Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 180024

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
724 PM EST Sat Feb 17 2018


Light snow is now advancing across wrn Lower Mi. The mid level ascent
appears to be strong enough to sustain the light snow as it tracks
across Se Mi this evening. The 00Z DTX sounding also showed
respectable lapse rates in the 700-500mb layer. So the forcing,
albeit brief, should support a period of light snow focused mainly
between 01Z and 04Z this evening. This will support an increase in
the chances of snow this evening. The brevity of the snow and overall
weak nature of the ascent should keep accums around a half inch or


Issued at 544 PM EST Sat Feb 17 2018


The region of forcing supporting the area of moderate snow extending
from metro Chicago across northern Indiana as of 22Z will weaken as
it tracks across Se Mi late this evening. Thus the intensity of the
snow is expected to diminish as it crosses the area in the 01Z to
05Z time frame. Nonetheless, some reduction in visibility to IFR in
light snow is possible this evening. With temps holding in the low
30s, some minor (half inch or less) of slushy accumulation is
possible). An MVFR stratus deck is already pushing into portions of
Se Mi in advance of the region of light snow. Expect the lower
clouds to continue to overspread the area this evening. While the
forcing will rapidly push east after 05Z, model soundings with
support of upstream observations indicate periodic low clouds will
affect the region until late (after 14Z) Sun morning with a push of
warmer/drier air from the south arrives.

For DTW...The heaviest snow is expected to fall well south of metro
this evening. Nonetheless, light snow will impact the terminal in the
02Z to 05Z time frame. Any accums will less than a half inch with
sfc temps holding in the 30s.


* High in ceilings below 5000 ft tonight. Moderate Sunday morning.

* High for ptype as snow this evening.

Issued at 315 PM EST Sat Feb 17 2018


Despite the thick canopy of high clouds around today, temperatures
were still able to rise into the low/mid 30s.

Strong upper wave tracking along/close to the southern Michigan
border late today. Bulk of isentropic assent/moisture advection
looks to be used up just to saturate the low/mid levels, and thus if
measurable snow is able to develop this evening, looking at half
inch or less.  Narrow axis of 850-700 MB specific humidity in the
1.5-2 g/kg range sliding through during evening, but already quickly
drying out after midnight, lowering to around 0.25 g/kg by 12z
Sunday. Mins dependent on low clouds scattering out or clearing, but
latest RAP indicating higher moisture/rh at 925 MB holding on
through majority of the night, and will thus hold temps in the 20s.

Pronounced upper level ridging/height rises to take place over the
Great Lakes Region during Sunday, with strong low level southwest
flow to lead to significant warming, as 850 mb temps rise to around
zero toward sunset and into the mid single numbers Sunday night.
Airmass will be very dry, as 850 mb dew pt depressions increase to
between 40 to 50 C Sunday evening. However, this will dramatically
change for early next week, as big convergence of Pacific/Gulf of
Mexico surges north and reaches southeast Michigan with PW Values
around 1.25 inches, which looks to be record territory for February.

Strong model consensus amongst Euro Ensemble members indicating
highs in the 60 to 65 degree range on Tuesday across the majority of
southeast Michigan, placing record highs in jeopardy.

One wave of low pressure tracking through on Monday will bring rain
showers, with active frontal zone then lingering over the area, with
cold front looking to slide through Tuesday night or Wednesday
morning. Marginal instability (showalter index falling to around
zero) leads to mention of thunder, but only acting to enhance
rainfall, as surface/near surface will be stable enough to preclude
severe concerns. One to two inches of rain is likely in the moisture
rich environment Monday through Wednesday morning, with 3 inches
certainly possible.

Positive tilted upper level trough axis lingering across the Rockies
Wednesday-Thursday will lead to just a modest shot of cold air (for
February standards) following the cold front, as high pressure (1040+
MB) slowly slides through the northern Great Lakes on Thursday.
Retreating high Thursday night-Friday, but surface ridge axis
potentially holding on long enough during Friday to get through the
day dry before a warm front lifts north.


Winds will remain out of the southwest with gusts topping out around
30 knots through this evening ahead of an advancing cold front.
Expect the higher winds gusts to be tempered a bit due to extensive
ice cover. Winds will veer to a more west-northwest direction in the
wake of the front overnight, but will not last long as southerly
flow kicks back in Sunday afternoon as a warm front lifts northward
through the Great Lakes. Winds gusts will again remain around 30
knots Sunday evening as the front lifts through the region.


A strong warm and moist advection regime will kick into gear Monday
through Wednesday ahead of a slow moving front. This warming and wet
trend will result in a full melt off of present snow cover across
southeast Michigan. Several periods of rainfall can be expected
during this time with widespread rainfall totals of 1-2" over the
course of Monday to Wednesday. There is still some uncertainty with
where the higher rainfall amounts will fall, but there is potential
for some locations to near 3 inches of rainfall where stronger
pockets of convection occur. While the melting snow will unlikely be
enough to support flooding, the potential for rainfall in
combination with the snow melt could cause some rises in area rivers
and streams. Ice breakup on area rivers and streams caused by warmer
temperatures will also be something to keep an eye on, which could
exacerbate any local flooding issues.


Record high temperatures will be possible across much of southeast
Michigan Tuesday. Here is a look at record high temperatures for
Tuesday, February 20th:

Detroit     63 (2016)
Flint       61 (1930)
Saginaw     62 (1930)

With the high moisture content, good chance to break the high
minimum records for February 20th as well:

Detroit     47 (1930)
Flint       45 (1930)
Saginaw     46 (1930)


Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.



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