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National Weather Service Green Bay WI
1157 am CDT Monday Sep 1 2014

Updated aviation portion for 18z taf issuance

Short term...today...tonight...and Tuesday
issued at 318 am CDT Monday Sep 1 2014

Line of convection which developed over Minnesota and Iowa Sunday
evening along and ahead of a cold front has diminished moving
into Wisconsin earlier this morning. Radar trends suggest the
focus of the convection this morning will first be over the
northwest half of the state as the short wave trough and initially
an upper jet couplet then lfq region of the upper jet lifts over
northwest Wisconsin including north central Wisconsin. Focus of
heavy rainfall will likely be over far northwest Wisconsin this
morning. Will need to diminish probability of precipitation elsewhere for a portion of
the early morning hours as per radar trends but cannot completely
remove due to available instability in the warm sector and likely
some shear available. Otherwise will focus on convection potential
as the front passes over for the second round as mu convective available potential energy approach
1200 late morning into the afternoon over central and northeast
Wisconsin. At 08z storms were already redeveloping near the frontal passage
over Minnesota and central Iowa early this morning and progressing
eastward with the front reaching western Wisconsin toward
daybreak. Storm Prediction Center slight remains mainly south of the area today so
will continue to leave out severe wording in the morning severe weather potential statement.

Will continue to linger a small mention of precipitation over far eastern
areas this evening until the frontal precipitation clears out. With partial
clearing possible tonight...threat of fog late tonight. Some
models keeping some middle level moisture around so clouds may aid
with preventing widespread dense fog for the Tuesday morning
hours for the start of most schools Tuesday.

Even though the surface front is well south on Tuesday and weak
high pressure settling...still some support this morning to keep a
small chance of showers. Broad upper trough remains with colder
air aloft to the north. WV loops also suggest a subtle short wave
currently over northwest Wyoming and southern Montana and tracking
eastward. Forecast soundings still indicate some middle level
moisture and instability in the westerly flow and a upper jet
sliding north as the upper heights gradually building late in the
day. Will add a diurnal trend to the showers and may consider
adding a small mention of thunderstorms and rain for the afternoon hours.

Long term...Tuesday night through Sunday
issued at 318 am CDT Monday Sep 1 2014

Models are in general agreement that a subtropical ridge will dominate
the southern Continental U.S. Through the forecast period. A positive-tilted upper trough
initially from Hudson Bay to the Pacific northwest is expected to break
off with the northern part of the trough moving from the northern plains Thursday
to Ontario on Friday. A frontal boundary preceding this upper trough will
bring the next chance of precipitation to NE WI during the late Wednesday through Friday
time frame. Hi pressure is then forecast to build into the region for next
weekend with temperatures falling below normal.

Weak surface hi to drift east toward the eastern Great Lakes/Ohio rive
valley Tuesday night bringing a return flow to WI. While a stray shower
cannot be completely ruled out Tuesday evening associated with the
departed shortwave trough...not confident enough to add to the forecast as
forcing/lift/instability practically non-existent. Thus...have
kept Tuesday night dry with sky conditions becoming at least partly
cloudy. Min temperatures to range from the lower to middle 50s north...middle to
upper 50s south.

Prevailing S-SW winds to bring increasing low-level moisture into
WI on Wednesday with dew points climbing into the lower to middle 60s and precipitable water
values surpassing 1.5" by 00z Thursday. As this occurs...a warm front is
expected to lift northeastward into at least southern WI and act as a focus for
shower/thunderstorm activity. Stronger warm air advection/Theta-E advection to take place
over the western half of WI...thus chance probability of precipitation placed over north-central WI...
scaling down to none probability of precipitation for eastern WI. Despite the increase in
clouds...maximum temperatures should be able to reach the 75-80 degree range
over the north and Lakeshore...lower 80s across the south.

Better chances for showers/thunderstorms arrive Wednesday night as the warm front lifts
north through the rest of WI. Instability steadily increases through the
night with models showing moderate to strong shear and a favorable jet
structure additional lift. May need to raise probability of precipitation into the likely
category based on the above-mentioned factors plus the strength of
the warm air advection. A mild and muggy night can be expected with min temperatures in
the lower to middle 60s north...middle to upper 60s south. Models are in fair
agreement in moving the shortwave trough across S-central Canada/northern
plains on Thursday with a cold front driving toward the western Great Lakes.
While better middle-level forcing to be located to our north...better
instability to be situated over WI with convective available potential energy rising to > 2k j/kg
and lifted indice's down to at least -6. Have kept moderate to hi chance probability of precipitation in
the forecast for now and will wait to nail the timing of the cold front
before raising probability of precipitation higher. Thursday could conceivably be the warmest/
most humid day of the extended forecast with maximum temperatures in the upper 70s
to lower 80s north...middle 80s over central WI and dew points either in
the upper 60s or lower 70s.

The cold front is prognosticated to sweep through NE WI Thursday night...therefore a
continuation of probability of precipitation are necessary. Too early to determine the
strength of these thunderstorms Thursday into Thursday night...but give the
instability and shear forecast to be in place...we will have to monitor
the situation in the coming days. Improving conditions expected on
Friday as the cold front exits to the southeast and hi pressure builds eastward from the
upper MS valley. Have kept a token pop in the forecast over east-central WI
into Thursday night...but believe a gradual decrease in clouds will take
place as cooler/drier air moves into WI.

This area of hi pressure to settle over the Great Lakes for next
weekend and bring a somewhat cool...but pleasant stretch of
weather to the region. Temperatures to be a bit below normal for both Sat
and Sunday.
&&

Aviation...for 18z taf issuance
issued at 1156 am CDT Monday Sep 1 2014

The main area of showers and isolated thunderstorms will exit
northeast Wisconsin early this afternoon. Some spotty showers along
the front will likely pass over central and north-central Wisconsin
this afternoon but not sure of coverage...so left out of taf sites
for now. MVFR ceilings will take a little longer to move
out...however...but should still see ceilings improve middle to late in the
afternoon.

Clearing skies this evening and diminishing winds will likely lead
to ground fog formation late tonight over north-c Wisconsin. The
gradient is a little tighter over central and east-central WI so
should not see as thick of fog as further north. A weak disturbance
will then arrive Tuesday morning and will provide a scattered shower
threat by midday.
&&

Grb watches/warnings/advisories...
beach hazards statement until 9 PM CDT this evening for wiz022-
040-050.
&&

$$

Short term.....Tdh
long term......kallas
aviation.......mpc

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