Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 200345
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1145 PM EDT Sun Mar 19 2017
A mid level short wave tracking across the northern Great Lakes has
enhanced the mid level moisture now advancing into wrn Lower Mi.
This coupled with very steep mid level lapse rates has supported a
decent coverage of showers and thunderstorms across NW Lower Mi and
cntl Lake Mi. The coverage and intensity of this convection should
decrease as it pushes east as it outpaces the better mid level
instability. Coverage upstream does however at least support a TEMPO
group for some showers late tonight. While there is a chance for
some thunderstorms late as the steeper mid level lapse rates do
eventually overspread Se Mi, the chances are too low to include in
the TAF attm. These late night showers will remain relatively high
based due to residual low level dry air. An influx of high low level
moisture during the day Monday will support additional chances for
showers, especially during the afternoon. Reductions in visibility
and lower ceiling heights during the day will also occur.
For DTW...The chances for showers will increase markedly after
daybreak. There will be some elevated instability present through
the day. Chances for thunderstorms do remain low enough to refrain
from mentioning in the terminal attm.
//DTW THRESHOLD PROBABILITIES...
* Low in ceilings below 5000 ft prior to daybreak. High after
* Low in thunderstorms late tonight through Monday afternoon.
Issued at 926 PM EDT Sun Mar 19 2017
A region of showers and scattered thunderstorms now pushing across
nrn and cntl Lake Michigan have developed along a lead mid level
moisture surge. This is preceding a deeper moisture plume now
lifting across Wisconsin. Regional 00Z soundings, including APX and
GRB, show steep lapse rates in the 700 to 400 MB layer contributing
to the convective nature of these showers. This initial influx of
isentropic ascent will encounter abundant dry air in the low levels
and a more stable mid level environment as it pushes across Lower Mi
over the next 3 to 6 hours. This will result in a diminishing trend
to the showers as they approach the forecast area, likely just being
virga or sprinkles/flurries as they track through Se Mi.
There will be a secondary moisture surge later in the night,
especially across the southern sections of Lower Mi. While the
900-800mb theta e gradient looks to hold off entering the forecast
area until after 12Z, ascent within the increasing mid level moisture
will increase in the 09Z to 12Z time frame. This will also occur
within increasing mid level lapse rates. This will support a chance
of showers (an isolated thunderstorm can not be ruled out) late
tonight/early Mon morning. The chances will be greater south of a
Howell to Detroit line. After dropping into the 30s this evening,
increasing low level southerly flow will support either steady
overnight temps or slowly rising temps into daybreak. Thermal
profiles should then quickly warm enough to support all rain.
Issued at 340 PM EDT Sun Mar 19 2017
Cloud trends remain the only real concern the rest of today through
tonight as high pressure is stacked over the region. As subsidence
continues to erode the lingering stratus, mid/high clouds will
already begin streaming back overhead in advance of the shortwave
and mid level trough that will track across the area on Monday.
Lingering cool airmass at the surface will keep temps down overnight
before flow flips from northerly to southerly. Some models try to
bring in some scattered showers prior to 12Z but low level dry air
and moistening of the column from the top down will take a while to
generate actual showers.
Nature of the Monday system continues to evolve. What first appeared
to be a weakening cold front extending south from a parent low
locked well north over Hudson Bay, now appears to be more of a mid
level trough axis with a weak shortwave drifting out of the central
plains, generating a region of height falls near the MI/OH border.
This scenario yields a bit higher pops for southern lower than
previously advertised with the cold front scenario. Lowered pops
across the north but leaving a chance mention as the trough swings
through. Chance to likely pops south of M59 toward the border closer
to the shortwave. Another change to the forecast was to introduce a
chance of thunder. Remnants of the elevated mixed layer upstream
will fold over the area with decent mid level lapse rates. Showalter
Index is around 0 or slightly below and decreasing as it slides
across the area. Boundary layer is much more stable so not expecting
anything to root at the surface but with the chance of a few
elevated rumbles, added it in the forecast for the southern four
Without a true cold frontal passage on Monday, temperatures will
stay in the upper 40s on Tuesday. This is until a secondary front
rotating around the dominate Canadian upper low swings down and
through the region with a push from a strong surface ridge nearing
1040mb dropping out of central Canada. Should remain dry Tuesday as
any support for showers remains to the northeast with the PV channel
and to our south along the baroclinic zone. This secondary front
will usher a colder airmass into the region with 850mb temps falling
below -15C. Expect colder temps Tuesday night in response to this
with temps down to around 20F.
Temperatures on Wednesday look to be the coolest in the extended
period as highs only warm into the middle 30s as arctic high
pressure continues to hold across the region. This high will start
pushing east away from the Great Lakes on Thursday allowing
southerly flow to take over. This southerly flow will let
temperatures warm back to more seasonal temperatures through the end
of the week. The next chance for precipitation is currently
forecasted to move in on Friday and into the weekend as a low
pressure system moves out of the southern plains.
Winds will remain rather light into this evening as high pressure
builds across the region. Modest southerly winds will develop late
tonight into Monday the pressure gradient increase somewhat between
this departing high pressure and low pressure tracking over Hudson
Bay. This low pressure system will pull a cold front through the
Central Great Lakes Monday afternoon, bringing a wind shift to the
northwest. The gusty northwest flow that this cold front brings will
extend through Wednesday as colder air filter back into the region.
While gale conditions are not expected, persistent northerly flow
will likely lead to Small Craft Advisory conditions, particularly
during the Tuesday night time frame when wind gusts of 25 to 30
knots can be expected over Lake Huron.
A cold front will move through Southeast Lower Michigan on Monday,
bringing a good chance of showers. While widespread heavy rain is
not expected, some locations, particularly along and south of I-94
where isolated thunderstorms will also be possible, may receive one
quarter to locally one half of an inch of rainfall from this system.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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