Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 220726
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
326 AM EDT Mon Apr 22 2024

.KEY MESSAGES...

- Frost Advisory Ongoing, Elevated Fire Danger Today

- Showers Tonight into Tuesday

- Another round of cold air mid-week

- Warm and potentially stormy next weekend

&&

.DISCUSSION...
Issued at 324 AM EDT Mon Apr 22 2024

- Frost Advisory Ongoing, Elevated Fire Danger Today

Observations show most of West Michigan is in the mid to upper 30s
right now, and expectation is that temps fall into the low to mid
30s by daybreak south of US10, where the growing season has begun,
given clear skies and light winds. Thus the Frost Advisory looks to
be in good shape.

Warming temperatures are expected today as shortwave ridging
dominates the forecast with highs in the low to mid 60s. Given RH
values falling into the 25-30 percent range, and 15-20 mph winds
gusting to 25, a period of elevated fire danger may develop in the
afternoon.

- Showers Tonight into Tuesday

Rain showers then increase late this evening as the low level jet
ramps up across Lake Michigan and spread from northwest to
southeast. Those clear the area by daybreak Tuesday, giving a window
of lower precip chances except for the chance some showers may sneak
into the I94 corridor.

Convective showers then develop Tuesday afternoon as low-level lapse
rates near 9C/km paired with modest mid-level lapse rates result in
a few hundred joules of CAPE developing in low-topped convection.
This pairs with lift from a passing shortwave and cold frontal
boundary to provide scattered to numerous showers. Moisture will be
lower with dewpoints in the upper-30s to low 40s however so only a
slight chance of thunder exists. Showers continue into early
Wednesday morning.

- Another round of cold air mid-week

Starting Tuesday evening the cold front will be through Lower
Michigan and we will again by under the influence of cold Canadian
air. This brings us yet again into a risk window for frost/freeze
with tender vegetation - including many of the the vaunted West
Michigan fruit crops. We`ll basically have two nights of concern -
both Tuesday night and again Wednesday night. One point of good news
is that it is starting to look like clouds may not clear out in time
on Tuesday night to produce a widespread freeze (except in far
northern areas), so that means Wednesday Night will be the one we
need to watch the closest. All the basic ingredients for a classic
late spring freeze are expected to be in place - surface high
pressure resulting in light winds, a dry lower atmosphere, clear
skies to allow radiational cooling, and 850 mb temperatures in the -
3C to -6C range. A silver lining here is that the models have backed
off the magnitude of this cold airmass (as indicated by 850 mb
temperatures) by a degree or two since yesterday.

- Warm and potentially stormy next weekend

We flip the switch back into warm air advection mode starting
Thursday, and this time it looks like our overall longwave weather
pattern will be changing. In other words, this should bring an end
to the rollercoaster weather and usher in a more sustained warm and
spring-like airmass (for at least the foreseeable future). Deep-
layer southwest flow associated with a building upper ridge over the
heart of the country will surge 850 mb temperatures in Grand Rapids
from -5C Thursday morning to +12C on Friday afternoon. This weather
pattern will also surge humidity into our neck of the woods, with
dewpoints pushing 60F by Saturday and Precipitable Water approaching
1.25. Moisture and instability are 2 of the 3 ingredients necessary
for storms, and the 3rd is some type of forcing mechanism, which
could come in the form of a vigorous shortwave that moves through
the upper Great Lakes sometime on Saturday. *Caveat* There remains
uncertainty with the timing and positioning of this shortwave, and
these elusive details will probably make the difference between
garden-variety rain showers and storms that get more organized and
potentially strong. Stay tuned throughout the week as we refine
these forecast details.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 131 AM EDT Mon Apr 22 2024

Light southwest winds will prevail overnight as a temperature
inversion keeps the gustier winds aloft. VFR conditions are
expected throughout the period, although high clouds will be on
the increase during the day Monday - especially during the
afternoon. Meanwhile, midlevel clouds around 5,000 feet will be
moving in from the northwest after sunset on Monday evening, with
the potential for a few rain showers developing by early Tuesday
morning.

&&

.MARINE...
Issued at 324 AM EDT Mon Apr 22 2024

Will issue a small craft advisory starting this afternoon (20z)
north of Whitehall and expanding to the Lake Michigan nearshore to
St. Joseph this evening (00z) as south to southwest winds ramp up
and conditions hazardous to small craft spread southward. Tuesday
night into Wednesday the strong winds switch to northerly as a cold
front passes through the region. Will run the advisory to Wednesday
morning for now, however subsequent shifts will evaluate extending
further into Wednesday as high resolution model data comes into
that window to see how fast winds and waves subside. Cannot rule
out some gales during this period given the strong low level jet
overhead, however the peak of the jet will be when stability over
the lake is higher meaning that confidence in gale force gusts is
too low for a gale watch or gale warning.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Frost Advisory until 8 AM EDT this morning for MIZ043>046-
     050>052-056>059-064>067-071>074.
MARINE...Small Craft Advisory from 8 PM this evening to 8 AM EDT
     Wednesday for LMZ844>847.
     Small Craft Advisory from 4 PM this afternoon to 8 AM EDT
     Wednesday for LMZ848-849.

&&

$$

DISCUSSION...AMD/Thomas
AVIATION...AMD
MARINE...Thomas


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