FXUS63 KGRR 221918 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 318 PM EDT Tue Aug 22 2017 LATEST UPDATE... .SYNOPSIS... Issued at 315 PM EDT Tue Aug 22 2017 An unseasonably strong cold front has moved through Southwest Michigan early this afternoon. The air is cold enough that it is kept our air temperatures from rising significantly this afternoon. Several additional pushes of colder air from central Canada will move into Michigan over the next few days keeping temperatures around 10 degrees below normal into the weekend. On Thursday as the coldest air moves into the area, we could see showers on the cold front. With the air so cold and Lake Michigan being so warm, we could even see a few lake enhanced light rains showers Thursday. Canadian Polar air will be brought in behind that front and the surface high that follows will take until Monday to get east of the area when a slight warm up will begin. && .SHORT TERM...(This evening through Thursday night) Issued at 315 PM EDT Tue Aug 22 2017 Little question the next few days will be much cooler than both what is normal for this time of year and what we have had over the past week or so. The only real question is will the air be cold enough and moist enough for lake enhanced rain showers. As it turns out it will be on Thursday so we continued to add showers to our zone and grids. The core of the polar jet will be over central lower Michigan Wednesday, so areas over our northern CWA just may see a few sprinkles (not actually in our forecast). On Thursday a decent shortwave dives into the eastern CONUS trough and that pushes the polar jet core south of Michigan. It also brings 850 temps to near 5c, which is 15c colder than the mean Lake Michigan surface temperature. There is just enough moisture between the surface and 700 mb to allow lake enhanced showers. Inland the air is unstable enough being on the cyclonic side of the polar jet for showers there too. Any showers would be light. A few cold air funnels are also possible. Largely for the same reason. The passage of the secondary cold front has a line of showers with it but that should gone by 5 to 6 pm so I believe skies should become mostly clear tonight. Temperatures should fall into the upper 40s north and lower to mid 50s south. Thursday night should be the coldest with clear skies and light winds, I could see locations like Leota having lows in the mid to upper 30s. Elsewhere this is likely to be coldest night with almost all inland locations having lows in the 40s. The last time GRR had a low below 50 was on the 2nd of June (46). Bottom line... pref- fall like weather for a few days. .LONG TERM...(Friday through Tuesday) Issued at 315 PM EDT Tue Aug 22 2017 Mid level ridging will dominate the weather across the region through most of the period. As a result...expect dry conditions with below normal temperatures. Surface high pressure will bring fall like temperatures Friday morning through Saturday morning...with a slow but steady warm up from Saturday through Tuesday as the high moves to the east and southerly winds redevelop. The tropical system expected to develop over the western Gulf of Mexico in the next few days could impact the local weather Monday onward...but uncertainty is high as the longer range models are handling the remains of this system differently. Widespread rainfall could be in store for West Michigan in the latter part of next week. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 103 PM EDT Tue Aug 22 2017 Radar shows a narrow line of showers along cold front north of KGRR. Band of clouds associated with these showers showing up well on visible satellite imagery. Widely scattered showers have also developed in deeper moisture ahead of the front. The front will move steadily southeast this afternoon and rain chances will decrease significantly once it passes any particular location. Will continue MVFR ceilings for the rest of this afternoon...with a clearing trend expected around 00z Wednesday. Some of the short range models indicate an increase in low level moisture between 09 and 12Z Wednesday...but will not include this in the TAFs at this time. && .MARINE... Issued at 315 PM EDT Tue Aug 22 2017 I will keep all headlines as is but will add water spouts to our forecast on Thursday since since the air is unstable enough. && .HYDROLOGY... Issued at 1240 PM EDT Tue Aug 22 2017 Area rivers are around normal levels for the time of the year and well below bankfull. Rainfall over the past 24 hours has mostly been under an inch, and only minor river rises have been observed. No significant precipitation is expected Wednesday through the weekend, so no river issues are expected. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement through Wednesday afternoon for MIZ037- 043-050-056-064-071. LM...Small Craft Advisory until 6 PM EDT Wednesday for LMZ844>849. && $$ SYNOPSIS...WDM SHORT TERM...WDM LONG TERM...MWS AVIATION...MWS HYDROLOGY...63 MARINE...WDM