Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 200911

Area Forecast Discussion
National Weather Service Green Bay WI
411 AM CDT Sun May 20 2018

Forecast discussion for routine morning forecast issuance

Issued at 410 AM CDT Sun May 20 2018

Relatively quiet weather the next several days, with just some
showers across the far southern part of the area early today, and
a chance of showers area-wide Monday afternoon into Monday night.

Little change in the large scale upper pattern is anticipated
during the period. The primary westerlies will remain across
Canada and the far northern U.S., with weaker, somewhat diffuse
branch of the flow across the CONUS. The pattern is not favorable
for widespread rains, with precipitation events likely consisting
of scattered showers. As such, total rainfall for the next week
is likely to be AOB normal at most locations. High temperatures
will warm and reach 8-12F degrees above normal by mid-week, then
probably drop back a bit by the start of the upcoming holiday
weekend. Dry air will allow for very large diurnal temperature
ranges, especially across the north which is in developing
drought. So despite warm days, overnight lows in the typical cold
spots may still drop to near freezing at times.

.SHORT TERM...Today...Tonight...and Monday
Issued at 410 AM CDT Sun May 20 2018

A persistent east-west band of showers has set-up over the
southern tier of counties of the forecast area. A few lightning
strikes have also been noted. The AWOS/ASOS sensors at KY50 and
KOSH indicate up to 1/3 of an inch of rain has fallen already. The
strongest cells have now slipped just south of the area. But
radar trends indicate scattered showers will linger into the
morning. The question is how long into the morning. The hi-res
short term models haven`t done a great job with this precip thus
far, with the HRRR about 30-40 miles too far south in placement.
The ECMWF (one of the few models to capture the northern extent of
the precip yesterday) indicates precip as far north as GRB at 12Z.
So will hold the back edge that far north through that point and
then slowly shift it south. Local mesoplots suggest the flow
around 850 mb is veering and generating weak isentropic lift
within the frontal zone, so going with a slow departure of the
showers seems reasonable.

Otherwise, clouds should decrease from north to south today,
though the high-level cirrus shield will probably linger. Sunshine
should allow the north to warm considerably today, while more
clouds and east winds keep the southern/eastern portion of the
area cooler.

The temperature gradient will flip tonight, as clear skies, light
winds, and dry air allows the north to drop off considerably. The
typical cool spots could drop to AOB freezing. Will allow the day
shift to make a final decision on frost/freeze headlines after
monitoring cloud trends.

An anticyclone shifting east out of the Great Lakes region will
leave a strong surface ridge trailing back into the area Monday.
Despite that, a shortwave that originated in the southern stream
trough over the southwest United States will approach the area
during the afternoon. Most of the models generated scattered
light precipitation during the afternoon (except for the NMM Hi-
Res WRF which generated nearly 2 inches of rain with a small
convective cluster near KATW). Spread chance PoPs northeast across
most of the area during the afternoon, but left the far northeast
dry since that area is farthest from the incoming system/moisture.

.LONG TERM...Monday Night Through Saturday
Issued at 410 AM CDT Sun May 20 2018

Zonal flow across the central United States at the beginning of
the period will give way to a building ridge next weekend. The
main story for this period will be the expected above normal
temperatures through much of the period.

For Monday night, high pressure will be located east of the area.
An upper level disturbance will approach from the west. The
combination of this feature and weak 850mb warm advection was
sufficient to increase rain chances across central and
northeast Wisconsin Monday night. Tried to focus highest rain
chances where the best lift was from the disturbance coinciding
with the 850mb warm advection. Did include thunder due to mid
level lapse rates around 6 C/KM. The models were divided about
lingering precipitation chances into Tuesday morning. Per
coordination with NWS offices to the south, will hold off
on adding a chance of rain for this period.

The main story Tuesday and Wednesday will be the very low
relative humidity readings across the north. Current forecast has
values in the 25 to 40 percent range with high temperatures in
the 70s and 80s. Would not surprise me if the relative humidity
values are lowered as we approach these days. For Wednesday night,
the models were hinting at another backdoor cold front that could
bring northeast or east winds to northeast Wisconsin. If this
occurs, high temperatures may need to be lowered by several
degrees on Thursday along the bay and lake.

The chances of showers and thunderstorms return Thursday, but the
better chances of showers and storms will be on Friday into
Saturday. Some of the severe weather parameters were indicating
some potential for stronger storms, if not severe. Not ready to
add severe wording in the Hazardous Weather Outlook (HWO) this
far out due to some uncertainty in the details and timing of the
event. High temperatures Friday and Saturday a little tricky
depending on cloud cover and precipitation. Only minor changes
made to account for our warm bias sites during the cold bias sites
at night.

.AVIATION...for 12Z TAF Issuance
Issued at 410 AM CDT Sun May 20 2018

MVFR ceilings should shift south and out of the area this morning.
Good flying conditions are anticipated after that happens, as high
pressure will dominate the area.

Issued at 410 AM CDT Sun May 20 2018

Rainfall amounts over the next few days are not expected to
alleviate the abnormally dry conditions across the north. Warm and
dry conditions are expected through Wednesday, resulting in an
elevated fire weather conditions and worsening drought conditions.
Relative humidities are expected to be in the middle teens to
lower 20s through Monday, with a slow moderation to 25 to 40
percent by the middle of the week.



SHORT TERM.....Skowronski
LONG TERM......Eckberg
FIRE WEATHER...Eckberg is the U.S. government's official web portal to all federal, state and local government web resources and services.