369
FXUS63 KDTX 170407
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1207 AM EDT Mon Jun 17 2024

.KEY MESSAGES...

- An excessive heat watch remains in effect Monday afternoon through
  Friday evening. Several days of highs in the 90s are expected this
  week, with afternoon heat indices of 95 to 100.

- Nighttime lows will only drop into the 70s over most of the area
  this week.

- Scattered to numerous showers and thunderstorms tonight/Monday and
  Tuesday afternoon will bring potential of localized torrential
  rainfall.

&&

.AVIATION...

A large cluster of thunderstorms now represents both earlier surface
based activity plus new development farther west fed more by
nocturnal mechanisms. The parent MCV still makes storms possible
farther north toward MBS although radar trends at forecast issuance
clearly favor PTK and the DTW corridor for several hours of
borderline MVFR/IFR conditions depending on rainfall intensity.
Other observational trends will be monitored for signs of greater
coverage of ceiling or visibility restriction within the frontal
zone. The shower/storm pattern then moves eastward by late morning
and VFR cumulus follows within the inbound heat and humidity for the
afternoon. A stray pop-up shower or storm is possible in this air
mass but with predictability too low for a mention at this point in
the forecast.

For DTW/D21 Convection... The leading edge of thunderstorms inbound
from LAN to JXN weaken to lighter showers in favor of new storms
farther west. It is possible the later activity holds together for
scattered storm coverage across D21 and at DTW after 08Z until about
12Z. Localized heavy rainfall is the primary hazard with this
activity until moving east of D21 by late morning.

DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms at the terminal late tonight into early
  morning.

* Moderate for ceiling 5000 ft or less mainly with convection late
  tonight and early morning.

&&

.PREV DISCUSSION...
Issued at 943 PM EDT Sun Jun 16 2024

UPDATE...

Trends of showers and thunderstorms are highlights of the forecast
for SE MI as scattered to numerous coverage is on track late
tonight, mainly after 2 AM through the morning. Ongoing activity
over SW Lower MI has upstream MCS/MCV origins and is still surface
based and outflow driven. It begins to weaken and decrease coverage
while running out of instability, a trend strongly suggested by the
surface based CAPE gradient shown in hourly mesoanalysis. The
ongoing storms could also spur a transition to elevated convection
as the parent MCV and larger scale background low level jet become
the primary drivers of new convection after midnight. Confidence is
higher on an elevated transition or new development as HREF provides
a favorable look of near zero surface based CAPE by 09Z/5AM while
MUCAPE rises to around 1500 J/kg 09Z-12Z. Predictability is lower on
identification of favored areas of SE MI with just scattered to
numerous coverage expected areawide as mid level theta-e is fully
ridged ahead of the NW to SE extending surface warm front. Locally
heavy rainfall is the primary hazard as model sounding and HREF mean
PW reach the 1.5 to 2.0 inch range after 06Z. A precip loaded 40 mph
wind gust is also possible while high freezing level and low CAPE
density limit hail potential. The parent MCV and any remaining
nocturnal activity exit into Ontario by late morning leaving heat and
humidity to gain traction through Monday afternoon.

PREV DISCUSSION...
Issued at 250 PM EDT Sun Jun 16 2024

DISCUSSION...

No changes to excessive heat watch issued last night, but this
certainly looks like just heat advisory criteria for Monday/Tuesday.

Considerable uncertainty with just how hot we get and if dew pts can
reach and exceed 70 degrees for any sustained period to support
excessive heat warning criteria, although the cumulative days/effect
of heat indices near 100 degrees still may be enough for future
shifts to possibly issue a a excessive heat warning for urban areas
vs heat advisory.

Another uncertainty of the forecast is with the showers and
thunderstorm chances this evening through Tuesday, as there is a lot
of upper level PV filaments riding up through the Mississippi River
Valley, which will be tracking through southeast Michigan, as the
upper level ridge builds over the northern Appalachians early next
week.

Upward revisions for pops have been made for tonight and Monday, as
cams are in pretty good agreement with the upper level
disturbance/MCV which came out of the Kansas City area slowly
tracking through southern Lower Michigan tonight, with the
instability/cape gradient making inroads as moisture advection ramps
up. Mid level lapse rates start out steep, 7.5 C/KM, but would then
weaken as the batch of showers and thunderstorms and convective
latent heat release tracks through southeast Michigan. Still, will
carry just high chance pops due to exact location/coverage
uncertainty, with torrential rainfall and even hail possible
(MUcapes increasing to 1500-2000 J/kg), with another limited
convective flare-up possible Monday afternoon as well.

Trajectories then show a shortwave coming out of the eastern Gulf of
Mexico on track to move into southeast Michigan late Tuesday. With a
respectable 0-6KM bulk shear of 30+ knots tracking into/near western
Lake Erie, which, coupled with the potential moderate
instability/cape would be supportive of strong to isolated
marginally severe storms, if activity is able to initiate. Low level
convergence near the Land/Marine interface the likely locations
within the backdrop of the low level southwest flow. Slow movement
of storms/potential back building with PW values aoa 1.75 inches
will draw concern for urban flooding, but at least airmass is not
true tropical, with 700 MB dew pts only progged to be near 3 C. With
said ingredients, Tuesday afternoon looks to be another good shot
for scattered coverage of showers and thunderstorms (25-50%). As
usual with these unstable air-masses, once the first cell goes, an
outflow boundary is then usually sufficient to get additional
activity to fire up during the peak heating of the day.

Bottom-line, the prospects for convection to start the work week is
decent, which should have some impact on max temperatures, likely
capping maxes in the low to mid 90s.

500 MB heights building for Wednesday-Thursday as the upper level
ridge center over southern New England retrogrades to the west makes
for a higher confidence forecast in temperatures rising solidly into
the 90s. However, even then, still some convective schemes getting
triggered in this generally uncapped environment as the jet
stream/strong westerlies hang around the northern Great Lakes. So,
certainly a lot of more weather elements to focus in on over the
coming days than just the heat.

MARINE...

A warm and humid airmass will set up over the Great Lakes through
early tomorrow morning and will last through the end of the week.
This will produce relatively stable near surface lake conditions.
The passage of a warm front will produce isolated to scattered
showers and thunderstorms this afternoon and evening for portions of
Lake Huron and the Saginaw Bay. Some strong thunderstorm induced
wind gusts aoa 30 knots and/or hail cannot be ruled out with today`s
late day activity, favored across northern Lake Huron. Wind
direction will veer from the southeast to the southwest after the
passage of the front. Additional isolated to scattered shower and
storm chances will exist tomorrow morning over the Great Lakes as an
upper-level disturbance moves over the region and again in the
afternoon, with additional chances returning Tuesday.

HYDROLOGY...

A moist and unstable airmass arriving tonight and continuing through
Tuesday will bring the potential of a few rounds of showers and
thunderstorms. The coverage is expected to remain mainly scattered,
but locations which experience strong thunderstorms will have the
potential for rainfall amounts to exceed 2 inches in a short period
of time, leading to urban/low lying flooding. There is this low
flooding potential late tonight into Monday, and then again Tuesday
afternoon. Otherwise, most locations remain dry or will be lucky to
see a quick half an inch of rain.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...Excessive Heat Watch from Monday afternoon through Friday evening
     for MIZ047>049-053>055-060>063-068>070-075-076-082-083.

Lake Huron...None.

Lake St Clair...None.

Michigan waters of Lake Erie...None.

&&

$$

AVIATION.....BT
UPDATE.......BT
DISCUSSION...SF
MARINE.......AM
HYDROLOGY....SF


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