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fxus63 kgrb 211929 

Area forecast discussion
National Weather Service Green Bay WI
229 PM CDT sun Jul 21 2019

Forecast discussion for routine afternoon forecast issuance

issued at 229 PM CDT sun Jul 21 2019

In Stark contrast to the last several days, much more tranquil
weather is expected for the upcoming work week.

The large scale pattern will undergo a significant amplification/
deamplification cycle during the forecast period. Amplitude will
peak during the middle of the upcoming work week as ridging from
an upper anticyclone over the central rockies expands north into
Canada while troughs deepen just off the West Coast and over
eastern North America. The higher amplitude will be short-lived
however, as the main westerlies flatten back to zonal across the
northern Continental U.S. And southern Canada by next weekend.

The large scale changes will result in a much quieter weather
pattern for the forecast area. The period will begin with near or
slightly below normal temperatures, which will gradually creep
upward to a few degrees above normal by the middle to latter part
of the period. Precipitation chances will be minimal until late in
the period, so amounts will probably end up below normal.

Short term...tonight and Monday
issued at 229 PM CDT sun Jul 21 2019

Partly cloudy skies prevailed across the region this afternoon.
Temperatures ranged from the lower to middle 70s north to
around 80 south.

For tonight, the fair weather cumulus will dissipate around
sunset. Mid and high clouds with upper trough approaching
from the west will move into the area this evening. Continued
the small chances of showers across portions of central Wisconsin
later this evening and overnight as the upper trough moves across
the region. Low temperatures tonight will be refreshing with
readings in the middle 40s to near 50 north, and in the 50s

On Monday, skies will start out sunny and then become partly
during the afternoon as fair weather cumulus clouds develop
by late morning. High temperatures will be in the middle to
upper 70s with dewpoint readings in the 40s north and in
the upper 40s to middle 50s south.

Long term...Monday night through Sunday
issued at 229 PM CDT sun Jul 21 2019

The large scale amplification will result in northwest upper flow
across the forecast area. That will bring a large anticyclone and
modifying air mass of Canadian origin across the area the next
several days. Plenty of sunshine and dry air will result in large
diurnal temperature ranges.

The anticyclone and low-level ridge will remain west of the area
through Wednesday, then begin to shift off to the east. That will
coincide with deamplification aloft, and gradually allow warmer
and more humid air to return to the area. The humidity will creep
upward, but dew points will still remain considerably below those
experience late last week. Although timing may need adjustment in
later forecasts, it appears there will be a chance of showers and
thunderstorms Friday and again Sunday as shortwaves embedded
within the main westerlies migrate across the region.

Changes to the Standard forecast initialization grids were minor.
The primary adjustment was to add chc/slgt chc pops to the east
for Tuesday afternoon as a weak shortwave digging into the eastern
noam longwave trough crosses the area during peak heating.

Aviation...for 18z taf issuance
issued at 1258 PM CDT sun Jul 21 2019

Surface high pressure nosing into the western Great Lakes under
continued zonal flow aloft will bring quiet weather throughout
the taf period. Besides the cirrus overhead, the subsidence
inversion remains relatively high up in the column today at or
above 10 kft agl. With surface heating and moisture from the rains
of recent days, just enough room/lapse rates exist to allow for a
robust cumulus response and perhaps an isolated shower/sprinkle
late afternoon and evening. As long as the cirrus doesn't limit
insolation, the most likely corridor for the cu development may be
over the far northeast cwa west of the Bay of Green Bay down to
areas west of the Fox Valley. A respectable shortwave will then
dive/pivot across the area late tonight that could extend midcloud
ceilings at or a light shower late tonight. Confidence in
development is low. Significant deep layer dry advection will
occur after 10z resulting in low sky fraction Monday.

Kosh...minor concerns for the taf period. Wind direction has
been fairly jumpy out of the north throughout the morning. Will
likely see wind direction trend northeast early this afternoon
before abrupt wind shift to due east with lake breeze at/around
22z. Potential exists for diurnal cu up this afternoon but with
lower confidence given inbound convective debris cirrus. Mesoscale
convergence zone appears to set up north and west of the terminal
that could, with recent rainfall moisture, lead to a robust
cumulus response. Very low potential exists for isolated shower
development north and west of terminal. A stray windgust to 15
knots will be possible conditional to any shower activity.

Windshift of interest include...northerly early this afternoon to
08010kt around 22z. Then, light northeasterly late
tonight...shifting to 35007kt around 12z.

Grb watches/warnings/advisories...


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