Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
602 am CST Thursday Dec 18 2014
Updated aviation portion for 12z taf issuance
Short term...today...tonight...and Friday
issued at 325 am CST Thursday Dec 18 2014
Cloud trends and temperatures are the main forecast concerns.
A weakening surface trough was situated over the northern half of WI
early this morning. Convergence associated with this trough was
combining with a shallow layer of moisture to produce widespread
stratus over the entire forecast area. Satellite showed that
clearing was progressing southwestward across the Upper Peninsula.
Concensus of 925 mb relative humidity forecasts suggest that drier
air will gradually push southwestward into the forecast area today and
tonight...but may not quite make it into central WI. In
addition...models show the surface trough weakening during the day...
with a surface high gradually edging into the region from the
northwest later today and tonight. The loss of surface convergence...
dry air advection and some daytime mixing should bring at least
partial clearing to about the NE two-thirds of the forecast area
by evening. Mostly cloudy skies may remain over central WI
today and tonight...then start edging back to the east late
tonight into Friday.
Used a blend of the previous forecast and the better performing
guidance sets for temperatures the next couple days. High
temperatures should be mainly in the middle 20s to lower 30s.
Lows tonight should be in the teens...except single digits
over far northern WI...where a fresh snow cover resides.
Long term...Friday night through Wednesday
issued at 325 am CST Thursday Dec 18 2014
The latest GFS and European model (ecmwf) ensemble means continue to indicate a
pattern change early next week as shortwave energy amplifies over
the center of the country during the Monday through Wednesday time period.
This buckling of the upper flow then results in a strong cyclone
lifting north across the Great Lakes during the middle of next
week. Though the details are far from certain...anyone with travel
plans next week should stay tuned to the latest forecasts. In any
event...will rely on the ensemble means late in the period...but a
blend of the GFS and European model (ecmwf) will work through 00z Tuesday.
Friday night through Saturday night...as pieces of weak shortwave
energy moves across the northern Mississippi Valley Friday
night...high pressure will exit into eastern Canada. Will see
clouds increase from west to east through the night though a dry
wedge in the middle-levels should prevent precipitation. The shortwaves will
move across Wisconsin on Saturday which should keep skies on the
mostly cloudy side...but soundings do not look quite as saturated as
last night. Will maintain a dry forecast. Continued cloudy on
Saturday night with ample low level moisture around from southerly
flow. Will raise low temperatures a degree or two...but little changes
were made elsewhere.
Rest of the forecast...southerly flow ahead of an amplifying trough
will keep clouds around on Sunday...and prognosticated soundings look
saturated...especially over the northwest half of the forecast
area. Will expand the small chances of snow. Weak lift will
continue Sunday night into Monday with low pressure taking shape to
the west. Enough warm air could be present for a mix of rain and
snow over central and northeast Wisconsin. Any precipitation should be
light over this period...but should become more widespread Monday
night into Tuesday night as the deepening trough moves overhead.
Then as intensifying low pressure moves northward on
Wednesday...colder air will be wrapping around the low which could
make for wintry travel across the region depending on the track of
the low. Gusty winds will also cause issues with any wintry
Aviation...for 12z taf issuance
issued at 551 am CST Thursday Dec 18 2014
Widespread MVFR ceilings covered most of the forecast area this
morning...though some IFR ceilings were observed over north central
WI. Satellite showed partial clearing headed toward far NE WI.
Clearing is expected to gradually work its way southwest across
the forecast today and early tonight...probably reaching the
rhi/grb/atw/mtw taf sites during the early to middle afternoon. The
clearing may not quite make it into central WI before stalling
out...so kept MVFR ceilings going at auw/County Warning Area through the entire taf