Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 201707
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1207 PM CDT Mon Mar 20 2017
.AVIATION(18Z TAFS)...VFR this period. Surface cold front dropping
through CWA with winds shifting more to the north. Some
accelerations possible near the lake esp as 925/850 winds ramp up
a bit later today into this evening. All in all cold advection
regime kicks in and sets up low level thermal trough into Tuesday.
Highest low level rh ends up being closer to the lake where
onshore trajectories briefly set up and bring at least some clouds
and maybe some flurries.
.PREV DISCUSSION... (Issued 930 AM CDT Mon Mar 20 2017)
MARINE...No siggy changes this update. Will be keeping an eye on
post-frontal wind regime. Winds expected to shift NNE with 925
millibar winds of 20 knots this afternoon. For now held off an
small craft headline but will continue to monitor trends.
PREV DISCUSSION... (Issued 632 AM CDT Mon Mar 20 2017)
AVIATION(12Z TAFS)...Inverted sfc trof wl be moving across
southern WI this morning. Still a potential for some sct-bkn low
clouds to develop along with feature, but so far only high clouds
blanketing southern WI with an area of mid clouds lingering near
the IL border. Confidence low at this point so kept low clouds sct
for today. Increasing northeast winds this afternoon as sfc trof
slides south of the area.
PREV DISCUSSION... (Issued 326 AM CDT Mon Mar 20 2017)
TODAY AND TONIGHT - Confidence...Medium to High.
700H warm air advection which triggered strong storms over northeast
CWA Sunday evening has since pushed well to the east of the area.
Focus is now on low level warm air advection associated with 850H
jet. However LLJ has been focused across eastern IA and northern IL
where numerous thunderstorms are currently located. This activity
is tracking ESE and should continue through the early morning.
However wl carry small pops in far south through the early morning
as elevated instability lingers across northern IL as low level
trof axis passes through.
Latest IR imagery shows mid-level clouds progressing steadily
eastward last several hours with only high clouds over most of the
area. Not seeing much stratus developing near inverted trof/front
at this time, but could still develop as it progresses eastward
across srn WI this morning. Bit more low level moisture drawn into
the low levels from storms to the south could help low clouds form
for a time as well. Otherwise, expect a milder day but can`t get
too excited due to the bkn-ovc cloud cover expected much of the day
and light winds becoming NE. Also, weak upstream 700H short wave
over Dakotas weakens as it progresses ESE but may bring a few light
showers to northern CWA later this afternoon, along with more mid-
level cloudiness. Increasing northeast winds will also cause
lakeshore areas to cool during the afternoon and evening as lake
surface temps are mostly in the 35 to 40 degree range. Benign
conditions to continue tonight with slightly colder temps.
TUESDAY AND WEDNESDAY... Forecast confidence is medium.
A cold front will drop through WI Tuesday in response to a shortwave
trough and surface low crossing Lake Superior. Gusty north-northeast
winds will accelerate down Lake Michigan faster than on land. Lake
temperatures are running 35-37F/2-3C range. 850mb temps are expected
to be in the -9 to -11C range and falling. The difference is
right in that preferred range for lake effect snow showers. Thus,
added a mention of flurries for now and increased sky cover
significantly when the anticipated lake band(s) affect southeast
WI (late Tue afternoon through overnight. Will continue to watch
for potential of measurable snow.
Wednesday should be a cold and clear day, with the exception of some
lake effect clouds due to easterly winds. Highs are expected in the
30s near the lakeshore and around 40 well inland.
THURSDAY THROUGH SATURDAY... Forecast confidence is medium.
Southerly winds with return flow around the high will usher moisture
back into southern WI by Thu evening. A weak shortwave could bring
light precip (snow) to northern WI late Wed night, but this should
miss southern WI or just give us flurries.
Warm frontal precip is expected to arrive late Thu afternoon or
evening. Models are coming into better agreement now. The strong
warm air advection should allow for this precip to be in the form of
rain across southern WI. Went with non-diurnal temp trend Thu night.
The weather pattern favors thunderstorms over the Midwest ahead of
this mid level trough over the Plains. There is a small chance for
thunder Thu night with the warm front, but probably a better chance
Friday along the cold front. Too early and uncertain to discuss
severe potential for southern WI.
Models diverge for Saturday. WI weather will depend on where the
closed upper low tracks.
SUNDAY AND MONDAY... Forecast confidence is medium.
It looks like a very active weather pattern for next week with a
series of shortwave troughs tracking into the Midwest from the
Plains. Temperatures appear warm enough for all rain.
AVIATION(06Z TAFS)...Skies are clearing across south central WI
although believe clouds at 3-4 kft will remain most of the night
and Mon AM near the IL border. Slight chances of showers and
tstorms will continue tonight into Mon AM especially near the IL
border. A weak cold front will pass Mon AM and moisture within the
frontal zone may lead to MVFR Vsbys around sunrise. Partly cloudy
skies are likely for much of Mon with mid level clouds possibly
increasing for late afternoon and evening.
LLWS may be possible into the early overnight via a swly 35-40 kt
Gusts to 22 knots reported at SGNW3 at 07z. Thinking this may be
related to outflow from earlier convection so expect winds to settle
down early. Light onshore flow wl turn to the north to northeast
this afternoon after cold frontal passage. Gusts with these winds
may get close to Small Craft levels. Recent MODIS imagery estimates
lake surface temps in the mid to upper 30s. With mild air remaining
aloft, hoping that low level inversion wl prevent stronger wind
gusts from reaching lake surface. In addition, GFS showing weaker
winds in the low levels compared to NAM and RAP. This is a weak
excuse however as NAM/RAP solutions typically better in forecasting
gusts over near shore waters. Due to low level inversion and model
discrepancy, wl hold off on issuing Small Craft for now. Better
chance for stronger wind gusts Tuesday night into Wednesday as much
colder air sags south across the Great Lakes.
Today/Tonight and Aviation/Marine...MBK
Tuesday THROUGH Sunday...Cronce