941 FXUS63 KGRR 211930 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 330 PM EDT Sat Sep 21 2019 LATEST UPDATE... Synopsis/Discussion/Marine/Hydro .SYNOPSIS... Issued at 330 PM EDT Sat Sep 21 2019 -Rounds of rain through Monday morning -Locally heavy rainfall of greater than two inches possible -Dry and cooler Monday and Tuesday; next chance of rain Wednesday -Beach Hazards continuing through Monday && .DISCUSSION...(This evening through next Saturday) Issued at 330 PM EDT Sat Sep 21 2019 Guidance continues to suggest the possibility of excessive rainfall and areal flooding in southwest Michigan, with the main threat being on Sunday evening as the final/main strong wave moves along the frontal boundary. 50-55 kt low level jet ahead of the approaching wave and high PWAT values around 2 inches will be interacting with the stalled frontal boundary during this time. Also a coupled jet structure at H2 will be present. There is also a heavy rain threat tonight and early Sunday, mainly along the lakeshore north of Holland. This event could produce 1-2" prior to the main event Sunday evening. Some conflicting signals exist as to where the swath of heaviest total rainfall might occur, with convective allowing models favoring a slightly more southern orientation than the synoptic models. Believe the synoptic models are probably the way to go since the main part of the event is related to the final wave on the front and there`s not much instability progged. Heaviest rainfall totals should end up falling north of a line from South Haven to Ionia. Amounts could easily exceed two inches, and some isolated amounts as high as 5 inches cannot be ruled out considering the tropical plume feeding north into this system. Some larger cities which appear the be candidates for flooding include Grand Rapids, Holland and Muskegon. A small svr wx risk could develop near/south of I-94 on Sunday night ahead of the approaching dry slot and sfc cold front which will extend south from the deepening sfc low passing across central Lwr MI. After a brief cool down Mon, temps rebound again Tuesday ahead of the next system/cold front which brings another threat of showers and storms on Wednesday. The cool down behind that front on Thursday is brief as well, with another rebound toward summer- like expected as we head into next weekend. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) Issued at 151 PM EDT Sat Sep 21 2019 Showers should remain scattered through this evening with little risk of thunder and conditions remaining predominately VFR. Rain showers becoming more widespread after midnight, with MVFR and IFR becoming more likely overnight at MKG and GRR. Better risk of seeing a tstm arrives on Sunday. Cigs are expected to remain VFR near and south of a line from AZO to LAN tonight into Sunday morning, although any heavier showers may temporarily drop vsbys to MVFR or IFR. Gusty south winds of 15-25kts will diminish to around 10 kts after 00Z, with the exception of MKG. LLWS is likely late tonight mainly south and east of GRR as sw winds increase to around 40 kts just abv the sfc. && .MARINE... Issued at 330 PM EDT Sat Sep 21 2019 Wave height have been building today and the Ludington buoy is currently up to 4 feet. Waves will continue to build tonight, with the larger waves also expanding farther south down the coast. The existing marine/beach hazard headlines look good and no changes planned, however extensions will probably be needed in Monday due to the cold advection behind the deepening/departing sfc low. && .HYDROLOGY... Issued at 151 PM EDT Sat Sep 21 2019 Several rounds of heavy rain will be moving through Lower Michigan starting tonight and lasting through Late Sunday/early Monday. At this point it looks like most spots will end up with a total of 1-2" of rain, with some spots possibly topping 3" by the time the rain ends Monday morning. This will cause some pretty good rises on most of the rivers in the area, but at this point no rivers are expected to exceed bankfull. The rivers that might approach bankfull are most likely the White and Pere Marquette rivers, where heavy rain last week has limited how much rain the soil is able to absorb. Of greater concern is the potential for localized short-duration flooding of some small streams as well as ponding on roadways at low- spots and in poor drainage areas. The heaviest rain is likely to fall in the communities along and west of US-131. The heaviest rain looks like it will fall Sunday evening and overnight, and be moving out of the area by Monday morning. Water on roads at night is much harder to see, so drivers should slow down and pay extra attention. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from 8 PM EDT this evening through Sunday evening for MIZ064-071. Lakeshore Flood Advisory from 8 PM this evening to 8 PM EDT Sunday for MIZ064-071. Beach Hazards Statement through Sunday evening for MIZ037-043- 050-056. Lakeshore Flood Advisory until 8 PM EDT Sunday for MIZ037-043- 050-056. LM...Small Craft Advisory until 8 PM EDT Sunday for LMZ846>849. Small Craft Advisory from 8 PM this evening to 8 PM EDT Sunday for LMZ844-845. && $$ SYNOPSIS...Meade DISCUSSION...Meade AVIATION...Meade HYDROLOGY...AMD/AH MARINE...Meade

NWS GRR Office Area Forecast Discussion


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