Thursday, November 6, 2014

Coldest Air Of The Season On The Way But, Possible Accumulating Snow First

Public weather briefing

Much cooler weather has settled into southern Wisconsin and it's here to stay. Winds will die down tonight and skies will clear allowing for good radational cooling conditions. Friday should start out sunny, but it will become mostly cloudy with a chance of showers late at night. Below normal temperatures are still excepted for the weekend with highs only in the 40s. Saturday looks to be the best day, but cool. Clouds will once again increase Sunday as attention turns to possible accumulating snow for Monday into Tuesday. Look for much colder conditions by Wednesday, With snow cover and an arctic airmass in place, highs Wednesday and Thursday may struggle to reach 30.


Tonight. Becoming mostly clear. Low around 26. Light winds.

Friday. Partly sunny, then becoming cloudy by afternoon. High around 42. Light wind becoming south around 5 to 10 mph.

Friday night. Mostly Cloudy. A chance of showers. Low around 36. South winds 5-10 mph turning northwest after midnight. Chance of rain 40%. Rainfall less than a tenth of an inch.

Saturday. Mostly cloudy skies early giving way to mostly sunny skies. High near 41. Breezy. Northwest winds 15-20 mph, with gusts to 30, mainly before noon.

Sunday. Partly sunny. High around 47. Low around 30. Southwest winds 10 to 15 mph shifting to the north late.

Outlook for Monday through Wednesday. Monday, snow developing by noon possibly becoming mixed with rain late. Highs on Monday in the low 30s. Veterans Day, light snow early giving way to partly cloudy skies and cooler with highs only around 30 and lows around 20. Wednesday, Mostly sunny, continued cool. Highs in the upper 20s and lows in the upper teens. [CONFIDENCE: LOW TO MEDIUM]

Forecast Discussion

Overnight: Subsidence and decreasing winds behind departing cyclone, will make for good radiational cooling conditions. 850 mb temperatures will hover around -5C allowing lows to dip to around 25. 

Friday and Saturday night: Friday will start out mostly sunny, but increasing warm air advection ahead of the next shortwave will increase clouds as the day wears on. 850 mb temperatures rise to 4 to 6 C and 925 mb temps rise to around 3 C. With decent  mixing, highs on Friday should rise into the low 40s. Only a slight chance of rain Friday night as both the NAM and the GFS have a cold front pushing through after midnight Friday night. The new 00Z NAM shows continued warm air advection and positive vorticity advection as well as moderate Q-vector convergence right along the front. 18Z GFS showing positive vorticity advection and warm air advection, but not as much as the NAM. After frontal passage, clouds will clear by midday Saturday along with subsidence behind shortwave to make for a cool and breezy day. Winds will gust to 30 mph behind front then subside by late afternoon on Saturday. Weak warm air advection develops Saturday night ahead of yet another weak shortwave.

Sunday through Veterans Day: Sunday looks to be the warmest of the next 5 days as weak warm air advection coninues with southwest winds. New NAM and GFS disagree on tuning of weak cold front for Sunday. GFS has it coming through in the morning, while the NAM has it coming though later in the afternoon. If earlier frontal passage occurs, temperatures will be cooler then current forecast. Monday and Tuesday the forecast is tricky. 18Z GFS run came into agreement with its last run and sets up a baroclinic zone just to our south. A rather potent shortwave will move along this zone causing a 850mb cyclone to develop ahead of it and move it northeast to over the area by 06Z Tuesday. Warm air advection along with positive vorticity advection will help cause vertical motion along this zone. GFS has precip in the form of snow to develop by 18Z Monday and continue Tuesday morning before tapering off. Liquid estimates are between .3 and .5 inches which would be about 4-5 inches. The ECMWF shows a much bigger storm system with a well organized surface cyclone passing south of the area across northern Illinois. This is a favored track for significant snow for southern Wisconsin if gulf of mexico moisture can get tapped. This run was similar to the 12Z run on Tuesday placed the surface cyclone in almost the same spot. After the storm exits, an arctic airmass will drop into the northern plains and upper midwest with 850 temps dropping to -12 to -14. Highs on Tuesday and Wednesday may struggle to reach 30 especially with a fresh snow pack. 

Ross Braatz   


  1. Stayed cloudy overnight so temps did not fall as much as anticipated. Forecast still looks on track with the obvious question mark being Monday's system. NAM now coming into agreement with the GFS though a bit warmer and further north with baroclinic zone. Confidence is growing in first major snow event beginning Monday

  2. Ross and Ryan - Overall a nicely done job with this particular set of blog posts! I think that you did a really nice job discussing some of the model variability with respect to the potential storm that ended up dropping most of the precipitation to our north. Furthermore, you integrated a lot of great diagnostics for precipitation and vertical motion throughout both of your blog posts. Some ways that these posts could have been further elevated would have to included some images that supplemented your discussion (i.e. something related to the development of the winter storm, etc). Additionally, make sure you provide some details about what the expected impacts may be from such a winter storm. For example, on the first day of your posts you note the development of the storm in your public briefing, but you don't provide much in the way of details there about what the impacts may be. You do fix this for the second day, however, which is good to see. Lastly, make sure that your write-up is grammatically sound, as there are a few typos throughout that I was able to catch, and don't forget to include a brief reflection discussing the overall success of your forecast! Overall, though, solid work here!


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