Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 210700 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
200 AM CDT Sun May 21 2017

.UPDATE...

Dense fog developed quickly around midnight tonight. Issued a
dense fog advisory. Some areas of dense fog toward south central
WI will be short-lived. Expect visibility to improve in the wake
of the occluded front which will track northeast through the area
overnight.

Showers and a few thunderstorms are expected along the
occluded front. There could also be some pea-sized hail with any
thunderstorms. The freezing level is only 10000 feet and I can see
50 dBZ above that level. There are also lower cc values in the
stronger cores with lightning, indicative of small hail. CAPE is
minimal, so not expecting severe size hail tonight.

&&

.AVIATION(06Z TAFS)...

Updated TAFs to include dense fog until the passage of the
occluded front from southwest to northeast overnight. There could
be some small hail in any thunderstorms along the occluded front.
The front is expected to be over Sheboygan at 7 am this morning.

&&

.MARINE...

Added a marine dense fog advisory for the overnight hours. Expect
fog to dissipate as winds turn southwest and drier air moves in
behind a front. There is a chance of thunderstorms with small
hail along this front. Expect the front to track northeast through
the night, reaching Sheboygan around 7 am.

&&

.PREV DISCUSSION... (Issued 1046 PM CDT Sat May 20 2017)

AVIATION(06Z TAFS)...

IFR conditions will prevail across the area ahead of an
approaching occluded front. Light winds and moist conditions has
lead to areas of fog. That front is still expected to lift into
the Madison area by 08-09z Sun and Milwaukee about 11-12z Sun.
Look for improving conditions in the wake of the front. It looks
like the southeast may improve to VFR CIGS/VSBYS by 13z and stay
there through much of the TAF period. The Madison area would
likely stay in MVFR cigs through most of the TAF period. There is
uncertainty across the southeast as those MVFR CIGS could push a
bit farther east and get into the Milwaukee/Waukesha/Kenosha by
afternoon.

PREV DISCUSSION... (Issued 851 PM CDT Sat May 20 2017)

UPDATE...

Occluded system lifting north as expected. At mid evening, the
Occluded frontal boundary/trough stretched from the IA/MN border
near KEST and KFRM, southeast to KCID, continuing southeast from
there. The front is lifting northeast and will reach Madison by 4
am and Milwaukee about 6 am. The baggy pressure pattern and moist
boundary layer is resulting in fog development with vsbys going
down to 1/2-3/4 mile. We may need a dense fog advisory if trends
continue to tank. There have been some decent showers and few
storms along the front down in Iowa and the HRRR continues to lift
that activity up here. But, we will have much less CAPE available
so should mainly be showers, but will keep a slight chc of storms
going for now. Temps have been warming this evening, so lows were
basically met early in the evening. Conditions should dry out
quickly and vsbys improve in the wake of the passing occluded
front.

MARINE...

Easterly winds and waves continue to diminish. The small craft
advisory will be allowed to expire south of Milwaukee at 9 pm and
for areas to the north at 1 am. Waves remain elevated to the
north. Southwest winds will approach small craft levels on
Sunday and Monday.

PREV DISCUSSION... (Issued 552 PM CDT Sat May 20 2017)

AVIATION(00Z TAFS)...

Surface low pressure will track from western Iowa to northwest
Wisconsin tonight into Sunday morning. An occluded front
stretching east from the low will swing north through the forecast
area between 06-13z Sunday. Look for southeast winds to veer around
to the southwest and west in the wake of the front. Showers and
possibly a thunderstorm may accompany the front as it passes
through. Additionally, winds will diminish in the trough axis that
defines the occluded front. We will see visibilities drop with
the weaker winds and CIGS will remain IFR until the trough swings
through. Look for MVFR CIGS thereafter through the TAF period.
The exception may be across the southeast where CIGS could go to
VFR for a time Sunday morning.

PREV DISCUSSION... (Issued 331 PM CDT Sat May 20 2017)

SHORT TERM...

Tonight and Sunday...Forecast Confidence is MEDIUM...

Rain associated with the mid level short wave, broad 850 jet, and
warm air advection will continue to lift north of the region this
afternoon. Then we will have a break in the rain until later this
evening. A surface low will move across Iowa into NW WI overnight
with an occluded front moving across southern WI. This brings
another chance for showers. There is up to 300 J/KG CAPE so still
a chance for some thunder. Some fog is possible until this front
clear the area.

The upper low will move across MN with cyclonic flow lingering
through Sunday. Low level moisture will hang on the backside of
this system so clouds will prevail through the day. The GFS is
showing some light precip but most other models are dry.

Sunday night through Wednesday...Forecast confidence medium.

The large occluded low over Ontario, Canada will continue to fill
for Sun nt-Mon. A shortwave trough rotating around the occlusion
will track ewd across central WI Sun nt with any rain chances
staying to the north. Another upper trough approaching from the
nw and occlusion will approach for Mon-Mon nt. A sfc trough will
develop with low level warm advection and a 850 mb thermal ridge
developing over srn WI. Thus sfc temps will rise to near 70F for
Mon. The approaching sfc trough/cold front and upper trough will
bring chances of showers for Mon aft-nt. Very marginal CAPE may
form so slight chances of tstorms Mon aft-eve over south central
WI.

The upper trough may then induce weak cyclogenesis from anywhere
from srn WI to nrn IL and ewd for Tue-Wed. Since the upper trough
may become an upper low while getting re-enforced with shortwaves
from the north, the system speed will be low. Thus rain is likely
on Tue and may linger into Wed. Below normal temps to prevail.

LONG TERM...Thursday-Saturday...Forecast confidence medium.

The large upper trough over the central and eastern Great Lakes
will slowly move ewd Thu-Fri. High pressure will arrive Thu nt-
Fri. The high will then shift ewd for Sat with sly flow and warm
advection. This period will thus see a gradual warming trend.

AVIATION(18Z TAFS)...
400-800ft ceilings will stick around through the evening. Some fog
is possible, especially in the east tonight, but confidence on
this is low. A weak front will move through overnight helping to
somewhat improve ceilings and fog. 1-2kt ceilings will likely
continue into Sunday but they may raise to 3.5-5kft in the east
Sunday afternoon.

MARINE...
Northeast to east winds will continue to weaken today. High waves
will linger through the evening as winds become southeast. There
is a small chance for showers and thunderstorms later this
evening. Southwest winds will approach small craft levels on
Sunday and Monday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory until 7 AM CDT this morning for WIZ046-047-
     051-052-057>060-064>066-070>072.

     Dense Fog Advisory until 3 AM CDT early this morning for WIZ056-
     063-069.

LM...Dense Fog Advisory until 7 AM CDT this morning for LMZ643>646.

&&

$$

Update...Cronce
Tonight/Monday and Aviation/Marine...99
Monday Night through Sunday...99



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