Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 270235
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
935 PM CDT WED OCT 26 2016
.UPDATE...Areas of light rain and drizzle will slowly diminish
through the late night. Weak low level convergence north of
passing low pressure will continue to generate the areas of light
precipitation but should start to rapidly diminish after 06z.
Persistent clouds and increasing boundary layer mixing should keep
fog more patchy later tonight.
.AVIATION/06Z TAFS/...Patchy light rain and drizzle will continue
to slowly diminish as low pressure over northeast IL moves off to
the east. Slight low level dring and increasing boundary layer
winds will allow cigs to rise to high IFR or lower MVFR levels
later tonight but will likely persist through much of Thursday.
.MARINE...Winds will continue to slowly subside as the pressure
gradient relaxes due to low pressure moving across northeast
Illinois toward lower Michigan. A lingering pressure gradient and
continued onshore flow will keep higher winds and waves ongoing
over the near shore waters, but wind gusts will remain below Gale
levels. Hence the Gale Warning has been downgraded to a Small
Craft Advisory for the rest of the night into early Thursday.
.PREV DISCUSSION... /Issued 315 PM CDT WED OCT 26 2016/
TONIGHT AND THURSDAY... Forecast confidence is medium.
The main upper trough is taking its time moving across Upper
Michigan today. The associated surface low will track across
northern IL and IN through tonight. The system will finally exit the
area after midnight.
The back edge of the higher returns on radar is steadily tracking
through southeast WI late this afternoon. While this is the end of
heavy/moderate rain, persistent upward motion and low level moisture
within the inverted surface trough overhead will lead to periods of
drizzle and light rain through early evening. I think the radar is
not quite picking up on the extent of the drizzle in southwest WI,
but surface observations are indicating persistent low visibility.
Winds will continue to diminish tonight as the surface low tracks
across northern IL and IN overnight and the pressure gradient
Clouds will linger through the day Thursday due to cyclonic flow
aloft and shallow low level moisture. This will keep temperatures on
the cooler side once again with highs around 50. Winds will be much
lighter out of the northwest.
Most of southern WI received 1.5 to 2.5 inches of rain over the past
24 hours. Rivers will rise over the next day or two, with a few
sites expected to reach bankfull levels or minor flood stage.
THURSDAY night and friday...Forecast Confidence Is High.
The mid/upper level shortwave exits the eastern Great lakes
Thursday evening as a weak ridge builds into the upper Mississippi
Valley. The ridge quickly flattens as a strong 115 knot 250 mb jet
max moves across the northern plains Friday.
Weak upper level divergence Friday with mainly weak 700 mb upward
motion Thursday night and Friday. A band of high 700 mb RH moves
across southern Wisconsin Thursday Night with drying Friday.
However 850 mb RH increases Friday afternoon, especially late.
Moderate 850/700 mb Warm air advection develops across the region
Thursday Night into Friday, as low pressure passes eastward
across the U.S./Canadian border to just north of Lake Superior.
A tight pressure gradient develops Friday in the area bringing gusty
south to southwest winds with warmer temperatures.
Friday night and Saturday...Forecast Confidence Is High.
The upper level flow remains zonal as a 120 knot jet max moves
across the Upper great Lakes. Weak upper level divergence and
upward 700 mb motion occurs mainly early Friday night and then
850 mb moisture dries Friday night with some increase from the
north Saturday with northeast areas possibly getting into the cold
advection stratocumulus shield.
A cold front then passes eastward through the area Friday night.
The NAM produces some very light QPF Friday evening but the GFS
and ECMWF are dry. The GFS and ECMWF also spreads some light
rain into portions of southern Wisconsin Saturday afternoon.
SATURDAY night and Sunday...Forecast Confidence Is High.
Both the GFS and ECMWF bring a very weak shortwave across
Wisconsin Saturday night and into Sunday morning.
High pressure builds into the Upper Mississippi Valley, but both
the GFS and ECMWF spread some rain across southern Wisconsin in
the stronger baroclinic zone.
Sunday THROUGH TUESDAY...Forecast Confidence Is Medium.
ECMWF/GFS are in decent agreement. A weak mid/upper level ridge
moves across Sunday night with a shortwave moving across Wisconsin
and lake Superior monday night.
Surface high pressure moves across the Great Lakes Sunday with a
brisk south flow Monday ahead of Low pressure over the Northern
Plains. The ECMWF is a little slower.
Monday Night and Tuesday...Forecast Confidence Is Medium.
The shortwave moves into southeast Canada Tuesday. Cold air
advection dominates behind a cold front.
Wednesday...Forecast Confidence Is Medium.
A weak mid/upper level ridge moves across Wisconsin Tuesday night
with an approaching shortwave moving across the northern plains.
Surface high pressure moves across Wisconsin and the Great Lakes.
xpect IFR ceilings and visibilities in the 1.5 to 3 mile range with
periods of light rain and drizzle through early evening as low
pressure tracks across northern IL. All the rain/drizzle should end
by sunrise Thursday. But, cigs will likely remain IFR through about
12z Thursday, then gradually lift thereafter. We might not reach VFR
levels until mid Thursday afternoon.
Strong east winds will diminish quickly this evening. Winds will
shift around to the northwest on Thursday but remain light.
East gale force winds will persist through late afternoon. This is
in response to an intense low pressure system tracking across
northern Illinois, to northern Indiana by later tonight. The winds
will diminish overnight with lighter northerly winds expected on
Low pressure tracking by to the north of the area on Friday will
generate gusty southerly winds that will likely result in small
craft advisory conditions for Friday into Friday night.
LM...SMALL CRAFT ADVISORY until 10 AM CDT Thursday for LMZ643>646.
TONIGHT/Thursday AND AVIATION/MARINE...MRC
Thursday NIGHT THROUGH Wednesday...Hentz