Oshkosh, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

893
FXUS63 KGRB 211148
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
548 AM CST Thu Nov 21 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- One to three inches of wet snow will impact far northeast and
  east-central Wisconsin this morning. The snow will likely
  change to rain by 9 to 10 am.

- Hazardous driving conditions are expected for the morning
  commute across eastern Wisconsin. Motorists should anticipate
  slippery and slushy roads, reduced visibilities, and longer
  commute times.

- Strong north or northwest winds gusting from 35 to 45 mph will
  be possible through the middle of the afternoon. Strong winds
  combined with wet snowfall may lead to isolated power outages,
  difficult travel, and loose outdoor objects being blown around.

&&

.DISCUSSION...
Issued at 316 AM CST Thu Nov 21 2024

Short Term...Today...Tonight...and Friday

Snow and wind trends the main focus as first widespread snow
event of the season unfolds.

Low pressure of 995mb is over eastern Upper Michigan early this
morning. As strong shortwave rotates counterclockwise around main
upper low over lower Michigan, the sfc low tracks to northern Lake
Michigan after daybreak, then slides south down Lake Michigan into
mid afternoon. This low will not stick around as it pushes into
northern Indiana by evening, before sweeping across the Ohio
Valley by late evening. Result for weather over Wisconsin will
be changeable with burst of snow early today, switching to rain by
mid morning with rain showers diminishing in coverage this afternoon.
Winds will ramp up this morning, peak midday, then diminish quickly
this afternoon.

Snow/Precip...Widespread precip along and ahead of the low is
spreading across Upper Michigan into northern and northeast
Wisconsin. Ptype is snow, except over portions of Door County and
over eastern Upper Michigan. Thus far, models are doing a good job
depicting the change from snow to rain as warming occurs in the
lowest 2kft. This switch from rain to snow arrives over our far
north between 10z-12z/4am-6am and to the south of US-10 between
13z-15z/7am-9am. Until then, surge of moderate snow with 2-3 hours
of heavier snow (snowfall rates of 0.5-1.0 inch per hour) is on
track to sweep southward across far northeast WI into eastern WI.
Been snowing here at NWS GRB since 2 am. Thus far, snow is more
fine flakes and are starting to see coating on grass and elevated
surfaces. Roads are just wet so far, but once the heavier snow
rates arrive, a thin coating of slush and snow likely will be able
to accumulate on untreated roads. Given temps in the lower 30s,
treated roads likely will remain wet. No significant changes to
going snowfall forecast amounts, general 1-3" with local 4+" in
area bounded by Fox Valley but inland from Lake Michigan. Snow
amounts elsewhere from northern to central WI will be from a half
inch to an inch. Also did feel it prudent to issue a Special Weather
Statement for areas not covered by an advisory as the snow will
result in locally slippery roads (as temps in these areas are a
bit colder) and a slower commute. Whatever snow accumulates will
melt early to mid afternoon as temps push into the lower 40s and
any precip occurring by that time will be rain.

Winds...Tricky aspect of this forecast. Currently gusty winds
have yet to develop over our area. Despite 40-50 kt winds at
1-2kft, warm air advection aloft leading to stable low-level
profile is not allowing much mixing of these winds. Expect this to
continue until later this morning once the snow switches to rain
and soundings show more mixing in the lowest 5kft. Generally, many
areas will see gusts of 30-40 mph by that time. Stronger gusts of
45+ mph could still occur in brief window late morning into early
afternoon near the bay and along Lake Michigan as the sfc low
passes to the southeast. Winds really quickly diminish after that
window of time though, so trimmed the wind advisory and gale
warning ending time to 21z/3pm and even that could be too long.

Tonight and Friday...As low slides farther east and high builds
over the northern Plains, a marginally cool northerly flow will
support clouds and some rain showers tonight, mainly near Upper
Michigan and across the bay and Door County. Temps not cool enough
for lake effect though, mainly just lingering low-level moisture
and weak lift. By Friday, kept small chance across Door County in
the morning, but mostly just looking at lingering clouds. Lows
tonight will be in the low to mid 30s north and in the mid to
upper 30s Fox Valley to the lakeshore. Highs on Friday around 40
north and into the upper 40s eastern WI.

Long Term...Friday Night Through Wednesday

There are two key messages for this part of the forecast: 1)  Light
precipitation remains possible from late Sunday into Monday.  2)
Temperatures will be trending colder next week.

Precipitation:  Shortwave energy will be moving east across the
northern Plains and northern Mississippi Valley from Sunday into
Monday which will support a weak surface low traversing the western
Great Lakes.  Weak overrunning will occur ahead of the shortwave on
Sunday and Sunday night, but models generally have only low chances
of precipitation due to poor saturation in the mid-levels.  It seems
that precip chances will increase later Sunday night into Monday
when better saturation is achieved thanks to troughing overhead and
northerly trajectories off Lake Superior in the low levels.  Thermal
profiles will be cooling by this time, thereby resulting in a wintry
mix or all snow as the main precip type over north-central WI
(mostly rain over eastern WI).  Some minor accumulations appear
possible over far northern WI.

Very light precip may be possible at times from Tuesday through
Wednesday, but predictability as well as impacts are low.

Temperatures:  Will be trending colder next week as mentioned above.
850mb temps will be fall into the -5C to -8C range, which would put
highs in the 20s and 30s.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 546 AM CST Thu Nov 21 2024

A deepening low pressure system over eastern Upper Michigan will
drop across northern Lake Michigan this morning, bringing moderate
to heavy snow to mainly far NE/EC WI through mid morning, before
warmer air changes the precipitation to rain as the low tracks
farther down Lake Michigan. Expect flight conditions of MVFR/IFR
over most of the forecast area, with LIFR conditions possible at
the eastern TAF sites through 14z during heavy snow. Occasional
light rain or showers will continue through the rest of the day,
along with MVFR/IFR conditions.

Wind...Northwest winds will increase as the low approaches this
morning, with gusts to 35 kts expected across much of the area
through early afternoon. LLWS will continue through mid-
afternoon. The strong surface winds and LLWS will diminish late in
the day.

Plan on IFR to MVFR conditions tonight with just some spotty light
rain showers. Winds will be from the northwest, gusting to 20-25
kts at times.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM CST early this morning for
WIZ022-073-074.

Wind Advisory until 3 PM CST this afternoon for WIZ022-039-040-
050.

Winter Weather Advisory until 9 AM CST this morning for
WIZ038>040-048>050.
&&

$$

DISCUSSION.....JLA/MPC
AVIATION.......JLA