textproduct: Grand Rapids

KEY MESSAGES

- Drizzle and Patchy Fog Today

- Warming With Rain Friday into Sunday

- Colder Pattern And Precipitation Arrive Mid Next Week

UPDATE

Issued at 518 AM EST Thu Dec 26 2024

Increasing radar returns across the northeastern CWA indicate that drizzle is becoming more widespread with some embedded rain showers. Given surface temperatures below freezing across this region, this brings increasing concern for travel impacts for the morning commute. Given that, have issued a Winter Weather Advisory for Gratiot, Montcalm, Isabella, Mecosta, Clare, and Osceola Cos. through 10am for the light glaze of icing associated with these showers. Also, observations show that areas of fog are occurring across those counties which may further support light icing potential. Further west, surface temperatures remain below freezing. However, with little radar returns impacts will be isolated given lack of substantial drizzle. The current Special Wx Statement covers this risk well.

DISCUSSION

Issued at 305 AM EST Thu Dec 26 2024

- Drizzle and Patchy Fog Today

Continued boundary layer moistening this morning is promoting areas of drizzle and fog across West Michigan this morning as evidenced by weak radar returns. Near and north of M46 surface temps remain at or below freezing meaning patchy slick spots are possible this morning from the fog/drizzle. Fog will also likely be dense at times in this region given a still depleting snowpack adding additional moisture. Have issued a Special Wx Statement to highlight the potential for isolated impacts for the first part of the morning in this area.

Patchy fog and drizzle remain likely through the day as abundant low- level moisture is supported by a secondary weak vort maxima. Though with temperatures above freezing it appears to be relatively benign. What will need monitoring is signals for more widespread fog across Central Lower Michigan later today and tonight as higher dewpoints advect over a dwindling snowpack.

- Warming With Rain Friday into Sunday

Southerly flow establishing itself across the region Friday drives a notable warmup into the weekend. 850mb Ts around 5C send highs into the 40s Friday and Sunday and even into the 50s for Saturday. However, this warmup will not come without the promise of rainfall for the region. Rainfall increases later Friday as a mid-level wave swings through the area from the southwest driving an occluding low in our direction. The rain continues into Saturday as the parent trough swings through the region before diminishing Sunday as a weak cold-front crosses the Upper Great Lakes. Impacts look to be low as our warmer pattern ensures only rain with this system while on the other end of the spectrum a lack of instability keeps thunder out of the forecast.

- Colder Pattern And Precipitation Arrive Mid Next Week

Behind the weak frontal boundary Sunday conditions look to be dry as we're located in the col between our departing low and our next system mid-week, with the colder air/polar jet remaining north keeping highs in the 40s.

However, mid-week marks the beginning of a pattern change for the region as a system ejects north out of the western US while a northern stream wave slides southeast at the same time. The timing and interaction between these waves will determine how this pattern change unfolds. As the wave arrives, the associated forcing makes precipitation likely Tuesday and Wednesday. The primary question will be p-type. If the northern stream wave and associated colder air can phase with the southern wave that will support more notable snow potential in the Great Lakes or Northeast (which the EPS is hinting at). If the colder air holds off until the southern wave and associated low exit, rain will be dominant until the colder air can arrive (which the GEFS/CMC suites lean towards). Once the colder air associated with the northern stream arrives, temps fall and some lake effect is possible given the very cold nature of the airmass. Specifics as to which scenario will occur during this changeover will become clearer in the coming days.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 637 AM EST Thu Dec 26 2024

Based on the latest trends, the lower clouds are likely to hold on longer. Light rain/drizzle has been forming over the area and also lifting northward out of Indiana. With this added moisture, the lower clouds should prevail through the period. We made some changes to the TAF's to reflect this. The surface temperatures are currently above freezing for the TAF in southwest Lower Michigan. They are projected to climb slowly today. Thus we will not feature any freezing drizzle in the TAF forecast at this time. Based on all this, we will feature primarily IFR and lower conditions through the period.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Winter Weather Advisory until 10 AM EST this morning for MIZ039- 040-045-046-051-052. MARINE...None.