Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Green Bay WI
342 am CDT Tuesday may 26 2015

Forecast discussion for routine morning forecast issuance

Synopsis...
issued at 337 am CDT Tuesday may 26 2015

Another widespread soaking rain today and tonight.

A pretty typical early summertime pattern has settled across
noam. The main westerlies will stay across Canada. A weaker but
very energetic southern stream will remain across the Continental U.S....with the
mean trough posn over the central states and a ridge near the East
Coast.

The general southwesterly upper flow will feed Gulf moisture into the
region...likely resulting in several rounds of sig precipitation. Precipitation amnts
are likely to end up well above normal for the period. Temperatures will
remain mild for the rest of the work week...though a cool-down is
likely for the weekend as strong northern stream upper trough progresses across
southern Canada and drives a cool Canadian anticyclone southeastward toward the
Great Lakes region.
&&

Short term...today...tonight...and Wednesday
issued at 337 am CDT Tuesday may 26 2015

Lots of details to work out with this forecast. Shortwave ejecting northeastward
from the Central Plains will bring strengthening frontal WV through
the region tda/tngt. The surface low is likely to track from SW-NE WI...so
at least the southeastern 1/2 of the forecast area will be in the warm sector.
Given the influx of moisture /sfc dewpoints in the middle 60s f heading
northward from Illinois/ that certainly opens the door to the possibility of
severe weather. But there are some pretty significant factors that could
work against severe weather as well. First...widespread cloud cover is
likely to limit destabilization. Second...fairly strong large-scale
forcing is likely to result in widespread shra/tsra...so there may
be limited opportunity for individual storms to organize. Will need
to monitor the sitn closely given the moisture and the potential
for shear to increase this afternoon as low-level winds back with the
approach of the surface low...but will probably need to get some breaks
in the clouds and have the onset of precipitation delayed from what is now forecast
for a more sig severe threat to materialize.

Heavy rain is also a concern...especially along and west of the
track of the surface WV. Upper deformation zone will pivot through this
region...and given the high precipitable waters ...a widespread rainfall of 1-2
inches is likely...with locally higher totals also possible.

Stayed fairly close to a blend of guidance values for
temperatures...though lessened the diurnal range a bit due to the
expected clouds and precipitation.

The very moist air with high dewpoints headed northward across Lake Michigan
could bring dense fog to the Lakeshore at times.

Long term...Wednesday night through Monday
issued at 337 am CDT Tuesday may 26 2015

After a brief respite from the precipitation Wednesday night through Thursday...next round
of showers/thunderstorms is set to overspread the region for the end of the
week before a drying trend is noted for the latter half of the
weekend into early next week. Main forecast focus to be on
timing/extent of the precipitation...potential for severe on Friday...and
depth of cooling for weekend temperatures.

Weak shortwave trough/associated shortwave to pull to our east Wednesday
evening...but may need to mention a lingering chance pop in the east
for a few hours into the evening. Otherwise...hi pressure over the eastern
Great Lakes and low pressure over the northern plains will continue to feed warm/
moist air into WI with a warm front draped over northern sections of the
Great Lakes. Cannot completely rule out a few showers in the vicinity
of the warm front...but with the low-level jet aimed at the upper MS
valley...prefer to keep the forecast area dry overnight. Min temperatures to
range from the lower 50s north and Lakeshore...middle 50s central/E-cntrl
WI.

The surface low tracks NE into the upper MS valley on Thursday as the warm front
lifts north into Lake Superior. This places NE WI squarely in the
warm sector with any precipitation either to our north with the warm front...or
west associated with the surface low/cdfnt. 800 mb temperatures to be around +14c
and if clouds can stay away long enough...inland locations could
easily reach the 80-85 degree range (warmest central wi).

Chances for showers/isolated thunderstorms begin to increase Thursday night from west
to east as the slow-moving cold front edges closer and shortwaves ride
northeastward into WI ahead of the primary upper trough situated over the central
Continental U.S.. showers/thunderstorms still look likely on Friday as the cold front finally
pushes east into WI. Convective available potential energy do approach 1k j/kg...lifted indice's fall to
around zero and bulk shear values do reach 35 kts. Problem for
severe would be the extensive cloud cover which would limit the
amount of instability that may be needed to allow any storms to
reach severe limits. Will have to keep an eye on storm strength over
the next couple of days. Maximum temperatures for Friday will be limited to the
lower 70s north/along Lake Michigan...upper 70s central/E-cntrl WI.

As the cold front continues to slowly sag south headed into the weekend...
precipitation chances should follow suite and diminish from north to south.
For Friday night...the fnt is still in the process of exiting WI...
thus will need to carry probability of precipitation especially over central/E-cntrl WI where
0.25-0.75" of rain is possible. By Sat...an area of hi pressure will be
situated over Ontario and funneling drier air into WI on brisk NE
winds. Precipitation should continue to push south...thus anticipate dry
conditions for the entire forecast area by Sat afternoon. Maximum temperatures on
Sat to be much cooler with readings ranging from the lower 50s along
the Lake Michigan shoreline...to near 60 degrees across central WI.

Have continued to favor the European model (ecmwf)/Gem models that allow the hi
pressure to dominate NE WI weather as opposed to the GFS which keeps
the old cold front closer to WI along with being farther north with a
nearly closed upper low. A dry easterly wind to prevail...thus a
cool end to the weekend with maximum temperatures in the 50's Lakeside...
mainly lower 60s elsewhere.

The hi pressure is forecast to slide east toward the Canadian Maritimes/
NE Continental U.S. By next Monday...but the western fringes of the surface hi to still
reach the Great Lakes. Meanwhile...the weakening upper low to slowly
move east across central sections of Illinois and not be a factor in our
weather. Therefore...prefer to run a dry forecast with gradually
warming temperatures closer to normal for the first day of June.
&&

Aviation...for 12z taf issuance
issued at 337 am CDT Tuesday may 26 2015

Generally poor flying conditions expected the next 24 hours due to
low clouds and precipitation. The most persistent low clouds and fog will be over
north-c WI...with a little more variable conditions to the S and east.
&&

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

$$

Synopsis.......skowronski
short term.....Skowronski
long term......kallas
aviation.......skowronski

National Weather Service Glossary of Abbreviations