Forecast Discussion for GRB NWS Office
FXUS63 KGRB 180346

Area Forecast Discussion
National Weather Service Green Bay WI
1046 PM CDT Mon Jun 17 2019

Updated aviation portion for 06Z TAF issuance

Issued at 230 PM CDT Mon Jun 17 2019

Seasonably cool weather is expected this week, along with some
showers at times (mainly early in the week). More humid conditions
and an increased chance for rain are likely for the weekend.

The current diffuse low-amplitude upper pattern across the
northern CONUS and southern Canada will persist for a bit longer.
But the westerlies will strengthen and amplify during the middle
to latter portion of the work week as jet energy begins to work
inland from the Pacific. That will initially lead to the
development of a strong upper trough over the Intermountain West,
and later downstream ridging over the Middle and Upper Mississippi
Valley. The ridge axis will begin to shift east by the weekend,
leaving the forecast area in a favorable location for heavy
rainfall at the downstream end of a long fetch of southwest upper

Daytime temperatures will remain near to modestly below normal
into the weekend, then trend upward. More humid conditions are
also likely by the weekend. Scattered showers early in the period
will result in light to moderate amounts. But the bulk of the
rain in the period is likely to occur during the second half of
the period as shortwaves ejecting out of the western trough begin
to affect the area.

.SHORT TERM...Tonight and Tuesday
Issued at 230 PM CDT Mon Jun 17 2019

The main forecast challenge remains timing/extent of precipitation
from later tonight through Tuesday. Temperatures appear to be near
seasonal normal for this time of year.

The 19Z MSAS surface analysis showed a weak area of high pressure
near Lake Huron, a cold front that arced from northwest MN through
southeast MN, then turned southwest through western IA. Another
area of high pressure was located over north-central ND. Radar
mosaic had picked up on showers/thunderstorms over southern MN and
northwest IA.

The modest cold front is forecast to push southeast into northwest
WI this evening and reach central WI by daybreak. There will also
be a weak mid-level shortwave approaching WI tonight that may
provide enough forcing to accompany the lift from the front, to
set off a chance of showers over most of the area (primarily after
midnight east). Instability looks weak enough to limit any
thunderstorms to widely scattered at best. Thickening clouds will
provide for a mild night temperature-wise with readings around 50
degrees north, middle 50s south.

The cold front is expected to slowly move through the rest of WI
on Tuesday and with additional weak shortwaves traversing the
region, anticipate more showers/thunderstorms to develop.
Instability remains marginal at best, so no strong storms to worry
about. Nevertheless, have raised pops up to high chance or likely
for eastern WI. Rainfall amounts overall will be modest with most
locations receiving 0.10-0.25" of rain with locally higher amounts
of up to 0.50" under any thunderstorms. Max temperatures to range
from the middle to upper 60s near Lake MI, to the middle 70s

.LONG TERM...Tuesday Night Through Monday
Issued at 230 PM CDT Mon Jun 17 2019

The likelihood of having a dry period during the middle to latter
part of the week looks better than yesterday. An area of low PWATs
is forecast to circulate back into the are from the east. That
combined with rising upper heights and increasingly anticyclonic
flow aloft favor dry weather.

Considerable uncertainty still exists concerning how quickly rain
chances will return late in the week, so PoPs late Thursday night
into Friday may require substantial adjustment in later forecasts.
Beyond that, showers and thunderstorms are likely at times during
the upcoming weekend. A heavy rainfall and/or severe weather
threat may evolve during the weekend, depending on exactly where
the primary frontal zone sets up.

The standard forecast initialization grids looked good for the
most part. The most significant change was to further reduce some
low-end PoPs in the mid-week time frame.

.AVIATION...for 06Z TAF Issuance
Issued at 1046 PM CDT Mon Jun 17 2019

Clouds will increase and lower tonight in advance of a modest
cold front dropping southeast from the northern Plains. Although
activity is very isolated tonight, coverage should pick up during
the day on Tuesday as the heating of the day provides a boost as
was the case during the day on Monday. Cigs are expected to drop
into the MVFR range with any showers/storms. The activity should
end across the north and west later Tuesday afternoon, but
continue across the far east into the evening hours.



SHORT TERM.....Kallas
LONG TERM......Skowronski

NWS GRB Office Area Forecast Discussion