000
FXUS63 KGRR 181150
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
750 AM EDT Thu Apr 18 2024

.KEY MESSAGES...

- Rain Showers Tonight into early Friday

- Cold Pattern For the Weekend

- Rain showers for Tuesday

&&

.DISCUSSION...
Issued at 321 AM EDT Thu Apr 18 2024

- Rain Showers Tonight into early Friday

The day starts out dry as mid-level shortwave ridging traverses the
area. A few showers are then possible in the afternoon with highs
today ranging from the mid 50s for our northwest CWA to the mid
60s for our southeast CWA.

More widespread rain is expected tonight into early Friday morning
as a surface low tracking to our southeast and a 700mb shortwave
supports robust low-level FGEN banding across our area. As this
banding comes into focus, QPF forecasts have been trending upward,
with a general 0.2-0.5 inches of rain expected and locally higher
amounts possible. Isolated thunder is possible near I94 as LI values
approach zero or go slightly negative tonight. However,
instability has trended down over the last 24 hours and with it
thunder chances.

Overall, this is a pretty progressive system with showers clearing
the area near sunrise Friday morning. As surface and upper-level
ridging and associated dry air slide in behind the showers,
Friday should feature ample sunshine. Model RH forecasts suggest a
pocket of mid- level moisture may keep some mid-level clouds in
place across Central Michigan while a few cirrus clouds may sneak
into southern Michigan but overall mostly sunny to sunny skies are
likely with highs in the 50s.

- Cold Pattern For the Weekend

Northwest flow at 850 mb prevails Saturday sending temperatures down
to well below normal values.  The 850 mb temperature anomaly reaches
13 degrees below normal during the day.  The thermal trough at this
level pushes through during Saturday, with temps bottoming out at
around -9 deg C.  These values will hold daytime highs in the 40`s.
There might be some lake effect clouds around as the delta T values
suggest some lake moisture may get drawn into the cool air mass.
Water temps were 4 to 6 deg C. Temps start to rise Sunday with
850 mb values climbing to around 0 deg C by evening. This will
allow for max surface temps to make a run above 50 degrees if we
can mix to that level. Overnight lows will likely dip below
freezing for inland locations Saturday night and possibly Sunday
night.

- Rain showers for Tuesday

A digging mid level shortwave arrives Tuesday.  This feature will be
generating precipitation during the day.  Models do vary on the
track of this wave.  The GFS is further south and allows for enough
cold air to filter into the north side of this system to lead to
some snow over our northern zones.  We are not ready to include that
in the forecast.  However the incoming ECMWF is sending temperatures
lower Tuesday afternoon/evening and ensemble temperature trends in
the models are lower.  We will lower max temps on Tuesday to try and
capture the trends.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 747 AM EDT Thu Apr 18 2024

The MVFR deck will be scattering out by mid morning. However mid
to upper level clouds will be streaming in and there will be some
virga falling out of those clouds for the middle part of the day.
The low levels saturate this afternoon that will support an
increased risk for rain showers and lower cloud bases. Conditions
will be going down to MVFR and the IFR at some point tonight. The
rain will pull away late tonight but the lower cloud bases will be
slow to improve.

&&

.MARINE...
Issued at 317 AM EDT Thu Apr 18 2024

Have cancelled the current small craft advisory as winds and
waves have dipped below levels hazardous to small craft. However,
late tonight will feature gusts ramping up to 20-25 knots from the
northwest and 3-5 foot waves, as such will issue a small craft
advisory from St. Joseph to Pentwater from early Friday morning to
Late Friday afternoon.

A brief break in winds and waves is expected later Friday before
winds and waves ramp up again Saturday as colder air makes its way
into the region making small craft advisory conditions likely.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 6 AM to 6 PM EDT Friday for LMZ844>848.

&&

$$

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