Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 171111
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
611 AM CDT Mon Jul 17 2017

.UPDATE...

Made a few tweaks to the sky grids to account for the band of
high clouds moving through this morning. Otherwise the forecast
remains on track. Looks like it`s shaping up to be a nice day.
Humidity will be on the increase starting tomorrow.

&&

.AVIATION(12Z TAFS)...

Patchy fog and 3.5 kft stratocumulus remain possible west and
northwest of Madison this morning. The area of stratocumulus over
Lake Michigan has stalled, and now appears to remain offshore in
the near term, so pulled the 3.5 kft cloud mention from the TAFs
for this morning. Prevailing VFR conditions are expected this
afternoon and evening, with cumulus possible around 3 kft. Winds
will be light and easterly.

&&

.PREV DISCUSSION... (Issued 346 AM CDT Mon Jul 17 2017)

TODAY AND TONIGHT...Forecast Confidence Is High.

Expansive 500 hPa anticyclone will elongate from the Desert
Southwest into the central/southern Great Plains. The Ridge will
flex northeast into the western Great Lakes on Monday, in response
to upstream wave energy across the Pacific Northwest/Canadian
Prairies and into the northern Great Plains. The mid/upper ridge
will bring modest height rises to the region, while supporting
surface high pressure across the western Great Lakes and into
southern Ontario and Quebec. The surface high will bring quiet
weather to our area for today and tonight.

Given the light low-level wind field associated with the surface
high, onshore flow is expected during the day, resulting in a west
to east temperature gradient across southern Wisconsin. Highs
should approach 80 in the Wisconsin River valley, with readings
holding closer to 70 by the Lake. Seeing a bit of 925 mb moisture
pushing onshore during the morning to early afternoon, which may
bring some stratocumulus to the Lakeshore this morning, followed
by scattered afternoon cumulus in the east.

Surface winds veer southerly Monday night as the surface ridge
departs to our east. This will bring some modest low-level warm
advection, resulting in overnight lows being a bit warmer than
those experienced this morning. Readings should range from around
60 in the far west and along the Lakeshore, to the mid 50s just
east of the Kettle Moraine.

TUESDAY THROUGH WEDNESDAY NIGHT...Forecast Confidence Is Medium.

Warmer and more humid conditions are expected to return to the
area during this period, as high pressure continues to move well
east of the region. Highs into the 80s are expected Tuesday and
Wednesday, with heat index values into the upper 80s to lower 90s
in most inland areas.

The NAM continues to deviate from the other models with trends
for Tuesday night, as it takes the cold front through the area.
The GFS/ECMWF/Canadian models take the cold front and stall it
across or just north of the area, with a quasi-stationary front
extending to the southwest of the area. Leaned toward this
solution for this forecast.

The models do show a 500 mb vorticity maximum crossing the area
Tuesday night, with a low level jet nose gradually veering over
the area. This will have good mean layer CAPE in the evening, but
should decrease overnight. Deep layer bulk shear is around 20 to
25 knots.

Thus, went with likely PoPs for thunder across the north mainly
later Tuesday night. SPC has area in marginal severe risk Tuesday
night. Most of the strong to severe convection from the northwest
should gradually weaken with time as it moves into the area. There
is the potential for some heavy rainfall, as favorable parameters
increase in value. This should move through the area later
Tuesday night into Wednesday morning.

Another round of convection is possible Wednesday night, as a
quasi-stationary front sets up to the south of Wisconsin. The main
driver for convection will be the low level jet nose, which will
gradually shift eastward across the area by later Wednesday night.
Most of the models bring a possible MCS across the area during
this time.

Have likely PoPs in the western counties later Wednesday night,
and may need to expand them eastward if future model runs show
more continuity. Decent elevated CAPE with strong deep layer shear
is expected Wednesday night, with some favorable heavy rainfall
parameters.

THURSDAY THROUGH SUNDAY...Forecast Confidence Is Medium.

Models are showing a general west northwest flow pattern at 500
mb across the region during this time. They bring several small
vorticity maxima through the area during this period. Some 850 mb
convergence may keep thunderstorms around the area Thursday.
Again, some strong storms are possible with heavy rainfall.

Yet another system then moves into the region for Friday into
Saturday. The low level jet takes aim at the region Friday into
Friday night, before shifting off to the east on Saturday. This
should help bring more chances for thunderstorms. Heavy rainfall
may be possible with some strong storms. It is still several days
away, and need more agreement with the models to bring more
confidence this far out. Warm and humid conditions should linger
into the weekend.

AVIATION(09Z TAFS)...

Patchy fog and 3.5 kft stratocumulus are possible mainly west and
northwest of Madison this morning. Another area of stratocumulus
will push west across Lake Michigan, and may reach the lakeshore
areas around 10-12z, producing scattered 3.5 kft ceilings for a
time. The greatest chance for this is from MKE south to ENW.
Prevailing VFR conditions are expected for this afternoon and
evening, with a few cumulus possible around 3 kft. Winds will be
light and easterly.

MARINE...

Light northeast winds during the morning will veer easterly this
afternoon, with onshore flow. Wave heights will be on the low
side. Winds veer southerly tonight and southwesterly on Tuesday.
Gusts on Tuesday could approach 20 knots, but wave heights should
remain low.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Update...SPM
Today/Tonight and Aviation/Marine...SPM
Tuesday THROUGH Sunday...Wood



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