Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 230419

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1219 AM EDT Tue May 23 2017


A baroclinic zone at 700mb will become increasingly more organized
tonight north of I 69, ahead of the amplifying midlevel trough over
the upper Mississippi River Valley. Uncertainty persists with
overall potential and longevity for precipitation as a shortwave
ridging component will also work across the area. Quite a little
consensus forming that a duration of light rain will be possible
under this front over the Tri Cities region. Included a tempo group
for the mid morning hours but did not want to get anymore
pessimistic than MVFR for Cigs. Otherwise, high confidence continues
that little to no precipitation chances will exist Tuesday morning
for the Detroit terminals. Most recent trend has been for higher
probs creeping into the percentages for greater than .25 inch qpf
Tuesday afternoon north of I 69. Wind is not expected to become an
issue during the next 24 to 36 hours.


* None.


Issued at 315 PM EDT Mon May 22 2017


Not much time to dry out, as rain chances increase over next 48
hours. 70-75 knot jet core at 500 MB/110-115 knots at 300 MB exiting
northeast early this evening, with moisture advection and right
entrance forcing already bringing a scattered/chance of showers
(remote chance of a thunderstorm) as we become modestly unstable
with LI`s nearing zero over Tri-Cities region. Narrow, but
potentially sufficient 850-700 mb Theta-E moisture axis, with PW
Values around 1 inch move over northern half of the CWA toward 12z
Tuesday, stalling out over the rest of southeast Michigan during
Tuesday. Modestly unstable daytime instability (MLcapes 250-500
J/kg), weak low level convergence, and leftover moisture axis could
be enough to trigger convection but upper level shortwave ridge axis
in place may be enough of a deterrent. Overall, will be favoring
mostly scattered coverage for both tonight and Tomorrow, with pops
hovering around 50 percent north of M-59 and quickly tapering off
south. MAV/MET guidance appears to be too aggressive tomorrow
compared to local probabilistic SREF weighted guidance. Inherited
temps tonight/tomorrow looked reasonable with low level warm
advection pushing 925 mb temps at or above 15 C by tomorrow
afternoon, supportive of lower 70s.

Large upper level low centered near northern Minnesota will sink
south into the Midwest Tomorrow and reaching the southern
Mississippi River Valley late Tomorrow. With placement of warm
conveyor belt arching back through the northern Ohio Valley. One
issue is the lead low/storm system riding along the Gulf Coast
Today/Tomorrow, reaching the Mid Atlantic Coast early Wednesday
morning. How much impact will this system have on the moisture
transport? It appears it will just have a temporary disruption/
impact, as the main low deepens over the Ohio Valley during
Wednesday. Good deformation showers expected to spread over
southeast Michigan by Wednesday evening, with substantial rainfall
(greater than half an inch), as 850 mb dew pts of 10 C arrive, per
12z Canadian/Euro. Although, 12z Euro may be exhibiting its typical
bias of over-deepening the low by Thursday morning, as nam is 8 mb
weaker, so not fully on-board with QPF in excess of 1 inch just yet
with what looks like modest instability.

An upper-level cut-off low situated over the Ohio Valley will bring
on and off rain chances throughout Thursday as temperatures peak in
the mid to upper-60s. The cut-off low is expected to push Northeast
throughout Friday as an upper-level ridge pushes across the Great
Lakes. This will act to scour out some cloud cover and bring
relatively dry conditions through the day, although some embedded
short-waves could provide the low chance for a light pop-up shower.

For the extended weekend, a weak surface low is expected to move
east across IN/OH Saturday into Sunday as an upper-level ridge
pushes across Michigan, which would hold prolonged rain chances just
south of the MI/OH border. Slightly better rain chances are
forecasted for Sunday as a trough swings through from the Central
Plains, pushing a weak warm front through southern Michigan.
Additional rain chances possible on Monday, although only the GFS
run is picking up on measurable rain chances as it develops and
pushes a low from IA into northern lower MI. Overall, the main
message for rain chances -- weak forcing will allows for spotty rain
chances during the extended period, with Friday into early Saturday
bring having the highest odds to stay relatively dry. Higher
confidence regarding forecasted highs -- Mid to upper-60s for
Thursday, with a warming trend into the 70s starting Friday and
continuing through Memorial Day.


Diminishing wind during the late afternoon and evening will allow
ongoing small craft advisories to expire on time. The wind will
continue to ease after sunset and remain light through Tuesday. A
weak surface trough will separate northern and southern Lake Huron
until dissipating Tuesday night in favor of the next low pressure
system. This low will produce an active rain pattern and bring up a
moderate northeast wind over marine areas Wednesday into Thursday.
The long fetch of onshore flow could result in waves exceeding small
craft advisory threshold for Saginaw Bay and southern Lake Huron.


Low pressure developing over the Ohio valley Wednesday will stall
and intensify through Wednesday night. A band of rain is expected to
develop on the north side of the system and spread into Lower
Michigan mainly during Wednesday night. Rainfall totals averaging
0.75 inch are likely with locally higher amounts in thunderstorms.
Ponding of water on area roads and in other prone areas is likely,
especially considering the widespread activity over the weekend that
left the ground saturated in most areas.


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



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