Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
357 am EDT sun may 3 2015
Short term...today and tonight
Surface high pressure will shift east off the middle-Atlantic coast
today. This will be in response to a large upper trough moving
through central Canada. As the upper trough pushes into Manitoba and
Ontario today...it will induce weak riding aloft over lower
Michigan. This should keep the middle-levels stable enough to prevent
any showers/thunderstorms from developing even as southwest flow brings a
slow but steady increase in moisture through the day. Overall
expecting a nice dry Spring day with some cumulus in the
afternoon/evening and high clouds streaming in off upstream
convection. Maximum temperatures this afternoon should reach into the
upper 70s to around 80. This is based on upstream temperatures over
the upper Midwest yesterday (warm air advection into michigan) and
increased mixing as a surface trough and cold front associated with
the upper trough to our north begin to edge nearer.
Upper trough will continue to work through Ontario tonight...pushing
the surface trough and cold front down the eastern u.P. And northern
lower Michigan by 12z. This location is per recent continuity and
consensus within the models...although the operational 03.00z GFS is
a little on the faster side and is not preferred. Low-level jet axis
will meanwhile surge up into northern lower Michigan...helping
provide moisture along the frontal boundary as h850 dew points rise to 8-
10c. Instability looks elevated tonight as convection ahead of and
along the front creeps into the Saginaw Valley and thumb...with
thunderstorms possible as middle-level lapse rates increase to between
7-8 c/km. Warmer air...clouds...and increased southwesterly gradient
will limit radiational cooling and hold min temperatures in the 50s to even
The cold front moving through the plains and Midwest today will be
on our doorstep Monday morning and remains on track to move steadily
through Southeast Michigan during the day. Morning activity will be a
combination of convective remnants from today's peak in the diurnal
cycle over the plains and Midwest combined with additional
development supported by the moisture axis building into lower
Michigan. This combination will provide sufficient coverage of
showers to maintain likely probability of precipitation during the morning over the Tri
Cities and northern thumb. The low level jet is modest in strength
judging by model 850 mb wind near 30 knots and the flow is more
aligned with the moisture axis than normal to the gradient. This
will limit the effectiveness of Theta-E advection to organize
development farther east during the morning but remains worthy of
chance probability of precipitation as slightly negative 850 mb lifted index is generated
over all of Southeast Michigan as the moisture axis builds overhead.
The moisture axis over south sections of the area during the morning
will figure less in shower coverage compared to points north but do
more to set the stage for the afternoon frontal passage. The key for
thunderstorm potential will be whether or not surface dewpoint will
actually make it into the lower 60s as indicated by the NAM and GFS.
The air mass over the Southern Plains today is a Gulf modified
Continental variety originating from the large area of high pressure
along the Atlantic coast. There are some 60 dewpoint observations on
the Texas Gulf Coast at press time...so there is at least a chance
modeled boundary layer moisture could spread this far north by
Monday afternoon. An upper 70s temperature and lower 60s dewpoint would
then be capable of surface based cape near 1500 j/kg by 21z south of
the Interstate 69 corridor. Model soundings show this scenario in a
moderate intensity/unidirectional wind field with 0-6km bulk shear
at 20 knots or less...good for Ordinary storms. Equally notable is
precipitable water indicated to build toward 1.5 inches in a deep
moist adiabatic profile but subject to the same concerns mentioned
above for the surface parcel moisture forecast.
Showers will remain likely with a chance of storms from the Detroit
metropolitan area southward Monday evening as the front slides south of the
Ohio border and stalls overnight. The latest models remain in good
agreement with each other and from run to run on a that solution as
an upper level ridge builds rapidly from the northern plains to the
Tennessee Valley. Rain potential is nudged into the likely category
south of I-69 as confidence in surface based and elevated convection
is increased by the presence of a strong upper jet over northern
Ontario and Quebec...in the westerlies downstream of the upper ridge.
The entrance region will be favorably positioned over lower Michigan
to sharpen the middle level frontal circulation and support multiple
rounds of showers and storms right into Wednesday.
The second half of the week will not be as rainy but warm
temperatures will continue into next weekend. A long wave trough
over the west will gradually mature through a blocking phase which
will help the ridge over the east broaden and persist. Global
solutions overlap on timing of the next front around the Saturday
period next weekend.
Favorable marine conditions will continue today as southwest winds
allow warm air to stream into the Great Lakes. Wind speed will
increase modestly today and tonight...ahead of the next cold
front...but stability will be high over the open waters and limit
wave growth. A cold front then remains on schedule to slide through
Lake Huron and lower Michigan late Sunday night and Monday...and
then stall near the Ohio border Tuesday. Showers and thunderstorms
are likely during this time...but most of the activity will focus
over the Southern Lake Huron basin and southward into Lake Erie
after the frontal passage Monday into Tuesday.
Aviation...issued 1154 PM EDT Sat may 2 2015
Dry low level air funneling into area on south to southwest flow
around large high pressure positioned southeast of the region and
maintain VFR conditions through the forecast period. Wind gusts of
15 to 20 knots will be possible by midday Sunday...especially for
kfnt/kmbs as the pressure gradient tightens to some extent.
//Dtw threshold probabilities...
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).