Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 161854

Area Forecast Discussion
National Weather Service Grand Rapids MI
254 PM EDT Sun May 16 2021


Issued at 254 PM EDT Sun May 16 2021

- A few showers across north central Lower MI this evening

- Greater rain chances late Tuesday into Wednesday

- Fire weather threat remains significant


.DISCUSSION...(This evening through next Sunday)
Issued at 254 PM EDT Sun May 16 2021

-- A few showers across north central Lower MI this evening --

There will be a chance for relatively brief rain showers in the
general vicinity of Clare County late this afternoon into early

Forecast details: CAM guidance, particularly recent HRRR runs, have
been fairly consistent with shower development in the mentioned
area. This is supported by water vapor imagery, which shows an
approaching weak PV disturbance currently entering northwest WI.
Additionally, the 12Z APX sounding indicates impressive cold
temperatures aloft //-23C at H5// which will mean favorable lapse
rates with gradually decreasing clouds helping afternoon insolation.

-- Greater rain chances late Tuesday into Wednesday --

For Tuesday night into Wednesday there are increasing chances for
showers and even thunderstorms. As noted previously, Monday and
Monday night look dry and scattered showers remain possible from
Wednesday into the weekend.

Forecast details: 16/00Z ECMWF ensemble is notably wetter with QPF
for the 24 hours between Tuesday evening and Wednesday evening. SPC
gives us a chance for thunder into Wednesday morning as well. From
Wednesday onward, forecast soundings feature weak conditional
instability associated with deep moisture and nearly moist adiabatic
lapse rates. It was noted previously that no significant forcing
mechanisms are foreseen, but it wouldn`t take much mesoscale forcing
(such as lake breeze circulations) to generate at least some
spotty precipitation in this environment.

-- Fire weather threat remains significant --

Precipitation amounts with any rain occurring Tuesday night into
Wednesday would most likely total under a quarter of an inch. This
would not make much of a dent in the drought. Minimum relative
humidities towards the end of the week look to be around 40 percent,
but this could easily go lower if highs are able to reach 90
degrees. Additionally, winds from the southwest will be increasing
with gusts perhaps approaching 30 mph by Friday afternoon.

How the fire threat evolves depends in part on mid-week
precipitation, but we are not seeing anything yet to reduce the


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 135 PM EDT Sun May 16 2021

VFR conditions expected through the period. Clouds with bases
below 7000 feet this afternoon are expected to dissipate early
tonight. Isolated rain showers may develop later this afternoon
well north of LAN. That activity would move east before dissipating
and therefore is not expected to affect any of the Southwest
Lower MI terminals.


Issued at 254 PM EDT Sun May 16 2021

No changes to previous thinking. Winds will be either light or
offshore through the period which will limit wave growth closer to
shore. Marine fog becomes a possibility starting around Wednesday as
we begin to see dewpoints making a run at 50 degrees over the colder
water surface. By the end of the week, with land temperatures
getting well into the 80s, we will be seeing a lot more active lake
breeze days.




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