Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 241427 AAB
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
927 AM CDT Mon Apr 24 2017
The forecast is on track this morning, with a very pleasant day
expected across southern Wisconsin. It will be cooler near Lake
Michigan, but otherwise most places should hit 70 today.
Persistent southeast winds will gust to 20 knots at times and
result in waves of 2-4 feet over the next couple days. Overall, it
looks like winds and waves will remain just below Small Craft
Advisory criteria through Wednesday.
.PREV DISCUSSION... (Issued 612 AM CDT Mon Apr 24 2017)
AVIATION(12Z TAFS)...VFR conditions expected for this forecast
period. Considerable upstream cirrus over MN/IA streaming eastward
will affect southern WI today but should thin a bit as it progresses
eastward. Light easterly winds will veer to the south to
southeast. Gusts up to 25 knots are possible this afternoon over
south central WI. Increasing low level winds look to remain just
below Low Level Wind Shear criteria tonight.
PREV DISCUSSION... (Issued 300 AM CDT Mon Apr 24 2017)
TODAY and TONIGHT - Confidence...High.
Light northeast winds, dry air and clear to partly cloudy skies have
allowed temperatures to fall into the mid 30s across eastern parts
of CWA early this morning. Temperatures may slip a few more degrees
through 12z before beginning to rise. Enough surface moisture
remains in place to produce some patchy dew and frost in these areas
Otherwise, low level winds will turn to the south to southeast as
high pressure over southern Canada and eastern Great Lakes moves
farther east and low pressure trough moves into the plains.
Despite shift to more southerly winds, deeper column RH wl remain
well southwest of the region and cutoff to the southeast by second
low pressure system moving through the southeast CONUS. Hence
only some passing cirrus clouds expected at times today with
partly to mostly sunny skies. 925H temps warm to 13-15 degrees
over inland areas which will allow temps to rise rapidly into the
60s by late morning and early afternoon with cooler temps likely
by Lake Michigan.
Some increase in higher level moisture will occur across WI tonight
as south winds continue to increase. These winds will carry a weak
short wave and this higher moisture across the area from the plains.
Hence an increase in mostly high clouds likely for tonight with
warmer temperatures. Atmosphere below 10K feet remains parched so
no precipitation expected.
TUESDAY THROUGH THURSDAY...Forecast confidence is medium.
A broad, amplified upper trough across the western CONUS will
slowly move to the east through the period, ejecting multiple
impulses toward the Upper Midwest. The strongest shortwave will
likely push through the region late Wednesday or early Thursday.
This will result in an extended period of cyclonic flow in the lower
levels. By Tuesday morning, an inverted surface trough will extend
from the Southern Plains into the far western Great Lakes. This
trough will slowly move eastward as low pressure develops in the
Southern Plains and moves toward Wisconsin. Differences exist in the
guidance with regards to system timing and track beginning
Wednesday, and obviously this introduces some uncertainty from
Wednesday and into Thursday. Nonetheless, the low will move through
at some point late Wednesday or early Thursday, bringing around
an inch of rain to portions of the CWA.
All guidance also brings some instability into SE WI on Wednesday,
though any instability will be limited by ample cloud cover.
However, given this marginal instability, strong system dynamics,
and 0-6 km bulk shear in the neighborhood of 50 kts, I cannot rule
out severe weather at this point. Accordingly, SPC has introduced
a marginal risk to the southeast CWA.
FRIDAY THROUGH MONDAY...Forecast confidence is low.
The broad upper trough over the western CONUS discussed in the last
section finally pushes through the Midwest toward the end of the
weekend, with remarkably good agreement at the 500mb level between
the GFS and Euro. All guidance also shows a strong surface low
developing in the Southern Plains ahead of the upper trough and
pushing into the Upper Midwest. Differences remain regarding the
timing and track of the low, but it still looks like this system
could drop significant rainfall amounts across the region next
VFR conditions will persist for Mon-Mon nt.
Northeast winds will turn to the southeast this morning as weak high
pressure slides farther off to the east and low pressure advances
into the central Plains. Tightening pressure gradient will result
in increasing wind speeds, but shallow stable layer should prevent
stronger winds from mixing down to lake surface. Breezier southeast
winds will linger through mid-week as low pressure eventually moves
across the western Great Lakes later Wednesday.
Near critical fire weather conditions are expected from late morning
through the afternoon. Humidities will lower to between 20 and 30
percent and breezy south to southeast winds will develop. Wind
gusts of 20 to 25 mph are expected as well. Daytime temperatures
away from Lake Michigan will peak in the upper 60s to lower 70s,
which is just under Red Flag Criteria. With the Fine Fuel Moisture
Code forecast for today remaining just below critical threshold, wl
hold off on coordinating Red Flag Warning with WIDNR/USFS
representatives. Another warm and breezy day lies ahead for Tuesday
but minimum daytime humidity values are expected to remain higher.
Today/Tonight and Aviation/Marine/Fire Weather...BSH
Tuesday THROUGH Sunday...MBK