Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
000
FXUS63 KMKX 240321
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1021 PM CDT MON MAY 23 2016

.UPDATE...The weak upper wave over E IA will track north into
NW WI by 12z Tue, while the axis of a swly 25-30 kt LLJ shifts
eastward into S WI. The eastern extent of the very marginal
elevated CAPE will only extend across SW WI during this time. With
weak lift and lack of appreciable CAPE, removed thunder mention
until Tue afternoon when sfc based instability builds. At that
time however, the weak upper wave will be to the north but with
another stronger shortwave trough following it over N MN and Upper
MI. A tail of PVA will extend south into S WI for the afternoon.
In addition, a lake breeze may develop at the shoreline but stay
there given the swly sfc flow. Thus went with chance PoPs for
thunderstorms during the afternoon with only little capping
present. The chances of tstorms will continue Tue night as a cold
front approaches late from the north.


&&

.AVIATION/06Z TAFS/...VFR conditions forecast from early Tue
morning into Tue night with the exception of near or in
thunderstorms. Sct-bkn050 is expected Tue into Tue night with
isold to sct tstorms. Sct tstorms are associated with a return of
humid and unstable air followed by a cold front late Tue night.


&&

.MARINE...Winds and waves will remain on the low side however sly
winds will veer to the nnely for late tonight, then ely for Wed.
A humid airmass flowing over the cold waters of Lake MI may lead
to fog formation tnt-Wed and possibly longer.


&&

.PREV DISCUSSION... /Issued 325 PM CDT MON MAY 23 2016/

SHORT TERM...

TONIGHT AND TUESDAY...Forecast confidence is medium.

Thunderstorms developed in a line from southeast MN to central IA to
NW MO this afternoon. They developed along the leading edge of a mid
level shortwave, in the right entrance region of the upper jet, and
on the nose of a weak low level jet (LLJ). These showers and storms
will diminish as they move east this evening since they will be
encountering drier air and a lingering surface ridge that is
currently over southern WI. The better shortwave energy will track
northeast through northern WI overnight. Thus, there is a chance for
showers and maybe a few thunderstorms to track across southern WI
after midnight through mid Tue morning, but these will be weak,
elevated, and not severe.

Wherever these showers/storms dissipate may play a role in
initiating convection again Tuesday afternoon. The other factor that
will influence thunderstorm development is another weak shortwave or
remnant MCV tracking through the IA/southern WI/northern IL area.
Models vary in the strength of this disturbance.  A couple of the
meso models show scattered thunderstorms developing along a line
through south central wi Tue afternoon.

The moisture and instability will be sufficient for thunderstorms.
Dewpoints have a decent chance of getting up to around 60. Model
soundings are showing tall skinny CAPE of less than 1000 j/kg with
around 20 knots of shear. The big question is the lifting mechanism.
Any forcing that triggers tstorms will be subtle. SPC kept southern
WI in the Marginal risk for severe weather which seems reasonable.
If stronger cells can develop, small hail is the main risk.

TUESDAY night AND WEDNESDAY...Forecast Confidence...Medium

The southwest mid/upper level flow becomes a little more zonal
Tuesday night as a 90 knot 250 mb speed max moves across the
Upper Great Lakes and the remnants of the ridge across the Ohio
River Valley. By Wednesday the ridge builds back into southeast
Wisconsin as a large trough digs into the southwest u.s. upper
level divergence increases tuesday night and continues Wednesday.
weak 700 mb upward motion begins Tuesday night and increases
Wednesday. as a southwest flow resumes at 850 mb, the 850/700 mb
temperatures and dew points increase Wednesday, especially over
the southwest half of the forecast area with the 850 mb warm front
lifting to the north.

The GFS is now dropping a surface boundary to the south by
sunrise Wednesday. the boundary then pushes north across much of
southern Wisconsin Wednesday. The Nam is similar, but the 00z
ECMWF keeps the surface boundary still across Northern Illinois.

The GFS pushes showers and thunderstorms back into much of
southern Wisconsin late Tuesday night and Wednesday morning,
while the slower 00Z ECMWF delays this until Wednesday afternoon.

The GFS forecast sounding at the Sullivan Forecast office has
zero to 1 km cape values increasing to 1500 joules/kg during the
afternoon, with little in the way of a cap. The severe parameters
do manage to get into the Severe category, and with a more
favorable shear profile exhibit some tornado potential. However
the 00Z ECMWF surface boundary remaining to the south would limit
the severe potential. The severe parameter CWASP increases to
around 75 on the GFS, and around 70 on the ECMWF.

Wednesday night and Thursday...Forecast Confidence...Medium

A southwest upper flow increases across southern Wisconsin ahead
of the main trough over the Rockies. The upper divergence weakens
late Wednesday night, but weak to moderate 700 mb upward motion
continues. The 700 mb rh is rather low, but is rather high at 850
mb and below with dew points rising into the lower 70s Wednesday.

The GFS tries has the warm front across central Wisconsin. The
ECMWF has as more diffuse pressure pattern with the trough and
frontal boundary.

The GFS forecast sounding at the Sullivan Forecast office has
zero to 1 km cape values increasing to 3300 joules/kg during the
afternoon, but has a rather strong cap just above 850 mb. The
severe parameters are well into the Severe category, with a
somewhat favorable shear profile for a tornado potential. The
severe parameter CWASP increases to around 72 on the GFS, and 68
on the ECMWF.

The severe weather potential will be determined to a large extent
on the placement of the surface boundary, which is difficult since
prior convective activity will place a role.

LONG TERM...

 thursday night and Friday...Forecast Confidence...Medium

Both the GFS and ECMWF now exits the upper trough over the
southern rockies and moves it into the Central Plains with a
continued southwest upper flow into southern Wisconsin. Both
models bring a weak subtle shortwave across Friday.

The GFS brings showers and thunderstorms into the forecast area
Thursday night into Friday, while the ECMWF is a little slower and
still has the main warm front near the Wisconsin/Illinois border.

With a more southwest return flow the severe parameter CWASP
increases to around 73 on the GFS, and 68 on the ECMWF.

Saturday through Monday...Forecast Confidence...Medium

The shortwave lifts northeast into the upper Mississippi Valley
Saturday and either into south central canada or across the Upper
Great Lakes Monday.

The surface low stays just west as it lifts across the plains and
towards Minnesota or northern Wisconsin Sunday. Both models bring
mainly moderate precipitation Saturday, then tries to dry things
out a little Sunday night and Monday.

AVIATION/00Z TAFS/...

VFR conditions are expected through much of the TAF period.
Thunderstorms over southeast MN and central IA this afternoon will
be decaying as they reach south central WI overnight. Therefore,
there is a chance of showers and a small chance for thunderstorms
at KMSN after about 5 am Tue, and perhaps KMKE/KUES/KENW through 9
am Tue. Brief MVFR conditions could accompany any rain that moves
in.

An additional round of stronger showers and thunderstorms is
possible Tuesday afternoon which would last into the evening.

MARINE...

South to southeast winds will remain steady through Tuesday
afternoon. Winds and waves are expected to remain below small craft
advisory levels through the week.  As a more humid airmass
approaches the area by Tuesday afternoon, we could see areas of fog
out over the cool Lake Michigan waters from time to time this week.

&&

.MKX Watches/Warnings/Advisories...
WI...None.
LM...None.
&&

$$

UPDATE...Gehring
TONIGHT/Tuesday AND AVIATION/MARINE...MRC
Tuesday NIGHT THROUGH Monday...Hentz



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.