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afdmkx

Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
1059 PM CDT Tue Jul 16 2019

Update...

A few intersecting convective outflow boundaries and a mid level
short wave moving overhead is keeping the activity alive west of
Madison, primarily over Iowa County late this evening. But,
intensity is beginning to diminish and infrared satellite tops are
warming lending support to the short range models wiping this out
over the next hour or so. We should then be fairly quiet across
the area until the next round pushes in tomorrow night.

&&

Aviation(06z tafs)...

The showers/storms around Madison and points west will likely
diminish by around 06z Wed. We could see some light fog across
the area late tonight and for a few hours after sunrise on
Wednesday. There's fog out over Lake Michigan and some of that
could drift inland a bit. Otherwise, expect VFR conditions across
the area through much of the taf period. Winds will generally
remain below 10kts through the period.

&&

Previous discussion... (issued 850 PM CDT Tue Jul 16 2019)

Update...still a few cells percolating across SC WI but expect
this activity to largely Peter out over the next couple hours.

Pc

Marine...hoisted a dense fog advisory for the lake to account for
upwelling of colder temps near the shore. Also seeing some
development across parts of the Northern Lake as well. Overall
pattern will be conducive to fog with higher dew points over the
relatively cooler waters.

Pc

Previous discussion... (issued 544 PM CDT Tue Jul 16 2019)

Update...

Main concern this evening will be trends with the convection just
west of the MS river. As mentioned in the recent prior fcst
discussion, this is driven primarily by diurnal heating with
deeper lift from a mid level short wave moving through. The low
level flow is weak. This should all settle down once we lose the
sun angle this evening, but they could sneak into areas west of
Madison before they die off. The current forecast has this
handled well for now, but will keep an eye on it. So far, it's
behaving itself.

Aviation(00z tafs)...

Overall, expect VFR conditions through the taf period. There could
be some late night/Post sunrise MVFR visibility fog on Wednesday. There
are storms just west of the MS river this evening and they could
sneak into areas well west of Madison before diminishing during
the evening. More showers and storms are possible Wednesday
evening. Winds will remain below 10kts during the period.

Previous discussion... (issued 337 PM CDT Tue Jul 16 2019)

Short term...

Tonight and Wednesday...forecast confidence is medium.

It appears the showers with the remnants of Barry will remain
over NE Illinois and far srn Lake Michigan for the remainder of the afternoon.
Otherwise, convection along the Minnesota/Iowa border is slowly moving
ewd. The overall flow and lift is weak but it is being supported
by a vorticity maximum that is expected to track to NE Iowa by
midnight and into nrn Illinois afterward. Based on the current movement
and sfc based cape of 2000 j/kg, will go with chances of showers
and tstorms west of Madison this evening.

Later tnt, a very weak cold front will drop swd from the nrn
Great Lakes into east central and se WI. Due to the late timing
and very weak convergence, will maintain a dry forecast with the
frontal passage. The Ely winds over far ern WI will maintain some
relief from the heat for Wed. Very warm and humid conditions with
heat index values in the middle 90s are forecast well inland.
Another concern for Wed aft is a mesoscale convective system that will likely be ongoing
over srn Minnesota. Most models either weaken it or dive it sewd, thereby
missing much of south central WI. Went with slight chance pops
west of Madison late in the day.

Long term...

Wednesday night and Thursday...forecast confidence is medium:

The low level jet will lean more into the area Wednesday night,
with increasing moisture and instability expected into the night.
A majority of models are suggesting a thunderstorm complex will
come rolling into southern Wisconsin later in the night into early
Thursday morning. The environment will certainly be supportive of
this scenario, so leaned the forecast in this direction. There
will be a chance these storms could be severe, with damaging wind
the main threat.

Lowered temps Wed night and Thursday a bit given the expected
storms and lingering cloud cover. The low level southwest flow
should help to to warm up by the afternoon if clouds get out of
here, so still looks like a pretty warm day. Could see heat index
values crack 100.

Friday through Sunday...forecast confidence is medium:

Models are in pretty good agreement that Friday should be the
hottest day of the week. It looks dry through the day, with the
warm southwest flow keeping dewpoints and temps aloft on the high
side. The lows Thursday night might struggle to fall much below
80, so Friday will get a running start with temps. The warmer end
of models have 925 mb temps in excess of 30c, which would suggest
the potential for surface temps to hit 100. Dewpoints won't need
to be particularly high for heat indices to reach the 105 to 110
range. Friday has the best chance to see heat headlines through
the end of the week.

Models have sped up with the timing of a cold front Saturday,
which has the potential to result in lower temps. A slower front
could mean temps similar to Friday, while a faster front would be
much less heat. Kept the southern forecast area on the hotter
side, with heat indices possibly cracking 100 again. There will be
a chance for storms with the front.

Sunday does look cooler, as the cold front should be south of the
area. Could be some storms lingering, particularly in the morning.
This storm chance will depend on how fast the front pushes
through.

Monday and Tuesday...forecast confidence is medium:

Temps should be back near normal early next week. Kept a slight
chance for storms, but models have been trending drier under high
pressure.

Aviation(21z tafs)...sct030-050 cumulus this afternoon but with
local MVFR cigs over se WI. Mostly VFR conditions for tnt with
local MVFR vsbys via light fog for early morning through sunrise.
More sct025-035 cumulus to follow for late morning and the
afternoon.

Marine...light to modest sswly flow over Lake Michigan will turn nely
from north to south across the lake tnt-Wed am in response to a
cool frontal passage. The winds will remain light until late
Wed nt when modest sswly flow will once again develop and
continue through Friday. This is in response to a couple low
pressure areas moving east across srn Canada.

&&

Mkx watches/warnings/advisories...
WI...none.
Lm...dense fog advisory until 1 PM CDT Wednesday for lmz080-261-362-
364-366-563-565-567-643>646-669-671-673-675-777-779-868-870-
872-874-876-878.

&&

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