Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 292308
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
708 PM EDT Wed Mar 29 2017


.AVIATION...

Ceilings AOA 10kft will thicken this evening and lower further
overnight as elevated warm front lifts into the area. FGEN along
this boundary may produce light rain/snow/virga KFNT north late
tonight, but most of the precipitation will fill in over region
between 10z-14z and persist the rest of the forecast as warm front
lifts up to Michigan/Ohio state line and moisture continues to
funnel NE into area in advance of approaching low pressure. With
terminals catch in ENE flow north of surface front, went ahead and
lowered ceilings notably from previous forecast (but not quite as
much as guidance suite attm). Most precipitation will fall as rain,
but period of -sn/-rasn will be possible KMBS (perhaps KFNT) early
on Thursday. Wind gusts of 20-25 knots will be possible Thursday
within tightening pressure gradient north of front.

For DTW...VFR tonight with ceilings thickening/lowering from 10-
12kft to 6kft. More rapid deterioration 10z-14z as area of rain
begins to expand into/over area. At best, cigs may hold MVFR to
borderline IFR by midday into evening. May need to lower further.
ENE winds will also gust into the 20-25 knot range Thursday.

//DTW THRESHOLD PROBABILITIES...

* Low for ceilings at or below 5000 feet through 10z, medium 10z-
  14z, high beyond 14z Thursday.

* High in precipitation falling as rain, but low that thunderstorm
  will impact terminal Thursday.

&&

.PREV DISCUSSION...
Issued at 346 PM EDT Wed Mar 29 2017

DISCUSSION...
Storm system will bring a wet, cold, windy, raw Thursday
across the area.  Surface and closed 500mb lows over the Kansas-
Oklahoma border will slowly head northeastward to about eastern lake
Erie by Friday evening.  Strong surge of moisture ahead of this
system will bring soaking rain for the area starting tonight through
most of Friday. First shot of precipitation will occur on a
narrow Fgen band modeled to develop tonight anywhere from the M59
corridor as indicated by the RAP to the I69 corridor shown by the
GFS to slightly further north and a tad later by the Nam. Current
satellite and radar trends seem to point more towards the Saginaw
Valley.  The forecast problem with any precip from this will be type.
As precip begins to develop lower levels will start off above
freezing which would allow any precip to reach surface as rain. But
with very dry low levels from cool dry northeast flow advecting in,
evaporative cooling and wet bulbing will shift profiles quickly to
right along or slightly below the 0c line mainly north of the M59
corridor. This will lead to a change to snow or rain/snow later
tonight. QPF should be on the light side less then two tenths. Any
snow will be wet with ratios around 8 to 1 leading to any
accumulations less then an inch as surface temps will remain in the
low to mid 30s.

More widespread and heavier overrunning rain will spread across the
entire area Thursday as surface warm front lifts to about the Ohio
border.  Warming in the lower levels will slowly push rain/snow line
northward but may not clear northern portions of Midland, Bay and
Huron counties as low level flow will remain more cooler east
northeast.  This will leave the possibility of more light
accumulations, mainly on elevated and grassy surfaces.  Elsewhere,
surface gradient will tighten as surface low deepens slightly
leading to a brisk and gusty easterly flow keeping highs only in
the upper 30s north to mid 40s far south.  Periods of rain will
continue Thursday night through Friday before exiting early Friday
night. There will also be a chance for convection Thursday
afternoon through Friday morning along and south of the elevated
warm front which should stall along the I69 corridor. Instability
will increases as low level warm moist advection combined with
steepening mid level lapse rates with the approaching 500mb low.
Highs Friday will be more mild in the low to mid 50s from the
Detroit area south as the surface low tracks right overhead, to the
40s north.

Saturday looks dry with high temps into the low to mid 50`s for the
afternoon hours. By Sunday afternoon, low pressure over the southern
plain states will have pushed NE into the Ohio Valley. This will
bring in weak chances for rain Sunday afternoon. Chances for rain
are expected to significantly increase for Tuesday; especially over
the southern portions of the CWA. At least some chance of rain will
linger through the week as low tracks over Lake Erie and into the
New England states. Temperatures remain mild through the period.

MARINE...

The central great lakes will remain situated between high pressure
positioned to the northeast and approaching low pressure lifting
from the central plains into the Ohio valley through the end of the
week.  The resulting tight gradient will maintain an extended period
of strong winds with an east to northeast component.   Easterly
winds strengthen beginning Thursday under weakly unstable
conditions.   Strongest winds Thursday night through Friday morning,
where a period of gusts to near gales will be possible over central
and northern sections of lake Huron.  Marginal conditions will
preclude issuance of a gale watch at this time.  Building wave
heights under this flow will eventually result in small craft level
conditions for the entire lake Huron nearshore waters and outer
Saginaw Bay late Thursday and Thursday night.  These conditions will
likely persist through Friday over most locations given continued
northeast flow.  Winds and subsequent waves heights will ease as the
the low exits eastward Friday night.

HYDROLOGY...

Multiple rounds of precipitation will lift across southeast Michigan
Thursday through Friday as low pressure slowly advances toward the
region.   Precipitation will arrive on Thursday along a lead warm
front.  The onset of precipitation Thursday morning will fall as
mainly rain, but a period of accumulating snow will be possible
across the northern Saginaw and thumb region.  Additional rainfall
will then occur on Friday as the main low pressure system lifts
across the eastern Great Lakes.  Rainfall amounts from three
quarters of an inch to one inch remain forecast over the two-day
period.  These amounts spread over two days should result in just
minor rises to area rivers and streams.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 5 PM Thursday to 10 AM EDT Friday for
     LHZ443.

     Small Craft Advisory from 5 PM Thursday to 4 AM EDT Saturday for
     LHZ421-441-442.

Lake St Clair...NONE.
Michigan waters of Lake Erie...Small Craft Advisory from 8 AM to 10 PM EDT Thursday for LEZ444.

&&

$$

AVIATION.....DG
DISCUSSION...DRC/DE
MARINE.......MR
HYDROLOGY....MR


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