Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211935

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
335 PM EDT Sat Apr 21 2018



As of 335 PM EDT...A dry afternoon continues across southeast
Michigan as surface high pressure remains in control. Dewpoints
plummeting into the 20s, and even upper teens across some areas, has
allowed it to feel even drier as RH values dip well below 40 percent.
High clouds spilling northeastward from a closed low parked over the
western Plains continue to filter in across most areas, although
gradually thinning out with time and slowly shifting southward with
the peak opacity. A nearly full day of sun across portions of the
northern Thumb into the Tri-Cities region has allowed these areas to
see the warmest temperatures so far, with Bad Axe actually coming in
as the hot spot so far peaking at 60 degrees; not too often that the
northern Thumb is the warmest spot in southeast Michigan on a spring
afternoon. Across the rest of the region, temperatures continue to
warm through the 50s, and will likely reach maxes of mid 50s for most
areas, with upper 50s to around 60 possible north of the I-69
corridor where insolation today has been greatest. Winds will
continue to remain light and variable outside of any lake-enhanced

High clouds will continue to slowly wisp away tonight, but may
linger until around midnight close to the Ohio border. With high
pressure overhead and light gradient flow, expecting full decoupling
of the boundary layer overnight as winds trend calm in most areas. A
slight increase in the low-level thermal field will act to negate a
full bottoming-out of low temperatures, but excellent radiational
cooling conditions will still allow lows to dip to around the
freezing mark, and below freezing across the Thumb.


Departing upper-level jet axis into the Mid-Atlantic region will
allow for ridging to continue building aloft Sunday, as the western
Plains closed low begins to slowly open up and meander southeast in
a quasi Rex block pattern. Low amplitude of these features will
limit blocking potential for just about a 24-30 hr period heading
into Sunday night before northern stream energy passing through
Manitoba/Ontario acts to break down the ridging overhead. As Monday
progresses, southeast Michigan will be in the pivot point of the
split flow pattern between the closed low drifting over the
Tennessee River Valley and a secondary piece of Pacific shortwave
energy diving southeastward off the northern High Plains.

Full daytime heating thanks to bountiful sunshine will allow for
well-mixed and dry boundary layers Sunday and Monday, keeping any
moisture advection trying to lift northward associated with the
closed upper low at bay south of the Ohio border. Thermal ridge will
also drift overhead during this timeframe as well, allowing for
continuing moderating temperatures. Highs on Sunday look to reach
into the lower 60s for most locations, with Monday being even warmer
as a southeasterly breeze picks up. Highs on Monday look to reach
well into the 60s, with 70 degree readings possible across inland
areas. Low temperatures Sunday night will fall into the mid and
upper 30s, with only 40s expected for lows Monday night.


An upper low slowly lifting into the Ohio Valley on Tuesday will
introduce shower chances to the region as temperatures remain mild
in the upper 50s to lower 60s. A quick-moving northern stream
shortwave diving into the region late Tuesday is then progged to
merge with the Ohio Valley low early Wednesday before quickly
exiting eastward keeping shower chances in the forecast through at
least the first half of Wednesday. Shortwave ridging will then cross
the region late Wednesday through Thursday bringing a period of dry
conditions ahead of the next northern stream wave progged to dive
southward into the region late next week. Another period of showers
is expected with the second wave along with a shot of colder air
that will bring highs back into the lower 50s.



High pressure maintaining its grip on the region through the weekend
resulting in light and variable winds and calm waves across the open
waters of Lake Huron, Lake St. Clair and western Lake Erie. Look for
light southerly winds on Monday as the surface high pressure drifts
east of Michigan. A slow moving mid level low pressure system
meandering across the southern US will lift northward into the Great
Lakes region late Tuesday into Wednesday. This will bring increasing
chances for precipitation and unsettled weather, which will continue
into the late week as a stronger trough is forecast impact the


Issued at 136 PM EDT Sat Apr 21 2018


Stable surface anticyclone centered directly over the Great Lakes
will keep VFR conditions with light and variable winds throughout
the taf period. Most abrupt wind shift with lake breeze push is
forecasted at KMBS and points northward, while flow trajectories
will begin out of the southeast at KDTW.


* None.


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



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