Scientific Forecaster Discussion
fxus63 kdtx 250706
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
306 am EDT Sat Mar 25 2017
There is a tight low to mid level baroclinic zone draped across the
Great Lakes early this morning. Meanwhile, the circulation
associated with the upper low now churning over Oklahoma is feeding
a plume of deep layer moisture into Illinois. During the night, the
frontal boundary across lower Michigan has remained active in two
locations; across northern lower mi within the 700-600mb layer and
across the central portions of the forecast area (m59 to I-69
corridors) closer to the 925mb portion of the frontal zone.
The hi res model suite all suggest the 925-850mb layer will become
more active during the early morning, aided by the ongoing deep
layer moisture feed across Illinois. This will support increasing
coverage of showers across the forecast area (aside from perhaps
locals south of the I-94 corridor). Weak elevated instability
along/south of the I-96 corridor has supported some thunderstorms
overnight. The overall persistence of this weak instability will
continue to support some additional thunderstorms. Enhancing the
forcing along the front is the ageostrophic response within a 140+
knot upper jet streak centered over srn Quebec. This forcing will
persist through the first half of the day today. The upper jet
streak will then become focused much farther east this afternoon. In
fact, some mid level ridging will develop across the ern Great Lakes
today as the upper low rotates into Missouri. These factors will
fracture/weaken the frontal forcing, leading to a diminishing trend
to the coverage of showers during the course of the afternoon and
Despite the approach of the associated sfc low pressure into
Missouri today, strengthening sfc high pressure across northern
Ontario drove the sfc cold front across the forecast area last
night. Marine modification under the Post frontal northeast winds
have resulted in a rather shallow but cold near sfc layer across se
mi. Temps actually dropped a good 20 to 30 degrees following fropa
last night. The easterly component of the sfc winds will persist
through the day, while Post frontal stratus continues to expand
across se mi. This will keep the front south of the area today and
will only support temps in the 30s and 40s, with the coolest
readings downwind of Saginaw Bay and Lake Huron with the NE winds.
The upper low will lift into the nrn Ohio Valley and srn Great Lakes
on Sunday but will dampen considerably as it does so. There are
differences among the 00z model suite with respect to timing and
location of this system as it approaches the region. Some upper
level diffluence and mid level deformation forcing will support some
regions of more persistent rainfall, the locations of which carries
a high degree of uncertainty at this time. Indications among the 00z
model suite are that the better rain chance overnight into Sun
morning will be to the west of north of se mi, with rainfall
probabilities over the forecast area increasing Sun afternoon. The
low level wind fields will turn more southern Sunday as the
associated sfc low lifts across lower mi. This will allow temps to
make a run into the 50s.
Mid level subsidence will overspread the region by Monday as the
remnant upper wave lifts off the northeast. There will not be any
cold air intrusions in the wake of this system, so Monday highs will
possibly rise into the 60s, dependent upon the degree of lingering
low clouds. There has been a noted trend toward a weaker and farther
south mid level short wave feature Mon night into Tuesday. Precip
chances have therefore been lower accordingly. Mid level ridging and
sfc high pressure will dominate during the mid week period. Easterly
sfc flow will however keep temps somewhat on the cool side. The
approach of yet another upper low by the medium range suite will
warrant the next chance of rain the end of the work week.
The slow moving frontal boundary has dropped south of Lake Erie
overnight bringing a wind shift to the northeast across all of the
eastern lakes. Winds will increase this morning reach 25 to 30 knots
across Central Lake Huron which will lead to waves in excess of 4
feet impacting the nearshore waters over the northern thumb region
during the day. Small craft advisories are in effect for Saginaw Bay
and a portion of the nearshore waters through most of the tonight
period. High pressure building across Ontario and Quebec with a low
tracking into the western Ohio Valley will then cause the winds to
veer more easterly which will take the higher winds into Northern
Lake Huron for the rest of tonight and Sunday. The weak low then
looks to slowly pass through Lake Huron on Monday, with generally
light winds right into Tuesday, but from the north behind the low.
Periodic showers will affect the region through the weekend as a
frontal boundary stalls just south of the state line. Though a
lengthy period with on and off showers, rainfall totals are only
expected reach 0.5 to 0.75 inches through the duration of the event.
The resultant runoff will likely increase flow rates and water
levels in local streams and rivers but flooding risks are mitigated
by the long duration of this rainfall.
issued at 1148 PM EDT Fri Mar 24 2017
Shallow cold front will be slowly edging south of the I-94 terminals
by 06z. Narrow band of surface/near surface based convection along
and immediately behind the front will transition to widespread light
rain elevated to the north of the front, especially kptk north late
tonight into Saturday. As cool, northeast flow in the low levels is
overrun by higher Theta-E air, expect widespread IFR/LIFR stratus to
develop as well. While rain may become less concentrated by midday
Saturday, low ceilings and vsbys in -dz and/or br will persist to
one degree or another for the rest of the forecast period.
For dtw...scattered showers have remained just north of terminal
during the evening and that trend looks to continue for several
hours before showers eventually expand over much of the area late
tonight. Ceilings are still expected to stair step down into MVFR and
eventually IFR/LIFR by early Saturday morning.
//Dtw threshold probabilities...
* high for cigs aob 5000 feet this forecast.
* Low confidence in cigs/vsby aob 200 feet or 1/4sm late tonight into
early Saturday morning.
Lake Huron...Small Craft Advisory until 8 PM EDT this evening for lhz422.
Small Craft Advisory until 4 am EDT Sunday for lhz421-441.
Lake St Clair...none.
Michigan waters of Lake Erie...none.