810
FXUS63 KGRR 052308
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
708 PM EDT Sun May 5 2024

.KEY MESSAGES...

- Cool tonight, high clouds through Monday night

- Risk for Thunderstorms Tuesday

- Unsettled and cooling down for the end of the week

&&

.DISCUSSION...
Issued at 202 PM EDT Sun May 5 2024

- Cool tonight, high clouds through Monday night

Latest visible loop shows stratus south of I-96 continuing to
erode from north to south as drier air moves south from Canada.
Concurrently, some high clouds from the lower MS Valley are
starting to move north toward Lower MI, but they are thin and
won`t do much to block the sun for the remainder of the day.

High pressure will settle over Lower MI tonight generating some
light winds and helping temperatures fall into the upper 30s
across the northern cwa to upper 40s over the southern cwa. There
may be a very isolated frost potential in low lying areas of the
northern cwa tonight, but not wide spread enough for headlines.

Monday looks like a mostly sunny day as upper ridging follows the
surface high across the state. High clouds will likely move in
from the southwest during the day and more so Monday night as a
warm front develops over the MO Valley and begins to move in this
direction.

HREF sky cover progs point toward increasing clouds throughout
the night as the warm front approaches; any precipitation
associated with the front will hold off until Tuesday.

- Risk for Thunderstorms Tuesday

Models continue to show a deeper trough pivoting in from the
southwest during the day on Tuesday.  We will have to monitor the
trends as a stronger mid level jet will be near or just south of
Southern Lower MI during the Tuesday aftn/eve hours.  This feature
will support favorable deep layer shear in that region. An
upper level jet will provide diffluence over Lower MI
during the afternoon/eve as well.  Models
vary on the projected SB instability with the NAM showing very
little while the GEM and GFS are suggesting we may top 1000 J/kg in
southern parts of the CWA, around Kalamazoo, Battle Creek and
Jackson.

- Unsettled and cooling down for the end of the week

A series of mid level troughs dig their way down through the Great
Lakes region for the end of the week drawing down cooler air from
Canada.  One surface wave tracks through the MI/IN border region
Wednesday night into early Thursday providing some rain. A secondary
surface wave arrives Saturday leading to another round of rain. By
Friday and continuing into Saturday, 850 mb temps are shown to make
a run at 0 deg C for northern parts of the CWA.  This would keep max
temps below normal. Those projected 850 mb temps would be cold
enough to lead to lake enhanced moisture so its likely to be
rather cloudy as well.  With precipitation forecasted, we could
easily end up stuck in the 50`s Friday and possibly into the
weekend.  Ensemble temperature forecasts have overall been trending
lower as well, adding confidence for cooler than normal
temperatures.  We will therefore lower the temperatures accordingly
in the forecasts.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 703 PM EDT Sun May 5 2024

Few to scattered high clouds are preventing completely clear
skies, regardless VFR is expected this evening. The thing to watch
will be during 03z-09z as a couple hours of southeast flow could
bring enough moisture off Lake Erie to lead to patchy fog or MVFR
cigs. Confidence in development of patchy fog or low clouds is
20-30 percent at JXN and even lower for all other TAF sites so
will leave VFR conditions at all sites with this TAF package. A
disturbance passing south of lower Michigan will lead to
widespread BKN cirrus overnight before clearing from north to
south Monday. Mostly sunny skies are expected in the wake of the
departing cirrus shield. Generally west to west-northwest winds
become light easterly winds overnight before southeasterly winds
of 5-10 knots are expected Monday.

&&

.MARINE...
Issued at 202 PM EDT Sun May 5 2024

No marine issues for the next 36 hrs as high pressure at the
surface and aloft move over the lake. Thunderstorms will pose a
marine hazard Tuesday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...MJS/04
AVIATION...Thomas
MARINE...04