Tuesday Night Outlook
Tuesday, February 27th, 2007Text From The RACES Tuesday Night Net:
High temperatures on Wednesday will be in the upper 30’s, with nightly lows in the lower 30’s. Thursday our highs will reach the mid-40’s, with lows swinging back to the upper 20’s for Thursday night. Friday through the beginning of next week high temperatures will stabilize in the lower to mid-30’s, with nightly lows in the upper teens to the lower 20’s.
A storm system will form over the Plains Wednesday and move into the Great Lakes on Thursday. This will bring us light rain on Wednesday afternoon, changing over to a mix of rain and snow Wednesday evening, then switching back to rain after midnight. Thursday we will see rain showers and a chance of thunderstorms. The SPC Day 2 Outlook currently places a slight risk for severe weather just south of the area. Thursday evening we will see light rain and snow showers, changing over to light snow showers after midnight. Friday and Friday night we will have a chance of light snow showers. The precipitation should taper off early Saturday morning, leaving the rest of the weekend mostly cloudy. Skies will clear to partly cloudy or mostly sunny by Monday and Tuesday.
Detailed Forecast Discussion:
The West Coast upper trough will deepen and translate eastward into the Rockies over the next 24 hours, inducing surface cyclogenesis across southeast Colorado. Models are in fairly good agreement with regards to the evolving system, with the system expected to track east-northeast toward the Great Lakes on Thursday. The GFS and NAM are similar with the strength and track of the storm, with the NAM being a bit stronger and further north. We’ll follow a blend of the two solutions for this forecast package.
The lead shortwave ahead of the main system is still forecast to eject east-northeast on Wednesday, spreading light precipitation across the forecast area from southwest to northeast during the afternoon. Forecast soundings indicate that the precipitation will be mostly liquid in form, with perhaps a little freezing rain or sleet across north-central Illinois north of I-88. Better chances for rain arrive Wednesday night, as isentropic lift increases markedly ahead of the approaching system. Enough warm air will be advected northward into the area that precipitation should continue to be mostly rain, except for a rain/snow mix along the Wisconsin border. Rain, possibly heavy at times, will continue into Thursday, as the surface low tracks from eastern Kansas into eastern Iowa. Scattered thunderstorms will also be a good bet, as elevated instability increases across the area. The best surface-based instability will remain further south across central and southern Illinois, where strong to potentially severe storms are possible as indicated by the latest SPC Day 2 Convective Outlook. The main hazard to the local area with this event will be potentially heavy rainfall, as a 50-60 KT low level jet brings ample Gulf moisture northward into the area Wednesday night and Thursday. The 12Z model runs and HPC guidance continue to indicate 0.5-1.0″ of rain, with locally higher amounts possible along the tracks of the scattered thunderstorms.
The low tracks into central Wisconsin Thursday night, bringing an end to the steady precipitation. Colder air will advect southward into northern Illinois overnight, changing any lingering precipitation over to snow. At this point, it appears the bulk of the wrap-around snow will occur just north and northwest of the forecast area. However, we could see a light accumulation across the area, with the highest amounts between 1-2″ along and north of I-80.
