Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
923 PM CDT Thursday Jul 30 2015
Update...overnight temperatures look in good shape. Should be a degree
or two warmer than last night. May see a few middle clouds spread in
late tonight from passing weak short wave trough.
Aviation/06z tafs/...VFR conditions to continue this forecast
period with more gusty west winds expected on Friday.
Marine...another breezy day is expected on Friday as little
change is expected in the low level wind profile and pressure
pattern. Hence pulled trigger on Small Craft Advisory for all
marine zones beginning mid-morning.
Previous discussion... /issued 416 PM CDT Thursday Jul 30 2015/
Short term...tonight through Sunday
Tonight and Friday...forecast confidence is high.
Passing 500 mb shortwave trough helping drive scattered showers and
a few thunderstorms in northern Wisconsin. This activity will remain
north of the area into early this evening. Diurnal cumulus will
dissipate by sunset across the area...and the gusty west winds will
The models are in good agreement with high pressure remaining well
south of the region...with low pressure well north. This will keep
the area dry tonight. The models do bring a surface trough through
the area Friday morning and early afternoon...but airmass will
remain quite dry so kept the dry forecast going.
Daytime heating and low level mixing Friday afternoon will bring
more gusty west northwest winds to the area...with gusts in the 20
to 25 knot range. Went with lows tonight a bit cooler than short
term blended model guidance. Highs Friday should reach the middle to
upper 80s...given similar conditions to today.
Friday night...forecast confidence high
Weak short wave Friday night with some middle-level moisture and
minimal elevated cape on NAM...less than 500 j/kg...with parcels
originating around 6k feet. Fairly strong low to middle level
frontogenesis driving Omega on NAM...though little cross isothermal
GFS drier with weaker Omega. Will continue dry forecast due to lack
of deep moisture...even on the more robust NAM. Consensus lows in
the upper 50s to lower 60s on track...with middle 50s in the cool
outlying low areas.
Saturday...forecast confidence high
GFS faster with bringing precipitation into the County Warning Area Saturday afternoon with
strong middle-level frontogenetic response to warm air advection. NAM
and most of the other models hold this strong forcing back to the
northwest through 00z Sunday. Will go with consensus probability of precipitation and keep
Saturday dry. Increasing cloud cover will hold highs in the upper
70s to lower 80s.
Saturday night and Sunday...forecast confidence medium
Models take a short wave trough across Lake Superior into southeast Ontario
Saturday night into Sunday morning. A weak short wave passing to the
SW strengthens due to convective feedback...especially on the
NAM...with accompanying increase in upper divergence farther north
on the European model (ecmwf) and NAM Saturday night...targeting more of the SW
portion of the state. All models depict increasing 850 mb winds
driving a thermal ridge across County Warning Area...but with some timing
differences. Will keep high chance probability of precipitation over the west in the evening
then spread them across the entire County Warning Area after 06z with the better
forcing signals. Precipitable water/S Jump Up to between 1.75 and 2 inches in the
SW...lowering to a maximum of 1.2 inches in the NE.
Long term...Sunday night through Thursday...forecast confidence
Differences begin to appear Sunday night between the 12z GFS and the
12z European model (ecmwf) with location of amplifying western ridge and subsequent
location of downstream closed 500 mb Canadian low for next week.
With the closer proximity of the closed low the European model (ecmwf) 850 mb temperatures
are initially cooler than the GFS...with the Gem in between...but
with stronger northwest flow the GFS drops below 10c for Tuesday then
modify toward similar levels for the rest of the extended.
Showers and storms along a surface cold front Sunday night into
Monday morning that stalls out over northern/central Illinois. European model (ecmwf) brings a
wave along stalled baroclinic zone Wednesday/Wednesday evening that
will lead to slight chance probability of precipitation over southern WI....with another short
wave bringing slight chance/chance probability of precipitation for Thursday/Thursday
VFR conditions are expected tonight and Friday across taf sites.
Quiet weather is expected...with high pressure remaining to the
south of the region. Gusty west winds are expected until around
sunset...with gusts to around 25 knots possible.
Lighter west winds are expected tonight...with clearing skies. Gusty
west northwest winds are expected late Friday morning into the
afternoon. Gusts of 20 to 25 knots are expected again during this
time. Mostly sunny skies are expected.
A Small Craft Advisory continues until 00z Friday for the nearshore
waters of Lake Michigan. Gusty west winds of 15 to 25 knots are
expected...with a tight pressure gradient between high pressure to
the south...and low pressure well to the north. High waves will
remain over the open waters.
Gusty west northwest winds are possible late Friday morning into the
afternoon...as the pressure gradient remains fairly tight with good
low level mixing with daytime heating. Gusts to 25 knots are
possible. A Small Craft Advisory may be needed for this period.
Lm...Small Craft Advisory from 9 am to 7 PM CDT Friday for lmz643>646.