Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
922 PM CST Friday Mar 7 2014
Update...synoptic scale forcing associated with right entrance region
of upper jet and frontogenetical forcing in vicinity of passing
cold front has caused patchy mostly -ra over southern WI this
evening. Top down p-type estimates and dual pol methods show there
may be some sleet mixed in with the rain. Back edge of this area
of -ra over south central WI moving to the east. However can not
totally remove probability of precipitation as secondary area of synoptic scale forcing
with upstream middle-level short wave over southern Minnesota/western Iowa may yet
bring another surge of light precipitation into southern WI overnight.
Radar mosaic is showing resurgence of dbz over central and
northern Iowa last hour or so. Bumped up overnight lows a few
degrees most areas as well.
Aviation/06z tafs/...mostly MVFR conditions to continue into
Saturday as colder air settles over southern WI.
Marine...tightening pressure gradient behind departing cold front
may result in occasional wind gusts to 25 knots later tonight into
Saturday morning. However due to borderline situation and
widespread ice remaining over the nearshore waters...will hold off
on issuing Small Craft Advisory.
Previous discussion... /issued 336 PM CST Friday Mar 7 2014/
Low level frontogenesis and surface cold front will be pushing
through the region this evening. Dry air at lower levels should hold
off any precipitation until the late evening. Right entrance region of an
upper jet and moderate Omega will provide some lift...however there
is better Omega early Saturday morning over Illinois where greater
precipitation is expected. Latest NAM has backed off on precipitation
keeping all but the far southern counties dry. GFS is an outlier
with slighlty higher precipitation amounts. Model consensus is for a few
tenths of an inch of precipitation overnight. Expecting a rain/snow mix
with any precipitation late this evening and then a dusting of snow is
possible after midnight...mainly south of Madison and Milwaukee
where the forcing is better.
High pressure pushes in from the northwest on Saturday ending precipitation
chances by daybreak. Skies are expected to clear during the
Saturday night and Sunday...forecast confidence...high
Northwest middle/upper flow behind the departing trough. Weak upper
divergence on Sunday...along with weak 700 mb upward motion...but
700 mb relative humidity is rather low so expect mainly high level clouds ahead
of the approaching upper level jet maximum. Although some high middle
level clouds possible.
850/700 mb warm air advection begins later Saturday night and
continues Sunday with 850 mb temperatures rising to around
4 celsius. Fairly brisk southwest low level flow.
Sunday night and Monday...forecast confidence...medium
Middle/upper flow is more zonal on Monday. Milder temperatures
expected Monday with the west flow at lower levels.
Tuesday and Wednesday...forecast confidence...medium
Middle/upper flow is zonal before a shortwave drops into the High
Plains Tuesday. The 00z European model (ecmwf) is more progressive with this
trough...moving it into the Kansas and Oklahoma area Tuesday
night...and towards the Kentucky/Tennessee area Wednesday.
Meanwhile the GFS and 06z dgex keep the trough back towards Utah
and Colorado. All models drop a northern stream shortwave into
Some light precipitation on the GFS and European model (ecmwf) late Tuesday...but
the European model (ecmwf) is drier.
The main surface low moves across the Kentucky and Tennessee
Valley with weak high pressure across Wisconsin.
Temperatures cool on Wednesday.
Thursday and Friday...forecast confidence...medium
The main trough pushes across the eastern U.S. Wednesday night and
Thursday with a second northern stream shortwave moving into the
upper Great Lakes later Friday.
Warm advection begins Thursday as low pressure moves across south
central Canada. Weak cold advection Thursday night and Friday
as the low moves into southeast Canada.
MVFR ceilings continue to push in from the west and will overspread all
of southern Wisconsin by late afternoon. A shortwave and cold front
will bring a chance for rain and snow showers mainly during the
evening hours. Some question as to precipitation type...with model
soundings right at the rain/snow threshold. Either way...precipitation
amounts are expected to be light.
Models are not in great agreement with the placement of
precipitation...with the NAM and mesoscale models painting out a narrow strip
across the central forecast area...generally from Lone Rock to
Madison to Milwaukee. These models mainly keep it dry north toward
Fond Du Lac and south toward the Illinois border. Other models such
as the GFS and European model (ecmwf) have been showing a broader area of precipitation.
Have just kept precipitation at all taf sites for now...but will keep an
eye on radar trends over the next few hours.
Lower ceilings are expected as the front/precipitation move through...and then
behind the front as colder air moves in. Will likely see a return to
VFR tomorrow as high pressure approaches.