Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 181732
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
132 PM EDT Mon Mar 18 2024

.KEY MESSAGES...

- Reinforcing shot of arctic air for Wednesday and Thursday with
  scattered snow flurries.

- Increasing likelihood for accumulating snowfall for Southeast
  Michigan late Thursday night into Friday.

&&

.AVIATION...

Light snow falling throughout much of the CWA, including DTW, with
ceilings creating MVFR conditions. Stratiform snow is expected to
break down within the next couple hours, giving way to more variable
and isolated snow showers. Omega spike spilling off the ridge to the
west will support these showers through approximately 0Z tonight.
VFR ceilings tomorrow as winds back to become more southwest and
lighten slightly. Slight chance of snow exists tomorrow as well, but
probabilities remain low, especially for the southern part of the
CWA including DTW. A deeper mixed layer in the afternoon/evening
will allow higher winds to mix down, with some gusts reaching over
20 knots.

.DTW THRESHOLD PROBABILITIES...

* High in precip type being snow today.

* High in ceilings aob 5000 this afternoon, medium tonight into
  Tuesday.

&&

.PREV DISCUSSION...
Issued at 318 AM EDT Mon Mar 18 2024

DISCUSSION...

The polar trough over the Central Great Lakes will result in another
day of below normal daytime temperatures (upper 30s). Plan view
perspective of geopotential heights show a narrowing of the trough
wavelength which will allow modest height rises to sneak into the
forecast area. Large scale support for synoptic scale lift is
lacking with no substantial absolute vorticity advection and
extremely unfavorable upper level jet forcing. The midlevel warming
will result in shrinking convective depths with active forcing
coming down to diurnal heating. Models support best thetae and
saturation into the bottom of the DGZ from roughly Metro Detroit
southward after 21Z. Did introduce PoPs for the late afternoon
period. The lack of moisture will limit snow amounts to perhaps a
light dusting on grassy areas.

The next northern stream upper level jet packet will dig into
western Great Lakes rather rapidly by 12Z Tuesday. Cyclonic
curvature to the jet maximum along with a well organized left exit
region is expected to result in an ageostrophic response and
isentropic lift over Lake Huron late tonight. Model soundings show
outstanding moisture/lapse rates above 12.0 kft agl. A major
limiting factor to precipitation will be a boatload of dry air in
the lowest 7.0 kft agl. The important grid edit for late tonight was
to increase PoPs in the Thumb. A minor snow accumulation will be
possible across Huron County early Tuesday.

A secondary speed maximum and attendant shortwave will help drive a
cold front through the region early Wednesday. Temperatures on
Wednesday are expected to be some 8 degrees cooler than the day
before. The cold air will again allow convective depths to push into
the DGZ. Low level moisture remains a problem for many areas but the
Thumb will need to be monitored as wind trajectories will be from
the northwest. Saginaw Bay could provide just enough enhancement to
bring another minor dusting to Huron County.

Upper level confluence, differential geopotential height rises, and
some anticyclonic curvature to the flow will result in stable
anticyclone over Southeast Michigan Thursday and most of Thursday
night. Depth of subsidence in the forecast soundings and time of
year considerations suggest sunshine Thursday.

An inflection in the polar vorticity reservoir and a coupled upper
level jet structure will allow for a wave of low pressure to pass
through the Great Lakes late Thursday night through Friday. Models
continue to show an outstanding leafing structure to what would be a
very good warm advection event. There has been consistency with
around 0.25 of inch of liquid equivalent. Will need to watch the
timing because if it pushes back a little more the precipitation will
fall during the daytime Friday. This could then compromise the snow
ratios. However, as it stands everything looks good for an
accumulating snowfall of a couple/few inches across the area.

MARINE...

Cold air advection remains ongoing as the weekend low still remains
over southern Quebec to start the day. This low will pull yet
another cold front down through the region today which is
collocated with the upper level trough axis which will drop through
the region as well. Cold air advection with the northwesterly winds
behind the front will keep unstable conditions going today and into
tonight. Wind gusts are holding in the 20 to 25 knot range but with
the cold unstable air and long fetch, waves will continue to be an
issue through at least the afternoon so Small Craft Advisories
continue today. Area of high pressure then slides in tonight and
Tuesday leading to improved conditions. A clipper will then dive
southeast through the region Tuesday night and Wednesday bringing a
another cold airmass and stronger winds which may reach gale force
over Lake Huron.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-422-
     441-442.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....BC
DISCUSSION...CB
MARINE.......CB


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