Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 260056
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
656 PM CST Sat Feb 25 2017

.UPDATE...

1000-500 mb thermal trough axis was located just to our west this
evening per thickness analysis. This trough will be located
overhead early tonight, coincident with surface ridging
protruding north from the southern Mississippi valley into the
western Great Lakes. Any temperature falls will occur early this
evening, with radiational cooling and only some scattered high
cloud cover.

Upstream clouds over Minnesota and Iowa are associated with an
area of focused mid-level warm advection, which is occuring ahead
of a shortwave trough over the northern Great Plains. These
clouds will overspread southern Wisconsin later tonight, with
steady or rising temperatures after midnight.

Forecast model soundings do show some saturation late tonight
within a 3 kft thick snow crystal growth layer from roughly 800 to
700 mb, with meso model composite reflectivity products picking
up on this with some light returns. However, atmospheric profiles
are very dry below 850 mb, so would expect this precipitation to
largely evaporate aloft. Will keep an eye on upstream obs this
evening to watch for any ground truth. At best, we could see some
flurries late tonight into Sunday morning.

Weak low pressure passes through the northern Great Lakes on
Sunday, as high pressure drifts off to our east. While
precipitation with this system should be confined to northern and
central Wisconsin, winds will increase owing to a 40 knot low-
level jet pointing into southern Wisconsin. Forecast soundings
advertise mixing up to around 925 mb (and even higher on the
GFS), suggesting wind gusts to around 30 knots are possible over
land areas during the daylight hours. These winds will be even
stronger over the nearshore waters, and will further assess this
with the marine update later this evening.

The 00Z TAF update is included below.

&&

.PREV DISCUSSION... /Issued 540 PM CST Sat Feb 25 2017/

UPDATE...

UPDATED FOR 00Z TAFS.

AVIATION/00Z TAFS/...

VFR through the TAF period. High clouds will increase this
evening, with mid-level clouds spreading in from west to east
tonight. Look for gusty southwest winds during the daylight hours
on Sunday.

PREV DISCUSSION... /Issued 307 PM CST Sat Feb 25 2017/

SHORT TERM...

TONIGHT AND SUNDAY... Forecast confidence is high.

Look for clear skies early this evening. Then mid level clouds
associated with warm air advection will slide into southern WI by
midnight. Temps will fall quickly during the evening, and then rise
a couple degrees by morning.

The nose of the low level jet will slide through southeast WI Sunday
morning, just ahead of a weak mid level shortwave trough. This could
be enough forcing for a few flurries/sprinkles toward central WI,
but northern WI will have the better chance of light snow. There
is quite dry air near the surface which will keep any precip
aloft from making it to the ground in southern WI. Max temps
Sunday will be in the lower 40s on gusty southwest winds.

SUNDAY NIGHT AND MONDAY...Forecast Confidence...High

Breezy southwest winds will push milder air back into southern
Wisconsin, with above normal temps likely.

Partly sunny skies are then expected Monday with high pressure
over the Great lakes Region. However lower level RH increases and
some stratocumulus could spread into the southeast late. Milder
temps will remain in the area, with highs running about 10 degrees
above normal for late February.

LONG TERM...

MONDAY NIGHT THROUGH WEDNESDAY...Forecast Confidence...Medium

Models in decent agreement showing two weak mid level shortwaves
in the southwest flow Monday night and Tuesday, as one Jet max
pushes across the Great lakes, while a second one is associated
with the advancing mid/upper trough that reaches the mid and upper
Mississippi Valley.

Weak low pressure passes across southern Wisconsin Tuesday into
Tuesday night. Should see some precip arrive by later Monday night
ahead of the low. With a non-diurnal temperature trend with rising
temperatures, the precipitation should be mainly rain as it
arrives. Any mixed precip that does form is expected to
transition to all rain by mid- morning on Tuesday as temperatures
continue to warm.

Models are showing a secondary main surface low to move in behind
the first departing low. As temps cool behind the first system,
this second low could bring a little snow Wednesday. There is less
confidence in this setup than with the first low due to model
differences with placement, timing and strength of the second
low. Models show this low strengthening, with the GFS a little
quicker with the cyclogenesis

THURSDAY THROUGH SATURDAY...Forecast Confidence...Medium

Could see a little snow Thursday as a weak shortwave and
associated surface trough moves through. Low and mid levels are
cold, so any precipitation would be light snow.

Decent agreement among models for Friday, showing high pressure
and cold temps. Temperatures will moderate again Saturday as the
high moves off to the east.

AVIATION/00Z TAFS/...

Skies will gradually scatter out from west to east this afternoon.
Mid level clouds will then spread into southern WI late this evening
with a warm front. Look for gusty southwest winds during the
daylight hours Sunday.

MARINE...

Brisk northwest winds will diminish this evening as strong low
pressure over southeast canada moves out of the region. The small
craft advisory will continue through 9 pm this evening.

Winds will increase out of the southwest Sunday morning. Gale force
gusts are expected for at least south of the North Point Light
during the daylight hours on Sunday. Expect gusty winds north of
there, but less confident on reaching gales. A small craft advisory
will be issued once the current one expires.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 9 PM CST this evening for LMZ643>646.

     Gale Warning from 8 AM to 6 PM CST Sunday for LMZ645-646.

&&

$$

UPDATE...SPM
TONIGHT/Sunday AND AVIATION/MARINE...MRC
Sunday NIGHT THROUGH Saturday...SPM



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