Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
627 am CDT Thursday Jul 31 2014
Updated aviation portion for 12z taf issuance
Short term...today...tonight...and Friday
issued at 343 am CDT Thursday Jul 31 2014
Precipitation trends...fog trends and temperatures are the main forecast
Showers had ended over central WI...and middle-level clouds were
gradually eroding over the SW part of the forecast area. Areas of
fog had developed over NC WI...with patchy fog reported
elsewhere. Dense fog was occurring over parts of Vilas...
Oneida and Lincoln counties.
Visibilities had already dropped to 1/4sm-3/4sm over Vilas...Oneida and
Lincoln counties early this morning...and will likely lower
some more over the next few hours. This same area had dense fog
yesterday morning. Given the potential for hazardous driving
conditions for the morning commute...have decided to issue a
dense fog advisory through 8 am.
Although some weak short-wave energy may move through the region
today...no significant forcing is expected. Drier Canadian
air...with precipitable waters around 0.75 inch...will move into northern WI
today...so any convection that develops should be isold/sct.
Modified forecast soundings support cape of 500-1000 j/kg...with the
best instability occurring over the SW half of the County Warning Area. Low level
convergence is expected to be strongest over far NE WI. Will
carry slight chance or chance probability of precipitation over most of the County Warning Area this afternoon
and evening...with the highest probability of precipitation over central and far NE WI.
Dry conditions are expected overnight...with patchy fog expected
to redevelop. Used a blend of the top-performing guidance sets
(which have been tough to beat lately) for temperatures today and
tonight. They support highs in the middle 70s to lower 80s...
except upper 60s and lower 70s Lakeside...with lows in the middle
40s to lower 50s north...to 55 to 60 south.
On Friday...moisture and instability is expected to increase a
bit during the day. Modified forecast soundings support cape of
1500-2000 j/kg...with lifted indice's of -5 to -7. An upper level trough
will move into the region late in the day...and should help
trigger thunderstorm development. Although deep layer shear is fairly
weak (10-20 kts)...the degree of instability and favorable wet
bulb zero heights around 10k feet support a threat of isolated severe thunderstorms
with large hail and damaging winds. High temperatures should be
quite similar to today...generally in the upper 70s and lower
Long term...Friday night through Wednesday
issued at 343 am CDT Thursday Jul 31 2014
Medium range models show that some deamplification will occur to the
ridge trough pattern across North America by early this weekend.
Will still have to deal with flattened troughing over the Great
Lakes...however...that will provide periodic precipitation chances. The
European model (ecmwf) and GFS remain in good agreement so will continue to blend
Friday night through Saturday night...the deep upper trough will
begin to lift to the northeast Friday night...but will continue to
provide scattered showers and isolated thunderstorms into the evening before
diminishing overnight. Then as the trough exits...weak shortwave
ridging builds across the region on Saturday. The previous shift
favored a dry forecast...and cannot argue with this reasoning though
the European model (ecmwf) continues to spit out light quantitative precipitation forecast over northeast Wisconsin.
Think this is overdone though. Then a shortwave will move into
Ontario and drag a weak front into northwest Wisconsin late Saturday
night. Will increase sky cover late but keep the area dry.
Rest of the forecast...the shortwave will push the front across the
region on Sunday which will give the region the next significant
chance of showers and thunderstorms. Then the models show the front
stalling across central Wisconsin Sunday night into Tuesday...though
its not exactly clear where the front ends up by Tuesday. Seems
that Sunday night and Monday offer better chances of precipitation rather
than Tuesday. Then another shortwave arrives by the middle of next
Aviation...for 12z taf issuance
issued at 623 am CDT Thursday Jul 31 2014
Widespread dense fog was occurring over north central WI early
this morning...with patchy fog over the rest of the area. Expect
the fog and low stratus to mix out before 14z. Daytime heating
may trigger a few showers and isld thunderstorms later this afternoon
and early evening. Added a prob30 group for showers at auw/cwa...
but left the other taf sites dry for now.
dense fog advisory until 8 am CDT this morning for wiz005-010-