Special Weather Statement, NWS Grand Rapids, MI

Area Forecast Discussion
National Weather Service Grand Rapids MI
329 PM EDT Thu Apr 29 2021

LATEST UPDATE...
Synopsis/Discussion/Marine

.SYNOPSIS...
Issued at 253 PM EDT Thu Apr 29 2021

- Scattered showers as the cold front drops down this evening

- A few thunderstorms possible Saturday afternoon into the night

- Rain with some thunderstorms starting up Sunday afternoon

&&

.DISCUSSION...(This evening through next Thursday)
Issued at 253 PM EDT Thu Apr 29 2021

- Scattered showers as the cold front drops down this evening

Showers and even a few thunderstorms have developed upstream in
Central WI ahead of the cold front tracking our way. This front
drops through the CWA this evening. While some instability
persists for a few more hours ahead of this front...by the time it
gets to our CWA...the instability and risk for storms should be
gone based on the recent high res models.  However we will need
to monitor the trends for the next few hours.

- A few thunderstorms possible Saturday afternoon into the night

Warm air advection strengthens over the shallower cold airmass
Saturday. This will lead to clouds and scattered showers. Weak
elevated instability develops for the afternoon and evening. This
could lead to an isolated thunderstorm. Severe weather is not
predicted given the elevated nature of the weak instability.
After midnight the forcing moves off to the east taking any
showers or storms with it.

- Rain with some thunderstorms starting up Sunday afternoon

Overall this is a trend for somewhat less precipitation with this
event. The mid to upper level low down over northern Mexico
lifts northeast and gets caught up in the deep southwesterly flow
aloft Friday into Saturday. This system moves into the OH Valley
Sunday into Monday. Abundant Gulf moisture arrives with values
approaching 1.5 inches. The potential for a half inch or more of
rain is still fairly high...which would be beneficial for many
area. Models are showing elevated instability Sunday afternoon the
with some models keeping it around through Monday. Thus a few
thunderstorms are possible.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 150 PM EDT Thu Apr 29 2021

IFR conditions will prevail for a few hours this afternoon at most
TAF sites in Southwest Lower MI. The low level moisture does
decrease from west to east as we go through the afternoon and KMKG
has already lifted into the MVFR range. All TAF sites will
eventually see VFR conditions by evening. New showers will be
moving in from the northwest during the evening though. They will
be scattered. A brief window of MVFR conditions exists behind the
departing showers towards midnight...but after midnight a drier
and colder airmass will start advecting in. Gusty conditions will
develop...especially Friday morning.

&&

.MARINE...
Issued at 253 PM EDT Thu Apr 29 2021

The increasing northwest winds and cold air advection will likely
lead to hazardous conditions for small craft starting up late
tonight and lasting into Friday. Headlines will likely be needed
for Saturday as well with a strengthening southwest to west flow.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory from 8 AM to 4 PM EDT Friday for LMZ844>849.

&&

SYNOPSIS...MJS
DISCUSSION...MJS
AVIATION...MJS
MARINE...MJS

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