Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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527 FXUS63 KARX 131152 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 652 AM CDT Mon May 13 2024 .KEY MESSAGES... - Wildfire smoke impacts continue this morning, with hazy/milky skies persisting into Tue - Rain chances across the far south today, but most locations will stay dry - Next rain chances move in Wed night/Thu with unsettled pattern into the weekend && .DISCUSSION... Issued at 220 AM CDT Mon May 13 2024 * SMOKE: improving this morning, more milky skies possible Tue The HRRR and RAP show improvement through the morning in near sfc concentrations. Vsbys per latest sfc obs are mostly very good with 6+ miles with just some spotty 3-5SM. Air Quality Alerts continue for MN and much of WI this morning. The RAP sinks more smoke from Canadian forest fires southward across the region tonight/Tue, but holds most of this a loft (above 8 kft). Near sfc smoke impacts are favored to hold well west. This suggests a milky sky for Tue but likely less impacts in sfc air quality. * RAIN CHANCES TODAY? Trending southward... Churning upper level trough/low was trekking slowly east across the southern plains early this morning. Spiraling bands rotating counterclockwise around the trough were interacting with a west-east running cold front that was easing southward across the local area (extending from the MN/IA border into northeast WI at early morning). Areas of showers and a few storms was the result, the bulk of which were located over IA. Track of the upper level trough, coupled with where the moisture transport/instability pool is progged to layout, suggests the bulk of the continued rain chances will hold across IA and northern IL, but northern fringes could spread into farther southern WI. There has been a trend pulling the rain chances farther south over the past couple days, and meso models continue this. * WED NIGHT/THU: rain chances, but how widespread? The long range guidance continues to suggest a shortwave trough in the northern portion of the flow will shift across the northern plains eastward over the upper mississippi river valley Wed night into Thu. Meanwhile, a piece of the energy in the southern portion of the flow looks to kick out of the southern plains and across the mid mississippi river valley during this time. Do these shortwaves merge in this split flow scenario? Stay separate? The GEFS members favor keeping them separate. Rain chances would then have to rely heavily on moisture transport, instability ahead of an associated sfc front. The EPS, on the otherhand, is a bit more stout with the northern stream shortwave, dropping it farther south...thus producing a bit more QPF and higher probabilities to get wet regionwide. Not clear on how this will shake out, but the models have been consistent in producing at least scattered showers/storms for this period...and model blend continues to produce chance to low end likelies (30-60%) for rain potential. Will stick with that for now. * END OF THE WORK WEEK/WEEKEND: more rain chances, uncertainties on when/where Progressive upper level flow persists for the end of the week with the GEFS and EPS promising quick moving shortwave ridges/troughs. Timing, location differences crop up (not unexpected), lowering confidence considerably on the resulting sensible weather outcomes. As it has the past few days, the differences in the ensemble members of each model suite cause the NBM (model blend) to spread out rain chances over several days - which in reality would likely be focused to smaller periods. Will hold with the blend which has low end pops (20-30%) through the weekend. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 626 AM CDT Mon May 13 2024 MVFR visibilities from haze and associated wildfire smoke extends in an east-west line from the Iowa-Minnesota border through western Wisconsin and north into central Wisconsin. Remains a challenging detail as a weak low pressure sags southeast through northern Wisconsin at 13.12Z TAF issuance. The associated weak cold front aligns with the aforementioned MVFR visibilities. Given a lack of sinking air (subsidence--high pressure) as well as daytime heating expected to push this colder air back north, expect VFR to return at both TAF sites (KLSE & KRST) through the early morning hours. The smoke gets pulled apart along this boundary from southeast Minnesota into western Wisconsin into the early afternoon, decreasing total particulates throughout the atmosphere and overall coverage. High pressure eventually exerts influence later today into tonight, turning winds clockwise (anticyclonically) out of east-northeast overnight. Therefore, given ongoing upstream wildfires, smoke and haze are expected to be more widespread. Have increased ceilings as model consensus suspected to not be picking up on upper level smoke. Haven`t introduced visibility restrictions as most likely after this TAF (13.12Z) period. Will be an important forecast detail. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...Air Quality Alert until noon CDT today for MNZ079-086>088- 094>096. IA...None. && $$ DISCUSSION...Rieck AVIATION...JAR