Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 131454 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
954 AM CDT Fri Oct 13 2017

.UPDATE...

Latest short term models have sped up the arrival of showers this
afternoon, so made changes to the forecast accordingly.
Additionally, bumped chances up a bit now that models are in
decent agreement with areal coverage of showers. Left mention of
thunder in for part of the area given some instability could creep
north of the WI/IL border this afternoon. Given the earlier
arrival of rain...nudged temps down a little for the afternoon.

&&

.MARINE...

Small Craft Advisory conditions are likely by later Saturday,
persisting through the day Sunday. May even have a period of gale
force gusts from later Saturday night into Sunday. Winds will
become offshore Saturday night, limiting the highest waves toward
open waters for much of this wind event.

&&

.PREV DISCUSSION... (Issued 704 AM CDT Fri Oct 13 2017)

AVIATION(12Z TAFS)...

Look for mainly MVFR conditions across the area this morning with
some VFR CIGS west of Madison. Those VFR conditions may become
more dominant this morning, however, by mid to late afternoon,
rain will quickly spread from west to east, becoming widespread by
early evening, then diminishing after midnight. Look for CIGS to
begin lowering to IFR in the rainy conditions tonight. Winds will
generally be light, but will back from southerly today to east
then northeast tonight as a trough of low pressure moves through.

PREV DISCUSSION... (Issued 316 AM CDT Fri Oct 13 2017)

SHORT TERM...

Today and tonight...Forecast confidence is high.

No real changes needed from the previous forecast. A trough will
sag southeast into the area. We get into a decent surge of mostly
elevated warm and moist air advection this afternoon into tonight
across a tightening 850mb baroclinic zone with the nose of the
low level jet pointing into southern Wisconsin. Isentropically,
there is a very quick lowering of condensation pressure deficits
this afternoon. Other than some drizzle this morning, the rain
should stay away through early afternoon, then it pushes in
quickly from the west by mid to late afternoon. The rain will peak
during the evening with the isentropic lift/saturation then
diminishing suggesting a weakening trend after midnight. A rumble
of thunder can`t be ruled out mainly south of Milwaukee and
Madison, but the available CAPE is quite elevated.

Saturday... Forecast confidence is medium.

We might see a break in the rain until mid Saturday morning due
to a loss of the main upper forcing, but persistent drizzle and
low clouds is likely. Winds will be increasing out of the east,
but temperatures will remain on the mild side.

The right entrance region of the upper jet will slide into
southern WI on Sat as a mid level trough digs through the central
Rockies. The resultant surface low will slide northeast along the
850mb baroclinic zone and undergo cyclogenesis as it moves through
southern WI Saturday afternoon. The dynamics are very strong with
this system, and precipitable water values around 1.75 to 2
inches are very high for this time of year.

We will see thunderstorms Saturday, any early thunder would be
associated weak elevated instability, and the prime time period
is during the afternoon and evening when the nose of the very
strong low level jet impinges on southern WI and we get into the
warm sector of the system. SPC has southern WI in a marginal risk
for severe storms. Low and deep layer shear will be very strong,
but the moist profile will keep CAPE values low. We could see some
hail and damaging winds with any stronger cells.

Heavy rain is a concern and we issued an ESF to highlight it, in
addition to us being in a WPC slight risk area for Excessive
Rainfall. Despite the quick- moving system, Sat afternoon and
night should bring a swath of 1 to 2 inches through portions of
southern WI. This much rain in a short amount of time can lead to
river rises and ponding of water in fields and ditches. Urban
areas are especially prone to localized flooding if storm drains
become clogged with leaves.

The cold front is expected to move southeast through southern WI
between midnight and 3 am Saturday night. Dry air behind the
front will help us clear out the precip quickly.

LONG TERM...

Sunday...Forecast confidence is high.

Dry and cold air will briefly take hold of WI on Sunday. Diurnal
cumulus due to steep low level lapse rates will keep us mostly
cloudy for much of the day. Cold advection on brisk northwest
winds will keep highs limited in the lower 50s.

Clear skies Sunday night should allow temps to drop into the 30s
inland from the Lake, so there is potential for our first Frost of
the season.

Monday through Friday... Forecast confidence is high.

The pattern becomes more zonal for the first half of next week
which means more above normal temperatures and fairly dry weather.
Lower 70s are possible by Friday. Another low pressure system on
the horizon could give us a round of rain next weekend.

AVIATION(09Z TAFS)...

A mix of MVFR and IFR CIGS this morning should become
predominantly MVFR this afternoon. We may see some patchy drizzle
this morning, otherwise we will stay dry into the early
afternoon. By mid to late afternoon, rain will quickly spread from
west to east, becoming widespread by early evening, then
diminishing after midnight. Look for CIGS to begin lowering to IFR
in the rainy conditions tonight. Winds will generally be light,
but will back from southerly today to east then northeast tonight
as a trough of low pressure moves through.

MARINE...

Small craft advisory conditions are expected later Saturday night
into Sunday night on the backside of a low pressure system moving
through the region this weekend. We may see west to northwest
winds reach Gale Warning levels late Saturday night into Sunday
morning.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Update...DDV
Today/Tonight and Aviation/Marine...Davis
Saturday THROUGH Thursday...Cronce



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