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