599
FXUS63 KGRR 301937
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
337 PM EDT Tue Apr 30 2024

.KEY MESSAGES...

- Gusty winds and a shower risk later tonight into Wednesday
  morning

- Warmer than normal temperatures ahead

- Several Chances for showers and storms ahead

&&

.DISCUSSION...
Issued at 255 PM EDT Tue Apr 30 2024

- Gusty winds and a shower risk later tonight into Wednesday
  morning

A 40 knot low level jet moves into the region late tonight into
Wednesday morning. This feature advects in a moist air mass with
PWAT values progged to reach around an inch based off of the
ensemble guidance. Given the moisture and lift, some shower
activity is expected to track in from the west as this the low
level jet arrives. If the upstream convection that develops this
evening diminishes slower than expected, a few thunderstorms could
make it across the lake, mainly around daybreak. SPC HREF MU CAPE
values is still struggling to show much if any instability so we
will keep the precipitation as showers for now. Any heavier
downpour could lead to gusty winds. A better shot for gusty winds
will be as mixing develops Wednesday morning. Base on projected
heights and the winds at those levels, we should see gusts topping
30 mph at times.

- Warmer than normal temperatures ahead

Overall zonal flow will continue through the rest of the week and
into next week. The positive height anomalies favor continued warm
air advection through this period. Latest Ensembles and anomalies
continue to show a prolonged period of +1 or greater anomalous
warmth into next week. That should keep daytime highs 5 to 10
degrees above normal. This correlates to Highs in the 70s through
the weekend.

- Several Chances for showers and storms ahead

A strong frontal boundary in between a retreating high and a large
upper level low moving along the Canada border should provide enough
moisture and instability for showers and storms late Thursday night
into Friday morning. The bulk of the cold air associated with that
system should remain north. There is a strong short wave associated
with that system and given the current gradient there should be some
mid to low level winds should provide enough shear for convection.
Latest mid range models continues to downplay the moisture
associated with it through there remains PWATS of an inch to 1.25
inches.

Another opportunity for precipitation will come in the form of a
tertiary trough on the back side of the above mentioned upper
level low. As that low exits to the northeast it will swing an
elongating trough through the Great Lakes. Behind that trough is
some cold air that though above freezing, current 850 mb temps
have it +2 to +3C which is should allow for a decent cold frontal
boundary that could aid convection. So isolated storms are
possible at this point, however it is a ways ahead so confidence
is low.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 139 PM EDT Tue Apr 30 2024

VFR conditions will dominate for the most if not all the forecast
period. Expect the winds to slacken this evening and then increase
and mix out early Wednesday morning. A front will bring gusty
winds beginning around 09Z with a strong LLJ which will cause Low
level wind shear 2KFT and below until around 13 to 14Z. The
timing for this shear is reflected in the TAFs. As the LLJ exits
expect lower cigs, after 15Z.

&&

.MARINE...
Issued at 255 PM EDT Tue Apr 30 2024

A low level jet will be moving into the nearshore zones overnight
and Wednesday morning. This feature will support increasing winds
and building waves. The flow will initially be south southeast
later tonight but it will veer to the southwest during the
morning. We will issue a small craft advisory for most marine
zones as a result.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 5 AM to 4 PM EDT Wednesday for
     LMZ845>849.

&&

$$

DISCUSSION...MJS/Ceru
AVIATION...Ceru
MARINE...MJS/Thielke