Scientific Forecaster Discussion
fxus63 kmkx 211658
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
1158 am CDT Thu Jun 21 2018
Update...bumped up daytime temperatures a couple degrees in
southwest where showers becoming more scattered. Otherwise,
showers shoul dbe spreading into the Milwaukee, Waukesha and
Watertown areas in next 1-2 hours. No changes to ongoing Flash
Flood Watch for now. 6 hour rainfall has remaining up to one half
inch across across the area covered by the watch and western County Warning Area.
Aviation(18z tafs)...lowest ceilings and vsbys expected across
southern County Warning Area closer to deeper surface moisture and higher
dewpoints. Ceilings will likely remain VFR in the north.
Previous discussion... (issued 1001 am CDT Thu Jun 21 2018)
Update...cut-off upper low over southern Iowa expected to take slow
east-southeast track into central/southern Illinois tonight. This will continue to
bring showers and possibly an isolated tstorm to southern WI
through tonight. Rainfall of 1 to 2 inches in the south is
possible, which may worsen ongoing rural field flooding. There is
a small potential for flash flooding to redevelop if the higher
rainfall rates linger over the same area for several hours. Hence
the Flash Flood Watch will remain in effect for the far south
Marine...added patchy fog to nearshore zones due to moist
easterly air flow and surface water temperature in the mid to
upper 50s in the near shore waters. Still expect waves to build to
small craft levels tonight.
Previous discussion... (issued 712 am CDT Thu Jun 21 2018)
Rain showers continue to spread into southern WI early this
morning. Precip rates are still light, but expect that to increase
later this morning into the afternoon as we should probably get a
few thunderstorms. There is a Flash Flood Watch for the southern
tier of counties for today and tonight. There was a small debate
about the headline title of flash flood vs. Areal Flood Watch. It
was agreed upon by the Quad Cities and Chicago offices to do a
Flash Flood Watch due to the greater concern for convection in
Ceilings are only MVFR to IFR in far southwest WI this morning and
VFR elsewhere. There will be a general northward trend of these
lower ceilings today, but they are not expected to make it into
msn, ues, and mke. As rain tapers off overnight and the low
pressure area gets closer, ceilings may drop down more.
Heavier rain showers with possible thunder will cause temporary
MVFR ceilings/visibilities today. There is not enough confidence
in the timing of these heavier bands to put in the taf yet.
Previous discussion... (issued 402 am CDT Thu Jun 21 2018)
Today and tonight...forecast confidence is medium.
A closed upper low and associated surface low will track across
Iowa/northern Missouri today and Illinois on Friday. This slow-
moving system will bring an extended period of showers to southern
Wisconsin. That 850mb baroclinic zone remains draped across
southern WI, along with a plume of very moist air with
precipitable water values of 1.5 to 2 inches. The steady easterly
850mb low level jet, waves of vorticity advection, and persistent
upper divergence are favorable for far southern WI (and northern
il) to get efficient rainfall over the next 24 hours. Southern WI
has already had 4 to 8 inches of rain over the past week and
another 1.5 to 2 inches is expected (with the possibility for
more). There should be a few thunderstorms, especially this
afternoon. Therefore, a Flash Flood Watch is in effect through
tonight for our southern tier of counties.
Temperatures will remain cool today in the mid/upper 60s due to
steady east winds, clouds, and rain. The northern counties toward
central WI should be able to warm into the lower 70s by the
afternoon with some filtered sunshine.
Friday through Sunday...forecast confidence is medium.
The closed upper low responsible for thursday's precip will push off
to the east on Friday, though cyclonic flow in the upper levels will
persist through Sunday. Unsurprisingly, the low level cyclone
will very slowly pull off to the northeast through the weekend,
leaving cool east to northerly flow in its wake. The northeast
winds will help to slowly dry out the low levels, but the slow NE
propagation of the cyclone center will keep enough moisture around
to keep most of southern Wisconsin socked in beneath broken
clouds through at least Saturday. Similarly, with diminishing
moisture and forcing as the low slides away, precip chances will
fade Friday before falling to near 0 by Saturday.
With winds swinging around from the east to the north and mostly
cloudy skies through at least Saturday, temperatures will remain
rather cool. Unsurprisingly, the raw model blends are coming in a
bit cooler than British Columbia blends and MOS, but everything is 5-10 degrees
below normal for Friday and Saturday.
Monday through Wednesday...forecast confidence is medium.
Upper level ridging will finally build in early next week, allowing
for high pressure and southerly winds in low levels on Monday,
translating into a rather nice day.
By midweek, a deep, slightly positively-tilted trough will swing
through the upper Midwest. Most guidance shows the surface cyclone
associated with this trough moving through Wisconsin early
Wednesday. The southerly flow ahead of this low will result in
rather robust moisture return, with both the GFS and Gem showing
pws in the 1.75 to 2 inch range by Tuesday evening.
With this ample moisture, and plenty of lift provided by the deep
upper trough, we should at the very least see plenty of showers
and thunderstorms. As it stands, the timing of the surface low
would really limit the potential for any storms to become strong
A mid-level deck of clouds is slowly overspreading all of
southern and east central WI from the south. Meanwhile, a
secondary deck of low clouds with MVFR ceilings is gradually
spreading into south central WI early this morning. Showers are
becoming more widespread as deeper moisture works its way back
into southern WI.
Expect steadier rain showers to develop this morning across far
southern Wisconsin. These showers will be efficient rain
producers. Isolated thunder is expected as well. Periods of rain
will persist through the evening and gradually diminish Friday
morning. Expect mainly MVFR ceilings of 1000 to 2000 feet in the
rain today. Lower ceilings are possible south of the main rain
band. Ceilings should remain VFR north of the main rain band.
Easterly winds will increase throughout the day and become
northeasterly tonight. This will help to build high waves. A Small
Craft Advisory GOES into effect this evening. Winds and waves will
diminish Friday night.
Persistent east to northeast winds will build high waves tonight
through Friday night. Dangerous currents along the shoreline are
expected during this time, especially during the daylight hours on
Friday. A beach hazards statement will be needed.
WI...Flash Flood Watch through Friday morning for wiz067>070-072.
Lm...Small Craft Advisory from 7 PM this evening to 4 am CDT Saturday