Area forecast discussion
National Weather Service Green Bay WI
904 PM CDT Wednesday may 22 2013
New information added to update section
Update...
issued at 902 PM CDT Wednesday may 22 2013
Slow moving area of light rain associated with pesky
middle-level circulation and associated deformation slowly waning
and becoming increasingly disorganized as northerly flow and
subsidence increases upstream. Going short-term forecast still
looking on track. Last few runs of the hrrr seem to have a decent
handle on the demise of this system with precipitation ending from
northwest to southeast overnight. Expect back edge of weakening
precipitation shield to move southeast of the forecast area by
around 10z or 11z followed by clearing skies after 15z Thursday.
Expect northeast winds to increase overnight with a few gusts of
25 to 30 miles per hour mainly over the Fox Valley from Green Bay south to
Oshkosh.
&&
Synopsis...
issued at 233 PM CDT Wednesday may 22 2013
Upper level system that has been sitting over the northern plains
the past few days was finally moving east...with the surface low
pressure sliding through southern Wisconsin this afternoon per
msas analysis. This surface low...combined with energy from a potent
shortwave that was swinging around the southeast side of the
upper level trough into the Great Lakes area...resulted in
widespread showers this afternoon. Some lightning was also
detected in this area of precipitation...mainly in the vicinity of a nose
of minor mu-convective available potential energy and the best forcing. Showers have become more
numerous through the morning and afternoon as a decent 300mb jet
streak moved over the state...with northeast Wisconsin sitting in
the right rear quadrant. Even though surface winds were out of the east to
northeast...this mornings 12z sounding out of grb and dvn showed
southwest flow aloft...which helped continue to pump moisture
into southern portions of the County Warning Area. Precipitable water values in
this area increased through the morning and occasional moderate to
heavy rain was reported in some locations just south of Oshkosh
and fdl. Further north...skies remained cloudy but no precipitation was
reported. Expect showers and isolated thunderstorms to continue to
push north and overspread the area through the rest of the
afternoon...with portions of eastern and central Wisconsin seeing
occasional moderate to heavy rainfall as the best forcing moves
through the state with the main upper level trough.
&&
Short term...tonight and Thursday
issued at 233 PM CDT Wednesday may 22 2013
Main forecast concern will be precipitation trends tonight and
early Thursday morning. Otherwise...skies will clear from
northwest to southeast as high pressure moves in from Canada on
Thursday.
Precipitation should overspread the entire area late this
afternoon...reaching the Upper Peninsula border by 21z-00z.
Generally showery conditions will persist through the early
overnight hours for the County Warning Area...with some moderate rain possible in
eastern Wisconsin. There has been a consistent signal from the
models for strong forcing 21z today through 03z tonight in central
and east central Wisconsin...and expect this time frame to be when
we will see the heaviest and most widespread rainfall. Bumped up
quantitative precipitation forecast a little in eastern Wisconsin from 00z to 06z Thursday to
account for possible heavier showers with this forcing. Continued
to keep isolated thunder in the forecast until 03z Thursday as
well...at which point any lingering mu-cape over 500 j/kg will
dissipate and the best forcing will move away from Wisconsin...so
precipitation will be mainly showers.
Dry air will rush in behind the upper level system late tonight
and should quickly usher out precipitation. This combined with
strong subsidence will result in showers ending in far northwest portions
of the County Warning Area around midnight. This trend will continue from
northwest to southeast through the early morning hours before the
last of the precipitation exits the Lakeshore around 15z Thursday. Sped
up the exit of precipitation/clouds a bit from the previous forecast due
to model trends...otherwise made few changes to what we had going
before. Temperatures will be chilly on Thursday as strong cold air
advection aloft sets up and gusty north winds develop.
Long term...Thursday night through Wednesday
issued at 233 PM CDT Wednesday may 22 2013
Main forecast concerns include frost/freeze potential on Thursday night...
whether or not to include precipitation chances for the Holiday weekend...and
temperatures throughout the period.
Hudson Bay high pressure will reside over the region for the end
of the work week...and through the Holiday weekend. A very dry air mass
will be in place Thursday night...with precipitable water values
dropping to 0.25 to 0.33 inch. Clear skies and light winds will allow
temperatures to plummet to below freezing across most of NC/far NE WI...
with readings possibly approaching 20 degrees in the typical cold spots.
Will issue a freeze watch for NC/far NE WI...where freezing temperatures are
likely. An Special Weather Statement will be issued for the rest of the County Warning Area...where patchy/
areas of frost are a good bet. Will need to watch central WI
closely...as forecast min temperatures are close to freezing.
The large high pressure will only drift slightly to the east over the
Holiday weekend...with the ridge axis setting up just to our east.
The European model (ecmwf) has been consistent in keeping any precipitation to our west and south
through the weekend...while the GFS/gefs attempt to bring some light
quantitative precipitation forecast into our SW counties by about Sunday. Have kept the forecast dry
through Sunday...and only mentioned a slight chance of showers from
Sunday night into Tuesday. Temperatures will remain a little below
normal through the weekend...with highs in the 60s.
A warm front is expected to lift north into the region Tuesday night
and Wednesday...and may bring a chance of thunderstorms and milder
temperatures to the forecast area.
&&
Aviation...for 00z taf issuance
issued at 713 PM CDT Wednesday may 22 2013
Slow moving area of IFR ceilings and broken area of light
rain associated with deformation zone will persist over the
forecast area this evening. However...water vapor imagery over the
past several hours indicates that surge of drier air over central
Minnesota to the Dakotas...associated with strengthening northerly
upper-level flow and subsidence...will work to graudually erode
deformation zone precipitation toward midnight.
Radar trends last couple hours support this as preciptation area
has been slowly weakening and becoming increasingly disorganized
from Green Bay...west to central Wisconsin. Latest hrrr forecast
seems to have a good handle on short-term trends and pushes
preciptation area southeast of the forecast area by around 10z or
so. Expect IFR ceilings to gradually improve to MVFR after midnight
from northwest to southeast...with VFR condtions to follow after
15z Thursday. Northeast winds expected to increase after midnight
especially over the Fox Valley...with gusts of 20 to 25 kts
expceted from grb southwest to atw and osh by 12z.
&&
Marine...
issued at 233 PM CDT Wednesday may 22 2013
High-end Small Craft Advisory issued for this afternoon through at
least Friday for gusty north to northeast winds. Gusts will get
close to gale force tomorrow late morning and early afternoon...
however the best mixing will occur after the stronger winds off
the surface begin to dissipate. So will keep the strong worded Small
Craft Advisory with just a mention of a few gale force gusts
possible. Persistent marine fog has begun to lift and visibilities
are coming up this afternoon as winds increase. Kept patchy fog in
the forecast until 03z Thursday...but at this point dew point
depressions and winds increase and fog should no longer be an
issue. Will remove fog mention from the mww.
&&
Grb watches/warnings/advisories...
freeze watch from late Thursday night through Friday morning for
wiz005-010>013-018-019-021.
&&
$$
Update.........Esb
synopsis.......Wolf
short term.....Wolf
long term......kieckbusch
aviation.......esb
marine.........Wolf
