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Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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470 FXUS63 KMQT 141620 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 1220 PM EDT Wed Aug 14 2024 .KEY MESSAGES... - Light rain showers possible over the north central this afternoon via the lake breeze. - Wet period with showers and some thunderstorms developing Thursday, continuing Friday, then ending west to east on Saturday. && .SHORT TERM /THROUGH THIS AFTERNOON/... Issued at 225 AM EDT Wed Aug 14 2024 High pressure continues to hang over the region today, keeping skies mostly clear into this evening. That being said, webcams, observations, and satellite imagery show some thin patches of fog developing across the Upper Peninsula early this morning, reducing visibilities here and there. While dense fog is not expected this morning, be alert for wildlife and other vehicles when going through the fog patches. Current observations have the temperatures in the mid 50s to mid 60s across the area; I`m thinking that the temperatures will lower a few more degrees before the sun rises. Once the sun rises, expect any fog to quickly dissipate. Moving into the daylight hours, expect a near rinse-and-repeat of yesterday. However, with more stable air in the mid levels expected today, convection will have a harder time getting fired-up this afternoon in comparison to yesterday. Therefore, while there is a small (20 percent or less) chance of seeing some lake-breeze induced rain showers this afternoon (mainly over the north central), I think CIN in the mid-levels will prevent any convection from achieving glaciation (i.e. the updrafts will not get high enough in the atmosphere for thunderstorms). Otherwise, expect temperatures and winds to be about the same as what they were yesterday, save for the Lake Michigan lake breeze going further inland in comparison to the Lake Superior lake breeze. && .LONG TERM /TONIGHT THROUGH TUESDAY/... Issued at 435 AM EDT Wed Aug 14 2024 Medium range model guidance is in good agreement on the large scale flow evolution over N America thru the weekend. As a group of shortwaves currently over the Pacific NW and Alberta/Saskatchewan progress eastward, mid-level ridging will modestly build northward into Saskatchewan/Manitoba Thu/Fri. In response, the shortwaves will consolidate into a modestly amplifying trof into the Great Lakes region Fri/Sat. Early next week, ridging will more sharply amplify from NM/TX northward thru central Canada with positive mid-level height anomalies maximizing to the w and nw of Hudson Bay. This will force the trof moving thru the Great Lakes region to gain amplitude over eastern N America early next week. Although there is disagreement on the amplitude/structure of the mid-level ridging thru central N America early next week, some degree of nw flow will be favored into the Upper Lakes. For Upper MI, this evolution of the flow with troffing developing thru the Great Lakes region will bring shra to the area Thu thru Sat. While all day rain is not expected, potential is high for all of Upper MI to see at least light to mdt rainfall over the course of the 3 days. Ensemble guidance suggests a 20-60pct probability of rainfall amounts of an inch or more by Saturday evening, highest probability w to s central. The rainfall is needed as the pattern has turned drier over the last few weeks. A large portion of Upper MI is currently running at 25-70pct of normal rainfall over the last 30 days with the largest area under 50pct over the w half of Upper MI. After a return to dry weather on Sun, there is uncertainty early next week on progression of shortwaves around the ridge or even thru it. Summertime NW flow can be notorious for producing diurnal convection with even the subtlest of shortwaves, so would not be surprised to see isold shra/tsra any day from Mon-Wed. Greater coverage of shra/tsra will occur if a more defined wave passes. Beginning tonight, in response to the trof/shortwaves moving across the Northern Plains, shra will advance toward Upper MI under a good surge of isentropic ascent and 850-700mb moisture transport. Opted for a middle of the road approach for timing, bringing shra potential into far w to s central Upper MI toward 12z Thu. Often slower is the way to go, and it is noted that some models hold off pcpn from crossing the WI/MI stateline until late Thu morning. Would not be surprised at all if later fcsts need to push back pcpn timing. During Thu/Thu night, modestly amplifying mid-level trof will move to the Upper Mississippi Valley with sfc low pres developing into northern WI. Surge of isentropic ascent and 850-700mb moisture transport ahead of the trof will spread an initial band of shra across the fcst area on Thu. Instability is very limited initially, so don`t anticipate much, if any, thunder with the leading band of shra. After the initial band of shra, shra coverage will be more on the sct/nmrs side. Models still show precipitable water increasing to 150-170pct of normal along with warm cloud depths increasing to around 12kft to increase warm rain processes. That will support the potential of locally hvy downpours. Sct/nmrs shra and some tsra will continue on Fri as troffing/potential weakly closed off mid-level low drift over the western Great Lakes while associated sfc low slowly moves e across northern WI or Upper MI. With ocnl shra and abundant cloud cover, high temps should be held to mostly the upper 60s/lwr 70s F. Any breaks in the cloud cover will boost instability, supporting an increase in thunder. However, with deep layer shear under 20kt (even under 10kt across much of the area), environment will not support organized storms and svr risk, even with any building of instability during the day. Hvy downpours would be likely with any tsra. Models diverge on how quickly the mid-level trof shifts e on Sat, and that affects pcpn fcst. Consensus of recent model runs, not just the 00z model runs, suggests some shra will continue on Sat, but diminishing/ending w to e. If faster solutions work out, Sat would be a dry day, at least across western Upper MI. Dry weather is then expected on Sun as trof continues shifting e of the area. As previously mentioned, Upper MI will remain under some degree of NW flow early next week, and during summertime, NW flow can result in isold convection with even the subtlest of shortwaves. Last day or so of medium range model runs have suggested that a more defined wave may arrive Tue or Wed, offering a better potential of something more than isold shra/tsra. Until models move toward some consistency, pcpn chc remains low in the 20-30pct range. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1219 PM EDT Wed Aug 14 2024 VFR conditions dominate through tonight as high pressure ridging slowly gives way to an incoming shortwave low currently over the Northern Plains. Rain will move into IWD towards the end of the forecast period with conditions dropping to MVFR. && .MARINE... Issued at 435 AM EDT Wed Aug 14 2024 With sfc high pres that provided light winds in recent days shifting e, winds will increase slightly, but still remain under 20kt today/tonight. During Thu/Fri, low pres will develop e and ne into WI/Upper MI, bringing increasing easterly winds to Lake Superior. Expect winds to gust up to around 25kt, particularly Thu aftn thru much of Thu night. Exact track of the sfc low will determine whether these stronger wind gusts continue on Fri, but it does appear that pres gradient will overall relax some, so winds should settle back a bit across much of the lake on Fri, especially across eastern Lake Superior which will be closer to the low pres center. As the low departs, a period of n to nw winds gusting to 20-25kt is possible Fri night into Sat, mainly across the e half of Lake Superior. Expect winds under 20kt on Sun as high pres ridging builds to Lake Superior. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...TAP LONG TERM...Rolfson AVIATION...07 MARINE...Rolfson