Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 152114
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
315 PM CST SUN JAN 15 2017
.TONIGHT AND MONDAY - Forecast Confidence...Medium.
A closed upper low, now evident in moisture channel imagery near El
Paso, will lift into the southern Plains Monday morning, before
emerging over the lower Missouri valley Monday evening. The upper
wave will escort a weak surface low, as it tracks northeast towards
northern Illinois Monday evening. Precipitation associated with the
low should spread into southern Wisconsin Monday morning, and
continue into Monday night. The primary concern is precipitation
types and amounts, with freezing rain of biggest concern.
A consensus of forecast models keep the surface low track to our
south. This would also keep the low-level jet and best thermal
advection out of our area, resulting in only weak warm advection
over southern Wisconsin by Monday afternoon. This favors light
sleet/snow at onset, with a transition to rain/freezing rain as the
warmer air arrives aloft by afternoon. The precipitation should
begin from the south during the morning and spread north through the
day. It`s possible that the precipitation start time could be
delayed a bit given some dry air in the low levels which must first
be overcome. All forecast models suggest that the precipitation will
be ongoing into Monday evening.
Things become a bit tricky when assessing the predominant
precipitation types Monday afternoon and evening. Warm air
associated with this system should sufficiently boost temperatures
aloft above freezing for a transition towards partially to fully
melted hydrometeors (in the form of sleet and/or rain/freezing
rain), with warm layer temperatures tilting more towards full
melting. Surface temperatures will lag the warmth aloft by a bit,
with some areas (especially north and west of Madison) perhaps
failing to rise above freezing. Applying Top Down Methodology to
area forecast soundings would suggest freezing rain as the most
likely precipitation type in our northwest, followed by a mix of
rain and freezing rain across central areas, and mostly rain in the
far southeast. Some concern for a more prolonged icing event in our
northwest, where subfreezing surface temperatures and sufficient QPF
could produce 0.1 to 0.2 inches of ice accretion. This could be just
enough to bring down some weak tree branches if realized. However
temperatures are borderline, which could end up reducing ice totals.
In general, our forecast suggests light icing up to 0.1 inches is
possible along and northwest of a Janesville, to Waukesha, to West
Bend line. The greater risk for 0.1 to 0.2 inches of ice would be
along and northwest of a Darlington, to Madison, to Sheboygan line.
Issued a Winter Weather Advisory for all areas where a light glaze
of icing or more is expected. Sleet and snow accumulations within
the advisory area will be limited to one inch or less. It`s
important to keep in mind that only a small amount of freezing rain
can create travel headaches on cold and untreated road surfaces.
.MONDAY NIGHT THROUGH WEDNESDAY - Forecast Confidence...Medium.
Will continue high pops Monday night as strongest synoptic scale
lift passes across southern WI. Enhanced lift due to left exit
region of upper jet grazing area as well as compact mid-level short
wave passing thru nrn IL/srn WI region. Critical thicknesses and
Top Down method show warm air in place at 00z Tue, however northern
and northwest areas may still be dealing with cold pavement and/or
surface temperatures resulting in continuing glazing. Hence wl carry
Winter Wx Advy for northern areas thru the night. There is also a
potential that total glazing may get close to a quarter inch in the
northwest CWA which may result in the Winter Wx Advy getting
upgraded to a Warning on Monday.
Secondary weaker short wave may bring more light precipitation to
the area on Tuesday. Colder air will be slow to return so mainly
light rain or a winter mix is possible on Tue with little solid
accumulation. Secondary wave exits area Tuesday night as dry
conditions return for Wednesday.
WEDNESDAY NIGHT THROUGH SUNDAY - Forecast Confidence...Medium.
Lack of any significant cold air intrustion over Wisconsin with
early week system. Hence with zonal flow on Wednesday, temperatures
should be able to warm to near or above seasonal normal provided
clouds thin as anticipated.
Several higher amplitude trofs moving across the eastern Pacific
into the western CONUS will cause our upper level steering winds to
back to the south to southwest southwest for the remainder of the
extended period. This will usher in unseasonably warm air into the
region with daytime temperatures rising into the 40s. Medium range
guidance in agreement on bumping cutoff low pressure in the southern
Plains northward into the upper midwest or Great Lakes around
Friday, followed by a second short wave trof on Saturday. Hence may
have to deal with several periods of -ra during this period of
VFR conditions into this evening. Clouds will lower and increase
tonight, with precipitation moving in from the south Monday morning.
The precipitation should arrive as a mix of sleet/snow in the
morning before transitioning towards rain/freezing rain by early
afternoon. Freezing rain is less likely in the southeast, including
MKE and ENW. Little to no snow and sleet accumulation. Ice
accretions from a glaze up to 0.2 inches, with the greatest amounts
possible northwest of MSN.
Light and variable winds will turn to the southeast on Monday ahead
of approaching low pressure. Tightening pressure gradient ahead of
the low will result in ESE wind gusts approaching Small Craft
Advisory levels late Monday into Monday night for a time. Gusty
west winds in the wake of the low will again approach small craft
levels later Tuesday into Tuesday night. Areas of fog will
accompany the expected precipitation Monday night into Tuesday. Fog
may become dense for a time as winds temporarily decrease.
WI...WINTER WEATHER ADVISORY from 5 AM to 6 PM CST Monday for
WINTER WEATHER ADVISORY from 10 AM Monday to 6 AM CST Tuesday
TONIGHT AND MONDAY/AVIATION...SPM
MONDAY NIGHT THROUGH SUNDAY/MARINE...MBK