Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
701 am EDT Friday Jul 3 2015
High pressure over lower Michigan this morning will hold over the
taf period...providing clear skies (below 15 kft) and very light
//Dtw threshold probabilities...
Previous discussion...issued 309 am EDT Friday Jul 3 2015
Short term...today and tonight
Dry airmass in place over Southeast Michigan this
morning...especially in the middle levels...as 00z DTX sounding
indicated a 700 mb dew pt depression of 30 c. Modest height
rises/modification of the airmass today compared to yesterday.
Guidance and 925/850 mb temperatures...18 c and 12 c respectively...point
to highs in the middle to upper 70s. The main hindrance...outside of
the cool start to the day (40s) will be some high clouds (25-40
kft/mainly south) as upper level jet (250 mb) works through the
Northern Ohio valley. Otherwise...the airmass will remain quite
dry with mean 1000-500 mb relative humidity around 30 percent.
Tonight the focus will be on the northern stream trough working
through the northern Great Lakes. With little to no height falls
extending into Southern Lower Michigan and 850-700 mb Theta-E axis
still displaced to our northwest through 12z Saturday...it looks to
be a struggle to get clouds into the County Warning Area...much less rain showers.
Very light/calm winds will result in another favorable radiating
night...with guidance temperatures in the 50s.
Long term...Saturday through Thursday
An upper trough axis will be departing to the east of lower Michigan early
Sat...eventually reaching Quebec and upstate New York by Sat
evening. Northwest flow aloft will drive a cold front into lower Michigan
during the first half of the day Sat. Model solutions continue to
show this front weakening/washing out as it pushes south across
lower Michigan during the later half of the day as the northwest flow aloft
weakens. The 00z model suite suggests this will favor thermally
driven surface troughing...more pronounced across the higher terrain of
north-central lower Michigan late Sat afternoon. The NAM and to some
extent GFS appear rather bullish with the degree of moisture pooling
over central Michigan. This leads to a little better cape and causes these
solutions to trigger convection. Adjusting surface dewpoints down a
little and considering that building middle level heights Sat afternoon
will support some middle level cap development suggests just late day
isolated convection at best...mainly across the northern half of the
forecast area where surface convergence is expected to be greater. Model
soundings do support good daytime mixing depths Sat which will
result in high temperatures in the low 80s.
Middle level heights will continue to build across lower Michigan into
sun...with a middle level short wave ridge then sliding east of the
area late Sunday into Monday. This will inhibit any convective
development Sunday and Monday. Developing southerly return flow late
Sunday will strengthen Sun night into Monday. This will support a
modest warming trend...with highs possibly reaching upper 80s by
A relatively high amplitude and progressive northern stream trough
axis is forecast to drive a cold front across the Great Lakes region
in the Monday night/Tuesday time frame. Although there remains timing
differences...the medium range model suite indicate that the
prefrontal southerly flow will transport ample deep layer moisture
into Southeast Michigan. So this system will bring the next good chance for
convection. A slightly cooler and drier airmass is then expected to
advect into Southeast Michigan in the wake of this frontal boundary.
High pressure will lead to favorable marine conditions across the
Great Lakes today. A cold front is forecast to weaken as it slides
south across the region on Saturday. This system should have minimal
impacts on the marine areas. High pressure will then build back into
the region for the rest of the weekend into early next week. The
next significant weather system forecast to impact the region will be
a cold front Monday night into Tuesday...providing the next good
chance for showers/thunderstorms.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
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at www.Weather.Gov/Detroit (all lower case).