Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
348 PM EDT Sat Oct 25 2014
Short term...this afternoon and tonight
Subsidence in the wake of passing cold front will lead to mainly clear
skies through tonight. Gusty west/northwest winds will also relax with
boundary layer decouping this evening. These decent radiational cooling
conditions...along with modest cold air advection...will allow the
temperatures to drop into the upper 30s/lower 40s...despite the fact
that many areas have reached the middle 60s late this afternoon. Winds
will gust to 20 miles per hour or better into early this evening before easing
begins by sunset or so.
Long term...Sunday through Friday
Ridging will bring dry weather and abundant sunshine to Southeast
Michigan on Sunday. However cold air will be in place behind the
departing cold front as 850 mb temperatures fall to 3 to 5 celsius.
Despite sunny skies the cooler airmass will mean highs will
generally be limited to the middle to upper 50s Sunday afternoon.
The ridge will track east Sunday night...allowing for warm air
advection to commence in earnest across the central Great Lakes on
Monday as 850 mb temperatures rise to 12 to 14 celsius. A warm front
will lift north through the southern Great Lakes on Monday...acting
as a trigger for showers and a few thunderstorms...mainly across the
north where the front will settle during the afternoon hours. A
shortwave tracking through the southern Great Lakes will assist in
precipitation development on Monday...with warm moist air and
increased instability bringing the chance for thunderstorms embedded
within the shower activity. Despite the passage of the warm
front...highs will vary greatly on Monday...with highs around 60
across The Thumb given a southeasterly surface wind off Lake
Huron...with highs around 70 near the Ohio border away from the main
precipitation and deeper into the warm sector.
The parent low associated with the aforementioned warm front will
develop over the western Great Lakes Monday night...then track east
through the northern Great Lakes Tuesday...dragging a cold front
through the central Great Lakes on Tuesday. Models have come in
better agreement this run...mainly the European model (ecmwf) which has come in
faster this run...more in line with the GFS in clearing the front
through by Tuesday. Although it is not lock step with the faster GFS
solution...it is in the same Ball Park to allow for likely probability of precipitation on
Tuesday given the higher degree of confidence in frontal passage sometime on
Tuesday rather than a possible frontal passage solution that is a whole 12
hours apart per the previous runs. Continued instability will keep
thunderstorms in the forecast during this time period until the cold
front clears the area.
With the better model agreement...it appears rain chances will be
off to the west by Tuesday night given the subsidence behind the
departing front. Therefore will dry out the forecast on Tuesday
night...with ridging expected to keep the weather dry into Wednesday
as a shot of cool dry air sends afternoon highs back down into the
lower to middle 50s on Wednesday.
A weak low pressure system is then on track to affect the central
Great Lakes during the later part of the work week. Given the weak
nature of this low pressure system it is not surprising that the
models are having a hard time resolving the timing and impact of
this low pressure system. There are hints that this system could
bring the first taste of winter to Southeast Michigan late in the
week...with some snow flakes possible across the area. However the
aforementioned issues with the exact timing and strength of this
system does not lend itself to a great degree of confidence this far
out...but it does bear watching with the upcoming Halloween Holiday
at the very end of the extended forecast.
The main feature in the extended forecast is a developing middle
latitude cyclone across the upper Mississippi Valley. This system
will deepen from 1002 to 994 mb as the low and attendant cold front
cross Michigan on Tuesday. Cool temperatures and dry conditions will
then settle in for the middle of the week until the next middle level
wave brings additional rain chances Thursday and Friday. Confidence
is low outside of the Tuesday rain event.
A strong low near James Bay will cause northwest winds to ramp up
over area waters this evening. The strongest winds will be over the
northern half of Lake Huron where a colder airmass will support
winds gusting to low-end gales. In addition...small craft advisories
are in effect for the exposed nearshore waters of The Thumb where
significant waves heights are expected to build to several feet.
Aviation...issued 115 PM EDT Sat Oct 25 2014
Remaining stratus will erode quickly early in the forecast as much
drier west/northwest flow overspread the area with the passage of a
cold front. Skies will remain clear-few through the rest of the
forecast period. Strong mixing will lead to some wind gusts to 25
knots this afternoon after frontal passage...with winds from 280-290 degree. The
loss of mixing will result in winds from 270 degree at under 10 knots
by this evening.
//Dtw threshold threats...
* low confidence wind gusts will exceed crosswind thresholds
Small Craft Advisory...outer Saginaw Bay and the nearshore waters
from Port Austin to Port Sanilac...from midnight Sunday to 4
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).