National Weather Service United States Department of Commerce

Forecast commentary -

Mid level moisture advection this evening proved rather efficient in generating at least light
showers across much of the area. Mid level moisture transport has been focused across central lower
Michigan. This has led to more persistent showers across the Saginaw valley and Thumb regions.
Earlier model solutions strongly suggested that the better convective potential through the
overnight would shift to the northern Great Lakes as a longer wavelength trough rotating across the
nrn Great Lakes lifts the low level jet into nrn Michigan. The ongoing quasi stationary mcs now over
the wi/il/ia border region adds a level of uncertainty to this. Recent satellite/radar trends
suggest a little more stationary forcing has set up across central Michigan. The resultant mcv from
this convective complex may sustain this region of enhanced moisture convergence across the northern
sections of the forecast area into the overnight. The approach of this mcv combined with increasing
elevated instability through the overnight will support a chance for thunderstorms. An update will
be issued to further increase convective chances across the northern portions of the forecast area.
The convectively induced troughing to the west may actually force some enhanced short wave ridging
across Lake Erie, which may be enough to limit convective chances to the low chance category across
the southern portions of the forecast area ( metro Detroit and points south ).

The elevated instability overnight will be marginal, so severe weather is not expected. Given the
excessive rainfall across central Michigan this past week, current radar trends bear some watching.
The expectation is for the convection to weaken as it pushes toward the Saginaw valley, which should
prevent excessive rainfall totals.

. . posted at 904 PM EDT Wed Jun 28 2017

Surface low pressure advancing towards the northern Great Lakes region will continue to push a warm
front up across northern Wisconsin and into western Michigan. Convection from this morning has
slowly weakened and continues to do so as it crosses into Michigan. The warm front did spark
development out ahead of the the morning convection as it moved across eastern Wisconsin. This is
what we have been watching with the activity slightly outpacing some of the model data. 12z
soundings from both DTX and APX showed quite a bit of drier air in the column with the ridging that
has been in place. While this has helped in holding off precip, moisture advection coming into the
area should help in maintaining some of the precipitation. Forecast is on par with the trends as the
northern half of the forecast area will see better chances for activity through the later afternoon
and into the evening. Rainfall amounts are expected to stay on the lighter side through early
Thursday morning, generally less than half an inch.

Surface based convection has already started to develop back across the midwest this afternoon. This
activity is expected to weaken as it pushes east overnight. Activity is then expected to increase in
coverage Thursday morning as the area remains in the warm sector coupled with the advancement of the
warm front across the area. There is still uncertainly in just how much coverage there will be as it
moves into the warm sector tomorrow morning. With instability increasing, SPC has nudged both the
marginal and slight risks northward with main concerns for strong winds during the afternoon and
evening periods. Going into Friday, chances are still there for storms as the cold front pushes
through. Friday looks to be the best chance for storms as opposed to Thursday, but again will be
dependent on how convection from the previous day plays out. The entire forecast area continues to
be highlighted in slight risk for Friday. Warm air advection will continue to bring warmer
temperatures into the area through the end of the week. Highs on Thursday are expected to be the
warmest for the week with highs warming into the lower 80s.

A wet weather pattern looks to be in store for southeast Michigan during the weekend into early next
week. The first wave of low pressure will move in on Saturday bringing the chance for showers and
thunderstorms diminishing by the afternoon hours. A high pressure system will then build into the
Great Lakes region on Sunday, bringing relatively dry weather, however, an isolated shower would not
be out of the question. Another wave of low pressure will then move through the region Monday
evening into Tuesday allowing for chances of showers and thunderstorms yet again. High pressure then
looks to move into the area on Wednesday, bringing drier conditions. Temperatures will remain
seasonal, with high temperatures hovering around the upper 70s to low 80s, and overnight lows in the

. . posted at 341 PM EDT Wed Jun 28 2017