Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 280725
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
325 AM EDT Fri Apr 28 2017

.DISCUSSION...

Somewhat brisk early morning conditions can be expected within gusty
post frontal southwest winds and temps in the 40s and low 50s. The
winds will diminish during the course of the morning as weak sfc
ridging expands overhead. The rapid departure of the upper low to
the northeast of the Great Lakes today will also support some
moderation in the low level thermal profile. Clearing of the low
clouds is already underway. While there will be some mid/high clouds
during the day, model soundings suggest insolation will be adequate
enough to promote good daytime mixing depths. This will support
afternoon temps well into the 60s. There will be a developing warm
front across the Mid Miss and Ohio Valleys today and tonight.
Frontogenesis will increase across srn Mi within the mid level
portion of the frontal boundary later this afternoon, persisting
through tonight. Mid level moisture will feed into this frontal
boundary and will support a chance of rain late this afternoon south
of I-94 and across the entire forecast area tonight. The more active
portion of the frontal boundary is expected to remain in the low
levels, in closer proximity to the instability feed. Thus QPF
amounts tonight across Se Mi should be fairly light (less than a
tenth of an inch).

Over the course of the weekend there will be a strengthening of the
mid level ridge over the sern US while the mid level low over the
central Rockies dives into New Mexico and the Texas panhandle.
Meanwhile, strengthening high to the north of Lake Superior will
drive cooler lake modified air into srn Mi by Sat morning, tightening
the thermal gradient along the sfc front south of the state. There
will be a good feed of gulf moisture into the mid Miss Valley and
lower Ohio Valley in advance of the upper low. This and good upper
jet dynamics will support a fairly active frontal boundary through
the weekend. The feed of drier low level air under northeast flow on
Saturday may prove a formidable limiting factor for precip over Se
Mi, particularly in the Saginaw Valley and thumb. The northeast flow
will however support fairly cool temps. There are indications in the
deterministic model suite that mid level short wave impulses will
support better mid level forcing and thus much better precip chances
from late Sat through Saturday night. Potential elevated instability
and higher deep layer moisture in advance of any mid level short
waves could support some higher intensity convective
showers/thunderstorms Sat night.

The upper low will eject into the central plains on Sunday/Sun
night. The feed of deep layer moisture will in turn be driven into
the Ohio Valley/srn Great Lakes. This along with good upper level
diffluence and strengthening baroclinicity along the low-mid level
front will support high probabilities of showers/thunderstorms. The
closed upper low and proximity of the mid level ridge off the east
coast does indicate a potential for the more widespread and
persistent rainfall Sunday to be focused west of the forecast area,
although there does remain agreement that the Tri Cities region may
lie within the region of more prolonged forcing. The NAM/GFS/Canadian
all drive the warm front into at least metro Detroit on Sunday.
There is likely to be a 30 to 40 degree temp gradient along this
front. It should be noted that the ECMWF does not lift the front into
Se Mi, certainly not out of the realm of possibilities. The upper
low will finally lift through the Great Lakes region late Monday
through Tuesday. This will sustain shower chances into early next
week. Colder air will also funnel into the region on Tues as the low
lifts to the northeast, keeping temps below seasonal norms through
next week.

&&

.MARINE...

A tight southwesterly gradient between low pressure lifting into St
James Bay and high pressure building over the northern Ohio Valley
and Eastern Great Lakes will maintain gusty winds over Saginaw Bay
this morning. Gusts to around 30 knots are expected before the
gradient relaxes mid-morning. Relatively light winds are then
expected late today and early tonight before strong high pressure
builds into Ontario and low pressure begins to organize over the
plains. This will provide an increase in north to northeast winds,
and potentially build waves high enough to necessitate another Small
Craft Advisory for the nearshore waters of Lake Huron including
Saginaw Bay. Wave heights will decrease on Monday as winds turn
southerly ahead of a cold front, but speeds will gust up to 30
knots.

As the area of low pressure approaches the Great Lakes, an
increasingly wet and unsettled pattern will develop through the
weekend. Thunderstorms will be possible by Sunday and Monday as the
area of low pressure slowly moves through the Great Lakes.

&&

.HYDROLOGY...

Dry weather is expected much of today before showers move into the
area this evening through early Saturday, primarily impacting areas
along and south of M-59. Rainfall totals are expected to remain
below 0.15 inches through late Saturday morning. Periods of
steadier, and potentially heavy rainfall are then expected Saturday
afternoon through Monday, with rainfall totals during this period
expected to range between 1.5 and 3.0 inches. The heaviest rainfall
will occur over the Saginaw Valley, with totals generally decreasing
as you move southeast towards Lake Erie, though thunderstorms will
bring locally higher amounts. Flooding may become a concern by Sunday
and Monday.

&&

.PREV DISCUSSION...
Issued at 1157 PM EDT Thu Apr 27 2017

AVIATION...

Late evening observations show widespread coverage of mixed VFR/MVFR
stratocu over Lower Michigan and containing a few sprinkles toward
FNT and MBS. Farther upstream, an intrusion of dry air is making a
convincing push through northern Illinois. This adds confidence to
the clearing trend expected over south sections of the terminal
corridor through the early morning, eventually spreading over the
south half of Lower Michigan before sunrise. The wind gust component
of the strong westerly flow has held on since sunset and will only
diminish slowly during the night as the pressure gradient remains
elevated and the boundary layer remains well mixed. Backing low level
flow during Friday morning will direct any remaining low clouds into
the northern Great Lakes and leave behind generous coverage of
higher clouds moving in ahead of the next low pressure system,
however rain is expected to hold off until Friday night.

//DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less tonight.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 1 PM EDT this afternoon for LHZ421-422-
     441.

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

$$

DISCUSSION...SC
MARINE.......HLO
HYDROLOGY....HLO
AVIATION.....BT


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at www.weather.gov/detroit.



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