Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 180945 AAA
AFDGRR

Area Forecast Discussion...UPDATED
National Weather Service Grand Rapids MI
545 AM EDT Wed May 18 2022

LATEST UPDATE...
Discussion

.DISCUSSION...(Today through next Tuesday)
Issued at 545 AM EDT Wed May 18 2022

-- Rain and Cool Temperatures Today --

Despite a pretty disorganized arrangement of waves between the low
level and upper levels, rain becomes increasingly likely by midday
as frontogenesis at 850-700 mb occurs overhead, to the north of a
weak surface low and warm front over northern Illinois-Indiana. The
presence of dry low-level air prior at the onset of rain, light east
winds, and thickening clouds should hold temperatures in the 50s. A
brief shot of 60s in southern Michigan is possible, but this could
be held back if more rain occurs there.

Members of the HREF continue to exhibit quite the variability in
where the west-east swath of heaviest rain will fall (over a half-
inch), and what the upper limit of rainfall is (locally an inch?).
The blended approach would place the best opportunity for soaking
rain amounts near or just north of I-96. Would expect there to be
overachievers and underachievers with rainfall today... thankful
this isn`t a snow forecast. Light rain falling from mid-level cloud
bases this morning should become heavier with decreasing cloud bases
from midday to late afternoon, then transitioning to drizzle to
close out the day as the ice-bearing clouds above 700 mb peel away.

-- Thunderstorm Chances Centered On Friday --

A deepening trough in the intermountain west, a building ridge over
the northeast US and eastern Canada, and increasing southwesterly
flow over the central US and Great Lakes will send our temperatures
back into the 70s on Thursday and possibly 80s on Friday. A
significant positively tilted upper level trough from Hudson Bay to
the northern Plains and Colorado Rockies will be in place on Friday,
while a surface low consolidates over Minnesota/Lake Superior and
propagates northeast. A cold front draped southwest of the low
toward Texas will be sliding southeast into Lower Michigan at some
point on Friday, possibly stalling out on Saturday. A stout
elevated mixed layer of southern high plains origins (from diurnal
mixing in Colorado, New Mexico, and West Texas on Thursday) will
advect over at least a portion of Lower Michigan on Friday,
contributing to moderate or strong instability with 1500-3000 J/kg
MLCAPE during the day and MUCAPE about 1500-2000 J/kg at night.
Interestingly this EML could contain smoke from New Mexico`s
historic wildfires, but this probably wouldn`t impact the forecast
here much compared the more meaningful uncertainty factors
mentioned below. Strong southwesterly winds in the low levels on
Friday could mix down during the day in the warm sector, getting
close to wind advisory levels here.

While the potential for severe winds and hail is there given the
amount of CAPE, strong wind fields, and 0-3 km shear, there remain
several limiting factors or unanswered questions. The first
unanswered question is how much elevated convection may try to move
into Lower Michigan with the warm front late Thursday night. Right
now the threat appears low but not zero, but it may not impact the
Friday afternoon/night chances too much anyway. Next has been the
question of the synoptic ridge amplitude and length between the
trough and ridge. The GFS and the majority of its ensemble members
yesterday was more subdued with the amplitude of the ridge, keeping
the EML farther southeast compared to the ECMWF and its ensemble
members, with an arrival of the cold front earlier in the day. The
00Z run of the GFS ensembles may be backing away from that idea,
given the increase in high temperature and CAPE for Friday. One of
the greatest limiting factors for thunderstorms on Friday may be the
magnitude of the cap. It`s possible the cap may not erode enough
until late Friday night, at which point the surface cold front may
undercut the warm, moist, and still potentially unstable mid-level
air. This scenario would be good for diminishing the threat of
damaging winds, though large hail would remain possible. If storms
do develop during the day Friday, the orientation of the
surface front parallel to the deep-layer flow and shear vector could
result in a line of storms with limited forward propagation,
undercut by their cold pool, which would keep strong winds confined
to narrower corridors. So, bottom line, it could be a blustery
Friday even without storms, but any that develop could produce
isolated to scattered severe wind and/or hail.

-- The Weekend into Next Week --

There is increasing model ensemble support for the cold front to
stall just southeast of the area on Saturday, then with a
developing wave moving northeast along the front, redeveloping
rain and embedded thunderstorms could affect portions of Lower
Michigan. This could be more of a heavy rain producer.

Cooler than normal temperatures and surface high pressure are
likely Sunday and Monday. The next upper level trough and
developing low pressure system are possible in the region
midweek, with moderate clustering among the ensembles for rain at
some point between late Tuesday and Thursday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 148 AM EDT Wed May 18 2022

Good confidence that VFR this morning will trend down to MVFR
then IFR this afternoon, possibly LIFR for part of Wednesday
night. Rain, perhaps moderate intensity at times, is likely for a
large part of the day as weak surface low pressure passes through
to our south.


&&

.MARINE...
Issued at 351 AM EDT Wed May 18 2022

Hazardous winds and waves for small craft should hold off until
Thursday night and Friday. A manageable breeze from the east is
expected today and on Thursday it should be from the south. May
have to watch for fog developing over southern portions of Lake
Michigan late this afternoon and evening as rain moistens the
lower atmosphere and winds become lighter and more variable. Water
temperatures are still in the mid 40s to lower 50s.

Southwesterly winds strengthen Thursday night into Friday and
conditions will become hazardous for small craft. Models show gale
force winds just 500 feet above the water. While this is warm air
moving over the cold lake which usually results in less mixing of
stronger winds due to a strong and stable temperature inversion, the
strength of the winds not far above the water would make gales
possible especially along the shore and in the harbors where high
momentum air tends to descend off the stable marine layer.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

DISCUSSION...CAS
AVIATION...CAS
MARINE...CAS


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