Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 121542
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
942 AM CST Sun Feb 12 2017

.UPDATE...

Sharpening mid/upper trough will continue digging into the upper
Midwest and western Great Lakes today, before sliding to our east
tonight. A surface cold front, attendant to low pressure tracking
east through southern Ontario, will push through southern
Wisconsin through the morning hours. The front will help scour out
the remaining low-level moisture, resulting in clearing skies.

Precipitation has ended over southeastern portions of the area, with
only areas of drizzle remaining. Some slippery spots were reported
on secondary and untreated roadways as pavement temperatures cooled
overnight. These conditions should improve through late morning as
temperatures warm, winds increase, and the sun comes out.

Speaking of winds, strong gusts aloft are starting to mix down into
the surface layer this morning, and this will continue into the
afternoon as the mixed layer deepens. Analysis of area forecast
soundings show around 35 to 38 knots sustained at 1 kft above ground
level, suggesting surface gusts on the order of 35 to 40 mph today.
While it`s not impossible that a few gusts could exceed 45 mph, not
enough confidence that this will be widespread enough to go with a
Wind Advisory at this time. Winds should quickly drop off this
evening as the pressure gradient relaxes.

Surface high pressure slides south into the mid Mississippi Valley
tonight, with anticyclonic low-level flow bringing some cold
advection on northwesterly winds. Lows tonight will drop into the
20s with clear skies and decreasing winds. Winds will back
southwesterly on Monday in response to low pressure sliding
southeast through Ontario. This will keep the mild temperatures
around, with highs in the upper 30s north to the mid 40s south.

&&

.AVIATION/18Z TAFS/...

Area of MVFR clouds are pushing through eastern parts of our area
late this morning. VFR conditions are expected once these clouds
depart within the next few hours. Strong winds will continue into
early evening with surface gusts of 30 to 35 knots. These winds will
decrease tonight, with VFR conditions continuing into Monday.

&&

.MARINE...

Gale Warning is in effect until 9 PM CST this evening across the
nearshore waters of Lake Michigan. A tight pressure gradient will
allow for gusty west northwest winds across the area during this
period. Frequent gusts up to around 35 knots are expected during
this time, with some 40 knot gusts possible. Waves of 3 to 5 feet
are expected, with the highest waves toward and over the open waters
of Lake Michigan.

The winds and waves will slowly subside later this evening and
overnight, as the pressure gradient weakens. A Small Craft Advisory
will be needed for this period, as the winds and waves slowly
weaken.

&&

.PREV DISCUSSION... /Issued 332 AM CST Sun Feb 12 2017/

TODAY...Forecast confidence is Medium.

700mb frontogenetical forcing has been decreasing across
southern WI since 06z as first area of more widespread light
wintery mix waned.  However areas of light mixed precip have been
redeveloping over mostly central and northern CWA in past 1-2 hours
as upstream sharpening mid-level short wave trof approaches.  Best
chance for light snow or sleet in northern CWA where low levels
slightly colder and drier allowing for some evaporative cooling.
Some light freezing rain/drizzle earlier across parts of
northern CWA per calls to county sheriffs.  Thinking better chance
for light snow or sleet in these areas next few hours so wl hold off
on posting advy but wl issue SPS to highlight concerns about
slippery roads early this morning.

By mid-morning as cold front exits area, expect bulk of light
precipitation to have ended with clearing skies.  3 hour pressure
rise of 3-4 mb wl affect southern WI later this morning and weaken
as it progresses eastward this afternoon.  Low level mixing
and strong low level winds behind departing cold front wl result in
windy conditions developing from mid-morning through early afternoon
and lasting for much of the afternoon.  Wind gusts of 32 to 36 knots
are expected, but an isolated gust to 39 knots is possible,
especially in susceptible southwest CWA.  The strong winds will
rapidly diminish early this evening as winds decouple and pressure
gradient begins to weaken.

TONIGHT...Forecast confidence is High.

Clear skies and diminishing winds will allow temperatures to fall
into the 20s overnight.

MONDAY - Confidence...Medium
High pressure will be sprawled out from the mid miss vly into the oh
vly.  Meanwhile low pressure proggd to track north of Lake Superior.
This will place srn WI in a region of a mild airflow with 925 temps
rising to 1 to 3c with the Euro the warmest solution. Column proggd
to mix up to almost 900 millibars and this would support temps
reaching at least into the low 40s.

TUESDAY AND WEDNESDAY - Confidence...Low to Medium
The GFS remains faster on bringing down a potent piece of energy
into srn WI quicker than the other models. This wave will be on the
southwest flank of a large 500 millibar low shifting from north of
Lake Superior to the northeast US this period. The GEM and ECMWF
also show this vort into srn WI but more in the Tuesday night time
frame. The GFS is also faster with the low level front as 850 temps
drop to -12c by days end Tuesday while the ECMWF and NAM hang on to
850 temps of -2 to -4c. The GFS is generating light qpf in the cold
advection regime Tuesday. The GEM shows this Tuesday night and the
ECMWF hints at this as well though the driest solution. For now will
maintain the Superblend pops which favors the quieter NAM MOS pops.
May need to introduce some small pops or flurries at some point in
this time frame. The low level thermal trough sets up Tuesday night
into Wednesday with 925 temps dropping to -6c to -9c so a chilly
regime (though pretty much normal for this time of year) will linger
into Wednesday night.

THURSDAY THROUGH SATURDAY - Confidence...Medium
Rising heights with warming temps this period. Coldest day will be
Thursday with lingering influence of low level thermal trough then
the waa takes hold. 925 temps will get back into positive territory
celsius on Friday and then push to near 10c or even higher for
Saturday. May need to eventually bump these Superblend temps even
higher especially for Saturday. Bufkit soundings do show with better
mixing we could easily get deeper into the 50s which the 2 meter
Euro guide is indicating. For now near 50 or low 50s gives the heads
up that a milder regime is on the way. This is expected to be a dry
period.

AVIATION/12Z TAFS/...Mostly VFR cigs associated with passing light
wintery mix affecting southern WI early this morning. However likely
to be a period of MVFR cigs associated with remaining high low level
RH and surge of low level cold air advection associated with passing
cold front this morning. Expect skies to clear later this morning
and afternoon with VFR conditions tonight.

MARINE...Tightening pressure behind cold front pushing through this
morning is still expected to produce strong gusty offshore winds.
Wind gusts will likely reach 35 to 40 knots.  Hence the Gale Warning
will remain in effect from mid-morning into the evening.  Winds will
likely remain at Small Craft Advisory levels for a time later in the
night.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...GALE WARNING until 9 PM CST this evening for LMZ643>646.

&&

$$

UPDATE...SPM
TODAY/TONIGHT AND AVIATION/MARINE...MBK
Monday THROUGH Saturday...Collar



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