Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
1026 am CDT Friday Jul 3 2015
Aviation/18z tafs/...elongated axis of high pressure stretches
from Central Plains through eastern lakes. Water vapor/rap vorticity
animation shows circulation across northern/eastern Illinois shifting east with
high clouds on northern fringe of this system on the decrease across southeast
WI. Expecting any convection from northern WI with northern energy/front to
dissipate before reaching taf sites later this evening. Overall
VFR conditions expected to persist into Saturday. Very weak trough
and weak upper wave will necessitate very small probability of precipitation for Saturday.
NAM and GFS show varying amounts of cape though moisture return
may not be quick enough given weak flow around upper Midwest. Will
be interesting to see if the 12z GFS backs off on the more robust
6z solution for Saturday.
Marine...modis lake surface temperature imager measured temperatures in
the middle to upper 50s late Thursday morning and Middle-Lake temperatures
around 50. Lake temperature remained in the cooler 40s farther
north over Central Lake Michigan in the vicinity of the Chippewa basin.
With light onshore winds expected to veer to the southeast and surface
dewpoints to remain near Southern Lake surface temperatures...not expecting
any significant fog to form this afternoon and evening. Latest Lakeshore
webcams show some light haze which should thin as the winds start
to stir a bit. Hence evening fireworks celebrations not expected
to be obscured.
Previous discussion... /issued 338 am CDT Friday Jul 3 2015/
Today and tonight...forecast confidence is high.
The shortwave trough over northern Illinois that is bringing the high clouds to
southern WI will move east to the lower Great Lakes by 00z. Most of the
high clouds will exit the area by afternoon but there will continue
to be some smoke in the upper atmosphere. To the north...an upper
trough will move across the northern Great Lakes today and tonight with its
weak cold front moving into northern WI this afternoon. The front will
continue to weaken tonight and reach central WI by 12z Sat. Precipitable waters will
increase to 1 inch late tonight and there may be scattered middle level clouds
moving into the northern County Warning Area via convective debris from northern WI.
Forecasted 925 mb temperatures today in the upper teens celsius supports
highs in the upper 70s inland. The lake breeze will develop by middle
to late morning with highs near 70f at the Lakefront. For tonight temperatures
will be warmer thanks to the warmer daytime highs but also due to
the high pressure area moving south with a light westerly flow expected.
Saturday and Sunday...forecast confidence...medium
Think there could be a few showers and storms Saturday...mainly
during the afternoon and evening. A very weak shortwave is prognosticated
to move through. Most of the lift Saturday seems to be in
response to low level convergence...with very little large scale
lift in the middle and upper levels. Dewpoints are probably a bit too
high on the GFS and NAM...likely resulting in overdone
instability. More conservative models still showing surface based
cape peaking at around 1000 j/kg...so some convection is not
unreasonable. Fortunately...shower coverage should be isolated to
scattered and will be diminishing in the evening...so hopefully
this will be little to no impact on firework shows.
Models are showing more instability Sunday...but less of a lifting
mechanism...so kept the dry forecast going.
Looks like high temperatures will be a couple to few degrees above normal
over the weekend most places...aside from near normal temperatures near
Monday through Thursday...forecast confidence...medium
Models are coming into better agreement with the timing of a low
pressure system and associated cold front on Monday. Should be a
good increase in moisture ahead of the front...with the GFS
increasing precipitable water values to around 2 inches. Cape
values not particularly impressive and 0-6 km bulk shear only
around 20-25 knots...so not concerned about severe threat at this
time. Looks like a decent chance for a round of afternoon and
evening Summer storms though...so increased probability of precipitation a bit more.
Should see temperatures right around normal Monday.
Any lingering precipitation should wind down early Tuesday morning...with
dry weather then expected though Wednesday. Models diverge beyond
that...with the GFS bringing a return of moisture and shower/storm
chances Thursday...while the European model (ecmwf) remains dry under high
Somewhat of a spread in model temperatures in the extended...with the
European model (ecmwf) maintaining cooler temperatures aloft behind the departing Monday
system...while the GFS has less of cool down and recovers temperatures
faster. Stuck near consensus of model temperatures due to the
uncertainty...resulting in forecast temperatures within a couple degrees
of normal values.
VFR conditions today and tonight. High pressure will be over southern WI
today and slowly move south tonight. The airmass will be too dry for
Today/tonight and aviation/marine...gehring
Saturday through Thursday...ddv