Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 270842
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
342 AM CDT Thu Jun 27 2019

.SHORT TERM...

Today And Tonight...Forecast Confidence Is Medium.

Main issue during this period will be thunderstorm chances and
severe potential for this afternoon into this evening.

Area of thunderstorms now over the Dakotas, associated with an MCV
and low level jet nose, is shown by most Convective Allowing
Models to push eastward into central Minnesota by early this
afternoon, following the MCV/low level jet nose and north of the
surface warm front. This activity may then intensify, or new
convection may develop, as it shifts more southeastward following
the Corfidi Vectors toward the area during the middle to late
afternoon. This would be in response to fairly robust mean layer
CAPE of around 2000 J/kg with varying magnitudes of deep layer
bulk shear.

This activity may then move through the area during the late
afternoon and evening, with more development possible near the
warm front and low level jet nose, which would be close to the
area. The CAMs are still varying with the timing, placement and
intensity of the convection later this afternoon through tonight,
so there remains some uncertainty with how things will evolve.

SPC is concerned about damaging winds with a potential line of
storms moving southeast through the area later this afternoon and
evening, given the amount of mean layer CAPE and enough deep layer
bulk shear. Think the slight risk for the area is reasonable.
Large hail is also possible with the amount of instability
available.

For now, kept higher end chance PoPs for the area for later this
afternoon into tonight, from west to east across the area. More
refinement of PoPs can be made once trends become more clear later
today.

It should be a rather warm and humid day, with highs possibly
reaching into the upper 80s inland. Cirrus from convection
upstream moving into the area may limit this potential somewhat.
Heat index values may push into the middle 90s if upper 80s are
reached for highs today. Depending on how much rain occurs during
this period, some fog may develop later tonight, but left out of
forecast for now.

.LONG TERM...

Friday through Friday Night...Forecast Confidence is Low to
Medium.

The uncertainty in this period is associated with the convection
that will occur today and where any resulting outflow boundaries
end up. Considering that models are struggling to handle the
current ongoing complex of storms, the forecast for Friday should
be met with some caution. Unlike today we won`t have any strong
synoptic forcing to trigger widespread convection. The lift will
likely be tied to WAA, diurnal heating, and any lingering outflow
boundaries present over the area. So, with that in mind have kept
chance PoPs in the forecast. Steep lapse rates aloft and a warm
and humid airmass will keep CAPE values between 3,000 to 4,000
J/kg for Friday. Upper level winds will be around 20kts or less so
slower storm motions could lead to very intense rainfall rates.
Damaging winds and large hail will also be possible with any
storms. Highs in the mid to upper 80s are expected and the humid
airmass will result in heat index values in the 90s.

Saturday through Wednesday...Forecast Confidence is Medium.

The upper level ridge to our west begins to shift east during this
period and with increasing subsidence and heights aloft expect
temperatures to warm a few more degrees over the weekend. Models
have been hit or miss in trying to show convection developing over
the weekend but given the warmer temps it`s possible that we could
see the capping inversion give way to a few storms each day. High
temps for both Saturday and Sunday could top 90 degrees for many
of our western locations. Couple those values with dewpoints in
the 60s to 70 degrees and Heat Indices could reach into the upper
90s.

Sunday night into Monday models have all been consistent in
showing the ridge weakening and pushing south in response to a
system moving out of the Dakotas and into the Great Lakes. It`s
possible that this feature will trigger an MCS that could dive
into the area late Sunday night.

The upper level ridge shifts even further south on Monday towards
the TN Valley. This will put us in a favorable pattern from Monday
through Wednesday for shortwaves riding the northern periphery of
the ridge into the area. We`ll maintain the south to southwesterly
surface winds which will keep the warm and humid airmass in place
for much of next week. There are chances for thunderstorms each
day next week.

&&

.AVIATION(09Z TAF UPDATES)...

VFR conditions are expected into this morning across the area.
Some high clouds will continue to rotate northeast through the
area into this morning. Winds will become southeast this morning,
becoming south in the afternoon inland and remaining southeast
closer to the lake. Some gusts to 18 knots or so may occur this
afternoon. Some diurnal cumulus is expected to develop as well.

Thunderstorms are expected to approach and possibly move through
the area from the west northwest by middle to late afternoon into
this evening. However, the exact track and timing remain in
question. For now, indicated VCTS during the latter portion of the
afternoon and evening, just to account for this possibility.
Exact timing and impacts will be further refined in later
forecasts.

&&

.MARINE...

Winds should be southeast to south today, becoming south tonight
and lingering into Friday across the lake. After light winds on
Saturday, south to southwest winds should develop for Sunday into
Monday. The strong inversion over the lake with the cool water
temperatures should limit any potential wind gusts above 20 knots
from mixing downward tonight into Friday. Waves should remain low
during this period.

There is the possibility of rounds of showers and thunderstorms
moving across the lake at times from later this afternoon into the
upcoming weekend. Strong storms are possible later this afternoon
into Friday, especially over the southern 2/3 of the lake. Locally
higher winds and waves are possible with any thunderstorms.

&&

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

$$

Today/Tonight and Aviation/Marine...Wood
Friday through Wednesday...Stumpf



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