Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 280813

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
413 AM EDT Wed Jun 28 2017


Upper energy pushing from the Central Rockies into the Plains this
morning will work across the Great Lakes tonight, at the nose of an
upper jet streak. Strong area of diffluence ahead of this feature
interacting with northeastward advancing warm front/surface low
pressure, and strong surge of the low-level jet will allow complexes
of thunderstorms to develop over the Plains and Upper Midwest today.
This activity should then progress eastward into Michigan during the
afternoon and evening. Best potential for activity to be sustained
as it progresses into the State looks to be more over Northern Lower
Michigan, where the nose of the 60+ knot low-level jet will work in.
Forecast soundings for Southeast Michigan still signal the influence
of the exiting area of high pressure and shortwave ridging, with
warmer mid-levels and a fairly dry airmass that will require better
forcing to overcome it and/or strong moisture transport before we
can see much activity. Forecast is dry for the first half of the day
before showers begin working into the area from upstream during the
late afternoon and evening. Activity will likely be in a state of
decay as it fights a more hostile airmass, leading to just shower
chances mainly north of I-69 through 03Z/11PM. Temperatures today
will moderate a little as weak warm air advection occurs on the
northern periphery of high pressure over the Ohio Valley. This
should boost max temps into the mid-upper 70s.

Some forecast models still drop an occluded front southward through
Lower Michigan during the overnight hours, while others at minimum
show strong theta-e advection within the warm sector south of the
warm front. Either could serve as a focus for renewed convection
over Southern Michigan as mid-level lapse rates steepen and low-
level jet core surges up through Central Michigan. Elevated
instability will increase as a result, with NAM/GFS Showalter
indices falling between -1 and -3C allowing thunderstorms to begin
developing. Most of the activity looks to still be focused over
Northern Michigan, potentially keeping areas near the Ohio border
dry until Thursday. Severe threat tonight looks limited, as does
coverage of convection overnight. Although 0-6km bulk shear values
increase to 30-40 knots, CAPE density above the low-level inversion
does not look too impressive for large hail. Elevated convection
will also limit wind gust potential. Heavy rain could occur with
thunderstorms, but fast storm motion and more limited coverage will
mainly keep the heavy rain threat north of the forecast area.

Convection forecast for the end of the week then become more
uncertain as it will in part become reliant on placement/coverage of
previous rounds of convection and recovery from them. General
message is that rounds of rain/thunderstorms will be possible
Thursday through at least Friday night.

Low-level boundary will continue to drop south through Southern
Michigan on Thursday as weak surface low lifts through the U.P. of
Michigan. Better coverage of convection will be roughly south of I-
69 as drier air works into northern Michigan during the afternoon.
SPC has areas south of I-69 in a marginal risk as instability builds
ahead of the boundary and storms become surface-based. Other
forecast themes for Thursday are breezy conditions, with warmer and
more humid airmass as dewpoints rise into the 60s.

Upper low over Alberta will be the next big player in our weather
for the end of the week. This wave will drop into the Midwest on
Friday, kicking surface low pressure across the Northern Great
Lakes. Warm front will lift through Lower Michigan Friday, bringing
another surge of warm air and moisture. Temps warming into the upper
70s to mid 80s with dewpoints well into the 60s should allow CAPE to
build through the day, while 0-6km bulk shear values increase to as
high as 40 knots in the proximity of the warm front. This will bring
a slightly higher severe threat, with SPC Day 3 outlook including
all of Southeast Michigan. Threat for showers/tstorms will continue
into the overnight hours as a cold front pushes through the region.



Southerly winds will develop in the wake of high pressure this
morning.  A moderate increase in wind speed may lead to a brief
period of gusts near 25 knots across Saginaw Bay this afternoon.
Maintenance of a firm southerly breeze into tonight will then
support a more definitive increase in gust potential, leading to
small craft conditions across Saginaw Bay.  The potential for
thunderstorms will exist tonight, particular across central and
northern sections of lake Huron.  Moderate southerly wind will
sustain a warm and unstable environment through the latter half of
the week.  This will maintain unsettled conditions, with the
potential for thunderstorms Thursday through Friday night.



Low pressure tracking into the northern great lakes will bring the
potential for rain and thunderstorms this evening and tonight.  The
greatest potential will exist north of I-69, where rainfall amounts
between one quarter and one half inch will be possible through
Thursday morning.  Additional showers and thunderstorms may develop
throughout Thursday and Thursday night as warm and increasingly
humid air builds into the region.  The threat for rainfall will tend
to focus south of the I-69 corridor during this time as a frontal
boundary sinks into the region.  Average rainfall amounts generally
less than one half inch, but localized higher amounts in excess of
an inch will be possible within any more concentrated areas of
thunderstorms.   Another low pressure system tracking west of the
region will maintain the threat for thunderstorms Friday and Friday
night.  Should a more focused region of heavy rainfall emerge, then
the potential for a corresponding rise of area rivers and streams,
as well as minor flooding will be possible.  While river flooding
continues to ease across central Lower Michigan, this corridor will
be the most susceptible to flooding risks.


Issued at 1143 PM EDT Tue Jun 27 2017


High pressure across the upper Ohio Valley will sustain dry
conditions with clear skies and light winds through daybreak. The
departure of the sfc high to the mid Atlantic Wednesday morning will
establish an increasing south-southwest gradient across Se Mi.
Deepening of the mixed layer during the course of the day will then
result in a modest uptick in the winds. Otherwise, dry air in the low
level will maintain clear skies below 10k ft through Wed afternoon.




Lake Huron...Small Craft Advisory from 10 PM this evening to 10 PM EDT Thursday
     for LHZ421-422.

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



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