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FXUS63 KGRB 191748
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1248 PM CDT Tue Jun 19 2018

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 324 AM CDT Tue Jun 19 2018

Cool with some showers in central and east-central Wisconsin
today. Otherwise, drier weather with seasonable temperatures and
humidities is expected for the rest of the work week. The next
chance for showers should hold off until the weekend.

The upper flow across North America is split into two primary
branches. The northern branch is almost completely across Canada,
with a ridge near the West Coast and a trough near Hudson Bay.
The southern branch across the CONUS is comprised of an upper low
within a trough over the intermountain West, and ridging
downstream over the Great Lakes region. A seasonably strong
frontal boundary was associated with the southern branch of the
flow, with very moist air stretched out along the boundary.
Both branches of the flow will be progressive, though progression
will occur more quickly with the southern branch. It appears as
though just enough amplification of northern branch trough will
occur to deflect energy from the southern stream trough south of
the area as it progresses across the Plains and into the eastern
United States. That should keep heavy rains with the very moist
air along the frontal boundary south of the area.

Temperatures across central and east-central Wisconsin will be
held down today by clouds and showers, otherwise readings
probably won't stray too far from seasonal normals for the rest of
period. The rainfall totals today will be much lighter than
during the weekend. With limited opportunities for rain
thereafter, amounts for the period will probably end up AOB
normal, giving the area a chance to dry out after all the rain
last weekend.
&&

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 324 AM CDT Tue Jun 19 2018

Although the surface frontal boundary was well south of the area,
the southern portion of the forecast area remains within the
frontal zone aloft. Plentiful moisture combined with weak forcing
will bring showers to about the southern half of the area today.
Instability is forecast to be limited, so will limit thunder
chances to the far south. The clouds and rain will hold
temperatures back in central and east-central Wisconsin, with more
warming expected across the north where some filtered sun is
likely.

The precipitation should finally sag south of the area late this
afternoon or this evening. Clouds will slowly decrease from north
to south. Sharpened up the north/south temperature gradient in
the overnight lows. With light winds and limited clouds tonight,
added patchy fog to the north for tonight.

Drier air should finally be in place across the entire area
Wednesday. That combined with mostly sunny (north) to partly sunny
(south) skies should allow temperatures to warm to near normal
levels for late June.

.LONG TERM...Wednesday Night Through Monday
Issued at 324 AM CDT Tue Jun 19 2018

Forecast concerns mainly revolve around precip chances later this
week when a closed upper low slowly tracks across the region. The
ecmwf and gfs appear to agree pretty well with this system so will
blend these two solutions for the forecast.

Wednesday night through Thursday night...A surface cold front will
remain relatively stalled over the mid-Mississippi Valley to the
Ohio Valley during this period. Occluded low pressure will be
traveling east along the boundary, and is projected to remain far
enough south to have little if any impact on our weather. Meanwhile,
Canadian high pressure will be building south over the northern
Great Lakes. Other than some cirrus at times from the system to the
south, east to northeast winds will keep a dry airmass over the
region. With relatively comfortable humidity levels, highs on
Thursday will mainly be in the middle to upper 70s. Lows in the 50s
each night except colder readings in the cold spots across the
northwoods.

Rest of the forecast...After dry weather on Friday, the low pressure
system will be lifting to the northeast on Friday night into
Saturday. This appears to be the next best chance of precipitation
for the region, though it appears the deepest moisture and most
significant precip will get shunted into the central Great Lakes.
Then it looks like Canadian high pressure will return for Sunday and
into early next week. With the cloud cover and/or potential for
showers, temps will fall back some on Friday and Saturday, before
returning to near seasonable norms on Sunday and Monday.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1247 PM CDT Tue Jun 19 2018

Mainly VFR ceilings prevailed across the area at midday and there
were scattered light showers and/or sprinkles across all but the
far northern part of Wisconsin. It is possible that ceilings could
lower into the MVFR range as the showers pass, but have kept with
VFR ceilings for now. There will probably be enough clouds across
the majority of the area to keep fog from becoming an issue
overnight. Have included some MVFR fog at times area later
tonight for much of the area, and IFR conditions at times in
north-central Wisconsin where there should be fewer clouds. May
need to hit the fog harder with the 00Z issuance.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MPC
AVIATION.......MG
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