Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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818
FXUS63 KMKX 200207
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
907 PM CDT Sat Oct 19 2019

.UPDATE...The showers are coming to an end while low stratus and
light fog is forming west of Madison. Farther to the west, near
the MS River, heavier fog is forming due to the clear skies and
light winds. If the stratus is able to clear over south central
WI, then heavier fog, possibly dense, will occur.


&&

.MARINE...Light to modest southerly winds will shift west to northwest
tonight with the passage of a weak cold front. High pressure of
29.9 inches over MO will move northeast across Lake MI for Sunday
afternoon and evening. Thus winds will become light and variable
for this time.

Southeast winds will pick up Sunday night into Monday ahead of a
stronger approaching low pressure system. The low of 29.4 inches
will move from South Dakota Sunday night to somewhere between
northwest Wisconsin and western Lake Superior Monday night, while
deepening to 29.1 inches. The winds will remain elevated and
become south to southwest later Monday into Monday night, and then
westerly by later Tuesday. Winds may gust to gale force at times
Monday through Tuesday night. Winds will be a little lighter
Wednesday, but will remain gusty and out of the west.


&&

.PREV DISCUSSION... (Issued 705 PM CDT Sat Oct 19 2019)

UPDATE...The narrow band of light rain over south central WI
will continue to lift newd and weaken early this evening. The
decaying winds fields and cold front will result in higher than
normal dewpoints for tnt while clearing skies progresses from
west to east across srn WI. This will result in fog development.
How low the vsbys drop is the question. Various guidances are
mixed with the results. Believe dry air moving into the region
just above the sfc could limit the fog, although locally dense
ground fog would probably still occur. There appears to be less
fog potential over far ern WI where the rainfall may not occur and
the clouds will not decrease until late. High pressure to settle
over the area for Sunday with any fog or low clouds dissipating by
late morning while high clouds will increase later in the
afternoon. Another mild day in the 60s is forecast.

AVIATION(00Z TAFS)...Local MVFR Cigs and Vsbys this evening over
south central WI with fog becoming more widespread after midnight
especially west of the MKE metro area. Vsbys with the fog will be
highly variable but locally dense ground fog will likely still occur.
VFR conditions are expected by 15-16Z Sunday.

PREV DISCUSSION... (Issued 331 PM CDT Sat Oct 19 2019)

SHORT TERM...

Tonight through Sunday...Forecast Confidence Is High.

A line of light to moderate showers is approaching the area this
afternoon. These are along a weak frontal boundary that will push
through this evening into the early overnight hours. With the main
upper level system lifting into central Canada, there is limited
forcing, so not expecting too much in the way of rainfall with
these showers. Satellite imagery and models do suggest some weak
frontogenesis in the mid levels as the front shifts east this
afternoon. That could support a few heavier showers at times.

Once the front clears the area to the east, clear skies coupled
with light winds and the recent rainfall could allow for the
development of fog overnight. Patchy dense fog is possible in any
areas that receive more rainfall this evening. Will monitor
overnight the potential for any fog products.

Since it`s a good setup for fog tonight, lows won`t dip much
below the 40 degree mark. Low clouds and fog linger Sunday
morning, but should be able to clear out by mid-morning. High
pressure building across southern Wisconsin will make for another
nice day on Sunday, with highs in the lower 60s with mostly sunny
skies.

Sunday Night Through Monday...Forecast Confidence Is High.

Models remain in decent agreement with trends during this period.
They bring deepening and then occluding low pressure from eastern
South Dakota into the western Lake Superior area. A strong cold
front pushes through the area on Monday, with decent low level
frontogenesis response. There is a good shot of warm air/moisture
advection ahead of the front later Sunday night into Monday
morning. Kept high PoPs for later Sunday night into Monday. Small
thunder chances were kept as well, with very weak CAPE ahead of
the front.

Southeast to south winds will become gusty later Sunday night
into Monday morning, and will become southwest and strengthen
after the frontal passage. Mild temperatures are expected, with
40s Sunday night and lower 60s Monday before the frontal passage.

LONG TERM...

Monday Night Through Wednesday Night...Forecast Confidence Is
High.

Cutoff 500 mb low will become nearly vertically staked with the
surface low Monday night into Tuesday, before moving off to the
northeast of Lake Superior Tuesday night into Wednesday. Various
500 mb vorticity maxima rotating around the 500 mb low should
bring chances for showers at times Monday night into Tuesday.
Drier air moving into the region later Tuesday into Tuesday night
should bring an end to the shower activity.

Gusty southwest winds will become west later Monday night into
Tuesday, remaining gusty Tuesday night before slowly weakening
Wednesday. Gusts of 28 to 32 knots seem reasonable for Tuesday,
when the strongest gusts will occur. These winds will bring colder
temperatures to the area, with highs generally in the upper 40s to
lower 50s, and lows in the 30s.

Models are trying to bring a weak surface low and cold front east
through the area later Wednesday into Wednesday evening, with a
500 mb vorticity maximum trailing it. These features may bring a
few showers to the area during this time.

Thursday Through Saturday...Forecast Confidence Is Moderate.

More uncertainty in this period, though models generally show a
broad 500 mb trough axis slowly moving east through the region. It
appears that strong low pressure will remain southeast of the
region Thursday night into Friday night per the GFS, with the
ECMWF delaying this low track until Saturday. For now, left PoPs
and temperatures with the blended models.

AVIATION(21Z TAF UPDATES)...

Light to moderate showers moving across southern WI this afternoon
will lower cigs down towards MVFR with bases as low as
1,500-2,000ft this evening. Cigs briefly improve after 03z but fog
is forecast to develop between 05-09z tonight with some locally
dense fog possible. Winds stay out of the S/SW ahead of the
showers then switch to W/NW and become light and variable
overnight. High pressure moving in on Sunday will keep skies VFR
and winds light and variable.

MARINE...

Gusty southerly winds continue across the lake this afternoon,
leading to higher waves for the northern half of the lake. Webcams
suggested some higher waves continue from Port Washington
northward, so will leave the Small Craft Advisory going until 7
PM this evening. Winds and waves taper off tonight as high
pressure builds into the region.

A strong system nears the area Sunday night, with winds
increasing out of the southeast. Winds could approach gale force
Monday afternoon ahead of the system for the open waters. Small
Craft Advisory conditions will be met Monday through Tuesday
night. Winds switch to the west on Tuesday and winds will again be
near gale force. Winds begin to diminish some on Wednesday, but
still remain gusty.

&&

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

$$

Update...Gehring
Tonight/Sunday and Aviation/Marine...Stumpf
Sunday Night through Saturday...Wood



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