880 FXUS63 KGRR 091753 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 153 PM EDT Tue Oct 9 2018 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 325 AM EDT Tue Oct 9 2018 Much above normal temperatures and muggy conditions are expected today with scattered showers and thunderstorms likely by late afternoon. A strong storm or two is not out of question with the main threats of small hail and gusty winds. A strong cold front will swing through Wednesday evening providing another opportunity for precipitation but the threat for severe weather continues to appear low. Much colder temperatures are then expected to close out the week with lake effect (rain) showers likely Thursday and Friday. The active pattern will continue into next week. && .DISCUSSION...(Today through next Monday) Issued at 325 AM EDT Tue Oct 9 2018 Currently, temperatures are in the mid 60s to upper 70s, which are 15 to 20 degrees above average lows for mid-October. With clear skies and relatively light winds, pockets of ground fog may develop toward sunrise favoring areas that saw rain over the past 24-36 hours. While a few spots may dip below 3 miles (which really isn't all too impactful), all fog is expected to mix out fairly rapidly by mid- morning. As we remain in the warm sector of an elongated mid- level trough centered over the Plains, temperatures today will once again be much above normal. A forecast based on persistence as well as 850 mb temperatures of +16 to +18 C suggest highs will reach the low to mid 80s this afternoon. With dew points remaining in the upper 60s to near 70 F, it'll still feel humid out there (especially by October standards). Like yesterday, diurnal convection is expected to develop this afternoon though coverage today should be higher thanks to a subtle low-level wave approaching from the south. Forecast MUCAPE topping out at 1500 J/kg, low- to mid-level lapse rates of 6-7 K/km, DCAPE of 800-1000 J/kg, and 0-6 km effective bulk shear of 25-30 knots suggests that a stronger storm or two is possible with the main threats of heavy downpours potentially mixed with small hail and gusty winds to 50 mph. In fact, a low-topped supercell or two seems possible similar to yesterday. However, the low-level shear will be unfavorable for anything to happen down low. After one more mild night, attention will turn to convective potential on Wednesday. As a 140kt 300 mb jet streak currently located over the Pacific Northwest races southeast, the wavelength of the trough that has been parked over the west half of the United States will shorten as the trough begins to lift northeast this afternoon. The aforementioned speed max will catch up with the parent trough early Wednesday enabling the development and rapid deepening of a surface low as it tracks from the Southern Plains to the Upper Great Lakes. Locally, the surface low will swing a cold front through Lower Michigan during the evening hours on Wednesday which will be the feature to watch. While forecast shear profiles (at least the magnitudes of which, not necessarily the shapes) will be favorable for some storm organization, instability parameters continue to look weak (at best) not-so-aided by mid-level lapse rates of 5-6 K/km. While PWATs will surge to 1.5-1.75" in advance of the front owing to efficient meridional moisture transport from the land falling Hurricane Michael, the rapid movement of the front suggests that the residence time of any shower or storm will be so short that flooding is unlikely. So, the expectation remains for a fast-moving line of strongly forced showers and embedded thunderstorms to swing through our area Wednesday evening with locally gusty winds possible, a scenario that matches up well with the Marginal Risk provided by SPC. Thursday will feature falling temperatures as 850 mb temperatures drop to -2 to -4 C by evening. Highs may struggle to get out of the 50s Thursday and Friday, with morning lows potentially supporting widespread frost (and even a freeze Saturday morning). However, with lake temperatures around the +18 C mark, it seems that lake effect clouds will be abundant starting Thursday and lasting through early portions of the weekend which may prove as a detriment to widespread frost/freeze, at least within counties bordering Lake Michigan. With lake-induced CAPE approaching 500 J/kg and growing inversion heights Thursday, lake effect (rain) showers are expected to develop with an uptick in intensity Friday an upper-level wave and associated reinforcing surge of cool 850 mb air moves into the Great Lakes. Looking ahead toward next week, we'll remain in an active weather pattern as is typically the case for October. Ample opportunities for precipitation will continue for the foreseeable future with signs of anything in frozen form still looking few and far between. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 152 PM EDT Tue Oct 9 2018 Mainly VFR today and tonight unless a shower or storm impacts a terminal which is a low probability scenario. Left thunder out of TAFs since the coverage/threat of convection looks to remain low, but will amend if it looks more promising later on. Showers and storms will be approaching from the west on Wednesday but the bulk of that should hold off until after 18Z. However some MVFR cigs and isolated showers may develop prior to 18z, especially west of LAN and JXN. South winds may gust to 20kts after times this afternoon, especially at MKG, then will relax a bit tonight before ramping up again Wednesday. && .MARINE... Issued at 325 AM EDT Tue Oct 9 2018 While southerly winds will remain gusty today, waves will remain in the 2-3 foot range highest near the points where exposure to southerly winds will be maximized. An uptick in wave heights is expected Wednesday morning as southerly winds intensify ahead of an approaching storm system, with a sharp shift in wind direction and increase in waves likely Wednesday evening as a cold front swings through the Great Lakes. Waves on Thursday and much of Friday will thus become hazardous to small crafts. Small craft advisories will likely be needed as early as Wednesday morning but definitely by Wednesday evening, lasting through much of Friday. && .HYDROLOGY... Issued at 1254 PM EDT Tue Oct 9 2018 The Kalamazoo and Grand Rivers continue to slowly drop as rainfall from last weekend works its way through the river system. Most small and medium-sized tributary streams are seeing falling water levels as well. The mainstem of the Muskegon river is rising slowly as the 1.0 to 1.5 inches of rain that fell yesterday morning drains into the river. A few showers and thunderstorms are possible across West Michigan this afternoon and evening, but are not expected to result in any flooding. The next chance for heavy area-wide rainfall arrives on Wednesday afternoon and evening as a strong cold front is set to move through our area. At this time it looks like many areas may see rainfall totals around 1 inch. This would cause the larger rivers to rise, but is not expected to cause any flooding on the mainstem rivers. Despite a few days break in the heavy rain, soils remain saturated and the smaller streams may see a quicker water level rise than normal. Sycamore Creek near Holt may rise to near bankfull by Thursday morning in response to Wednesday evening rainfall, but is not expected to reach flood stage. What will also need to be monitored is the potential for urban areas to be overwhelmed by heavy rainfall if the storms linger over the same areas repeatedly. && .CLIMATE... Issued at 325 AM EDT Tue Oct 9 2018 Here are the Record Highs for Today and Wednesday: GRR...10/9: 84 in 1939, 10/10: 85 in 1949 MKG...10/9: 83 in 1905, 10/10: 84 in 1913 LAN...10/9: 84 in 1939, 10/10: 83 in 1879 AZO...10/9: 86 in 1939, 10/10: 87 in 1938 && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ SYNOPSIS...Borchardt DISCUSSION...Borchardt AVIATION...Meade HYDROLOGY...AMD CLIMATE...AMD MARINE...Borchardt