Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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342
FXUS63 KDTX 200702
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
302 AM EDT Sun May 20 2018

.DISCUSSION...

An elongated region of sfc high pressure will expand from northern
Minnesota/Lake Superior this morning into northern Lower Mi this
afternoon within mid level confluent flow across the northern lakes.
There has already been a push of shallow cool air across Se Mi
within the low level north-northwest flow preceding the sfc ridge
axis. This shallow cool layer has led to a deepening low level
inversion, supporting ample low clouds and fairly widespread
drizzle. Persistent low level northerly flow this morning will
advect drier boundary layer across Se Mi, this will end the drizzle
from north to south across the area during the early morning hours.

The cluster of showers/thunderstorms across SW Wisconsin overnight
have struggled to to make much progress to the east. There will be a
push of lower mid level theta e air across srn Mi from the north
today which will hold any semblance of elevated instability well to
the south and west of the area. There will also be subtle mid level
height rises across Lower Mi through the day. These factors will
make it unlikely for ongoing convective activity across srn WI to
advance into Se MI. While low clouds will tend to diminish from
north to south across the area during the course of the day, the
shallow cool air will limit mixing depths and likely hold afternoon
highs mainly in the 60s, with much cooler readings along the Lake
Huron shoreline.

The sfc high will build into Se Mi tonight. Mid/high level clouds
will likely inhibit radiational cooling potential across the
southern half of the forecast area. The likelihood for clearing skies
across the Saginaw Valley and thumb combined with the dry airmass
will warrant min temps into the low 40s (with some upper 30s
possible across the thumb).

There is a fair amount of model divergence with respect to timing
and amplitude of short wave impulses lifting out of the upper
Midwest and traversing srn Mi Monday into Tuesday. This will affect
the strength of mid level southwest flow which in turn will
determine the degree of mid level moisture/instability advection
into Se Mi. In light of the confluent flow overhead, preference lies
with those solutions which dampen the upper energy more
significantly, thereby only supporting just low chances of
convection (mainly south of M-59). High pressure will strengthen
across the Great Lakes midweek behind an amplifying mid level trough
over eastern Canada, supporting dry conditions across Se Mi. Mid
level ridging will then expand across the Great Lakes toward the end
of the week, leading to a steady warming trend.

&&

.MARINE...

Light winds today as high pressure builds into the area. Light winds
will persist through at least Wednesday, as high pressure more or
less holds over Lake Huron. Chance of showers and thunderstorms
early next week will be mainly confined to Lake St. Clair and Lake
Erie.

&&

.PREV DISCUSSION...
Issued at 1157 PM EDT Sat May 19 2018

AVIATION...

The ragged south edge of postfrontal stratus lingered near the Ohio
border during the evening resulting in variable ceiling conditions
along the DTW corridor. This occurred while low level flow was light
west to northwest. A continued veering wind trend toward the north
to northeast will allow greater coverage of IFR/MVFR to move
southward over the entire area during the night and as IFR becomes
more dominant, especially in terms of ceiling but with some fog/drizzle.
Thunderstorms over southern Wisconsin at midnight are expected to
dissipate to the west, or weaken to light showers/stratiform rain
that could reach SE Michigan during the afternoon. This activity will
not disrupt the improving trend in ceiling and visibility
anticipated as surface high pressure builds southward from the
northern Great Lakes.

For DTW... Borderline IFR/MVFR ceiling will become more firmly IFR
during the night. Post frontal northwest wind becomes light north to
northeast through the morning potentially requiring northeast traffic
flow operations. Ceiling and visibility improve into MVFR during
early afternoon.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less through early afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

DISCUSSION...SC
MARINE.......SF
AVIATION.....BT


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