Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 251958
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
358 PM EDT Tue Jun 25 2019

.DISCUSSION...

Uniform westerly flow trailing yesterday`s cold front left lower
humidity over SE Michigan today. This combined with breezy
conditions and mostly sunny sky is producing a pleasant day across
the region as high temperatures top out in the upper 70s and lower
80s.

Low level wind backs slightly tonight and directs modest moisture
return ahead of the next weak cold front moving across the Midwest.
The front gets pushed eastward by the short wave riding along the
south flank of the central Canadian upper level trough and preceded
by a well defined MCV moving through southern WI and northern IL.
Convective potential associated with these features is the primary
forecast concern for tonight as the W/SW flow draws some instability
into the central Great Lakes. The MCV presents the first chance for
activity in our area tonight as it initiated and continues to
organize pockets of surface based convection. This activity is
capable of reaching our area during the evening with some modest
strength keeping in mind MLCAPE effectiveness lingers past peak
heating this time of year. That being said, convective intensity
still has diurnal dependency as evidenced by the wide range of
MLCAPE projections offered in CAM output. Surface analysis showing a
return of lower 60s dewpoint ahead of the MCV supports estimates
closer to 1000 J/kg across southern Lower Michigan at 00Z. This is
expected to sustain at least scattered coverage of showers and
thunderstorms but which are past peak intensity as they reach SE
Michigan and then decrease/weaken from there to the east toward
midnight as the diurnal trend more fully plays out.

Not far behind and a little farther north is the larger scale short
wave more directly involved in progression of the surface front.
Regional scale models indicate a dull looking mid level moisture
axis extending SW to NE along and ahead of the front from which
additional showers and ordinary thunderstorms are possible
overnight. The moisture axis also marks a plume of lapse rate near
6.5 C/km and 850 mb LI around -2 C on which the southern fringes of
the short wave can add some forcing during a small time window
overnight before the wave exits eastward before sunrise.

Neutral forcing to weak subsidence trailing the short wave in more
zonal flow aloft brings dry conditions to start Wednesday and we
begin a transition to more of a mid summer pattern. Convective
trends have low predictability due to upstream MCS activity and
associated MCV influence, the depiction of which in NWP will change
with each forecast cycle. What can be said with a little more
confidence is regarding the front moving through late tonight and
early Wednesday that stalls near the Ohio border for the mid to late
week period. This is a good approximation for the position of the
instability gradient and the track of any organized storms Wednesday
night through Thursday.

Warm and humid summertime airmass to reside over the Great Lakes
through the extended period which will bring several rain and
thunderstorm chances late this week and again early next week. To
start, a weak shortwave and associated weak cold front will travel
across Michigan throughout Friday which will bring the chance for
showers and thunderstorms throughout the day. Saturday will again
bring the chance for diurnally driven showers and thunderstorms
during the afternoon and evening period, as daytime heating erodes a
low-level cap. A high pressure system is then forecasted to move
south from Ontario Sunday afternoon and will center over the Great
Lakes by Monday morning, which will greatly diminish rain shower and
thunderstorm chances Sunday afternoon into at least Monday morning.
Anticyclonic flow from the approaching high pressure system will
also act to push a cold front through at least the Thumb region,
which will diminish temperatures slightly across SE MI down into the
lower-80s to even the upper-70s (mid to upper-70s over the Thumb).
Prior to the passage of the front, forecasted highs are in the low
to mid-80s across SE MI, with upper-80s possible across across the
urban heat island Metro area. Flow to turn more zonal to start early
next week which will return daytime highs back into the mid to upper-
80s and will bring the chance for showers and storms Monday into
Tuesday.

&&

.MARINE...

Winds across the central Great Lakes waterways will remain gusty
until this evening. W/WSW sustained winds will drop to around 10
knots by 00Z, gusting to less than 15 knots overnight. A stable
marine layer has helped offset stronger winds, keeping wave heights
below 3 feet with an amplitude reduction expected overnight. The
Small Craft Advisory over Saginaw Bay has been allowed to expire
before 20Z as winds should remain weaker than 20 knots, diminishing
further this evening ahead of thunderstorms. An evolving convective
complex is currently working eastward across Lake Michigan bringing
a chance for lightning and locally gusty winds after midnight.
Chances diminish after 09Z before additional thunderstorm activity
may diurnally develop on Thursday and Friday. Warm and light
offshore flow is expected into the weekend becoming more variable on
Saturday.

&&

.PREV DISCUSSION...
Issued at 146 PM EDT Tue Jun 25 2019

AVIATION...

VFR conditions will prevail across the terminals for the remainder
of the daylight hours. Cloud coverage will primarily be limited to
FEW diurnal cu near or above 5 kft. Winds will remain in the 10 to
20 knot range with occasionally higher gusts until 00Z as strong
upper level zonal flow mixes down to the surface. Wind speeds drop
off after a surface inversion develops this evening once diurnal
heating is cutoff. Directionally, winds had veered a bit more toward
the north than initial thinking, but still expecting a return to
W/WSW flow after 18Z. Large amount of uncertainty with how in-tact a
distant convective cluster will be once it approaches the terminals
tonight. Right now, decided to add VCSH for KPTK/KFNT/KMBS within a
brief 02Z to 05Z timeframe with cigs dropping to somewhere around 5
kft as moisture briefly works through aloft overnight.

For DTW...With sustained winds AOB 20 knots from W/WSW between 18Z
and 00Z, runway operations will not be impacted due to crosswinds.
Should narrowly avoid any convection after 00Z thus kept TAF dry,
but the chance is non-zero. Mentioned a two hour window for broken
cigs near 5 kft with passing moisture aloft.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms between 00Z and 06Z.

* Medium for bkn cig drop to 5 kft between 03Z and 05Z.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

DISCUSSION...BT/TF
MARINE.......KK
AVIATION.....KK


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