Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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539
FXUS63 KMKX 250005
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
705 PM CDT Sun Sep 24 2017

.UPDATE...

With high pressure situated over the Great Lakes, little change
to the previous forecast was needed. I did trim back the pops
early tomorrow afternoon. I did this because the GFS is the only
guidance showing QPF across our west before 00z, and the support
on the GFS is quite weak.

&&

.AVIATION(00Z TAFS)...

VFR conditions will remain in place through the TAF period.
Tomorrow will be quite similar to today, with perhaps more
scattered 5kft clouds. River valley fog remains a possibility, and
showers should begin to move into our west Monday evening.

&&

.PREV DISCUSSION... (Issued 237 PM CDT Sun Sep 24 2017)

SHORT TERM...

Tonight and Monday...Forecast confidence is high:

High pressure to the east will pull away tonight into Monday as a
weak trough approaches. Southerly low level flow between the
approaching trough and departing high will keep an unseasonably
warm airmass in the area. Temperatures tonight and tomorrow will
be fairly similar to the last 24 hours. The main difference will
be in increase in moisture which will produce more clouds. Thus
decided to go with high temps tomorrow just a little lower than
today.

Seems like enough moisture/instability for a couple
showers/storms in the west by tomorrow evening, so left some low
precip chances in there.

Monday night and Tuesday...Forecast confidence...High

A lead upper shortwave moves into the Upper Mississippi Valley
region Tuesday evening, with the upper jet across eastern
Minnesota and northwest Wisconsin. Upper level divergence is
neutral or weak across southern Wisconsin, but 700 mb upward
motion increases Tuesday afternoon south central sections. 700/850
mb RH increases south central. Surface based CAPE west and
northwest of Madison rises to 1500 Joules/kg, but only around 500
Joules/kg of zero to 1 km mixed layer Cape. With the marginal
forcing and shallow layer of moisture around 800 mb, will keep
shower and thunderstorm chances in the low to medium range.

The surface cold front does make it through south central
Wisconsin Tuesday afternoon.

LONG TERM...

Tuesday night and Wednesday...Forecast confidence...High

The lead upper shortwave moves to the north of lake Superior,
with the upper jet across Wisconsin. Moderate upper level
divergence overnight, lingering far southeast Wednesday morning.
Moderate 700 mb upward motion southeast Tuesday evening, then
downward motion spreading in from the west. Little in the way of
zero to 1 km mixed layer Cape. Soundings do show moistening over
the atmospheric column. With the marginal forcing lifting
northeast, will keep shower chances in the low to medium range.

The surface cold front makes it through southeast Wisconsin
Tuesday evening. Strong drying occurs Wednesday behind the cold
front.

Thursday through Sunday...Forecast confidence is Medium

The upper trough re-establishes itself over the Upper Mississippi
Valley Thursday, and over the Great Lakes Friday. Cooler air
(near normal) is expected, with some instability showers possible
with the upper trough, mainly Thursday night and Friday.

A large surface high moves across Saturday on the ECMWF, but is
quicker on the GFS.

Warm air advection begins on the GFS later Saturday, and on Sunday
on the slower ECMWF.

AVIATION(18Z TAFS)...

VFR conditions are expected through Monday as southern Wisconsin
sits under the western edge of high pressure. The only exception
could be a little river valley fog later tonight into early Mon
morning. Few-Sct diurnal cumulus are likely this afternoon and
again Monday afternoon. Could see an isolated shower/storm in the
west by tomorrow evening.

MARINE...

Light winds and low waves are expected for the first couple days
of this week.

&&

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

$$

Update...BSH
Tonight/Monday and Aviation/Marine...DDV
Monday Night through Sunday...Hentz



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