Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Milwaukee/Sullivan WI
943 am CST Thursday Nov 26 2015
Pretty straight forward forecast through the remainder of the
day...as coverage of rainfall will continue to increase.
By middle afternoon...precipitable water values are still expected
to be on the very high end of what is possible this time of the
year. Temperatures and dewpoints will slowly rise through the day ahead
of an approaching cold front...with well above normal
highs...especially in the southeast.
Coverage of rainfall will continue to increase today...with
widespread rainfall expected this afternoon into tonight. May see
a brief transition to a wintry mix later tonight into Friday
morning as colder air moves in behind the departing cold front.
This mix should have little or no impact given how warm it will be
into this evening.
Ceilings will continue to lower today...with low ceilings then expected
overnight. Will probably see slow improvement Friday as
colder/drier air works into the area...with a possible return to
VFR by later in the afternoon.
Visibilities will probably go down within heavier rainfall.
Otherwise...not expecting much reduced visibility...as threat for
fog looks like less than previously thought given how fast snow
Previous discussion... /issued 511 am CST Thursday Nov 26 2015/
Today and tonight...confidence medium.
Has been hard to get more than scattered showers and drizzle with
periodic weak short wave energy and pockets of Omega moving out
ahead of positively tilted 500 mb trough. The lack of deep
moisture seen on area rap soundings should increase later this
morning and afternoon with persistent warmth and moisture
advection...with precipitation becoming more widespread with
increasing isentropic lift and layer q-vector convergence...as
region comes under right entrance region of jet maximum that
strengthens from 140 knots to 160 knots by this evening.
GFS and European model (ecmwf) continue to be faster than NAM in bringing a surface
wave up along the surface trough bisecting the state from
southwest to northeast this afternoon and evening. Strengthening
frontogenesis provides the forcing for the steadier...heavier
rain across the County Warning Area late this afternoon into this evening.
Still looking at rainfall totals reaching between 1 inch and 1.7
inches across the area. This will add to the water from melting
snow already moving into area rivers and streams. Statements are
out for rivers in the southern County Warning Area that are approaching bankfull
stage...with a few possibly going into flood if forecasted rain
amounts are realized.
Will see a transition to a mix of rain...snow and some sleet as
cold front drops southeast behind the departing wave...with little
to no accumulations expected by Friday morning.
Temperatures will rise a bit this morning into the upper 40s northwest to
middle 50s in the far southeast...then steady through the afternoon before
dropping with the cold front passage late tonight.
Friday... forecast confidence medium.
Colder air will slip into southern WI through the day Friday...
quicker in the lower levels than the upper levels. This means there
is a window of opportunity for some sleet mixed in with rain and
snow. Drier air will be settling in with the cold air on Friday and
models are trending drier. The 06z NAM came in nearly dry for the 12-
18z time period. Any mixed precipitation will be short-lived and low-
Saturday through Sunday... forecast confidence high.
Surface high pressure will set up over the northern plains and upper
Midwest on Saturday and then expand east over the Great Lakes
through the weekend. Winds will be light out of the north with
temperatures near seasonal normals with highs in the 30s and lows in
A favorable north-northeast wind will allow for a long fetch over Lake Michigan
and lead to some lake effect clouds early Saturday morning in far
southeast WI. Lake temperatures are around 45f/7c near southeast
WI... and 850mb temperatures are expected to drop to around -3c with even
colder 925mb temperatures. Delta-T values look a little low for lake effect
but not by much. At a minimum... there will be some lake clouds over
the area. The NAM is showing light quantitative precipitation forecast with this feature and it is
not out of the question.
Monday through Thursday... forecast confidence medium.
A closed upper low over the western states will drift into the
northern plains early next week. Another mild and wet system is
expected to cross the middle Mississippi River valley on Sunday ahead
of that upper low... but the latest models keep the precipitation to the
south of the WI/Illinois border.
The upper low should cross WI Tuesday morning and bring another round of
precipitation Monday afternoon/night through Tuesday night. Models are in
fairly good agreement for timing and actually temperature profiles
with this system. There should be some mild air surging into
southern WI on the leading edge so expecting it to begin as rain.
Colder air will wrap into southern WI from west to east Monday night so
there will be a transition to snow but this will occur within the
dry slot. Surface temperatures should be right around freezing... so
the snow will be wet and not amount to much. Southern WI should see
some light deformation area snow Tuesday afternoon and evening... but
the majority of the snow will fall in central and northern WI.
Wednesday and Thursday... forecast confidence medium.
Ridging will lead to dry weather and seasonal temperatures for the
middle of next week.
Slower than expected movement of a surface low through the area
has delayed more widespread rain into southern Wisconsin until
later this morning and afternoon...continuing into this evening.
MVFR conditions will hold into the late morning...then ceilings anbd
visibilities will trend down to IFR and possibly some LIFR as the heavier
precipitation moves in. Gusty south winds will lower as the wave of low
pressure through this afternoon and early evening...with winds
turning north and strengthening with passage of a cold frontv
Will continue Small Craft Advisory as is for now but watching
for winds speeds to increase after they fell off overnight as
expected. If winds do not increase as much as forecast...may have
to end this current advisory witht he middle-morning update. Looking
for steadier rain and possibly some periods of dense fog as higher
dew point air moves over the lake as a weak low pressure area
moves northeast along surface trough draped across the region.
This trough will turn into a cold front behinds the departing low
later tonight...with winds turning north and increasing. Small
Craft Advisory conditions will return overnight into Friday for
these strengthening north winds that will produce gusts to near
gale force for a time Friday.
Lm...Small Craft Advisory until 6 PM CST this evening for lmz645-646.
Small Craft Advisory until noon CST today for lmz643-644.
today/tonight and aviation/marine...rem
Friday through Wednesday...mrc