Scientific Forecaster Discussion
fxus63 kdtx 240157
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
957 PM EDT Sat Jun 23 2018
A round of showers with generous coverage and heavy rainfall
developed during peak heating and are now diminishing and exiting
into Canada. The activity was concentrated within the surface trough
lingering over the region roughly centered on the M-59 corridor.
Impressive was the coverage and intensity on radar from late
afternoon through mid evening with only a handful of lightning
strikes for the duration. Now, with the loss of daytime heating,
expect only an isolated shower until later in the night.
The next round of showers will also feature heavy rainfall potential
as the pattern expands over central lower Michigan after midnight.
Development will be driven by the upper low over the Midwest as it
moves through the southern Great Lakes. This system appears
respectable in strength judging by evening water vapor imagery and
plenty capable of dynamic interaction with the surface trough
lingering over Southern Lower Michigan. The upper low will strongly
sharpen the low and mid level moisture axis and produce a strong
deformation pattern over central lower Michigan, including the Tri
Cities and northern thumb. Measures of elevated instability, such as
850 mb Li, are neutral to slightly unstable which makes thunderstorms
less of a concern once again. However, moisture remains deep judging
by model soundings saturated to the tropopause with 700 mb dewpoint
ranging in the single digits above zero. The strong deformation
forcing is expected to focus bands or cluster of showers in a west to
east fashion with a west to east motion for a few hours during
Sunday morning before the moisture axis deflates eastward. There
should still be at least scattered coverage of showers lasting well
into the afternoon as the pattern shifts eastward and the associated
cold front slides through the region. Categorical pops in the going
forecast look good with the evening update highlighting heavy
rainfall potential a little more, and in line with the wpc marginal
issued at 758 PM EDT Sat Jun 23 2018
A break is in store from the heavy shower activity during late
afternoon and early evening. A few showers around the jxn area could
survive toward ptk and dtw but the rest of the evening will
otherwise be dry until new showers begin developing from mbs to fnt
toward midnight. In between will be a wide variation of ceiling
within the leftover surface trough over Southeast Michigan and before the
next front moves down from the northern Great Lakes. The associated
low pressure system will bring increasing coverage of showers all
areas overnight through Sunday morning along with a downward trend
into IFR ceiling and visibility both ahead of and immediately Post
front. Afternoon improvement is expected north to south as the front
exits into Ohio by late Sunday afternoon.
For dtw... just a few showers around for the remainder of the
evening followed by a trend from VFR to MVFR and then to IFR
overnight. A very low chance of a thunderstorm along the passing
front Sunday afternoon.
Dtw threshold probabilities...
* high for ceiling 5000 feet or less late evening through Sunday.
* Low for thunderstorms Sunday afternoon.
issued at 357 PM EDT Sat Jun 23 2018
Convection within the convergent corridor along the periphery of the
surface circulation is waning as an open wave structure develops in
the lower troposphere in response to a more diffuse pattern of mid-
level forcing. Some level of activity will likely persist for the
next several hours within the remnant surface trough, particularly
as modest isentropic ascent increases ahead of the next upstream
wave presently lifting east-northeast through Illinois. Limited instability and
loss of heating will further limit intensity and coverage, but very
slow storm motion will still potentially produce locally heavy rain.
Strong nwp consensus on overall evolution tonight through Sunday as
the resident airmass remains in place for one more day. Diminished
moisture quality owing to developing dry northeast flow should be
more than offset by stronger forcing. Any remnant activity within
the aforementioned surface trough will tend to consolidate over The
Thumb and possibly portions of northern lower as mid-level
deformation becomes increasingly well defined tonight through midday
Sunday. Substantial increase in pops warranted across the northern
counties for late tonight into Sunday. Incoming confluent flow in
the wake of this wave will then quickly usher the developing frontal
zone across the area during the afternoon, leading to a transient
shower threat Worth an increase in pops to the high chc/low likely
range. Steady onshore marine winds may also cause low end Lakeshore
flood concerns invof Essexville in Bay County by Sunday aftn.
Building high pressure and 850mb temps around 11c may allow
temperatures to approach the upper 70s under full sun, but cirrus
peeling off a wave undercutting the ridge will be Worth watching as
it may suppress temps a few degrees.
Upper-level troughing and an embedded pv anomaly will push from
southern Minnesota into northern lower Michigan and will bring
likely rain and thunderstorm chances to Southeast Michigan both Tuesday and
Wednesday. Increased southwesterly flow will continue to advect warm
and moist air ahead and during the passage of the pv anomaly, as
noted by 850 mb dew points ranging between 10 - 15c and precipitable water values
averaging 1.60 inches.
The pv anomaly and upper-level trough will push east out of Michigan
by 06 - 12z Thursday and will bring a period of dry conditions as a
surface high and upper-level ridge builds across the state. High
pressure centered across the eastern Ohio Valley will allow for
strong warm air advection to take place towards the end of the week as 850 mb
temperatures soar from 13c Thu 12z up to near 23c by Sat 00z. For
reference, record Storm Prediction Center climatological 850 mb temperatures reside
around 20 - 22 c. Daytime highs in the lower 90s are now reflected
in Friday and saturday's forecast, however, a bump into the mid-90s
may be necessary over the next day if models continue to suggest 850
temperatures between 21 - 23 c in conjunction with minimal cloud
cover. Overall, confidence is very high in regards to above normal
temperatures by the end of the week.
Broad and weak low pressure will slowly exit the central Great Lakes
tonight into tomorrow. Light and variable winds this afternoon into
tonight will become light north/northeasterly flow less than 20
knots in the wake of the departing low pressure on Sunday. Still
a chance for showers during the first part of Sunday before dry
weather returns Monday as high pressure returns to the Great Lakes
region. A warm front lifting through the area will lead to chance
for showers and thunderstorms on Tuesday, with increasing southeast
Showers will redevelop tonight, especially along and north of I-69,
continuing into early Sunday afternoon. Total rainfall amounts will
generally be a half an inch or less. Although locally higher amounts
will be possible, flooding is not expected. Drier air will work into
the region late Sunday and into Monday as high pressure builds
Lake St Clair...none.
Michigan waters of Lake Erie...none.