Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 192300
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
700 PM EDT Tue Mar 19 2019


.AVIATION...

The onset of nighttime cooling will lead to a clearing of the
remnant diurnal cu field over the next couple hours and will lower
the south-southwest winds speeds around/shortly after sunset. Se Mi
will remain under the influence of departing sfc high pressure
through the night. So other than a few high clouds, this system will
sustain clear skies into early Wed morning. A deepening low pressure
system will advance into Lower Mi Wed afternoon/evening. This system
and its associated moisture transport will allow widespread rain,
with steadily lowering ceilings, to advance across Se Mi during the
course of the afternoon Wednesday.

.DTW THRESHOLD PROBABILITIES...

* High in ceilings below 5000 ft late Wed afternoon and evening.

* High in precip type being all rain Wed afternoon and evening.

&&

.PREV DISCUSSION...
Issued at Detroit/Pontiac MI 342 PM EDT Tue Mar 19 2019

DISCUSSION...

Confluent flow aloft and departing left entrance jet streak region
leading to weak subsidence and continued quiet weather across
Southeast Michigan this afternoon and evening. Surface heating and
boundary layer growth paired with enough moisture in the low levels
today has allowed for the development of stratocumulus across the
region, while surface high pressure moving into the Appalachians has
resulted in light southwest return flow. Low clouds will clear out
again this evening as daytime mixing wanes. Lack of abundant cloud
cover tonight will allow for decent radiational cooling potential,
but the increasing gradient due to the departing high pressure will
keep winds slightly elevated and prevent full cooling potential from
being realized. Low temperatures in the lower 30s still look good
for tonight.

Rain returns to the forecast tomorrow as an amplifying upper
shortwave swings through the Great Lakes from the north and a weak
surface low develops over the Lower Peninsula. Another shortwave
visible in water vapor imagery over western Nebraska this afternoon
will swing into the mid-Mississippi Valley Wednesday afternoon and
lead to a southwesterly 40 kt low level jet that will transport
ample moisture to the southern Great Lakes ahead of the northern
shortwave. Widespread light rain will develop during the early
afternoon into the evening as height falls move in, becoming more
scattered overnight as the trough axis moves overhead. Rain will be
the primary precip type, but some wet snowflakes have the potential
to mix in north of I-69 late Wednesday night as the low pressure and
main area of precip move out. QPF has trended upward with latest
model guidance, so have increased rainfall totals - more details are
described in the Hydrology section below. Modest southwest flow will
persist through the day Wednesday with gusts in the afternoon up to
20 to 30 mph. Modest warm advection and good mixing in this flow
will help temperatures reach the mid to upper 40s before clouds
thicken and rain sets in.

A weak cold front will pass through early Thursday and usher in dry
air aloft from the northwest which will shut off any lingering
showers during the morning hours. Thursday will be dry and
seasonable with temperatures in the mid 40s. However, there will be
another chance for light rain and snow for the eastern Thumb
overnight into early Friday as another shortwave dives southward
into the region. The bulk of the precipitation looks to remain to
the east.

High amplitude ridge sliding across the central US on Friday. The
result will be a mostly dry end to the work week with Michigan
placed on the east side of this ridge. The exception being a slight
chance for some lingering light precipitation on Friday across the
Thumb region under NNW flow behind the passing cold front. High
temperatures will dip into the mid/upper 30s and low 40s for Friday
before temperatures trend upward through the weekend. Expecting
mostly sunny skies through the majority of the weekend as surface
high pressure moves through the Great Lakes region. Temperatures
warming into the 50s by Sunday as 850 mb temperatures increase to
around 2C.  Precipitation chances return to the forecast late Sunday
as the ridge breaks down and weak waves track over Michigan with a
cold front also advancing southward. Passing cold front will
maintain precipitation chances into Monday morning with high
temperatures Monday afternoon cooling back into the 30s and 40s.

MARINE...

A rather complicated near surface pressure pattern will evolve the
next day or so, as two systems attempt a merger over the Great Lakes
region on Wednesday. Winds will respond by initially ramping up from
the southwest tonight into Wednesday areawide, with highest gusts
exceeding 25 knots on Lake Huron. Winds and waves will relax
somewhat, as the combined low pressure system weakens over the
region, Wednesday night. A modest west-northwest flow will become
established on Thursday before increasing in strength Thursday night
on the way to possible northerly gale conditions on Friday over Lake
Huron. Expect ice breakup to continue with the changing wind
conditions and relatively mild weather.

HYDROLOGY...

Light rain is expected to overspread southeast Michigan Wednesday
afternoon with rather uniform rainfall totals of three to four
tenths of an inch. Most mainstem rivers have subsided significantly
over the last several days. The additional precipitation will only
serve to slow the steady decrease with no additional river flooding
expected. Susceptible collection areas, that likely already contain
run-off water, will swell with the additional precipitation.

&&

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

$$

AVIATION.....SC
DISCUSSION...TF/AA
MARINE.......Mann
HYDROLOGY....Mann


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