Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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377 FXUS63 KARX 020848 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 348 AM CDT Sun Jun 2 2024 .KEY MESSAGES... - Dense fog this morning will erode quickly with the June sun angle. Then, a nice day! - Two rounds of showers and storms will affect the area late tonight into Monday and Tuesday again. Rainfall amounts look to be in the 1-2" range for most places. River rises should be expected, with some minor flooding on rivers possible. - Tuesday afternoon and evening still look on track to bring a stronger system through with at least a small chance of severe storms. && .DISCUSSION... Issued at 347 AM CDT Sun Jun 2 2024 This Morning`s Fog GOES low cloud imagery showing fog continuing to expand through WI mainly at 08Z. Development overnight has been more like a classic river valley radiational fog event with the river valleys preferred and other areas then follow. Will continue to monitor the fog development for any changes to the advisory area this morning. Tonight and Monday`s Shower and Storm Chances GOES water vapor loops upstream over the western CONUS show trough energy shifting through the intermountain region but quite disorganized without one hot area of concentration. Two areas draw out slightly in the imagery...near Glacier Nat Park in MT and another wave in NV. Both are players in the forecast for tonight and although the northern wave had 250mb height falls of 60m/12h in ern WA, the NV wave consistently is being convectively enhanced on its way to the local area per CAM guidance. Instability is racing northward tonight with widespread 30-35kt 850mb winds in the radar VWPs over the Dakotas and Neb with 1000 J/Kg of MUCAPE now into swrn ND and ern MT. The 0 MUCAPE line is near or west of I-35 at 07Z. Small convective areas are present on the eastern 850 mb moisture transport convergence gradient from ABR to west of OMA. As the northern MT shortwave trough shifts east today, surface low pressure near the MT/WY border will continue shift east, with the entire pattern, and then weaken and dissipate per RAP forecasts. By 00Z, the MUCAPE gradient is on about I-35 along with the eastern gradient of the moisture transport convergence suggesting that activity should be held west of the area or diminishing rapidly as it shifts east of I-35. Thus, kept rain chances low toward I-35 late today. There are plenty of questions how the overnight details in the storms/showers will evolve with the latest 02.06Z HRRR suggesting an early evening system affecting IA/MN. Overnight the CAPE is slow to shift east and the consensus CAM output suggests waning convection from the northwest, with a convectively enhanced wave /current NV wave/ shifting across IA and into WI for the main rain chances by Monday morning. This wave in IA will enhance the warm advection and moisture transport toward Monday morning, leveraging the moist pool over IA and steered into WI by the mid-level flow. It appears the wave will be into eastern WI by peak heating which could cause a minor severe storm threat east of the area Monday. 02.00Z HREF shows some updraft helicity tracks in srn WI. Will have to monitor this timing closely as any slower timing would pull a threat back into swrn or central WI. Precipitable water values climb to about 1.5" so rainfall rates will be good provided the intensity of the systems moving through are decent. Coverage of storms is still of lower confidence as the system shifts east with a discomfort hanging my hat on a convectively enhanced wave for higher /80%/ rain chances, thus have backed down a bit on those in WI. Tuesday`s Severe Storm Potential Not much has changed in the weather system forecast for Tuesday, although a slight southern track to the dynamic lift and wave track has been noted over the last 24 hours. The instability pool present on Tuesday will be good with ~1500 J/KG of ML CAPE to ~I-90. Even though a moderately strong trough is positioned in the eastern Dakotas late Tuesday, the diffluent flow east of the trough causes quite "meh" mid-level flow and deep layer shear in the warm sector. Even the 0-3km shear is marginal /10-20kts/. Thus, it appears storms will initiate on a stronger cold front near I-35, quickly becoming a linear non- severe system shifting east. Some pulse severe hail storms are possible Tuesday later afternoon initially but current indications are a low threat of a more organized severe weather event. SPC has placed IA/MN and northwest WI in a marginal risk for Tuesday which seems appropriate. There may be a small area of higher risk right on the front during the initiation period. Better storm chances appear to be over southern IA where the wind shear may be better. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1040 PM CDT Sat Jun 1 2024 Maintained a period of LIFR fog at KLSE/KRST early Sunday, although confidence is somewhat higher for dense fog at KLSE (60-90%) compared with KRST (30-60%). Otherwise, VFR conditions are expected through Sunday with increasing southerly winds. There is a lower chance (20-40%) that some weakening showers could reach KRST by later Sunday, but the higher chances for organized showers/storms are expected beyond this TAF period on Sunday night. && .HYDROLOGY... Issued at 347 AM CDT Sun Jun 2 2024 Inspection of some of the Hydrological Ensemble Forecast System Output at the river forecast points in the area suggest that about 3-4" of rainfall would be needed to reach minor flooding on most of the area rivers. There are a few that are a bit more susceptible to lower rainfall amounts to attain minor flooding: the Turkey, Cedar, Lemonweir and the Yellow in WI (already elevated). Forecast rainfall will be refined as we get closer to the Tuesday evening rainfall but at this time it seems 1-2" total seems reasonable for these progressive systems. Thus, believe these two systems will mainly lead to within bank rises. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Dense Fog Advisory until 9 AM CDT this morning for WIZ017-029- 033-034-041>044-053>055-061. MN...Dense Fog Advisory until 9 AM CDT this morning for MNZ088-095- 096. IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ010-011- 029-030. && $$ DISCUSSION...Baumgardt AVIATION...JM HYDROLOGY...Baumgardt