Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 181729
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1229 PM CDT Fri May 18 2018

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 429 AM CDT Fri May 18 2018

Warmer today. Some showers over east-central Wisconsin overnight
into early Saturday, then across the area during the latter half
of the weekend.

The primary westerlies will remain across Canada and the far
northern U.S. during the forecast period. Troughs off the West
Coast and over eastern Canada will bracket a ridge that will
gradually edge east from the West Coast to the intermountain West.
To the south, a weaker branch of the flow will persist across the
CONUS. That branch currently has a troughs across the West and
over the Mississippi/Tennessee Valley. The eastern trough will
lift out during the next couple days while the western trough
remains in place throughout the period.

Other than Sunday which will be a cooler day due to clouds and
scattered showers, temperatures during the first half of the
period should stay fairly close to seasonal normals. Readings will
warm to above normal for the middle to latter part of next week.
There will be several opportunities for precipitation. But at this
point they look more like events that will generate scattered
showers rather than widespread rains. So the best guess is
that rainfall totals at most locations will end up AOB normal for
the period. That`s not ideal for the north which has recently been
classified as entering D0 drought conditions on the latest Drought
Monitor.
&&

.SHORT TERM...Today...Tonight...and Saturday
Issued at 429 AM CDT Fri May 18 2018

Quiet weather is expected today through this evening as the
forecast area remains within a surface ridge extending westward
from an anticyclone passing from Ontario to Quebec. A dry air
mass will linger across the area, with mixing out of moisture
probably lowering dew point temperatures even further during the
afternoon. Although today will be warmer than yesterday,
low-level trajectories across Lake Michigan will hold back
temperatures some (especially in the east), and limit the depth of
the mixing. Anticipate wind gusts this afternoon of 15-20 mph
which will increase the fire danger some but not enough to warrant
a headline.

Meanwhile, the remnants of the Mississippi/Tennessee Valley upper
trough will begin lifting north. The system will begin to spread
clouds across the area during the evening, with rain chances
arriving after midnight. Precipitation coverage over southern IL
early this morning is pretty high, so took PoPs up to likely for
the far southeast part of the area. Based on the LDS, the system
was generating very little lightning, so left thunder out of the
forecast. The northern extent of the precipitation in eastern
Wisconsin is very much in doubt. A handful of the models
(including the ECMWF) drove precipitation almost to Washington
Island. Expanded chance PoPs to that area, but confined the likely
PoPs to the MTW area where almost all the models agreed on having
precipitation.

The system will shift off to the east early Saturday. That will
allow a cold front from the Plains should begin pushing through
the area. Timing and precipitation chances differed considerably
among the models. Would have really preferred to have chance PoPs
into N-C WI by late in the day, but given the lack of model
consistency/agreement stuck with the standard initialization grids
which just have the rain chance reaching the northwest corner of
the area by 00Z.

.LONG TERM...Saturday Night Through Thursday
Issued at 429 AM CDT Fri May 18 2018

Still some significant differences in the timing of the system
Sunday into Monday night depending the model of choice. A Canadian
high pressure system is also expected to gradually sink southward
early next week which could have a significant impact on
precipitation trends and amounts. Will have small chances of rain
Saturday night, then remove any mention of rain Sunday across the
north. Bufkit soundings indicated a large dry area in the low
levels of the atmosphere at Rhinelander that would suggest it
would be too dry to rain. Next system approaches from the west
Sunday afternoon. The GFS/WRF/Canadian keep the precipitation well
south or west of the area. However, the ECMWF is the odd model
out as it brings in rain to the area, except the far north Sunday
afternoon into Sunday night. The other models were slower with the
system which will bring it into the area Monday into Monday night
and linger it into Tuesday morning.

Higher confidence of dry weather Wednesday and Thursday as the
Hudson Bay high will dominate the weather pattern with warm
temperatures and low relative humidity readings. Do not see any
real strong winds to help spread any fires, especially across the
north where this region was just recently added to the D0
(abnormally dry) on the National Drought Monitor. The chances
of rain are expected to return next Friday. Temperatures at
or slightly below normal to start the period due to cloud cover
and potential rain. Temperatures by the middle of next week should
be at or above normal, especially away from the bay and lake.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1229 PM CDT Fri May 18 2018

VFR conditions to prevail this afternoon through the evening as
high pressure pulls farther away from the region. A system moving
northeast into parts of Illinois and Indiana is forecast to bring
lower cigs/vsbys to much of northeast Wisconsin after midnight,
along with a chance of showers. Expect cigs to drop into the
IFR/MVFR range late tonight into Saturday morning, especially over
eastern WI. Some improvement is expected Saturday afternoon,
however a cold front moving into Wisconsin could bring additional
rain chances to the region.
&&

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

$$

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



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