536 FXUS63 KGRR 111150 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 750 AM EDT Thu Oct 11 2018 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 309 AM EDT Thu Oct 11 2018 Mostly cloudy skies and much cooler temperatures are expected today with light lake effect (rain) showers mainly west of US-131. Lows tonight will dip into the upper 30s with continued cloud cover. A similar story is expected Friday and Friday night, though temperatures are expected to be colder into Saturday morning. A widespread frost is possible Saturday morning. After a dry Saturday, lake effect (rain) showers will ramp up again Sunday and last into early next week. && .DISCUSSION...(Today through next Wednesday) Issued at 309 AM EDT Thu Oct 11 2018 Currently, temperatures are falling areawide in the wake of a strong cold front. As expected, west/northwesterly winds have picked up this morning with a few spots gusting as high as 30 - 40 mph. The region of cold air advection responsible for our falling temperatures and gusty winds is captured nicely in infrared satellite imagery with a nearly solid stratus deck encompassing much of the Upper Mississippi River Valley and Great Lakes. Indeed, we've exchanged our summer-like pattern for one that looks much more like winter especially considering the parade of upper-level shortwaves embedded within northwesterly flow aloft expected to swing through the Great Lakes over the next 7 days. Today, mostly cloudy skies will prevail with continued gusty northwesterly winds. With 850mb temperatures falling to -2 to -3 C by this evening, high temperatures will struggle to get out of the upper 40s. Considering lake temperatures are anywhere from +16 to +18 C (though admittedly there's some churning out there right now with large waves), lake-induced instability will likely lead to light lake effect rain showers mainly west of US-131 but patchy drizzle is possible elsewhere. So, today will be quite a bit different than the past few. Tonight, cloud cover will continue at least across the western half of the area due to lake-induced instability. Clouds may become more broken than overcast across the east half which leverages concern for frost potential, mainly east of US-131. Continued gusty winds even with somewhat lesser cloud cover may be just enough to prevent frost from developing, so we'll let the day crew take a closer look. The first of many shortwave troughs/clipper systems will pass through the Great Lakes Friday though model guidance is somewhat all over the place with the placement of the associated surface feature. It seems the convective-allowing models favor at least part of Lower Michigan seeing light precipitation but the more certain impact to our area will be an uptick in lake effect rain showers (e.g. 850 mb temperatures will cool to -3/-4 C with deepening inversion heights). Low temperatures Friday night may be the coldest we've seen all season owing to continued cold air advection (reinforced by the aforementioned clipper system), so the potential for frost or even a freeze is higher. Confidence remains low, however, owing to the potential for continued lake effect cloud-cover. Brief mid-level ridging on Saturday suggest a dry day before the next clipper swings through on Sunday. While the best upper-level forcing will pass north of Lower Michigan Sunday, a band of light rain is likely along a southeastward-moving cold front. On-and-off lake effect precipitation will then prevail Sunday evening through early next week, reinforced by yet another clipper by midweek. Note that 850 mb temperatures may flirt with the -7/-8 C mark at times next week, which is an arbitrary threshold for snow in October. With this in mind, it seems feasible a few snowflakes may mix with rain with any lake effect precipitation next week. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) Issued at 750 AM EDT Thu Oct 11 2018 MVFR ceilings will be widespread and prevalent much of the next 24 hours. Cloud bases will be between 2,000ft and 3,000ft much of the time. Ceilings may lift at times to 3,500 or so however. The clouds are developing off of Lake Michigan in a lake effect mode. Some scattered lake effect rain showers will be possible much of the next 24 hours, but we are not expecting restrictions to visibility. Winds will be gusty from the west between 12-30 knots all day, subsiding a bit tonight, to 8-13 knots. && .MARINE... Issued at 309 AM EDT Thu Oct 11 2018 Cold air advection over relatively warm lake waters will continue efficient mixing leading to west/northwesterly winds of 20-30 kts with gale force gusts to 35 kts through this afternoon. As such, the Gale Warning was extended to 4 PM EDT. Waves will remain above 4 ft through at least midday Friday. Marine headlines will likely be needed Saturday night and into Monday and again on Tuesday/Wednesday as winds and waves respond to a parade of weather systems. && .HYDROLOGY... Issued at 1235 PM EDT Wed Oct 10 2018 Rain has moved back into the area from the south. Since yesterday, the threat for widespread heavy rain (enough to cause river flooding) has continued to decrease. Generally, between 0.5 and 1.0 inches of rain is likely across most of the area over the next 12 hours. Since the current airmass is loaded with plenty of moisture, we will need to keep a close eye on rainfall rates at individual locations (especially urban areas) in case any thunderstorms track over the same locations repeatedly, which could cause localized flooding/drainage issues. Otherwise, it looks like the area will shift into fall mode for the next several days at least as this hot, humid, and wet weather pattern moves off to the east and away from our area. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...Gale Warning until 4 PM EDT this afternoon for LMZ844>849. && $$ SYNOPSIS...Borchardt DISCUSSION...Borchardt AVIATION...Duke HYDROLOGY...AMD MARINE...Borchardt