Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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850
FXUS63 KMKX 221756
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1256 PM CDT Tue Aug 22 2017

.UPDATE...

Push of drier air now working through the area behind a
reinforcing cold front, with dewpoints dropping into the 50s.
Northwest winds should remain gusty through the afternoon, and
decrease towards sunset.

Cyclonic flow prevails tonight as a closed upper circulation
traverses the upper Great Lakes. Skies will clear this evening,
with good radiational cooling allowing temperatures to drop into
the 50s (perhaps even a few upper 40s in spots).

We`ll remain in northwest flow tomorrow with a shortwave trough
dropping through the western/upper Great Lakes. Cooler air will
ooze down from the north, with 925 mb temperatures falling into
the 10 to 12 degree range by Wednesday afternoon. Some cloud cover
is possible (especially in the east) in association with the
approaching upper wave. Otherwise look for cooler temperatures
with highs in the lower to mid 70s.

&&

.AVIATION(18Z TAFS)...

SCT-BKN 040-060 cumulus will dissipate around sunset. SKC
thereafter. Gusty NW winds up to 25 knots will decrease this
evening. VFR conditions will continue into tomorrow.

&&

.PREV DISCUSSION... (Issued 1009 AM CDT Tue Aug 22 2017)

UPDATE...

Secondary cold front is in the process of working through the
area this morning, with winds veering to northwesterly behind it
and dewpoints dropping off into the 50s. Adjusted winds and cloud
cover to account for this. Also, with cold advection firmly
established, lowered high temperatures by a few degrees for today.
Look for gusty northwest winds to continue through this evening
before easing later this evening.

MARINE...

Offshore winds remain close to Small Craft Advisory levels, with a
few gusts to 25 knots. Holding off on an advisory for now, but
will continue to monitor. Small Craft will need to exercise
caution today. The gusty northwest winds will veer northerly and
weaken late tonight and Wednesday morning.

PREV DISCUSSION... (Issued 628 AM CDT Tue Aug 22 2017)

UPDATE...Secondary front will sweep through southern WI through
mid-morning. Mid-level moisture already diminishing and will see
areas of stratus decrease later this morning as drier air in low
levels surges in from the northwest. Chance for any showers
continues to diminish in southeast WI.

AVIATION(12Z TAFS)...Areas of MVFR stratus wl diminish later this
morning as drier air in the low levels surges in from the
northwest. Few-sct cumulus may linger into the mid-afternoon.
Northwest winds will pick up and gust up to 25 mph.

PREV DISCUSSION... (Issued 327 AM CDT Tue Aug 22 2017)

TODAY AND TONIGHT...Forecast Confidence Is Medium To High.

Few showers popping up last several hours over eastern CWA as
initial surface front moves through. Low to mid level moisture
then begins to decrease as drier air surges in from the northwest.
However a surge of moisture from the south may be just enough to
combine with secondary approaching front from the northwest to
trigger a few additional showers over eastern CWA through 12-13Z.
Also, this area receiving additional synoptic forcing from passing
right entrance region of upper jet. Forecast soundings show
little if any elevated instability, so wl hold off on any T
mention.

Area of stratus moving across southern WI in wake of first front.
Expect another round of stratus associated with approaching
second frontal boundary. Rapid drying of atmosphere later this
morning should thin and dissipate the stratus for the bulk of the
afternoon. Breezy northwest winds will develop this morning but
with sunshine returning and mild start, expect temps to recover
into the mid 70s to around 80. Dry air will become entrenched
across southern WI tonight and along with boundary layer mixing,
will prevent fog formation.

WEDNESDAY THROUGH THURSDAY NIGHT...Forecast Confidence Is Medium.

Models are in pretty good agreement with showing northwest flow
at 500 mb lingering across the region during this period. They
are showing a rather potent 500 mb shortwave trough/vorticity
maximum sliding southeast through the area later Wednesday night
into Thursday morning.

At the surface, high pressure slowly slides southeast into the
the western Great Lakes region. The GFS is the only model that
shows light QPF with the passing shortwave trough later Wednesday
night into Thursday morning. Low levels in area forecast soundings
from the GFS remain rather dry during that time.

For now, left low end PoPs for showers in some areas during that
time. May see diurnal cumulus clouds develop by each afternoon.
Temperatures below seasonal normals are expected Wednesday into
Thursday night.

FRIDAY THROUGH MONDAY...Forecast Confidence Is Medium.

Models are in general agreement with keeping the region in
northwest flow at 500 mb during this period. They are trying to
show a broad trough sliding southeast through the region Sunday
into Monday. There are timing and placement differences between
the models with this feature.

At the surface, high pressure should slowly slide to the east
northeast across the central Great Lakes region into southeast
Ontario Canada Friday into Monday. The influence of the high may
keep the area dry during this period, which is what the models
have trended towards.

For now, kept low end PoPs for showers Saturday night into
Monday, which may need to be lowered or removed later on, if this
dry trend continues. Temperatures look to remain a little below
seasonal normals.

AVIATION(09Z TAFS)...

Periods of MVFR stratus will affect the area this morning. Bulk
of the stratus will thin and dissipate as much drier air surges in
late this morning and afternoon, with VFR conditions then
expected. Breezy northwest winds will gust to 20-25 knots.

MARINE...

Breezy northwest winds will get very close to Small Craft
Advisory levels today and tonight. In fact, a few gusts to 25
knots are likely, but are not expected to be frequent enough to
issue the advisory at this point. Small craft will need to
exercise caution. The gusty northwest winds will veer to the north
and weaken late tonight and Wednesday morning.

&&

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

$$

Update...SPM
Today/Tonight and Aviation/Marine...MBK
Wednesday THROUGH Monday...Wood



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