NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 181910
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
210 PM CDT Wed Mar 18 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Wintry mix expected tonight into Thursday, but there remain
  uncertainties in where primary swath of precipitation occurs and
  what surface temps will be when precipitation occurs. There is
  a 20-40% chance for a light glaze or more of ice, mainly from
  central WI to the southern Fox Valley.

- Temperatures rising back above normal by late this week. Warmth
  peaks Friday into Saturday. The rising temperatures will lead
  to snowmelt and increased flows and rising levels on rivers and
  streams. Several rivers may reach bankfull or even minor flood
  stage.

&&

.DISCUSSION...
Issued at 209 PM CDT Wed Mar 18 2026

Near term into early this evening...low clouds were slow to
depart today in wake of the light snow and freezing drizzle.
Clearing is beginning to push over western WI. Temps have risen
into the mid to upper 30s where skies have cleared. Partial
clearing may make it into central WI this afternoon and into
eastern WI early this evening before clouds increase with next
clipper system. Depending on duration of clearing, temps may reach
into the upper 30s over central WI late today. This will impact
ptype tonight.

Clipper system tonight into Thursday: System is currently over
southern Manitoba. Sharp gradient to warm layer aloft has caused
multiple ptypes from southern Manitoba to northern MN today. Warm
layer aloft moves into western WI this evening then slides east-
southeast through the overnight. 900mb 0c line seems to be best
proxy for ptype differentiation upstream. Steeper mid-level lapse
rates also present leading to more convective appearance to precip
upstream. Precip arrives over western area after 7pm this evening,
but there are differences in where precip occurs due to lack of
mid-level saturation seen on soundings. Also, even where warm
layer is present, sfc temps are hovering right around freezing.
Complicated in terms of where precip will be and ptype resulted in
not issuing an advisory yet. Did see shift to where 20-40% chances
of at least a coating of ice were showed up, arcing from Marathon
and Wood counties east-southeast to at least southern Fox Valley.
Once precip and ptype is more apparent this evening, it is possible
an advisory or SPS can be issued. Majority of precip exits south
of the area after 5a Thu, but limited impacts to the morning commute
could still occur where there is icing overnight.

Beyond this system, next clipper system Thursday night with rain/snow
stays mainly north of our area over Upper Michigan. NBM probabilities
of even 0.01 inch of QPF are barely 10% along the WI/MI border, lesser
elsewhere. The more noteworthy story through Friday will be the warming
trend with highs reaching the 40s on Thursday, and 40s to lower 50s
on Friday. Light onshore winds will keep the Lake Michigan shoreline
cooler both days. Fog could also occur Thursday night into Friday
morning as the snowpack begins to melt with overnight lows staying
in the lower to middle 30s. Extent of fog, stratus will impact high
temperatures Friday and/or Saturday. Current chances of seeing 50
degrees are 40-70% Friday and 50-85% on Saturday. Spread is high
though, likely due to if the low clouds/fog result in cooler temps.
Sounds like spring.

Later in the weekend, stronger cold front slides across the region
bringing a chance of rain/snow Saturday night into Sunday. WSSI-P
shows signal for at least minor impacts from snow and/or ice. Current
forecast has low range pops, but some deterministic models would
suggest more. Will need to keep eye on this time frame even though
NBM probs are low (20-25%) for >1" snow and >0.01" ice. After this
system moves through, high pressure moves in for early next week
with temps at or slightly below normal.

Snowmelt/Flooding Risk: As temperatures warm later this week into
the weekend, the snow melt will result in increasing fast flows
and rising river levels. Some rivers could reach bankfull or even
minor flood stage. At this point though with lack of a rapid,
significant warmup and any heavy rain events, we are not expecting
widespread flooding. This will have to be monitored as we progress
through the end of the month.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 105 PM CDT Wed Mar 18 2026

Light wintry mix has ended, but stratus (IFR to MVFR) remains.
Expect the stratus to briefly improve to MVFR-VFR late this
afternoon into early this evening before a clipper system
arriving this evening spreads another wintry mix across the area.
Greatest risk for freezing rain and light icing will be late
evening through the overnight hours from central WI to the
southern Fox Valley. Where the swath of steadiest wintry mix
(mainly rain, freezing rain) occurs, vsby will drop to 2-4SM and
cigs will drop to IFR. The wintry mix shifts south of the area by
daybreak on Thursday. IFR to MVFR cigs will persist with light S-SE
winds.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....JLA
AVIATION.......JLA