Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 241657 AAA
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1157 AM CDT MON OCT 24 2016
High pressure over Minnesota is expected to slide east across the
region this afternoon and tonight. The high will continue to
bring dry conditions this afternoon across the area, with cool
temperatures and slowly diminishing winds. Highs should reach the
middle 50s in most areas, a little warmer than the 925 mb
temperature fields from models.
Light winds and mostly clear skies are anticipated toinght, as the
high moves across the area. These conditions should allow lows
tonight to drop into the middle to upper 30s in most areas. Patchy
frost can be expected away from Lake Michigan. Do not anticipate
a Frost Advisory for the southeast six counties at this time,
unless lows can get a few degrees colder over a large area.
The high moves out of the region on Tuesday, and allows for east
southeast winds to develop over the area. 12Z run of the NAM
remains dry for Tuesday afternoon, with a fair amount of dry air
below the 700 mb level.
The 12Z GFS/Canadian models continue to bring some QPF into the
southwestern portions of the area on Tuesday, with more moisture
in the low levels. They also have the influence of some
differential cyclonic vorticity advection with a passing elongated
500 mb vorticity maximum. Currently have chance PoPs in the
western counties Tuesday afternoon, and will continue to evaluate
if they need to be raised.
VFR conditions are expected this afternoon, tonight into Tuesday
across TAF sites. High pressure will slide east across the region
this afternoon and tonight, before moving east of the region
Tuesday. The high will bring mostly clear skies this afternoon and
into tonight, with middle to high clouds moving east into the
area on Tuesday.
North to northwest winds will continue to weaken this afternoon,
with light and variable winds tonight. Light east southeast
winds are then expected Tuesday. There is a possibility for rain
showers to affect Madison Tuesday afternoon, but will leave
mention out of TAFs for now due to some uncertainty.
Small Craft Advisory is in effect for the western nearshore waters
of Lake Michigan until 18Z this afternoon. The pressure gradient
continues to slowly relax, as high pressure moves into the region.
This should allow gusty north winds to continue to weaken this
afternoon. Subsequent waves are expected to diminish below 4 feet
across the nearshore waters by early this afternoon. Anticipate
that the Small Craft Advisory will be allowed to expire at 18Z.
Good shot at Small Craft Advisory conditions for later Tuesday
night into Wednesday night. Low pressure is anticipated to slide
east across the region during this period. Gusty winds and
building waves are expected later Tuesday night into Wednesday,
with high waves lingering into Wednesday night. Offshore wind
gusts may get close to 20 knots or so Thursday as well.
.PREV DISCUSSION... /Issued 341 AM CDT MON OCT 24 2016/
TODAY AND TONIGHT...Forecast Confidence High.
Quiet cool weather today and tonight as broad high pressure builds
into the region. Some early clouds as band of stratocumulus with
secondary weak trough sags through CWA but band is shrinking as it
moves south, in line with hi-res model RH trends. Should see mostly
sunny skies by mid-late morning. Cold advection drops 925 mb temps
to around 4C to 5C, supporting cool highs in the mid 50s.
Warm advection mid to high level clouds begin to move in from the
west overnight limiting temp drop, especially over South Central WI.
Will see temperatures dip after sunset and then steady out
around/after midnight. Mid-30s lows away from the lake will
bring patchy frost.
TUESDAY - Confidence...Medium
Influence of lingering anticyclonic flow regime will be in place.
LLJ axis is well to our west across wrn IA and MN. The GFS continues
to be the most aggressive model in the eastward extent of qpf
associated with increasing 850/700 waa and leading moist advection.
However the ECMWF and GEM keep qpf across the far western cwa or
well west of the area per the NAM. In the absence of a mid level
vort and the positioning of the LLJ the GFS scenario looks a bit
bullish. The Superblend has pulled back on the POPS a bit and
prefer this backed off approach at this point.
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT - Confidence...High
For days now the models have been sending a strong signal for a wet
and unsettled period. Best moisture surge arrives Tuesday night into
Wednesday morning as axis of LLJ pivots eastward ahead of the
sfc/850 circulation appch from Iowa. The sfc/850 low track from the
GFS/ECMWF takes it across northern IL while the GEM is a bit farther
north into srn WI. DCVA associated with the 500 millibar trough/vort
will be aiding in vertical motions. The Superblend temp guidance may
be a bit generous given that srn WI will be seeing the likelihood of
a cool wind driven rain. Potential still there for some decent
rainfall totals so will retain the highlighting of heavy rainfall in
the HWO. Models in decent agreement in a quicker shift of this
system off to the east Wednesday night so like the Superblend
gradual decrease in POPS throughout the night. Cloud cover likely to
persist throughout the night as LLVL RH progs show extensive 85-95
pct across much of the state.
THURSDAY - Confidence...Medium
The low level thermal trough erodes during the afternoon with
surface/850 ridging taking hold. The GFS and GEM show building
heights with increasing 500 millibar ridging. The ECMWF hangs
on to more cyclonic flow a bit longer. Will go with the dry look
to the Superblend pops.
FRIDAY - Confidence...Medium
After a one day break the models are showing another mid level wave
approaching with the GFS and GEM being quicker than the ECMWF. The
surface low tracks near Lake Superior on the GFS/GEM and closer to
GRB on the ECMWF. The progs show a nice bump in the 850 temps ahead
of the low with the waa regime. So will stick with the Superblend
POPS which has shra chances with the waa and the trailing cold front
which arrives either late Friday or Friday night on the ECMWF.
SATURDAY - Confidence...Medium
Cold advection is proggd by both the GFS and ECMWF with the GFS
showing a colder solution with some 850 temps of -2c to -5c. The
ECMWF has 850 temps around 0c. the ECMWF shows a strip of light
qpf during the morning while the GFS is dry. There is an
elongated/sheared vort and caa in place so precip potential
looks quite small but will leave the slight pops for the morning
SUNDAY - Confidence...Medium
A surface high shifts to our east and sets up a mild return flow,
especially on the GFS which shows a decent westerly 850 waa pattern
that sends 850 temps towards 10c. However the ECMWF is less
pronounced with this and shows a little more vort action in the wnw
500 flow that results in some light qpf and a cooler thermal low
level profile, so will keep the small Superblend pops for now.
AVIATION/12Z TAFS/...Watching mainly VFR level stratocumulus deck
as it begins to shrink as it drops through southern Wisconsin.
Even if it holds together, it should clear south of the IL/WI
border by 1030 AM. Enough surface pressure gradient over the east
for a few gusts to 20 knots with morning mixing until gradient
relaxes mid-late morning as high pressure builds over the western
Great Lakes. Clear skies and light winds tonight with patchy
frost/fog but will leave TAF sites VFR through the period.
MARINE...Extended the Small Craft Advisory until 1 PM today as NNW
winds over the lake are still gusting to 22 to 25 knots and waves
at the mid- lake buoy are in the 5 to 6 foot range and the Wilmette
buoy still reporting 5 foot waves. Enough gradient over the lake
through mid morning to keep winds up a bit longer than earlier
expected and delay waves from subsiding below criteria until late
this morning/early this afternoon.
Another Small Craft Advisory will likely be needed for Tuesday night
into Wednesday night, as low pressure moves across the region. Gusty
winds and high waves are likely during this period.
LM...SMALL CRAFT ADVISORY until 1 PM CDT this afternoon for
TODAY/TONIGHT AND AVIATION/MARINE...REM
Tuesday THROUGH Sunday...Collar