Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
420 am CDT Wednesday may 22 2013
Today and tonight...forecast confidence medium to high
New shower development over NE Illinois will stream north-northeastward into southeastern WI
early this am. The showers and possible thunderstorms will then expand by
late morning as a fairly strong shortwave trough pivots northward through
the region from its current position over MO. The main upper low
will then move eastward across southern WI tonight. Model output and forecast
soundings show precipitable waters over an inch through this period with moist
adiabatic to slightly conditionally unstable conditions through this
period. These moist conditions along with weak flow aloft and areas
of low level convergence will make for good precipitation efficiency and
moderate to possibly sometimes heavy rainfall rates. Forecasting an
average of an inch of rain for today and tonight but localized
amounts of 2 inches or more are possible.
Thursday through Friday night...forecast confidence is medium to
high.
Last 500mb vorticity maximum slides southeast through the area
Thursday morning...with NAM/GFS area forecast soundings showing
some low to middle level moisture lingering. Thus...will keep probability of precipitation
going Thursday morning. Tight pressure gradient will keep gusty
north to northeast winds going as well.
Cold air advection during the afternoon pushes southward through
the area...as the 500mb vorticity maximum exits the region.
Downward motion scours out the moisture during this time per area
forecast soundings. Cool temperatures are expected Thursday...as
winds remain onshore and slowly weaken.
Short term models show high pressure sliding southeast across the
region Thursday night. This will allow for decoupled winds inland
and cold temperatures per 925mb and MOS guidance temperatures.
Lows should drop into the middle to upper 30s and perhaps a bit
colder...which could lead to some frost. Added patchy frost for
most of the area.
High pressure will start to slide east of the region Friday. Area
forecast soundings continue to remain dry Friday...so kept this
period dry. Some recovery in highs for Friday are anticipated...as
slightly warmer 925mb temperatures push into the area. Onshore
winds will keep Lakeshore areas cool.
NAM tries to push an area of focused 850mb warm air advection and
frontogenesis response into the western portions of the
area...along with an 850mb low level jet nose. European model (ecmwf) also tries to
bring in quantitative precipitation forecast to the far west...with the GFS and Canadian keeping
these features west of the area. For now...will continue to
mention low probability of precipitation in the west for Friday night.
Saturday through Tuesday...forecast confidence is low to medium.
The GFS and European model (ecmwf) differ greatly with most features during this
period. The GFS shows a west to east oriented warm front setting
up to the southwest and south of the area Saturday through
Monday...before pushing northward toward the area on Tuesday.
500mb vorticity maximum slides just south of the area late
Saturday into Saturday night...with another passing just south
Sunday...before a third one moves through the area Monday night.
This setup brings several rounds of showers and storms through the
region.
After passing quantitative precipitation forecast with the focused warm air advection and low
level jet nose Saturday...the European model (ecmwf) keeps the effects of high
pressure across the area. It keeps the system the GFS had
affecting southern Wisconsin well south of the region. Either
setup would have onshore winds for most of the period...keeping
temperatures cool near the lake. For now...will use consensus probability of precipitation
and temperatures for this period.
&&
Aviation/12z tafs/...showers will overspread southern WI this am and
continue through tonight as low pressure moves across the region. Local
MVFR visibilities from early this am will give way to MVFR ceilings and visibilities
with the rain. Ceilings and visibilities will lower to IFR levels for tonight.
&&
Marine...a Small Craft Advisory is in effect late tonight into Thursday
night for brisk north winds and high waves. The high winds and waves
will develop when low pressure moves east of Lake Michigan and the
pressure gradient increases. Much lighter winds and waves are
expected for Friday when high pressure moves over Lake Michigan.
&&
Mkx watches/warnings/advisories...
WI...none.
Lm...none.
&&
$$
Today/tonight and aviation/marine...gehring
Thursday through Tuesday...wood
