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fxus63 kgrb 201107 
afdgrb

Area forecast discussion
National Weather Service Green Bay WI
507 am CST Wed Nov 20 2019

Updated aviation portion for 12z taf issuance

Short term...today...tonight...and Thursday
issued at 305 am CST Wed Nov 20 2019

Low stratus and fog will persist early this morning across
portions of central and north-central Wisconsin as a ridge of high
pressure tracks through the region. Although visibilities have not
fallen to one quarter of a mile across much of the area, will
leave the dense fog advisory in effect as there are a few places
with lower visibilities.

Low clouds will plague the area throughout the day as the high
drifts east and a low pressure system approaches from the west.
Daytime highs are expected to rise into the upper 30s to lower 40s
during the afternoon hours.

The aforementioned low will approach the area later tonight, then
push northeast through the western Great Lakes on Thursday. Timing
of the rain to start the event looks to be a bit later than
previous runs, a trend that has been on track from previous runs.
Precipitation type looks to be rain tonight with abundant low
level warm air as overnight lows stay in the 30s. Snow is then
expected to mix in across north-central Wisconsin Thursday morning
as cooler air advects in behind the low, with mainly snow and some
freezing rain or drizzle possible during the afternoon hours with
the loss of some mid level moisture. 1 to 2 inches of snow could
fall across far north-central Wisconsin on Thursday before the
snow abates and the freezing drizzle or rain mixes in. Given the
timing of the freezing drizzle or rain, during the afternoon
hours, and the snow expected to fall beforehand the impact from
the freezing precipitation is expected to be minimal.

The system will also bring quite a bit of rain as it moves through
the area later tonight into Thursday. Precipitable water values will be around 1
inch, which is around the Max moving average for kgrb. The system
is forecast to bring anywhere from 0.50 to 0.75 inches across the
north, with 0.75 to 1 inch across central and east-central
Wisconsin. While it has been a while since the area has seen this
much rainfall, the frozen ground will prevent the rain from being
absorbed into the soil. Therefore there could be some flooding
concerns as the rainfall runs off instead of being absorbed into
the ground.

In addition, Lakeshore flooding will be a concern as southerly
winds increase later tonight into Thursday morning ahead of the
approaching low. Any beaches facing south could experience
Lakeshore flooding or erosion as water builds up on already High
Lake levels on Lake Michigan and the Bay of Green Bay.

Long term...Thursday night through Tuesday
issued at 305 am CST Wed Nov 20 2019

A split flow regime to continue across the Continental U.S. Into early next
week with a progressive northern stream to run across the northern
tier of states. The mean flow is forecast to merge over the
western Continental U.S. Early next week as a strong shortwave trough drops
southeast from the Pacific. This trough will dig southeast into
the Southern Plains by Tuesday and potentially set the stage for a
big storm somewhere across the Midwest/Great Lakes mid-week. There
is still plenty of uncertainty regarding this system, especially
given the new 00z European model (ecmwf) which has delayed the system by a good 48
hours and is not nearly as strong as earlier runs had indicated.
Until then, precipitation trends over northeast WI look minimal
with temperatures after Friday going at or slightly above normal.

A mid-level shortwave trough is expected to sweep into the Great
Lakes region Thursday night, however little moisture to be left
behind by the departed system, thus most of northeast WI will be
dry. The exception would be north-central WI where modest cold air advection and
a northwest wind to bring a small chance of lake effect snow
showers mainly to Vilas County. Any accumulation would be minor
(one-half inch or less). Temperatures will be a little tricky
depending on how long clouds hang around as high pressure begins
to build into the area after midnight. For now, have readings in
the upper teens to lower 20s north, lower to middle 20s south. The
high pressure to stretch from the Central Plains northeast into
the Great Lakes on Friday, ending any lake effect snow chance for
north-central WI and bringing sunshine back to the area. Despite
the sun, temperatures will be below normal as readings only reach
the upper 20s to lower 30s north-central, lower to middle 30s
elsewhere.

This high pressure sags a bit south (southern plains to southern
sections of the great lakes) Friday night, but will remain our
main weather feature. Anticipate mostly clear to partly cloudy
skies through the night with min temperatures to range from the
upper teens north-central, to the middle 20s east-central WI.
Models send a weak cold front into WI by late Saturday, however
any Gulf moisture to be tied to a southern stream system moving
through the Ohio/Tennessee valleys, therefore no precipitation is expected
over northeast WI on Saturday. Partly cloudy skies are forecast
with Max temperatures edging upward into the middle to upper 30s
north, upper 30s to around 40 degrees south.

This weak cold front slips through the rest of WI Saturday night
with no impact on our weather. Quiet conditions to continue
through Sunday with weak surface ridging in the vicinity. Not much
change in air mass aloft should bring Max temperatures on Sunday
similar to Saturday, which is actually normal for late November.
Another cold front is forecast to move southeast into the western
Great Lakes late Sunday night or Monday morning and even though
this front is a little strong than its predecessor, a lack of
moisture appears to preclude any mention of precipitation. We
probably will see an uptick in cloud cover with skies partly to
mostly cloudy. Max temperatures for Monday to be in the upper 30s
north, lower 40s south.

The original thinking was for a deepening shortwave trough into
the southern rockies which would allow for cyclogenesis to
develop over the Southern Plains Monday night. However, the new
00z European model (ecmwf) has thrown a wrench into what initially looked like a
big mid-week storm for the Midwest/Great Lakes. Anticipate the
models will continue to wobble on both timing and intensity of
this system in the coming days, thus confidence is very low at
this time.
&&

Aviation...for 12z taf issuance
issued at 506 am CST Wed Nov 20 2019

Widespread low stratus and some reduced visibility continues to
linger across much of the area. Conditions varied from VFR across
the east, to IFR conditions across the west. These conditions are
expected to linger through much of the taf period with some LIFR
visibility possible across central and north-central WI this
morning. Some improvement will likely occur, especially in
visibilities, during the day into the evening. Steady rainfall and
deteriorating conditions back to IFR and LIFR are expected later
tonight as a low pressure system approaches from the west. Low level wind shear
may also develop at each of the taf sites tonight as a
temperature inversion strengthens across the area.
&&

Grb watches/warnings/advisories...
dense fog advisory until 9 am CST this morning for wiz005-010-
018-030-035-036-045.
&&

$$

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