306
FXUS63 KGRR 260611
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
211 AM EDT Fri Apr 26 2024

.KEY MESSAGES...

- Another Cold Night

- Showers and Thunderstorms Arrive Friday Night

- Warmer with Rounds of Showers and Storms Saturday into Monday

&&

.DISCUSSION...
Issued at 343 PM EDT Thu Apr 25 2024

- Another Cold Night

We have issued a Freeze Warning for interior sections and a Frost
Advisory for the counties bordering Lake Michigan for tonight. The
airmass will be modified a bit from last night and return flow
begins late tonight as the surface ridge begins to move east, but
model soundings still show an very dry airmass through 12Z Friday
with precipitable water down near 0.15 inches. This should allow
temperatures to drop quickly like last night. There could be some
wind picking up by 12Z...but we still expect temperatures to drop
to around 30 in the warning area and lower 30s in the advisory.

- Showers and Thunderstorms Arrive Friday Night

Return flow increases Friday but it will take a while to moisten
the column of the very dry atmosphere and showers will probably
hold off until Friday evening although clouds will be in the
increase in the afternoon with isolated showers possible across
the southwest zones late in the day.

A large area of isentropic ascent and strong warm advection
pattern combine with the arrival of deep moisture to bring
increasing chances for rain Friday night and elevated instability
should be enough for isolated thunder and some heavier downpours
late Friday night. We will keep the categorical POPs across the
northwest half of the forecast area where the axis of deeper
moisture and lift will be.

- Warmer with Rounds of Showers and Storms Saturday into Monday

Low confidence at present in convective trends for Later Saturday
Afternoon and Evening. A conditionally favorable environment for
organized convection will be present given MUCAPE values of over
1000 J/kg as moisture climbs in strong SW flow, and deep layer shear
values climbing to 35-45 knots given the low and mid-level jets in
place. However, this is contingent on storms being able to develop
which is in question given weak to no forcing in place given the
frontal boundary and shortwave remain to our west. If storms can
develop, organized convection is possible which is covered by the
current SPC marginal to slight risk across the CWA. It will be
breezy however with NBM probs of 90+ percent for gusts over 30 mph
for much of the area and 10-20 percent for 40+ mph, with warm air
advection somewhat limiting gust potential. NBM 20-30 percent precip
chances seem reasonable later Saturday.

As the warm front sits to out north Sunday a second round of showers
and storms is expected across Central Lower, especially in the
northwest CWA towards Ludington aided by a shortwave to our
northwest and the right entrance region of the upper-level jet.
Given CAPE values north of 1000 J/kg thunder is likely and deep
layer shear is still decent so Sunday will need to be watched too.

Showers then expand across the CWA Sunday Night into Monday as the
cold front drifts south before clearing the area Monday evening.
CAPE values on the ECMWF and GFS still look to be above 500 J/kg so
thunder continues to be possible.

Dry conditions for Tuesday as a period of surface ridging drifts
over the area before chances increase for showers increase
Wednesday/Thursday as a shortwave drives through before a trough
passes overhead.

850mb temperatures climb into the teens this weekend into early next
week causing temperatures to climb into the 70s with low (around 10
percent) chances that areas exceed 80 degrees. Highs will be well
into the 70s, which is over 10 degrees above normal, through at
least Tuesday making it feel like summer.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 212 AM EDT Fri Apr 26 2024

A warm front will slowly lift towards the Great Lakes region over
the next 24 hours from the Central Plains. Clouds will gradually
lower and thicken during this time frame. Mainly clear skies are
found across the area at 06Z which will remain the case through
sunrise. High clouds with bases near 25,000ft will spread in
during the morning hours and lower to 7,000-10,000 feet by 00z
this evening. Rain showers will spread in after 00z, with the best
chances in this TAF period occurring in the 03Z to 06Z time frame
towards Lake Michigan.

Winds will be from the east and southeast the next 24 becoming
gusty during daylight hours. Today winds of 15 to 25 knots will be
common.





&&

.MARINE...
Issued at 343 PM EDT Thu Apr 25 2024

Winds will increase on Friday and Friday night. A SCA may be
needed by late Friday afternoon or evening continuing into early
next week as a persistent pressure gradient keeps southwest winds
elevated and waves building over 4 feet to as high as 8 feet north
of Pentwater.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Frost Advisory until 8 AM EDT this morning for MIZ043-050-056-
     064-071-072.
     Freeze Warning until 8 AM EDT this morning for MIZ044>046-051-
     052-057>059-065>067-073-074.
MARINE...None.

&&

$$

DISCUSSION...Ostuno/Thomas
AVIATION...Duke
MARINE...Ostuno