Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
337 am CDT Thursday Jul 28 2016
Today...forecast confidence medium
Main area of precipitation over northern and central WI has been
firing in region of strong differential cva ahead of short wave and
deep moisture convergence on eastern side of inverted surface trough
along the surface baroclinic zone and in the most-unstable cape
gradient, which has been slowly collapsing south. Isolated to
scattered showers/storms over southern WI with weaker DCVA.
Individual cells have been short-lived with little shear to support
updrafts in weak flow with 500 mb winds around 25 knots and speeds
in the single digits below 750 mb on area forecast soundings.
Showers and storms will taper off for a time as this initial wave
exits to the east this morning, then chances increase ahead of
another wave coming across from the eastern Dakotas and the inverted
surface trough sagging into SW WI and lingering through the
afternoon before slowly collapsing south this evening.
Will have higher chance to likely pops in the western County Warning Area closer to
the low-level convergence along the surface trough axis, tapering to
slight chance in the far east. Clouds and precipitation will limit
high temperatures to the mid 70s.
Tonight...forecast confidence medium
Scattered showers and storms will taper off from northwest to
southeast as the inverted trough sags into Illinois and drier air finally
streams in on northeast winds. However lingering low-level
convergence and a continuing parade of short wave energy will keep
at least chance pops in the forecast through the overnight.
Temperatures will cool into the lower 60s away from Lake Michigan,
with some upper 50s in the far northwest County Warning Area.
Friday and Saturday...forecast confidence...medium
A slow moving trough is expected to kick off more showers and storms
on Friday. East to northeast low level flow will keep deeper
moisture and better instability across the west/southwest portions
of the forecast area. May struggle to see any precip at all in the
east. Storm motion will be slow but will have a westerly component,
so did keep some low pops most places in the east.
It looks drier Friday night and Saturday, though the NAM and
Canadian are slower to scour out deeper moisture as they hang
onto the trough longer. The GFS and European model (ecmwf) would suggest mainly dry
conditions for this period. Decided to hang onto some pops per the
slower/wetter NAM and Canadian solutions.
Should see high temps a couple/few degrees below normal for Fri and
Sat, with highs in the mid/upper 70s.
Sunday and Monday...forecast confidence...medium
It should be dry Sunday and Monday with southern Wisconsin sitting
under the western portion of high pressure, while the next
approaching trough will still be well to the west. High temps are
expected to be a tad above normal in the low to mid 80s most
Tuesday and Wednesday...forecast confidence...medium
Deeper moisture is progged to return Monday night into Tuesday.
Additionally, some warm advection aloft and a shortwave will
provide lift for showers and storms by later Monday night. The
best chance for storms is expected to be on Tuesday as the wave
moves through. Left some low pops in for Wednesday as models are
showing a weak wave may bring a few showers/storms.
Temps Tue/Wed will be largely dependent on the timing of
clouds/precip. Overall though, will likely see highs a few
degrees above normal.
Some spotty IFR stratus cigs developing in areas that saw scattered
showers/storms during the overnight. Will monitor trends but not
expected to last long at any one site nor become widespread.
Otherwise expect VFR conditions with MVFR cigs/vsbys with scattered
showers and thunderstorms expected to develop later this morning and
afternoon. Exception may be western County Warning Area including kmsn where
upstream MVFR cigs will dip in with inverted surface trough.
Looking for light easterly winds to turn northeast and become gusty
around 20 knots in the far east for a time today.
Drier air working in as trough drops south should raise cigs back up
to VFR tonight, though onshore winds may advect enough lake moisture
for cigs to linger near MVFR levels overnight.
Looking for northeast winds to rise to 10 to 15 knots with gusts to
20 knots this afternoon in the northern zones in tightening pressure
gradient behind inverted trough lingering over SW WI. Southern zones
not as gusty with a weaker gradient, and waves everywhere remain
just below Small Craft Advisory criteria so will not issue a
headline at this time. Will add "small craft should exercise
caution" phrase to the forecast for the northern zones.
Today/tonight and aviation/marine...rem
Friday through Wednesday...ddv