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fxus63 kdtx 180413 
afddtx

Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1213 am EDT sun Aug 18 2019



Aviation...

Line of storms now working east of the taf sites should be the end
of precipitation for the night. Could see a bring period of light
fog or stratus in it's wake early this morning. Afternoon cu field
will thicken in advance of the next trough that will swing through
in the late afternoon or early evening. Indications are for a
widespread thunderstorms to initiation and slide eastward across the
taf sites generally between 20-00z with this trough but a few
isolated storms could start as early as 18z. Storms could be strong
to severe during this time.

For dtw...there is a small chance of showers lifting northeast over
the Airport early in the forecast but mostly dry conditions are
expected so will lean that way with the taf. Cumulus field will thicken
this afternoon with a couple hours of storms expected sometime late
this afternoon, most likely 20-00z. Storms could be strong to severe
during this time.

Dtw threshold probabilities...

* low for ceilings aob 5k ft this morning, moderate this afternoon
and beyond.

* Moderate for thunderstorms between 20z to 00z.

&&

Previous discussion...
issued at 352 PM EDT Sat Aug 17 2019

Discussion...

A subsidence bubble bringing capping along with some dry air has
effectively prevented much precipitation from developing across
southeast lower Michigan through the early afternoon. A few high
clouds with scattered cu is allowing for a good amount of sunshine,
which has resulted in temperatures increasing into the low to mid
80s. Main adjustment for today has been to increase pops and quantitative precipitation forecast
slightly and expand coverage northward into the M-59 corridor for
this evening. Scattered convection early this afternoon is
developing in response to a shortwaves moving along the frontal
boundary to the south. Later day convection will come from a mesoscale convective vortex
taking shape across Southern Lake Michigan and eventually moving
across lower Michigan. These will bring convection along and south of
the I-94 corridor over the next few hours with activity developing/moving
across the M-59 area closer to the 6-8 PM time frame. Greater severe
potential resides south of the Michigan border. However, MLCAPE
values of around 500-1000 j/kg with 0-6 bulk shear values of 20-30
kts and steep low level lapse rates will bring the possibility of
strong storms with gusty winds and brief heavy rainfall across
portions of the southern County Warning Area. Loss of daytime heating and weaker mid
level lapse will decrease thunderstorm potential into tonight as
activity moves out of the area by around 2 am.

Longer wave trough axis will move across the northern plains tonight
as a deep low pressure system rotates across central Canada. A
nocturnal mesoscale convective system is forecast to move across the upper Midwest into the
western Great Lakes region tonight supported by a strengthening low
level jet at the base of this trough. Remnants of this system are
expected to generate a mcv(s)/multiple shortwave impulses that are
forecast to move across lower Michigan tomorrow. Ahead of this
system will be increased southwesterly flow advecting greater
moisture into the area. A conditional severe risk will be present
for tomorrow as a moderately unstable airmass sets up with 0 to 6 km
shear of at least 30-40 knots supporting this risk. Still some
uncertainly with how early day convection and cloud cover will limit
instability later in the day. If early day convection dissipates
across Lake Michigan or western part of the state, this will lead to
a greater potential for severe weather across Southeast Michigan
during the late afternoon early evening time frame. Strong low level
flow with the negatively tilting trough axis will make damaging
winds the main threat with large hail and locally heavy rainfall
also possible. A well mixed boundary layer tapping into strong
southwest flow aloft will also bring some windy conditions with
gusts of 20-30 mph kicking in by early afternoon. Convection will
push east of Michigan by around midnight tomorrow night as the
trough axis pivots into the eastern Great Lakes.

High pressure slides into the region on Monday with a weakening
surface front helping push the instability axis across far lower
Michigan. This will limit precipitation potential to the I-94
corridor and south. The lack of cold air advection will keep high
temperatures for Monday in the 80s for much of the area. The
exception will be in The Thumb where temperatures along The Thumb
shoreline will be in the mid/upper 70s.

Pseudo zonal flow over the northern conus, with 588 dam heights over
Southern Lower Michigan on Tuesday, leading to another very warm
day (upper 80s). The upper level flow will then buckle, with a
seasonable strong upper level trough/cold pool taking residence over
the Great Lakes region by Thursday morning, sending 850 mb temps
into the single numbers.

Sprawling high pressure (1022+ mb) will build in for Thursday-
Friday, and likely last through much of the weekend, supporting dry
and pleasant temperatures for August, but a bit
cool/below normal on the mins (40s not out of the question for
normally colder locations Friday morning).

Toughest part of the extended forecast remains in the Tuesday
evening-Wednesday morning time frame with the frontal passage, as
12z models (euro/Canadian/icon) have all trended drier. Two reasons,
one there looks to be a thunderstorm complex developing over Iowa on
Tuesday, disrupting moisture transport into our area. Second, warm
mid levels ahead of the front (10 c at 700 mb) could be sufficient
to provide a cap, and a dry/limited convection frontal passage is on
The Table. Thus, no reason to deviate from the blended low chance
pops in the 18z Tuesday-18z Wednesday time frame at this time.

Marine...

Weak southwest flow will continue tonight. There is a chance of
thunderstorms with a weak system for the southern lakes region.
South-southwest winds increase on Sunday afternoon as a low pressure
system lifts into the western and northern Great Lakes. This system
will bring a good chance for showers and thunderstorms Sunday
afternoon into Sunday evening, with locally higher wind and waves to
be expected in any thunderstorm activity. The cold front will push
through lower Michigan before weakening on top of the Michigan/OH/in
border region. High pressure fills back in and leading to lighter
wind and waves on Monday and Tuesday. However, that stalled frontal
boundary may lead to additional shower/thunderstorm activity over
Lake Erie and Lake St. Clair.

Hydrology...

Scattered thunderstorms this evening and during the early overnight
hours will be developing on the next moisture surge. Precipitable
water in excess of 1.75 will reach into Metro Detroit by midnight.
While storm motion will be east-northeast around 30 mph, new
convection will develop on the upwind side of ongoing convection
which could lead to some short-fused training. Isolated locations
across Metro Detroit south to the Ohio border could get in excess of
an inch of rain with the thunderstorm activity tonight.

Scattered showers and thunderstorms will likely again on Sunday
afternoon and evening as a low pressure system tracks through the
Great Lakes. The air mass over the region will be characterized by
dew points near 70 degrees and precipitable water values of 1.50 to
1.75 inches. This will likely result in heavy downpours within any
convective activity. Activity is likely to have forward propagation
with good cold pools developing leading to storm movement at least
40 mph. Basin-average rainfall totals of 0.25 to 0.50 inches look to
be the most likely. Isolated higher totals will be limited to any
location that see repeated thunderstorms.

&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Aviation.....Tf
discussion...aa/sf
marine.......rbp
hydrology....rbp

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