Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 291139
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
639 AM CDT Sat Apr 29 2017

.UPDATE...


&&

.AVIATION(12Z TAFS)...

VFR conditions this morning with mainly mid level clouds south and
high clouds north. CIGS will lower this afternoon as more rain
moves in from the south. MVFR CIGS toward evening, then IFR CIGS
and VSBYS tonight with rain. A few thunderstorms possible toward
sunrise Sunday far southeast as a warm front pushes across central
Illinois, then into northern illinois Sunday afternoon. Persistent
brisk northeast to east winds across southern Wisconsin.

&&

.PREV DISCUSSION... (Issued 251 AM CDT Sat Apr 29 2017)

TODAY AND TONIGHT...Forecast Confidence Is High.

Expect a brief lull in the rain this morning. Then a long period
of rain will begin this afternoon.

A large trough extends across the Rockies, which will strengthen
today as is moves east into southern and central Plains. A strong
jet across the Great lakes will lift a little north, as a jet max
rounds the base of the trough across western Texas. Upper
divergence and 700 mb upward motion increases across southern
Wisconsin today, and remains quite strong this afternoon and
tonight.

A 700 mb 50 knot jet max lifts north into southern and especially
southeast Wisconsin this evening. This lifts the 700 mb warm
front north and will reach into southern Wisconsin, bringing in
more moisture and ample lift to compliment the upper level
forcing. This will kick off an extended period of rainfall, as
the surface low lifts northeast into eastern Kansas tonight,
bringing a strong warm front across central illinois.

Precipitable water values will have increased to around 1.00 inch
today, and near 1.30 inches tonight.

Elevated instability looks minimal, so wl hold off on any
thunder, until early morning Sunday in the far southeast, as the
850 mb warm front approaches from the south.

SUNDAY THROUGH MONDAY NIGHT...Forecast Confidence Is High.

Main issue this period will be continued chances for heavy
rainfall and areal/river flooding. It appears that the models are
showing strong upward vertical motion fields Sunday into Sunday
evening. This is with strong low level frontogenesis response
fields across the area Sunday, with 850 mb convergence and the
nose of the 850 mb jet into the area.

Area forecast soundings are quite moist through the air column
during this time, with elevated CAPE of a few hundred J/kg on the
NAM, a little less on the GFS. Kept the high PoPs for Sunday into
Sunday evening, and increased the thunder chances somewhat.

Good amounts of QPF are forecast to occur in the area Sunday into
Sunday evening, highest in the southeast counties. Amounts of
1.00 inch in the northwest counties, to 2.50 inches in the
southeast counties, are forecast for Sunday into Sunday evening.

Precipitable water values rise into the 1.50 to 1.65 inch range by
early Sunday evening, which is at the top end of climatology for
this time of year. CIPS analogs also show a 1.5 sigma value for
precipitable water at 00z Monday, supportive of the heavier QPF
values. This rainfall may cause more of the area rivers to rise,
which may result in those rivers reaching minor flood stage. Will
continue to monitor this period for possible areal flood watches
in later forecasts, if the models stay consistent with the QPF
values.

The low and associated closed 500 mb low become nearly vertically
stacked later Sunday night into Monday, as they slowly shift
northeast into the region. The cold front moves northeast through
the area later Sunday night, as the low occludes to the west. Cold
air advection on gusty winds develops later Sunday night into
Monday morning, with the gusty winds lingering into Monday night.

It still looks like showers will occur later Sunday night into
Monday, but QPF values will be much lower. The shower activity
should slowly weaken into Monday night, as the system moves out of
the region. May see a few flakes mix in as the rain showers taper
off Monday night, with the colder airmass moving into the area.

TUESDAY THROUGH FRIDAY...Forecast Confidence Is Medium.

Models in this period are showing high pressure moving across the
region Tuesday into Wednesday, as low pressure remains to the
south of the area. This should bring a period of dry conditions
to the area, though low clouds may linger Tuesday before
scattering out Tuesday night into Wednesday. Temperatures will
remain below seasonal normals during this period, warming somewhat
on Wednesday.

GFS was trying to show light QPF with a passing 500 mb shortwave
trough Wednesday night into Thursday in parts of the northern and
western counties. The ECMWF is well to the northwest with these
features, and the Canadian is somewhere in the middle of these two
models. They then differ somewhat with features into Friday. Thus,
will lean toward consensus blend of models for temperatures and
PoPs for later in the week. Temperatures may return more toward
seasonal normals by later in the week.

AVIATION(06Z TAFS)...

Rain is all but gone at this point, with just a little drizzle or
light rain hanging on in the northeast. Mainly dry weather is
thus expected for the rest of the night, with more rain moving in
later Sat morning into the afternoon.

Some lower ceilings continue to push in from the south. These are
expected to hang on across mainly the southern half of the
forecast area through at least early tonight, with ceilings
returning to VFR by early morning. More low clouds are likely to
return from the south by later Sat afternoon with the next batch
of rainfall.

MARINE...

A long duration of Northeast to east winds will create high waves
through Sunday. A Small Craft Advisory is in effect until
afternoon, with a Gale Warning from late afternoon into tonight.
A strong low will then track across central Wisconsin, with
strong southwest to west winds behind an occluded front Sunday
night into Monday. A period of gale force winds after this front
is also possible.

HYDROLOGY...

Precipitable water values rise into the 1.50 to 1.65 inch range
by early Sunday evening, which is at the top end of climatology
for this time of year. CIPS analogs also show a 1.5 sigma value
for precipitable water at 00z Monday, supportive of the heavier
QPF values during this time.

Total rainfall of 1.50 inches northwest, to nearly 3.50 inches
southeast, are forecast from tonight into Monday night, with most
of it falling tonight into Sunday evening. This rain would cause
more of the area rivers to rise, which may result in several
rivers reaching minor flood stage. Will continue to monitor this
period for possible areal flood watches in later forecasts, if the
models stay consistent with the QPF values.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 4 PM CDT this afternoon for
     LMZ643>646.

     Gale Warning from 4 PM this afternoon to 4 AM CDT Sunday for
     LMZ643>646.

&&

$$

Update...Hentz
Today/Tonight and Aviation/Marine...Hentz
Sunday THROUGH Friday...Wood



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