Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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851 FXUS63 KMQT 291136 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 736 AM EDT Mon Apr 29 2024 .KEY MESSAGES... - Occasional showers and some drizzle and fog today. Fog may be locally dense at times in high terrain. - Active pattern continues as three low pressure systems track across the region over the next week. Above normal temps/precip are expected including thunderstorm chances. - Elevated fire weather conditions are possible over the west half of Upper Michigan on Wednesday, but will depend on the preceding precipitation. && .SHORT TERM /THROUGH THIS AFTERNOON/... Issued at 316 AM EDT Mon Apr 29 2024 Water vapor imagery and RAP analysis show shortwave/mid-level low over eastern SD. At the sfc, associated 1005mb low pres is over sw MN. The low has started to occlude, and from the occluded front, a warm front extends across northern IA to southern Lwr MI. Main push of isentropic ascent in advance of the wave supported a solid area of shra that has lifted n of Upper MI during the night, leaving behind mostly just areas of -dz and some fog. This break in shra extends into WI. More shra are developing closer to sfc low and aforementioned fronts. These shra extend from sw MN into southern WI. Current temps across the fcst area are in the mid 30s to lwr 40s F. Mid-level low will begin to open up today as it lifts toward western Lake Superior. At the sfc, the associated sfc low will track from sw MN to the vcnty of Ironwood by 00z. It does not look like the warm front will make it into the U.P. Instead, the occluded front will lift to near the MI/WI stateline by 00z. As a result, being ahead of the occluded front, expect a gloomy day for the most part with some areas of -dz and fog. Fog may be locally dense at times in higher terrain. There will be shra at times as well. Closer to axis of 850- 700mb moisture transport, eastern fcst area should generally be favored for more frequent shra this morning into early aftn. A subtle shortwave will also be lifting across that area. Shra will become more nmrs mid to late aftn across the w and central as opening mid-level low approaches. Approaching occluded front will also aid this shra development. There is a little cape avbl for parcels lifted from top of inversion, but cape profile is very thin, suggesting little potential of thunder. Fcst will not reflect any thunder mention today. With winds maintaining an easterly component thru the day, knocked high temps down from previous fcst. Expect highs around 40F across the Keweenaw, mid to upper 40s central and e, and low 50s F w. These highs will occur late in the day, closer to 00z. && .LONG TERM /TONIGHT THROUGH SUNDAY/... Issued at 411 AM EDT Mon Apr 29 2024 Ongoing period of active weather continues with only minor changes to going forecast as three low pressures spin across the area this week. Even though there are several chances for rain between 00z Tuesday and 12z Thursday, total rainfall amounts are expected to be light (less than 1/4 inch). The final low pressure that lifts across the area Thursday and Friday is more likely (40-60%) chance to bring moderate rainfall amounts (greater than 1/2 inch). The grand ensemble also indicates a low (10-25%) chance for heavy rainfall amounts (greater than 1 inch). Starting with tonight, most of the rain associated with the first low pressure will already be north/east of our area. However, the surface low tracks directly across our area with low-level moisture convergence implying a chance for fogginess. Confidence was too low to include in the forecast at this time, but model soundings imply better chances in the poorly mixed boundary ahead of the cold front. A dry frontal passage is currently favored, but there may be some sprinkles/drizzle along and ahead of the front. Model soundings also show potential for a few hours of post-frontal upslope drizzle for the Copper Country Tuesday morning associated with moisture wrapping around the surface low. Elsewhere, morning stratus tries to scatter to cumulus during the afternoon especially south-central where west winds are downsloping. Cloudiness should be more stubborn closer to Lake Superior so I shaved a few degrees off Tuesday`s high temps. A vigorous 500 mb shortwave approaches from the west Tuesday evening and becomes negatively tilted as it pivots across the area Tuesday night. There`s very little time for moisture to return ahead of this disturbance for destabilization and the nocturnal timing further limits thunder potential. However, there`s very good agreement in convection bubbling up along the cold front to our west Tuesday afternoon. These storms appear to grow upscale into an MCS that reaches the MI/WI state line a few hours after midnight. If a sufficiently organized cold pool develops then favorable low level shear vectors and impressive synoptic forcing may be adequate for the MCS to persist across our area. At this time, that potential appears most likely across the western UP mainly between Ironwood and Houghton. Any storms that make it into our area should be elevated and therefore are mostly a novelty instead of a hazard. The window for rainfall is brief (~3 hours) leading to light rain amounts less than 1/4 inch. The mesoscale details of convection feedback onto the surface pressure pattern leading to a low confidence forecast for Wednesday. The main area of uncertainty is just how windy it will get as a much drier air mass allows for deep mixing. Subjective analysis of model guidance suggests the strength of overnight convection may be directly correlated with magnitude of winds Wednesday afternoon. A well-organized MCS may result in mesolow formation and locally strong pressure gradients whereas a weak/dying MCS would not. It`s worth noting that the probability of gusts >45 mph appears to have diminished below 10%. Regardless of winds, mixing up to around 6kft into a mid-level dry layer indicates RH values should dip below 30% and perhaps even lower. The combination of gusty winds and low RH indicates potential for elevated fire danger, but several rounds of recent rainfall implies wet soils/fuels that should limit the threat. High pressure builds Wednesday night but increasing upper level clouds should prevent temps from bottoming out, but they`ll still be ~25F cooler than Wednesday`s highs of 65-70F. Model guidance has trended substantially toward a low pressure developing on Thursday then tracking across our area Thursday night. As a result, rain chances increase on Thursday as the warm front lifts north then rain chances end behind Friday`s cold front. Additional generally light rain chances continue through next weekend signaling a continuation of the pattern bringing above-normal temps/precip to Upper Michigan. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 736 AM EDT Mon Apr 29 2024 With low pres and occluded front lifting toward Upper MI today, expect low stratus to dominate the area along with some fog, especially where sfc winds are upsloping. There will be -shra and -dz at times at well. LIFR will prevail at IWD/CMX/SAW thru this aftn. With upsloping e to ese winds at CMX/SAW, conditions may slip blo airfield landing mins at times, especially at CMX. As the low lifts to the ne of the area tonight, expect improvement to IFR at IWD/SAW. CMX may end up with LIFR thru the night as upsloping e winds shift to upsloping w winds. The easterly winds today at CMX will be gusty to 25-30kt thru mid aftn. && .MARINE... Issued at 411 AM EDT Mon Apr 29 2024 East-northeast gales to 40 kts are occurring across most of the lake tonight with gusts up to 45 kts at the Twin Ports. Gales to 40 knots continue this morning before diminishing around midday then ending this afternoon. Significant wave heights up to 14 ft are possible this morning between Duluth Harbor to the Bayfield Peninsula and near Isle Royale. Waves fall below 8 ft this evening. A low pressure tracks across the lake tonight switching easterly winds to westerly and allowing winds to fall below 20 kts over the west half this evening and after midnight across the east. West winds are expected to remain mainly below 20 kts through Tuesday. East to south east winds increase to 20-25 kts Tuesday night, becoming westerly and increasing to 25-30 kts behind a cold front on Wednesday. There is a low 10-30% chance for westerly gales up to 35 kts on Wednesday with the highest chances on the windward Keweenaw shoreline. Winds quickly diminish below 20 kts Wednesday night and stay light until the next low pressure approaches on Thursday bringing another episode of gusty easterly to northeasterly winds. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... Gale Warning until 5 PM EDT /4 PM CDT/ this afternoon for LSZ162-243>246-263>266. Small Craft Advisory until 11 PM EDT /10 PM CDT/ this evening for LSZ240-241-247-248. Small Craft Advisory until 8 PM EDT this evening for LSZ242. Small Craft Advisory from 5 PM this afternoon to 4 AM EDT Tuesday for LSZ243>246. Small Craft Advisory until 5 PM EDT this afternoon for LSZ249>251. Lake Michigan... Small Craft Advisory until 11 AM EDT this morning for LMZ221. Small Craft Advisory until 4 PM EDT this afternoon for LMZ248- 250. && $$ SHORT TERM...Rolfson LONG TERM...EK AVIATION...Rolfson MARINE...EK