Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

000
FXUS63 KMKX 151141
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
641 AM CDT Sat Jul 15 2017

.AVIATION(12Z TAFS)...
Look for any patchy fog this morning to burn off quickly. Then VFR
conditions are generally expected through the TAF period. Cooler
northeast winds later tonight could introduce some MVFR CIGS
across the area. There is a chance of thunderstorms this evening
ahead of an approaching cold front from the northwest. The period
of concern for KMSN would be 01-04z Sun, and 03-06z at KMKE. A
brief period of MVFR CIGS/VSBYS may accompany any activity that
moves through. Look for light and variable winds to turn southwest
this morning and increase ahead of the cold front. Winds will
shift to northwest then northeast late tonight into Sunday
morning behind the front.

PREV DISCUSSION... (Issued 314 AM CDT Sat Jul 15 2017)

Today...Forecast confidence is high.

A nice day is on tap for southern Wisconsin as high pressure in
place early in the morning gradually slides off to southeast
during the day. Any rain will hold off until evening. Lower
dewpoints early on will see modification into the 60s as an
increasing southwest flow ahead of an approaching trof/cold front
pulls in moisture from the southwest. GOES 16 total precipitable
water shows an axis of higher moisture stretching from northwest
Missouri north through Minnesota. That will lean into Wisconsin
ahead of the front. Our current PW value of around .50 to .75
inch is expected to increase to 1.25 to 1.5 inches ahead of the
front. So, we`ll feel a noticeable increase in humidity as we push
into the late afternoon, especially over south central Wisconsin.

Tonight...Forecast confidence is medium.

The Storm Prediction Center outlook for tonight across southern
Wisconsin remains unchanged. Most of the area is under a slight
risk of severe storms. We expect a line of scattered thunderstorms
to develop later this afternoon across central Wisconsin, then
move rather quickly south southeast into southern Wisconsin
during the evening. Any severe storm activity will be isolated.
These will be along and ahead of the cold front, supported by the
axis of higher moisture and a weak mid level wave dropping
through. This is classic northwest flow stuff, with the main
threat large hail and strong gusty winds. There is a dry layer
that may add to some evaporative cooling supporting the gust
potential.

With regard to concerns about rainfall across Walworth, Racine
and Kenosha counties...rainfall amounts should be on the light
side as the speed of the storms will be rather quick. Even if an
area gets elevated amounts, it will be localized and should have
little or no impact on river level trends.

SUNDAY AND MONDAY...Forecast confidence is medium.

A 500 hPA ridge will elongate across the southern CONUS from the
Desert Southwest into the Southern Plains. An extension of the mid-
level ridge will branch poleward into the western Great Lakes with
building heights aloft. This will support surface high pressure, as
it centers near Lake Superior on Sunday, and remains anchored there
into much of Monday. Anticyclonic flow around the high will promote
north to northeasterly winds through this period, bringing a cooler
and drier flow off Lake Michigan into the eastern counties. This
will hold temperatures just a tad below seasonal normals, with
highs mostly in the 70s and lows in the 50s.

TUESDAY THROUGH THURSDAY...Forecast confidence is medium.

A more progressive zonal pattern takes hold, with a series of
shortwave perturbations bringing chances for both strong
thunderstorms and heavy rainfall at times. The first chance may
develop Tuesday night into Wednesday morning, possibly in the form
of a decaying MCS diving south from Minnesota and northern Wisconsin
overnight. Will need to keep an eye on this for heavy rain potential
given favorable parameters for high precipitation efficiency. In
particular, we`ll see warm cloud depths approaching 4.5 km, and
precipitable water values approaching 2 inches. Moisture transport
into central/southern Wisconsin is maximized from roughly 06-12z
Wednesday, before the deeper moisture slides off to the east
Wednesday afternoon. A few stronger storms are possible, given
around 35 knots of westerly shear and MLCAPE around 500-700 J/kg
Wednesday morning. It will feel increasingly muggy by Tuesday night,
with dewpoints climbing to around 70.

There is some uncertainty with convective trends later on
Wednesday, as this will depend somewhat on when any morning
precipitation departs and on where any residual outflow boundaries
end up. It`s possible that we may end up dry for a time during
the afternoon before convection chances increase by Wednesday
night. Regardless, it should feel plenty warm and humid with
temperatures climbing well into the 80s and dewpoints reaching the
lower to perhaps mid 70s.

There is good general agreement among the deterministic guidance in
driving one or more convective complexes east across portions of the
region from Wednesday night into Thursday. The 14.12z ECMWF and
14.18z GFS solutions would target central to southern Wisconsin as
having a better chance for precipitation from this. The new
15.00z GFS run is somewhat of a departure, keeping the better
moisture transport and precipitation chances during this period to
our south across Iowa and northern Illinois. We`ll obviously need
a little more time to see things clearer, but be aware that this
is another period to watch carefully for heavy rain and strong
thunderstorm potential.

FRIDAY AND SATURDAY...Forecast confidence is medium.

The focus for precipitation should shift largely to our south on
Friday, as the surface convergence axis drifts into northern
Illinois. Shower/thunderstorm chances should return for Saturday as
broad low pressure progresses through the Upper Midwest and western
Great Lakes. Near to above normal temperatures are expected.

&&

AVIATION(12Z TAFS)...

Look for any patchy fog this morning to burn off quickly. Then VFR
conditions are expected through the TAF period. There is a chance
of thunderstorms this evening ahead of an approaching cold front
from the northwest. The period of concern for KMSN would be
01-04z Sun, and 03-06z at KMKE. A brief period of MVFR CIGS/VSBYS
may accompany any activity that moves through. Look for light and
variable winds to turn southwest this morning and increase ahead
of the cold front. Winds will shift to northwest then northeast
late tonight into Sunday morning.

&&

MARINE...

Winds and waves will be below small craft advisory levels today
with light and variable winds becoming southwest this afternoon.
Northeast winds arriving in the wake of a passing cold front on
Sunday could bring small craft advisory conditions Sunday into
Sunday evening.

&&

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

$$

Update...99
Today/Tonight and Aviation/Marine...Davis
Sunday THROUGH Friday...SPM



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.