Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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660 FXUS63 KGRR 221603 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 1203 PM EDT Sat Jun 22 2024 .KEY MESSAGES... -Potential severe weather and flooding today/this evening -Dry Monday, strong storms possible Tuesday/Tuesday night -Dry Wednesday/Thursday, storminess returns next weekend && .UPDATE... Issued at 1137 AM EDT Sat Jun 22 2024 Based on the latest wave model forecasts, we expanded the small craft advisory and beach hazards statement one county/zone further north. One area of heavy rain was tracking through the Pentwater to Ludington region. It appears that fairly widespread amounts of around an inch may accompany this initial batch. Additional heavy rain is likely this afternoon and evening with the storms in southern WI tracking east northeast. Off of SPC`s meso analysis page, PWAT values were around 2 inches in this region with really impressive 925-850 mb moisture transport going on. 12z soundings from GRB and APX support an efficient warm rain event along with warm topped convection with the MPL well under the trop. Rainfall rates could easily top an inch per hour. Thus we will maintain the flood watch. As for the severe potential, low level convergence was maximized closer to the warm front over the northern zones with divergence flow further south. Instability was building throughout the area with ML CAPE values up to 500 J/kg and bulk effective shear values over 30 knots. An area of stronger 0-1 km shear vectors was noted west of Pentwater and moving northeast. The flow remains relatively divergent for much of the CWA for a few more hours so we may struggle to develop widespread convection. However by mid afternoon and more so late afternoon we could start to see an increase in the low level convergence which would support newer storm development. We will also need to monitor the trends of the storms in southern WI as when the try to track into the CWA, they could generate enough low level lift to persist. Given the favorable instability and shear at that time, we could end up with an organized cluster of storms rolling through. Until then, it appears the northern parts of the region is the favored location for strongest storms given stronger 0-1 km bulk shear values through mid afternoon. && .DISCUSSION... Issued at 332 AM EDT Sat Jun 22 2024 -Potential severe weather and flooding today/this evening A warm front has lifted to the northern cwa early this morning where it`s expected to become quasi stationary today. Low pressure in Nebraska will move ENE toward Wisconsin by this afternoon. A strong southwest flow ahead of the low is helping to bring in moisture-rich air and precipitable water values in excess of 2 inches is expected today. There will be some destabilization ahead of the low across the northern and central cwa today. Thunderstorms will likely spread east from Wisconsin. CAPE values are not particularly impressive. However, shear values increase to 45 knots this afternoon. An impressive LLJ is progd to move toward the northwest CWA this afternoon. A weak short wave aloft will aid in convective generation. It`s possible that as the shear increases we could see some low topped supercells develop. Impressive helicity values around 400 m2/s2 move over the northern rows this afternoon near the frontal boundary. It`s not out of the question a tornado or two could spin up along the boundary. As the low crosses northern Lower around 00z, the trailing cold front will begin to move south. Showers/storms will form along the cold front and move across the rest of the cwa during the evening and overnight. Areas south of I-96 will likely see a bit more destabilization today due to a bit more sunshine. And so any storms that form along the cold front will be able to tap into that instability. Strong wind gusts and torrential rainfall will be the main threats. Precipitation will be ending by Sunday morning. Today will be the last day of the Heat Advisory. Heat indices will top out in the mid 90s again today. A cold front will move across the state tonight leading to highs in the 75 to 80 degree range Sunday. -Dry Monday; strong storms possible Tuesday/Tuesday night Monday will feature sunshine and comfortable temps/humidity with surface ridging in control before a warm front returns on Tuesday and sends back the heat and humidity for a day. GFS has SB Capes exceeding 3000 J/KG Tuesday afternoon once the warm sector arrives, setting the stage for the possibility of some stronger storms by evening as a cold front and H5 shortwave trough approach from the northwest. -Dry Wednesday/Thursday; storminess returns next weekend The cold front exits early Wednesday and we dry out by afternoon as cooler/drier air arrives from the north. High pressure settles in for Thursday with dry weather still prevailing, but then models diverge which leads to low confidence timing the return of our next chance of showers and storms. The more progressive GFS has rain chances returning already on Friday whereas ECMWF holds off until Saturday. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 745 AM EDT Sat Jun 22 2024 Showers and storms impacting MKG and GRR through Noon with ocnl MVFR/IFR vsbys then the rain lifts primarily north of these two terminals this afternoon before returning again this evening. Otherwise VFR weather prevailing all day for the terminals south and east of GRR. The potential for showers and storms does not really ramp up across this area until after about 02Z tonight. Winds increasing to 12-22 kts out of the southwest by Noon today. After the passage of a cold front late tonight the storm threat ends then lower cigs in the MVFR or IFR category will press southward after 06Z. && .MARINE... Issued at 332 AM EDT Sat Jun 22 2024 Wind and waves will increase behind a cold front tonight necessitating a Small Craft Advisory and Beach Hazards statement south of Grand Haven. Wind and waves will decrease late tonight. Additionally, thunderstorms will pose a threat to boaters and beachgoers today and tonight. && .HYDROLOGY... Issued at 332 AM EDT Sat Jun 22 2024 Very juicy air with precipitable water values north of 2 inches are expected across the cwa today. A stationary frontal boundary over the northern cwa will focus showers and thunderstorms today. Any of these storms will be capable of producing torrential rainfall. Training echos will be an issue today and local probability matched mean values hint at the potential for 2 to 4 inches of rain along US-10 in an area that saw locally heavy rainfall from storms yesterday. As a result, we have issued a Flood Watch for the northern 3 rows of counties from noon today through 6 am Sunday. Local flooding of poor drainage areas is possible. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Flood Watch through late tonight for MIZ037>040-043>046-050>052. Beach Hazards Statement from 8 PM EDT this evening through Sunday morning for MIZ050-056-064-071. Heat Advisory until 8 PM EDT this evening for MIZ056-057-064>067- 071>074. MARINE...Small Craft Advisory from 8 PM this evening to noon EDT Sunday for LMZ844>847. && $$ UPDATE...MJS DISCUSSION...Meade/04 AVIATION...Meade MARINE...04 HYDROLOGY...04