FXUS63 KDTX 200350
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1150 PM EDT Thu Jul 19 2018
High pressure to the east of the region will continue to dominate
conditions across Se Mi through Friday morning, providing light
southeast winds and clear skies below 15k feet. The approaching
upper low will shed an axis of deep moisture into Se Mi on Friday.
During the morning, much of this convection will be weakening as it
approaches Se Mi with a more stable environment in place across
the area. Diurnal destabilization within this moisture and a
increasingly favorable upper level lift will warrant showers and a
good chance of thunderstorms late Fri afternoon through the evening.
For DTW...Daytime heating within the moisture plume that will lift
across the area will support a chance of TSRA basically anytime
Friday afternoon. Latest Hi Res model suite suggest the most
probable time period for convection will be late (after 21Z).
.DTW THRESHOLD PROBABILITIES...
* Low in cigs aob 5000 feet Friday afternoon and evening.
* Moderate in thunderstorms late Friday afternoon and evening.
Issued at 344 PM EDT Thu Jul 19 2018
Anticyclonic flow regime of the last few days now exiting east as
height falls associated with the upstream closed low begin to spread
into the area. Temperatures in the low 80s and dewpoints in the 50s
this afternoon are characteristic of the resident dry airmass that
extends westward into much of Wisconsin, Indiana, and far eastern
IL. Areas of shower and thunderstorm activity are ongoing within the
1.5"+ pwat plume that demarcates the airmass boundary which extends
from southeast Minnesota to the lower portions of the Ohio River
Valley. Isentropic ascent and increased convergence along the lead
edge of this moisture axis will support either continued or
redeveloping convection over Illinois and Iowa overnight,
particularly as upper PV advection increases. Loss of deeper forcing
for ascent as forward progress of the low almost stops altogether by
Friday morning warrants a reduction to chc pops as any band of
showers lifting through the CWA should be both transient and
weakening. Deep layer cyclonic flow and ongoing moist advection will
force dewpoints well into the mid or even upper 60s by late Friday,
posing a threat for thunderstorm development within the weakly
sheared, but very moist environment. 12z model progs suggest
activity will be focused along a second wave embedded within the
parent low over SW Lower Michigan late Fri afternoon before
spreading east through 00z. Cooler mid-level temps open the door for
moderate destabilization late in the day, but late arrival of
forcing and the likelihood of extensive cloud cover casts doubt on
potential. Instead, the more likely outcome is a relatively quick-
moving heavy rain threat late eve/first half of the night with any
stronger convection capable of producing small hail and/or wind
gusts to around 40 mph. Shower/tstorm chances will be pervasive
heading into the first half of the weekend. Lack of steering flow on
Saturday will favor some degree of a heavy rain threat depending on
degree of destabilization beneath the upper low.
By Sunday, the low pressure system that had been situated over the
are will weaken and slide southward away from the region. Scattered
showers/storms will come to an end by late Sunday as high pressure
builds in. For the most part, the area will then remain dry going
into next week with only slight chances for some shower activity. As
upper level riding builds in next week, temps will rebound back into
the mid 80s.
Southeast winds gradually increase with a minor wave response
tonight and Friday as low pressure organizes and moves toward the
south end of Lake Michigan. Southeast winds look to peak around 20
knots on Saturday, with low pressure then sinking southeast into the
Ohio Valley late in the weekend. This will allow for winds to become
northeast, but will be light into early next week.
Increasingly moist and modestly unstable conditions as low pressure
slowly tracks through the region will lead to periodic bouts of
showers and thunderstorms Friday into the upcoming weekend. Highly
variable rainfall amounts are likely depending on the eventual track
and pace of this system. Latest forecast calls for rainfall amounts
ranging from a half an inch to an inch and a quarter during this
period. Some localized amounts in excess of this are certainly
possible in thunderstorms, leading to poor drainage flooding.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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