northeast behind the front,
temperatures fell 5 to 10 degrees at Green Bay and Appleton.
Meanwhile, scattered light rain and snow showers continue to pass
over northern WI, north of Merrill and Antigo.  Quite a temperature
difference between Land O Lakes where clouds and precip have kept
temperatures in the middle 30s, and Wautoma where the mercury has
reach 70 degrees.  As the front waffles first south tonight and then
north on Monday, cloud trends and relative humidities are the main
forecast concerns.

Tonight...The cold front will settle across southwest Wisconsin to
northern Illinois.  However, this front will remain shallow, since
moderate return flow will already start ramping up at 850mb during
the evening.  As a result, do not think the cloud cover will make it
that much further south, and trended more optimistically with the
sky cover.  Regardless, the clouds should retreat north overnight as
cirrus invades from the west.  With a brisk east wind, temps falling
to near 30 in the north to the upper 30s over the southern Fox

Monday...The cold front will retreat northward as winds veer to the
southeast with low pressure moving across the central Plains.  Very
dry air over the mid-Mississippi Valley will return northward, which
should provide high temps in the 60s and low relative humidities.
Mid and high clouds will increase in western areas through the
afternoon, but the airmass is too dry below 12kft for precip
chances.  Winds, however, will become gusty, with some gusts up to
30 mph possible.

.LONG TERM...Monday Night Through Sunday
Issued at 309 PM CDT Sun Apr 23 2017

Active weather expected for the rest of the week, with potential
for at least two significant synoptic scale weather systems. The
jet energy for these systems is still out over the Pacific Ocean,
so the models are still having some trouble coming up with a
consistent track for these systems, which of course is important
for bit precipitation type and amounts.

The first system arrives Tuesday afternoon or evening as a strong
upper jet lifts northeast from southeastern Colorado with some
weaker jet energy moving across the northern Plains. These
systems phase to some degree and produce several waves of low
pressure that move northeast along a nearly stationary front from
Oklahoma to Lake Michigan. The models are a bit further west with
these systems than they were yesterday, which makes snow in
northern Wisconsin less likely. There should be periods of
significant rainfall Tuesday night through Thursday, which will
probably result in some minor flooding, as several rivers and
streams are currently near or above bankfull.

Another system looks to arrive Saturday or Sunday, but there is
even less model agreement with that system. The GFS and ECMWF do
agree that it moves well west of the forecast area, which could
bring some heavy rains and then a threat of severe storms if it
unfolds as depicted.

.AVIATION...for 06Z TAF Issuance
Issued at 1124 PM CDT Sun Apr 23 2017

The cold front that arrived yesterday will lift to the north as a
warm front today. The main effect of this frontal passage will be
increasing southeast winds, which will gust to 20 to 25 knots at
most locations. Mainly middle and high level clouds are
anticipated through the TAF period, along with VFR conditions.

LLWS is expected to develop Monday evening, as surface winds
decrease and winds aloft increase to 35 to 45 kts.


Issued at 309 PM CDT Sun Apr 23 2017

As the cold front lifts back north as a warm front across the
western Great Lakes on Monday, warmer temperatures will return along
with gusty southeast winds and low relative humidities. Near
critical fire weather conditions are possible on Monday afternoon as
temperatures rise into the 60s, winds gust to 20 to 30 mph,
and relative humidities bottom out in middle to upper 20s.



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