Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 191559 AAA
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1059 AM CDT TUE JUL 19 2016
Latest ESRL/HRRR run seems to have a decent handle on convection
in central Iowa at this time. This model, along with most other
mesoscale models, weaken the current convection as it shifts east.
More then develops as the whole area shifts to the southeast this
afternoon. This activity may clip the far southwestern counties
late this afternoon and early this evening, but most of the area
should be dry. This track makes sense with the expected mid level
flow and where the best moisture and instability reside.
May add more clouds into the western counties, where cirrus
blowoff from the convection in Iowa is moving through. May see few
to scattered diurnal cumulus development inland this afternoon as
well. Temperatures may need a small increase this afternoon, but
overall appear reasonable in the middle 80s inland. Easterly winds
will keep lakeshore areas in the 70s to around 80.
POP trends look reasonable at this time for tonight into
Wednesday. The best forcing for upward vertical motion will be
focused along the Mississippi River area to the northwest of the
forecast area later tonight into early Wednesday morning.
This is where the convection should move from, and slide
southeast through at least western portions of the area Wednesday
morning into the afternoon. Eastern areas may have a slightly
smaller chance, but there is uncertainty with the timing and areal
coverage of any storms at this time. Latest mesoscale model runs
suggest parts or most of Wednesday may end up dry.
Left likely POPs as is for now. Heavy rainfall is possible with
high precipitable water values and somewhat slow storm motions. We
can certainly use some rain across the area, especially in the
Expect VFR conditions for this afternoon into this evening at TAF
sites. Light easterly winds are expected this afternoon, shifting
south tonight into Wednesday. May see light fog form later tonight
into Wednesday morning, with a more humid airmass moving into the
An area of thunderstorms should move through the area Wednesday.
There is some uncertainty if and when the storms will affect TAF
sites. Madison has the best shot during the morning hours, with
the eastern sites later in the morning and into the afternoon.
Will use vicinity thunder in TAFs for now, until better confidence
on timing and areal coverage is found. MVFR/IFR ceilings and
visibilities are possible in any storms.
Light easterly winds and low waves are expected this afternoon
across the nearshore waters. Light winds will shift south tonight
and remain so on Wednesday. Waves should remain low.
There should be an area of thunderstorms that moves through the
area Wednesday. There is some uncertainty if and when the storms
will reach the nearshore waters, but will continue the likely
thunder mention in the forecast for now for Wednesday. Any storms
would produce gusty winds and locally high waves.
.PREV DISCUSSION... /Issued 333 AM CDT TUE JUL 19 2016/
TODAY AND TONIGHT...Forecast confidence is medium.
High pressure will move from the nrn Great Lakes to the ern Great
Lakes through the period. A shortwave trough currently over wrn NE
will track across SD today and reach wrn WI by 12z Tue. Ahead of the
shortwave trough, a warm advection will pattern will gradually shift
ewd across IA and MN today and move into the western half of WI
through the night as the LLJ veers into the state. MLCAPEs reach
slightly higher than 1000 joules west of Madison by late today with
MUCAPEs tonight around the same values. Have slight chances of
thunder this afternoon well west of Madison and then gradually
spread the PoPs ewd through the night with likely PoPs from Madison
wwd between 09z and 12z. PWs rise to 1.75 inches over south central
WI and storm motion will fall to 15 kts during this time so heavy
rainfall is possible. High temps today will be similar to yesterday
but cooler near the lake due to an earlier lake breeze. Low temps
tnt from mid 60s to near 70.
Models continue to come into better agreement that it will be a wet
day on Wednesday. A shortwave will be moving through an increasingly
moist and unstable airmass, with low/mid level warm advection and
upper divergence adding to the overall lift. Storms may be ongoing
in the west at daybreak, with periods of storms likely through much
of the day as the wave slowly moves through. With precipitable water
values of around 2 inches per the GFS and NAM, locally heavy
rainfall is certainly possible. Could see a few strong to severe
storms given 0-6 km bulk shear of 35-45 knots and increasing mixed
layer cape from the west. New SPC Day 2 Convective Outlook has
maintained a Marginal Risk for severe storms across the forecast
Bumped high temps down a bit given the increasing confidence in
precip and cloud cover much of the day.
THURSDAY AND FRIDAY...Forecast Confidence...Medium
The main story for late in the week remains the expected hot and
humid conditions. Southerly low level flow ahead of an approaching
trough will likely push temps and dewpoints high enough Thursday for
heat indices of 100 to 110. Still expecting the lower values to be
in the northeast, where there will be a chance for storms in the
afternoon. Additionally, winds may be southeast for a time near the
lake in the northeast CWA, bringing in some cooler temps.
There is now less certainty with temps and heat indices Friday, as
models have sped up the trough passage. Temps will still be above
normal, though it`s looking like they won`t be as hot as previously
expected. Also, could see somewhat lower dewpoints behind the
departing trough and surface front. With the adjustments to
temps/dewpoints, new forecast heat indices are in the 95 to 103
range most places. These could be on the warm side given the ECMWF
temps and dewpoints. Now looks like onshore winds near the lake, so
biggest drop in heat indices from previous forecast is in the east.
Given the expected hot conditions Thursday and the new uncertainty
with Friday, decided to just keep the Excessive Heat Watch as is for
SATURDAY THROUGH MONDAY...Forecast Confidence...Medium
Kept chances for storms going for the weekend, as another trough
approaches, eventually moving through by Sunday afternoon. Above
normal temps will likely persist Saturday, cooling back toward
Have some low pops Monday per the ECMWF dropping another wave
through. The GFS has high pressure overhead though, so pretty low
confidence in these pops. Should see temps right around normal
AVIATION/00Z TAFS/...VFR conditions today and into the evening.
KMSN may then see tstorms toward sunrise on Wed. Cig and vsby
restrictions are expected with the pcpn. Patchy light fog may also be
possible late tnt due to the arrival of a humid airmass.
Light nly winds this morning will veer ely by afternoon, then veer
sly tonight into Wed. Wave heights will remain relatively low.
WI...EXCESSIVE HEAT WATCH from Thursday afternoon through Friday
evening for WIZ046-047-056>058-062>072.
TODAY/TONIGHT AND AVIATION/MARINE...Gehring
Wednesday THROUGH Monday...DDV