Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000 FXUS63 KGRR 022322 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 622 PM EST Fri Dec 2 2016 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 314 PM EST Fri Dec 2 2016 Quiet weather with little impact can be expected through Saturday night. Just a lot of cloud cover expected with a chance of a sprinkle or flurry on Saturday. Temperatures will remain near seasonal levels. The area will see a weak system move through the area Sunday and Sunday night. This is expected to bring some light snow to the area from late Sunday morning through Sunday evening, before changing over to drizzle or freezing drizzle Sunday night. Low chances of precipitation can be expected for the early portion of next week. We will see colder air move in for the end of next week with some snow. Lake effect could kick in fairly well late next week. && .SHORT TERM...(This evening through Sunday night) Issued at 314 PM EST Fri Dec 2 2016 Our main focus is on the latter portion of the fcst period where some accumulating snow will be possible across most of the area. Until then, fairly quiet weather is expected. The radar for SW Lower MI is very quiet this afternoon. A band of light showers with a weak short wave moved through earlier, and has since slipped south of the CWFA. In it`s wake, inversion heights have dropped and the DGZ has become unsaturated. Lake effect clouds will be the main feature. The cloud cover will keep temps from dropping too much tonight. We should remain mostly dry on Sat, but can not rule out a few flurries and/or sprinkles in the afternoon hours. We see a slight increase of the moisture layer on Sat that will come close to touching the DGZ. This occurs as an upper shear zone to our SW lifts NE toward the area. Temps should be above freezing once again, so nothing to be concerned about with this. We will see light snow spread in from the west across the area late Sunday morning through Sunday afternoon. We will see a couple of short waves in the nrn stream phase over the Plains before moving into the Great Lakes region. Good warm and moist advection aloft ahead of the upper wave going negative tilt will supply the forcing for this event. Amounts generally still look to be around an inch or two with this event, especially on the grassy areas. temps look like they should be around or just above freezing for most of this event. This will limit the impacts on the road to where local snow rates might briefly become a little better. Areas near the lake might see less with a little warmer sfc temps. The snow should transition to some light drizzle or freezing drizzle Sunday evening as the deep moisture is lost, but low level moisture and lift remains. Model consensus is that temps will likely rise a tad behind the snow and remain freezing. There is a chance temps could remain a little cooler due to fresh snow. With this in mind, we have a mention of drizzle or freezing drizzle Sunday night. .LONG TERM...(Monday through Friday) Issued at 314 PM EST Fri Dec 2 2016 A shot of colder air is still poised to arrive by the middle of next week along with lake effect snow showers. Some questions remain about the exact timing and degree of the colder air and whether we will largely stay dry Monday through Wednesday until this colder air arrives. Initial concerns center on precip chances on Tuesday. An upper low across Mexico will traverse Texas on Monday and help reinvigorate Gulf flow into the southeast U.S. Sfc low development between the GFS and ECMWF is more agreed upon with the 12z runs as this storm system looks likely to track near the Ohio Valley region and largely miss our area. Pops are still warranted especially near/east of I-69 to account for precip on the far NW edge of this system. Rain looks like the predominant type but snow may mix in as well. Some wobbles in storm track are possible of course, but secondary low development off the Carolinas may preclude a more northward track of this low toward the Great Lakes. It is noted that the GEM is slower and a bit further NW but the solution is questionable given the low development off Carolina and where the H500 shortwave trough is located. The GFS is still quicker than the ECMWF and GEM with when the -15C air at H850 arrives. In fact, it is at least 24 hours quicker. Looking at the H500 longwave pattern, the GFS simply has the large upper low more expansive and further south than either the ECMWF or GEM. This has implications on when the lake effect gets going and which commutes next week will be impacted by snow. The target window for any significant lake effect will either be centered on the Wednesday-Thursday time frame (GFS) or Thursday-Friday (ECMWF) depending on which model solution verifies. At any rate, at least Thursday looks like a wintry day for WNW flow areas including Muskegon...Grand Rapids...and Holland. The DGZ is saturated (with lift) and the column may potentially become deeply saturated (up to H500 or higher) Thursday night and Friday which would occur as WNW winds likely turn NW. Boundary layer winds of 20- 30 kts should not be high enough to shear the bands apart (minimizing accums), so organization of bands may occur. Several inches of snow look possible at this early stage for the favored WNW/NW flow areas for the duration of the event. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 611 PM EST Fri Dec 2 2016 Mostly MVFR conditions are expected to prevail into Saturday morning as the low levels remain moist. That may start to change Saturday afternoon. The wind begins to shift as warm air advection starts to develop. It may take some time to diminish the clouds though. A few light snow showers will be possible later tonight...especially closer to Lake MI...but the risk for IFR looks low right now. Icing conditions will persist within the clouds. && .MARINE... Issued at 314 PM EST Fri Dec 2 2016 We will be cancelling the Small Craft Advisory just a little early this afternoon. Conditions seem to have quieted down enough per the mid-lake buoy and coastal web cams along the shore. Most of the weekend can be expected to have conditions below advisory conditions. Winds aloft will come up late Sunday, but will likely not be realized at the surface. The next best chance for advisory conditions would be toward Tuesday night. && .HYDROLOGY... Issued at 314 PM EST Fri Dec 2 2016 The Maple River continues its slow climb toward bankfull, and may reach that stage by early next week. A tenth to quarter inch of liquid equivalent precip, in the form of snow for much of the area, is expected late Sunday. Additional chances for precipitation will arrive the latter part of next week, most likely in the form of lake effect snow. This moisture should have little impact on rivers in the short term. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ SYNOPSIS...NJJ SHORT TERM...NJJ LONG TERM...Hoving AVIATION...MJS HYDROLOGY...CAS MARINE...NJJ

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