Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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664 FXUS63 KGRR 181746 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 146 PM EDT Tue Jun 18 2024 .KEY MESSAGES... - Heat Advisory in Effect for Most of our Area - Chance of Thunderstorms Today - Heat/Humidity Persists Through The Work Week - Small Chances for Precipitation Wednesday Night and Thursday - Cooler Weather Behind a Cold Front Sunday && .UPDATE... Issued at 1117 AM EDT Tue Jun 18 2024 Mid level WV imagery shows a decent wave now entering southwest parts of Lower MI, tracking northeast. MU CAPE values are roughly 1000 to 2000 J/kg with ML values about half that. Low level CAPE is forecast to build early this afternoon. Several CAMs suggest we may see renewed convection starting up around 18z. Stronger wind gusts/outflows will likely be the main risk, although the SPC Meso`s RAPs output suggests the DCAPE remains low this afternoon, so some uncertainty as far as how organized the outflows will become. We did raise POP`s to account for the better confidence for some storms given the combination of CAPE and lift. We may struggle to reach 100 degree HI`s given the clouds but we will maintain the hazard for now. The current CFW mentions Grand Haven for hazardous swim conditions and the south side of that pier looks like they will be impacted. && .DISCUSSION... Issued at 342 AM EDT Tue Jun 18 2024 - Heat Advisory in Effect for Most of our Area Hot and humid conditions are expected again today and tomorrow with continued south to sw flow waa and ridging in place. H8 temps of around 19-20 C with ample sun the next couple of days will result in high temps reaching the lower to middle 90s. This combined with dew pts well into the 60s to lower 70s will yield heat indices near 100 degrees. Therefore the heat advisory headline remains in effect for most of our area. - Chance of Thunderstorms Today A consensus of latest CAMs and 00Z HREF all suggest that convection over our far northern fcst area early this morning will continue to drift ne and out of our area during the next hour. Tranquil wx is then expected for most of the morning. There is potential for an upper level disturbance and potential mcv over far southern IL/IN to move to the nne and potentially trigger convective development into our area by late morning. This will be something to monitor as we will have at least 1000-1500 j/kg of sb/mu capes in place with relatively strongest instability over our eastern fcst area. Severe wx potential today looks low overall. However I would not rule out isolated strong to severe convection with moderate to strong instability this afternoon and model fcst soundings showing strong low level lapse rates. However deep layer shear remains low so this is mainly a pulse storm environment with potential for localized downbursts. - Heat/Humidity Persists Through The Work Week We see no need to change our headlines regarding the heat on the end time, which is currently 800pm Friday. 500mb heights remain high in the 590s dm through the end of the week. The 592dm 500mb height contour is all the way north of our entire forecast area at 18z on Friday and you do not see that very often. 850mb temperatures via the ECMWF, which is clearly the model to follow regarding temperatures as the GFS has been low as we have ramped into this heatwave, show values of +18C to +20C all the way into Friday. These values should continue to produce highs around 90 into the lower 90s potentially. We very much may need to extend the Heat Advisory into Saturday as that looks to be the warmest day potentially of the entire warm spell. 850mb temperatures spike to +22C. So, we are staying the course on the current heat headline. We urge folks to continue to check on people without air conditioning as there is no relief at night (we sit at 81 degrees at 320am this morning in Grand Rapids). Dew points are forecast to remain in the upper 60s to around 70 so heat index values will make a run at 100 each afternoon. The cumulative affect of the heat will add up as we continue to move forward. - Small Chances for Precipitation Wednesday Night and Thursday A weak front will move into the area from the north Wednesday night and Thursday with some small chances for showers and thunderstorms. We do not think this will be enough to knock the heat down significantly and therefore no changes to headlines. The ECWMF hints at it and it may be the case where we do not see much in the way of precipitation from this front. The ridge will be fairly stout at that time with warm temperatures in the mid levels. Could see precipitation being less and less in the models as we approach Wednesday night and Thursday. - Cooler Weather Behind a Cold Front Sunday Models may be a tad quicker with the front that changes the airmass, not moving in potentially late Saturday night. Either way, we will see much lower dew points and cooler temperatures as we head into the latter half of the weekend. The front will come with a chance of showers and thunderstorms as it moves through. 850mb temperatures drop back into the lower teens C on Sunday/Monday which will be welcome after all the heat. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 146 PM EDT Tue Jun 18 2024 Main changes were to refine timing for thunder threat this afternoon and to include LLWS for MKG and GRR terminals. A north to south axis of showers and thunderstorms may develop in the 18-19Z timeframe, originating from an approximate AZO to GRR line and moving east towards the BTL/JXN/LAN terminals later this afternoon. Detail certainty is lacking so went with VCTS at the mentioned terminals for now. A distinct upper level disturbance swinging through the area will be responsible for this different low level wind profile overnight that justifies some LLWS. Additionally, there is less concern for precipitation overnight compared to the past couple of nights due to unfavorable upper level support. && .MARINE... Issued at 342 AM EDT Tue Jun 18 2024 A small craft advisory and beach hazards statement is in effect for the northern half of the lakeshore from this morning through much of Wednesday. The southerly gradient will become sufficiently strong enough to cause wave heights to reach around 3 to 5 feet from Whitehall to Manistee. Wave heights will subside a bit late this week as winds weaken somewhat. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement through Wednesday afternoon for MIZ037- 043-050. Heat Advisory until 8 PM EDT Friday for MIZ043>046-050>052- 056>059-064>067-071>074. Air Quality Alert from midnight tonight to midnight EDT Wednesday night for MIZ050-056-057-064-071. MARINE...Small Craft Advisory until 4 PM EDT Wednesday for LMZ847>849. && $$ UPDATE...MJS DISCUSSION...Laurens AVIATION...TJT MARINE...Laurens