NWS-Green Bay Forecast Discussion

 

						FXUS63 KGRB 281152
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
652 AM CDT Thu Mar 28 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Winds chills in the single digits and teens this morning. Highs
  moderate closer to normal today, then slightly above normal on
  Friday.

- A fast moving shortwave will bring a wintry mix to the forecast
  area Friday evening through Saturday morning. Confidence is
  increasing in potential for frozen precip with minor ice and/or
  snow accumulations across central and northern Wisconsin.

- Another round of wintry precip is possible early next week,
  although the track and timing for this system is still
  uncertain.

&&

.DISCUSSION...
Issued at 337 AM CDT Thu Mar 28 2024

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

Precip / Clouds:

Cyclonic flow across the western Great Lakes has keep low/mid
and high clouds (with some breaks as well) and lingering light
snow showers/flurries around much of the night, with the most
persistent snow showers across northern WI. The light snow
activity will wane through the morning hours as low pressure
pushes away from the region and drier air advects in from the
west. Any minor accumulations (a tenth or two) will be confined
to far north-central WI. The cyclonic flow will also keep some
clouds over the far north through the day, with more sunshine as
you head south. Mid and high clouds will increase from the
southwest on Friday as the next system approaches.

Winds / Wind Chills / Temps:

Limited to no CAA overnight and slowly decreasing winds aloft kept
gusts to under 20 mph for most of the night. Winds chills in the
single digits and teens are expected this morning. Winds will
begin to pick up again this morning as mixing increases after
sunset. But winds aloft will be weaker today, generally between
20-25 kts. This will hold surface gusts to between 15-25 mph,
with a few gusts to 30 mph possible, mainly in east-central WI.
As the surface ridge builds over the area tonight, winds will
become light. Southeast winds will slowly pick up during the day
on Friday.

Temps will moderate back closer to normal today as the coldest air
exits to the east and as weak WAA pushes in from the west. Highs
look to be in the 30s across central and north-central WI, and in
the low to possibly mid 40s across eastern WI. Lows tonight will
drop mainly into the teens and 20s. Continued WAA will allow for
temps on Friday to climb into the mid 40s and low 50s, slightly
above normal for the end of March. Onshore winds will keep cooler
readings near Lake Michigan.

Long Term...Friday Night Through Wednesday

Main concerns for the extended remain on two rounds of wintry
precip that are set to impact the forecast area: the first
arriving Friday evening and the second arriving Sunday evening.
Confidence is increasing in potential for frozen precip accompanied
by some ice accumulation across northeast Wisconsin Saturday
morning. There is still some uncertainty in the track of the early
week system and hence where precip will set up.

Weekend precip chances... A mid-level shortwave will spin up a
surface low across eastern Iowa on the nose of an upper-level jet
Saturday morning. The warm sector to our south will come pre-
conditioned with deep Gulf moisture which will briefly make its
way up into southern Wisconsin. Light precip will begin to lift
north across Wisconsin Friday evening out ahead of this warmer
air. Precip will likely start as rain south of Highway 29 where
surface to 800 mb temperatures remain above freezing. The question
remains how far north this warmer air will extend and where the
transition from rain to freezing rain will occur. Most medium-
range models (NAM and RAP-ext) are showing a strong signal for a
warm nose from ~850 to 750 mb with surface temperatures at or
below freezing. This type of thermal profile would support periods
of moderate freezing rain or even ice pellets mixing in across
central to northeast Wisconsin. Whether or not we see ice pellets
or sleet depends on how deep the near-surface freezing layer gets
and if it will be sufficient to re-freeze precip. Overall, precip
type remains a hindrance to the forecast. The recent suite of
model runs now seem to be targeting northern Wisconsin,
specifically near/along the UP border, for highest QPF amounts of
~0.2 to 0.4". Overall forecast confidence remains low to medium
for this event.

Early week precip chances... Active weather will continue into the
beginning of the week as another system brings a second round of
wintry precip to the region. A robust trough crossing from the
west coast to the Rockies will generate a Colorado low that will
track northeast into the Great Lakes. The path of this low is
still pretty variable, although recent model guidance is hinting
at a more southerly track that would keep the warm sector as well
as the bulk of the moisture to our south. Rain and snow both look
to be possible with this system, although amounts and
accumulations are still uncertain. The influence of Hudson Bay
high pressure to the north also suggests that there could be a
sharp cutoff in the northern extent of precip across the CWA. Lake
enhancement would also be possible on the back end of the
departing low as winds back to northerly and a cold air advection
regime settles in. Regardless, changes to the forecast are still
ongoing at this stage.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 652 AM CDT Thu Mar 28 2024

A lingering flurry is possible near the MI border this morning.
Otherwise, look for dry conditions through the TAF period. A few
MVFR ceilings are possible at times, mainly across north-central
WI (RHI) as some model guidance wants to develop a high-end MVFR
cloud deck later today into this evening, but confidence too low
to include. Otherwise, VFR conditions are expected. West winds
will gust to around 20 kts today, then winds will become light
tonight.

&&

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

&&

$$

DISCUSSION.....Bersch/Goodin
AVIATION.......Bersch