Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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048 FXUS63 KGRR 291436 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 1036 AM EDT Sat Jun 29 2024 .KEY MESSAGES... - Locally Heavy Rain Before Sunrise This Morning - Low Chance for Showers and Storms This Evening - Warming Trend early next week - Risk for Thunderstorms later Tuesday into Wednesday && .UPDATE... Issued at 1035 AM EDT Sat Jun 29 2024 As expected, widespread morning rain has moved off to the east, leaving us in cloudy but drier conditions. A few breaks of sun are trying to develop, which is a trend that should continue as the day unfolds. The big question remains how much shower/storm redevelopment happens this afternoon. 12z HRRR and NAMNest are both trying to generate a broken line of storms by 18z that primarily affects the far southeast corner of our counties (i.e. Jackson area), but confidence in this redevelopment is still limited. However, extremely humid air continues to move into the area this morning, so any breaks of sun will allow temps (and instability) to begin climbing quickly. && .DISCUSSION... Issued at 340 AM EDT Sat Jun 29 2024 - Locally Heavy Rain Before Sunrise This Morning Scattered to widespread rain continues to move through as an upper trough descends into the region and a surface low approaches from the west. Prefrontal surge in moisture as already pushed surface dewpoints into the mid to upper 60s. Certainly a moist environment early this morning with PWATS around 2+ inches. As mentioned in the AFD update last evening, the 00z HRRR painted a 4+ inch narrow swath of rain right along the I-94 corridor. Fortunately recent runs have not continued that 4+ inch trend, but nearly all subsequent runs have advertised the potential for some areas within the I-96 to I- 94 corridors to get up to 2 inches of rainfall early this morning. The 00z SPC HREF Probability Matched Mean supports this expectation while painting a few swaths of 1-2 inches across the southern half of lower Michigan between 2am to 8am this morning. MRMS 3 hour QPE already highlights areas in Allegan with receiving a swath of 1 inch rainfall, and with more heavy rain on the way we will be monitoring for possible flood headlines this morning. Few embedded thunderstorms are possible in this cluster of showers, but high Convective Inhibition and low instability early this morning will put a hamper on severe potential. Most of the showers should be to our east before CIN erodes and diurnal instability recovers. - Low Chance for Showers and Storms This Evening More isolated shower and thunderstorm activity is anticipated this afternoon into tonight as a cold front sweeps in from the northwest. Diurnal instability rebounds into this afternoon while 500mph winds build overhead supporting deep-layer shear. Noting enough kinematics to support thunderstorm development with the progression of the cold front, a few strong to severe storms may develop this afternoon and evening along the front. Due to the cold front being estimated to sweep through near to after 00z, enough of a cap may begin to develop to limit too much activity the further south it progresses, though there are some suspicious looking soundings that say otherwise. High-resolution models advertise an isolated shower/thunderstorm potential which seems reasonable but still worth monitoring. - Warming Trend early next week High pressure at 850 mb will be centered over the northern Great Lakes region to start the day Monday. Northeast winds over Lower Michigan will keep the cool air in place on Monday with the low level thermal trough overhead as shown by the models. Ensemble temperature graphs reflect this cooler airmass with max temperature values staying in 70`s. However the 850 mb high pressure system shifts east of the area Tuesday and warm air advection develops. The warm air advection then persists through Tuesday and possibly beyond. Ensemble temperatures plots show a steady warmup for this period with max temperature values returning to normal by Wednesday. - Risk for Thunderstorms later Tuesday into Wednesday Models are sagging a cold front in our direction later Tuesday and into Wednesday. There`s some uncertainty if this system will push through the area or not. They do show the PWAT`s climbing back up towards 2 inches later Tuesday along with some instability. Given the moisture, lift and instability, it does look like some storms will be tracking towards the CWA as that front sags in our direction later Tuesday. Northwest zones, including the Ludington area will feature the highest POP`s. Further southeast, given the uncertainty for the front to push through, we will taper the POPs off with Jackson featuring the lowest POP`s. The latest ensemble 24 hr qpf values from the GFS and CMC show a decrease in the values but the do suggests a fairly high probability for precipitation as most members show some QPF. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 718 AM EDT Sat Jun 29 2024 The main area of thunderstorms was pushing east of KJXN at this time with a few showers extending further west towards KBTL. At this time it appears the risk for further storm development early this morning is somewhat diminished given the radar trends. The IFR cloud deck never materialized but we have widespread MVFR around and those lower clouds are likely to linger for a few hours this morning. We are seeing some breaks in the cloud cover over Lake MI at this time. This afternoon we do destabilize again but confidence on the coverage of any storms is low. As a result we did not include thunderstorms in any of the TAF sites for the afternoon/evening. Continue to monitor later forecasts for possible inclusion of thunderstorms if conditions become more favorable. && .MARINE... Issued at 1035 AM EDT Sat Jun 29 2024 The only change this morning is that we`ve gone ahead and issued the Small Craft and Beach Hazards statements for the upcoming hazardous conditions. The worst conditions are expected Sunday morning, but overall conditions will be hazardous for most of tonight and most of the day Sunday. All zones will be impacted. Previous Discussion: A cold front will sweep through this afternoon and evening shifting winds to the northwest. Waves will quickly build late tonight and reach near 4 feet after midnight and will increase further into Sunday morning. Waves will peak in the 4 to 6 foot range Sunday morning and will gradually diminish into Sunday afternoon. A SCA and BHS will likely be needed for Sunday morning to early afternoon. Weather conditions will not be idea for beach weather, with potential upwelling and temperatures in the 60s. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from 10 PM EDT this evening through Sunday evening for MIZ037-043-050-056-064-071. MARINE...Small Craft Advisory from 10 PM this evening to 10 PM EDT Sunday for LMZ844>849. && $$ UPDATE...AMD DISCUSSION...MJS/Thielke AVIATION...MJS MARINE...AMD