Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 071622 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1022 AM CST Thu Dec 7 2017

.UPDATE...

Flurries should gradually diminish across southeast Wisconsin over
the next few hours, as drier air works into the region. Clouds
should gradually mix out as well with the drier air working into
the area. Westerly winds should remain gusty through the afternoon
as well, as the rather tight pressure gradient and low level
mixing linger. Highs look to remain in the lower to middle 20s,
per 925 mb temperatures expected.

Middle level clouds should move southeast through the area later
tonight into Friday morning, with weak 500mb differential
cyclonic vorticity advection. The pressure gradient should remain
rather tight tonight into Friday morning, with winds backing to
the southwest. It should then weaken later on Friday. Below normal
temperatures are expected tonight and Friday.

There is some potential for the snow for Friday night to begin to
move into the northern portions of the area later Friday
afternoon. Still evaluating this potential, and there may be some
changes to the forecast as far as timing goes with the onset of
the snow.

Wood

&&

.MARINE...

A rather tight pressure gradient will continue this afternoon,
with westerly winds gusting to around 20 knots. A few gusts may
reach or exceed 22 knots, but it should not be frequent enough for
a Small Craft Advisory. High waves will remain over the open
waters of Lake Michigan.

The pressure gradient will remain rather tight tonight into Friday
morning across the area. There is the potential for southwesterly
gusts to reach or exceed 22 knots during this period. Thus, a
Small Craft Advisory may be needed for portions of this period.
High waves will again remain over the open waters of Lake
Michigan.

Wood

&&

.PREV DISCUSSION... (Issued 604 AM CST Thu Dec 7 2017)

UPDATE...Scattered flurries will continue to diminish across the
area next 1-2 hours as last vestiges of passing mid-level trof
move off to the east. Areas of low clouds will also thin and
decrease through the morning, with a period of clear skies later
this morning and afternoon. Warm air advection mid-clouds will
likely return late today into this evening.

AVIATION(12Z TAFS)...Scattered flurries will continue to diminish
across the area next several hours. Pockets of MVFR clouds
associated with flurries should decrease and thin with VFR
conditions returning this morning as well.

PREV DISCUSSION... (Issued 302 AM CST Thu Dec 7 2017)

SHORT TERM...

TODAY and TONIGHT - Confidence...Medium to High.

Few light snow showers and flurries will continue to affect the area
through 12Z as last vestiges of mid-level short wave trof pass
through the area.  Strongest lift associated with low-level
frontogenetical forcing has slide south of the area several hours
ago.  Any additional accumulation will be a dusting at best.  Expect
decreasing cloud trend later this morning into the early afternoon
due to weak short wave subsidence and influx of drier air in the low
to mid levels.  Some high clouds may return due to secondary much
weaker short wave currently over nrn MN/Can passing through the
area.  Backing low to mid level winds will allow slightly warmer air
to return to the area later today and tonight.  An increase in mid-
level RH will result in thicker clouds returning to the area for a
time tonight.  Atmosphere remains drier below 4k ft so wl hold off
on any flurry mention at this time. Today`s partial sunshine will
help the temperature rebound a few degrees into the low to mid
20s most areas, with wind chills in the single digits to low
teens.

LONG TERM...

Friday through Saturday...Forecast confidence is high.

We are expecting a quick round of 1 to 3 inches of snow Friday
evening. This will impact people who have evening plans, as roads
may become snow covered and slippery. Winds will be light while
it`s snowing, and then increase through the overnight hours as the
snow tapers off.

Snow should hold off across southern WI until early Friday
evening (6-8 pm), then spread through quickly during the evening
hours and taper off from nw to se after midnight. This is due to a
potent shortwave coupled with the left exit region of an upper jet
diving into the Upper Midwest pairing with decent low- mid layer
frontogenesis. A sufficient depth of 4000 feet of saturation
within the dendritic growth zone, along with -5 to -8 ubar/sec of
omega will lead to a period of widespread, accumulating snow.
Visibility will likely drop to 2 miles or less at times and
quickly accumulate on surfaces.

Models agree on 0.10 to 0.15 inch of QPF as the upper trough and
associated surface low pivot over Lake Michigan. Snow will be on
the drier side with ratios around 17:1. This equates to 1 to 3
inches of snow accumulation, with higher amounts east of Madison,
especially toward Sheboygan.

Light snow or flurries may linger into Saturday morning, but the
main story is the brisk northwest winds causing wind chills around
10 degrees during the day.

Sunday through Thursday... Forecast confidence is medium.

A large upper trough will keep southern WI in brisk northwest flow
until further notice. Shortwaves rounding the base of the trough
will bring rounds of light snow about every other day. Timing of
the snow is still uncertain, but one round should track through
southern WI Sunday night or Monday, and another one Tue nt into
Wed. Each could bring 1 to 3 inches.

AVIATION(09Z TAFS)...Brief period of MVFR cigs possible early
this morning with passing light snow showers and flurries. Most of
the forecast period will be VFR as drier air settles in behind
exiting low level trof. Some lower VFR clouds will likely return
to the area later today and this evening ahead as slightly warmer
air returns to Wisconsin. Gusty winds are again expected today,
but the gusts will remain mostly below 20kts.

MARINE...Will continue Small Craft Advisory until 12Z.
Racine Reef observing platform continuing to record gusts of 20 to
25 knots last several hours.  Gradual decrease in gusts is expected
through the morning. Possible a few gusts up to 25 knots could
linger beyond 12Z, but with decreasing trend, will forego extension
of SCA at this time.  Winds will remain breezy from the WNW today
and then shift to the WSW tonight.  Gusts could reach Small Craft
levels once again tonight ahead of an approaching cold front.
Several passing low pressure systems will result in periods of gusty
winds over the weekend.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Update...Wood
Today/Tonight and Aviation/Marine...MBK
Friday THROUGH Wednesday...Cronce



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