302
FXUS63 KGRR 131344
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
944 AM EDT Sat Jun 13 2026
.KEY MESSAGES...
- Thunderstorms expected this evening into Tonight
- Showers and storms Tuesday and Wednesday
- Slightly cooler than normal through the 7 day forecast
&&
.DISCUSSION...
Issued at 356 AM EDT Sat Jun 13 2026
- Thunderstorms expected this evening into Tonight
The main focus of the 7 day forecast is on thunderstorms this
afternoon and evening and whether or not we have a severe threat
with these storms. The bottom line up front is there are small
chances for severe, especially this evening. We are in a SPC
marginal threat for severe weather today and agree with that
assessment. Really there are quite a few factors going for
convection today. Starting aloft, there is a 100 knot upper level
jet overhead with some suggestion for a slight coupled jet
structure. At the very least we look to be in a right front quad
of a jet streak which will aid overall lift today. At 500mb we
have 50 knots of flow, so the upper level variables one looks for
are there. At 850mb we have around 30 knots of wind which is more
than enough to aid convective development. In terms of low level
moisture, +13C 850mb dew points are sufficient for storms as are
the middle 60s dew points that are forecast. Deep layer shear is
around 40 knots with MUCAPE values of 1,000 to 2,000 j/kg. So
there really is a lot going for severe weather this evening.
Machine learning models like Nadocast are also showing a threat
for wind and hail over much of the area. If there was one slight
negative its that the moisture through the depth of the atmosphere
is a little bit down from what could be there today. PWATs are
around 1.6 which could be higher in the month of June, but that is
plenty to work with as well. We expect scattered showers and
storms to slowly work southward with an advancing cold front this
evening and overnight. Chances increase up along U.S. 10 around
22Z. Again, hail to around 1 inch or so and wind gusts to around
60 mph look to be the main threats.
- Showers and storms Tuesday and Wednesday
A deepening 500mb trough will be in place over much of the
forecast period a mid level shortwave and associated surface cold
front will move through during this time frame. Monday, and
Thursday/Friday look mainly dry at this point.
- Slightly cooler than normal through the 7 day forecast
Given the troughing and potential for clouds and showers feel our
highs will be near to slightly below normal. Highs will be
comfortable in the 70s with lows dipping into the 50s.
&&
.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 651 AM EDT Sat Jun 13 202
Limited aviation concerns today at the Southwest Lower Michigan
TAF sites. There is one though and that is a gusty southwest of 15
to 25 knots that should occur much of the day. Skies will be clear
to partly cloudy with clouds bases at or above 8,000 feet for the
most part.
The focus this evening and tonight is on the threat of
thunderstorms. We are expecting a broken line of showers and
storms to work from northwest to southeast through the TAF sites
starting at 23Z at MKG and ending at JXN around 10Z-12Z.
&&
.MARINE...
Issued at 940 AM EDT Sat Jun 13 2026
Expanded the Beach Hazards Statement to include Ottawa County
today based on current observed wave heights and an upward trend
likely into late morning and afternoon. Winds are currently
gusting around 20 knots at the lakeshore with higher gusts
expected today. Waves are already around 3 ft and should nudge
higher during the day mainly near and north of Grand Haven. The
SCA was also expanded to include Holland to the north. After
subsiding waves tonight, another phase of 3-5 ft waves is likely
near and south of Whitehall Sunday.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through late tonight for MIZ037-043-050-
056.
MARINE...Small Craft Advisory until 2 AM EDT Sunday for LMZ846>849.
&&
$$
DISCUSSION...Duke
AVIATION...Duke
MARINE...Hoving
NWS GRR Office Area Forecast Discussion
