Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
1042 PM CDT Sat Jul 4 2015
Updated aviation portion for 06z taf issuance
Short term...tonight and Sunday
issued at 243 PM CDT Sat Jul 4 2015
Main forecast issues are having to deal with the minimal chance of a shower
or thunderstorm early this evening and to what affect the smoke plume
aloft will have on temperatures.
The 19z msas surface analysis indicated a very weak frontal boundary
draped west-northwest-east-southeast across central WI (roughly from eau-Fox cities). Hi
pressure was situated over Lake Superior and from the middle-MS valley
to the southern Great Lakes. The radar mosaic remained quiet for the
time being with a mix of fair weather cumulus...hi clouds and smoke
from the Canadian wildfires making for a partly sunny afternoon.
Even though the radar remained quiet thus far...cannot dismiss the
possibility of a few showers/thunderstorms in the vicinity of the frontal
boundary early this evening. Any precipitation would diminish fairly
quickly with the loss of daytime heating. All in all...the vast
majority of the area will remain dry for any 4th of July
festivities. During the overnight hours...an increasing SW flow aloft
into WI will start to lift the remains of this boundary north as a
warm front...reaching the Upper Michigan border by daybreak (assuming the
boundary even hold together as it is very weak). Have included
some patchy fog once again as skies to be mostly clear...winds to
be light/variable and dew points hover around 60 degrees. Min temperatures
are expected to be near the dew points which tranlates to readings
mainly in the upper 50s to lower 60s.
A tightening pressure gradient over WI between hi pressure approaching the
New England states and low pressure over the Central Plains...will bring a
prevailing southerly flow into WI resulting in a push of warm air advection. 800 mb
temperatures are forecast to rise to around +15c and with skies to remain
mostly sunny...NE WI is looking at perhaps the warmest day of the
year. Look for maximum temperatures to range from the middle 70s near Lake Michigan...
to the lower to middle 80s north and mainly middle 80s south. Potential is
for temperatures to even be a couple of degrees warmer...however the smoke
aloft from the Canadian wildfires may prevent this from happening.
Long term...Sunday night through Saturday
issued at 243 PM CDT Sat Jul 4 2015
A developing low pressure system over the upper Mississippi Valley
will slowly track east through the northern Great Lakes region
Monday and Monday night...bringing a cold front through northeast
Wisconsin as it passes to the north. Out ahead of the approaching
cold front temperatures will become quite warm as 850 mb
temperatures soar into the middle to upper teens celsius Monday
afternoon. Upper level winds will turn more southwesterly...which
should push the smoke plume north which should help high
temperatures soar well into the 80s. However a complicating factor
will be the speed of the approaching cold front and any upstream
convection which may cause anvil clouds to limit high
temperatures. Under ideal circumstances high temperatures would
reach the upper 80s with even a few 90 degree readings possible.
However the speed of the front and associated clouds from upstream
convection will prevent forecast highs from reaching these lofty
levels with this forecast. Instead will raise highs a few
degrees...staying in the middle 80s across much of the area away
from the lake.
The cold front itself is forecast to move through during the
afternoon and evening hours. If convection can get going ahead of
the front it will have 1000 to 2000 j/kg of MLCAPE to work with as
well as 40 to 50 knots of 0 to 6 km shear. Despite the shear and
instability there will be a strong cap in place with a long skinny
cape profile. Heavy rain looks to be fairly certain with this
setup...however the severe potential seems to still be up in the
air...although it is still possible.
Once this low tracks off to the east high pressure will bring
quiet dry conditions back to the western Great Lakes for the
middle part of the work week. A few weak low pressure systems may
bring the chance for showers and thunderstorms towards the end of
the week and into the early part of next weekend...however these
chances will be in the slight chance category given the
unorganized nature of the aforementioned lows.
Aviation...for 06z taf issuance
issued at 1041 PM CDT Sat Jul 4 2015
High clouds and a smoke layer are likely across northern and
central Wisconsin tonight. Smoke may reduce visibility to 3 to 5
miles in some places. Ground fog is also possible between 09z and
12z. Sunday should be sunny with some smoke or haze reducing
visibility to 5 miles in some areas.