Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 200407
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1207 AM EDT Sat May 20 2017


.AVIATION...

Shower activity tied to synoptic scale stretching deformation has
all but peeled east of the area. Will continue to see the 850mb
frontal boundary remain in place over southeastern Michigan tonight.
This will keep midcloud in the picture particularly south of the Tri
Cities tonight. Amplifying shortwave ridging will keep precipitation
out of the region through the overnight. Question is on timing of
precipitation onset tomorrow. There is enough signal that suggests
convection from MO will lift northward overnight, sliding northward
within the crux of the main theta e ridge and moisture transport.
Larger scale ridging will be dominant which should work in dampening
out prior precipitation as it arrives, however, midlevel lapse rates
appear steep enough to allow for shower potential. Decided to go
with a tempo grouping for showers in the 17-19Z time window. Strong
midlevel trough and associated surface low pressure system advancing
out into the central Plains this evening and tonight will set the
stages for developing and strengthening easterly flow. Expectations
are for a stiff breeze Saturday between 10 and 20 knots.

//DTW THRESHOLD PROBABILITIES...

* Low confidence in cigs aob 5000 feet tonight medium confidence
  Saturday afternoon Saturday.

&&

.PREV DISCUSSION...
Issued at 347 PM EDT Fri May 19 2017

DISCUSSION...

MCV and remnant convection from over the Plains last night will
continue to work east across the Ohio Valley and Lower Michigan
through the late evening. Activity has been encountering mid-level
dry air and subsidence provided by upper ridging as it progresses
into the region, allowing only light showers to survive. Slightly
steeper mid-level lapse rates could allow for a rumble of thunder
near the Ohio border, but potential is very low. Showers will exit
the area late tonight as the MCV moves east and upper ridging
prevails. Clouds overnight will help offset cool airmass, keeping
min temperatures in the low 40s to near 50.

Larger upper low over the intermountain west will slowly lift
northeast, reaching southwest Ontario by Sunday night. This system
will be the major player on our weather through the weekend,
bringing unsettled conditions. Elevated portion of the warm front
associated with this system will lift into Southeast Michigan
tomorrow. Isentropic ascent does not look all that impressive, and
with better moisture still upstream and rising heights in advance of
the low, not expecting much in the way of showers and thunderstorms
during the day tomorrow. Easterly flow off the Great Lakes and
position on the north side of the warm front will have an impact on
temperatures, holding highs in the upper 50s to low 60s well inland
of the lakeshores, with mid 60s expected only well inland.

Better chance for rain still looks to be Saturday night through the
first half of Sunday as surface low pressure lifting north through
the Western Great Lakes pushes a good theta-e plume across the area
and a shortwave trough axis pivoting around the main upper low lifts
across Lower Michigan. Cold front will follow late in the day,
ushering in drier air and ended chances for rain. Steeper lapse
rates will also provide a chance for thunderstorms. Temperatures
will moderate Sunday in southerly flow ahead of the front, warming
into the 70s.

Isolated showers will be possible throughout Monday as a series of
upper-level disturbances swing around an upper-level low pressure
system located north of the Great Lakes. A lull in precipitation
chances will be possible Monday night into Tuesday morning before a
surface low pushes northeast from Iowa into Michigan Tuesday into
Wednesday, bringing much higher precipitation chances, with PoP
values forecasted in the 50s to 60s. While PoP values will diminish
Wednesday into Thursday as the low pushes Northeast out of the Great
Lakes region, continued chances for spotty showers will be possible
over the weekend as the GFS and GEM model runs display a warm front
pushing into Michigan.

In terms of temperatures, daytime highs are expected to stay normal
to slightly below normal through the extended forecast period, with
Wednesday and Thursday exhibiting the coolest trends, with highs
peaking in the low to mid-60s.

MARINE...

Northeast winds mainly in the 15 to 20 knot range will maintain
higher waves over the southern Lake Huron basin, and small craft
advisories have been extended. Even as the flow shifts to the East
overnight, waves up around 4 feet likely clipping outer Saginaw bay
and northern tip of the thumb region Saturday morning. Winds will
continue to veer, and become southeast late in the day, with modest
increase into the 15 to 25 knot range Sunday night, with channeling
up across the northern third of Lake Huron producing gusts around 30
knots. Low pressure sliding north of Lake Huron will lead to wind
shift to the southwest late Sunday, with strongest winds, around 20
knots, over Saginaw Bay and central Lake Huron. Wind speeds then
reaching and exceeding 20 knots across all nearshore waters on
Monday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 10 AM EDT this morning for LHZ442-443.

     Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-422-
     441.

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

$$

AVIATION.....DRK
DISCUSSION...HLO/AM
MARINE.......SF


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at www.weather.gov/detroit.



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