Scientific Forecaster Discussion
fxus63 kmkx 180502
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
1102 PM CST sun Nov 17 2019
The precipitation is diminishing very rapidly now as the mid level
wave pushes off to the east. We'll see the low clouds, fog and
some drizzle/flurries linger for a few more hours. Temperatures
will be hovering close to the freezing mark tonight, so be alert
for icy patches on roads and sidewalks. Monday is dry.
IFR conditions will cover most of southern Wisconsin tonight into
Monday morning. The bulk of the precipitation will have ended by
the start of the tafs at 06z Monday. We will see the low clouds
and restricted visibility tonight with improving conditions later
Monday morning. We could also see drizzle and flurries linger for
a few hours at the start of the tafs early this morning.
Otherwise, there is no decent drying expected so the MVFR and IFR
cigs will be an operational concern through Monday night. Winds
will remain light from the northwest to west.
Previous discussion... (issued 836 PM CST sun Nov 17 2019)
Temps cooled about 1 to 2 degrees more than expected from central
Dane County into southeast Wisconsin. This resulted in a
changeover to all snow in many areas. Some areas still had a mix.
Thankfully, the precip is light and any accumulations are generally
limited to elevated and grassy surfaces. Where the main precip
area ends, there is some fog and light drizzle lingering to the
west for a few hours. Temps will continue to hover close to the
freezing mark, so be prepared for unexpected slippery spots
Light southwest winds will continue to veer northwest tonight into
Monday as a low pressure trough of 29.8 inches slowly moves east
across Ontario tonight. Westerly winds will then continue Monday
night into Wednesday morning. A more amplified low pressure system
is expected to push into the region Wednesday night into
Thursday, possibly bringing a period of strong winds.
Previous discussion... (issued 455 PM CST sun Nov 17 2019)
Surface temps remain above freezing by a large enough margin to
preclude any concerns for unexpected snow accums this evening.
We're seeing some graupel and snow mixing in with the higher
intensity precipitation, but once that wanes it GOES right back to
liquid. The recently issued forecast and discussion (below) are
on track, so no changes at this time.
The rain, possibly mixed with light snow at times, will continue
across the southeast through this evening. Temperatures will
remain above freezing, so no accumulations are expected.
Ceilings will lower to IFR levels across all of southern Wisconsin
early this evening, but lift to MVFR levels after midnight over
parts of south central Wisconsin, including kmsn. The southeast WI
taf sites will likely stay IFR through about 12z Monday. MVFR
conditions will likely continue through Monday night as another
weak weather system comes through. Light winds are expected
through the taf period.
Previous discussion... (issued 300 PM CST sun Nov 17 2019)
Tonight and Monday...forecast confidence is medium.
A relatively large area of light rain with some graupel or snow
mixing in has overspread much of srn WI. This area of rain is
associated with the stronger portion of the upper trough that will
track across Illinois tnt. This organized area of rain and mix at times will
continue over se WI into the evening before dissipating around
midnight. Temps will remain above freezing into this evening so
no snow or ice accum is expected. A weak cold front will pass this
evening with weak sly winds shifting to wnwly. A weak sfc ridge
will settle over the area on Mon but not enough subsidence or dry
air advection is expected to dissipate the stratus.
Monday night and Tuesday - confidence...medium
a quick hitting mid level wave along with a low level trough will
result in some light precipitation potential later Monday night into
early Tuesday. Both the GFS and NAM soundings show little if any potential
for ice production in the dendritic growth region. So precip type will
be driven by lower level temps. While cloud cover may end up holding
in some of the above freezing conditions from monday's highs, there
are still some guid numbers that gets down to near freezing or a
little below. Will thus mention some freezing rain potential, although
actual coverage/duration of the any freezing precip is uncertain with
the 3 hourly GFS MOS and GFS BUFKIT soundings show a warmer boundary
layer likely being more supportive of more in the way of rain. The
trough shifts east early on Tuesday taking any very light precip potential
with it. Clouds will likely be stubborn to depart on Tuesday with presence
of low level thermal trough.
Tuesday night and Wednesday - confidence...medium
quiet ridging in the works for Tuesday night, then a waa regime sets
up ahead of developing low pressure in the plains. Should see widespread
40s across the area as the high shifts east and the return flow sets
Wednesday night and Thursday - confidence...medium
this is shaping up to be a mild and wet period. Low pressure will be
riding northeast with the warm front to our north with an airmass
supportive of rain. Models are in agreement with the low track which
would keep the snow potential well to our northwest. Some of the
temps in the southeast may eventually need a little boost as we draw
closer. The rain should continue into at least Thursday morning.
Should enough moisture linger into the afternoon or evening, increasing
cold air advection would allow for a mix or a little light snow
but any accumulation looks quite unlikely at this point.
Friday through Sunday - confidence...low to medium
a period of cold air advection will persist on Friday then there is
some divergence over the weekend withe the European model (ecmwf) clipping US with some
light snow Saturday/Saturday evening. Will go with the dry look of
the GFS this period with the Gem giving a nod in that direction as
Aviation(21z tafs)...cigs will fall to 600-1500 feet later this
afternoon and early evening as the low levels become saturated by
the rainfall. The low stratus will then continue tonight into Mon
afternoon. Vsbys will fall to 2-5sm with the rain this afternoon
and evening. Light fog may develop late tnt which would keep the
vsbys in the same range.
Marine...modest southerly winds will continue into the evening as
low pressure of 29.8 inches weakens as it slowly moves east across
Ontario tonight. Winds will veer to the west to northwest late
tonight into Monday morning behind a cold front but remain light.
Westerly winds will then continue Monday night into Wednesday
morning. A more amplified low pressure system is expected to push
into the region Wednesday night into Thursday, possibly bringing a
period of strong winds.