Scientific Forecaster Discussion
fxus63 kdtx 211921
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
321 PM EDT Fri Jul 21 2017
Upper level ridge center over/near Oklahoma this afternoon with the
top of the ridge flattening out over northern plains with the jet
energy tracking through, as upper level wave/low over southern
Alberta is on track to move through Lake Superior on Sunday, leading
to a cool down for early next week.
Very warm day over Southeast Michigan, as temperatures are pushing
toward 90 degrees, but fortunately dew pts are under 70 degrees.
Broken line of convection extending from the upper Mississippi River
valley southeast into western Ohio Valley through much of the day
has kept the good Midwest moisture bottled up west, and there is now
a clear consensus the deep moisture will be tracking through Chicago
area this evening and riding along and south of the Michigan border
late tonight, with mesoscale convective system complex propagating toward the Max instability
over the Ohio Valley, supported by corfidi vectors as low level jet
veers around to the west/northwest. Bulk of heavy rain will likely
fall along and just south of the border, and with the failure of good
low level moisture transport and destabilization (12z NAM keeps
1000-850 mb cape under 1000 j/kg) the prospects for severe storms is
very low/almost nil (exception being right near southern Michigan
border). This includes during the day on Saturday as well, as
Southeast Michigan resides in the subsidence wake of the departing
mesoscale convective system and flow is out of the northwest, with continuing lack of
instability and what looks to be strong mid level cap in place (700
mb temps around -12 c per 12z euro). The 12z Euro also maintains
1000-850 mb CAPES under 1000 j/kg for the most part, but surface low
is bit deeper (1006-1007 mb) tonight, placing Lenawee County is a
concerning triple point position around 12z Saturday, with 50 knots
at 850 mb, and corresponding 38 knots of 0-1 km bulk shear. Still,
based off current trends, good chance this boundary will end up being
a bit farther south.
Previous mentioned upper wave/trough tracking through northern Great
Lakes on Sunday will bring cold front through Southeast Michigan
during the day, but moisture looks to be lacking to support much
more than scattered coverage, with 0-6 km bulk shear around 40 knots
drawing some concern for isolated severe storms, but mid level lapse
rates look marginal and majority of solutions still indicating
1000-850 mb CAPES under 1500 j/kg.
Some lingering showers will be possible early on Monday as low
pressure departs the region. High pressure will then build into the
region through the day as a thermal trough swinging through keeps
monday's highs in the mid to upper 70s. High pressure will remain in
place through Tuesday bringing pleasant and dry conditions with
highs topping out near 80 and lows in the mid 50s to near 60. The
next chance for thunderstorms returns during the midweek period as a
weak cold front drops through the region. Slightly milder, more
humid air will advect ahead of the front on Wednesday allowing highs
to increase into the mid 80s.
Light and variable winds will transition toward south to
southeasterly on Lake Huron Saturday morning as a frontal boundary
extends across the southern Great Lakes. Wind gusts will remain
below 20 knots, while waves will undergo a slight uptick during the
afternoon. Low pressure will expand across lower mi on Sunday, while
high pressure expands across Quebec. This will lead to an increase
in southeast winds on Lake Huron Sat night into Sunday, especially
the northern half of the lake. Winds will then back to the north
Sunday night into Monday as low pressure exits to the east and high
pressure builds in from the west.
issued at 1248 PM EDT Fri Jul 21 2017
Southeast Michigan will remain under the influence of weak high
pressure through the duration of the afternoon and evening. There is
a dome of drier air across the region associated with this high. The
result has been a decrease in sfc dewpoints. This will inhibit
diurnal cu development and will prevent any late evening or early
overnight reduction in sfc visibility. Convective redevelopment is
expected to take hold across the upper MS valley and wrn Great Lakes
tonight. The sfc front and instability axis is expected to remain
south of the state. Thus the more widespread convective activity
will likely pass south of Detroit. There is still however a good
chance for a region of showers with some embedded thunderstorms to
develop north of the main convective complex, impacting portions of
se mi late tonight into Sat morning.
For dtw...the light flow will promote afternoon lake breeze
development. This will result in a wind shift toward the southeast
late this afternoon (21z time frame). Winds speeds with the lake
breeze will remain relatively weak (mainly under 7 knots).
//Dtw threshold probabilities...
* medium for thunderstorms late tonight (after 09z) through Saturday
* Medium for cigs aob 5000 feet late tonight and Saturday.
Lake St Clair...none.
Michigan waters of Lake Erie...none.