Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
336 am CDT Tuesday Apr 28 2015
Today...forecast confidence is high.
Quiet weather today with surface high pressure and middle-level ridging
between departing cyclonic flow around closed low over eastern
Canada and approaching 500 mb trough currently moving across the
Dakotas. Leading edge of middle level clouds associated with the trough
may reach the far northwest towards 00z.
Temperatures only a degree or two warmer than Monday as 925-850 mb thermal
ridges ahead of the trough just make it into the western County Warning Area by 00z.
Northerly winds not as strong and gusty as Monday with weak
gradient...however onshore NE flow keeps Lakeside areas cooler...and
developing East Lake breeze in the afternoon expected to bring cool
air to at least The Kettle Moraine by 00z.
Tonight...forecast confidence is high.
500 mb trough moves across region ahead of closed 500 mb low that
reaches Lake Superior by 12z Wednesday. Weak forcing...mainly cva-
driven...moves across in the evening but meager moisture so no
precipitation with only some middle-level clouds to mark passage of
trough. The clouds and 925-850 mb thermal ridges moving through
overnight will keep lows around 40 in the east...and lower to middle
40s in the west.
An upper low will drop slowly southward through the Great Lakes on
Wednesday and Wednesday night. Looks like enough lift via middle
level vorticity maximum and low level convergence for a chance for showers.
Given cold core aloft...seeing enough instability in models to
mention slight chance of thunder. Onshore winds will likely
diminish the shower/storm threat toward Lake Michigan...though
north-northwest shower/storm motion will probably allow some
precipitation to drift toward the lake. Precipitation chances should wind down
by late evening. Will likely see high temperatures comfortably into the
60s away from Lake Michigan...with the onshore winds keeping it
cooler near the lake.
Friday through Monday...forecast confidence...medium
It looks mainly dry Friday and Saturday as high pressure slides
eastward through the region. A few showers not out of the question
Saturday as the high departs...but not enough model agreement for
probability of precipitation at this time.
There is then a chance for showers/storms Sunday/Monday as low
pressure moves through the area.
Expect temperatures to be above normal for the weekend into early
VFR conditions through the forecast period. Weak gradient will keep
northerly winds light today...turning east with a developing lake
breeze this afternoon that will reach The Kettle Moraine by
00z...affecting mainly the eastern taf sites.
A middle-upper level trough of low pressure will cross the region
tonight...but meager moisture so no precipitation...with only some
middle-level clouds to mark passage of trough.
Very low relative humidity values of 22 to 30 percent are expected
again this afternoon inland...with higher values near the lake with
onshore winds. Winds will be light across the area. Relative
humidity values will be slightly higher Wednesday afternoon with a
chance of rain showers...but should still be in the 30 to 35 percent
range over south central Wisconsin in the afternoon...with 40 to 45
percent over southeast Wisconsin away from the lake.
Today/tonight and aviation/fire weather...rem
Wednesday through Monday...ddv