Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
945 PM CDT Friday may 22 2015
Update...went a little milder with low temperatures tonight given scattered-broken
high clouds. The high clouds should become more scattered late tonight and
Sat am as the shortwave trough deamplifies. Middle level clouds
may then become broken at times Sat afternoon due to warm
advection at that level. High temperatures in the middle 70s away from the
lake look good.
Aviation/06z tafs/...sct-bkn middle to high clouds for Sat and
Sat evening. A light southerly flow is expected.
Previous discussion... /issued 332 PM CDT Friday may 22 2015/
Tonight and Saturday...forecast confidence is medium.
Models are in good agreement with high pressure sliding to the east
southeast tonight and Saturday. Elongated 500 mb vorticity maximum
is expected to shift east northeast into the area later tonight into
Saturday. Area of middle to high clouds associated with this feature
is expected to move in. May have to bring them in quicker than
currently forecast...will make final adjustments to timing of these
clouds if needed.
Some of the mesoscale models are generating scattered light rain
showers Saturday afternoon. Area forecast soundings show some
moisture and very weak mean layer cape above 5000 feet above ground
level. However...think that upward vertical motion will be too
weak...and low levels too dry...for any showers to reach the ground.
Kept dry forecast going for now.
925 mb temperature trends suggest lows dropping into the lower to
middle 40s east and upper 40s west. Highs Friday should reach the middle
70s inland...and around 70 Lakeside. Lake breeze will cool things
off near the lake in the afternoon.
Short term...Saturday night through Monday night
Saturday night...forecast confidence medium
Decent frontogenetic response with warm air advection and forcing
with passage of lead short wave. However cross sections and
soundings remain dry below 5k feet over the eastern County Warning Area. Deeper column
moisture and stronger 700 mb Omega moves into western areas closer
to stronger low-level winds after 06z...so will have higher chance
probability of precipitation there...tapering off quickly to the east with most of southeast WI dry
through 12z Sunday. Southerly flow keeps lows in the mid50s...with
upper 40s to low 50s closer to Lake Michigan.
Sunday and Sunday night...forecast confidence medium
Will walk higher probability of precipitation from west to east across forecast area during
the day Sunday as low-level jet shifts east...with the higher probability of precipitation
Sunday evening as the strongest winds push into the state. Overall
forcing for ascent aided by upper level divergence in right entrance
region of upper jet. Forecast soundings still showing limited
instability with a weak warm layer centered around 760 mb and a
moist adiabatic profile holding both surface-based and elevated cape
to 600 j/kg or less...though NAM has a pocket of 1000 j/kg in the
far west. Will have thunder there...with mainly rain showers and a
few embedded thunderstorms expected elsewhere in the County Warning Area. Southeast
winds will limit highs to the low 60s along the lake...warming to
the upper 60s to lower 70s away from the lake. Lows Sunday will only
fall into the lower 60s inland...with low to middle 50s in the far
Monday and Monday night...forecast confidence medium
Better probability for thunder on Monday...especially if the GFS
solution pans out with the forecast area well into the surface warm
sector. Potential for severe somewhat limited with backing winds
above 10k feet and a continuation of limited instability with a
moist adiabatic profile. However the tall-skinny cape and the
southerly flow bringing Gulf moisture with precipitable waters in
the 1.7 to 1.8 inch range indicate potential for some widespread
beneficial rain. Temperatures warm into the 70s everywhere with south-
southwest winds limiting influence of the lake.
All models indicate precipitation tapers off in the afternoon with a dry
punch...more pronounced on the European model (ecmwf) and Canadian...wrapping into
southern WI. Precipitation tries to develop along trailing surface trough/cool
front...but this feature washes out as surface low weakens/opens up
as it tracks from the North Dakota/Minnesota border region into SW Ontario.
Consensus lows in the 60s look reasonable.
Long term...Tuesday through Friday...forecast confidence medium
Models differ after Tuesday with timing of short wave energy in southwesterly
flow regime...leading to chance slight chance probability of precipitation through the
extended. Best potential for a dry period looks to be Wednesday
afternoon into Wednesday night. Then precipitation chances return with the
moist flow ahead of another trough moving out from the SW U.S.
Into the Southern Plains Thursday/Thursday night phasing with a
strongernorthern stream trough. In spite of the
precipitation...temperatures look to remain above seasonal norms through
Aviation/00z tafs/...VFR conditions are expected across taf sites tonight
and Saturday. High pressure over the region will drift to the east
southeast during this time. Light east winds will become southeast
tonight and south into Saturday.
Lake breeze with southeast winds are expected at Milwaukee and
Kenosha Saturday afternoon. Middle to high clouds will gradually
move east northeast into the area tonight and Saturday.
Gusty south to southwest winds are expected to occur on Memorial
Day...as a tight pressure gradient develops across the area.
Frequent gusts of 22 to 25 knots are possible across the nearshore
waters of Lake Michigan. A Small Craft Advisory may be needed for
tonight/Saturday and aviation/marine...wood
Saturday night through Friday...rem