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Area forecast discussion 
National Weather Service Milwaukee/Sullivan WI
319 PM CST Tuesday Nov 24 2015

Short term....tonight and Wednesday...forecast confidence medium

Middle level clouds will continue slowly lift northeast out of the
forecast area through late afternoon. Should see mostly clear to
partly cloudy skies then this evening and overnight. Given the
propensity of the NAM to over saturate the low levels with snow on
the ground...leaned forecast toward drier low levels and less clouds
through the night. Winds will be picking up at the surface as a low
level jet comes not particularly concerned about fog

Surge of low/middle level moisture will arrive from the west later
tomorrow morning and into the afternoon. Skies will turn
cloudy...with drizzle and/or a few showers expected. May see some
fog develop as well by late dewpoints rise into the
middle/upper 30s over the snow cover. Temperatures will also be on the
rise under the mild southerly flow though...which may leave enough
of a dewpoint depression during the day to limit fog.

Leaned forecast temperatures toward the European model (ecmwf) and Canadian solutions for the NAM/GFS have been overdoing cooling from snow

Wednesday night through Thursday night...forecast confidence

Rain chances will be on the increase Wednesday night as a 250mb
jet streak located over northern Minnesota through Ontario Canada
will intensify...with jet streak magnitude of 120+ kts at its
core by 06z Thursday. The entrance region of the jet will slowly
translate to the east...putting southern WI in the right entrance
region of the jet...enhancing upper level divergence. This will
help lead to chance to likely rain across the forecast area. The
melting snow...along with these chances of rain...will help lead
to areas of fog Wednesday night/thurs. Morning.

Chances of precipitation will increase even further as a 500mb
shortwave trough is prognosticated to develop out of the Texas Panhandle
region and eject northeast into the MO/IA/S WI region. Isentropic
Omega increase to values near 20 ubar/S according to the 24.12z
GFS. A corridor of an enhanced 850-700mb deformation zone will be
coupled with this middle level shortwave. This will lend the support
for periods of light to moderate rain during the day Thursday.
Precipitable water values will be well above seasonal normals thanks to enhanced
low level jet...bringing a warmer and moister airmass to S WI.
NAM and GFS BUFKIT soundings indicate precipitable water values could reach 1 to
1.2 inches Thursday night to Friday morning...providing plenty of
moisture for rainfall. These amounts are slightly below those from
the previous model runs. At the moment...current quantitative precipitation forecast amounts for
Thursday through Friday morning will be between 1 and 1.6 inches.

The primary concerns remain the potential for Rising River levels
Thursday night...including the Fox and Pecatonica rivers...due to
rainfall in addition to melting snow. The Rock River also will
likely respond but more slowly in Rock County. Hydrologic
statement highlights this threat.

Long term...Friday through Tuesday...forecast confidence low

As the shortwave trough departs...cold air advection increases across
S WI...which could support a period of wintry mix Friday morning
before the atmosphere dries out once the low level jet moves off to the
east. NAM soundings at Madison show a freezing rain/ice pellet
precipitation type...while the GFS soundings at Madison show all snow.
The good news is conditions will dry out eventually by Friday
afternoon from west to east across S WI. Went with light snow in
our northwest to light rain in the southeast...with mainly wintry
mix/ice pellets for now...but confidence remains low in the
precise locations for the precipitation types.

Surface high pressure and middle level ridging will quiet conditions just
in time for the weekend. However...colder temperatures will return
as 24.12z GFS 925mb temperatures drop to near zero degrees c 12z
Saturday. High temperatures for the weekend look to stay in the
upper 30s across much of the forecast area...with lower 40s in our

A closed low over the western U.S. Will slowly drift into the plains
Sunday. Timing of this movement is still uncertain. Another surge of
moisture is expected to lift into S WI on Sunday. The latest GFS and
European model (ecmwf) suggest temperatures will be warm enough for rain...but
transition to a mix late Monday into Tuesday.


Aviation/00z tafs/...

Middle level clouds will clear out of the forecast area by
evening...with mostly clear skies to start the evening. Forecast
soundings later this evening then show a pretty good inversion in
the lower levels as warmer air aloft continues to push into southern
Wisconsin. NAM soundings probably overdone again with low level
saturation though due to the snow on the ground...and this is
supported by VFR conditions most places in the NAM MOS. Opted to go
with VFR conditions through the night...especially considering more
wind than last night.

Decided to put mention of low level wind shear in tafs for later
tonight into Wednesday low level jet comes overhead.
Bulk shear from surface to 2 kft will be around 30 a
borderline event.

Deeper moisture is expected to push in from the west late Wednesday
morning and into the afternoon. Much better chance to see lower ceilings
and maybe some lower visibilities develop with this moisture surge. Should
see some drizzle or a few showers also develop late morning and



Decided to issue a Small Craft Advisory from late tonight through
Wednesday night. Southerly winds will increase tonight into
Wednesday ahead of a trough of low pressure. The along shore winds
will build some higher waves...the highest across the northern
marine zones. Northern cut of the advisory runs a bit longer than
the southern one given the earlier start and later end of higher


Mkx watches/warnings/advisories...
Lm...Small Craft Advisory from 9 am Wednesday to 4 am CST Thursday
for lmz645-646.

Small Craft Advisory from 3 am Wednesday to 6 am CST Thursday
for lmz643-644.



Tonight/Wednesday and aviation/marine...ddv
Wednesday night through Tuesday...jts

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