866 FXUS63 KGRR 160543 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 143 AM EDT Sun Oct 16 2022 LATEST UPDATE... Aviation .DISCUSSION...(This evening through next Saturday) Issued at 350 PM EDT Sat Oct 15 2022 - Relatively Quiet Weather into Sunday Morning We have a break in our cold and showery weather pattern of late for tonight into early Sunday. We have an occluded low tracking through Michigan tonight. The triple point of this system tracks near I-80. Normally we would get precipitation from that sort of set up. In this case through there are two jet cores, one south of us and the other over northern Michigan. Also the air at mid levels through the central and southern Great Lakes is rather dry above 850 mb. With the northern branch of the polar jet north of us, that is where the precipitation is expected tonight. The bottom line is we should see at least partial clearing tonight but with chilly low temperatures. - Cold With Mixed Rain and Snow Early This Coming Week Once that systems clears the area, the coldest air of the season to date comes our way and largely stays in place into Wednesday. This cause is helped by a 150 knot polar jet speed max topping the upper ridge over the Northwest Territories tonight that digs sharply into the eastern trough. By Monday morning it is entering northern Minnesota. This then reforms, farther south, the upper low over northern Michigan by late Monday and it remains in place into Wednesday before it starts lifting out to the north and east. The coldest air actually largely stays west and south of us. That is typical at this time of year, since the lakes warm the air that passes over them. With the lake near 14c and 850 temperatures near -5 (ish) from Monday into Wednesday this creates considerable lake instability. The deeply cyclonic flow will help keep the showers going through this period. There is enough lake instability (500 to 1000 j/kg from the NAMNEST) cause thunderstorms over Lake Michigan Monday into Tuesday. The mean wind that drives the direction the showers will move rotate from westerly Sunday to northwest Monday and to nearly north by Monday night into Tuesday. So those area in those time frames are favored for the greatest precipitation. The main question is how much of this will be snow? The models show the coldest air staying west and south of our area. Even so, the wet bulb zero heights are near the threshold of 1500 ft for snow from Monday morning into Tuesday. Convection could cause this to be more snow than rain inland of US-31 and Tuesday morning with the north to northwest winds, we could get a dominant band set up. That could mean snowfall amounts well over 3 inches in parts of inland Allegan and Van Buren county, maybe western Kalamazoo. Some minor wet snow accumulations are possible elsewhere Monday into Wednesday morning. - Warmer and I mean Truly Warmer by Next Weekend Eventually another system on the north Pacific wave train, which develops a 180 knot jet core just south of the Bering Sea Wednesday, digs a trough off the west coast. That builds a serious upstream ridge over the eastern CONUS by the weekend of the 22nd to the 24th. Current thickness and 850 temperature forecast suggest highs well into the 60s Saturday and near 70 on Sunday. This is well shown by the ensembles of both the GFS and ECMWF. This would be warm weather with sunshine. && .AVIATION...(For the 06Z TAFS through 06Z Sunday night) Issued at 137 AM EDT Sun Oct 16 2022 A band of mid clouds are moving across sw Lower early this morning ahead of a cold front that is beginning to cross the lake. We're likely to see a few hours of MVFR cigs later this morning before VFR cigs round out much of the afternoon. Once colder air starts to pour over the lake late in the afternoon, lake effect showers will develop and continue through the rest of the period. MVFR cigs can be expected after 00z. && .MARINE... Issued at 350 PM EDT Sat Oct 15 2022 The next approaching frontal system will increase the winds and waves into this evening, that is till around midnight. The winds and waves do decease some toward morning but forecast wave heights do not fall below the 3 to 5 foot range. The next system, the one with the coldest air heads our way later Sunday and arrives early Monday. Once there it largely remains in place into midweek. Our high res models show wind gusts in the 35 to 50 knot range from Monday into at least Tuesday evening. Given all of this we have a SCA into Monday evening than we go into gale watch early Monday morning and run that into Tuesday evening. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...Small Craft Advisory until 5 AM EDT Monday for LMZ844>849. Gale Watch from late tonight through Tuesday evening for LMZ844>849. && $$ DISCUSSION...WDM AVIATION...04 MARINE...WDM