Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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896 FXUS63 KARX 281948 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 245 PM CDT Fri Jun 28 2024 .KEY MESSAGES... - A few more showers/storms tonight. A conditional severe risk this evening, moreso for northeast IA. - Aside from spotty light showers, mostly north Sat afternoon, dry and cool conditions expected Sat into Mon. - More showers and storms Monday night into Tuesday. Heavy rain threat. Conditional severe threat Tuesday into Tuesday evening. && .DISCUSSION... Issued at 245 PM CDT Fri Jun 28 2024 * REST OF THE AFTERNOON/TONIGHT: storm chances - conditional severe threat for northeast IA into the evening Extensive cloud cover has persisted into the early afternoon while the morning rains have moved east/south of the local forecast area. The clouds are inhibiting daytime heating, thusly working against sfc destabilization. A thin line of showers/storms has developed in southern MN/IA on the western flanks of the cloud, on the edge of the MLCAPE plume (100-250 J/kg), a small region of differential heating plus what looks like a remnant MCV (per watervapor imagery). These should continue to push east, but will quickly run out of instability a loft. CAMS models continue to provide a wealth of potential outcomes, almost by the hour, lowering confidence in how the evening will unfold. A few things to focus on though. The MCV should continue to provide enough lift for shower/storm production into the evening as it shifts across the area. Again, instability is limited. With RAP/HRRR soundings holding the cap in place (thanks clouds), effective wind shear will be mostly above 1 KM...with fairly short hodographs. Not sure there is much there to support whatever CAPE can be realized. To the west a cold front is advancing east and right around the boundary RAP/HRRR soundings show some uptick in instability profiles, although still suggesting the CAP could hold (non sfc based). Showers/storms should develop along the front, but likely more favored along the southern flank - in Iowa. These would have a bit more promise for strong/severe upscaling with a deeper instability pool, moisture axis to work with. In additional to all this is the potential interplay of the low level jet. Currently the RAP has a fairly steady stream of 850 mb moisture transport from IA into central WI, with a gradual shift eastward ahead of the front through the evening. Not much convergence. However, the HRRR refocuses the jet into southwest WI by 00-02z, resulting in blossoming of convection. Instability still limited at best and doesn`t have a lot of strong-severe support. Overall, a few more showers and storms this evening. A conditional severe risk continues, but more focused into IA and associated with the cold front. Certainly a scenario to monitor. * SAT NIGHT/MON: cooler, drier Aside from a shortwave trough/cold air advectively driven afternoon shower chances, mostly north of I-94 Sat, the local area is looking at a few dry days for a change. High pressure at the sfc slides across the region Sunday while a shortwave upper level ridge edges over the upper mississippi river Mon morning. EPS/GEFS paint highs for most of the area in the lower 70s - a consistent signal with only a few degree spread in the 25/75 percentiles. Meanwhile, the LREF suggests little chance (0 to 10%) to warm into the upper 70s Sun/Mon. So, expect cooler, but perhaps welcomed conditions to kick off the new week. * MON NIGHT/TUE: more rain, storm chances - heavy rain threat Long range guidance remains in good agreement with driving ripples of upper level energy eastward from the PAC NW, with the progressive zonalish flow tracking them over the upper mississippi river valley Mon night/Tue. Broad low level thermodynamics will precede the upper level forcing while an attendant north-south running sfc cold front currently set to track across the region Tue afternoon/eve. Potential 300 mb jet streak Tue could enhance lift along the front via its right entrance region. Broad area of rain should break out/shift in from the west late Monday afternoon, night in response to the thermodynamics. Not much for instability at this time but couldn`t rule out at least a few storms thanks to the nose of a 50 kt 850 mb jet. Favoring mostly rain though. Moving into Tue, more bits of shortwave energy/MCV will come into play along with the cold front. Questions on how much cloud cover/rain early in the day will be lingering with impacts on atmospheric recovery/destabilization. SBCAPE in the LREF currently progged from 1-1.5+ J/kg in the afternoon with favorable deep layer shear to support strong/severe storm development. VERY conditional with a lot of unknowns - that may not become more clear until the actual day. While the severe threat is murky at this time, the potential for heavy rain is a bit more clear. PWs in the LREF pushing near 2+" while ECMWF and NAEFS PW anomalies creep up to 2.5. EFIs even edging above 0.70. Add in the persistent low level jet and moisture transport with warm cloud depths from 4 to 4.5 kft and the setup is very favorable for heavy rain. Obviously how the system unfolds, where the variety of forcers set up/move, and potential training are all important factors that are much less clear. Still, as it sits, the setup is there and will have to be watched closely - especially given the ongoing flooding and/or high running river systems. More water is not needed. * THU/FRI RAIN CHANCES The GEFS and EPS continue to trend toward rain chances for the end of the new work as the both shift an upper level shortwave from the PAC NW eastward across the region. However, not all their members agree on timing/placement for the resulting QPF - a few even suggest it could be dry, shifting the pcpn away from the area. Less agreement compared to some previous model runs. Given the currently progged upper level dynamics, still looks like a good shot for rain, albeit with potential to shift in location/timing. On the plus side. the heavy rain parameters via the GFS are shifting more south and east of the local area. A trend the area would welcome given the recent heavy rain and expectations as we move into the early part of the new week. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 111 PM CDT Fri Jun 28 2024 MVFR to IFR ceilings have prevailed into the early afternoon, with lowered ceilings (NBH probs for MVFR 70+%) continuing into this evening/early tonight. Additional chances for showers and thunderstorms increase this afternoon and evening. However, with lower confidence in exact evolution of these storms will remain with a vicinity mention of thunder for now. Will continue to monitor and make short term updates if necessary. Increased south winds ease some tonight before turning more northwest and increasing into the day Saturday. && .HYDROLOGY... Issued at 425 AM CDT Fri Jun 28 2024 With three more periods of precipitation ahead - today into tonight, Monday/Tuesday, and Thursday/Friday - area rivers will remain swollen. Both of those first two rounds in particular show the potential for many areas to pick up around another 1-2". Given this and the large amount of water flowing downstream, the Mississippi River is expected remain in minor to moderate flood through at least the next five days. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Rieck AVIATION.....EMS HYDROLOGY...Ferguson