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Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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902 FXUS63 KDLH 142111 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 411 PM CDT Wed Aug 14 2024 .KEY MESSAGES... - Widespread rain and thunderstorms move in late this afternoon and evening. Severe weather is not expected. - Locally heavy rain is expected Thursday, especially along the North Shore, which could lead to elevated streamflows and ponding of water. - Cooler temperatures expected Thursday, followed by a warming trend through the weekend. && .DISCUSSION... Issued at 410 PM CDT Wed Aug 14 2024 A period of wet weather will finish up our work week, with rain and embedded thunder moving in tonight, continuing to spread across the area on Thursday, then pulling out Thursday night into Friday. This is a very fall-like system, with mainly elevated instability. Mid level lapse rates (700-500mb) increase to around 6.5C/km late tonight and Thursday but only across our southern third or so of the forecast area. Surface based CAPE builds to near our area Thursday afternoon and evening, but not quite into the forecast area. Lift for tonight is going to be mainly synoptically driven, with a good 850mb moisture plume and shortwaves moving across the area ahead of a potent upper level shortwave approaching the area. I have delayed the onset of precipitation tonight a small amount as things do appear to be a little slower than the models are currently depicting. Thursday that surface based CAPE comes into play, and together with Precipitable Water values up near an inch and three quarters, we are looking at some fairly significant rainfall totals over northwest Wisconsin, ranging from a half inch to nearly an inch. Rainfall for northern MN will be slower, with totals more in the quarter to three quarters of an inch, with one significant exception. The strong southeast winds moving across Lake Superior will interact with our terrain, the warmer surface waters in the mid 60s and the instability to produce much higher rainfall rates there, with total amounts ranging from 1 to 3 inches. We have had some upwelling cool the lake surface temperatures immediately along the North Shore, so it will be interesting to see if we can detect how that affects the rainfall patterns tonight into Thursday. The clouds and rainfall on Thursday will produce a chilly day, with high temps in the mid 60s to low 70s, but these should rebound into the 70s for Friday. The upper low remains in our vicinity for Friday, so have kept chance pops going into Friday, but then they should pull out of the area with the upper low on Saturday. Highs on Saturday to warm back up into the 70s and low 80s. While we currently have a dry forecast Saturday, I would not be surprised if we need to add in some diurnally driven showers. After Saturday, we will be in an extended period of northwest flow aloft, with ridging to our west and troughing over the East Coast. A ridge of high pressure at the surface should keep our weather quiet on Sunday, but that slides to our east and we begin getting shortwaves diving across the forecast area beginning Monday, which brings precipitation chances back into the area for at least the first half of the work week. This should also bring near to above normal temperatures. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1240 PM CDT Wed Aug 14 2024 Expect gradually deteriorating conditions through much of this TAF period. Rain with some embedded thunder to move into the terminals after 03z from the southwest, gradually overspreading all of the terminals by 15z. Ceilings will gradually lower to MVFR/IFR, accompanied by MVFR visibilities in -SHRA and BR. The lowest conditions will be found at KDLH, KHIB, KBRD and KHYR. Southeast winds less than 10 kts will gradually increase to gust up to 20kts for the southern terminals. At this time LLWS does not appear likely, but there are stronger winds aloft and we may need to add it in for Thursday morning. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 410 PM CDT Wed Aug 14 2024 East to northeast winds on the lake today will gradually increase tonight into Thursday, before backing into the north Thursday night into Friday and decreasing. Wind gusts and building waves should produce hazardous conditions for Small Craft during the day on Thursday into Thursday night before diminishing again into Friday. With fairly high confidence in these conditions, have gone ahead and issued a Small Craft Advisory for Thursday into Thursday night. Waves will stay built up with the northerly winds on Friday, but not enough to require lingering Advisories. Winds become northwest Friday night into Saturday and diminish to 5 to 15 knots. For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt. && .DLH WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. MARINE...Small Craft Advisory from 1 PM Thursday to 4 AM CDT Friday for LSZ140-141. Small Craft Advisory from 10 AM Thursday to 4 AM CDT Friday for LSZ142-143. Small Craft Advisory from 10 AM to 10 PM CDT Thursday for LSZ146-147-150. && $$ DISCUSSION...LE AVIATION...LE MARINE...LE