Area forecast discussion
National Weather Service Green Bay WI
1004 PM CDT Sat may 18 2013
Updated aviation portion for 06z taf issuance
Short term...tonight and Sunday
issued at 250 PM CDT Sat may 18 2013
Precipitation trends to be the primary focus over the next 24 hours as
active weather to occur over the plains and then attempt to move
northeastward toward the western Great Lakes.
The 19z msas surface analysis showed an area of hi pressure over western
Quebec with a pair of weak low pressure areas over the plains. A broad
south wind between these weather features was bringing Gulf
moisture northward with dew points in the upper 50s to lower 60s over the southern
half of WI. Radar mosaic showed most of the shower activity from
this morning had fizzled out leaving sky conditions ranging from
mostly clear to mostly cloudy.
Well-pronounced upper trough will continue to dig across The Rockies tonight as
the pair of low pressure systems to reside over the plains. Gulf
moisture will be abundant and continue feeding north through the central
Continental U.S.. as the low-level jet increases through the night and several
shortwaves eject northeastward from the upper trough...expect to see another
round of showers/thunderstorms develop over the plains and move NE into the
upper MS valley/Midwest overnight. For NE WI...all this activity should
remain to our west leaving the region under partly cloudy skies
with relatively light winds. This scenario could lead to fog
formation as low-level moisture gradually increases so have added
this potential to the forecast. Away from Cool Lake Michigan...inland min
temperatures to be mild with most locations only dropping into the 50s.
The upper trough is forecast to enter the plains and have a negative tilt
to it on Sunday which when combined with sufficient instability/
shear/moisture...should lead to an active weather day across the
plains and middle-MO valley. The overnight convection to our west will
try to push east into WI Sunday morning...but is also expected to
weaken as the low-level jet weakens. The main question for our
forecast is whether the atmosphere to our west will be able to destabilize
sufficiently to allow the next round of storms to fire and push eastward
Sunday afternoon. Moisture to be plentiful with precipitable water values around
1.5 inches (almost 200 percent of normal) and dew points climbing
into the lower 60s. Convective available potential energy should surpass 1k j/kg with sub-zero lifted indice's.
If convection can fire to our west...these storms would move into
a favorable environment and produce at least locally heavy rain
with a small chance of hail. Have focused higher probability of precipitation over central WI
for Sunday afternoon...but kept the east mainly dry as any activity
would hold off until sunset. A Summer feel to the air on Sunday with
maximum temperatures away from the lake reaching the upper 70s to lower 80s along
with some humidity.
Long term...Sunday night through Saturday
issued at 250 PM CDT Sat may 18 2013
Models are in good agreement that a cutoff low will
slowly drift from the Central Plains to the western Great Lakes
before lifting out and weakening by the end of next week. There
should be plenty of chances for showers and thunderstorms. Much of
the activity will be elevated and north of a nearly stationary
warm front. Severe threat is mostly to our south near and south of
the surface warm front. Slow moving showers and thunderstorms
could produce locally heavy rain but soil has begun to dry and
river levels have fallen recently. Flood threat would probably be
limited to small streams and urban areas.
Upper low lifts out Thursday with northwest upper flow following
with cooler and drier air for the end of the week. There is some
frost potential Friday night and Saturday night with light winds
and dry air.
&&
Aviation...for 06z taf issuance
issued at 924 PM CDT Sat may 18 2013
As winds diminish tonight...patchy fog expected which would send
visibilities down into the MVFR category. Cannot rule out a brief IFR ceiling
as well over the rhi taf site where more rain has fallen over the
past 24 hours. VFR conditions should return around 15z Sunday as low
level moisture mixes out. Precipitation chances to increase over central WI by
Sunday afternoon as a warm front starts to lift northward into SW WI.
&&
Grb watches/warnings/advisories...
none.
&&
$$
Short term.....Kallas
long term......rdm
aviation.......jkl
