Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 210831
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
331 AM CDT SUN AUG 21 2016
.TODAY AND TONIGHT...Forecast Confidence Is Medium.
Weak low pressure trof rotating around departing southern Canada
low pressure, and low level cold air surge, will bring a period
of lower clouds to southern WI this morning. A light shower or
sprinkle may affect northeast CWA. Weak forcing slides off to the
east late this morning.
However, sct-bkn cumulus likely to redevelop in lingering moist,
cyclonic flow. May be just enough instability to set off a few
isold -shra over ern CWA in the early to mid aftn. Otherwise,
cyclonic flow flattens late today into tonight, as upper level
jet axis shifts east of the area, and thermal trof slides off to
the east as well.
Hence, expect mostly clear skies for tonight. Boundary layer
winds will weaken enough to allow patchy fog to develop over far
western areas late tonight, with widespread fog in the WI river
valley. Clouds and cooler air in place will hold daytime temps
peaking in the low to mid 70s, with 50s tngt.
.MONDAY THROUGH TUESDAY NIGHT...Forecast Confidence Is Medium.
Models are in decent agreement with trends Monday into Tuesday.
Zonal flow at 500 mb transitions into a ridge during this period.
At the surface, high pressure southeast of the region allows for
south to southwest winds to develop, as the pressure gradient
tightens somewhat. This brings some warm air advection into the
region. Area forecast soundings remain fairly dry during this
period. Thus, quiet weather with warming temperatures and
increasing dew points are expected during this time.
Models show a little more uncertainty for Tuesday night, as they
differ on the timing with the next 500 mb shortwave trough sliding
northeast into the region. The NAM/GFS/ECMWF bring this feature
into southwest Wisconsin by 12Z Wednesday with light QPF in the
western counties. The Canadian is slower amd keeps the area dry.
Area forecast soundings show moisture advection into the region
helping bring a rather moist adiabatic lapse rate profile, with
some modest elevated CAPE. Continued to bring in chance POPs for
Tuesday night in forecast.
.WEDNESDAY THROUGH SATURDAY...Forecast Confidence Is Medium.
The GFS/ECMWF bring the 500 mb shortwave trough northeast through
the region Wednesday morning, with the cold front sliding east
through the area later Wednesday into Wednesday night, exiting to
the east Thursday. GFS forecast soundings showing decent mean
layer CAPE at times, with steadily increasing deep layer shear as
the front approaches the area.
Continued the consensus POPs for thunder Wednesday into Wednesday
night, then lowering Thursday with some lingering showers. Warm
and humid conditions are expected during this period.
High pressure should then build into the region Thursday night
into Friday night, bringing less humid conditions and a period of
quiet weather. Chances for precipitation return Saturday, with
next system shifting northeast into the region. More uncertainty
exists this far out in the forecast, so stayed close to consensus
POPs and temperatures.
Period of MVFR cigs likely to affect TAF sites this morning, as
low pressure short wave trof moves southeast through srn WI. Small
chance for a brief light shower or sprinkle, mainly north of TAF
sites. Expect sct-bkn cu to reform for several hours, after weak
short wave forcing slides southeast of the area later this
morning. Hence, not expecting significant clearing until mid
afternoon or later.
Will continue Small Craft Advisory through mid-morning. Still
receiving recent observations of west to northwest wind gusts of
20 to 25 knots just offshore, including Racine Reef Light and
Atwater Buoy. Gradually weakening pressure gradient will allow
wind gusts to fall below 22 knots later this morning into the
Offshore winds will continue through tonight, with winds backing
to the south on Monday. Latest MODIS imagery shows that the
offshore winds have resulted in upwelling of cooler subsurface
water along the near shore waters. Lake surface temp has cooled
into the 50s.
LM...SMALL CRAFT ADVISORY until 10 AM CDT this morning for LMZ643>646.
TODAY/TONIGHT AND AVIATION/MARINE...MBK
Monday THROUGH Saturday...Wood