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000 
FXUS63 KMKX 261823
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
123 PM CDT Sun Mar 26 2017

.UPDATE...

A few observations are still reporting dense fog, but with
occasional improvement. Expecting slight improvement through the
afternoon, so allowed the dense fog advisory to expire.
Highlighted the localized areas of dense fog in a Special Weather
Statement. Will continue to assess, as we may need to re-issue a
dense fog advisory for later this afternoon through tonight.

The baggy surface pressure gradient will remain over southern
Wisconsin all the way through Monday. Expect intermittent fog and
drizzle, along with low clouds. 

&&

.AVIATION(18Z TAFS)...

Low clouds, fog and drizzle will continue to be a problem across
southern Wisconsin tonight and all the way through Monday as weak
low pressure slowly crosses the area. There should be a brief
period of ceiling/visibility improvement this afternoon, then
conditions will go back down tonight. Things should improve once
again Monday afternoon, but could go down again Monday night. 

A note about the Milwaukee observations today: the tower 
visibility is being reported as one quarter mile since it is 
within the low clouds. This is the prevailing visibility showing 
up in the METAR observation and is being coded correctly. The ASOS
is reporting surface visibility of 3SM and webcams confirm this. 

&&

.PREV DISCUSSION... (Issued 1034 AM CDT Sun Mar 26 2017) 

UPDATE...

Calls to a few counties and area web cams informed us that there 
were still areas of dense fog across Lafayette and Green counties,
but other counties were seeing improvement in visibilities.
Therefore, extended dense fog advy for Lafayette and Green until
noon, and allowed the other counties to expire. Another batch of
rain moving through south central WI should help dissipate the
dense fog.

The warm front is expected to nose into southeast WI late this
afternoon. This will help temps rise into the 50s and should
diminish the precip. Expecting light rain showers off and on 
elsewhere with highs in the 40s. 

MARINE...

Extended the marine dense fog advisory until 7 pm this evening as
low pressure tracks across southern Lake Michigan. This lines up
with the timing of fog headlines over the open lake. There is a
chance that visibilities could take until midnight to improve in
the wake of the low pressure.

PREV DISCUSSION... (Issued 650 AM CDT Sun Mar 26 2017) 

UPDATE...

Issued dense fog advisory south central in the counties bordering
Illinois closer to the approaching low with lighter winds. May 
need to expand a little more north. However rain pushing north 
from northeast illinois is causing a slight improvement in the 
visibilities far southeast. 

AVIATION(12Z TAFS)...

IFR/LIFR cigs and Vsbys are expected to persist through the day 
over most of the areas as low pressure moves slowly northeastward 
across far southeast Wisconsin. Areas near the Illinois border in 
southeast Wisconsin should get into the cloudy warm sector 
briefly late this afternoon with MVFR cigs. Scattered showers with
patchy drizzle will continue, with more persistent rainfall in 
the east.

PREV DISCUSSION... (Issued 320 AM CDT Sun Mar 26 2017) 

SHORT TERM...

TODAY and TONIGHT...Forecast confidence is medium.

A closed mid/upper low over southeast Iowa will drift across the 
Wisconsin/Illinois border area today. The associated weakening 
surface low will take a similar path, with the center reaching 
southern Lake Michigan late this afternoon. Periods of light rain 
associated with the upper divergence and 700 mb upward motion will 
move across southern WI from south to north through the day, 
especially east.  

Expect low clouds and areas of fog and drizzle in between the rain 
through much of the day, especially east. There is a chance for 
dense fog, especially near the lakeshore later tonight into Sunday 
morning as winds become light and the surface low moves over.  Far 
southeast Wisconsin may get into the cloudy warm sector briefly this 
afternoon, pushing temperatures into the lower to mid 50s.  

Expect the low pressure to further weaken over the central Great 
Lakes tonight.  Northern areas will be close enough to lingering mid-
level circulation to warrant continuing a chance for some light rain 
during the evening.  This system will finally get nudged far enough 
east of the area by late tonight diminishing or ending ending the 
light rain chances.

MONDAY...Forecast confidence is medium.

Guidance remains generally split during this period. While all 
models show a weak wave passing though the central CONUS on Monday, 
the Euro/Canadian show a much more zonal pattern across the upper 
midwest than the GFS/NAM. Unsurprisingly, the surface low that will 
be in eastern OK on Monday morning is progged to have a more NE 
track in the GFS/NAM and a more easterly track in the ECMWF/GEM. 
Therefore the track favored by the GFS/NAM would bring a good chance 
at precip to the CWA, bringing some modest dynamics in the form 
of divergence aloft, DCVA, weak WAA, and even some 
frontogenitical forcing in the mid to low levels. The ECMWF/GEM 
track would keep much of that forcing to our south, leaving SE WI 
largely dry. All solutions keep the lowest levels saturated 
through the period, so at the very least we're looking at another 
dreary day with cloudy skies, and at worst we're looking at light 
rain on an off through the day.

This is essentially the same split-solution scenario we were 
looking at on Saturday morning. Citing support from the Euro 
ensemble members, WPC favors the flatter solution, and this seems 
reasonable. However, given the track of the GFS/NAM and some 
support from the GEFS members, cannot rule out a chance at rain on
Monday.

LONG TERM...

TUESDAY AND WEDNESDAY...Forecast confidence is medium.

Generally zonal flow is expected in the mid to upper levels as 
ridging works into the region while high pressure builds in at the 
surface. The biggest discrepancies in the models are in the lower
levels. All guidance shows a period of CAA from Tuesday morning 
through Wednesday, but the CAA is stronger in the GFS/NAM due to 
the passage of the low on Monday. As such, there is a split in the
temperature forecasts with the GFS/NAM about 5-10 degrees cooler 
than the Euro/Canadian. Will lean toward the Euro/Canadian 
solution, though will be keeping temperatures along the lake cool 
to account for onshore winds.

THURSDAY AND FRIDAY...Forecast confidence is low.

The split solution trend continues into the end of the week. All 
guidance shows a deep cutoff low in the southwest on Wednesday, 
gradually working its way to the NE. In the GFS, the cutoff low 
passes well to the south of the state before transitioning into an 
open wave on Friday once its over the central Great Lakes. This 
would result in generally zonal flow over our area through this 
period. Meanwhile, the Euro and Canadian have the low transitioning 
to an open wave on Thursday over the Great Plains, bringing much 
more meridional flow to the western Great Lakes on Thursday and 
Friday.

At the surface, this all translates to a low tracking either just 
south of the Ohio River (GFS), through central Illinois (Euro) or
through southern Wisconsin (Canadian). The southerly track of the
GFS keeps southern WI completely dry whereas the other tracks 
would translate into copious amounts of precip across the CWA. In
fact, if the Euro solution were just a few degrees cooler, it 
would be showing a setup for a pretty significant snowstorm. This
far out, it's tough to favor one solution to another, so will 
generally be sticking with the blended guidance and we can 
reevaluate at the solution becomes clearer.

SATURDAY AND SUNDAY...confidence is low.

All guidance continues to show a split flow regime, with yet another 
cutoff low over the desert southwest and a northern stream shortwave 
pushing though the upper midwest. There are pretty significant 
differences regarding the timing and intensity of this wave, but it 
does look like a shortwave will pass the region toward the end of 
the weekend. At the surface, high pressure will build into the 
region in in the wake of the low pressure system mentioned in the
previous section, followed by another low pressure system.

AVIATION(06Z TAFS)...

Low clouds are expected to persist through Sunday as low pressure
moves slowly northeastward. Scattered showers with patchy drizzle
will continue tonight, with more persistent rainfall possible
tomorrow morning, especially in the east. Could see some lower 
visibilities form tonight as the winds become lighter.

MARINE...

The early morning expiration of the Small Craft Advisory still looks 
reasonable, as waves should fall below criteria by then as a weak 
surface low moves across southern lake michigan this afternoon. 

Low level moisture will continue to increase into this morning, 
keeping the threat for dense fog going in the south as the low 
pressure moves across. The fog will likely spread farther north,
so Marine Dense Fog Advisory has been expanded north to Sheboygan.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory until 7 PM CDT this evening for LMZ643>646.

&&

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