Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 130157
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
857 PM CDT Thu Oct 12 2017

.UPDATE...

&&

.MARINE...
Winds will become southwest after midnight and increase slightly. A
strong low pressure system will move through this weekend. A Small
Craft Advisory is likely Saturday and Sunday. South winds on
Saturday will become westerly overnight. Gusts will approach gale
force late Saturday and early Sunday.

&&

.PREV DISCUSSION... (Issued 637 PM CDT Thu Oct 12 2017)

UPDATE...
Drizzle continues to spread across eastern WI in association with a
mid level shortwave. The clearing line upstream has slowed its
eastward progression and RH fields show moisture filling back in upstream
as the front approaches. So it looks like clouds will continue
through the night and drizzle may linger later tonight with
another shortwave.

AVIATION(00Z TAFS)...
Ceilings will be around 1000-1500ft this evening with IFR at
times in south-central WI. Some drizzle and patchy fog is expected
tonight. There may be some improvement in far eastern WI later
tonight or Friday morning. MVFR ceilings are expected midday
Friday, especially for far southeast WI but will be lowering in
the evening as a front and precipitation approaches.

PREV DISCUSSION... (Issued 230 PM CDT Thu Oct 12 2017)

DISCUSSION...

Tonight - Confidence...Medium
Widespread stratus across the Great Lakes trapped beneath
pronounced low level inversion. Low level RH progs do suggest some
of the erosion/clearing push across northeast MO/western IA may
shift in here for a time later tonight. Overall, lingering
influence of surface high shifts east with more of a southerly
flow taking shape ahead of a cold front that is proggd to work
into NW WI later tonight. NAM is putting out some spotty light
QPF. Given depth of dry air within the column this would be a
drizzle signal.

Friday and Friday night - Confidence...Medium
The cold front swings through the area. Rain chances will be in
the increase especially during the afternoon. 850 baroclinic zone
tightens up with some lower level frontogenetical forcing
expected. Some elevated instability noted so have retained the
thunder mention into Friday evening. So have high POPS across the
area for Friday evening with the low level forcing and along
stream upper jet divergence noted.

Saturday and Saturday night - Confidence...Medium to High
Main concern this period as warm moist airmass will be sent
northeastward into the area ahead of a low pressure system. Shear
is very favorable along with the dynamics. Left front quad of 850
jet and right rear quad of upper jet favor appreciable column
lift. Greatest threat zone where model CAPE values are highest are
in south central WI during the afternoon/early evening with
instability proggd to wane heading east into the evening. However,
seeing some better signals as well for the lower level inversion
to be eroded in parts of southern WI near and south of warm
frontal boundary which sets up a potential severe scenario into
southeast WI as well into the evening. Looks like another tricky
low CAPE/high shear scenario setting up. SPC has started this
trend with the Marginal Risk now into southern WI. This looks good
for now. But if anything the trend looks more favorable for some
severe wx potential into our area Saturday afternoon/evening.

Sunday through Thursday - Confidence...Medium to High
Overall quiet and increasingly mild period. Sunday we`ll see a
cold advection signal in the wake of the departed low. Gusty
northwest winds will be bringing in the cooler airmass. With
enough decoupling Sunday night could be setting up for some frost
potential in parts of the CWA. 925 temps will rebound back above
10c from as soon as Tuesday right into Thursday, so more
unseasonably mild weather will be making a comeback.

AVIATION(21Z TAFS)...Moisture trapped beneath pronounced
inversion with widespread MVFR cigs (some IFR) expected to persist
well into this evening. Visible satellite loop shows gradual
erosion occuring across MO trending northeast. The LLVL RH progs
bring a window of drying across srn WI in the 03-12z time frame.
Extrap of back edge in MO suggests 04z or thereabouts for when
some breaks could work in here. Starting to see it break up a bit
across IA as well. So some hope for overnight breaks though in the
interim seeing some drizzle development take place. Any breaks
short-lived as moisture increases again ahead of cold front which
results in shower chances increasing across srn WI during the
afternoon.

MARINE...Main focus will continue to be centered on winds and
wave development heading into the weekend as potent low pressure
heads towards the Great Lakes. Expecting small craft headlines to
be needed as this feature moves through.

&&

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

$$

Update Aviation and Marine...Marquardt
Tonight through Thursday...Collar



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