Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
327 am EDT Wednesday Aug 24 2016

Discussion...

Most noteworthy part of the forecast will center around potential
for showers and thunderstorms today and Thursday, as well as a
return to humid conditions. Shortwave trough pushing across Iowa and
Wisconsin will lift across Michigan today, embedded within broad
southwest flow between a large upper trough advancing through
central Canada and and upper level high over the deep south.
Increasing southwest flow will advect in warmer air and moisture
over the next few days. There will be a small risk for a shower or
even a thunderstorm during the mid to late morning on the leading
edge of strong Theta-E advection and weak isentropic ascent.
Thinking, however, is that the dry air currently in place (evidenced
by 24.00z DTX raob) may only allow for virga at best. The better
chance for showers/tstorms will arrive in the afternoon as the upper
shortwave crosses the area, and as dewpoints in the mid-60s to near
70 advect in from upstream. Mixed layer cape values around 1000 j/kg
(per gfs) and some dry air in the lower levels may allow for an
isolated severe wind gust to 60 mph during the afternoon and
evening, but widespread severe weather is not anticipated. Humidity
will also increase today as dewpoints rise, combining with slightly
above normal temps to create heat index values in the low to mid
80s. Overnight lows will also remain quite warm (close to 70) as
dewpoints remain elevated.

Additional moisture looks to arrive tonight and Thursday as the
approaching upper trough taps into a plume of monsoonal moisture
seen on water vapor imagery extending north of New Mexico and West
Texas. Latest model runs raise precipitable water values up near 2 inches once
again. Still expecting fairly quiet conditions overnight as weak
shortwave ridging and subsidence build in behind the shortwave.
Models continue to show some smaller shortwave features tracking
near the Michigan/Ohio border however, and will retain lower chance pops
there. Upper trough will track into Ontario Thursday, pushing the
surface trough across Michigan during the afternoon. Showers and
thunderstorms should again develop by afternoon ahead of the trough
in a warm and humid airmass. A few stronger storms could develop
near the Ohio border where a mid-level speed Max will strengthen
wind fields. Storms will also be capable of very heavy rainfall
given tall skinny cape profiles on forecast soundings and high precipitable water.
Warm start to the day and continued warm air advection will favor
Max temps solidly in the 80s, with heat indices south of M-59
reaching above 90 assuming no interference from early day
convection.

Drier air will work into the area behind the surface trough and then
especially behind a cold front that will arrive overnight. High
pressure should provide dry weather for both Friday and Saturday.
Temperatures will cool into the mid 70s to low 80s, with lower
dewpoints providing much more comfortable conditions. Upper trough
working across the Great Lakes will then bring the next chance for
showers and thunderstorms Saturday night through Sunday night,
however coverage at this time looks low as better forcing slides
north of the area.

&&

Marine...

A warm front will move through the lakes Wednesday afternoon/evening
bringing scattered showers and thunderstorms. A cold front will
follow shortly behind the warm front across Northern Lake Huron and
slowly drop southeastward during the day Thursday and clear to the
east and south by early Thursday night. More scattered showers and
thunderstorms are likely with the cold front. Winds will be modest
from a southerly direction ahead of the warm front then tone down a
bit after passage. Winds will become northwesterly Friday behind
cold frontal passage. High pressure will bring light and variable
winds Saturday then more southerly Sunday as it moves off to the
east and a cold front approaches from the west. This front may
bring showers activity across Lake Huron Sunday afternoon.

&&

Hydrology...

A trough of low pressure will track through the Great Lakes region
today and Thursday. Shower and thunderstorm potential will increase
along a a warm front that will lift through the area today, then
persist along a cold front as it pushes southward across the state
on Thursday. Basin rainfall averages of around .50 inch will be
possible north of M 46 through Thursday, while basin rainfall
averages to the south of M 46 may range between .50 and 1.00 inch.

&&

Previous discussion...
issued at 1223 am EDT Wed Aug 24 2016

Aviation...

The next low pressure system will continue to organize over the
Midwest for the remainder of the night. This system will fuel
showers and thunderstorms that will move mostly south to north while
the entire pattern drifts eastward and a slower pace. That means VFR
will persist over Southeast Michigan through morning in the form of
thickening high clouds with light south wind. The plume of moisture
shown over the Midwest to lower Ohio Valley will then make progress
through lower Michigan and produce increasing coverage of high based
showers during the afternoon. The advancing moisture will behave
like a warm front only without much restriction below VFR outside of
heavier showers or possibly a thunderstorm during afternoon into
early Wednesday evening.

For dtw... VFR in mostly clear sky initially will then become
thickening high clouds through the night into late morning. Light
south wind will gradually increase humidity and produce clusters
of showers with lower ceiling mid afternoon into early Wednesday
evening. Thunderstorm potential continues to have late day timing
with limited coverage.

//Dtw threshold probabilities...

* medium for ceiling 5000 ft or less Wednesday afternoon.

* Low for thunderstorms Wednesday afternoon.



&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Discussion...hlo
marine.......cb
hydrology....cb
aviation.....Bt



You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit.

National Weather Service Glossary of Abbreviations