Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 180800
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
300 AM CDT Thu May 18 2017

.DISCUSSION...

Tonight and Wednesday...Forecast confidence is high.

A fast moving low pressure system takes a track across the Lake Superior
period region this evening. A cold front trailing southwest from the
low will drop into our western forecast area this evening, reaching
the WI/IL border by sunrise Wednesday.  We should see some showers
along and ahead of the front as it moves through and there is just
enough CAPE on the soundings to support an isolated rumble of
thunder.

Winds will become northeast Wednesday morning as high pressure moves
across south central Canada. High temperatures will occur early in
the day, then fall through the afternoon east as brisk, cool east
winds, thickening cloud cover, and rain take over.

The entrance region of the exiting northern stream upper jet across
the upper Great lakes, along with an approaching southern stream jet
from the central Plains will result in increasing upper divergence.
Also the nose of the 45 knot low level jet, moving into northeast
Iowa and southern Wisconsin Wednesday afternoon along a tight 850mb
baroclinic zone will increase the low level moisture convergence.
This forcing should bring rain and scattered, elevated thunderstorms
to the area late Wednesday afternoon, as the surface warm front over
northern Illinois begins to lift north. Some storms will have hail
potential due to 450 Joules/kg of elevated CAPE far south toward
evening.

Friday and Friday night - Confidence...Medium
Mid level ridging early in the day gives way to increasing
southwest mid level flow with trough approaching. The surface high
will be maintaining a northeast flow. The models are showing a
little better precip advancement into the area though the GFS
keeps the rain held back to the western cwa. Some lingering
influence of the dry ne feed probably holding things back at least
a little bit. However seeing the 850 jet ramp up with some better
moisture advection taking place. So will go with the highest pops
spreading into the southwest with lower pops in the northern and
eastern cwa. 850 LLJ translates eastward so plenty of moisture
feeding in on increasing southerly flow. Even though primary mid
level low is still in the Plains seeing evidence of some lead
waves coming through in the southwest flow which will help to
boost pops somewhat. The 00z ECMWF and and GEM are not too bullish
on the precip keeping best qpf to our southwest while the GFS is
the most aggressive bringing the qpf max into the area. Went with
the Superblend pops for now. Seeing several hundred J/KG above
fairly pronounced low level inversion, so will keep thunder
mention in place.

Saturday - Confidence...Medium
Better consensus for rain/tsra with 850 speed max impinging on the
area along with some upper divergence associated speed max on
eastern side of advancing trough. Low pressure proggd to near nrn
IA or srn MN and head northeast from there Saturday night. A mid
level dry slot works in fairly quick Saturday evening which helps
to lower qpf amounts from sw to ne.

Sunday - Confidence...Medium
The low is proggd to lift to near or north of Lake Superior. Cold
advection regime will be in place. Broad mid level cyclonic flow
and some low level troughing could result in some shra potential.
Only the GFS is latching onto any qpf with the ECMWF dry.

Monday through Wednesday - Confidence...Medium
This period will be marked by the evolution of a closed off low
across the Great Lakes or Ohio Valley as energy rides southeast
around the Canadian vortex and forms a new circulation.
Low level cyclogenesis occurs to our south or east which results
in periods of shra with an overall cool regime as wind flow will
be off the lake or northerly esp for Tuesday and Wednesday.

&&

.AVIATION(06Z TAFS)...VFR conditions are expected through today.
Look for brisk south winds, reaching gusts to 25 to 30 knots
inland, especially away from Lake Michigan. The winds near the
lake are not as strong due to the inversion. these winds will
gradually veer to the south during the afternoon and should
increase. Winds will then diminish in speed this evening. Low
pressure tracking across northern Wisconsin will drag a cold front
into southern Wisconsin this evening. The front should reach KMSN
by around 03-05z and KMKE about 07-09z Wed. A band of showers
will be ahead of the front. CIGS will likely drop to MVFR levels
in the wake of the front.

The cold front will become stationary across northern Illinois
Wednesday morning, before lifting north during the evening.

&&

.MARINE...A tight pressure gradient between exiting high pressure
and low pressure tracking across Lake Superior this evening will
bring a rather short period of elevated south winds into this
evening. The strongest winds and largest waves will be found up
toward Sheboygan. The lake breeze and resultant inversion have
kept lake shore winds a bit lower. A small craft advisory has been
issued into this evening.

East winds and waves should reach small craft advisory conditions
again Wednesday evening ahead of strong low pressure that will track
across central Wisconsin Thursday morning.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 3 PM CDT Saturday for LMZ643>646.

&&

$$
Today/Tonight and Aviation/Marine...Hentz
Friday through Wednesday...Collar



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