Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 182326
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
626 PM CDT Fri May 18 2018

.UPDATE...

No major changes to the forecast at this point. Rain showers are
pushing northwest across the southeastern half or so of the area
at this hour. Several waves of light rain is expected through the
evening and first part of the overnight as an upper low pushes
across the Ohio Valley.

&&

.AVIATION(00Z TAFS)...

Scattered light rain showers will push northwest across the area
this evening into the overnight hours. Lower ceilings will build
in later this evening, with some fog also possible late tonight as
low level moisture increases. Flight conditions should fall to IFR
after midnight, and may fall to LIFR near the lake (affecting ENW
and MKE) before daybreak on Saturday. A gradual improvement is
expected through the day Saturday, though low clouds may linger
across the eastern portion of the area into the late afternoon.

Expect winds to be east to northeast through the period.

&&

.PREV DISCUSSION... (Issued 250 PM CDT FRI MAY 18 2018)

TONIGHT AND SATURDAY...Forecast Confidence - Medium.

Upper low over eastern MO will continue to get nudged northeast
during the period in response to upstream western CONUS trof sliding
eastward.  Upper low over eastern MO is expected to move northeast
across northeast IL into lower MI as it gradually weakens and fills.
Southeast winds on its northern periphery will usher deeper column
moisture into southern WI through the evening.  Precipitable water
values nearly double to around 1.5" in the southeast.  Weak low
level warm air advection and pieces of mid-level energy rotating
around the upper low wl bring some light showers into the eastern
CWA.  Some light showers may affect the southeast as soon as the
late afternoon as they rotate northwest from northeast IL.  The
upper low is expected to shift off to the east on Saturday, ending
the shower threat by afternoon.  As the low level winds turn
northwest on Saturday, a cold front and inverted low pressure trof
upstream over northwest WI will sweep across southern WI into the
evening.

SATURDAY NIGHT THROUGH MONDAY...Forecast Confidence - Medium.

Possible a few showers may affect parts of southern WI Saturday
evening as the front/trof slides through, especially in the west and
north.  Will keep the rest of the area dry for now. Central Plains
low pressure will then move along this trof as it transitions to a
stationary frontal boundary draped across the central MS Valley
region on Sunday and Sunday night.  ECMWF and GFS trending farther
southward with this feature resulting in less instability and lower
lapse rates across the area.  Hence pulled thunder threat from
Sunday/Sunday night period. Secondary weak area of low pressure may
pass closer to southern WI later Monday, so wl keep small thunder.
Passing systems will be weak so QPF will be lighter, which will
allow current rivers in Minor Flood stage to continue to slowly
subside.

EXTENDED PERIOD...

MONDAY NIGHT THROUGH FRIDAY...Forecast Confidence - Medium.

A benign period is expected with weak zonal steering flow aloft
transitioning to weak long-wave ridging across the central CONUS
later in the period.  Temperatures look to remain above seasonal
normal for much of the period with weak east to southeast surface
winds resulting in cooler by the lake conditions most days.   A weak
frontal boundary wavering across the central MS Valley region may
occasionally trigger a few showers that may brush southern WI but
nothing organized or widespread anticipated.

Otherwise, increasing likelihood for a tropical system affecting
southeast CONUS late in the period may affect timing of short waves
expected to move across the Plains into the Upper Midwest on Friday
and through the weekend but precipitation chances likely to increase
during this period.

&&

MARINE...

Gusts to around 20 knots will continue into the evening due to
pressure gradient across southern Lake MI.  Weakening pressure
gradient later tonight will linger through Saturday.  Diminishing
winds and increasing low level moisture should allow patchy fog to
develop over the cool near shore waters on Saturday.  The winds will
pick up Saturday night as a cold front slides south across southern
Lake Michigan, which will also end the fog threat.  Wind gusts
behind the front are expected to remain below Small Craft Advisory
levels.

&&

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

$$

Update...Boxell
Tonight/Saturday and Aviation/Marine...Boxell
Saturday Night through Friday...99



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