Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 171011
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
611 AM EDT Sat Jun 17 2017


.AVIATION...

Complex weather pattern through the taf cycle with several rounds of
showers and thunderstorms possible. Each successive round will
affect future potential so timing out any storms is tough. In the
end, remained focused on the fronts and weak low pressure systems
for timing and will amend as needed. MBS and potentially FNT may
see the most activity as activity ripples along boundary over
western lower which may bleed into these terminals. The other
terminals south of PTK may be far enough removed from the boundary
to keep them dry until this afternoon. Good chance of seeing
convection spread across all terminals this afternoon as wave tracks
across the region during peak afternoon heating. Additional chance
comes overnight in advance of a cold front. Outside of any
convection or showers, mainly VFR conditions will prevail.

For DTW...Large storm complex upstream will likely spread cloud
debris across the terminal today. Confidence still low in
thunderstorm potential this afternoon/evening, as this cloud debris
may limit greater destabilization.  Best window for late day
development now remains highlighted prob mention.  Another window
for TSRA comes tonight.

//DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms today and tonight.

* Low for ceilings aob 5000 ft through the period.

&&

.PREV DISCUSSION...
Issued at 250 AM EDT Sat Jun 17 2017

DISCUSSION...

Active period setting up over the next 30 hours or so as several
batches of thunderstorms lift east-northeast through the region in
advance of upper low/trough which will dig into the upper midwest
from its current position in south central Canada.

Initial activity during this time frame can be expected early in the
morning today as several clusters of showers/thundestorms along lead
shortwave trough within broad west/southwest flow around upper low
shift into the region. These batches of convection currently extend
from northern Lake Michigan back to far southern Wisconsin, with a
bit more activity likely filling in between these two main areas as
modest low level jet on the order of 20-25 knots veers and feeds
some degree of higher theta-e air into activity before weakening in
the mid morning time frame. Current hires models suggest the best
coverage will be over the northern 1/2 of the forecast area, but
some chance will exist area-wide, especially in the 10z-15z range.
With both instability and shear values rather low, no severe wx is
expected with this activity.

Next round of convection will come mid afternoon into this evening
as low pressure, likely enhanced by MCV associated with massive MCS
over the Missouri Valley, lifts northeast into area from southern IA.
Best forcing with this feature appears most likely over the northern
forecast area with additional activity firing southward in response
to mesoscale forcing from whatever active convection is associated
with this system by mid/late afternoon. By that time, deep layer
shear is a more respectable 30-40 knots, which would lend itself to
better storm organization. Instability will be a trickier call and
will depend on the evolution of morning convection. If main path
does end up over the northern forecast area, there theoretically be
at least modest instability on the order of 1500 J/kg poised over
southern areas. Suffice to say, even if details are vague at this
point, there should be some potential of severe weather with this
afternoon/evening convection.

Main jet stream support from the synoptic system itself will spread
into area later tonight as significant jet dig into upper midwest
around base of evolving upper low. This feature and associated
shortwave will induce cyclogenesis which will spin up just west of
the area. Severe weather will remain possible even during the late
tonight period as upper support and a bit more of a boost in deep
layer shear most likely overcomes slightly lower instability values.
There will probably be two somewhat distinct area of convection with
this low pressure, first overnight as notably higher theta-e air is
drawn north through area overnight in advance of this developing
circulation and then early Sunday morning as the low lifts into
northern lower Michigan a drives a cold front through the region.

Thereafter, expect an expansion of the upper trough over the region
early/mid next week as additional jet energy continues to feed into
region. This will lead to a cooler stretch of weather in the Monday
through Wednesday time frame with some moderation possible Thursday
into Friday as upper pattern evolves back to something closer to a
zonal flow as upper trough lifts north of the New England states.
Expect high temperatures in the 70s for much of the week, warming
back into lower/mid 80s late in the forecast period. There will
remain the chance of scattered showers and also some thunder within
unsettled pattern under upper troughing. This will be most
pronounced during peak heating in the afternoon/early evening.

MARINE...

Trough of low pressure deepening to our west with a developing low
pressure system that will track through central and northern MI
tonight. This low will drag a cold front through the region early
Sunday. Though southerly flow will increase ahead of the front,
winds still looks to remain below 20 knots through the next couple
days. Best chance at higher wind speeds will come on Sunday as
southwest flow increases briefly behind the front with intrusion of
cooler air. There also remains a chance of thunderstorms this
weekend. Best chance will come this evening and tonight as the low
rides north along the trough. These storms will have the potential
to become severe, with damaging winds up to 50 knots the biggest
threat.

HYDROLOGY...

Current airmass continues to support thunderstorm
chances through Sunday. A cold front sweeping across the area Sunday
afternoon will bring an end to the precipitation chances for a short
time. Several rounds of storms could affect Mid MI through Sunday,
whereas locations across southern MI stand the best chance this
evening into tonight. Rainfall amounts will vary considerably due to
the hit or miss nature of the thunderstorms, but localized areas
could receive an inch or more of rain in a short period of time.
This could result in ponding of water on roads and low lying areas.

&&

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

$$

AVIATION.....DRK
DISCUSSION...DG
MARINE.......DRK
HYDROLOGY....DRK


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