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Area forecast discussion 
National Weather Service Green Bay WI
416 am CDT Wednesday Apr 1 2015

Forecast discussion for routine morning forecast issuance

Short term...today...tonight...and Thursday
issued at 415 am CDT Wednesday Apr 1 2015

Temperatures...precipitation trends...the threat of thunderstorms...and elevated fire
weather conditions...are the main forecast concerns for the short-term period.

Southerly return flow was ramping up over the upper Mississippi Valley...
in advance of low pressure and an associated cold front over the wstrn
Dakotas. Increasing warm air advection was producing some virga or light sprinkles
from a 10-12k feet cloud deck over northwest WI...but have not seen any reports
of precipitation reaching the ground.

Have kept some low-end probability of precipitation over northern WI to account for weak
elevated convection due to warm air advection associated with a 45-55 knots low level jet and
steep middle-level lapse rates today. However...the best precipitation chances will
continue to be focused along and ahead of a cold front that will sweep
across the region tonight into Thursday morning. This front will be
accompanied by precipitable water values of 1.0-1.2 inches...800 mb lifted indice's
of zero to -3 and upper level support from the rrq of a 110-120 knots
jet. Have made minor adjustments to slow down timing a bit...but
otherwise kept likely to low-end categorical probability of precipitation and moderate quantitative precipitation forecast
amounts in the forecast tonight and Thursday morning. Have also
kept the chance of thunderstorms in the forecast due to previously
mentioned elevated instability...moisture and forcing.

South winds gusting to 25 to 30 miles per hour will bring mild air into the
region today...with temperatures getting into the 50s/60s most places...
with a few readings around 70 in central WI and cooler upper 40s
near Lake Michigan due to southeast winds. Also raised temperatures into the
lower to middle 60s on Thursday due to afternoon sunshine and deep
mixing. West winds will gust to 25 to 35 miles per hour during the afternoon.

See the fire weather section below for information on elevated fire
danger.

Long term...Thursday night through Tuesday
issued at 415 am CDT Wednesday Apr 1 2015

Mean flow across the Great Lakes through this weekend to be from the
northwest behind the passage of a cold front (thu ngt)...a shortwave trough
(fri) and the movement of a closed upper low around Hudson Bay (fri-
sunday). The mean flow then turns SW for early next week as a
substantial upper trough moves into the western Continental U.S.. main forecast challenge
is associated with this upper trough as pieces of energy eject northeastward
through the central Continental U.S. And interact with a quasi-stationary fnt draped
from the Central Plains to the East Coast. While temperatures over NE WI will
warm a bit...this pattern will lead to a stretch of unsettled
weather with several chances for precipitation.

Secondary cold front sweeps through WI Thursday night with a gradual wind shift
from the west to the N-NW. Little moisture left behind over the
region after the passage of the first cold front (wed ngt)...thus no
precipitation mentioned in the forecast for most of the forecast area. The
exception would be Vilas County where lake effect snow showers and/or
flurries are possible as cold air advection pushes into WI. 800 mb temperatures over Western
Lake Superior drop to around -12c by 12z Friday and with favorable
trajs...cannot rule out a little light snow. Delta-T values are
only in the lower teens...thus do not anticipate much (if any)
accumulation. Min temperatures to range from the middle to upper 20s N-cntrl...
middle 30s east-central WI.

A trailing weak shortwave trough to move into the western Great Lakes on
Friday...but with little forcing or lift evident...this feature should
also pass through with little fanfare. The lake effect threat across
Vilas County will remain marginal through Friday morning and become even less
favorable Friday afternoon as a ridge of hi pressure builds across the upper
MS valley and sends drier air into WI. Maximum temperatures will remain below
normal with readings only reaching the upper 30s to lower 40s north and
the Lakeshore...middle to upper 40s south.

The surface ridge slides across WI Friday evening and already be headed
toward the eastern Great Lakes by daybreak. Hot on the heels of this
surface ridge...the models bring a fast-moving weak clipper system into
the upper MS valley. Expect to see clouds from this system to
already be overspreading at least northern WI late Friday night...but any
precipitation should remain to our west. The initial mostly clear to partly
cloudy skies with light winds will allow temperatures to fall to around 20
degrees far north...middle to upper 20s south. This weak clipper is prognosticated
to move east-southeast into the Great Lakes on Sat...accompanied by a cold front
and a middle-level shortwave. Moisture availability looks marginal...
but there may be enough lift/forcing to at least need the mention of
a small pop across NE WI. A slight tug of warmer air ahead of this
clipper should help boost maximum temperatures into the 40-45 degree range north...
upper 40s to lower 50s south.

Forecast for the latter half of the weekend remains uncertain...depending
on how far the cold front can sag before pulling upper stationary. All the models
develop a frontogenetic band of light precipitation along/just north of this
stationary fnt...thus the fnt's location is key to precipitation chances over NE WI
Sat night into Sunday. Latest thinking has the fnt reaching southern WI
before stalling...thus this leaves central/E-cntrl WI vulnerable to the
precipitation potential during the late Sat night/Sunday morning time frame
before the fnt slips farther south into northern Illinois Sunday afternoon.
Have raised probability of precipitation for the southern half of the forecast area during this period
and with temperatures falling below freezing Sat night/early Sunday morning...
we may have a minor snow accumulation to deal with. Too much
uncertainty yet on how this will play out...thus will hold off on any
potential accumulation in the fcst/hwo.

Forecast confidence remains low headed into the new work week with the
models continuing to show different locations for the quasi-stationary
fnt. If the fnt remains to our south...Monday could be dry with a dry
east wind from hi pressure over Ontario. However...if this fnt begins
to drift north a little on Monday...this would increase our precipitation chances.
For now...have followed the consensus solution which keeps chance probability of precipitation
over the entire forecast area for Monday and Tuesday. Precipitation type will also continue
to be problematic as temperatures fall below freezing at night and rise
into the 40s during the day. One positive from all of this would
be enough precipitation falls to alleviate the dry conditions over the region.
&&

Aviation...for 06z taf issuance
issued at 101 am CDT Wednesday Apr 1 2015

VFR conditions are expected to be present through most
of the taf period. Will see periods of scattered to broken
middle-clouds pass overhead through Wednesday afternoon ahead of the
next storm system. Winds on Wednesday will turn to the southeast
and become strong and gusty during the afternoon as well. Showers
and thunderstorms will be moving in from the west late Wednesday
evening with ceilings lowering and visibilities falling to MVFR within the
heavier showers.
&&

Fire weather...
issued at 415 am CDT Wednesday Apr 1 2015

Fire danger will be elevated over central WI this afternoon as
temperatures approach 70 degrees...south winds gust to 25 to 30 miles per hour and
relative humidity drops to around 30 percent.

Another period of increased fire danger is possible on Thursday
afternoon...as a dry slot brings clearing skies and gusty west
winds to the region...and relative humidity drops into the
20 to 25 percent range in the Sandy soil regions of NC/c/NE WI.
The big question will be whether or not grasses and other fine
fuels can dry out sufficiently after receiving moderate rainfall
tonight/early Thursday.
&&

Grb watches/warnings/advisories...
none.
&&

$$

Short term.....Kieckbusch
long term......kallas
aviation.......mpc
fire weather...kieckbusch

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