Forecast Discussion for GRB NWS Office
FXUS63 KGRB 192021

Area Forecast Discussion
National Weather Service Green Bay WI
321 PM CDT Thu May 19 2022

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Friday
Issued at 321 PM CDT Thu May 19 2022

Main focus is on thunderstorm potential over the next 18 to 24
hours or so. As mentioned in previous discussions, a warm front
has tried to move north across WI, but has struggled to move much
today, leading to lower confidence in severe storms. A cold front
is expected to move through after midnight into Friday morning,
which could also bring rain and thunderstorms.

Late afternoon and evening...Watching observations from the past
few hours it is evident the surface warm front is hung up across
northern Illinois and extends west into northeast Iowa and
southern Minnesota. As a result, moisture has not surged into WI
as expected with dew points in the 40s and low 50s, and virtually
no instability has developed. A few thunderstorms have developed
across western WI but the lightning activity diminishes by the
time it reaches central WI, resulting in just showers moving into
central WI as of 3:00 PM. Probability guidance (Warn on Forecast
System particularly) shows very low probability of greater than
50dBZ radar returns through 00Z. With the warm front situated
well to the south along with the temperature, moisture, and
instability gradient, think this area across southern MN and
northern Iowa has a much better chance of severe storms, as also
noted by SPC, which doesn`t leave much left for central and north
WI through much of the afternoon and evening. Maintained PoPs as
showers are possible along with a few thunderstorms. Cannot rule
out some hail or perhaps gusty winds, especially across central WI
if activity to the west manages to maintain itself and clip
central WI.

Overnight...The next feature will be the surface cold front which
is progged to sweep across the state overnight. Development of
thunderstorms across central and northeast WI looks a little
better during this time period, but confidence is still low.
Instability may be able to increase late this evening and tonight
up to 1000 to 1500 J/kg with 0-6km shear close to 60 kts. This
leads to a better chance for thunderstorms and possibly severe
storms, with large hail and damaging winds the main threat. May
need to watch for flooding potential if any showers or storms
train over the same area, but given pwats are still in check heavy
rain potential is also lower. Lows tonight will range from the
50s to low 60s.

Friday...Lingering activity is possibly throughout the morning,
particularly across eastern WI. With some instability still around
cannot rule out some thunderstorms as well. Any precip should
clear out by early afternoon, with some clearing of clouds across
central WI during the late afternoon. Highs will be in the upper
60s to low 70s.

.LONG TERM...Friday Night Through Thursday
Issued at 321 PM CDT Thu May 19 2022

The main highlights from this forecast period are the chances for
precipitation throughout the weekend paired with below normal

Friday night through Sunday...The cold front that brought showers
and thunderstorms to the region earlier on Friday will slide
southeast of the region into Friday evening. While cooler and quiet
conditions are anticipated for the rest of Friday night, models
indicate a secondary weak cold front moving southeast across the
state from northwest WI to southeast WI by Saturday morning. Despite
weak forcing, there may be enough to generate a few light showers in
northwest and north-central WI into the evening. For Saturday,
precipitation from the nearly stalled cold front to the southeast of
WI will attempt to spread northwest towards the forecast area due to
some influence from the RRQ of the upper-level jet and mid-level f-
gen. There is still some uncertainty with the precipitation coverage
across the forecast area, however, the best chance for precipitation
will be across east-central WI. Although the better instability and
mid-level lapse rates will be to the south of the forecast area
Saturday afternoon, cannot rule out the small chance for a few non-
severe thunderstorms in east-central WI. Low to mid-level moisture
will linger over the forecast area Saturday night into early Sunday
and combine with energy from a mid-level shortwave and upper-level
trough sweeping across the region, to produce additional scattered
showers. High pressure will then build into the region throughout
the remainder of Sunday and into Sunday night. High temperatures for
Saturday and Sunday will be below normal with readings mainly
ranging from the low 50s to low 60s.

Rest of the extended...Dry conditions are anticipated for Monday as
high pressure remains over the forecast area. However, there is
potential for frost to develop, mainly across the Northwoods, into
early Monday morning with morning low temperatures falling to the
middle 30s. Models diverge from one another beyond Monday and
struggle with the evolution of the next shortwave/trough that may
bring precipitation to the region sometime Tuesday or Wednesday.

.AVIATION...for 18Z TAF Issuance
Issued at 105 PM CDT Thu May 19 2022

Mainly VFR conditions early this afternoon with some developing cu
across northern WI leading to MVFR cigs. The main aviation issue
becomes the potential for showers and thunderstorms this afternoon
into Friday. Scattered development is likely, first from a warm
front approaching the area late this afternoon and evening, but
there is uncertainty on how far north this warm front will get.
Followed by a cold front sweeping across overnight. Timed out
most likely timing of showers and storms for each TAF site, but
confidence is medium- low as the environment is complicated and
one event will determine the next. Outside of any storms, expect
mainly VFR conditions with MVFR cigs possible at times late
tonight and Friday morning.



LONG TERM......Hykin

NWS GRB Office Area Forecast Discussion