Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
336 am CDT sun Oct 23 2016
Today...forecast confidence is medium.
Short wave trough and compact 500 mb vorticity maximum over North
Dakota will move southeast across northern Wisconsin this morning
and afternoon, reaching west-central lower Michigan by 00z Monday.
The associated surface low will track farther south, moving
southeast from near msp at 12z across the state this morning and
afternoon to Western Lake Erie by 00z Monday, with a trailing cold
front reaching the Illinois/WI border area around 00z.
Matching current area radar returns with Storm Prediction Center mesoanalysis fields
indicates showers in northern Minnesota are tied closely to compact and
strong area of 700-400mb differential cyclonic vorticity advection
along with deeper column moisture reflected in higher mid-level rh,
which given the expected track of the vort Max would keep showers
north of the County Warning Area. European model (ecmwf) and NAM are clipping the far NE corner of
the County Warning Area with light showers between 18z and 00z, but lack of deep
moisture would indicate no more than a few sprinkles and confidence
too low to mention at this time. Pre-frontal sun and warmth will
raise high temperatures into the mid-upper 60s by early this
Tonight...forecast confidence is high.
Clearing skies and cold advection, with 925 mb temperatures dipping
to between 2c and 4c will produce low temperatures in the mid to
upper 30s, with enough surface wind to produce enough mixing to
prevent temps from going lower.
Monday - confidence...high
a large surface high will dominate. The 500 millibar regime shows
building heights in an increasing anticyclonic northwest flow.
Coolest 850/925 temps are proggd to be in the northeast cwa with a
slow erosion of the low level thermal trough.
Monday night - confidence...medium
lingering influence of surface ridge axis combined with clear skies
should allow for temps to dropoff into the early/mid evening before
mid/high clouds increase per 300-500 rh progs. So went with a non-
diurnal temp trend. If window of time increases between evening drop
and when clouds arrive confidence will be boosted for inclusion of
frost into the grids.
Tuesday - confidence...medium
low level jet axis remains to our west with lingering dry low levels likely to
be a bit stubborn to erode especially given the better moisture
influx to our west. Have kept some higher probability of precipitation in our west in the
afternoon to account for the GFS scenario. However the 00z European model (ecmwf)
keeps the qpf largely out of the cwa. If the European model (ecmwf) trends hold we
will be able to scale back the probability of precipitation in the east from what superblend
currently has going. It does look like the GFS is developing too
much precip too far east into the lingering ridging especially
given the late day position of low level jet well to the west.
Tuesday night and Wednesday - confidence...medium to high
best combo of synoptic forcing and moisture influx overlap as 500
millibar shortwave arrives and 850 llj translates towards eastern
WI. This will aid in moisture transport into our area. Seeing some
influence from right rear quadrant of departing upper jet Max
through the eastern lakes region. Still some differences on the
track of surface low with the European model (ecmwf) bringing the low into srn WI and
while the GFS has it across central Illinois. So the European model (ecmwf) has a more
northward placement of the qpf Max. So probability of precipitation continue on the high
side and some heavy rain totals (highest in western cwa) still look
reasonable so have retained this mention in the severe weather potential statement.
Thursday - confidence...medium
the GFS has trended away from last nights cutoff scenario and
has trended more in line with the progressive European model (ecmwf) solution. However
the European model (ecmwf) is slower to completely shift the mid level trough axis
east of WI relative to the GFS. So some lingering shra chances are
still in place across mainly eastern WI.
Friday - confidence...medium
surface high gradually builds in though lingering surface
trough and perhaps some upper support may generate some light shra.
Probability of precipitation pretty low at this time.
Saturday - confidence...low
fairly large differences between GFS and European model (ecmwf) with the GFS showing
the high dominating though a band of qpf developing and merging with
precip to our south associated with next low/baroclinic zone.
However the European model (ecmwf) shows a more pronounced 500 millibar trough
arriving with a more northward positioning of more organized shra
into WI versus the GFS focus more to the south of WI. For now will
go with the blended guidance.
Aviation/12z tafs/...patchy fog will dissipate by mid morning with
clear to sct sky cover and VFR conditions until a VFR cloud deck
overspreads the area with approach and passage of low pressure
late this morning and afternoon. South to southwest winds will
shift northwest and increase to 10 to 20 knots behind a trailing
cold front that reaches the WI/Illinois border around 00z Monday. Winds
will ease tonight with VFR conditions through the remainder of the
Marine...a tightening surface pressure gradient around approaching
low pressure will not affect the nearshore zones with higher winds,
and thus higher waves, until the low passes by and a cold front
drops through the area late this afternoon/evening. Winds and waves
are marginal for a Small Craft Advisory so will add a cautionary
statement for small craft in this nsh issuance and let next shift
assess need for a headline.
Today/tonight and aviation/marine...rem
Monday through Saturday...collar