Scientific Forecaster Discussion
fxus63 kdtx 132326
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
726 PM EDT sun Oct 13 2019
Cold core of upper level low is overspread Southeast Michigan this
evening. Very subtle 700-500mb equivalent potential temperature
advection along the sharp mid to upper level pv gradient has been
good enough to support a very fleeting band of sprinkles over north
half of cwa after 20z. Based on radar trends any remaining potential
for sprinkles will end by the start of the taf period. Strong 900-
800mb cold advection will occur after 06z tonight leading to Stout
stratus deck for all areas. This stratus deck is expected to blanket
the area to begin the day and transition into stratocumulus as
daytime heating tries to raise cloud bases. Mixed due wester
gradient flow will ease with setting sun, then increase modestly 10-
20 knots again Monday.
Dtw threshold probabilities...
* low for cig aob 5kft tonight and Monday morning.
issued at 358 PM EDT sun Oct 13 2019
The large low pressure system remains cut off and stalled over Lake
Superior today and begins a slow eastward drift tonight. A plume of
moisture wrapping around the south flank of the system has been
fixed over central lower Michigan splitting our area with clouds to
the north and full sun to the south. Temperatures reaching the lower
60s under full sun deepened the boundary layer into a solid wind
field south of the cold front. This allowed wind gusts to reach the
30 mph range frequently during the afternoon period which is
expected to quickly subside toward sunset.
Back to the north, the moisture axis is producing rain of varying
intensity on the light end of the spectrum mainly in the Tri Cities
area. This activity is along and behind the slowly moving cold front
that is expected to accelerate eastward with a boost of upper level
support. The support is shown in afternoon satellite imagery as a
smaller scale circulation rounding the base of the larger upper low
and producing a trough of height falls set to move across lower
Michigan tonight. An additional flare up of showers occurs along the
front and within the moisture axis due to the additional upper
support and during the lingering boost from daytime peak heating.
The front and shower pattern exits eastward toward midnight and is
followed by a surge of air cold enough to activate Lake Michigan.
Expect clouds will be plentiful overnight into Monday morning with
an isolated lake induced shower possible before sunrise. The clouds
and lingering surface wind mitigate frost potential except possibly
for some patchy coverage in Midland and Bay counties toward sunrise.
The trough of height falls rotating across lower Michigan tonight
starts the entire low pressure system on an eastward drift during
Monday. Consensus of model projections shows a respectable low level
thermal trough surging into lower Michigan taking 850 mb temperature
down to about -5c. The colder air maintains lake stratocu through
the day and holds high temperatures around 50 for afternoon highs,
still a solid 10 degrees below normal for nearly mid October.
Surface high pressure then builds into the southern Great Lakes and
initates a clearing trend toward Monday evening. This leads to an
exchange of stratocu for cirrus Monday night which model data
suggests is mostly thin and hard to trust for a temperature impact.
The most favorable time window for frost then remains overnight
through sunrise Tuesday.
High clouds thicken quickly Tuesday morning as the next low pressure
system moves into the upper Midwest by Tuesday afternoon. The shortwave
trough tracking through the Pacific northwest this afternoon arrives
late Tuesday/Tuesday evening with the surface low/reflection now
progged to track through northern lower Michigan, per 12z
Euro/Canadian. Two shots at rain showers, first one comes late in the
afternoon/late in the day with the isentropic ascent/warm front and
then in the late evening with the cold front and 850-700 mb
moisture/Theta-E axis tracking through, as precipitable water values climb to around
1 inch. If anything, outgoing pops appear low, and would lean a bit
Turning colder and breezy behind the low on Wednesday, as 850 mb
temps fall at or slightly below zero, with wind gusts aoa 30 mph at
the surface looking likely based off 850 mb winds near 35 knots.
Cold cyclonic flow probably enough to generate scattered light
showers with steep low level lapse rates during the day.
Winds staying up Wednesday night may be enough to prevent frost as
temperatures fall at least into the upper 30s/around 40 degrees. A
ridge of high pressure to slide over the the central Great Lakes
Thursday night, presenting a better shot at frost/freeze headlines
as temps should fall into the 30s with the favorable radiating
conditions. Amplified East Coast trough, leading to a longer period
of upper level northwest confluent flow over Southeast Michigan,
which allows surface high/ridge to persist right into Friday before
warm advection pattern spreads in Friday night into Saturday, with
850 mb temps making a run aoa 10 c. Weakening cold front tracking
through on Saturday perhaps touching off a few showers, but 12 Euro
suggest otherwise (dry).
Fresh southwest flow will gust to near-gales, especially over
central Huron, through tonight. Wind will then gradually ease as it
veers to westerly in the wake of the front. Waterspouts will be
possible within the cold air through Monday afternoon. After a brief
reprieve Monday night into Tuesday, southeast wind will ramp up in
advance the next low pressure lifting into the northern Great Lakes.
Cold northwest flow filling in behind the cold front will will have
the potential to gust to gales by late Wednesday.
Michigan...Lakeshore Flood Warning until 8 PM EDT this evening for miz063.
Lake Huron...Small Craft Advisory until 8 PM EDT this evening for lhz442-443.
Small Craft Advisory until 10 am EDT Monday for lhz421-422-441.
Lake St Clair...Small Craft Advisory until 8 PM EDT this evening for lcz460.
Michigan waters of Lake Erie...Small Craft Advisory until 8 PM EDT this evening for lez444.