Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 211810 AAA
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
110 PM CDT THU JUL 21 2016
Thunderstorms that moved through the northern and eastern portions
of the area this morning have pushed an outflow boundary to a
southeast Rock County to northwest Iowa County line. The airmass
to the northeast of the outflow boundary has cooled off from
precipitation, with dew points dropping somewhat. The debris
clouds from the convection are slowly moving out of the area.
We should see enough sunshine to get temperatures and dew points
high enough to just reach Heat Advisory criteria in the southern
half of the area. It may be tough toward the southeast counties if
winds do not shift southwestward. Areas southwest of the outflowboundary
remain hot and humid, and should just reach Excessive Heat Warning
criteria. Some uncertainty here with trends, but think these
headlines will remain the same with the afternoon forecast
Thus, kept that headline in the southwest three counties, with a
Heat Advisory elsewhere in the south half of the area, as well as
Sauk County. Forecast temperatures and dew points for Friday look
to keep heat index values similar to today. Some uncertainty here
as well, depending on if we get more storm development.
Other issue is thunderstorm chances this afternoon into Friday
across the area. Outflow boundary across the southwest counties
may help kick off some thunderstorm activity this afternoon into
this evening. However, it will have to deal with a decent cap
aloft with the hot and humid airmass trying to push into the area.
There will be a surface to 850 mb boundary sagging southward
through the region tonight into Friday. Not a lot of upper support
is seen over the area. Mesoscale models are showing spotty
convection developing in eastern parts of the area later tonight
into Friday morning.
Likely will continue to use lower end POPs for now through
Friday, given the good amount of uncertainty here. Large CAPE with
weak to modest deep layer shear suggests isolated severe risk,
with locally heavy rainfall possible with high precipitable water
VFR conditions are expected at TAF sites this afternoon, most of
tonight into Friday across TAF sites. There may be a period of
light fog later tonight into Friday morning, with light winds and
moist airmass across the area.
A frontal boundary will slide southward across the region tonight
into Friday. There are chances for thunderstorms with the front
during this time, but uncertainty exists with if and how
widespread any storms may be. Thus, will leave out any thunder
mention in TAFs for now.
Winds should shift south to southwest this afternoon, with some
gusts to 20 knots or so possible. Winds should become lighter
tonight into Friday morning, as the front moves through the area.
Winds should gradually veer to the northwest to north later on
Friday, with northeast winds possible at the eastern sites.
Areas of fog continue across the nearshore waters of Lake
Michigan, in the wake of the storms. May see dense fog at times
into the weekend, until the dew points lower early next week. The
best shot for dense fog will be with periods of light winds. Dense
Fog Advisories may be needed at times into this weekend.
There is a chance for thunderstorms into Friday, as a frontal
boundary slides south across the region. Some uncertainty here
with if and how widespread the storms may be.
.PREV DISCUSSION... /Issued 436 AM CDT THU JUL 21 2016/
TODAY AND TONIGHT...The severe MCS over nw WI and ern MN continues
to move sewd being fueled by strong thetae advection and resultant
MUCAPEs of 3000 joules. Do not see why it would not continue into
srn WI and went with likely PoPs over the nrn and ern CWA for now.
Believe the SVR potential will remain with the MCS through the
morning. Due to the rain cooled air and morning cloudiness,
cancelled the heat headlines north of Madison and Milwaukee.
Confidence was lower on taking the same action elsewhere. Also those
areas may still reach heat criteria on Friday whereas to the north
it probably won`t. Only 20-30 PoPs for thunderstorms from later
this afternoon and tonight.
FRIDAY... Forecast confidence is medium.
There is a good chance for quiet weather across southern WI on
Friday. Any convection today and/or tonight should push outflow
boundaries south of the WI border by Fri. If not, a surface trough
making its way through the region should be south of WI by midday.
The hot air will have a chance to build into central WI and expand
into south central WI during the day Fri, so as long as there are no
thunderstorms, we should be able to reach heat advisory criteria in
the southwest half of the MKX forecast area Friday.
SATURDAY AND SUNDAY... Forecast confidence is medium.
Warm air advection (WAA), the nose of a low level jet and weak
shortwave activity will bring a decent chance for showers and
thunderstorms to WI Saturday. There is a better chance in the
afternoon than morning. Persistent WAA will keep the thunderstorm
chances going Sat night. Southern WI is in a marginal risk for
severe storms due to decent elevated CAPE.
A stronger shortwave trough tracking through the Northern Plains
will drag a surface trough/cold front through WI Sunday afternoon.
There should be thunderstorms with this front, with a chance for
severe due to strong cape but only marginal shear.
MONDAY THROUGH WEDNESDAY... Forecast confidence is medium.
It looks like a cooler and quieter weather pattern is in store for
southern WI for the first half of next week with high pressure over
the Great Lakes.
Both the GFS and ECMWF are showing a potent shortwave tracking
through the Upper Great Lakes for the middle of the week which will
bring our next chance for storms.
AVIATION/12Z TAFS/...A low stratus deck will continue over south
central WI this morning until thunderstorms pass from nw to se
through srn WI from 1330z through 1800z. Strong gusty winds, reduced
vsbys and cigs are expectd with the storms. Scattered cumulus is
then expected afterward. Tonight, stratus and light fog may form
especially due to the wet conditions from today`s rain.
MARINE...Sly flow is expected today and tonight but the wind flow
will likely be interrupted by a thunderstorm complex that will pass
later this morning. Strong gusty and variable winds are possible
during that time. Dense fog may occur at times from this afternoon
into the weekend due to a very moist airmass over the relatively
cooler waters of Lake MI.
WI...EXCESSIVE HEAT WARNING until 7 PM CDT Friday for WIZ062-067-068.
HEAT ADVISORY until 7 PM CDT Friday for WIZ056-063>066-069>072.
TODAY/TONIGHT AND AVIATION/MARINE...Gehring
Friday THROUGH Wednesday...MRC