Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
547 am EST Thursday Mar 5 2015
VFR conditions will prevail this forecast period as the center
of a sprawling high pressure system builds just south of the area.
Scattered-broken cirrus along the northwest edge of developing East Coast
storm will shift east and just expect few-scattered diurnal cumulus by
midday. Light northerly flow will become northwest today and then
southwest around the northern periphery of the aforementioned high
as it shifts across the Ohio Valley tonight.
//Dtw threshold probabilities...
Previous discussion...issued 359 am EST Thursday Mar 5 2015
Short term...today and tonight
Another very cold airmass will build through the area today as
Arctic high pressure settles into the middle Mississippi Valley with an
extension of this high extending east into the Great Lakes and Ohio
Valley. Temperatures will only climb into the middle/upper teens within
this airmass as some upper level cloudiness also impedes solar
insolation to a degree. These temperatures are some 25f below
average for the first week of March.
As this high continues to settle southeastward tonight...expect
another very cold night with lows falling to around zero...plus or
minus a few degrees. The only thing staving off an even colder night
will be a southwest return flow around this high. While this wind
will help keep the boundary layer partially mixed...it will also
produce wind chill readings below zero overnight. In fact...wind
chills will approach 15 below zero from I-69 north late tonight.
While this is the criterion for an advisory...will allow the day
shift to further elevate as these readings are only reached for a
short time and are marginal for a headline.
Long term...Friday through next Wednesday
The sprawling cold dome of surface high pressure will settle south
of the Ohio River valley during the day on Friday. The pressure
gradient on the northwest periphery of the anticyclone will
strengthen leading to classic breezy return flow setup. There will
most likely be a heavy diurnal component to the breeze...with
southwesterly windspeeds reaching the 20 to 30 miles per hour range after the
noon hour. Increasing clouds during the afternoon hours in addition
to remnant midlevel cold air slow to dislodge will keep temperatures
in the middle 20s for daytime highs.
A pair of fresh northern stream jetlets are forecasted to dig
southeastward into the Great Lakes region early Saturday. The
response in front of these jetlets will be for a shortwave ridge and
associated Theta-E ridge to flash across the state. There remains
uncertainty with regards to the exact trajectory of the inbound
shortwaves. There has been a lack of both inter and intra model
continuity. This is important for a couple of reasons...exactly how
far northward temperatures can moderate on Saturday...and also where
best forcing for precipitation will exist on placement and timing. A
dry Arctic airmass preceding the shortwave suggests dry air will be
a problem. It remains difficult to go with anything above a chance
pop. Thermal forecasts continue to support all snow as a ptype despite
temepratures that are expected to climb above the freezing mark.
A weak system overall...with another jetlet diving into the region
will limit much if any cold air advection in the wake of the
Saturday wave. Temperatures Sunday will again be relatively
mild...in the middle 30s.
Surface high pressure will settle over the Ohio Valley and southern
Great Lakes today and tonight...bringing fairly light winds and
quiet weather to the area. A low pressure system will then slide
across northern Ontario Friday...while high pressure remains over
the Ohio Valley. This will bring an increase in southerly winds
Friday morning through Friday evening. Winds look to be the
strongest over portions of Lake Huron...with gusts currently looking
to reach between 30 and 40 knots. A gale watch remains in effect for
the central portion of the lake...including Saginaw Bay...for Friday.
Lake Huron...gale watch from Friday morning through Friday evening for lhz362-
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).