Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/09/21

Area Forecast Discussion

National Weather Service Green Bay WI

 1036 PM CDT Sat May 8 2021

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Sunday
Issued at 303 PM CDT Sat May 8 2021

Main focus in the short term is on cloud and temperature trends
through tonight, and then a small chance of showers on Sunday.

Late Afternoon...Widespread cu field developed late this morning
and afternoon and composite radar imagery at 1930Z shows some weak
returns in far northeast WI. Doubt much if any of this will reach
the ground due to cloud bases around 7kft and T/Td spreads of
about 30 degrees, but kept a chance sprinkles in the forecast for
the late afternoon and early evening in northeast WI.

Tonight...The diurnal clouds will dissipate this evening, but
high clouds are starting to stream in from the west due to the
system in the central Plains. There has been some uncertainty on
how thick these cloud will be over the GRB forecast area tonight,
how far north they will reach, and whether there will be any gaps.
Guidance seemed to be in a general agreement showing a few hours
of clear to partly cloudy skies across the north tonight, with
more clouds across central and east- central WI. Stuck with this
cloud trend and adjusted min Ts accordingly. This results in min
Ts in the upper 20s and low 30s across northern WI, and in the
middle 30s elsewhere. Opted to issue a Freeze Warning across the
north where temperatures are most likely to fall below freezing. A
little less confident on any frost farther south due to cloud
cover, and the fact there could be a sharp temperature gradient,
but opted to issue a Frost Advisory for one tier of counties in
central WI over towards Door County where lows could reach 32 to
34 degrees in parts of these counties.

Sunday...Frost/freeze concerns wane quickly by mid-morning and
temperatures will rise into the 50s by the afternoon (slightly
cooler in the upper 40s along Lake Michigan). This is about 10
degrees below normal for early May. Meanwhile, expect mostly
cloudy skies and the chance for a few afternoon showers. Forecast
soundings once again show steep low and mid-level lapse rates
during the afternoon as cooler air advects in at 850mb. The best
chance for afternoon showers is west of the Fox Valley.

.LONG TERM...Sunday Night Through Saturday
Issued at 303 PM CDT Sat May 8 2021

An upper level low will keep cool weather in across the western
Great Lakes during the early part of the week. This will bring
several chances for additional frost/freeze headlines across the
region. The cyclonic flow will also mean some clouds and the
chance for some light precipitation across central and east-
central Wisconsin Sunday night, then across northeast Wisconsin on
Monday as shortwaves track through the flow.

Upper level ridging and height rises will then build in during the
middle part of the week, which will keep the weather dry and begin
a period of slowly warming temperatures through the rest of the
week and into the weekend. Temperatures are expected to rise
around or even slightly above normal by next weekend. The riding
will slide a bit east late in the week, as several weak upper
level disturbances bring the chance for light showers at times
late in the week and into next weekend. The best chance for
precipitation will likely be during the afternoon and evening
hours as daytime heating offers a modest boost in instability.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1036 PM CDT Sat May 8 2021

Good flying weather expected through Monday. High based cumulus
clouds are expected by afternoon both days which will slowly
dissipate during the evening hours. Some virga or brief rain
showers are possible Sunday afternoon.

Frost is possible on aircraft parked outside in northern
Wisconsin tonight, and across much of the area Sunday night,.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 8 AM CDT Sunday for WIZ020-022-030-031-074.

Freeze Warning until 8 AM CDT Sunday for WIZ005-010>013-018-019-
021-073.
&&

$$

SHORT TERM.....KLJ
LONG TERM......Kurimski
AVIATION.......RDM



...Update to aviation forecast discussion...



 .DISCUSSION...
Issued at 259 PM CDT Sat May 8 2021

1930Z water vapor imagery showed a closed low over western MT with a
shortwave rotating through the base of the trough over the central
Rockies. A low pressure system as been steadily deepening across
southwest KS and southeast CO. The warm front extending northeast of
the surface low had lifted into south central NEB and far northeast
KS.

Severe thunderstorms remain probable tonight as guidance from the
CAMs as well as the synoptic scale solutions develop a complex of
storms and move them east along the warm frontal boundary tonight.
If there has been a trend in the CAMs, the HRRR has been a little
west with the initiation of storms and slower to bring them into the
western parts of the forecast area. Otherwise they`ve been pretty
consistent. Aircraft soundings near MCI show a substantial capping
inversion near the warm front at 18Z and one near ICT at 1822Z also
shows a cap over the warm sector. With the shortwave still to the
west, will need to wait for storms to form near the triple point and
move east. Forecast soundings from the NAM and RAP continue to
forecast a mid level weakness in the wind field causing the
hodograph to have an inflection. This would suggest storms would
tend to split with cell mergers causing disruption with the updrafts
and this seems to be what the CAMs depict this evening. However the
low level jet is progged to strengthen as the shortwave moves into
the plains and 12Z NAM forecast soundings show a brief window just
ahead of the cold front where the hodograph elongates and loses the
inflection. So there could be a risk for tornadoes into the evening,
especially if a supercell storm could set up on the south of the
convective cluster with uncontaminated access to the warm sector.
There continues to also be a large hail risk and damaging winds.
Some of the forecast soundings analogs show the potential for hail
over 2 inches in diameter and with storms expected to congeal into a
line, damaging winds may be the more widespread hazard to deal with
tonight.

As for flash flooding, there is a bit more uncertainty in excessive
rainfall for a couple reasons. First storms look to be fairly
progressive. If there was going to be a training concern, it would
be along the warm front, but eventually the cold front should catch
up and push the convection east and south. Second, models have
trended further north with the axis of heaviest rainfall, and this
makes some sense as the warm front has lifted into southern NEB.
North central and northeast Kansas missed out on the isolated
rainfall this morning and flash flood guidance of 2+ inches an hour
support the idea that the ground could take a quick one or two inch
downpour. Ultimately I think any flash flooding risk is going to be
to isolated for a watch and driven by repeated convection over the
same spot which isn`t a forgone conclusion.

Something else to be concerned with tonight are the gradient winds
behind the surface low. Models show the pressure gradient increasing
as the low passes south of the forecast area. There is the potential
for winds to remain up overnight and into Sunday morning, but it
looks like the stronger pressure gradient forcing and wind gusts are
coincident with the convection expected to occur. Even the HRRR
keeps wind gusts below advisory levels. Think that if the gradient
winds could reach advisory levels, it would be brief and right after
storms pass, with the gradient beginning to relax shortly after
storms move out. Because of this have opted not to issue a wind
advisory and will monitor trends.

Rain is expected to push east of the forecast area fairly early in
the day Sunday with surface ridging building in. Cloud cover for a
good portion of the day along with low level cold air advection is
expected to keep temps in the 50s on Sunday and breezy north winds
will make it feel cooler than that. The surface ridge remain over the
central plains through Wednesday keeping temps below normal. There
remains some potential for rain Monday through Wednesday as models
show some energy kicking out from the west and riding over the
central plains. There has been some variability in model runs with
respect to the energy lifting out across the area and as a result
POPs have bounced around a little bit. At this time it appears the
better forcing for precip may impact the area Tuesday. But
confidence in POPs is only so-so. Return flow redevelops Thursday
with temps warming into next weekend. Differences between the GFS
and ECMWF lead to more uncertainty in the forecast by Saturday, so
did not stray from the national blend of models. This has chances
for showers and thunderstorms Thursday night through Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 610 PM CDT Sat May 8 2021

Only minor changes to going forecast. Convective complexes slowly
taking shape to the west and thunderstorm impacts are on track
for the next several hours. Post-complex winds continue to veer
into the end of this forecast though MVFR cigs will likely
persist.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

DISCUSSION...Wolters
AVIATION...65