Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 160448
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1148 PM CDT Wed Aug 15 2018

.UPDATE...

Main concern overnight will be fog development. This should
largely be tied to those locations that saw rainfall earlier
today, suggesting that the southwestern part of the forecast area
will see the most widespread fog potential. Ob trends will be
watched overnight for the potential need for a Dense Fog Advisory.

&&

.AVIATION(06Z TAFS)...

Fog and stratus will continue to develop overnight across the
area. KMSN is likely to see the greatest impacts, with fairly
widespread fog expected by sunrise. Further east, fog will be more
patchy. Even then, stratus should produce IFR to perhaps even LIFR
conditions at all terminals at some point overnight into early
Thursday morning.

Fog/stratus will dissipate by mid morning, with widespread showers
and thunderstorms developing by mid day into the afternoon hours.
As was the case on Wednesday, the most widespread activity looks
to remain just west of the lakeshore area, so kept KMKE and KENW
dry for now, with showers and vicinity thunder at KMSN and KUES.
Similar to Wednesday, activity will dissipate fairly quickly as
the sun sets Thursday evening.

&&

.MARINE...

Light easterly winds tonight will become northeasterly and then
northerly by late Thursday, continuing into Friday. The northerly
fetch will allow waves to build into the 1-3 foot range from
Thursday night through late Friday.

Thunderstorms will again be possible across the nearshore waters
tomorrow, with a generally dry stretch of weather expected until
early next week.

A stronger storm system may affect the region early in the week
next week, but exact details remain unclear at this time. It`s
possible that winds and/or waves may exceed Small Craft Advisory
levels with this system.

PREV DISCUSSION... (Issued 218 PM CDT Wed Aug 15 2018)

DISCUSSION...

Tonight and Tomorrow...Forecast Confidence is Medium

Scattered showers and thunderstorms will continue through the
evening hours. Precipitable water values of 2 inches will be
generally uniform across southern Wisconsin. While the moisture is
readily available and a weak mid level trough will provide some
areas with the instability they need to get showers and
thunderstorms going, the overall instability of the CWA is
relatively low. Sporadic showers and thunderstorms will be
largely driven by pockets of instability combined with diurnal
heating. As soon as the sun goes down, showers and thunderstorms
will begin to taper off.

Given light winds and overnight lows similar to projected dew
points, widespread fog is possible tomorrow morning due to the
high level of available moisture. Dense fog could be possible in
some low lying areas and river valley.

Temperatures will be in the low 80`s for most of the CWA tomorrow
with cooler conditions by the lake. Warm temperatures and
dewpoints in the low 70`s could kick off another round of showers
and thunderstorms especially across the southwestern part of the
state. Storms tomorrow will be as scattered as they were today,
with a general lack of instability showers and thunderstorms will
be overall patchy.

Thursday night and Friday - Confidence...Medium
Surface low will be shifting east through the eastern Lakes. Some
hang back troughiness and influence of positive tilt upper trough
could keep the shower potential lingering a bit into the evening
hours. Low level rh progs show cloud cover could linger into Friday
morning with low level thermal trough in place.

Saturday and Sunday - Confidence...Medium
Expecting a quiet period with surface/850 ridging building in. This
along with an overall anticyclonic regime in the mid levels supports the
going dry forecast.

Monday and Monday night - Confidence...Medium
Main forecast challenge centers on handling of mid level energy and
strength of associated downstream cyclogenesis. The 00z ECMWF and
00z/12z GEM both showed overly strong northerly placed lows developing
with potentially some feedback issues in place. The usually stronger GFS
is weaker and further south though the GFS is a little weaker.
The 12z GFS came in with several bullseyed vorts within the
overall trough axis. So all models are showing a decent chance of
some rain around here but the evolution of this low strength and
track still has some doubt to it, especially given the time of
year. Also the ECMWF had showed a strong low for this latest
system and it turned out much weaker, so will be interesting to
see if future model runs continue to show a strong low.

Tuesday and Wednesday - Confidence...Medium
A period of cold advection/low level thermal troughing looks likely
in the wake of the departed system. The morning model runs have come
in with a weaker/drier look with a secondary wave for Tuesday that
the 00z run had. Will stick with blended guidance at this point.
High pressure will then dominate for Wednesday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Update...Boxell
Tonight/Thursday and Aviation/Marine...Boxell
Thursday Night through Wednesday...99


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