Forecast Discussion for GRB NWS Office
FXUS63 KGRB 241924

Area Forecast Discussion
National Weather Service Green Bay WI
224 PM CDT Sat Aug 24 2019

Forecast discussion for routine afternoon forecast issuance

Issued at 224 PM CDT Sat Aug 24 2019

Another quiet day tomorrow, then some showers and thunderstorms
Monday into Monday night. Seasonably cool and mainly dry weather
will settle into the area for the latter part of the work week.

Slow progression of the large scale pattern is expected for the
next few days. That will allow the upper ridge presently across
the area to shift to the East Coast, while an amplifying trough
pushes east across the Plains. The trough will slow mid-week as
an upper low closes off over western Ontario, then begin to lift
toward northeast Canada late in the week.

The expected large scale pattern is probably more typical of
early autumn than late summer. Though day-to-day temperature
variations are expected, readings will generally be AOB normal.
The main precipitation event will be tied to the passage of a
frontal system through the area Monday and Monday night. While a
widespread significant rainfall is likely during that time frame,
only a few rounds of scattered light showers are expected during
the rest of the period. The result will probably be near to
slightly below normal amounts for most locations.

.SHORT TERM...Tonight and Sunday
Issued at 224 PM CDT Sat Aug 24 2019

The latest RAP analysis and satellite/radar imagery show high
pressure centered over northern Ontario but stretching across much
of the western Great Lakes early this afternoon. Onshore winds and
daytime heating have contributed to a widespread cu field across
the region. Temperatures are running a degree or two warmer than
yesterday. Looking upstream, the next system is moving slowly over
the Plains with a narrow moisture channel extending from the Gulf
Coast to North Dakota. Because of the strong high over the Great
Lakes, this system will be slow to approach the area. So the main
forecast concerns continue to revolve around clouds and temps for
tonight and Sunday.

Tonight...The center of the sprawling high pressure system will
slowly shift east to the eastern Great Lakes, northeast Ontario
and Quebec. The pressure gradient will tighten somewhat with wind
trajectories remaining out of the southeast. 1000-850mb winds are
projected to remain until 20 kts, which usually indicate surface
winds will decouple. But with a little more wind in the boundary
layer, lows should be a little warmer than last night, and range
from the low 40s north to mid 50s over the southern Fox Valley.
Clouds should dissipate with loss of heating early this evening.
But a few clouds may also drift into northeast WI from off Lake
Michigan late tonight.

Sunday...High pressure will continue to slowly drift away from the
region while the system over the Plains moves into the
Mississippi Valley. Trajectories out of the southeast will
continue to provide a steady stream of dry air in the mid and
lower levels. However, forecast soundings and the cu rule indicate
should see ample fair weather clouds build again by late morning.
Low level temps continue to warm, which should put highs in the
low to middle 70s.

.LONG TERM...Sunday Night Through Saturday
Issued at 224 PM CDT Sat Aug 24 2019

The main long-term forecast issue is honing in on the timing of
precipitation with the frontal system crossing the area at the
start of the work week. Overall, the 12Z guidance trended slower
with the arrival of the precipitation and with the timing of when
the bulk of the rain will fall. Adjusted the forecast (PoPs and
QPF) accordingly. The southwest portion of the forecast area was
included in the marginal risk of severe weather on the morning SPC
SWODY3 product. The 12Z guidance suite indicated limited
destabilization will occur during the day, so at this point the
risk of severe storms does not appear great.

Deep westerly flow behind the front will support temperatures a
little above normal on Tuesday, then readings will drop to below
normal for a couple days as the large-scale upper trough settles
over the region. Scattered light showers will also be possible at
times, especially across the north.

The default forecast initialization grids based on a broad-based
blend of guidance products seemed reasonable, so no significant
changes were necessary.

.AVIATION...for 18Z TAF Issuance
Issued at 1155 AM CDT Sat Aug 24 2019

Scattered to broken fair weather clouds between 3500 and 4500 ft
can be expected to persist through the afternoon. Some clearing
via lake breeze is likely to occur from east to west, starting
along the lakeshore early this afternoon, and moving inland to the
Fox Valley by late afternoon. Skies will become mostly clear this
evening as the clouds dissipate. A few more lake clouds may drift
inland along the lakeshore late tonight, before fair weather
clouds become more widespread again by around 15z Sunday.



LONG TERM......Skowronski

NWS GRB Office Area Forecast Discussion