Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1152 PM EDT Wednesday Jul 9 2014
High pressure will maintain clear skies and light winds through the
morning. The latest temperature and dewpoint spreads at the terminals
suggest any ground fog will remain patchy and too low of a chance to
include in the terminals. A scattered to broken cumulus field is again expected to
develop early Thursday afternoon. Based on expect temperature and
dewpoints...bases are expected to fall between 4500 and 6000 feet.
//Dtw threshold threats...
* medium confidence in ceilings at or below 5000 feet Thursday
Previous discussion...issued 340 PM EDT Wednesday Jul 9 2014
Short term... tonight
Lingering showers sustained by weak upper forcing and steep
middle-level lapse rates will dissipate with the loss of diurnal
heating this evening. Dissipation of cumulus will probably lag a bit
behind given persistence of cyclonic flow aloft/continued upper
forcing, so allowed for a slower clearing of skies especially across
eastern portions of the County Warning Area. Mostly clear skies are expected to be
in place by midnight as cyclonic flow weakens and surface pressure
rises commence at the surface. Combination of light northerly
gradient supportive of light to calm winds at the surface and mostly
clear skies will allow overnight lows to fall into the low 50s to
around 60 in the city.
Surface high pressure sprawled across central Canada and the Central
Plains today will slide over the Great Lakes for Thursday with the
main weather impact being continued support of below normal
temperatures. This time of year...that means pleasant conditions
with low humidity...but the surface high will combine with
subsidence downstream of the short wave ridge aloft to also ensure
dry conditions in our area. The forecast will then be reduced to
about 50-50 coverage of shallow cumulus and wind conditions influenced by
differential heating and lake breeze development. The surface high
centered over Lake Huron will favor a slightly stronger and farther
inland onshore flow into The Thumb where afternoon temperatures will
struggle to break 70. Lower to middle 70s look reachable over the rest
of Southeast Michigan with the benefit of July sunshine. Thursday night
will then set up to be another clear and cool one. The coolest
guidance is preferred and offers Friday morning min temperatures in the
upper 40s to lower 50s, about 10 degrees below normal, but above
records that are in the lower to middle 40s for 11 July.
The surface high and low level thermal trough will be driven
eastward during Friday by the next low pressure system in central
Canada. This system is indicated in satellite imagery today over
British Columbia and appears well sampled by the current model
cycle. Solutions are in good agreement with timing and placement of
the system over Manitoba by Friday. Zonal upper flow across The
Rockies will lead to the usual Lee side surface trough over the
plains which will combine with the Manitoba system for moderate low
level jet formation. Expect a plume of higher Theta-E air to develop
into the Great Lakes Friday night into Saturday and support
convective complexes that will likely be in some sort of decaying
stage based on the north to south orientation of the moisture axis.
This will also mark the return of warmer and more humid air that
will last through the weekend.
A cold front will move into the northern Great Lakes on Saturday
and Sunday bringing a chance of rain showers and thunderstorms to
the area through the weekend. Another cold front associated with a
low pressure system over northern Ontario will begin to move
across Southeast Michigan Monday. This low and cold front will
keep rain chances across the area through the remainder of the
extended period. High temperatures will remain in the upper 70s to
low 80s through Sunday before dropping into the low to middle 70s on
Monday and Tuesday after the passage of the cold front.
Wind and wave conditions will become more favorable tonight through
Thursday as high pressure settles over Lake Huron and lower
Michigan. Light wind will return from the south during Friday but
will have little consequence on wave height. The south wind will
bring warmer and more humid air into the region with a chance of
showers and thunderstorms Friday night through the weekend.
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).