Area Forecast Discussion
Issued by NWS Green Bay, WI
FXUS63 KGRB 270438
Area Forecast Discussion
National Weather Service Green Bay WI
1138 PM CDT Sun Mar 26 2017
Updated aviation portion for 06Z TAF issuance
.SHORT TERM...Tonight and Monday
Issued at 318 PM CDT Sun Mar 26 2017
The latest RAP analysis and satellite/radar imagery show low
pressure spinning along the Illinois/Wisconsin border early this
afternoon. Rain showers continue to wrap around the low across much
of eastern WI. Where its not raining, periods of drizzle are
occurring into north-central WI. Visibilities improved with the
arrival of more persistent showers, but dense fog does exist in
close proximity to the surface low. Looking upstream, broken clouds
prevail all the way into eastern North Dakota. As the low lifts
northeast, precip trends are the main forecast concern.
Tonight...Low pressure will be moving northeast from southern Lake
Michigan to Lake Huron tonight. The most persistent showers will
likely occur over northeast Wisconsin during the evening where the
warm conveyor belt wraps around the upper circulation. Progged
soundings indicate that saturation remains pretty deep up to 700mb
for most areas through the night though, so even if showers have the
highest coverage over the northeast, cannot rule out isolated
showers and/or areas of drizzle elsewhere. Winds will lighten a bit
through the night, which will support lowering visibilities with the
ample moisture in place. However, dense fog appears only possible
near the center of the surface low, that will pass southeast of the
area. So think we may escape without a dense fog advisory, though
it may be close along the lakeshore. Without any semblance of
temperature advection in addition to the widespread low clouds,
expect little fall of temperatures tonight. The warmer temperatures
should confine any freezing precip right near the U.P. border, if
there is any.
Monday...The upper low will exit the region, but will see a weak
shortwave move across northern WI and the Upper Peninsula. This
shortwave will bring a chance of showers, but coverage should be
limited due to weak forcing. Otherwise, cloudy conditions should
prevail for much of the day with little dry air to push out the
moist airmass. North-central WI has chance for partial clearing
late in the day behind the shortwave. Highs will return into the
low to mid 40s.
.LONG TERM...Monday Night Through Sunday
Issued at 318 PM CDT Sun Mar 26 2017
After wet period across the area, the long term will start off on
a drier note, but another system at the end of the week will
bring wet/wintry weather back as another low pressure system
tracks across the Great Lakes. No drastic temperatures swings are
expected, with near to above normal readings.
For Monday night, lingering light showers or sprinkles are
possible as low pressure passes across the Ohio Valley, a mid-
level trough passes across Lake Superior, and a departing upper
jet Monday evening is quickly followed by an approaching upper jet
overnight into Tuesday morning. Think slight chance pops will
cover for the evening hours. Drier air works into the area by
Tuesday, so dry conditions are expected. Tuesday looks to be the
best chance to see some sunshine this week, but forecast
soundings are showing some lingering moisture both at low and mid-
upper levels which could lead to some clouds. Tuesday also looks
to be the warmest day of the week, with highs in the upper 40s to
lower 50s for most locations.
Surface high centered over northern Ontario early Wednesday will
extend/shift south and east into the Great Lakes on Wednesday.
The surface high along with mid-level ridging will provide for a
dry day. An impressive moisture push from the west and southwest
ahead of the next low pressure will bring mostly cloudy to the
area by afternoon as a thick mid layer cloud deck is expected,
with some lower clouds possible too.
Dry weather looks to hold on until early Thursday morning, then
all eyes will be on an approaching low pressure system. The mid-
upper closed low will eject out of southwest U.S. during the day
on Wednesday, then be on our doorstep Thursday morning (GFS a
little slower). The GFS remains farthest south with the system
and only brushes central and east central WI with some precip.
ECMWF/Canadian remain farther north. Other smaller scale
differences exist, especially with where the deformation band will
set up on Friday.
Temp profiles will be critical as the precip arrives on Thursday
(and through the whole day if current trends continue), with the
heaviest precip in the Thursday afternoon/evening timeframe and a
secondary max possible sometime on Friday as the low pressure
passes just to our south/east. The way it looks now, low level
temps and wet-bulb temps look to be just cool enough for
evaporative cooling effects to allow the precip to start off as a
wintry mix Thursday morning, assuming the precip arrives on time.
As the heavy precip moves in later in the day, a change over to
rain is expected for the entire area. That said, the heavier
precip will keep the temp profile very close to the rain/snow
line, so there is a chance the precip could stay a wintry mix
longer, especially over the north. A change over back to a mix is
possible Thursday night as temps cool. This far out a blend of the
models seems reasonable (least confidence in the GFS), but
adjustments will likely be needed as we get closer to the event
and confidence on how low level temps will behave becomes more
After the system pulls out on Friday, dry weather returns to the
area on Saturday as brief ridging builds across the Great Lakes.
Chances for precip arrives again on Sunday as a fast moving
clipper type system crosses southern Canada, but models differ on
how far south this system will track.
.AVIATION...for 06Z TAF Issuance
Issued at 1138 PM CDT Sun Mar 26 2017
Mainly IFR ceilings expected through midday or early
afternoon Monday. Visibilities will generally be VFR or MVFR where
there is some light rain showers. Conditions may become VFR Monday
evening. Confidence is not high, as wet ground and light winds may
produce additional low clouds and fog.