Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Green Bay WI
319 am CDT Tuesday Aug 4 2015

Forecast discussion for routine morning forecast issuance

issued at 315 am CDT Tuesday Aug 4 2015

Seasonable temperatures with the next substantial opportunity for
rain late this week.

Upper trough centered over eastern Ontario will gradually weaken the next
few days. That will leave a relatively low amplitude band of
westerlies across the northern Continental U.S.. the mean ridge posn will be over The
Rockies/Western Plains...with a weak trough over the east. It looks like
there will be some tendency for upper anticyclone center within the
subtropical ridge to strengthen over the Southern Plains during the
latter half of the period.

Temperatures will vary from day to day with the passage of weather
systems...but probably not deviate too far from seasonal normals.
Isolated-scattered rain showers are expected over NE WI today...but the next
substantial chance for precipitation will occur during the latter part of the
work week. It seems likely that most areas will get some rain...but
probably not enough to bring totals for the 7 day period up to
normal. The caveat is that gauging precipitation amnts in convective sitns
is always just one well-placed mesoscale convective system can supply enough
precipitation for the whole week.

Short Wednesday
issued at 315 am CDT Tuesday Aug 4 2015

Shortwaves dropping southeastward around the western flank of large scale trough
generated isolated-scattered rain showers over northestern WI yesterday. Weak returns continued to
stream southeast across Lake Superior and Upper Michigan early this
morning...and WV imagery indicated another shortwave poised to cross
the area again mid-day. So increased probability of precipitation a bit in the far NE for
today...and expanded them a bit southwestward. Still looking at isolated-scattered
coverage through...with not everybody getting rain.

Some of the guidance hinted at precipitation tomorrow afternoon...either in
return flow on the back side of departing anticyclone or in lake-
breeze convergence zone. But didn/T see enough support in terms
of instability to add that to the forecast yet.

Made some minor adjustments to temperatures today/tngt/Wed based on highs
yesterday and 850 mb/1000-850 mb thickness trends.

Some of the hi-res short range particular the
rap...indicated a fairly distinct wind shift to the NE would work
southward down the lake and Bay this afternoon. That/S a fairly common
occurrence in sitns such as worked that trend into the
wind grids. Not expecting strong gusts behind the front at this
point...but the wind shift will probably be sharp enough to be of
importance to boaters.

Long term...Wednesday night through Monday
issued at 315 am CDT Tuesday Aug 4 2015

Plenty of potential forecast pitfalls in the medium range models
tonight. The GFS is most aggressive in generating precipitation in the
warm advection zone Wednesday night...while the Canadian and European model (ecmwf)
only bring precipitation across northern WI. The Canadian and European model (ecmwf) are
also well aligned with a shortwave moving across the region Thursday
night into early Friday. Even though there are no signs of this
shortwave in the ensemble means...prefer the European model (ecmwf)/Gem blend through
Friday. Thereafter...spread becomes too large to select a clear
model consensus.

Wednesday night through Thursday night...high pressure will be
centered across the central Great Lakes at the start of Wednesday
evening...before shifting east as warm advection moves into the
region late. The warm advection in concert with middle-level fgen will
lead to a chance of showers across north-c Wisconsin late in the night.
As low pressure moves into the northwest Great Lakes on
Thursday...chances of showers and storms will also spread into
central WI. Then low pressure will move into western Wisconsin
Thursday night spreading widespread showers and thunderstorms over
all of north-c and NE WI.

Rest of the forecast...showers and storms could linger into Friday
then exit Friday night as a shortwave moves east of the region.
Models are all over the place this weekend...but potential is there
for dry conditions on Saturday before precipitation chances increase again
late in the weekend into early next week. Temperatures are tough
pending rain chances...but potential for warmer temperatures than
advertised on Thursday and also late in the weekend.

Aviation...for 12z taf issuance
issued at 315 am CDT Tuesday Aug 4 2015

Primarily VFR conditions expected. Could see some patchy mifg late
tonight...mainly in c/N-c WI. Will make issuance time decision on
whether or not the chance will be great enough to warrant inclusion
with tempo group in the tafs.

Grb watches/warnings/advisories...


short term.....Skowronski
long term......mpc

National Weather Service Glossary of Abbreviations