Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
1029 PM CST Wednesday Mar 4 2015
Updated aviation portion for 06z taf issuance
Short term...tonight and Thursday
issued at 252 PM CST Wednesday Mar 4 2015
Main concern for tonight will be the potential for low wind chill
readings and possible headlines. Northwest winds will continue to
diminish this evening and overnight. Areas that will be cold
enough (north-central) for wind chill headlines may not meet the
wind requirement for a Wind Chill Advisory. Per coordination with
surrounding offices...will highlight with a Special Weather
Statement. Lowered minimum temperatures for locations like Land O
Lakes...Tomahawk and Merrill where winds may go calm towards
Mostly sunny skies will prevail on Thursday...although it will
still be very cold with highs around 20 degrees below normal
for this time of year.
Long term...Thursday night through Wednesday
issued at 252 PM CST Wednesday Mar 4 2015
Guidance is in generally good agreement with a weak upper ridge
near the northern US Pacific coast...with a trough to its
southeast around Baja California California. This generates a split flow with
a broad eastern trough in the northern stream and southwest flow
across the southeastern US. A series of shortwaves will travel
through the northern trough this weekend into early next week.
Both moisture and lift may be limited factors. Precipitation...if
any...would be light for any of the passing features. After those
move through the big story becomes warming temperatures. This
would be a real warmup...with potential for temperatures to not
just approach seasonal norms...but even exceed them for more than
an isolated day.
Thursday night and Friday...
a surface high will slide south of the area...shifting winds
southwesterly. This will start a trend of warm air advection and
introduce enough moisture to increase clouds...cutting off the
fall of temperatures before falling as low as in previous nights.
However these winds...despite beginning warm air advection...will
likely bring US one more night of subzero wind chills. A very weak
shortwave looks to pass through the area but with meager moisture
and very weak lift generated by the trough...keeping the forecast
dry. Still...a flurry may not be impossible.
With the shortwave and its associated low clear out...the trailing
cold front will swing through the area Friday...by now there may
be enough moisture return for more than just clouds and so bring
in a chance for flurries across the area. Pre-frontal southwest
winds...look to bring a milder day to the region with temperatures
near or a shade below normal.
Friday night through early next week...
in the wake of the cold front there will be a -blink and you miss
it- surface ridge while the next clipper moves into the northern
sections of the Great Lakes late in the night. This ridge will
have only little Success in clearing out the clouds...so
temperatures will not fall significantly. Lows should range from
the middle teens to the lower 20s. Model runs today have trended
towards a vorticity maximum digging further into Wisconsin...even with a
secondary maximum filament streaming through central and east central
Wisconsin. Correspondingly...the best potential for light snow has
also shifted south late Friday night into Saturday morning. Chance
probability of precipitation have been extended a little further south from the Michigan
border. A slower GFS drags snow potential through Saturday...but
the rest of the models bring in another brief surface ridge to cut
any precipitation off. Will drag some very low probability of precipitation into the afternoon to
hedge for slower motion...but the preference is to keep the
pattern of quickly moving systems.
The unsettled weather pattern continues Sunday as yet another
shortwave tracks across Ontario. This had previously been the
favored clipper...but now a lack of moisture return with a more
productive preceding shortwave limits its potential in the
guidance. Do not like to completely eliminate precipitation potential
as jet placement and frontogenesis are both more favorable with
this clipper than previous ones...but there still is the question
of available moisture. Will leave in slight and chance probability of precipitation and
bide time to see how things evolve. Without much in the way of
airmass modification...high temperatures on Sunday will again be
primarily in the 30s and very near seasonal norms.
Sunday night into early next week will again repeat a very brief
surface ridge ahead of yet another clipper barreling through the
area...prevailing southwest winds will continue warm air
advection. This final clipper looks to stay well north of the
area...with the best forcing up in Canada. With less impact from
the clipper expected...we could very well see highs on Monday
meet or even clear 40 degrees.
Tuesday and beyond...
by this point...the aforementioned upper ridge out west looks to
break down. The result will be southwest flow streaming
Pacific...rather than Arctic...air into the region. Should this
scenario play out...we can look for temperatures to continue
rising into the midweek. If we can get good melting of what snow
exists in the southern parts of the area...it would not be
unreasonable to see our first 50 degree temperature of the year
occur. Though the time range is cause for warm lovers to temper
their excitement...this signal has existed in the guidance for
some time now...giving at least a little more confidence than
usual for a week out.
Aviation...for 06z taf issuance
issued at 1029 PM CST Wednesday Mar 4 2015
Now that winds have settled down...good flight conditions /VFR
category/ are anticipated for the next 24 hours as high pressure
passes SW of the area.