-- Discussion containing changed information from previous version are highlighted. --
089
FXUS63 KGRR 290212
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1012 PM EDT Sun Apr 28 2024

.KEY MESSAGES...

- Cold Front brings rain/thunder on Monday

- Multiple Chances for Showers and Storms This Week

- Warm Temperatures Through The Saturday

&&

.UPDATE...
-- Changed Discussion --
Issued at 1007 PM EDT Sun Apr 28 2024

Minimal instability remains south of the warm front tonight.
Mainly showers are expected overnight but some thunder can`t be
ruled out. A steadier batch of showers is indicated by the 00z
HRRR to arrive in the 06z-12z time frame. This activity is
currently located across eastern Missouri but will head our way
overnight. Looks like a wet morning commute especially along and
west of a Big Rapids to Battle Creek line.
-- End Changed Discussion --

&&

.DISCUSSION...
Issued at 352 PM EDT Sun Apr 28 2024

- Cold Front brings rain/thunder on Monday

Extensive cloudiness into this afternoon has so far muted any
strong updrafts, although a few showers and towering cu have
managed to form in the past couple hours across the southern half
of the forecast area. Cannot rule out a few strong storms into
early evening with deep layer shear values of 25 to 30 knots.
Breaks in the clouds and surface heating could overcome the
stabilizing influence of the extensive rain showers from last
night into this morning.

For tonight, we will watch whatever showers/storms are able to
develop but they should diminish after sunset as sfc based
instability diminishes, then look for showers and storms pushing
in ahead of the advancing cold front overnight into Monday
morning. Expect the bulk of those showers to come through between
roughly 8 AM and noon on Monday with the potential for some
stronger storms across the eastern forecast area as the airmass
destabilizes. Scattered showers persist along and behind the cold
front into Monday evening before drying works in from the west.

- Multiple Chances for Showers and Storms This Week

Tuesday will be the best chance for dry weather in the long term
portion of the forecast thanks to a surface ridge and upper-level
ridging forecast to move overhead. Ensemble probabilities have
trended downward with precipitation chances for the Tuesday night
into Wednesday timeframe due to questions on low-level moisture even
with a vorticity maximum swinging through. An isolated shower can`t
be ruled out north of M20 but given low confidence will leave the
dry NBM PoPs as is.

Showers and Thunderstorms more likely Wednesday into Thursday as a
surface low to our west lifts a warm frontal boundary across Lower
Michigan. Thursday could be the most active day of the long term
period as MUCAPE values increase near to above 1000 J/kg Thursday
afternoon in both ECMWF and GFS guidance with a 30-40 knot low-level
jet. A shortwave then swings through the area Thursday night into
Friday driving a front through keeping rain chances going.

Predictability in the longwave pattern decreases notably into next
weekend. While there are signals in cluster analysis and model
guidance for a trough to setup over the central United States by
next weekend, there is considerable variation in both the positioning
and amplitude of this feature.

- Warm Temperatures Through The Saturday

Highs in the 60s are expected for Tuesday as a weak thermal trough
quickly passes through the region. Temperatures warm for the mid to
late work week into the 70s, with the 80s not out of the question,
as southwest flow brings plenty of warm air into the Central Great
Lakes.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 743 PM EDT Sun Apr 28 2024

The first item of interest for aviation operations is a front
that is dropping down from the NE through the KLAN and KGRR areas.
This front has really nothing with it, but there is a distinct
wind shift from the South, to the NE. This should be in place for
a couple of hours, and will likely not reach the other airports.

The next item is rain chances. There are some rain showers
developing north of all of the SW Lower terminals. There may be a
few spotty showers this evening into the overnight hours at the
I-96 terminals, but nothing too widespread. Thunder can not be
ruled out, but the chance seems low enough during the night to
keep it out for now. The terminals are likely to stay VFR for most
of the night. Some stratus to the NE of KLAN and KGRR should be
held back.

There does look to be a more widespread area of showers that moves
in from W to E starting around 10-12z. These showers are likely to
bring conditions down to IFR at the I-96 sites closer to the wave.
The I-94 terminals are likely to drop down into the MVFR category.
These showers will move out then from 16-18z, and conditions will
improve a category or two at each site.

A few showers, and maybe a storm will remain possible then from
18-00z. Coverage looks quite limited and uncertain, so for now
will go with VCSH. As we near this time frame and certainty
increases, fine tuning of this period will occur.

&&

.MARINE...
Issued at 352 PM EDT Sun Apr 28 2024

Webcams and satellite do not show any extensive areas of dense fog
over Lake Michigan this afternoon as winds have apparently been
able to prevent its formation. We will keep mention of patchy fog
in the marine zones for this evening.

Winds and waves increase Monday afternoon and a Small Craft
Advisory may be needed although conditions looks marginal.

&&

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

&&

$$

UPDATE...Hoving
DISCUSSION...Ostuno/Thomas
AVIATION...NJJ/Thomas
MARINE...Ostuno