211 FXUS63 KGRR 232340 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 740 PM EDT Fri Jun 23 2023 LATEST UPDATE... Update/Aviation .UPDATE... Issued at 740 PM EDT Fri Jun 23 2023 Dropped POPs for this evening based on radar trends as showers are ending as they move west into drier air. The lake breeze is currently stalled west of Grand Rapids and no sign of cu building along it, much less showers. Lowering sun angle will also limit any chances of showers the rest of the evening. && .SHORT TERM...(This evening through Saturday night) Issued at 333 PM EDT Fri Jun 23 2023 - Chance for Showers and Isolated Thunderstorms This Evening - The focus this evening is on colliding lake breeze boundaries potentially generating showers and storms. A lake breeze off of Lake Michigan will push eastward/inland this evening and that can already be seen on both radar and satellite. A lake breeze/precipitation enhanced boundary is moving westward from Southeast Lower Michigan at this time as well. Ob sites in the center of the state from KMOP to KLAN to KFPK have already switch to the east. These colliding boundaries should occur in the KGRR to KBTL vicinity late this afternoon and early evening. MUCAPE values are still quite low, < 500 j/kg at this time. If we can increase these values toward 500 j/kg some thunder is possible, otherwise we are looking more at scattered showers. We have 30-50 pops in the forecast to cover this scattered precipitation event. With the loss of daytime heating we will lose what little instability we have and precipitation should end by 10-11pm. - Mainly Dry, Quiet Weather Saturday and Saturday night - We expect mainly dry weather on Saturday as we will be beneath shortwave ridging aloft between the two upper lows (one over the Eastern Great Lakes and one in the Northern Plains). Cannot rule out an isolated showers towards KJXN Saturday afternoon. Saturday night we feel the bulk of if not all of the precipitation associated with the upstream Northern Plains low will remain west of us through 12z Sunday. Cannot rule out some showers approaching our western CWA however towards Sunday morning. .LONG TERM...(Sunday through Friday) Issued at 333 PM EDT Fri Jun 23 2023 - Showers and Storms Sunday with Severe Weather Possible - The biggest concern through the long term is the potential for strong to severe storms Sunday. Latest mid range models continue to show a large upper level low moving through the upper mid west Sunday morning. The low will bring a short wave through the IL- IN-MI region with sufficient vertical motion and moisture present for convective development. While the latest NAMnest DCAPE values are higher than what will be realized, there is the potential for 1000 to 1500 J/kg of DCAPE with this system. That could lead to damaging winds. A 30-35 knot low level jet will be associated with this system which should provide ample shear for organized convection. Max temperatures will be in 80s which should be enough diurnal heating. If convection moves in late Saturday night this could weaken instability and therefore may negatively affect the potential for severe storms on Sunday. In addition, the strongest winds in the mid levels are currently forecast to be south of Michigan which corresponds to where the SPC marginal and slight risk areas are located. Currently we are only in a general thunder outlook from SPC, but the bottom line is there is a possibility of strong to severe storms in our area on Sunday. The greatest severe weather threat right now appears to be south of our area, but we will be monitoring this time frame as the main focus of the forecast going forward. POPS will continue to be increased with widespread QPF totals Sunday into Monday of over a half an inch with upwards of an inch along and to the south of the the I 96 corridor. Locally heavier amounts in storms could be possible. Overall, trends have been upward in QPF via the ECMWF ensemble mean and the WPC QPF. Given the ongoing drought these trends are in the right direction. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 740 PM EDT Fri Jun 23 2023 VFR conditions this evening. Areas of MVFR expected overnight across central and eastern Lower Michigan along with patchy IFR as the relative humidity is higher there. Winds will go light and variable overnight then light northwest on Saturday. && .MARINE... Issued at 333 PM EDT Fri Jun 23 2023 The period of light winds and a lack of waves will continue tonight and on Saturday. The script begins to flip a bit as we get into Saturday night and Sunday as a low pressure system moves our direction from the Northern Plains. Saturday night the winds will have an off shore component increasing into the 10-20 knot range most likely. Waves should hold in the 1-2 foot range in the nearshore zone. Sunday and Sunday night, winds will be southerly in the 15 to 25 knot range. Waves may push into the 2-4 foot range, potentially a bit higher. Convection on Sunday will affect the wave field as well, so locally higher wind and waves are possible. A period of lower wind and waves will stretch from Sunday night into Monday as the upper low will be overhead. Stronger winds and larger waves are expected Monday night through Tuesday night as northerly cold air advection winds increase during this time frame. 15-25 knot winds or even 20-30 knot winds from the north will likely generate waves large enough to reach SCA criteria. The wind alone will reach SCA levels. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ UPDATE...Ostuno SHORT TERM...Duke LONG TERM...Ceru AVIATION...Ostuno MARINE...Duke