Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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097
FXUS63 KMKX 230157
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
857 PM CDT Tue May 22 2018

.UPDATE...
Clouds have continued to clear this evening. There is a lingering
area stretching west to northwest of Madison, but it`s shrinking.
There continues to be some concern for fog late tonight into
Wednesday morning. Soundings look pretty dry above the shallow
boundary layer. So, the fog looks like it may end up being shallow
and mainly in the favored low spots. But, local visibilities could
drop to 1/4 mile for a time between about 5-7am Wed morning. The
forecast is in good shape.

&&

.MARINE...
There may be some fog across the marine area overnight into early
Wednesday morning, but it`s expected to move out within a few
hours of sunrise on Wednesday. Otherwise, quiet conditions over
the nearshore waters for the next few days.

&&

.PREV DISCUSSION... (Issued 612 PM CDT Tue May 22 2018)

UPDATE...

There`s some clearing of the clouds due to diurnal trends into the
evening, especially over the southeast. A more stubborn area west
of Madison is stuck under the high pressure ridge axis and may be
tough to clear. It could even expand as we cool tonight. Also,
areas in the east that cleared out may fog in due to the usual
ingredients...clear skies, light winds, elevated dew points.
Current forecast looks good. &&

AVIATION(00Z TAFS)...

MVFR CIGS over south central Wisconsin will be slow to clear under
a stagnant high pressure system. They should continue to erode,
but very very slowly. They may even stall or expand slightly in
the calm and cool night. The east is clearing steadily due to
drier air moving in off the lake. This is an area most susceptible
to some dense fog development between about 10-12z Wednesday. All
of the low clouds and fog should clear by about 14z Wednesday
with VFR conditions for the remainder of the TAF period.

PREV DISCUSSION... (Issued 247 PM CDT Tue May 22 2018)

DISCUSSION...

Tonight and Wednesday...Forecast Confidence is medium.

Weak northwesterly flow will prevail aloft tonight, as southern
Wisconsin remains downstream from the mid to upper level ridge
axis located over the Great Plains. Surface high pressure will
settle over southern Lake Michigan tonight, with light and
variable low-level winds. Cloud cover should partially scatter
out this evening and early tonight, setting the stage for fog
development given light surface winds and antecedent surface
moisture. The timing for any potential dense fog appears to be
somewhat later than yesterday per model guidance, which suggests
visibilities don`t really tank until after midnight. We`ll need to
keep a close eye on timing the fog this evening should conditions
deteriorate faster than anticipated. Lows tonight will drop off
into the 50s.

Rising heights aloft will occur on Wednesday as some weak
perturbations crest the central CONUS ridge and ride the upper
flow into the upper Mississippi Valley. Showers and thunderstorms
will accompany the upper level disturbance, but protective
influence of low-level ridging should be enough to keep this
activity west of our area through tomorrow evening. Have removed
PoPs from our far west during this time, as it appears we`ll stay
dry through 00z Thursday. Southerly winds will bring warmer
temperatures into the area, with winds turning more southeasterly
by Lake Michigan. Highs will range from around 80 well inland to
the upper 60s along the Lakeshore.

Thursday and Friday - Confidence...Medium
Mid level ridge axis and influence of lower level anticyclonic
flow regime should keep southern WI more in the drier/more stable
airmass this period. However the western and northwest cwa is
closer to where some return flow type shra could develop with
models very close with some light qpf there. As we get later into
Friday the mid level ridge slips east and some energy starts to
work into the area. Surface trough draws closer and low level
moisture transport ramps up as well so feel more confident in
expanding some pops into the area beginning Friday afternoon. 925
temps are proggd to nudge into the low 20s celsius so warmup on
the way.

Friday night through Sunday night - Confidence...Medium
Pattern looks overall warm and unsettled. 500 millibar flow is
northwest with an overall weak though somewhat cyclonic look. In
the low levels the 925 temps will continue to support a warm
regime with temps in the low/mid 20s celsius. So some areas will
be well into the 80s. The surface/850 pattern looks overall
diffuse with some troughing. So some chances will be sprinkled
here and there within this period but not expecting any all day
rains. No indication of any organized severe potential either. The
temps may eventually may need boosting in some areas but for now
content with the idea of inland areas heading well into the 80s.

Memorial Day and Tuesday - Confidence...Medium
The GFS and GEM are indicating the potential for a backdoor cold
front. GFS and GEM show this arriving Monday night. However the
12z ECMWF shows this feature arriving on Memorial Day. Warm/humid
in place ahead of this feature so must keep some mention of
shra/tsra in the forecast on Monday with some lingering showers
into Tuesday though looks like that would be early as the
focusing boundary shifts to our south.

AVIATION(21Z TAFS)... Flight conditions will improve into early
evening with MVFR to VFR ceilings. Ceilings and visibilities are
expected to lower later tonight, with fog development likely. Some
of the fog may become dense, with the greatest chance for this
tonight after midnight. However there is some uncertainty in both
how widespread and how quickly any dense fog will develop. For
now, advertised 1 to 1/2 SM visibility in the TAFs, but this may
require amendments tonight depending upon how things unfold. The
key message however is that the potential for IFR/LIFR
visibilities exists later tonight. Any fog should rather quickly
mix out by mid morning on Wednesday, with ceilings rising to MVFR
thereafter.

MARINE...Drier air pushing down the lake has cleared out the fog.
Therefore the dense fog advisory has been cancelled. However, dense
fog may again develop tonight, so remain alert for rapidly changing
visibility during this time. Otherwise, light winds and waves are
expected for tonight into Wednesday.

&&

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

$$

Update...Davis
Tonight/Wednesday and Aviation/Marine...SPM
Wednesday Night through Tuesday...Collar



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