Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 280224
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
924 PM CDT THU OCT 27 2016
.UPDATE...Weak isentropic omega and upglide contributed to a few
sprinkles getting shaken out of the mid clouds that quickly spread
across southern WI during the evening. Received a trace here at
MKX as well as at KMKE. These sprinkles will be ending shortly as
the weak forcing and lower condensation pressure deficits on the
300 omega surface slide off to the southeast. Mid-clouds most
likely acted as a seeder-feeder mechanism for the sprinkles.
Low clouds continue to erode across southeast and parts of south
central WI. Increasing boundary layer mixing north of developing
warm front should continue the erosion, however increasing
southeast low level winds may serve to advect upstream large
stratus field lingering over central Great Lakes and northern OH
valley region. Can not get a feel for dissipation of low clouds
due to widespread mid-high clouds over the area. More confident on
removing fog mention in the western CWA for late tonight due to
increasing boundary layer winds and considerable cloud cover
expected during the late night.
.AVIATION/06Z TAFS/...See above discussion regarding clouds. Still
think increasing boundary layer winds from the SSE may advect more
MVFR cigs into the area during the late night. Confidence low on
cloud forecast into Friday morning.
.MARINE...Light and variable winds will turn to the southeast
overnight and then veer to the south as low pressure moves through
the northern Plains, resulting in a tightening pressure gradient.
Still expect some gusts to gale levels in northern zone.
.PREV DISCUSSION... /Issued 323 PM CDT THU OCT 27 2016/
TONIGHT AND FRIDAY...Forecast confidence is medium.
Low to mid level clouds will linger this evening and overnight as
residual moisture slowly moves to the northeast. Sfc high pressure
will eventually make its way across Illinois and southeast of
Wisconsin this evening, which will result in weakening winds. Drier
air will also translate into southern Wisconsin overnight, which
should bring more broken sky cover than overcast. Higher dewpoint
temperatures in our western most tier of counties will support some
patchy to areas of light fog, which is forecast to remain west of
Madison. However, some of the latest guidance is suggesting that fog
will be more widespread across the area than previous runs.
An area of low pressure will eventually make its way across the
northern Great Plains and into northern Minnesota during the day
Friday. We will be right in between the sfc high and low pressure
systems, which will result in a tight pressure gradient. So,
southerly winds look to intensify, with wind gusts up to 30 kts over
land Friday afternoon and evening. Additionally, a 60+ kt low level
jet (LLJ) is progged to move through the area Friday afternoon and
into the evening. Wind gusts Friday will depend on how high boundary
layer mixing reaches to mix down the LLJ.
Friday night and Saturday...Forecast Confidence Is High.
The upper level flow remains zonal as a 130 knot jet max moves
across the Upper Great Lakes and Canadian border area. Mainly
weak upper level divergence and upward 700 mb motion occurs with
moderate upward motion especially during the early afternoon that
extends into the late afternoon late afternoon far southeast.
700 mb RH increases saturday afternoon ahead of a weak 700 mb
850 mb moisture dries Friday night except near the Illinois border
area. 850 mb RH increases, especially south during the afternoon.
A cold front enters southern Wisconsin Friday night, but does not
exit the far southeast until early evening Saturday.
The NAM produces some very light QPF Friday night but the GFS and
ECMWF are still dry. The models then spread some light rain
across portions of southern Wisconsin Saturday afternoon.
SATURDAY night and Sunday...Forecast Confidence Is High.
Both the GFS and ECMWF exits a very weak shortwave across
Wisconsin Saturday night with a weak upper ridge building into the
Upper Mississippi Valley Sunday. Little in the way of upper
divergence or upward motion after the shortwave exits Saturday
evening with 700 mb drying behind the departing trough axis. The
low levels dry a little later Friday Night.
The GFS and ECMWF produce some rain with the mid level trough
axis and baroclinic zone Saturday evening. High pressure then builds
into the Upper Mississippi Valley later Saturday night and across
the Great Lakes Sunday.
Sunday Night and Monday...Forecast Confidence Is Medium.
A rather strong mid/upper level shortwave moves across the Rockies
Sunday Night and into the Northern Plains Monday. This forms a
strong low across western South Dakota that reaches northern
Minnesota by early Monday evening. A brisk south wind will briefly
bring warm air back into Southern Wisconsin Monday. Both the GFS
and ECMWF keep southern Wisconsin dry.
Monday Night and Tuesday...Forecast Confidence Is Medium.
The shortwave moves into southeast Canada Monday night.
Cold air advection dominates behind a cold front. The models do
not produce any showers with the cold front.
Wednesday...Forecast Confidence Is Medium.
A west/southwest upper flow extends across Wisconsin Wednesday.
The ECMWF brings Surface high pressure across Wisconsin and the
Great Lakes. However the GFS stalls the front across northern
Illinois with showers along the Illinois border area.
Thursday...Forecast Confidence is Low.
The GFS builds an upper ridge across Minnesota and the Western
Mississippi valley, while the ECMWF has a much weaker ridge.
The GFS builds a surface high across Wisconsin with the ECMWF
having the high much farther north with a trough pushing into
southern Wisconsin with rain.
MVFR cigs will improve to VFR later this evening as drier air moves
into the area. There is the potential for some MVFR fog overnight,
especially in the western areas, as higher dewpoint temperatures
move in. The MSN TAF site looks to be the most likely to see fog
development, but latest short-term guidance is suggesting that fog
may develop farther east over the UES area, so watch for these
Winds look to intensify starting Friday morning due to a tightening
pressure gradient and strengthening low level jet (LLJ) of 60+ kts.
Wind gusts could reach up to 30 kts over land. With the
strengthening LLJ, there is a concern for low level wind shear
Friday afternoon and into the evening.
An area of low pressure looks to develop and translate across the
northern Great Plains into northern Minnesota Friday. Southerly
winds look to intensify starting Friday morning as surface pressure
gradient strengthens. Winds gusts will likely reach to 30 kts, with
some gusts reaching gale criteria, especially from Sheboygan to Port
Washington due to better fetch over the Lake Michigan waters. So, we
have issued a Gale Warning from Sheboygan to Port Washington from
noon Friday through 1 AM CDT Saturday, and a Small Craft Advisory
from Port Washington to Winthrop Harbor from noon Friday to 6 AM CDT
Saturday for the remaining nearshore zones.
LM...SMALL CRAFT ADVISORY from noon Friday to 6 AM CDT Saturday for
SMALL CRAFT ADVISORY from 1 AM to 6 AM CDT Saturday for LMZ643.
GALE WARNING from noon Friday to 1 AM CDT Saturday for LMZ643.
TONIGHT/Friday AND AVIATION/MARINE...JTS
Friday NIGHT THROUGH Thursday...Hentz