FXUS63 KGRR 290845
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
345 AM EST Sun Jan 29 2023

LATEST UPDATE...
Discussion/Marine

.DISCUSSION...(Today through next Saturday)
Issued at 345 AM EST Sun Jan 29 2023

-- Snow / mixed precip diminishing later this morning --

Snow continues to fall across much of the forecast area as of 3 AM. 
This snow is occuring in an environment of low/midlevel 
frontogenesis and weak moist symmetric stability, with a persistent 
multi-banded appearance noted on KGRR radar reflectivity. These 
mesoscale bands have recently been oriented WSW-ENE, roughly 
parallel to the mean low/midlevel isotherms. Surface obs indicate 
that mainly light snow is occuring, but occasional bursts of heavier 
snow--with visibilities of 1/2 mile or less--have been reported in 
recent hours.

Elsewhere, generally along the I-94 corridor and into northwest IN, 
precip has a cellular/showery radar appearance. This activity is 
occuring in an environment of transient/weak conditional instability 
in the 850-700-mb layer, as evident in HRRR profiles. Mixed precip 
types--including sleet and freezing rain--have been reported in 
recent obs in this region, and HRRR profiles continue to suggest 
that a brief period of mixed precip is possible this morning along 
the I-94 corridor. Any icing is expected to be very light.

No changes are planned to the existing winter headlines with this 
update. Short-range guidance continues to suggest that precip will 
end by late morning as midlevel frontogenesis departs eastward and 
subsidence/drying occurs in the dendritic growth layer.

-- Turning colder; light lake-effect snow Mon-Tue --

Surface high pressure will build into the region beginning tonight. 
This high will be preceded by pronounced low-level cold advection, 
with 850-mb temps falling to near -18C by Mon night. Some lake-
effect snow activity is expected on Mon with onshore boundary-layer 
flow. However, the combination of QG forcing for subsidence and 
anticyclonically curved low-level flow will contribute to fairly low 
inversion heights (around 4 kft) near the lakeshore. Background 
moisture profiles are also shown to be quite dry, likely yielding 
a fairly shallow convective cloud layer. These factors suggest 
that snowfall accums on Mon will likely be light. Inversion 
heights may increase somewhat on Tue with the approach of a 
shortwave trough, but model time-height sections still show rather
limited moisture.

-- Continued below-normal temps for Wed-Fri --

EPS and GEFS guidance continues to suggest that transient 
disturbances with any appreciable precip will likely remain south of 
the region through the week, mainly confined to the active 
baroclinic zone to be found across the southern CONUS. A midlevel 
shortwave trough in northwest flow may glance the region on Thu, 
with an associated cold front likely progressing through the region, 
but chances for synoptic precip are low. Another surface high will 
likely build into the region around Fri. Confidence is high for 
continued below-normal temps during this period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 104 AM EST Sun Jan 29 2023

KGRR radar reflectivity continues to show widespread SN affecting
much of Lower Michigan, including MKG/GRR/LAN. Where steady SN is
occuring, IFR/LIFR conditions will continue this morning. SN
intensity continues to be modulated by distinct mesoscale banding,
as evident on radar reflectivity, and occasional bursts of +SN
have been observed. For this reason, a TEMPO group for 1/4SM +SN 
has been included at MKG/GRR through 09z.

Farther south, at AZO/BTL/JXN, precip coverage has been 
relatively sparse, with VFR conditions observed as of 05z. 
However, a recent uptick in reflectivity across southern Lower MI is
noted on KGRR radar, with additional precip approaching from 
northeast IL and northwest IN, as evident in regional 
reflectivity. Recent HRRR guidance suggests that brief -FZRA is
possible at JXN, which has been included in a TEMPO group.

Precip coverage will diminish late in the morning, with
visibilities likely becoming unrestricted. However, widespread
MVFR/IFR cigs are forecast to continue.

GRR Airport DSS Update:
No major changes to the briefing information provided on Saturday.
Briefly heavy snowfall rates (of 1/2" per hour) are possible
through 4 AM. Snow will likely end by 8 AM, but flurries are 
possible thereafter.

&&

.MARINE...
Issued at 345 AM EST Sun Jan 29 2023

No changes are planned to the existing SCA through this afternoon. 
Northeast winds at present will back north later today, allowing 3-5 
ft waves to build in the nearshore waters from South Haven 
southward. 

After a lull this evening/tonight, northwest winds will strengthen 
on Mon as an area of high pressure builds into the region. Highest 
waves (6-8 ft) are expected between Grand Haven and South Haven. 
Another SCA, likely covering all zones, will be needed.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 10 AM EST this morning for 
     MIZ037>040-043-059-064>067-071>074.

     Winter Storm Warning until 10 AM EST this morning for MIZ044>046-
     050>052-056>058.

LM...Small Craft Advisory until 4 PM EST this afternoon for 
     LMZ844>849.

&&

$$

DISCUSSION...Kenyon
AVIATION...Kenyon
MARINE...Kenyon