Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
340 am CDT Tuesday Mar 11 2014
Today and tonight...forecast confidence - medium.
Will follow concensus of 00z European model (ecmwf)/GFS and Canadian in keeping
strongest synoptic scale lift to the south of WI tonight. 00z NAM
strong outlier due to its much deeper upper trough digging and
slower eastward movement. This has occurred earlier in the winter as
well with NAM guidance. 00z NAM also farther north with coupled jet
over southern WI later tonight while European model (ecmwf) and GFS south in
central/northern Illinois. Fortunately 06z NAM appears to have come into
better agreement with other short term guidance.
Strong area of layer frontogenetical forcing spreads into southern
WI later this morning and afternoon...in combination with enhanced synoptic
scale lift from right entrance region of upper jet. Hence will
continue high probability of precipitation today. Colder...drier air will spread into
southern WI on increasing north winds this afternoon and tonight. Top-
down method and critical thickness favor light rain possibly
becoming mixed with light snow this afternoon. Not impossible an
enhanced band of snow showers could produce some slushy
accumulations in the north but expect most of the light snow to melt
during the day. By this evening...the light mixed precipitation should be
diminishing with the emphasis shifting to the developing low
pressure to the south. Southern WI looks to remain on the northern
fringe of this system. May be a break in the precipitation for a time this
evening before snow spreads back into far southeast WI later tonight.
Far southeast may end up getting 1 to 2 inches of snowfall
overnight. In addition...strong northeast winds due to tight
pressure gradient and steep lapse rates over the now open waters of
the nearshore will allow wind gusts of 30 to 35 miles per hour to affect
Lakeshore areas after 05z. Day shift will need to contemplate whether a
Winter Weather Advisory may be needed for late tonight into early Wednesday.Coming
Wednesday - confidence...medium
blustery day shaping up with gusty north winds. Models keying
more on lingering light synoptic snow. Main concern will focus on
lake effect potential. 850 temperatures drop to - 16c to -18c creating
more than favorable Delta-T. BUFKIT soundings show better
fetch...north-northeast in the low layers in the morning but inversion height
quite low and more borderline Delta-T then. During the afternoon
winds shift a bit more north-northwest though Delta-T becomes extremely
favorable then with higher inversion heights. For now will likely
key the pop forecast on lingering synoptic snows and not jump on
lake effect just yet. Temperatures in most areas will struggle to make it
past 20 so wind chills in the single digits quite likely.
Thursday - confidence...medium
upper flow becomes broadly anticyclonic with decent warm
advection setting up once again. 12z European model (ecmwf) most aggressive with
925 temperatures warming back above 0c...while the 00z NAM and GFS showing
925 temperatures at or below 0c. Will keep small probability of precipitation confined to the northeast
County Warning Area where better adiabatic Omega coincides with lowering of
condensation pressure deficits.
Friday - confidence...medium
thermal ridge in place at 12z. With 850 front passing through
cold advection will get underway. Shortwave rides in from the
northwest. Moisture better to the north so will keep dry forecast
intact. GFS shows a bit more pronounced cooling than the GFS...so
a blended 925 temperature approach still suggests highs in the low/middle
Saturday - confidence...medium
cyclonic 500 millibar flow. Low level trough in place as well.
Surface high building towards Lake Superior. Timing of winds
shifting to the NE will be a key. Potential for some lake effect
shsn later Saturday into Saturday night with favorable onshore
flow. 850 temperatures drop off into the negative teens celsius.
Sunday - confidence...medium
surface high in place. However upper flow is cyclonic. European model (ecmwf)
shows a better shortwave southwest of WI keeping precipitation just
south. Will be a close call. Kept the allblend slight probability of precipitation in
place for now.
Monday - confidence...low
warm advection signal once again. European model (ecmwf) about 4-5c warmer than
the GFS. Pattern suggests dry weather for southern WI. European model (ecmwf) shows warm air advection
induced precipitation across parts of northern WI...while the GFS is completely
dry...so quiet allblend probability of precipitation look OK at this point.
Aviation/12z tafs/...VFR conditions expected to transition to MVFR
and likely lower for a time. Area of -ra will spread into southern
WI today and transition to periods of -sn tonight. Combination of
-sn and strong winds will likely create low visibilities at kenw tonight.
Marine...strengthening low pressure to the south of the Great Lakes
later today will move east into the Ohio Valley tonight and increase
pressure gradient across Lake Michigan. Latest high res visible
image from Tuesday shows much of the near shore waters have been cleared
of ice due to the recent stronger offshore winds and warmer
temperatures. Hence open waters will create more unstable
conditions and steep lapse rates over the near shore waters. These
conditions will allow wind gusts of 35 to 40 kts to mix down to
surface later tonight into Wednesday morning. Hence will Post Gale Warning
with small craft conditions likely to persist Wednesday afternoon and evening.
Lm...Gale Warning from 10 PM this evening to noon CDT Wednesday for
Today/tonight and aviation/marine...mbk
Wednesday through Monday...collar