Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
702 am EDT Tuesday Sep 1 2015
Existing IFR/MVFR visibility restrictions in fog will lift 13-14z as
daytime heating ensues. Some increase in moisture will today will
provide a greater potential for a period of scattered-broken VFR diurnal cumulus
for the afternoon period. Similar environment tonight will again
promote fog and/or low stratus development...favoring a period of
low MVFR/IFR at all terminals during the early morning period.
//Dtw threshold probabilities...
* medium for ceiling at or below 5kft after 18z today
Previous discussion...issued 340 am EDT Tuesday Sep 1 2015
Short term...today and tonight
High amplitude upper ridging will mark conditions through tonight as
it centers squarely over Southeast Michigan. The incremental
increase in mean thicknesses and high degree of insolation...under a
background of light southwest flow will effectively nudge daytime
temperatures up another tier today. Highs of middle and upper 80s
remain on point for this afternoon given the mixing potential and
850 mb temperatures of 17c. Dewpoints inching up into the upper 60s
will provide a noteworthy uptick in humidity as well...with heat
indices creaping toward 90 degrees.
Consolidated shortwave energy and accompanying core of slightly
cooler middle level temperatures will continue to drift east-northeast
across the Ohio Valley today. While the center of this circulation
and subsequent better ascent/lapse rates will reside south of the
Ohio border...there remains an outside chance for a shower/
thunderstorm to develop across par southern sections this afternoon
and evening as the outer periphery glances across this region. This
continues to warrant an isolated mention from the Ohio border up
through the I-94/Ann Arbor-Detroit corridor.
Pattern persistence suggests another round of at least patchy
/locally dense/ fog again tonight...although a light southwest wind
may tend to favor a very low stratus deck instead. The elevated
near surface moisture content will cap lows in the vicinity of the
upper 60s most locales by morning.
Upper level ridge building/expanding north through the plains
Wednesday/Thursday...allowing for modest height falls and surface
high pressure to build in from Ontario on Thursday...leveling off
our warmup...and likely supporting cooler temperatures on Thursday compared
to Wednesday. Latest guidance and 850 mb temperatures up around 20 c on
Wednesday still suggesting maxes near 90 degree.
Several shortwaves embedded in the upper level northwest flow will
muddle the forecast...as well as backdoor cold front sliding through
Wednesday night. Moderate instability building on Wednesday...with
MLCAPES in the 1500-2500 j/kg range. 00z NAM is too moist...with
surface dew points in the middle 70s...and thus forecasted 4000 j/kg of
cape looks unrealistic. Although 0-6 km bulk shear values will be
low...below 15 knots...with the dry middle levels and corresponding
high downdraft convective available potential energy (1500 j/kg)...can't totally rule out isolated
severe storms if they do in fact develop late in the day. Per 00z
GFS...middle level cold pool (-11 c at 500 mb) tracking through the
central Great Lakes Wednesday night could prove sufficient to
develop/sustain some convective activity as weak frontal boundary
also progresses southward. Middle level lapse rate (700-500 mb) also
look to be running high 7+ c/km. Sharpening west to east 850-700
mb Theta-E gradient setting up on Thursday. 00z Euro is slowest
and stronger with shortwave trough over the western Great Lakes
Wednesday night...tracking into lower Michigan on
Thursday...supporting higher probability of precipitation. Clouds...light northeast
flow...and possible convective activity will likely keep maxes
down in the low to middle 80s on Thursday.
Warm and humid air over the central Great Lakes will promote light
winds and possible fog at times. A weak cold front passing through
Wednesday night will bring the risk of showers and
thunderstorms Wednesday afternoon through Thursday. Light southerly
winds today into tomorrow will shift to a northerly direction behind
the front as we head into Wednesday night...continuing into Thursday.
Michigan...dense fog advisory until 9 am EDT this morning for miz047>049-
Lake St Clair...none.
Michigan waters of Lake Erie...none.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).