Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
246 am CDT Friday Sep 4 2015
Forecast discussion for routine morning forecast issuance
Short term...today...tonight...and Saturday
issued at 240 am CDT Friday Sep 4 2015
The recent rainfall from last night combined with light winds and
breaks in the cloud cover has caused widespread fog with patchy
dense fog across much of northeast Wisconsin. Some stratus
advecting west over east central Wisconsin and middle level clouds
advecting north across central Wisconsin will help to limit fog
potential across those areas...with north central and portions of
central Wisconsin being the most fog prone areas this morning. As
was the case for the last several days...the fog should dissipate
later this morning a few hours after sunrise.
Once the fog Burns off it will be a rather pleasant day across
northeast Wisconsin with highs in the upper 70s to lower 80s and
lower humidity with dew points falling into the middle 60s. The
lower dew points and drier airmass should keep the weather dry
today as the main shortwave energy stays to the east. Therefore
will remove slight chance probability of precipitation from this afternoon from the
A pv anomaly...currently seen on water vapor over western
Nebraska...will ride along the ridge in place across the upper
Mississippi Valley today and tonight...eventually tracking through
northern Wisconsin late tonight and early Saturday morning.
Although the nwp models do not pick on the precipitation
associated with this feature...the hi-res models seem to do a
better job capturing this as they bring a swath of showers and
thunderstorms through the County Warning Area late tonight and into Saturday. In
addition there appears to be a return of higher dew point air by
Saturday...with dew points around 70 degrees once again expected
across the region. Given the impressive look to the shortwave
over western Nebraska and better moisture will introduce low
Chancy probability of precipitation in the forecast late tonight into Saturday with this
Fog formation tonight will depend highly on if and when storms
arrive...as well as cloud coverage associated with the convective
activity. Given the 30 probability of precipitation and pattern over the last few days
will leave the fog in across the area tonight. Much like this
morning...clearing during the evening should allow overnight lows
to fall into the lower to middle 60s before clouds from the
shortwave arrive. The return of hot and humid conditions on
Saturday will push daytime highs back into the lower to middle 80s
as 850 mb temperatures warm back up to around +20 celsius.
Long term...Saturday night through Thursday
issued at 240 am CDT Friday Sep 4 2015
A shift in the 500mb pattern is expected during the period.
Eastern ridge is expected to flatten by early next week...
then 500mb ridge will build across western North America with
downstream troughing across central North America. Temperatures
will remain above normal through early next week... then return
to or slightly below normal by the middle to end of next week.
Main concern for the Holiday weekend will be the chances of
showers and thunderstorms. Continued the small chances of
thunderstorms across the far north Saturday night. Chances for
rain will increase during the day with best chances well north
and west of the Fox Valley. 850/925mb temperatures would support
temperatures in the upper 80s and lower 90s across portions of
east-central and northeast Wisconsin. If thicker cloud cover
arrives earlier in the day...temperatures could be a few degrees
lower than advertised. Showers and thunderstorms will be likely
across much of the area Sunday night. Severe weather is not
anticipated...although locally heavy rainfall and gusty winds are
possible with the stronger storms. Showers and thunderstorms will
linger into Labor Day...with highest chances across the east.
There is some question what will happen Monday night into Tuesday
morning as the Canadian/GFS push front far enough south for a dry
period. The European model (ecmwf) does not share this solution...thus will keep
the small chances for rain in there for the time being. These
differences would have a significant impact on rain chances on
Tuesday as well. If European model (ecmwf) model is correct...would need
substantially higher chances of rain that what is in the latest
forecast. Little changes made to the remainder of the forecast.
Aviation...for 06z taf issuance
issued at 1031 PM CDT Thursday Sep 3 2015
Due to clear skies and light winds along with surface dewpoints
in the 60s...patchy fog already showing up late this evening.
Patches of stratus were also noted. Anticipate MVFR/IFR
ceilings/visibility conditions will be on the increase overnight. As has
been the case the last few mornings...will take much of the
morning if not all to improve conditions to VFR levels.