Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 161802

Area Forecast Discussion
National Weather Service Green Bay WI
102 PM CDT SUN OCT 16 2016

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Monday
Issued at 328 AM CDT Sun Oct 16 2016

Fog trends this morning, precipitation trends and the potential
for severe thunderstorms tonight into Monday, and much above
normal temperatures will be the main forecast concerns.

A cold front was moving through northeast and central WI early
this morning. Partial clearing was occurring in the wake of the
front, which was allowing areas of fog and patchy dense fog to
develop. Given a lack of widespread dense fog, will hold off
on an advisory and just mention locally hazardous travel
conditions in a Special Weather Statement and the Hazardous
Weather Outlook.

The main band of showers and embedded thunderstorms has stayed
south of the forecast area during the overnight hours, so
precipitation has been removed from the forecast. Fog should mix
out by mid-morning and lingering stratus will shift south of the
region before midday. The afternoon should be partly to mostly
sunny, with above normal temperatures in the 60s to around 70

Surface/850 mb warm fronts will make a strong surge into the
region tonight, as a 40 kt LLJ develops. PWATs will climb back
to 1.0-1.5 inches, and elevated instability will increase (H8 LI`s
-2 to -4 and mid-level lapse rates of 7-7.5 c/km) overnight. Have
increased pops to likely to categorical over the entire forecast
area. There is a marginal risk of elevated severe thunderstorms
with large hail, especially over the northwest two-thirds of the
CWA, where deep layer shear will increase to 60+ kts, and 0-3km
Helicity will be 300-500.

Expect showers and thunderstorms to taper off in the morning as
the 850 mb warm front lifts toward Lake Superior. However, the
surface front will set up across northern WI during the afternoon,
and provide a focus for additional thunderstorm development.
Once again, instability (SBCAPE of 1000-1500 j/kg) and deep
layer shear (60-75 kts) will be more than sufficient for severe
thunderstorm development, especially where forcing is enhanced
near the frontal boundary. SPC has all of northern WI in a
marginal risk for severe thunderstorms. To the southeast of the
frontal boundary, very mild temperatures are anticipated, with
highs in the lower to middle 70s.

.LONG TERM...Monday Night Through Saturday
Issued at 328 AM CDT Sun Oct 16 2016

Model guidance has come into agreement with a deepening area of
low pressure and shortwave trough that will cross the Great Lakes
Monday night into Tuesday morning. Once this feature departs,
attention turns to a progressive/deepening mid-level trough that
is forecast to reach the central CONUS mid-week and east-central
NOAM by week`s end. ECMWF remains most consistent with this trough
and has the UKMET on its side. The GFS, which has struggled
mightily with this system, now has come around toward the same
solution. For northeast Wisconsin, precipitation chances will
increase with the approach of the trough (Wed. night/Thursday)
with temperatures going from above normal to below normal.

Models agree on taking a strong area of low pressure from the
Upper MS Valley northeast through northern sections of the Great
Lakes into southeast Ontario Monday night. The passage of the
surface low will also drag a cold front into Wisconsin during the
overnight hours. Finally, a northeast-moving shortwave trough is
forecast to lift in a similar track as the surface low. Best lift/
forcing expected to be in the vicinity of the surface low/
shortwave trough which would favor higher pops across northern
Wisconsin. May need to watch storm intensity into Monday evening
as shear is forecast to be very strong (70+ knots), although
limited instability may prevent storms from becoming severe. SPC
has placed much of the northern half of Wisconsin in a marginal
risk Monday evening, so this situation will need to be watched.
Min temperatures to be in the lower to middle 50s north, middle
50s to around 60 degrees south.

A few showers could linger across the area into Tuesday morning
until the cold front clears Wisconsin. Otherwise, we will reside
between systems with weak high pressure moving into the Midwest by
Tuesday afternoon. Expect to see more sunshine as the day wears on
with temperatures starting a downward trend that will continue
through the rest of the work week. For Tuesday, max temperatures
to be 5 to 10 degrees cooler than Monday with readings in the
lower 60s north-central, lower to middle 60s central and middle to
upper 60s east-central Wisconsin.

While the weak high pressure moves into southern sections of the
Great Lakes Tuesday night, models now suggest that a weak surface
trough will move into the western Great Lakes. A stray light rain
shower or some sprinkles cannot be ruled out, however lift is so
weak and any activity appears too isolated to even mention in the
forecast. May bring in more clouds than first thought and this
should help keep min temperatures in the lower 40s north-central,
to around 50 degrees near Lake MI. Weather is expected to remain
benign over the Great Lakes through Wednesday as the main action
should be the primary mid-level trough that is forecast to move
into the central Plains by 00z Thursday. Temperatures will
continue their steady decline with maxes in the lower to middle
50s far north-central WI, generally upper 50s to lower 60s

Models have come into much better agreement with both the movement
and strengthening of the mid-level trough by Thursday. This now-
longwave trough is progged to extend from southern Ontario south-
southwest to the southern Plains by 00z Friday. While the main
precipitation shield to extend along the old front (from Tuesday)
from the Gulf Coast to the eastern Great Lakes on Thursday, the
increasingly cool air mass aloft over Wisconsin could kick off a
small chance of instability showers over northeast Wisconsin
Thursday afternoon. By far, most locations will remain dry with
max temperatures on Thursday to range from the upper 40s north-
central, to the middle 50s east-central Wisconsin.

The longwave trough is forecast by most models to continue
steadily moving east, reaching the eastern Great Lakes on Friday
and eventually eastern NOAM by next Saturday. The trough may still
be close enough on Friday to combine with a little cyclonic flow
and potential lake enhancement to perhaps set off a slight chance
of light showers mainly over eastern Wisconsin. Otherwise, the
mean flow over the western/central CONUS to become zonal with weak
ripples racing along the northern tier of states. Do not see any
systems to impact our area on Saturday so prefer to keep the day
dry. Coolest temperatures should be on Friday with the trough
nearby (middle 40s to lower 50s), but anticipate the start of a
warm-up on Saturday (around 50 to the middle 50s) as winds turn
southwest aloft.

.AVIATION...for 18Z TAF Issuance
Issued at 102 PM CDT Sun Oct 16 2016

VFR conditions will prevail across the forecast area through the
end of the day. Showers and thunderstorms are expected to move
into central and north central Wisconsin late this evening and
continue to the east overnight, as a warm front pushes northeast
across the state. IFR with scattered MVFR conditions should
prevail across the area overnight in low clouds and fog. Showers
and storms should end by morning, but it may take a while to get
rid of the fog and low clouds.



SHORT TERM.....Kieckbusch
LONG TERM......Kallas
AVIATION.......MG is the U.S. government's official web portal to all federal, state and local government web resources and services.