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000
FXUS63 KGRR 191140
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
740 AM EDT Fri Apr 19 2024

.KEY MESSAGES...

- Rain Showers End Early With Breezy Conditions Today

- Temperatures Fall Near Freezing Friday Night

- Below Freezing lows for the Sun to Mon

- Potential for a few storms Tuesday

&&

.DISCUSSION...
Issued at 248 AM EDT Fri Apr 19 2024

- Rain Showers End Early With Breezy Conditions Today

The current rain shield associated with a surface low progressing
northeast across the Central Great Lakes will exit the area by 12z
with drier air expected behind it. Most of the area will be mostly
sunny today, however late this afternoon some moisture in the 850-
700mb layer approaches areas north of M20 bringing a cloud deck that
will cross the area overnight.

One thing to watch today will be RH values, especially across
southern Michigan. Given the lighter nature of QPF tonight, some
guidance like the HRRR is trending towards lower minimum RH
values towards 30 percent this afternoon. If we can mix towards
lower RH values, breezy conditions with winds gusting 20-30 mph
may lead to a window of elevated fire weather concerns.


- Temperatures Fall Near Freezing Friday Night

Given the recent stretch of warmer weather, vegetation is starting
to become vulnerable to freezing temperatures. As troughing sets in
over the area and cold air advection begins, overnight temperatures
fall into the low to mid 30s. However, surface winds likely won`t
die off into the overnight hours thanks to a gradient associated
with a surface high to our west.This may keep enough mixing to
avoid a sharp near-ground temperature inversion.

Saturday then features partly cloudy skies becoming mostly sunny
during the afternoon. Continuing cold air advection will keep highs
in the 40s.

- Below Freezing lows for the Sun to Mon

The northwest flow continues Saturday night into Sunday keeping any
significant warming away from the region.   The flow then backs to
the west southwest for Sunday night into Monday.  Cooler than normal
temperatures will continue given this pattern.  Ensemble temperature
forecasts continue to support surface temps going below freezing at
night, especially for inland locations.  No noticeable trends were
seen in the latest runs. We will therefore maintain the current
forecasts showing a potential for subfreezing temps both nights. The
wind will likely not go calm for Saturday night, but later Sunday
night the wind will likely be lighter.  So some frost my occur then.

- Potential for a few storms Tuesday

Models are tracking the next wave of low pressure eastward through
northern parts of Lower MI Tuesday. The GFS does draw up enough
instability to warrant a few thunderstorms.  The Canadian and ECMWF
are more conservative with the instability but do show a similar
track, with southwest winds over the CWA on Tuesday.  We will
therefore feature a chance for thunderstorms for southern parts of
the CWA ahead of the frontal passage. Bulk shear values through 500
mb are shown to be strong with steeper mid level lapse rates so
trends will need to be monitored closely.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 734 AM EDT Fri Apr 19 2024

The area of light rain and low level moisture east of KLAN will
continue to push eastward over the next hour or two leading to
conditions become VFR for Southwest Lower MI. Gusty west to
northwest winds will develop as the mixing height increases and
leads to the gusty conditions. Some VFR clouds will start to move
back in later in the day and the winds will diminish slightly by
sunset.

&&

.MARINE...
Issued at 246 AM EDT Fri Apr 19 2024

Winds and waves will build over the coming hours resulting in
conditions hazardous to small craft today. Going small craft
advisory for all nearshore waters between St. Joseph and Manistee
through 8pm looks to be in good shape. A brief lull in winds and
waves, mainly Holland and points south, is possible this evening
before winds and waves increase again into Saturday. The small craft
advisory likely will need to be extended into Saturday to cover this
second surge in winds and waves.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ844>849.

&&

$$

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