Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 230209
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
909 PM CDT Wed Mar 22 2017
...EVENING MARINE UPDATE...
The forecast is on track. See the previous evening update for
Brisk southerly winds and building waves are expected on Thursday
as the pressure gradient strengthens. A Small Craft Advisory is
in effect from Thursday morning through the evening hours.
.PREV DISCUSSION... (Issued 645 PM CDT Wed Mar 22 2017)
Mid-level ridge axis is to our west this evening, with warm
advection clouds bringing some light returns to area radars over
Minnesota and Iowa. Most of this precipitation isn`t reaching the
ground, owing to the very dry airmass in the lower levels. Area
forecast soundings suggest this dry layer remaining in place
around 850 mb, so feel comfortable keeping PoPs out of the
forecast for the evening. It`s not impossible we could see a few
flurries later tonight however.
Return flow sets up late tonight towards morning as surface high
pressure slides off to our east. Our coldest temperatures should
be realized early tonight, as warm advection and increased cloud
cover allow temperatures to hold steady or even rise a bit towards
Top down saturation is expected on Thursday, with rain chances
beginning during the afternoon to early evening hours. Models
still suggest around 200-300 Joules of MUCAPE available, so
isolated thunderstorms remain possible during the afternoon and
AVIATION (00Z TAFS)...
An area of mid-level clouds will move from west to east across
southern Wisconsin this evening. Prevailing ceilings should remain
above MVFR levels. While we are seeing some light precipitation
falling from these clouds over Minnesota and Iowa, most of this is
not reaching the ground due to very dry air in the low levels.
This trend should continue, with dry conditions this evening.
Ceilings will gradually lower during the day on Thursday, with
rain shower chances increasing during the late afternoon to
evening. Showers will continue on and off into the weekend. Low-
level wind shear is possible after 00Z on Friday as winds increase
around 2 kft.
PREV DISCUSSION... (Issued 336 PM CDT Wed Mar 22 2017)
TONIGHT AND THURSDAY...Forecast Confidence is high.
High pressure will gradually lose its grip on the region a cyclone
slowly develops in the lee of the Rockies. In the upper levels, a
large ridge will build in with a few embedded shortwaves passing
over the region on Thursday. Closer to the surface, the warm front
extending from the lee cyclone will reach well to the north of
southern WI, planting us firmly within an area of WAA. Mid clouds
within the WAA currently over MN/IA will continue to push east,
reaching southern WI this evening, with the lower levels gradually
saturating through the night and into tomorrow.
Good agreement that the lowest levels will not saturate until after
at least 18z Thursday, so pulled back on the PoPs tomorrow. Precip
will become more likely on Thursday afternoon as the lower levels
saturate. Most guidance does show at least some instability building
in tomorrow afternoon, so included a mention of thunder.
In the near term, do have some concerns regarding the isolated
showers embedded in the upstream clouds extending from NW MN into
north central IA. The echoes from these showers are more expansive
than what the meso models are showing, and based off of cigs within
the showers, it appears that moisture is extending lower than the
synoptic models would indicate. Fortunately, dewpoint depressions
over the area are currently around 20 degrees, and the southern end
of the showers does appear to be eroding as is pushes east.
Accordingly, will leave precip chances out of tonight`s forecast,
but they may need to be added later.
THURSDAY NIGHT THROUGH SUNDAY...Confidence remains high.
For Thursday night and Friday, a surface warm front will push to
just north of our forecast area Thursday night then stall
briefly...the h8 boundary will be over far northern Wisconsin on
Friday. So, the focus for the higher rainfall numbers will likely
be between these two features, or central Wisconsin. This will
also allow 925mb temps to max out around 10-13C across far
southern Wisconsin, potentially pushing surface temps into the
upper 60s. If we get any decent sunshine along the stateline, we
could even see a few 70s reported.
The front will then get suppressed south Friday night and Saturday
as building high pressure across southern Canada increases the
northeast winds over the western Great Lakes, bringing a surge of
colder air south (with a lot of help from the cold waters of Lake
Michigan and Superior).
As the surface front sags south into southern Wisconsin, so will
the focus for on and off showers. A deep, closed and stacked low
pressure system will track from Missouri Friday night, to northern
Indiana by Sunday night. That slow track will keep it wet across
the area into Sunday. These closed and occluded lows are very
unpredictable with respect to resolving the smaller scaled rain
bands that will rotate around it. Especially as the system weakens
late in the weekend and becomes wrapped with dry air. At this
point it`s best to only say it will be wet from time to time over
the Friday through Sunday time period. The higher chance for rain
is in the Friday night through Saturday period across southern
MONDAY...Forecast confidence is medium.
A second low pressure system will be following quickly on the
heals of the first one, but passing much farther south. At this
point it looks like we could have some isolated showers around,
but nothing really organized as drier air will be working in.
TUESDAY AND WEDNESDAY...Forecast confidence is medium.
High pressure should return this period providing dry conditions
with temps hovering close to normal for late March.
Cigs on lake effect clouds are gradually rising while the spatial
extent of the clouds is quickly diminishing. Clouds should mostly
clear out in the next few hours. MVFR cigs might hold out for
another hour in MKE, but given the current trends, think either
skies will scatter or cigs will make it above 3kft very soon.
Another round of mid clouds will move in this evening ahead an
approaching low pressure system. Cigs will stay above MVFR for
this period, but will fall once the low gets closer and rain
moves in to the west on Thursday afternoon and across the rest of
the area in the evening.
Southerly winds will pick up tomorrow as high pressure moves to the
east of the area and low pressure develops to our west. It is
probable that winds and waves will reach the low end of SCA criteria
tomorrow morning, so have hoisted a SCA beginning tomorrow
morning and lasting into tomorrow evening.
LM...Small Craft Advisory from 10 AM to 7 PM CDT Thursday for LMZ645-
Small Craft Advisory from 10 AM Thursday to 1 AM CDT Friday for
Tonight/Thursday and Aviation/Marine...BSH
Thursday Night through Wednesday...Davis