Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221515
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1115 AM EDT Thu Jun 22 2017

.UPDATE...

As the warm front moves northward through the region, the main story
for the afternoon will be increasing heat and humidity over SE
Michigan. The remaining showers and residual clouds will decrease
during early afternoon and allow surface heating to ramp up through
the day as surface moisture lifts dewpoint to near 70F. Late
afternoon highs near 90 will then produce heat index reaching into
the mid 90s for a few hours during peak heating. This is below
headline criteria but will feel much different compared to the last
few days.

The afternoon temperature trends will unfold as the warm sector
associated with low pressure to our west builds strongly over lower
Michigan. This is expected to inhibit convection initially as a cap
develops in the 850-800 mb layer which will leave in question
whether afternoon and evening storms will be able to form as shown in
many of the mesoscale and synoptic model solutions. The key here
will be if deeper low level moisture can arrive this far north from
the Ohio/Tennessee valleys and help erode the cap. The 12Z upper air
analysis does show 850 mb dewpoint in the upper teens available for
advection into the southern Great Lakes which would build potential
for at least scattered shower/storm development late in the daytime
heating cycle.

&&

.PREV DISCUSSION...
Issued at 643 AM EDT Thu Jun 22 2017

AVIATION...

Early morning convection along warm front should mainly affect KMBS
once small batch along I-94 shifts east 11z-12z. Aside from stray
activity, it should then be pretty quiet until late afternoon into
the evening as higher theta-e air continues to stream into area.
Coverage should range from isolated/widely scattered I-94 to sct-bkn
KMBS nearer the front. Front settles south through area overnight as
low pressure passes east. While some convection will probably still
exist, very hard to envision the scenario. With Hires models largely
fading activity away as more southern boundary over the Ohio Valley
activates, will leave post 03z-06z period dry. Some indication of
lower stratus filtering into area as well, but confidence in this
aspect of forecast is low as well.

For DTW...Early morning shras/tsras should be east of terminal by
12z. Expect VFR conditions into this evening with gusty southwest
flow to 25 knots or a bit more. Scattered convection may fire again
late in the day, but no more than PROB30 given position of main
forcing along front well north.

//DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms impacting terminal this evening.

* Low for ceilings aob 5kft tonight.

PREV DISCUSSION...
Issued at 347 AM EDT Thu Jun 22 2017

DISCUSSION...

Water vapor imagery paints a good picture of the major players
affecting the forecast over the next few days. Strong, nearly zonal,
jet over the Canada/US border is currently nosing into the Northern
Midwest with mature low pressure system crossing into Manitoba tied
to the left exit region of said jet. A cold front tied to this low
is draped through the Midwest southwest through West Texas and New
Mexico.  The jet max will push the northern extent of the cold front
eastward through today and tonight while the southern portion,
already suffering from weak flow, runs up against Tropical Storm
Cindy lifting further north up the Mississippi. A second wave diving
into the developing mid level trough will propel the entire system
eastward tonight into Friday. Resulting longwave trough will then
reside over the Great Lakes through about the middle of next week
before ridging attempts to regain control of the region.
Temperatures will run below normal, in the 70s, through the duration
of the forecast with the exception coming today where highs approach
90 in many locations. Some 80s will linger on Friday ahead of the
cold front, but then the 70s take over. Precipitation chances will
exist through next week as fronts/troughs rotate through the main
longwave trough. Timing these individual events will be the focus
through the coming days.

First issue with the forecast is the developing warm frontal
boundary being forced north on the nose of a strengthening 850mb low
level jet. Models have come down some with the winds speeds in this
jet, now maxing out around 40 knots for the most part. Also
narrowing the corridor of higher winds, tighter to the cold front
upstream away from SE MI. Convection is already firing over WI and
Lake MI along the lead edge of the instability/theta e gradient
draped southward through western lower MI. Models continue to
advertise convection expanding in coverage along the front as the
system bleeds eastward. Unfortunately most hires is struggling with
the convection early on, though the RAP and some versions of the
HRRR are starting to latch on. Current placement of the convection,
and eastward propagation of system in general means the Saginaw
Valley stands the best chance of getting clipped by this band of
storms. Potential for development further south and east remains
low, but there is some light shower activity over northern IL
showing there is a chance. Will continue likely/definite pops north
with only a chance south with the best window from 09-14Z before the
forcing lifts north and strong warm air advection caps the
atmosphere.

For the rest of today, though models consistently show MUCAPE around
1000-1500 J/kg (all elevated) with about 30 knots of bulk shear,
weak ridging slides through with a cap extending from around 5-9kft,
and an overall lack of forcing aloft, see precipitation hard to come
by this afternoon so will go mostly dry. The one caveat to this is
bands of deeper moisture emanating northward out of TS Cindy. This
could lead to some shower activity on the weak theta e gradient, but
models did trend slower/further south with this feature so will hold
off on getting too excited about it.

We then turn our attention to the cold fropa late tonight into
Friday morning. Strong PV filament rotating around the parent low
will send the front through SE MI around 16-20Z. PWATs ranging from
1.5 to 2 inches will cover the region as the front slides through.
Warm mid levels and prefrontal trough crossing early in the morning
hurt its chances of producing much severe weather. Also the
strongest ll jet seems to refocus further east although there will
be a narrow channel of higher winds along the front. And upper level
forcing is lacking as the right entrance region of the jet and
strong PV filament lag behind the front.

Biggest threat with any storm will be heavy rainfall as atmosphere
becomes very moist with dewpoints well into the upper 60s and PWATS
previously mentioned over 1.5 inches. Orientation of the front
largely west to east parallel to the flow will lend to some training
before the front becomes more progressive. Locations across mid MI
stand the best chance of seeing excessive rainfall. As for severe
weather potential, best chance will be late this evening ahead of
the cold front while CAPE and shear are at their highest. Strong
winds and large hail will be the primary threats. Additional chances
will exist along the cold front Friday morning as stronger winds
aloft and frontal forcing slide though. Best chances for both fronts
will occur mainly north of I69.

MARINE...

Southerly flow will gradually increase and veer to the southwest as
a warm front lifts north through lower Michigan. Showers and a few
thunderstorms will be possible early this morning along this front,
mainly over portions of Lake Huron. Additional showers and storms
can be expected later today along this frontal boundary as moisture
and instability increase. Passing low pressure will force the front
southward late tonight into Friday with convection sinking south
with it. Winds will back to the west northwest and remain from that
general direction through the weekend. An unseasonably cold airmass
this weekend will bring the chance for light showers across most of
Lake Huron.

HYDROLOGY...

Showers and thunderstorms will be possible early this morning as a
warm front lifts through lower Michigan, mainly along and north of
the I-69 corridor. Additional showers and thunderstorms can be
expected late today into tonight as an influx of moisture spreads
over the region in advance of an approaching low pressure system.

Initially, this activity will again focus over the northern forecast
area, but the passage of the low pressure late tonight will allow
the frontal boundary and associated convection to sag south through
the remainder of the area. Any lingering showers and thunderstorms
will sink south of the region Friday. All told, localized rainfall
amounts may reach an inch or more, especially from around Flint on
north into the Saginaw Valley.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.

&&

$$

UPDATE.......BT
AVIATION.....DG
DISCUSSION...DRK
MARINE.......DG
HYDROLOGY....DG


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