Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 180830
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
330 AM CDT THU AUG 18 2016
TODAY AND TONIGHT...Forecast Confidence Is Medium.
Very warm and humid today under a light southwest flow ahead of
developing low pressure over the plains. The thunderstorm complex
just south of the border early this morning should mostly stay south
and weaken as we head toward sunrise. It`s not out of the question
a few rogue storms could clip southern Lafayette/Green county before
they die out.
We do see some weak sfc troughing across the area today and this
could combine with the better convergence along the lake breeze in
the east to fire off some isolated showers/storms this afternoon.
Moisture is limited aloft, so not real confident in the development.
Nearly all of the models depict something in the east. There is a
general overproduction of qpf in the east in these patterns, but the
consensus of solutions is tough to ignore.
Our next chance for showers and storms starts to creep in later
tonight as we see the low level jet modestly increase and push into
western Wisconsin. An MCS should see its genesis over North Dakota
this afternoon, then progress southeast with time, reaching western
Wisconsin after midnight. It should be weakening by this time and
could move into our nrn tier of counties before 12z Friday. We are
in a marginal risk for severe thunderstorms across the north with
this scenario. Some of the models are painting a more widespread
shower/storm chance across the entire area later tonight, but this
seems overdone given how far ahead of the front that would be.
For now will keep the south and east dry tonight, but pops may be
introduced if the evidence builds.
FRIDAY... Forecast confidence is medium.
A longwave trough will slowly make its way across the Upper Midwest
and Great Lakes region late in the week. Weather should be fairly
quiet in southern WI on Friday since we will be capped and there
really isn`t a strong trigger for storms. We will still be in the
warm and humid air mass, so expect max temps in the upper 80s and
heat indices in the mid 90s, highest in the Lake Michigan counties.
This falls just below heat advisory criteria.
A leading shortwave trough tied to the right entrance region of the
upper jet and the nose of the low level jet will lead to increasing
thunderstorm chances over central WI Friday night. The ECMWF brings
this leading trough into southeast WI quicker than other models, so
added slight chance PoPs to southeast WI for late Friday afternoon.
Decent elevated instability will help to sustain any line or cluster
of thunderstorms that track into southern WI Friday night. Thus, SPC
continues to include the western MKX forecast area in
slight/marginal risk areas. Damaging winds are the main threat.
SATURDAY... Forecast confidence is medium.
By Saturday morning, the surface low will arrive in southwest WI,
with the main upper trough just to the west over south central MN
and central IA. The GFS and ECMWF have similar timing and synoptic
characteristics, but the NAM creates an unrealistically strong
There is more confidence on Showers and thunderstorms occurring
across southern WI Saturday morning than in the afternoon. Expect
showers to taper off from west to east behind the cold front
Saturday afternoon/evening. Most models have the precip out of
southern WI by midnight Sat night.
Saturday will begin warm and muggy. Lack of sunshine will keep
temperatures cooler than the previous couple of days. Cooler and
drier air will work its way into the region later Saturday night.
SUNDAY... Forecast confidence is medium.
Cyclonic flow will linger over the Great Lakes through Sunday night
leading to plenty of cloud cover, a chance for light showers, and
temperatures topping out in the lower 70s. Winds will be a little
brisk out of the northwest during the afternoon. It will be a good
day to open the windows as dewpoints drop into the mid 50s. Sunday
night lows are expected to drop into the lower 50s inland from Lake
MONDAY AND BEYOND... Forecast confidence is medium.
Ridging and warmer air will begin making a comeback on Monday and
continue into the middle of next week. The GFS continues to bring
some warm air advection precip to southern WI Monday night, but kept
the forecast dry for now. The next best chance for showers and weak
storms will be Wed into Thu. Temperatures will be closer to normal,
in the mid to upper 70s, for most of the week.
Morning fog will bring areas of MVFR/IFR VSBYS through about 14z
this morning. Thereafter, the rest of the TAF period should be VFR.
There is a very small chance of showers and storms over eastern
Wisconsin this afternoon, but confidence in that happening along the
lake breeze is quite limited. Late tonight, we`ll be keeping an eye
on an approaching thunderstorm complex from the west and northwest.
It is expected to stay north of the TAF sites through the end of the
TAF period. Southerly winds will generally remain below 10 knots
through the period, with a southeast lake breeze kicking in at KMKE
and KENW early this afternoon.
Winds and waves should remain below small craft advisory levels
through the weekend. Southeast winds today will shift to south then
southwest tonight as low pressure approaches from the west. Those
south to southwest winds will be maintained through Saturday, then
shift to northwest Saturday evening in the wake of a passing cold
TODAY/TONIGHT AND AVIATION/MARINE...Davis
Friday THROUGH Wednesday...MRC