Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 221456 AAA
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
956 AM CDT MON AUG 22 2016
Mostly sunny skies and near normal temperatures are expected today
under high pressure. No significant changes to the forecast are
anticipated through the afternoon hours.
VFR conditions will prevail through Tuesday under the western
periphery of high pressure. The high will be a bit farther east
tonight than last night, with a tightening pressure gradient ahead
of approaching low pressure. Only had fog in the river valleys
last night and it might be a stretch to repeat that tonight given
increasing low level winds.
Will likely see diurnal VFR cumulus Tuesday along with increasing
high level clouds.
Latest RAP forecast soundings and HRRR surface maps supporting a
gradual increase in southwest winds through the rest of the morning,
with winds shifting south by early afternoon as surface pressure
gradient tightens between departing high pressure and a trough of
low pressure moving east from the Plains into Minnesota/Iowa
tonight. Though strengthening, winds and waves will remain below
Small Craft Advisory criteria through Tuesday but will approach
criteria from Port Washington north Tuesday night.
.PREV DISCUSSION... /Issued 332 AM CDT MON AUG 22 2016/
TODAY AND TONIGHT...Forecast Confidence Is High.
A quiet period is expected through tonight. Low level ridge axis
will shift to the east this morning, allowing low level winds to
increase from the south. Plenty of sunshine and south winds will
result in a warmer day, with temperatures recovering back to
around seasonal normals for mid-August.
Winds will veer to the south to southeast by Lake Michigan this
afternoon, causing temperatures at the shore to stabilize, and
likely even slip a few degrees, due to cooler nearshore waters.
Low level jet will be focused to the west today, and to the north
tonight, as mid-level high pressure ridge builds briefly back
into the region. Possible some mid or high clouds may graze
southern WI this aftn and tonight, as warm air and mid-level
moisture surges in from the Central Plains.
Despite light boundary layer winds over western CWA, and low
dew point depressions, seeing very little fog development on
webcams and surface observations. Hence wl confine fog mention to
WI River valley, and far west closer to low level ridge axis
early this morning.
TUESDAY THROUGH WEDNESDAY NIGHT...Forecast Confidence Is Medium.
Models remain in good agreement with showing a 500 mb ridge
sliding northeast through the region on Tuesday. A tightening
pressure gradient should result in increasing south winds. High
pressure will remain to the southeast of the region. This should
continue to bring warmer air into the region. Area forecast
soundings are still fairly dry on Tuesday, so kept forecast dry.
May see winds back southeast along the lake in the afternoon.
Models then are in decent agreement with bringing a 500 mb
shortwave trough northeast into Wisconsin late Tuesday night into
Wednesday morning. In addition, a low level jet nose at 850 mb
points into eastern Iowa into northern Illinois later Tuesday
night, before weakening and shifting to the east Wednesday
Area forecast soundings show a quick moistening of the air column
late Tuesday night, lingering into Wednesday morning. There is
some elevated CAPE with modest deep layer shear. Increased POPs
into likely category by Wednesday morning across most of the area.
Cold front then moves east through the region Wednesday afternoon
and evening, then off to the east by later Wednesday night.
Frontogenesis response with the front is fairly weak during this
time. Still, adjusted area forecast soundings show some mean
layer CAPE again, with modest deep layer shear.
Continued likely POPs into the afternoon, with POPs lowering
Wednesday night. Precipitation during this time may be more
scattered in nature, with the weaker upward vertical motion
Storm Prediction Center has area in Marginal Risk for severe
storms on Wednesday/Wednesday night. Given the modest deep layer
shear and modest CAPE, this seems reasonable. However, any cloud
cover with the precipitation may limit CAPE values.
In addition, heavy rainfall may be possible during this time, as
several parameters are favorable. Precipitable water values reach
2.00 inches on both NAM and GFS for Wednesday. A lot will depend
on how unstable it gets, as well as how strong the shear and
storm propagation gets. Warm and humid conditions are expected.
THURSDAY THROUGH SUNDAY...Forecast Confidence Is Medium.
GFS/ECMWF are showing cold air advection behind the front for
Thursday, with high pressure pushing east across the region
Thursday night and Friday. This should bring a period of quiet
weather, with less humid conditions.
These models then bring a 500 mb shortwave trough northeastward
into Minnesota and northwest Wisconsin on Sunday, with southwest
flow across the region Friday night into Saturday night. Most of
the QPF with the warm air advection remains just west of the area
Friday night, then shifts into the area Saturday into Sunday.
For now, will continue to have POPs for showers and storms for
most of this period. Friday night may end up dry, if the models
continue to trend westward with QPF and forcing for upward
vertical motion during that period. Warm and humid conditions
should prevail during this time.
VFR conditions expected for the period. Some light fog may affect
TAF sites early this morning, but any visibility restriction will
be brief, not more than an hour or two. Better boundary layer
mixing should prevent significant fog later tonight, despite
slightly higher low level relative humidity.
A quiet period through Tuesday, with winds turning onshore late
this morning or early afternoon. With the backing winds, Lake
Michigan lake surface temperatures should rebound back into the
mid 60s to lower 70s, as the cooler upwelling waters currently in
the nearshore waters gradually warm.
MODIS image from Sunday evening measured the lake surface
temperature anywhere from the mid 50s at the shore off of Ozaukee
and Sheboygan counties, to the upper 60s toward the open waters.
Tightening pressure gradient ahead of a cold front will cause
increasing south to southeast winds Tuesday night into Wednesday.
Gusts will approach Small Craft Advisory levels during this
TODAY/TONIGHT AND AVIATION/MARINE...MBK
Tuesday THROUGH Sunday...Wood