Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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689 FXUS63 KMQT 211951 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 351 PM EDT Tue May 21 2024 .KEY MESSAGES... - First round of showers and thunderstorms are already ongoing and will lift north over the west half of the UP potentially bringing small hail and stronger winds. - Second round of thunderstorms moves from west to east this evening into tonight, bringing mainly some heavy rain showers and winds; there is a slight chance for all severe weather threats along this line. - Windy conditions develop behind the system on Wednesday. && .SHORT TERM /THROUGH TONIGHT/... Issued at 319 PM EDT Tue May 21 2024 This afternoon brings the first wave of showers and possibly some isolated thunderstorms to the UP with a second and more noteworthy round expected this evening into tonight. A slight risk from the SPC over the south-central seems to fit well for the going forecast with potential for all severe weather threats accompanying the second line of thunderstorms. Latest WV imagery and RAP analysis has the first shortwave currently over MN and northwest WI which is lighting up the radar data over the western UP. This will continue to expand north and east over the west half of the UP as the shortwave and mid level warm front lift north, aided by isentropic ascent. With current RAP analysis showing SBCAPE around 100 j/kg with mid level lapse rates below 6.5 C/km and the 5/21 12z HREF mean SBCAPE holding around this through the afternoon as the boundary lifts north, some isolated thunderstorms are possible to bring some small hail. Severe weather is expected to hold off until the second round. The more vigorous shortwave is currently situated over east NE with the associated sfc low over west IA. This shortwave trough will take on an increasingly negative tilt as it lifts north-northeast through the Upper MS Valley this evening and then across northern MN and into Ontario later tonight. The associated sfc low will rapidly deepen today aided by strong upper divergence from a coupled upper jet structure (right entrance region of a 130 kt jet max over northern Ontario and the left exit region of a 110 kt jet max over the Southern/Central Plains). The most recent HREF mean has the low deepening to around 984 mb near the MN/Canadian international border by 12Z Wed as the center tracks just west of Lake Superior later tonight. With this more northwest sfc low trend in the last 24 hours has increased the severe weather potential. CAMs are in fairly good agreement on this second round developing a QLCS over the western UP this evening, quickly tracking east into tonight. With bulk shear around 45-50kt, MUCAPE up to 1000 j/kg, and mid level lapse rates around 7C/km, some severe thunderstorms are possible. With strong LLJ around 60-70 kts, this should contain the severe weather threats to winds. That said, mid level lapse rates could support hail up to 1 inch and low LCLs around 1kft with some low level helicity does leave a low chance (~2% chance along WI state line) for a quick tornado spin up. The limiting factor for severe weather is the timing of the storms, as we progress into the evening and lose daytime heating, storms are expected to weaken. Another factor in limiting severe potential for the eastern UP is onshore flow off Lake Michigan. Most locations will see between half an inch to inch of rainfall from this system with the highest amounts west. Models show shower coverage diminishing significantly late tonight as we get into the dry slot behind the front along with q-vector divergence/subsidence as the system continues to lift north. Lows tonight will stay mild in the 50s, cooler in the west. && .LONG TERM /WEDNESDAY THROUGH TUESDAY/... Issued at 350 PM EDT Tue May 21 2024 The extended forecast is dominated by two low pressure troughs during the period, one west of Thunder Bay and north of the Arrowhead of Minnesota by Wednesday morning, and another over the Seattle area Wednesday morning making its way across the Upper Midwest Friday afternoon through Friday night. While the first low will be northwest of Lake Superior Wednesday, strong winds from behind the first low will be the main story for the long term, creating windy conditions across the area (especially the west where a High Wind Watch and Wind Advisories were issued). As an impressively deep 986mb low continues lifting northwest from just west of Thunder Bay towards James Bay Wednesday, a strong low- level jet from between 5 and 30 thousand ft will move across Upper Michigan, allowing for windy conditions to develop over the U.P., particularly the west where the strongest winds of the LLJ reside. While 70 mph is the highest possibility (<10% chance), winds up to 50 to 60 mph are expected across the western U.P. along the lakeshores and the Keweenaw. This will cause unsecured items to the lofted away and for driving to become hazardous in spots. Therefore, a High Wind Watch and a Wind Advisory have been issued for Ontonagon and Gogebic counties Wednesday. While I`m confident that Ontonagon will see wind gusts up to 45 mph, I`m only around 60% confident that Ironwood and northward will see gusts up to that high. Likewise, I`m only 70% confident that northern Houghton and Keweenaw counties will see wind gusts up to around 60 mph Wednesday too. The main concern is how well we will mix the higher winds down to the surface across the area Wednesday; with low-level stratus looking to hang on until the afternoon hours, we have have a more difficult time doing so. Nevertheless, the friction that the land will cause along the lakeshores (as well as the increase in elevation) will help to increase the wind speeds too. As we move into Wednesday night, we will lose the diurnal mixing from the sunlight, and thus more stable air in the boundary layer will prevent the higher winds aloft from mixing down. While we will likely (80+% chance) see breezy conditions continue over the Keweenaw Wednesday night, expect calmer winds across the rest of the U.P. by midnight. Besides the winds Wednesday, there is a 20% chance that we will see some light rain showers moving through the central and east Wednesday before more light rainfall from moisture that`s wrapped around the low returns and brings isolated showers and thunderstorms back over the western half by the afternoon hours. As the low continues to pull away Wednesday night, some of the CAMs hint at a line of light rain showers moving over the western half late as a secondary shortwave rotates around the low over us. However, the shower activity is expected to die out Thursday morning as weak ridging begins to build back into the area. With warm air advection returning to the area Thursday, expect highs in the 60s near the Great Lakes to the 70s in the interior areas. With mostly sunny skies being over the area Thursday, we could see some strong dewpoint depressions develop, possibly getting min RHs down into the low 30 percents in the interior west. There is a chance that some convection will pop up during the afternoon hours Thursday as a localized sfc low moves through the U.P.. Whether this occurs or not will depend if this sfc low materializes, and if so where it tracks. As it stands right now, I think the NBM`s 30% handles these rain chances fairly well. Our second big low of the period looks to impact us around the Friday through Friday night time period. While we are looking to be initially dry Friday, especially over the east where min RHs could dip into the lower 30 percents, rain showers and thunderstorms from the approaching low look to move into the west by no later than the afternoon. I lowered thunderstorm chances from likely to chance wording over the interior west late Friday afternoon into early Friday evening as guidance could change rapidly over the next 3 days in regards to the track of the low (and thus thunder chances). That being said, should everything come into place and the low track just right, we could see some severe weather return to the western half as MUCAPEs could get over 1000 J/kg and 0-6 km bulk shear be around 40 to 50 knots. As the cold front of the low moves over the U.P. Friday night and Saturday morning, expect the rain chances to cease behind it. Dry weather returns for this weekend as ridging builds across our area. For the beginning of next week, model guidance begins to significantly diverge; we could see dry conditions and ridging continue, or we could see a Colorado low lift through the Plains into the Great Lakes and bring more rainfall to the area. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 202 PM EDT Tue May 21 2024 As a strengthening low pressure system currently over western IA lifts north into northern MN tonight, two rounds of showers and thunderstorms will move though the area with it. The first one is already progressing its way over the west third of the UP bringing SHRA to IWD. This will continue expanding north and west over the west half of the UP into this evening bringing SHRA to CMX and some VCSH to SAW. While this first round may bring some thunder, confidence remained low so VCTS and TSRA were left out for the first round of precip. A line of stronger thunderstorms is expected to accompany a front lifting through the area this evening into tonight. TSRA arrives first at IWD around 0Z Wednesday, then the line progresses to CMX and SAW around 2-3Z Wednesday. MVFR conditions are expected to accompany these showers and storms tonight with IWD and SAW lowering to IFR late. Gusts to 25-30 kts are expected at all sites tonight into Wednesday. LLWS is also expected this evening and tonight as a strong low level jet moves across the area. While windy conditions continue on Wednesday behind the low pressure system, expect vis and cigs to return to VFR through the day. && .MARINE... Issued at 353 AM EDT Tue May 21 2024 Early this morning, wind gusts across the lake are light. However, an unseasonably strong low pressure system approaches Lake Superior this afternoon and evening resulting in rapidly increasing northeast winds across western portions of the lake. Northeast winds increase above 20 knots midday Tuesday over the far western lake then increase to 35-40 knot gales by Tue evening (60-90% chance). While the likelihood of gales is high, there is uncertainty in whether high-end gales can be achieved. Late May gales are rare due to the stable air immediately above the lake, but the strength of the surface pressure gradient close by the low pressure should support at least gales to 40 knots today. While a brief respite from gales is expected overnight in the west, the environment behind the low will make it much easier to tap into the low-level jet Wednesday, leading to high end gales expected (50+%) over the west half of Lake Superior with a few storm-force gusts possible (~20%), but current model guidance has storm force gusts isolated and brief, so most marine products will reflect gales to 45 knots. As the low continues to quickly depart, winds fall below gales late Wednesday and below 20 knots Thursday afternoon. Another low pressure will pass through the Upper Great Lakes region Friday, but is likely (75+%) to be much weaker and uncertainty exists regarding the track of the low, so the current forecast reflects 20-25 knot gusts Friday afternoon with gusts near 20 knots through Saturday. Other marine hazards include chances (30-50%) of thunderstorms over the lake this afternoon in the west and across all of Lake Superior tonight, with a 5-15% chance of severe winds associated with the thunderstorms along with small hail. With the first round of gales this evening, significant wave heights will be highest in the far west at near 12 ft, with the Wednesday gales forcing waves as high as 15 feet in the north-central portions of the lake. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... High Wind Watch from Wednesday morning through Wednesday evening for MIZ001-003. Wind Advisory from 9 AM EDT /8 AM CDT/ to 10 PM EDT /9 PM CDT/ Wednesday for MIZ002-009. Lake Superior... Gale Warning until 8 PM EDT /7 PM CDT/ Wednesday for LSZ162. Gale Warning from 7 AM EDT /6 AM CDT/ to 8 PM EDT /7 PM CDT/ Wednesday for LSZ240-241. Gale Warning from 10 PM this evening to 11 PM EDT Wednesday for LSZ242>244-263-264. Gale Warning from 2 AM to 11 AM EDT Wednesday for LSZ245>251- 265>267. Lake Michigan... None. && $$ SHORT TERM...Jablonski LONG TERM...TAP AVIATION...Jablonski MARINE...GS