Scientific Forecaster Discussion
fxus63 kmkx 190336
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
936 PM CST Sat Nov 18 2017
Update...stratus continues over much of southern WI and will
gradually clear from west to east late tnt-sun am. Otherwise
forecast is on track for cold temps late tnt-sun.
Marine...a Small Craft Advisory is now in effect until noon on
Sunday as nwly wind gusts have stayed below gale force. High waves
of 3-7 feet will subside to 2 to 4 feet by sunrise with wind gusts
falling below 22 kts by noon on Sunday.
Previous discussion... (issued 544 PM CST Sat Nov 18 2017)
Update...the main upper trough axis will exit early this evening
but another shortwave trough will dig sewd from Canada, reaching
Lake Michigan by 12z sun. The shortwave and continued cyclonic flow will
help maintain bkn-ovc stratus tnt but enough dry air should arrive
during the daylight hours of sun am for clearing. Cold temps
expected by late tnt and continuing into sun.
Aviation(00z tafs)...broken MVFR cigs will remain over much of
srn WI tnt with clearing around sunrise or shortly after on sun.
Brisk nwly winds will continue tnt and gradually subside and
become wly on sun.
Previous discussion... (issued 312 PM CST Sat Nov 18 2017)
Tonight through Sunday...forecast confidence is high.
Precipitation has ended across the entire area as of early
afternoon. Gusty north to northwest winds will continue into
tonight, as low pressure lifts north into the eastern Great
Lakes. Low clouds should slowly clear from west to east tonight,
as heights rise behind the passing mid level wave.
Temperatures will fall into the low to mid 20s overnight, as
colder air filters in from the north.
High pressure pushing across the southern US will allow winds to
become westerly, and eventually southwesterly Sunday. Sunday looks
cool and dry, with highs in the low to mid 30s.
Sunday night through Tuesday...forecast confidence is high.
Models are in pretty good agreement with trends during this
period. Northwest flow at 500 mb on Sunday night becomes more
zonal by Monday. The air column is rather dry during this period,
so will continue the dry forecast. Below normal temperatures are
expected to linger over the area.
Warm air advection with gusty southwest winds develops Sunday
night into Monday night, which will allow for a mild day on
Monday. A cold front slides southeast through the area later
Monday night, with strong cold air advection into Tuesday on
northwest winds. Thus, colder temperatures return for Tuesday.
A broad 500 mb trough slides southeast through the Great Lakes
region Tuesday, with strong differential cyclonic vorticity
advection passing through. Things look dry at this point, with
just some clouds moving through later Monday night into Tuesday
Tuesday night through Wednesday...forecast confidence is high.
Models are generally showing 500 mb flow remaining northwesterly
during this period. High pressure slides southeast from the
northern plains into the middle Mississippi River valley Tuesday
night into Wednesday. This should continue to bring quiet weather
to the area. Below normal temperatures should continue as well.
Wednesday night through Saturday...forecast confidence is medium.
GFS/European model (ecmwf) are showing a cold front sliding southeast through the
area Wednesday night or Thursday morning. There are 500 mb
vorticity maxima within northwest flow that slide through the area
with the cold front. The European model (ecmwf) is the only one with quantitative precipitation forecast over the
area, with the GFS to the north. For now, will keep Wednesday
night into Thursday dry.
Another low passes north of the region Friday night on the
GFS/Canadian, with the European model (ecmwf) bringing the low closer to the area
later Friday night into Saturday. The European model (ecmwf) has much more quantitative precipitation forecast and
upward vertical motion with this system than the other models.
Kept the consensus blended pops and temperatures for this period.
Cigs will slowly improve this afternoon into tonight, eventually
beginning to clear late tonight into Sunday. Winds will be the
main concern, with gusty northwest winds continuing overnight.
Winds will become westerly and eventually southwesterly Sunday.
Gale conditions will continue across the nearshore waters into
tonight. Winds may be a bit marginal near the shore, but will be
stronger near the open waters. Wave heights will peak this
evening, and slowly diminish heading into tomorrow. A Small Craft
Advisory will likely be needed with the expiration of the Gale
Warning late tonight.
Winds will become westerly and then southwesterly Sunday into
Monday. Small Craft Advisory conditions may again be met Monday
night into Tuesday, as another frontal boundary approaches the
Lm...Small Craft Advisory until noon CST Sunday for lmz643>646.