Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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418 FXUS63 KGRR 220739 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 339 AM EDT Sun Sep 22 2024 .KEY MESSAGES... - Showers and isolated storms this afternoon, then dry and cooler - Rain chances Monday Night through Wednesday - Model differences in latter half of work week && .DISCUSSION... Issued at 339 AM EDT Sun Sep 22 2024 - Showers and isolated storms this afternoon, then dry and cooler A cold front is slowly moving east across central WI early this morning. Showers and thunderstorms continue to develop ahead of this front and we`ll likely see rain this afternoon as the front moves over the cwa. Based on forecast soundings, instability is the lacking ingredient this afternoon. LI`s are largely above 0c and CAPE values are generally a couple of hundred joules/kg as the front moves through. There is good moisture convergence along the front thanks to a 40 kt LLJ and precipitable water values that climb to near 2 inches. Shear values are decent, though, at 40 kts. We`ll continue with the idea of most locations seeing rainfall. Roughly a quarter to half inch of rain is expected before the front moves through and precipitation moves east. RH progs suggest that clearing will occur from the northwest late tonight and spread across the cwa Monday. After highs in the mid 70s today, highs will be around 70 Monday. - Rain chances Monday Night through Wednesday Shortwaves in both the southern and northern streams will converge on the Great Lakes in the early to mid week time frame. A surface low will move into the area on Tuesday lingering in the area Tuesday night. Deeper moisture can be seen on GFS Bufkit overviews from Monday night through much of Wednesday. We have 30-60 pct chances for precipitation (highest south) as the low moves through the area. PWAT values reach the 1.00 to 1.50 inch range with the low, so precipitation amounts could be locally towards 1.00 inch, but most areas will stay well below that. - Model differences in latter half of work week Differences between the ECWMF and GFS begin to show up Wednesday night in terms of how the upper pattern evolves. The GFS has more in the way of ridging through the Thursday through Saturday time frame, while the ECMWF has an upper low nudging our direction from the mid Mississippi valley. Bottom line at this point is we will feature dry weather for much of the Wednesday and Thursday time frame. Model blends give us isolated chances for rain Friday and Saturday. We will roll with that at this point, as confidence is low in the most likely solution at this point for day 6 and 7. Temperatures will be near normals early in the week with the clouds and precipitation, warming to above normal once again by the end of the week. 70s for highs look likely Thursday and Friday. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 214 AM EDT Sun Sep 22 2024 A cold front is located upstream tonight stretching from portions of Central Wisconsin into Eastern Iowa. VFR weather is occurring well east of the front here in Southwest Lower Michigan with scattered areas of MVFR near the front off to our west. Showers and thunderstorms are occurring at 06z especially over southern Wisconsin. The front will make steady progress to the east today and move through Southwest Lower Michigan in the afternoon and evening hours. MVFR conditions will show up this afternoon as lower ceilings fill in, which will trend to IFR in the late afternoon and evening. Ceilings will dip below 1,000 feet between 21z and 02z near and just behind the front. At this point have showers in the forecast, but we may need to add some thunder with time as the threat gets closer. The thunder threat is not significant or high, but will come between 18z and 23z. Isolated to scattered storms are possible. && .MARINE... Issued at 339 AM EDT Sun Sep 22 2024 North winds will increase behind the cold front today. Wave progs indicate waves will increase to 4-7 feet north of Whitehall this afternoon. The higher waves will work south with time. We issued a Small Craft Advisory and Beach Hazards Statement from this afternoon through Monday morning for the hazards. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from this afternoon through Monday morning for MIZ037-043-050-056-064-071. MARINE...Small Craft Advisory from 4 PM this afternoon to 11 AM EDT Monday for LMZ844>849. && $$ DISCUSSION...Duke/04 AVIATION...Duke MARINE...04