Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 151909
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
309 PM EDT SAT OCT 15 2016
There was a notable increase in low level moisture across Se Mi
today, which led to some low stratus/strato cu. Low level moisture
depth is a little greater across the Saginaw Valley where low clouds
may persist through the evening. Afternoon mixing, with the help of
20+ knot winds atop the shallow stable layer, led to some erosion of
the earlier stratus deck elsewhere. The southwest gradient will
increase during the night, inhibiting the depth of the nocturnal
stable layer. This combined with increasing sfc dewpoints will
maintain mild nighttime mins in the 60s overnight.
A mid level wave now over Manitoba will lift to James Bay by Sun
morning, dragging an associated cold front into northern Mi. Showers
and a few thunderstorms will develop/increase in coverage this
evening across the upper MS valley and wrn Great Lakes within the
entrance region of an upper jet max in the base of the
aforementioned trough. The resultant strengthening of the mid level
frontal circulation combined with an axis of higher mid level theta
e air arriving from the southern high plains will lead to this
increase in precip coverage this evening. The mid level fgen and deep
layer moisture plume will slide across the Saginaw Valley and thumb
region late tonight, supporting numerous to widespread showers.
There will also be a few thunderstorms in light of the deep
conditionally unstable layer above the mid level front.
The southward movement of the mid level front and sfc boundary will
slow on Sunday as they become aligned west to east and parallel to
the flow aloft. The mid level forcing will also slowly weaken amidst
a backdrop of rising mid level heights, especially during the later
half of the day. Moisture quality will still be quite good (precip
water around 1.5 inches and 850mb dewpoints around +13c). Given the
weakening forcing, coverage of precip is expected to decrease during
the morning as the lingering mid level forcing slides south across
the area. The axis of deep moisture and weak instability overhead
will still support a chance of convection Sun afternoon through Sun
night. Forecast highs around 70 look reasonable given the expected
cloud cover. Any prolonged breaks in the afternoon could however
allow daytime temps to rise well into the 70s as the sfc cold front
is likely to stall across central Michigan.
The proximity to the frontal boundary will support weak winds Sun
night. With abundant low level moisture present for October, there
will be a good chance for some fog development, likely lasting into
Mon morning. Increased low level southwest flow will force the front
north as a warm front Monday morning. Added low/mid level
convergence within the strengthening warm air advection regime will
pose a chance of thunderstorms late Sun night into Mon morning
across the Saginaw Valley and thumb. The front will remain north of
the forecast area Mon afternoon through Mon night in response to sfc
low pressure moving across the upper Ms Valley into the nrn Great
Lakes (resulting from a fast moving short wave impulse lifting into
Minnesota from the nrn plains). This will place the forecast area in
the warm sector Monday. Breezy and mild conditions can be expected,
with afternoon highs possibly hitting 80. The degree of low level
warming will also cap the environment to convection Mon afternoon
Current progs suggest frontal passage Tuesday will be delayed enough
to allow another very warm fall day. Limited moisture and little to
no upper level support will support a mostly dry forecast. The low-
mid level front looks to stall near or just south of our area for
the middle into the end of the week, taking on a SW/NE orientation
ahead of an inbound full-latitude upper trough. Potential for an
overrunning type situation to bring wet weather to the region for
the end of the week, with the ECMWF depicting a particularly wet
scenario. Plenty of uncertainty still exists with respect to the
progression of the upper trough, however. Regardless, temperatures
should return to AOB normal by the end of the week.
Strong southerly flow, topping out between 20 to 30 knots this
afternoon will diminish late tonight as the weak cold front clears
Lake Huron Tomorrow. Winds shifting to the northwest behind the
front during the day, but remaining light, below 15 knots. Light and
variable winds Sunday Evening giving way to increasing south to
southeast winds for Monday, but still only topping out around 20
knots, with slightly stronger south to southwest winds for Tuesday.
Deeper moisture over southeast Michigan coupled with an approaching
cold front Tonight will trigger showers and possible thunderstorms
north of the I-69 corridor late Tonight. Showers and possible
thunderstorms will then sink south during the day on Sunday.
Rainfall amounts expected to run on average around one-quarter of an
inch. However, locations that experience thunderstorms or heavier
showers, most likely Tri-Cities region, will receive higher totals
around one half an inch, to possibly as high as one inch.
Issued at 1243 PM EDT Sat OCT 15 2016
Good moisture surge lifting through southeast Michigan Late this
morning supported high IFR/low MVFR deck of clouds, but
mixing/clearing already has made inroads past Wayne county, and
suspect southern TAF sites (dtw-det-yip) to be VFR/ceiling free
below 5000 Feet through Tonight. Moisture axis holding back across
Western Michigan and approaching cold front makes for difficult call
across MBS and FNT/PTK. Higher confidence with MVFR/LOW VFR clouds
holding across MBS, with showers and possible thunderstorms
developing late Tonight. FNT/PTK look to be muddled in the middle,
both in terms of showers overnight and in between MVFR/low VFR
ceilings vs NO Ceilings. South-Southwest winds generally in the
8-16 knot range through much of the TAF period.
For DTW...Partly cloudy skies expected to persist into early evening
hours at least, and probably much of the night before clouds and
possible showers return by Morning.
//DTW Threshold Probabilities...
* Low in ceilings below 5000 ft through Tonight, medium tomorrow.
* Low for thunderstorms during Sunday.
Lake Huron...Small Craft Advisory until 6 AM EDT Sunday FOR LHZ421-422.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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