955
FXUS63 KDTX 160725
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
325 AM EDT Sun Jun 16 2024

.KEY MESSAGES...

- An excessive heat watch is 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 possible.

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

- Isolated showers and thunderstorms are possible Monday, with
  scattered showers and thunderstorms on Tuesay.

&&

.DISCUSSION...

A mid level short wave impulse over Iowa will track across Upper
Michigan and eastern Lake Superior this afternoon and evening. CAMs
solutions indicate the southern portion of the associated region of
convection will generally weaken/fall apart as it approaches central
Lower Mi this afternoon as a result of the dry and stable airmass
entrenched across Se Mi. Veering of the low level flow toward the
south-southeast today will advect much warmer air into Se Mi (925mb
temps pushing +22C). While large scale subsidence may limit mixing
depths to a degree, model soundings and probabilistic guidance
supports afternoon highs in the mid to possibly upper 80s, with
cooler readings near the lakes.

The forecast for the remainder of the week will revolve around the
development of an abnormally strong mid level ridge (heat dome)
across the Mid Atlantic and Ohio Valley and the resulting heat wave
that is expected to affect southeast Michigan. The expansion and
strengthening of this ridge will begin tonight and persist into
midweek. Increasing southerly flow circulating around this ridge
will drive very warm air into Se Mi by Monday. The lead edge of
higher mid level moisture will expand across Se Mi tonight. Despite
steep mid level lapse rates arriving in tandem with this moisture
plume, model soundings indicate the moisture capped by a warm layer.
This will limit convective chances to isolated. Growth of the
daytime mixed layer on Monday will drive afternoon highs into the
mid to possibly upper 90s under continued low level warm air
advection. Model soundings suggest the low level moisture will be
shallow, which will allow some drying of the boundary layer through
diurnal mixing. This should keep heat indices relatively close to
actual air temperatures. There has been some degree of model
agreement in suggesting some short wave impulses lifting into Se Mi
within a plume of deeper moisture Tuesday/Tuesday night. This will
warrant a chance of thunderstorms. The GFS ensemble members have
been a little more bullish with moisture, resulting in greater
convective coverage and thus a little cooler daytime highs (upper
80s to mid 90s). With a little higher sfc dewpoints, afternoon heat
indices will likely rise well into the 90s, pending timing/coverage
of any convection.

By midweek, medium range model solutions show 500mb heights to be an
anomalously high 598-600 dm centered over the Mid Atlantic. This ridge
is forecast to undergo some westward expansion across the Ohio
Valley from mid week into next weekend. Subtle placement differences
in the ridge axis and southward extend of the baroclinic zone
forecast across the northern Great Lakes will have some impact on
high temperatures across southern Michigan. The GFS and its ensemble
members have been a little farther south with the ridge axis with
greater convective chances over southern Michigan, thus a little
cooler. The ECMWF and Canadian solutions have been farther north and
warmer across Se Mi. In fact, several ECMWF solutions have extreme
heat persisting into next weekend. Based on the latest array of
ensemble members and trends in the 00Z model suite, there is enough
confidence in a prolonged period of heat to issue an excessive heat
watch for all of Southeast Michigan through Friday. This watch will
be issued for the cumulative effects of multiple days of high
temperatures in the 90s and warm nighttime conditions as opposed to
a specific day or two when heat indices may break 100.

&&

.MARINE...

A warm and humid airmass will set up over the Great Lakes today
through early tomorrow morning and will last through the end of the
week. This will produce relatively stable near surface lake
conditions. Showers and thunderstorms remain possible today, focused
mainly across northern Lake Huron initially through this morning,
with a second round possible this afternoon and evening for all 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. This stronger storm potential will be favored
across northern Lake Huron. Additional isolated to scattered shower
and storm chances will exist tomorrow and Tuesday over the Great
Lakes as an upper-level disturbance moves over the region.

Otherwise, south to southwest flow will become established through
early next week after the passage of the warm front. Some breezy
conditions with gusts to 20-25 knots will be likely today as flow
transitions from southeast to south-southwest, but otherwise gusts
stay around or below 20 knots through the early week with the stable
conditions in place.

&&

.PREV DISCUSSION...
Issued at 1153 PM EDT Sat Jun 15 2024

AVIATION...

Thicker high clouds overhead at forecast issuance shift northward
late tonight leaving mostly clear sky in the morning. At the same
time, surface high pressure positioned over southern Ontario begins
an exit toward the New England coast while still supplying dry
easterly boundary layer wind that gradually veers toward the south
by afternoon. The still dry low level air mass inhibits any cumulus
development while another round of mid and high clouds arrives ahead
of a warm front strengthening along the MS valley region. These
clouds are associated with showers and thunderstorms ongoing across
the Midwest which are projected on a track into the northern Great
Lakes through the afternoon into Sunday evening.

For DTW/D21 Convection...No thunderstorms are expected late tonight
through Sunday evening.

 DTW THRESHOLD PROBABILITIES...

* None.


&&

.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...SC
MARINE.......AM
AVIATION.....BT


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at www.weather.gov/detroit.