Portage, Michigan 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

026
FXUS63 KGRR 250721
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
321 AM EDT Fri Apr 25 2025

.KEY MESSAGES...

- Showers and Storms Today

- Dry and Mild Weekend

- Chance of Thunderstorms Tuesday

&&

.DISCUSSION...
Issued at 320 AM EDT Fri Apr 25 2025

- Showers and Storms Today

The arrival of an upper-level trough will lead to cyclogenesis along
a front stalled across lower Michigan. Shower activity for the first
part of the day will be relatively scattered given the best mid-
level height falls/forcing remain northwest of the forecast area.

Southerly flow ahead of the low will bring 50s to possibly lower 60s
dewpoints by the afternoon hours. This will allow CAPE values to
build to 1000-1500 J/kg. RAP forecast profiles show steep low-level
lapse rates and minimal convective inhibition by the afternoon,
supporting the development of late day showers and storms. The best
coverage will be across the southeast CWA in the relative warm
sector and ahead of the front. Timing for this afternoon development
will be roughly 4p-8p which the various CAMs show well. Severe
weather is not likely given modest effective shear of 25-30 knots.
However, an isolated strong storm cannot be completely ruled out
southeast of a Marshall to Lansing line if a storm can briefly
organize in the marginal environment.

- Dry and Mild Weekend

Ridging and high pressure arrive for the weekend, bringing dry air
into the region. Northerly flow will keep temperatures on the cool
side. Highs will be in the 50s to low 60s, which is seasonable for
this time of year. Dry air and subsidence will also support plenty
of sunshine.

- Chance of Thunderstorms Tuesday

Models continue to have decent agreement on the overall synoptic
pattern into early next week. Warm and moist advection out ahead of
a mid-level wave will send temperatures into the 70s, and possibly
even the low 80s Tuesday. This will also send dewpoints into the low
60s supporting a buoyant sector developing across southern lower
Michigan. The mid-level wave will send a cold front across the area
Tuesday, though questions as to when remain. The GFS solution drives
the front through faster, holding the better convective potential to
the south and east where instability will be able to build. On the
flip side, the ECMWF suite of solutions has a slower front, which
would put more of the CWA in play for thunderstorm development.

Given high ambient shear, in excess of 50 knots, this timing will be
crucial to the potential for severe weather. With the uncertainty
in timing, the relatively best potential for severe storms would
be across the southeastern CWA, where an earlier front solution
may still allow some instability to build. This analysis is
supported by the latest medium range ML guidance. We will need to
continue to monitor trends in frontal timing over the coming days
given the implications on convective potential.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 150 AM EDT Fri Apr 25 2025

VFR conditions are expected until showers and thunderstorms
develop this afternoon and evening. The best potential for
thunderstorms will be along and east of an AZO to LAN line between
18Z-00Z. Farther west of this line there is lower confidence of
thunderstorms. Any precipitation may just remain scattered showers.
With the round of showers and storms, ceilings will gradually
lower to IFR values with winds becoming more northerly.

&&

.MARINE...
Issued at 320 AM EDT Fri Apr 25 2025

No marine issues presently, but that will change later today. Winds
from the north increase this afternoon with the departure of a low
pressure system and associated increase in gradient flow. Mixing
down of gusts to around 30 knots and increasing waves will lead to
conditions becoming hazardous to small craft this afternoon through
late Saturday. The current Small Craft Advisory looks to be in good
shape. Winds diminish for Sunday as gradient flow weakens, before
our next system approaching Monday causes them to ramp back up.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 5 PM this afternoon to 8 PM EDT
     Saturday for LMZ844>849.

&&

$$

DISCUSSION...Thomas
AVIATION...RAH
MARINE...Thomas