Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
501 PM CDT Wednesday Jul 29 2015
Aviation/06z tafs/...no change.
Marine...expanded Small Craft Advisory to include Wind Point to
Winthrop Harbor zone as expect wind gusts to exceed threshold of
22 knots for several more hours. Winds should drop off rapidly
Previous discussion... /issued 322 PM CDT Wednesday Jul 29 2015/
Tonight and Thursday...forecast confidence is high.
High pressure will shift into Missouri with low pressure to the
north of the state. A pair of shortwaves will slide across the
region within northwesterly middle level flow. The dry airmass will
bemain in place. West winds of 5 to 10 miles per hour will keep lows around 60
despite the cler skies. West-northwest winds should become gusty
again Thursday. Expect highs in the middle 80s with dew points in the
50s on Thursday.
Thursday night and Friday...forecast confidence...high
A northwest flow with a 90 knot speed maximum moves across the upper
Great Lakes with a shortwave. Fairly weak upper level
divergence...although the 700 mb upward motion increases to
moderate values Friday morning and into the southeast Friday
afternoon. 700 mb dewpoints increase as a west 700 mb winds
increase to almost 50 knots Friday. An 18 degree celsius 850 mb
thermal ridge pushes across southern Wisconsin by noon Friday as
8950 mb dewpoints also rise.
The surface trough/cold front moves across southern Wisconsin
Friday afternoon. Zero to 1 km mixed layer cape increases to 1000
to 1500 joules/kg especially far southeast middle afternoon ahead of
the front. Soundings are fairly dry...but a shallow moist layer
around 700 mb does result in an inverted v type sounding. The GFS
begins to develop mainly over the southeast middle afternoon...before
increasing south over northern Illinois. However due to the
overall dry sounding will keep rain chances out.
Friday night and Saturday...forecast confidence...high
The northwest upper flow continues with not much in the way of
upper divergence. A dry 700 mb begins to increase a little toward
evening. Surface dew points are rather low and mix out toward
noon...but rise late Saturday as the winds become more
southwest...with the center of the surface high over the middle
Saturday night through Monday...forecast confidence...medium
A weak small shortwave moves across southern Wisconsin Saturday
night...with a second Sunday afternoon/Sunday night. Slight timing
differences between the GFS and European model (ecmwf). Also the 00z European model (ecmwf) drops
the base of the upper trough over central/eastern Canada more into
Wisconsin on Monday.
Both the GFS and European model (ecmwf) brings showers/thunderstorms across
southern Wisconsin Saturday night into Sunday morning. With
another period of showers/thunderstorms Sunday night and Monday
morning with a surface trough/cold front.
Tuesday and Wednesday...forecast confidence...medium
The Canadian upper trough moves slowly east with the northwest
flow continuing across Wisconsin Tuesday. The upper flow becomes
a little more zonal Wednesday. The 00z European model (ecmwf) has a stronger
shortwave moving into southern Wisconsin Wednesday afternoon.
A surface high moves across Wisconsin Tuesday and off to the east
Wednesday. Both the GFS and European model (ecmwf) bring an area of
showers/thunderstorms towards southcentral Wisconsin Wednesday
VFR conditions expected through the taf period with a dry airmass in
place. West-northwest winds will increase Thursday afternoon with
gusts around 20 kts likely.
Westerly wind gusts at small craft levels will continue through the
afternoon then subside this evening. On Thursday afternoon west-
northwest winds will gust 20 to 25 kts near Sheboygan and possibly
down through Milwaukee. A Small Craft Advisory may be needed.
Lm...Small Craft Advisory until 8 PM CDT this evening for lmz643>646.