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Area forecast discussion 
National Weather Service Green Bay WI
639 PM CDT Thursday Jul 31 2014

Updated aviation portion for 00z taf issuance

Short term...tonight and Friday
issued at 337 PM CDT Thursday Jul 31 2014

Precipitation trends are the main forecast concerns through
Friday.

The air mass across the forecast area quickly destabilized this
morning once the fog dissipated. Cumulus formed in the unstable
air...some of which developed into scattered showers and isolated
thunderstorms across central and east central Wisconsin this
afternoon. Shower/storm development was aided by some upper level
support that was visible in water vapor imagery. Mesoanalysis
indicated MUCAPE values in excess of 1000j/kg in the area where
the showers and storms developed. Surface observations showed
surface dew points in the upper 50s and lower 60s across the
southern part of the forecast area...to middle 40s to lower 50s
in the north. A wind shift was also evident from between mnm and
sue...southwest to between osh and y50. Did not hear of any hail
as of 20z...though wbz height is lower than it was on Tuesday when
there was plenty of hail.

Expect showers and storms to gradually die off during the evening.
The surface pressure gradient is forecast to remain weak enough
for some fog to develop again overnight...with lowest visibilities likely
to be in north central Wisconsin. Also expect areas of fog over
Lake Michigan to persist due to high dew point air and Cold Lake
waters.

Expect the atmosphere to destabilize early Friday. The unstable
air mass and a more significant short wave moving across Wisconsin
will result in showers and thunderstorms developing by midday.
BUFKIT time sections from the 12z model runs shows higher convective available potential energy
on Friday than today. Storm Prediction Center had a 5 percent chance for severe across
the area on day 2...so likely and low end chance probability of precipitation prevail for
Tuesday.

Used best performing guidance mixed with the previous forecast for
temperatures tonight and Friday.

Long term...Friday night through Thursday
issued at 337 PM CDT Thursday Jul 31 2014

Northwest flow will continue early in the period...before becoming
more zonal by the end of the period. Temperatures should run at or
slightly above normal.

Showers and thunderstorms will linger into Friday evening...
especially across central into east central Wisconsin. Otherwise...
dry conditions expected late Friday night and Saturday morning.
Enough instability to add a small chance of showers and storms
across the far south Saturday afternoon.

Next system will approach from the northwest Saturday night...but
should affect the area on Sunday. Some questions still remain on
frontal position and how quick precipitation arrive late Sunday
night into Monday morning...and how far south convection will make
across our area Sunday.

Next week turns interesting as European model (ecmwf) model depicts several
complexes on thunderstorms moving across our central and southern
counties Monday through Wednesday. Since models have a hard time
handling convection/outflow boundaries...was thinking precipitation
trends will shift southward due to outflow boundaries shoving the
front further south. High temperatures each day will be dependent
on cloud cover and convection trends.
&&

Aviation...for 00z taf issuance
issued at 614 PM CDT Thursday Jul 31 2014

Afternoon instability and weak upper disturbance have led to more
afternoon showers and thunderstorms. Activity is expected to continue
to lessen in coverage and intensity with loss of insolation. Fog
again to be issue overnight with light winds and clearing. Have
trend towards last nights visibility for tafs.&&

Grb watches/warnings/advisories...
none.
&&

$$

Short term.....Mg
long term......eckberg
aviation.......te

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