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000 
FXUS63 KGRB 251944
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
244 PM CDT Thu May 25 2017

Forecast discussion for routine afternoon forecast issuance

.SYNOPSIS...
Issued at 244 PM CDT Thu May 25 2017

The holiday weekend will start out mild with just some scattered
light precipitation, but likely end on a little cooler and more 
showery note.

The upper pattern over eastern North America will gradually 
transition from a somewhat blocky regime to fairly consolidated 
northwest flow during the period. The upper low currently over the
eastern Great Lakes region will shift east. That will allow the
upper flow to temporarily back to the southwest ahead of the next
approaching upper system dropping southeast from Canada. That 
system will slow and linger in the Lake Superior region next week
as ridging strengthens back upstream along the West Coast.

Temperatures will be near seasonal normals early in the period,
then drop back to a little below normal in the developing
northwest upper flow next week. There will be several 
opportunities for precipitation, but most precipitation events
look to be composed of scattered to numerous showers rather than
widespread soaking rains. As such, amounts are likely to end up 
near normal for the 7 day period.
&&

.SHORT TERM...Tonight and Friday
Issued at 244 PM CDT Thu May 25 2017

Satellite and a few developing radar returns suggest some
sprinkles or light showers could still develop over northeast
Wisconsin during the late afternoon. The cellular clouds across
the area will dissipate with the loss of heating, and mid and high
clouds with the next system are still pretty far to the west. So
backed down on skycon for tonight. Light winds under the ridge
axis could allow some fog and stratus to form however, especially
in the east.

Precipitation chances for Friday look modest at best. The upper
ridge will be flattening across the area as upper speed max and
mid-level shortwave drive into the region from the west. But 
moisture will be limited and mid-level lapse rates are modest. So 
kept PoPs in the chance category, with the best chances across the
west and southwest.

.LONG TERM...Friday Night Through Thursday
Issued at 244 PM CDT Thu May 25 2017

500mb pattern across North America will be dominated by a western
ridge and eastern trough. Northwest flow pattern will continue
across the western Great Lakes through much of next week. Weak
disturbances and associated weak cold fronts will trigger
showers and some thunderstorm activity from time to time during
the period. 

For Friday night, any instability showers should end during the
evening, except across the far north where a few showers may
linger overnight. Per latest numerical guidance, did add some
patchy fog into the forecast. On Saturday, a weak boundary will
move across central and northeast Wisconsin. This feature may
trigger a few showers along it. Based on the latest model trends,
expand rain chances eastward as the lakebreeze boundary may also
trigger shower activity. Any shower activity should end Saturday
evening. Attention then turns to another shortwave and associated
cold front that moves into the region during the day Sunday. This
system still has some intrigue with respect to potential
thunderstorm activity. Models continued to show 300 to 500 J/kg
of cape, lifted indices dropping to 0C to -5C depending on model
of choice, and steep mid level lapse rates around 6.5 C/KM. What 
makes this event more intriguing is that the 0-6km wind shear
has substantially increased to 25 to 30 knots compared to
yesterday. Low wet bulb heights around 7000 feet also noted
along with some dry air in the mid levels. If this feature 
should move into the area during the peak heating of the day,
some of the storms could produce some gusty winds, small hail
and brief heavy rain. Model timing is somewhat uncertain, but
will need to watch. Any thunderstorm activity should end Sunday
evening.

More instability showers are in the forecast for Memorial Day
along with a slight chance of thunderstorms. The northwest flow
pattern and disturbances moving through the mean pattern will
bring off and on chances for showers Tuesday and Wednesday. Could
not rule out a thunderstorm during this period, but too low to
put into the forecast at this time. Low confidence in the dry
forecast for Thursday based on the weather pattern. Mild
temperatures are expected this weekend, then trend below normal
for much of next week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 113 PM CDT Thu May 25 2017

Satellite showed Cu increasing during the late morning and early
afternoon. Expect that to continue for a few more hours, but bases
will be VFR except for a few locations in east-central Wisconsin.
Expect some fog to form tonight, especially over east-central
Wisconsin where the ridge axis will be located. Main question is 
how widespread it will become. Opted to handle with tempo IFR 
conditions in the TAFs for now, but will need to monitor that 
closely to see if that will be sufficient.
&&

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

$$

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