Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 190738
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
338 AM EDT Wed Apr 19 2017
Well-defined baroclinic zone stretches from the Straits into
southwestern Nebraska at press time. Weakening low-level jet
associated with the system departing to our north and east is
supporting a scattered coverage of showers early this morning. As
the wind field and attendant convergence continues to weaken,
coverage is expected to gradually wane over the next few hours.
Quiet day expected across most of the area with fropa occuring early
and dewpoints falling into the 40s across the north. However,
ongoing southwest flow in advance of the front will support an
increasing chance of convection south of M59 this afternoon. Progged
soundings are only weakly capped and suspect the frontal circulation
may be sufficient to generate convection on its own, particularly as
T/Tds increase toward 75/60+F near the MI/OH border. Low density
cape profiles of around 1000 j/kg and sub-optimal shear pose an
isolated risk of sub-severe hail and wind at best, the greatest risk
near the border. One item worth watching is any convectively induced
shortwave emerging from ongoing activity along the front in eastern
Nebraska early this morning. Any such wave would likely lift toward
the southern CWA within the prevailing flow and could yield an
uptick in coverage by late afternoon.
The next shortwave in the sequence is in the process of emerging
over the front range, cyclogenesis taking place on the western
reaches of the aforementioned baroclinic zone. The resultant
nocturnal LLJ currently supporting the eastern Nebraska convection.
As the cyclone deepens and the surface low lifts toward southern
Wisconsin early Thursday, today`s front will assume a warm front
character as it lifts back to the north. Weak isentropic ascent will
likely limit shower coverage for most of the night, but the arrival
of a 40+kt LLJ warrants a categorical mention for the Tri-Cities
region and the Thumb. 00 NWP generally depicting less impressive
lapse rates than 24 hours ago, suggesting a very limited to nil
severe hail threat with any elevated convection through tonight.
Model consensus that warm frontal boundary will likely be lingering
over the CWA on Thursday morning as the upper wave approaches from
the west. Arrival of steeper lapse rates and T/Td south of the front
potentially exceeding 75F/60F supports MLCAPE of 1000-1500 j/kg
while elevated instability exceeds 500 j/kg to the north. Strong
forcing along the prefrontal trough and deep unidirectional wind
field oriented roughly perpendicular to the convective line will be
strongly favorable for a severe wind threat posed by bowing
segments. Strongly veered deep layer wind field north of the front
may compensate for lower instability meaning a hail threat is in
play for all locations. Aside from solid bulk convective parameters,
there is particular concern regarding the position of the surface
warm front Thursday afternoon. Should it fail to clear the CWA, as
suggested by the 00z ARW for example, a corridor of strong low-level
instability and greatly enhanced SRH immediately along the front
will exist for the production of low-level mesocyclones/tornadoes.
Greatest tornado threat at this time appears most likely to reside
somewhere north of M-59.
High temps fall into the 50s for the remainder of the week as
strongly confluent flow aloft builds into the great lakes and low-
levels come under increasing influence of surface high pressure.
Moderate southwest wind this morning will ease as a cold front lifts
through the region. A period of northerly winds immediately behind
this front will remain modest during the day. The approach of
strong low pressure will then bring an increase in northeast winds
tonight and Thursday across portions of lake Huron. The potential
still exists for gusts to reach near gales late tonight and early
Thursday across the northern third of Lake Huron. A gale watch
remains in effect for this corridor. In addition, this will result
in small craft conditions for higher waves along the nearshore
waters and Saginaw Bay beginning late tonight and likely lasting.
through Friday. An unsettled period will showers and thunderstorms
possible, particularly tonight and Thursday.
A cold front sliding through the region will bring a chance for
showers and thunderstorms today, particularly south of the M-59
corridor. Unsettled conditions will persist areawide tonight and
Thursday, as this front lifts back northward and a strong low
pressure system tracks into the region. The potential will exist
for localized rainfall amounts in excess of 1 inch, particularly
should a concentrated region of thunderstorms track across the same
areas. The Tri-Cities will be more favorably positioned to witness
heavy rainfall tonight through Thursday. The potential for some
minor flooding will exist, particularly given the wetter than
average conditions noted in recent weeks.
Issued at 1154 PM EDT Tue Apr 18 2017
Mid level moisture transport ahead of an approaching cold front has
led to a few high based showers across western and central Lower Mi.
There may yet be a few showers which track across the region prior
to the cold front. The low probability of occurrence and brief
duration of those that do occur will preclude mention of shra in the
TAFs attm. The front will move across MBS around 12Z, but will only
slowly push through the rest of Se Mi during the course of the day,
not exiting south of metro Detroit until late afternoon. There will
be a veering of the winds to the north with the passage of the
front. Regional observations suggest low level moisture may be
lacking, thus prevailing VFR conditions will be carried through the
For DTW...The front will settle across metro Detroit during the late
afternoon. There will be a build up of instability south of this
front, which may support a late day thunderstorm.
//DTW THRESHOLD PROBABILITIES...
* Low for cigs at or below 5000 ft tonight through Wednesday
* Low for thunderstorm occurrence Wednesday.
Lake Huron...Gale Watch from Thursday morning through Thursday evening for
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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