525 FXUS63 KDLH 060527 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 1227 AM CDT Mon Sep 6 2021 .DISCUSSION...(This evening through Saturday) Issued at 356 PM CDT Sun Sep 5 2021 Summary: scattered rain showers and isolated thunderstorms will diminish by this evening, leading to a dry and quiet Labor Day. This break will be short-lived though, as another system builds into the Northland for Monday night through Wednesday. Some storms could be strong to severe Monday night/Tuesday morning. We will continue to see scattered showers, and some isolated thunderstorms capable of producing small hail and locally gusty winds, through the early evening hours as a compact mid-level shortwave with a decent lobe of positive vorticity advection moves through. This shortwave is embedded in a upper-level trough, with a nearly vertically-stacked upper-level low that will gradually shift off to the east this evening and overnight tonight. High pressure will build in in its wake, leading to a quiet, but cool, night ahead. With the high pressure ridge axis expected to translate right over the Northland, light winds will help support favorable radiational cooling, resulting in overnight lows in the lower to middle 40s. Some patchy fog is also a possibility tonight. This high pressure should remain in control for most of the day Monday, so Labor Day looks to be a pleasant day to get outdoors. Southerly flow will help support warm air advection, leading to high temperatures in the lower 70s east to the upper 70s west. The quiet weather conditions will be short-lived though, as a strong upper-level trough builds into the region. This trough, along with an attendant upper-level jet streak of ~130 knots will help to strengthen a surface low. Intensification should occur over the Northland, so we should see increasing chances of showers and thunderstorms Monday night into Tuesday morning, expanding from northwest to southeast. The biggest change to the forecast is an inclusion of a Marginal Risk (1 out of 5 risk) of severe weather across the northern two-thirds of our forecast area. Storms will be fueled by increasing mid-level lapse rates, with values around 7 to 8 degrees C/km and most-unstable CAPE values around 500 to 1500 J/kg per the 05.12z GFS and NAM models, sufficient instability for elevated convection. Additionally, a 35 to 45+ kt nocturnal low- level jet will be in place on the southern periphery of the trough, leading to favorable deep-layer shear. Pwat anomalies don't appear to be above climatology, so heavy rainfall isn't anticipated, but some areas could see total rainfall between one to three-quarters of an inch in total from Monday night through the day Wednesday. For Thursday through Sunday, conditions will largely be dry, with the exception for the potential for another mid-level shortwave passing through the Northland Friday night through Saturday. However, uncertainty remains on the timing of the precipitation, given some spatial differences among the global models. Some modest instability may result in some thunderstorms. Near to below average temperatures will be common next week, with highs in the upper 60s to lower 70s. && .AVIATION...(For the 06Z TAFS through 06Z Monday night) Issued at 1226 AM CDT Mon Sep 6 2021 VFR will be the prevailing flight category, but IFR fog is likely over portions of the forecast area - especially those areas under the surface ridge (a line from HIB to HYR) where winds will be light and skies will be clear following todays' shower activity. Fog should be around for several hours just before sunrise before lifting and mixing out as the ridge moves eastward and the winds pick up. Eventually, late in the TAF period LLWS is possible as a front moves south from Canada bringing thunderstorms to the border country. && .MARINE... Issued at 356 PM CDT Sun Sep 5 2021 Gusty northwest winds this afternoon will taper off this evening as an area of high pressure will build into the region tonight. Small Craft Advisories remain in effect through 7 PM CDT across much of western Lake Superior. Winds will remain from the northwest tonight, but they should be on a weakening trend. Wave heights will also diminish overnight tonight near the Apostle Islands. Labor Day Monday will be dry and calmer, with winds turning more southerly as the high pressure ridge axis passes through the region. A stronger system will build across western Lake Superior late Monday night into Tuesday, bringing increasing chances of thunderstorms, some of which could be strong to severe. As the system strengthens, a tight surface pressure gradient will develop for Tuesday, resulting in strong westerly winds. A Small Craft Advisory across western Lake Superior will likely be needed for late Monday night, continuing into the day Wednesday. && .PRELIMINARY POINT TEMPS/POPS... DLH 47 74 57 70 / 0 10 50 30 INL 41 76 53 67 / 0 10 70 60 BRD 47 81 57 72 / 0 0 30 10 HYR 43 74 55 71 / 0 0 50 30 ASX 45 76 56 73 / 0 0 50 40 && .DLH WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. LS...None. && $$ DISCUSSION...JTS AVIATION...Wolfe/KSE MARINE...JTS