Scientific Forecaster Discussion
fxus63 kdtx 131801
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
101 PM EST Wed Nov 13 2019
The periphery of a shortwave trough has begun to encroach on the
central Great Lakes region early this afternoon. Low level jet enhancement
feeding off Lake Michigan moisture has led to some lighter snow well
to the northwest of the taf sites, but should shift eastward and
weaken slightly after 00z. Synoptic diagnosis indicates the wave
digs/pivots in late this evening with this primary forcing focused
further north such that the bulk of the snowfall should be confined
to kmbs, kfnt, and maybe kptk. Went with only prob30 -shsn for kftn
and kptk given the higher uncertainty, particularly for the latter.
Broadly expecting cigs/vsbys to drop to MVFR around snow onset time,
but brief periods of IFR are not out of the question, especially at
kmbs. Elsewhere, VFR should hold through Thursday with 10-15 kt S/south-southwest
flow which will weaken overnight.
For dtw...VFR into tonight with overcast mid cloud deck holding for most
of this afternoon and evening. Cigs lower to about 6 kft by 02z and
hold through midday Thursday. There is a chance for a brief coating
of snow for dtw overnight, but confidence is too low to warrant a
taf mention given uncertainty in placement of any small/brief
showers that may develop. Cigs lower to MVFR ahead of an approaching
boundary Thursday afternoon.
Dtw threshold probabilities...
* low confidence for ceilings at or below 5000 ft tonight through
* Low confidence for snow tonight through Thursday evening.
issued at 350 am EST Wed Nov 13 2019
High pressure sliding through the region overnight with clear skies
and calm winds atop a fresh snowpack has resulted in efficient
radiative cooling conditions. Temperatures are mainly hovering in
the mid single digits with our typical cold spots at or even below
zero. The coldest air within this current thermal trough is behind
US now as the airmass will moderate through the day with southerly
flow and waa ahead of the next system targeting the region tonight.
The effects of the waa won't really be felt at the surface today as
highs are limited to the mid/upper 20s. Air is too cold to start,
clouds will prevent much help from the sun, and initially waa will
be felt in the mid levels. There is a chance that a wedge of warmer
air will lift up through the southern few counties late in the day
which could boost temps up closer to 30.
A long wave trough will swing through the region tonight bringing
the next chance of snow. After 00z this evening, a cold front will
drop into mid Michigan as a mid level wave tracks along it. Isentropic
ascent ahead of it will saturate mid levels but very dry boundary
layer will be tough to overcome for most of Southeast Michigan initially.
Moisture quality is low as pwats only rise from about 0.3" up to
0.5" during peak forcing, and soundings show the dry low levels
struggle to ever truly become saturated. Narrow corridor of fgen
aided by left exit region of a 90kt jet will pair with the weak
front to help showers develop though. Best chances will be along and
north of i69 where up to an inch can be expected. As the front
continues south toward morning, the shortwave will be exiting
eastward leading to lower totals as one heads south. Snow should
start falling later this evening ending by Thursday morning.
There is a chance that weak cold advection on the backside of the
cold front will advect some lake effect showers off Lake Michigan through
the morning Thursday. A slight SW wind component will keep the bulk
of this cloud band and light showers along and north of M59. High
pressure will reduce inversion heights and bring in drier air
helping to shut if off for the afternoon.
High pressure will hold Friday through the weekend resulting in a
precip free forecast. Though the airmass will slowly moderate
through this time, 850mb temps look to hover in the low single
digits keeping the stretch of below average temps going (highs
mainly below 40f). The next longwave trough looks to swing through
Monday bringing the next chance of precip.
Relatively calm boating conditions will be short-lived as high
pressure departs to the east and causes a stronger pressure gradient
to build over the open waters on Wednesday, bringing the return of
20-25 knot wind gusts with at least a small potential for low-end
gales over Northern Lake Huron. While funneling up Saginaw Bay may
enhance winds enough to support occasional 25 knot gusts, scenario
appears marginal and transient enough to forgo headlines. The same
GOES for an gale potential as there is a better chance that gusts
remain closer to 30 knots or Northern Lake Huron.
Winds will then settle back down tonight into Thursday before
increasing again from Thursday night into Friday as another cold
front clips the area. Once again, expect gusts to generally top out
near 30 knots over northern portions of the lake. However, with the
wind direction veering from westerly to northerly on Friday, wave
action will build from north to south and may eventually reach Small
Craft Advisory criterion late Friday into Friday.
Record low maximum temperatures for November 13
Detroit area....21 (1911)
Flint area......19 (1986)
Saginaw area....21 (1986)
Record lows for November 13/14
Detroit area...12/13 (1911/1986)
Flint area.....12/12 (1986/1986)
Saginaw area...12/11 (1986/1933)
Lake St Clair...none.
Michigan waters of Lake Erie...none.