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Area forecast discussion
National Weather Service Green Bay WI
655 am CDT sun Apr 20 2014
Updated aviation portion for 12z taf issuance
Short term...today...tonight...and Monday
issued at 344 am CDT sun Apr 20 2014
Msas analysis indicated a cold front extending from wstrn Lake Superior
through far northwest WI and central Minnesota. A warm front was stretched out
across central WI...as evidenced by early morning temperatures in the middle
to upper 50s. Showers were ongoing over roughly the northwest
two-thirds of the forecast area...due to forcing with rrq of a 90
knots jet...and warm air advection/moisture convergence on the nose of a 40-45 knots
low level jet.
Dynamic forcing is expected to weaken over the region this
morning as the upper jet streak shifts east...and 850 mb flow
veers west. Showers should to become less organized and scattered
as the morning progresses. Think that showers and isolated thunderstorms will
attempt to reorganize over parts of central WI and the southern
Fox Valley later in the afternoon...as warm air advection/moisture convergence
redevelops...and elevated instability arrives. A mild day is
on tap...with highs mainly in the upper 50s to middle 60s...except
upper 40s to middle 50s along the lkshr.
Expect showers and isolated thunderstorms to be focused over the southern
half of the forecast area tonight...in the vicinity of the stalled
frontal boundary...where the best moisture and elevated instability
will reside. Temperatures should be quite mild again over c/ec
WI...with lows in the upper 40s and lower 50s. Readings in the
upper 30s and 40s are anticipated farther north.
The rrq of an upper level jet will pull across the area on
Monday...as low pressure and an associated cold front pass through
the region. Showers and isolated thunderstorms will continue along and ahead
of the cold front. Mild temperatures in the 60s are anticipated
across the forecast area...except along the lkshr...where 50s will
Long term...Monday night through Saturday
issued at 344 am CDT sun Apr 20 2014
The medium range models remain in good agreement with the large
scale features through Friday and will continue to blend the GFS and
European model (ecmwf).
Monday night through Tuesday night...the cold front will have passed
to the east at the start of Monday night...and cold advection will
take place behind the front. Models remain persistent in showing
enhanced low level relative humidity in the cold advection regime...indicative of
the possibility of low stratus pushing southeast across the forecast area.
Will continue to show this possibility. High pressure builds into
the region on Tuesday. After morning clouds lift...should see ample
sunshine albeit with cooler temperatures. Highs returning to the 40s and
50s. Mostly clear and cool on Tuesday night with high pressure in
control. Lows in the 30s to low 40s.
Rest of the forecast...high pressure will slide to the east on
Wednesday while a warm front lifts northeast across the plains into
the northern Mississippi Valley. Am skeptical that rain can push
into the area on Wednesday as quickly as the GFS depicts but the
European model (ecmwf) is now also quicker...so will leave the chance going. Better
chances of rain will arrive over western sections of the forecast
area Wednesday night and across the entire area on Thursday. Decent
rains should occur on Thursday ahead of a deep trough and cold
front. Precipitable waters will be increasing to over an inch and a few
thunderstorms look possible despite questionable instability. Once
the front exits Thursday night...cool and showery weather to
continue on Friday...and then just remaining cool on Saturday.
Aviation...for 12z taf issuance
issued at 650 am CDT sun Apr 20 2014
Showers are expected to become more scattered later this morning...
then increase again late this afternoon and evening. Some thunderstorms
are also possible this afternoon and tonight...but confidence in
the location and timing is too low to add them to the tafs right
now. Conditions should be VFR for most of today...but ceilings and
visibilities should gradually lower to MVFR/IFR in most locations tonight.
Have continued some borderline low level wind shear for the first couple hours of