236
FXUS63 KDTX 161850
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
250 PM EDT Sun Jun 16 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 showers and thunderstorms tonight/Monday and Tuesday
  afternoon will bring potential of localized torrential rainfall.

&&

.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.

&&

.PREV DISCUSSION...
Issued at 109 PM EDT Sun Jun 16 2024

AVIATION...

VFR conditions hold today into tonight within ridging with initial
cluster of showers/thunderstorms over Lake Michigan bypassing the
region to the north/northwest this evening (relatively close call
for KMBS though). Will introduce prob30/tempo groups for early Mon
morning thunderstorm as 12z model suite has latched on to solution
which will bring small MCS/cluster of convection into the area. The
mesoscale system bringing this activity is currently tracking thru
SE IA/NE MO with active convection early this afternoon. A veering
LLJ of 30+ knots will usher in much higher theta-e air overnight
into Monday and this should allow for this system to fester all the
way east into the area before dissipating by mid morning as LLJ
forcing wanes during diurnal convection min.

For DTW/D21 Convection...A small cluster of thunderstorms will be
possible early Monday morning (first guess 10z-13z). With a rapid
increase in moisture during this period, localized downpours could
be quite heavy within certain pockets of this cluster.

DTW THRESHOLD PROBABILITIES...

* Low for thundestorms impacting the terminal ~10z-13z.

* Low for ceilings aob 5kft with convection Monday morning.


&&

.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.
&&

$$

DISCUSSION...SF
MARINE.......AM
HYDROLOGY....SF
AVIATION.....DG


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