NWS Forecast Discussion
FXUS63 KDTX 201105
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
705 AM EDT Sat Jul 20 2019
Chaotic cigs within a field of convective remnants will nonetheless
be VFR and tend to thin through the first half of the day. Trailing
outflow extending back to Minnesota will provide the focus for
renewed convective development this afternoon and/or a boundary
along which the developing convection in South Dakota can track east
into the area. One way or another, confidence is high enough to
warrant a TEMPO for tstorms at all sites by 21z. Prevailing
southwest flow, gusty at times today, will weaken veer to WNW
.DTW THRESHOLD PROBABILITIES...
* Low for a cig aob 5kft early in the period.
* High for tstorms in KDTW airspace after 22z.
Issued at 435 AM EDT Sat Jul 20 2019
Heat and humidity peak today with another round of high temperatures
in the mid to upper 90s while dewpoint holds or returns to the mid
and upper 70s. The Excessive Heat Warning remains in effect. The
plan for the Tri Cities and northern Thumb is to maintain the heat
advisory as clouds and outflow from the early morning MCS remnants
have a greater and more prolonged cooling impact compared to points
south. The area does have potential to rebound back to near heat
warning criteria during the afternoon as convective outflow washes
out and larger scale SW wind restores hot and humid air to all of
The potential for the heat warning/advisory to be extended into
tonight hinges on the coverage and duration of thunderstorms during
this afternoon and evening. The early morning MCS remnants continue
to dissipate through sunrise leaving stable conditions across the
region for the rest of the morning. The general thunderstorm
scenario is then for redevelopment during the afternoon and involves
the outflow from the early morning MCS, the cold front across the
northern Great Lakes and Midwest, and the upstream MCS moving across
the northern Plains and upper Midwest. Expect the first storms of
the day to initiate near the I-69 corridor around mid afternoon.
This is where the remnant outflow/differential heating boundary is
likely to maintain some character and closer to the edge of the mid
level thermal ridge/cap. The profile of temperatures aloft remains
very warm, warmer than the customary 20C 850 mb and 10C 700 mb
capping temperatures which have been unreliable due to the
exceptionally high surface dewpoint and boundary layer moisture
depth. This is expected to continue today and result in 0-1 km
MLCAPE well into the 2000 J/kg range. This with a wind shear profile
on the weaker side compared to points north but still adequate for
at least multicell organization. The stronger wind profile and
larger scale support to the north and west along the cold front
helps sustain the Plains MCS into the Midwest where it becomes
surface based during the afternoon with a chance to migrate into
Lower Michigan along the instability axis tonight. Likely/numerous
POPs are warranted for the coverage anticipated by both components
of storm potential today. The SPC slight risk encompasses most of SE
Michigan for the primary hazard of damaging wind.
The combination of aggregate storm outflow and larger scale forcing
take the cold front very near the Michigan border tonight with some
residual showers and storms possible Sunday. Humidity lingers but
temperatures in the 80s result in heat index "only" in the 90s
Sunday afternoon. Even cooler and less humid conditions remain on
track to arrive with high pressure by Monday which last through mid
The primary concern through Sunday continues to be thunderstorm
potential over the waters. Overlake stability limits overall
potential but intense lightning, severe wind, and small hail will
remain threats through this time, particularly for nearshore areas.
Building high pressure will usher the resident unstable south
bringing an end to the thunderstorm threat for the first half of
Moist airmass characterized by PWAT values in excess of 2 inches
remains in place through today. Thunderstorm potential is similar to
yesterday in that there will be an opportunity for both local
convection as well as an upstream complex propagating into the area
from the west. Any back building or training thunderstorms will be
capable of producing several inches of rain in a short period
resulting in urban and small stream flooding or flash flooding.
MI...Heat Advisory until 8 PM EDT this evening for MIZ047>049-053>055.
Excessive Heat Warning until 8 PM EDT this evening for MIZ060>063-
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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NWS DTX Office Area Forecast Discussion