Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 151719
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1119 AM CST Sun Jan 15 2017

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 354 AM CST Sun Jan 15 2017

Quiet today, then a round of mixed wintry precipitation early
in the work week. Temperatures warming to significantly above
normal.

During the upcoming week, a strong negative upper height anomaly
is forecast to develop and expand southward along the West Coast
while a positive anomaly consolidates over eastern Canada. Once in
place, the positive anomaly is forecast to retrograde west across
Canada while the southern portion of the negative anomaly shifts
east across the southern CONUS. The result will be split flow that
will become increasingly blocky with time. By the end of the
period, the pattern looks like something more typical of March.

Once the modifying arctic air mass now across the area departs,
the splitting of the flow will ensure air masses of Pacific origin
dominate, resulting in significantly above normal temperatures for
the middle to latter part of the period. With at least one and
possibly two southern stream systems affecting the area,
precipitation amounts will probably end up above normal for the
period.
&&

.SHORT TERM...Today...Tonight...and Monday
Issued at 354 AM CST Sun Jan 15 2017

Quiet weather expected today and tonight, and at least for the
morning on Monday.

The center of a large sprawling anticyclone will begin to shift
off to the east today, though it will ridge back into the area
tonight into Monday. The southern stream system lifting out of the
Desert Southwest will begin to approach the area Monday afternoon.
Forecasting this system has been (and will likely remain) a real
challenge. The models have again slowed the arrival of
precipitation with the system. There has now been a substantial
southeast shift in the storm track as well. Updated forecast grids
to delayed the arrival of the precipitation relative to the
previous forecast, and would not be surprised if a further such
adjustment is needed in later forecasts.

Precipitation type will also be an issue. The delay in the onset
is allowing the core of the cold air to release off to the east
before precipitation arrives, but a corresponding south/east shift
in the track of the system allows the low-level flow to maintain a
more northerly component. Best guess now is that precipitation
breaks out as a mix of RA/FZRA/IP and then quickly changes to snow
for a time as evaporative cooling temporarily drops temperatures
prior to the arrival of warmer air aloft.

The uncertainty in precipitation type and amounts, as well as the
delay of the precipitation primarily into the fourth and fifth
forecast period preclude the issuance of headlines with the
morning forecast.

.LONG TERM...Monday Night Through Saturday
Issued at 354 AM CST Sun Jan 15 2017

System for Monday night and Tuesday is the main concern for this
period as the southern stream system will interact with the
northern stream system across the northern plains. Models
continue to trend a little further south and east compared to
the last several days. This has opened the door to several
possibilities including the far north receiving little or no
precipitation, more snow than mixed precipitation across the
northern half of the state, and the possibility of more icing
across the Fox Valley.

Bufkit soundings suggesting a period of snow shortly after the
onset of the precipitation, then transition to sleet and freezing
rain and then to rain across much of the area Monday night into
Tuesday. Based on the latest guidance and model trends, the
greatest icing appears to be just north and west of the Fox Valley
with lighter icing over the far north. The Fox Valley has its own
unique challenges with more qpf and some significant differences
in surface temperatures Monday night. The MET guidance has
temperatures rising above freezing later Monday evening while the
MAV guidance has temperatures remaining near 30 for the entire
night at Green Bay. With winds turning to the northeast off the
ice covered bay, the temperature scenario depicted by the MAV
guidance is plausible. Will need to watch the Fox Valley to see if
ice accumulations will need to be raised on the day shift.
Currently have a tenth of an inch or less.

Any mixed precipitation to change over to liquid on Tuesday from
south to north. Slower recovery in road temperatures will lead to
a chance of light freezing rain Tuesday afternoon over the far
north. A small chance of light rain or snow will continue Tuesday
night across the east. The big story for this rest of the week
will be the mild air with highs in the 30s and 40s. The next
chance of rain or snow will not be until Friday night and
Saturday.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1119 AM CST Sun Jan 15 2017

VFR conditions are expected for the most part through noon Monday
as an area of high pressure begins to slip farther to the east.
There may be another round of patchy fog across parts of central
WI later tonight which could lead to MVFR vsbys. Otherwise, look
for flying conditions to gradually deteriorate from south to north
late Monday afternoon into Tuesday as a system approaches/then
moves through the Great Lakes. A mix of precipitation, including
sleet and freezing rain, can be expected.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Eckberg
AVIATION.......Kallas



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