Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 221409

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
909 AM CDT Thu Mar 22 2018

.UPDATE...No appreciable changes to forecast at this time.



.MARINE...Quiet today with light winds associated with high
pressure. Small craft advisory conditions still looking likely for
Friday night through Saturday night associated with tightening
pressure gradient with low pressure passing to our south.



.PREV DISCUSSION... (Issued 646 AM CDT Thu Mar 22 2018)

UPDATE...Will need to watch upstream cloud cover over eastern
MN/IA pushing ESE. This area was expected to thin as it progresses
east into better subsidence and drier air. Clouds may push into
western CWA for a time later this morning but still expecting
clouds to thin as they move east.

AVIATION(12Z TAFS)...Expect VFR conditions through the TAF
period. Area of low VFR and patchy MVFR clouds upstream over MN/IA
expected to thin but some of the clouds may advance into western
parts of CWA later this morning.

PREV DISCUSSION... (Issued 344 AM CDT Thu Mar 22 2018)


Quiet conditions to continue this period as dry northwest flow
ahead of large upstream ridge over central CONUS continues to feed
dry low to mid level air into the region. Area of upstream low
clouds over MN should thin and break up as it progresses eastward
today. Also, area of warm air advection precipitation to pass to
the southwest of southern WI. Some high clouds from this system
may brush the area today. Otherwise, dry low levels should result
in a partly to mostly sunny day. 925H temperatures warm to around
0-1C in the west so daytime temps are expected to peak a few
degrees warmer today. A lake breeze will develop near Lake
Michigan by early afternoon causing temperatures to level off in
the east. Eastern areas should still climb into the lower 40s
before the lake breeze develops. Under mostly clear skies and
light winds, temperatures will fall back into the 20s tonight.

Two main periods of concern are Friday night into Saturday and
Monday night into Tuesday night.

Friday and Saturday - Confidence...Medium.
Only minor changes offered by the 00z suite of model output this
morning. The GFS/ECMWF/NAM/GEM continue to converge on a preferred
solution for this time frame. Mid/high level moisture will begin
to increase during the day Friday as cyclogenesis in the lee of
the central Rockies begins.

Surface low pressure will quickly accelerate to the east heading
into Friday night. Very tight thermal gradient in the low to mid
levels of the atmosphere will result in strong frontogenetical
forcing. Meanwhile, an east/southeast low level flow will provide
persistent dry air advection over much of the area. It is this
battle between strong forcing aloft clipping portions of
southwestern/south central WI and formidable dry air advection in
the low levels that provides uncertainty to the forecast.

Overall, model QPF placement lines up well with the large scale
forcing and is well agreed upon by the model guidance, with a
very sharp cutoff on the east/northeast periphery. There are,
however, differences in amounts, particularly across Lafayette,
Iowa and Green counties closer to max swath of QPF. The
ECMWF/NAM/GEM provide peak values around/just above 0.75" while
the GFS is closer to 0.40". In perusing cross sections, the GFS
really has a hard time budging the low level dry air. In addition,
GEFS and SREF means have trended downward with QPF. With the core
of the highest (and rather substantial) omega values remaining
just off to the southwest and all guidance supporting the stiff,
dry east/southeast low level wind fetch, it is prudent to give
credence to lower QPF potential.

With snow ratio values in the 9:1/10:1 range, the snowfall
forecast was bumped up a bit in Lafayette, Iowa and Green
counties, where 3-6" is possible. A very sharp decrease in
snowfall to the northeast was maintained, with amounts dropping to
less than an inch a mere 30 miles away. At this point, the best
period of snowfall looks to be from 9 PM Friday to 9 AM Saturday.
As was mentioned by the day shift, ECMWF is keeping low QPF around
into Saturday afternoon and this trend will need to be monitored.

Interests in southwestern/south central WI should stay abreast to
the forecast as even a minor shift in the heaviest axis of
precipitation could result in a substantial increase/decrease in
potential snow amounts.

Sunday and Monday - Confidence...Medium.
Quiet weather is expected as high pressure dominates our weather
regime. Lows in the 20s and highs well into the 40s expected. A
few 50s are possible for Monday.

Monday night onward - Confidence...Medium.
Our next weather maker approaches Monday night, providing periodic
rain chances into early Wednesday. This looks to bring a decent
rainfall to the area with amounts in the 0.50" to 1" range
possible. Temperatures will remain seasonably mild.

VFR conditions to continue this forecast period. Large area of
lower MVFR clouds over MN expected to thin and break up as it
progresses east this morning and today. Some high clouds may
brush the area today due to area of warm air advection
precipitation passing by to the southwest of the area. Light
winds will turn onshore by afternoon in the eastern areas.

Expect light offshore winds to turn onshore late morning and
early afternoon and continue into this evening. Strengthening low
pressure passing well to the south of Lake Michigan will result in
a tightening pressure gradient and increasing east winds Friday
night. Wind gusts may reach 30 knots later Friday night into
Saturday with wave heights possibly reaching Xx feet. A Small
Craft Advisory will likely be warranted for this period. Latest
GOES-16 imagery measured the lake surface temperature around 36



Today/Tonight and Aviation/Marine...MBK
Friday THROUGH Wednesday...Gagan is the U.S. government's official web portal to all federal, state and local government web resources and services.