Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KMKX 180549 AAC
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1149 PM CST Thu Jan 17 2019

.UPDATE...

00Z GFS and Canadian are also showing the 0.25 inch QPF swath
trying to clip the far southern counties Friday night, similar to
the NAM. Thus, frontogenesis and upper divergence jet coupling may
be influencing things more into the far southern areas. May need
adjustments upward with snow amounts in these areas.

Also, may see more snowfall in Sheboygan County, depending on
where the lake enhancement and single lake effect snow band set
up. Models are indicating that Sheboygan County may be more prone
to see this occur. Thus, amounts and headlines may need adjustment
into that area as well. Areas from Milwaukee south near the lake
look to have the best chances for the heaviest snowfall, with the
favorable delta T values, fetch and low level moisture/inversion
heights.

&&

.AVIATION(06Z TAFS)...

MVFR ceilings, some down to 1500 feet, should gradually move
eastward and out of the area by early Friday morning. A period of
VFR conditions with light northwest to north winds are then
expected, becoming northeast by midday Friday.

The snow will move eastward into the area Friday afternoon and
early evening, reaching the terminals between 23Z Friday and 01Z
Saturday. Expect moderate snow with visibility values of 1 mile or
less in southern parts of the area Friday night into Saturday
morning, with ceilings of 1000 feet or less. These conditions
should remain Saturday afternoon into Sunday near Lake Michigan,
depending on where the lake effect snow band sets up.

Snowfall rates could reach 1/2 to 1 inch per hour in the heaviest
snow bands, mainly in southern parts of the area and near Lake
Michigan. Stay tuned for later updates on amounts, intensity and
timing of the snow, as we get closer to the event.

&&

.PREV DISCUSSION... (Issued 950 PM CST Thu Jan 17 2019)

UPDATE...

The light snow showers have moved east of the area, with low
clouds lingering. These clouds should gradually move west to east
out of the area overnight into early Friday morning. Some
uncertainty here as the back edge of the clouds are slow to move
east. Kept lows in the middle teens north to the lower 20s far
southeast, in case low clouds take more time to move out.

00Z NAM showing a 0.25 inch-plus area of QPF associated with middle
level frontogenesis/upper jet divergence coupling/600 mb warm air
advection clipping the far southern parts of the area Friday
night. Will see if other models bring this heavier QPF into the
far south or keep it just to the south.

Other concern is amount of lake enhancement Friday night into
Saturday morning, and then the single lake effect snow band for
Saturday afternoon into early Sunday.

Delta T values are quite favorable, with the fetch becoming
favorable Friday night into Saturday morning, lingering into
Saturday night. Enough low level moisture and inversion heights
exist to add a fair amount of additional snowfall near Lake
Michigan, especially for areas south of Milwaukee. Need more
certainty on where the single lake effect band will set up.

MARINE...

Nearshore Waters...

Gusty onshore winds are expected Friday night into Sunday across
the nearshore waters of Lake Michigan. Frequent gusts of 25 to 30
knots are possible during this time. Waves should build to 4 to 7
feet during this time as well. A Small Craft Advisory will likely
be needed for Friday night into Sunday. Freezing spray is likely
during this period as well.

May see gusty south winds up to 25 knots Monday into Tuesday, as
another low pressure system moves toward and through the region.

Open Waters...

Gusty northeast to north winds are expected Friday night into
Sunday across the open waters of Lake Michigan. Frequent gusts to
30 knots are possible during this time. May see a few gusts near
gale force Saturday over the southern half of the lake. For now,
will hold off on a Gale Watch, and see if these winds increase.
Waves will build during this time. Freezing spray is likely as
well.

May see gusty south winds up to 30 knots Monday into Tuesday, as
another low pressure system moves toward and through the region.
Waves should build again during this period.

PREV DISCUSSION... (Issued 709 PM CST Thu Jan 17 2019)

UPDATE...

Combination of 500 mb vorticity maximum moving through the area,
along with relatively low to mid-level saturation, helping drive
area of light snow showers/flurries across the eastern parts of
the area early this evening. There has been a dusting at the
office near Sullivan, and at the Madison airport earlier in the
evening. Thus, may see this occur over the rest of the area into
mid-evening.

In addition, light freezing drizzle may occur in southeastern
parts of the area, with a lack of ice crystals in forecast
soundings there. Saw a couple of UP reports from AWOS sites
earlier, so this may be occurring as well. Both the dusting of
snow and light freezing drizzle may cause slick roads this
evening. This activity should move east of the area by mid to late
evening.

Will await the 00Z model runs to see if anything changes with
regards to the snow event for Friday afternoon and Saturday
morning, lingering in the far east into Sunday. Not expecting any
headline changes to occur at this time.

Main issue will be where frontogenesis band sets up with the
system snow, as well as the lake enhancement near the lake. Other
issue will be where lake effect snow band will set up for Saturday
afternoon into Sunday. These will have a big influence on
snowfall intensity/amounts/location.

AVIATION(00Z TAFS)...

Light snow showers will continue to move through the eastern parts
of the area, and the eastern terminals, through the middle to late
evening hours. A dusting of snowfall is possible. Some light
freezing drizzle may occur as well in far southeast Wisconsin.
These may cause slick areas on runways.

MVFR ceilings, some down to 1500 feet, may linger until later
tonight, moving out of the area from west to east by early Friday
morning. A period of VFR conditions with light northwest to north
winds are then expected, becoming northeast by midday Friday.

The snow will move eastward into the area Friday afternoon and
early evening, reaching the terminals between 23Z Friday and 01Z
Saturday. Expect moderate snow with visibility values of 1 mile or
less in southern parts of the area Friday night into Saturday
morning, with ceilings of 1000 feet or less. These conditions
should remain Saturday afternoon into Sunday near Lake Michigan,
depending on where the lake effect snow band sets up.

Snowfall rates could reach 1/2 to 1 inch per hour in the heaviest
snow bands, mainly in southern parts of the area and near Lake
Michigan. Stay tuned for later updates on amounts, intensity and
timing of the snow, as we get closer to the event.

PREV DISCUSSION... (Issued 232 PM CST Thu Jan 17 2019)

DISCUSSION...

Tonight and Friday Forecast Confidence is High

Flurries toward central Wisconsin will continue through the
afternoon. This is associated with a mid level shortwave and weak
surface convergence. Soundings show some moisture lingering in the
lower levels this evening as the upper layers dry out. The forcing
will be east of here by then so don`t think there will be any
freezing drizzle.

Low level flow will become northwest and increase slightly tonight as
high pressure moves across south-central Canada with an inverted
trough sinking into Minnesota. The slightly increased winds and drier
air should scour out the cloud cover. The back edge of the cloud
cover has worked its way into central Minnesota. The clearing will
allow temps to cool into the teens toward central Wisconsin.

Clouds will increase from the west later Friday as warm air
advection and a shortwave approaches. Northeast winds will increase
as the day goes on as low pressure strengthens in the southern
Plains. Snow will move in quickly during the afternoon from west to
east during the afternoon into the evening.

Friday night through Saturday night...Forecast confidence is high.

The forecast reasoning with respect to forcing, etc, remains
unchanged. We have two main forecast concerns. The first will be
the system snow, with an F-gen area moving from northern Iowa
across southern Wisconsin Friday afternoon into Friday night. The
upper jet structure suggests we get into a period of decent jet
coupling between the northern stream over the northern Great Lakes
and a srn segment moving through the Mid Mississippi/Ohio River
Valleys. This generates an impressive ageostrophic circulation
and deep omega over our area, especially Friday evening. That
pushes off quickly later Friday night.

This brings us to our second forecast concern. We get into a
prolonged favorable wind fetch down Lake Michigan that could put
the southeast into a rather long duration snow event. The winds
are more east northeast Friday night, so the lake should just
bring some enhancement to the system snow...without the impact of
a focused heavy snow band. However, as we get into Saturday and
Saturday night, winds turn more northeast and we see rather strong
low level convergence along the shore highlighting the potential
for a productive lake effect band. Just where that sets up is
tough to determine this far out, but the models continue to focus
on Milwaukee/Racine/Kenosha counties. The lake effect should shut
down by Sunday.

So, we expect a snowfall max over far southwest Wisconsin and also
over the far southeast. Lower amounts will be found between these
two areas and north of I-94/Madison.

In addition to the snow, brisk winds of 15 to 20 mph will produce
some blowing and drifting snow.

Winter headlines have been posted and will be refined over the
next few forecast shifts.

Sunday and Sunday night...Forecast confidence is high.

High pressure should bring cold but dry weather. Lows Sunday
morning and again Monday morning will be in the single digits with
highs on Sunday only in the mid teens...a little more than 10
degrees below normal. Not unusual for mid to late January.

Monday through Thursday...Forecast confidence Medium.

Mid level ridging will move in for Monday pushing the arctic high
off to the east. Then, another low looks to be taking aim on the
region. The GFS and ECMWF show a deeper system and prolonged QPF.
Track this far out is still uncertain which will play a role in
precipitation type, but consensus at this point is mainly snow. A
mid level trough will dominate the region with surface high
pressure sinking into the plains later in this period, behind the
low. This will keep temperatures on the cool side.

AVIATION(21Z)

Generally 2000-2500 ft ceilings will prevail today with some 1000-
1900 ft ceilings at times this evening. Flurries will continue
mainly from Madison and Milwaukee north through the afternoon. VFR
conditions are expected later tonight through midday Friday. Light
northwest winds will dominate tonight becoming northeast on Friday.
Gusts to 20kt are likely later Friday. High clouds will move in from
the west late Friday morning. Then lower ceilings and snow will move
in quickly from the west late Friday afternoon and evening.

MARINE...
Light winds will become westerly this this evening and will increase
and become northwest tonight. Expect gusts to 20 knots tonight and
Friday for the open waters and nearshore. Low pressure will move
from the southern Plains into Tennessee Friday night into Saturday.
This will bring gusty north to northeast winds through the weekend
with building waves. Gales are possible on Saturday, mainly for the
south half. An arctic airmass will move in for the weekend so expect
freezing spray with the gusty winds.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from Friday evening through Saturday morning
     for WIZ060-065-066-070>072.

     Winter Storm Watch from Friday afternoon through late Friday
     night for WIZ067>069.

     Winter Weather Advisory from 6 PM Friday to noon CST Saturday
     for WIZ059-064.

     Winter Weather Advisory from 3 PM Friday to 6 AM CST Saturday
     for WIZ056-062-063.

LM...None.
&&

$$

Update...Wood
Tonight/Friday and Aviation/Marine...Marquardt
Friday Night through Thursday...Davis


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.