Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 191041
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
441 AM CST Thu Jan 19 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 307 AM CST Thu Jan 19 2017

Active period of weather through Friday with fog potential this
morning and mixed precipitation event for tonight into Friday
morning. Cloud trends later today will again impact high
temperatures for the day.

Early this morning light southwest winds were combining with
increasing moisture to produce areas of fog this morning. Web
cams and observations suggest dense fog was becoming more
widespread over parts of central and north central wisconsin.
Anticipate dense fog to diminish later this morning followed with
some decrease in the clouds. Not confident with clouds clearing
out today compared to Wednesday due to light winds in the west to
east ridge and increasing clouds from the south with the approach
of a short wave in the southwest flow aloft.

Another round of a wintry mix is possible late tonight into friday
morning across the area. Considered a winter weather advisory for
the period due to the possible ice accumulation on surfaces
between 0.05 and 0.10 inches. Timing of the arrival of the
accumulating precipitation is in question, with the nam keeping
much of northcentral and northeast Wisconsin dry tonight.
Consensus is up to a quarter inch of precipitation reaches
central and part of east central Wisconsin between 09z and 12z,
with guidance temperatures near freezing. The Surface
temperatures hovering around the freezing mark so ice accumulation
issues likely impacting cold surfaces versus trees and power
lines. Will gradually taper off pops Friday afternoon and with
mainly rain as type after the mix potential diminishes Friday
morning. Some differences with forecast soundings later tonight
across the north, the GFS is promoting a bit more snow due to more
cooling aloft.

Will issue a SPS to include the fog and slippery roads this
morning and then the wintry mix later tonight into friday
morning.

.LONG TERM...Friday Night Through Wednesday
Issued at 307 AM CST Thu Jan 19 2017

Concerns revolve around small precip chances through this portion of
the forecast.  Medium range models continue to struggle with the
upcoming split flow and relatively blocky pattern.  Not confident in
any one particular model given the lack of consistency as of late,
so will use a general model blend through Monday. Then models
diverge wildly in regards to the cyclone progged to cross the center
of the country during the middle of next week. Forecast confidence
erodes to low by this time.

Friday night through Saturday night...A band of precip will be
lifting north over far northern WI and the Lake Superior region on
Friday evening.  Though subsidence increases slightly behind the
wave, moisture depth up to 800mb still looks sufficient for
widespread low clouds and drizzle/freezing drizzle depending on the
temp for most locations into late Friday night. The best chance for
freezing drizzle will occur over north-central and far northeast WI
where road temps are expected to be colder than farther south. Then
a secondary shortwave could bring another round of light
precipitation on late Friday night into early afternoon Saturday,
with the threat of wintry mix continuing over the far north through
mid Saturday morning. Behind this second wave, think mostly cloudy
skies will most likely continue, with better chances for drizzle
over central and north-central WI than over eastern parts of the
state through Saturday night. Temps should not move very much due to
all of the clouds around.

Rest of the forecast...Could see a break in the precip on Sunday due
to a lack of any significant shortwaves, but not entirely confident
with that approach. Cyclonic flow will remain aloft, so should at
least see mostly cloudy skies. An inverted trough will then shift
into eastern WI Sunday night into Monday, which will bring precip
chances back into the picture. Temps aloft will be cooling off some,
so could see a rain/snow mix develop over central and north-central
WI, and mostly rain in the east. Rather cloudy conditions look to
persist through mid-week, and will watch the potential for a cyclone
to traverse the region during this time. A gradual cooling trend
should also begin early to middle of next week.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 441 AM CST Thu Jan 19 2017

Widespread IFR/LIFR cigs and vsbys due to dense fog
will improve slightly in the morning and then briefly to VFR levels
this afternoon. An upper trough of low pressure over central
states this morning will track northward into the western great
lakes region tonight. Deteriorating conditions will develop from
south to north as a mix of precipitation spreads northward.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CST this morning for WIZ005-010-
018-019-030-035-036.
&&

$$

SHORT TERM.....TDH
LONG TERM......MPC
AVIATION.......TDH


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