Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 010148
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
848 PM CDT Sun Apr 30 2017

.UPDATE...Per SPC Meso analysis axis of 500 MUCAPE nudging a
smidge northward from northern IL. Some of the cells producing
some lightning in cntrl IL are trending a bit weaker as they get
closer to WI/IL border but enough MUCAPE combined with the forcing
associated with DCVA within ne quad of circulation center in
central Plains to keep mention of thunder going. Strong inversion
in low levels will make it tough for any convectively driven
winds to reach the surface. Mid level lapse rates not impressive.

PC

&&

.MARINE...No changes to Small Craft Advisory as gusty northeast
wind regime remains. Still looks like a lull later tonight as low
trends closer and gradient slackens vcnty trough axis. Southerly
winds will ramp back up Monday as low moves to our north.

PC

&&

.PREV DISCUSSION... (Issued 638 PM CDT Sun Apr 30 2017)

UPDATE...Bouts of shra will continue to rotate acrs southern Wi
assoc w/DCVA from slow moving closed low centered on KS/OK
border. Meso models continue to show an initial band moving
through this evening with a more robust rain area (perhaps a
little thunder) arriving in the 03z-07z time frame. Pressure falls
assoc with the surface reflection of this system suggests surface
low will move into southern WI with easterly flow shifting to the
south towards morning. Any slackening in the gradient may result
in some foggier conditions taking hold with the very moist low
levels. Ongoing stratus not far off the deck so wouldn`t take much
to lead to some lower vsbys with any dropoff in
mixing/slackening gradient/winds.

PC

AVIATION(00Z TAFS)...IFR/LIFR cigs widespread across srn WI in
the cool/moist easterly regime ahead of low pressure shifting
northeast from MO. Expecting to see a couple rounds of showers
this evening. Isold thunder possible but not likely. Concern
later tonight into Monday morning is fog potential. Any slackening
in pressure gradient with low in area could result in a period of
low visibilities. All in all expect these very low ceilings to
persist through the night with slow improvement on Monday to MVFR
conditions as the morning wears on with more of a southerly wind
regime taking hold.

PC

PREV DISCUSSION... (Issued 300 PM CDT SUN APR 30 2017)

TONIGHT AND MONDAY - Forecast Confidence...High.

Low pressure will approach from the southwest tonight, moving
through Wisconsin just to the northwest of the forecast area on
Monday. This will bring continued rounds of showers late this
afternoon through Monday. Kept precip chances pretty similar to the
HRRR, showing a first band late afternoon and early evening, then a
more widespread round of showers mid/late evening into the first
part of tonight. Kept chance of thunder going with showers late
afternoon into tonight. Shower activity tomorrow is progged to peak
during the afternoon hours.

Lows will be near normal tonight, but highs will be 10 or so degrees
below normal Monday despite a milder southerly wind.

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

Lingering low to mid level convergence and nearness of occluded low
pressure should continue to generate at least scattered rain showers
for a time Monday night.  Some minor differences in low level
thermal profile Monday night as colder air settles over southern WI.
NAM about 1-2C colder than GFS and ECMWF by 12Z Tuesday.  Forecast
soundings do show the potential for some snow mixing in with the
rain showers.  Due to uncertainty with regards to strength of colder
low level air, will confine mention of snow showers to northwest CWA
for now.

Lingering cyclonic curvature and steep low level lapse rates may be
able to generate a few more showers on Tuesday.  Otherwise, a drying
trend can finally be expected beginning Tuesday night, continuing
through the bulk of the week.

925H temps will fall slightly to 1-4C Tuesday night as weak high
pressure builds into the area.  This will diminish the boundary
layer mixing.  Frost may develop later in the night but still some
uncertainty regarding lingering cloud cover.  So will hold off from
adding to forecast but wl continue to mention the possibility in
Hazardous Weather Outlook.

EXTENDED PERIOD...

WEDNESDAY NIGHT THROUGH SUNDAY - Forecast Confidence...Medium.

Still looking rather quiet with temperatures getting closer to
seasonal normal for early May. Wisconsin will be on the northern
periphery of the southern stream of a developing split flow regime
by mid-week. Deep moisture will be bottled up farther south along
the main southern stream. Developing low pressure in this southern
stream will remain well south and southeast of Wisconsin on Thursday
and Friday.  As this low and upper level wave amplifies, stronger
northwest steering winds will return to the western Great Lakes by
the end of the week and persist through most of the weekend.  A
weakening short wave in this northwest flow may trigger a few
showers in parts of Wisconsin later Thursday into Thursday night.
Otherwise, short wave ridging should keep southern Wisconsin dry
into the weekend.

While the medium range guidance is in fairly good agreement through
Friday, there is some divergence of solutions over the weekend.
ECMWF and Canadian slower in exiting long-wave troffing off eastern
CONUS, while GFS more progressive.  Hence GFS faster in returning
warmer air to the region over the weekend with more zonal steering
winds returning by Sunday, while other guidance maintains colder NW
steering flow.  While coldest night may be Tuesday night with frost
potential, overnight lows during the extended period looking to
remain near or slightly below normal for early May, with lows in the
upper 30s to lower 40s.  The warmest day may be Saturday ahead of a
possible back door cold front passing through. ECMWF continues to
show this feature sweeping through on Saturday.

Planting of tender vegetation should hold off until the second week
of May. CIPS Analogs showing temperatures averaging closer to
normal. The extended period of dry weather will also allow the soil
to dry.

AVIATION (18Z TAFS)...

Now that the rain has ended in the east, it will be mainly dry until
next rounds of rain with a little thunder arrive from the south late
afternoon into the evening. This rain will wind down south to north
late this evening into early tonight. More showers are likely on
Monday as low pressure moves into northwest Wisconsin.

Low clouds will persist through Monday, though should see somewhat
higher bases by Monday afternoon. Visibilities will be 1-3 miles at
times as rain moves through.

MARINE...

A Small Craft Advisory remains in effect through much of Tuesday
given persistent breezy winds. Waves will eventually ease a bit by
Mon/Tue as winds become along shore to offshore.

HYDROLOGY...

Observed rainfall the last day or so and forecast rain the next
couple days is less than what was expected. As a result, the concern
for river flooding is diminished. Still should see several rivers to
bankfull and a couple reaching flood stage.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 5 PM CDT Tuesday for LMZ643>646.

&&

$$
Tonight/Monday and Aviation/Marine...DDV
Monday Night through Sunday...MBK



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