Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
722 am EDT Wednesday Oct 7 2015
Pockets of middle level cloud will shift across the region this morning
as a weak cold front drops through. This process will support a scattered
to broken coverage of lower VFR diurnal cumulus for the afternoon hours.
There may be some renewed expansion of lower cloud tonight as the
flow veers to easterly. Confidence on this development remains low
given the increasing depth of dry air.
For dtw...lingering MVFR visibility restrictions in shallow fog will
lift by 13z. Weak cold frontal passage midday...providing a wind
shift to northwesterly. A period of late day scattered-broken cumulus carrying
ceilings at 3500-5000ft.
//Dtw threshold probabilities...
* medium in ceilings below 5000 feet today...low tonight.
Previous discussion...issued 348 am EDT Wednesday Oct 7 2015
Short term...today and tonight
Gradual height falls within the southern periphery of a closed low
lifting across Hudson Bay will ease a weak cold front across Southeast
Michigan early today. Minimal frontal convergence and a general
lack of greater moisture quality/depth will leave this frontal
passage dry. Both upstream satellite trends and recent model relative humidity
fields indicate a broader ribbon of elevated moisture content
contained within the 850-700 mb layer embedded along and just behind
this feature. This points toward seeing a partial coverage of cloud
enhanced via the ensuing cold air advection and subsequent
steepening lapse rates as diurnal heating takes a greater hold. At
least partial insolation with solid mixing potential will offset the
advective process...allowing for highs largely within the middle and
upper 60s range.
Surface high quickly translating across the upper Great Lakes will
bring a veering/easterly component to the low level flow tonight.
This may favor some renewed expansion of lower stratus overnight as
moisture works in underneath the inversion. Tough call given the
increasing depth and strength of the dry layer just above...which
may limit the overall coverage. Lows Thursday morning bottoming out
in the 40s.
Long term...Thursday through Tuesday
Upper trough axis is forecast to move into the u.P. Of Michigan and
Wisconsin Thursday...swing through Michigan...then work east into
eastern Ontario by Friday morning. Upper height falls and right
entrance forcing from a jet streak over Canada will support surface
low pressure tracking across the central Great Lakes late Thursday
and Thursday night. This will spread more unsettled weather and some
rain into the area.
Frontal boundary that will settle into the area today will lift
north again on Thursday as southwest flow increases ahead of the
approaching trough. Could see a few showers Thursday along the warm
front as it tightens and lifts north. NAM/GFS show isentropic ascent
increasing along/north of the M-59 corridor (290-295k
surfaces)...and will introduce some lower probability of precipitation through the late
morning and early afternoon from there northward. Lift will have to
first overcome preceding dry airmass...as the front will delineate
the juicier airmass...and mostly expecting virga and a few light
showers. As noted...moisture advection will ramp up behind the warm
front...fed into the area on a 40kt low-level jet late Thursday and
Thursday night. Precipitable water values are forecast by models to surge up to
about 1.5 inches. This moisture will work with the incoming cold
front...pva...right entrance region forcing to produce an area of
rainfall Thursday afternoon through Thursday night. 7.00z runs of
both the GFS and Euro came in faster with the moisture...and the
forecast was adjusted to take this into account. Cold front will
sweep through the area late Thursday night/early Friday
morning...shunting moisture to the southeast and ending chances for
Cool northerly flow behind the front and gusty winds will bring very
fall-like condtions for Friday. Maximum temperatures should only reach
into the upper 50s to low 60s Friday afternoon...with even cooler
conditions on Saturday.
Upper ridging extending up through the western half of the U.S. And
Canada will position an expansive upper ridge over the Central
Plains Friday. Pattern will be progressive...with the ridge shifting
over Michigan for the weekend. GFS and Euro have become more
consistent with bringing an upper trough through the Great Lakes
early next week...although they exhibit some timing differences.
Will keep the forecast dry...especially since neither model is
showing any real influx of moisture into the area with this system.
After a cool end to the week...increased southerly flow ahead of
this next trough should boost temperatures for early next week.
Forecast highs by Monday are back around 70.
Winds will increase from the north today as a cold front slips down
through the area. Winds will be strongest over Lake Huron...where
speeds will reach 15 to 20 knots. A low pressure system passing
through the Great Lakes will then allow gusty southerly winds to
develop on Thursday...before they flip to the north late Thursday
night and Friday behind a cold front. Gusts look to remain at 25
knots or less...but the duration of the north winds and long fetch
over the lake could allow waves to build high enough to necessitate
small craft advisories for portions of Southern Lake Huron on
Friday. The low will also spread rain into the area...and perhaps a
few thunderstorms. High pressure will bring lighter winds for
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).