FXUS63 KGRR 171515

Area Forecast Discussion
National Weather Service Grand Rapids MI
1115 AM EDT Wed Jul 17 2019


Issued at 315 AM EDT Wed Jul 17 2019

- Risk for severe storms very late tonight through Thursday night
into Friday

- Excessive heat likely Thursday through Saturday into early Sunday


Issued at 1040 AM EDT Wed Jul 17 2019

Surface low associated with the remnants of Barry continues to
track east and away from the area, while a ridge high pressure
begins to gain control over the Central Great Lakes. Chance for
showers/tstorms remains low today as moisture moves away, but
could see a few cells pop up this afternoon and evening as the
lake breeze moves inland and meets up with easterly flow over the
rest of the Lower Peninsula. Dry weather is favored for most of
the night, but watching potential for remnants of an MCS to
approach towards sunrise. Light winds and surface ridging will
also favor patchy fog once again.

Otherwise, looking at a fairly warm day with highs in the
mid/upper 80s and heat index values in the upper 80s to low 90s.
Hotter and more humid stretch of weather still expected for the
rest of the week.


.DISCUSSION...(Today through next Tuesday)
Issued at 315 AM EDT Wed Jul 17 2019

Primary short term fcst concerns involve assessment of
convective/svr wx potential late tonight through Thursday night
into Friday and excessive heat concerns Thursday through at least

Fair and very warm and humid wx is fcst for the vast majority of
our fcst area with high temps well into the 80s and dew points
mainly in the upper 60s to lower 70s. Most of the day will be dry
but there is a small chc for a pop-up shower or storm due to lake
breeze convergence and building instability from heating later
today. The US-131 corridor looks most favored for the stronger sfc
convergence and possibly a few showers or storms later today.

An MCS will approach our area from the wnw late tonight fueled by
the llj and instability. The severe wx threat will most likely
stay to our west tonight but the diminishing MCS could still
bring some briefly gusty winds and heavy rain late tonight into
Thursday morning. I would not completely discount potential for
severe wx early Thursday morning as the MCS/remnants of the MCS
roll in depending on how well organized the MCS becomes.

As instability ramps back up later Thursday and Thursday night
one or several more rounds of convection are expected. Strong to
severe storms are possible with potentially strong instability
developing Thursday aftn/evening (SB Cape values potentially
reaching at least 3000 j/kg) in conjunction with favorable (30-40
kts) deep layer shear for organized convection.

Relatively warm temps aloft should cap potential for convection
Friday. Excessive heat and humidity is forecast Thursday through
at least Saturday with high temperatures well into the 90s daily
and heat indices well into the hundreds.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 750 AM EDT Wed Jul 17 2019

Areas of IFR/LIFR due to low stratus lifting/mixing out this
morning, with SCT-BKN VFR cumulus deck prevailing this afternoon.
Can't rule out an isolated shower or storm this afternoon, but
feel the risk is too low to include in the TAFs.

Moist air mass may lead to some areas of fog again tonight, but
thinking primarily MVFR rather than IFR vsbys. Slight chance that
tstms will be crossing Lake MI and apchg MKG just prior to 12Z
Thursday, but main threat appears to be after 12Z.


Issued at 1040 AM EDT Wed Jul 17 2019

Main issues to watch in the next 48 hours will be potential for
thunderstorms early Thursday morning through Friday and increasing
winds tomorrow. Thunderstorms will carry the threat for lightning
and strong winds. Winds on Thursday will increase out of the west
and may allow waves to build into the 3 to 5 foot range along the
Lake Michigan shoreline. This would pose a threat to swimmers as
well as operators of small craft along the Lake Michigan




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