Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
933 PM CST Friday Feb 27 2015
No change in low temperatures. Winds have not decoupled
completely over south central/southeast Wisconsin. Infrared image shows
area with fresh snow over eastern Iowa and northwest Illinois has
become calm with temperatures dropping to around -10. With light
winds will not have any wind chill advisories.
VFR clear conditions tonight with some high/middle clouds expected
by Saturday afternoon. Light southwest winds tonight. The surface
high moves off the the east.
Previous discussion... /issued 218 PM CST Friday Feb 27 2015/
Tonight and Saturday - confidence...high.
High pressure will move from Indiana to the East Coast bringing a
clear night and a sunny Saturday. There is good agreement among
models of -14c 925mb temperatures which yields min temperatures in the negative
single digits under a strong inversion. Winds will be light out of
the southwest which is enough to create wind chill values down to
-15 to -19 early Saturday morning.
Warm air advection starts Saturday afternoon on southwest flow.
Expect highs in the middle to upper teens. Middle level clouds will push
into SW Wisconsin late Saturday afternoon ahead of the next system.
Saturday night and Sunday...forecast confidence is medium.
A fairly low amplitude system will be skirting by primarily to the
south of the area during this time. The best moisture and forcing
will be south. Backed off on probability of precipitation for Saturday night as we/ll
still be under the dominating influence of high pressure with the
moisture return likely holding off until Sunday. Will keep a very
small mention of light snow across the southern tier...but keep it
dry elsewhere. As a weak surface trough arrives on Sunday...some of
the moisture to the south will be pulled farther north and at this
point we should see some light snow across the area...especially
over the eastern forecast area. Much lower chance west and north
of Madison. The southeast could see about an inch of accumulation
while Madison looks like 1/2 inch...less to the north/west. A
Sunday night through Monday...forecast confidence is high.
Cold high pressure arrives for this period. Any lingering light
snow will exit the southeast quickly during Sunday evening.
Monday night through Tuesday night...forecast confidence is
Looks like an unsettle period with low pressure moving in. This
is one of the more energetic systems we/ve seen in some time and
has the potential to dump some accumulating snow...maybe some ice
in the far south. In a classic process...the upper flow backs to
the southwest with a digging large amplitude trough over the Central
High plains...up through central Canada. Ridging exists over the
eastern U.S. This opens the door to better moisture transport and
exposure to the influence of some short wave energy moving
northeast through that flow.
For this far out...the models are in pretty good agreement. That
being the GFS/European model (ecmwf) and the Canadian Gem. They all show some form
of surface low development occurring on Tuesday with the low
moving roughly over the Chicago area. The GFS is more amplified
than the ec and the Gem. The earlier runs were a bit farther south
than the current 12z runs this morning. They all now suggest the
precipitation starting out as light snow Monday night with a warm layer
getting up into the southern 1/3 of the forecast area on Tuesday.
This would bring a wintry mix of possibly rain/freezing rain and
some sleet. Way too early to get cute on where this will lay out
as the track is likely to fluctuate going forward. If the low GOES
south by just 50 miles...all of southern Wisconsin could be
snow...if it GOES north by that amount...much of southern
Wisconsin could see a mix and maybe all rain along the Illinois border.
In the area that looks like all snow at this time...roughly north
of a Milwaukee to Madison line...there could be 4 to 6 inches of
Confidence on the details is low...but confidence is high that
we/ll see some precipitation.
Wednesday through Thursday...forecast confidence is high.
High pressure arrives with plenty of cold air in the wake of the
exiting low. So cold and dry for the latter half of next week.
VFR conditions expected through the period with light winds. Middle
level clouds will move into southwest WI late Saturday afternoon.
Winds will be light out of the southwest as high pressure passes to
tonight/Saturday and aviation/marine...spm
Saturday night through Friday...Davis