Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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147
FXUS63 KMKX 270201
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
901 PM CDT MON SEP 26 2016

.UPDATE...

With clear skies winds have decoupled a bit with most little in
the way of gusts. Winds will increase again Tuesday along with
clouds pushing in from the north as the mid/upper low sags south.

&&

.AVIATION/06Z TAFS/...

Mainly SCT clouds expected overnight with a strong low near lake
Superior. Low level wind shear is possible this evening as winds
weaken at the surface, but confidence is not high enough at this
time that it will reach the threshold to put in the TAFs. Winds
look to remain from the west and will increase Tuesday. As the mid
level low drifts south, vfr cigs will spread in from the north
Tuesday morning and become MVFR Tuesday evening with scattered
showers.

&&

.MARINE...

West to southwest winds have diminished with clear skies as sfc
pressure gradient remains tight across the area, with a strong low
near lake Superior. Gusts look to intensify during the day
Tuesday, but they should be weaker than those Monday. Winds are
only around 10 to 15 knots along shore, but with warm waters and
cool air advecting over, wind gusts Will be over 25 kts towards
open waters tonight. With surface heating wind gusts will increase
tuesday along shore. Small Craft Advisory remains in effect for
all nearshore zones until 7 PM Tuesday.

Waterspout nomagram as well as Non-Supercell Tornado Parameter
and Enhanced Stretching Potential indicate the potential for
waterspouts Wednesday as winds turn to the north and nearshore
convergence develops along the west shore. will continue slight
chance for waterspouts in the nearshore forecast for Wednesday.

&&

.PREV DISCUSSION... /Issued 407 PM CDT MON SEP 26 2016/

TONIGHT AND TUESDAY...Forecast Confidence - Medium.

Clouds will linger over our northern counties overnight tonight as a
mid to upper level trough eventually sags southward. The 850 low is
cut-off and doesn`t move all that much through Tuesday, staying
stationed over Lake Superior. This will keep S WI in the cold air
advection/northwest flow regime through Tuesday. 850 temps look to
decrease during the day Tuesday so cloud cover should thicken. 925
mb temperatures look to drop into the 6-7C range, so lows tonight
should drop into the mid to upper 40s. There is some uncertainty
with this, however, as cloud cover lingers north. Areas underneath
cloud cover may stay in the upper 40s, depending on how much the
cloud cover hangs on.

A maxima of positive vorticity advection will swing through Tuesday
morning, which should support a slight chance of a shower in the
north. Precipitation chances will increase in the afternoon as
a secondary mid level wave within the cut-off low translates south.
Wind gusts don`t look to be as strong Tuesday compared to Monday but
could still gust up to 25 knots.

TUESDAY NIGHT AND WEDNESDAY...Forecast Confidence High

Models are latching on to the typically slower progress of closed
lows in handling the deep closed low currently near the northern
shores of Lake Superior on satellite images. They have not only
slowed the progress of the low, but are farther west with the track
than previous runs as it drops south from the western Lake Superior
area Tuesday night, and only reaching the lower Michigan/NE
Indiana/NW Ohio border region by Wednesday evening.

This will keep cloudy and cool conditions across the CWA under the
cyclonic flow, with periodic light showers/sprinkles as vorticity
maxima rotate around the main low. There is a good chance for
showers to be ongoing from Tuesday afternoon through the evening
with the differential CVA-driven forcing ahead of a vigorous vort
max/short wave trough.

Scattered light showers are expected Wednesday due to a combination
of forcing from the continued presence of weak vorticity maxima
moving through the area, instability with daytime warming, coupled
with low-level convergence along a weak surface cold front/wind
shift line. The clouds will hold low temperatures up in the mid-
upper 40s but limit highs Wednesday to the upper 50s to lower 60s.

WEDNESDAY NIGHT AND THURSDAY...Forecast Confidence Medium

Closed system finally drifts far enough to the southeast Wednesday
night with ridging and the leading edge of surface high pressure
building in to bring an end to the rain chances. While mid-level
drying overspreads the area, low-level relative humidity forecasts
are still fairly moist, especially in the east. Expect scattered to
at times broken diurnal cumulus coverage that will limit daytime
heating.

LONG TERM...THURSDAY NIGHT THROUGH MONDAY...Forecast Confidence
Medium.

Models are taking the cut-off low down to the vicinity of the
eastern Ohio River Valley, then drift it back to the north-northeast
(GFS and Canadian) or north-northwest (ECMWF). With the surrounding
offices, we trimmed the blended PoPs that are heavily influenced by
the ECMWF but still keeps slight chance PoPs in the eastern CWA
from Thursday night through Saturday night.

The farther east GFS solution allows upper ridging and a surface
high to build back in Sunday, while the ECMWF holds pcpn over the
area until Sunday night. Will go with the more optimistic and drier
solution through Sunday night. Blended solution also influenced by
earlier runs that brought pcpn with return moisture flow ahead of
the next wave into the west Monday and across the forecast area
Monday night. Latest runs of both the GFS and ECMWF keep area dry
and if trend continues small PoPs can be pulled. At, or slightly
above normal temperatures expected through the extended.

AVIATION/00Z TAFS/...

VFR cigs look to persist into the evening. Diurnal stratocumulus
clouds will continue into the early evening before dissipating, with
mainly SCT clouds expected overnight. Gusts will weaken some
this evening, but could still reach into the 15 to 20 kt range. Low
level wind shear is possible this evening as winds weaken at the
surface, but confidence is not high enough at this time that it will
reach the threshold to put in the TAFs. Winds look to remain from
the west and southwest into the evening.

MARINE...

West to southwest winds will continue with gusts up to 25 kts
possible overnight as sfc pressure gradient remains tight across the
area. Gusts look to intensify during the day Tuesday, but they
should be weaker than those Monday. With gusts over 23 kts, Small
Craft Advisory remains in effect for all nearshore zones until 7 PM
Tuesday.

Waterspout nomagram as well as Non-Supercell Tornado Parameter
and Enhanced Stretching Potential indicate the potential for
waterspouts Wednesday as winds turn to the north and nearshore
convergence develops along the west shore. Have put slight chance
for waterspouts in the nearshore forecast for Wednesday.

&&

.MKX Watches/Warnings/Advisories...
WI...None.
LM...SMALL CRAFT ADVISORY until 7 PM CDT Tuesday for LMZ643>646.

&&

$$

UPDATE...Hentz
TONIGHT/Tuesday AND AVIATION/MARINE...JTS
Tuesday NIGHT THROUGH Monday...REM



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