Area Forecast Discussion
Issued by NWS Green Bay, WI

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690
FXUS63 KGRB 220904
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
404 AM CDT Sun Oct 22 2017

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 401 AM CDT Sun Oct 22 2017

Showers ending from west to east today. Temperatures much closer
to seasonal normals for next week.

The current amplification phase of the large scale pattern will
peak Tuesday, with a ridge along the West Coast and a trough
around 85W. There will be a brief flattening/retrogression of the
primary features during the middle to latter part of the week,
before they reamplify and return to their current locations by
the end of the period.

The unseasonably mild air of the past week will be displaced off
to the east by a cold front crossing the area this morning.
Readings will still be 5 to 10 F degrees above normal today and
Monday, before they return close to seasonal normals for the rest
of the period. The proximity of the longwave trough to the
forecast area will result in several opportunities for
precipitation. Amounts are likely to end up near to modestly above
normal for the period. Normal precipitation for a week at this
time of year is about 0.50 to 0.60 inch.
&&

.SHORT TERM...Today...Tonight...and Monday
Issued at 401 AM CDT Sun Oct 22 2017

The primary short-term forecast issue is detailing precipitation
trends. Unfortunately, models differed considerably on that aspect
of the forecast. So confidence in PoPs during the first 12-15
hours of the forecast is lower than typical for that time frame.

Based on the LDS, lightning with the rain band across central and
north-central Wisconsin has ended. Radar returns have been
diminishing as well. That fits pretty well with the model
forecasts, but it`s not real clear where we go from here. Since
yesterday, the models have been indicating precipitation would
blossom again later this morning as the RRQ of an upper speed max
passes through the region. That still seems reasonable, but there
are differences on to what extent it happens and where the bulk
of the mid-late morning precip will occur. The short-range
guidance (HRRR/Experimental HRRR/RAP) favor east-central
Wisconsin. The NAM/ECMWF/Canadian bisect the forecast area from
central through northeast Wisconsin. The GFS focuses it back in
central and north-central Wisconsin. There hasn`t really been
enough redevelopment of the precipitation yet to make an
assessment based on radar. So with nothing solid to latch onto
yet, trended PoPs slowly downward across the west (where they
start very high because it`s currently raining) and upward in the
east. The differences in handling the precipitation affect the
departure time of the rain band as well, with solutions ranging
from little rain anywhere after 18Z to rain still on the lakeshore
after 00Z.

Clearing will follow tonight. Clouds will increase Monday, and
there will be a chance of showers as upper flow backs sharply
ahead of the main upper trough digging into the area.

Based temperatures today into this evening on a blend of hourly
temperature products to account for the atypical diurnal trends
caused by the FROPA. Took mins several degrees below guidance at
the typical cool spots tonight due to the clear skies and
diminishing winds. Edged maxes up a little in the east on Monday
as the air behind the initial front is of Pacific origin and not
that cold.

.LONG TERM...Monday Night Through Saturday
Issued at 401 AM CDT Sun Oct 22 2017

Main concern for this period will be the strong fall storm moving
across the Great Lakes region Monday night into Tuesday night.
Models continue to struggle with the track and intensity of the
system due to phasing issues with the southern stream system
across the lower Mississippi River valley and the northern stream
system deepening across the northern United States on Monday.
Since this is a phasing system, would expect the models to differ
over the next 24 hours with strength and location of the system.

For Monday night, the chances of showers will increase through the
night as system moves across the Great Lakes. It appears that
winds will also be on the increase late Monday night as well.
Cloudy, windy and showery conditions are expected on Tuesday
as the low deepens to the east. Strong winds will be during
the daylight hours based on the model runs tonight. The strongest
wind gusts are expected across northern Door County due to deeper
mixing off the warmer waters of the bay of Green Bay and funneling
through Deaths Door. Gusts over 40 mph are possible, but could be
even higher depending on the outcome of the phasing of the
northern and southern stream systems. 12z model run from yesterday
morning would have suggested gusts of 50 to 60 mph. Will have to
wait and see how this storm strengthens.

The strong winds will gradually decrease Tuesday night as the low
moves away from the area. A weak disturbance will bring another
chance of showers on Wednesday. It appears Wednesday night will be
dry as weak high pressure moves across the region. Beyond
Wednesday night, the confidence in the forecast wanes due to
timing differences of the next system Thursday and Friday, and
possibly into next Saturday depending on the evolution of the
system. Temperatures at or maybe even slightly below normal during
the period. This is a far cry from what we have seen this month.
Through the 21st, Green Bay is averaging 8.7 degrees above normal!
&&

.AVIATION...for 12Z TAF Issuance
Issued at 401 AM CDT Sun Oct 22 2017

LLWS will linger this morning. The other aviation forecast concern
is the low clouds with the frontal rain band. Ceilings with that
have not been very uniform this far, but suspect they will settle
into the MVFR range beneath the second wave of precipitation when
it gets here. Will make issuance time decision on the specifics
of handling that in the TAFs.
&&

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

$$

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



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