Thursday, October 9, 2014

Beautiful Fall Weather Persists

Public Weather Briefing

**A Frost Advisory has been issued for Dane County until 1:00am Central Time Friday**

Delightful fall conditions will continue through the coming weekend. Daytime temperatures will continue to be in the mid 50s for the next week. Clear skies and light wind spell a recipe for frost Friday and Saturday morning. Perfect fall football weather this Saturday with minimal clouds, winds around 5mph, and a high in the upper 50s. A chance of rain comes in Monday morning, as much as .4inches, but conditions will return to those like this weekend on Tuesday morning.


Tonight. Clear skies, light winds of about 2-3mph. Low 36. Slight chance of frost.

Friday. Partly cloudy with winds around 5-8mph. High of 56.

Friday night. Calm, clear skies. Low 34. Chance of frost.

Saturday. Mostly sunny with high of 57. Light winds out of the south.

Sunday. Partly cloudy becoming overcast in the afternoon. Southerly winds of 10mph. High of 55.

Outlook for Monday through Wednesday. Cloudy through Monday into Tuesday morning with a moderate chance of precipitation Monday afternoon. Rain totals of .4 inches. Temps expected to remain in the mid 50s. [CONFIDENCE: MEDIUM]

Forecast Discussion

A surface anticyclone will enter the Madison area from the northwest Friday and Saturday, whose subsiding air and dry conditions further substantiates our calls for frost. Moving into Monday, we expect a trough axis to form west of our area through Minnesota. As this formation is typically associated with downstream upper ageostrophic divergence, we can expect some vertical motions to help support the possibility of rain. Also supporting our claim is the warm air advcetion from the wave to our west. The 300mb GFS analysis shows a weak jet entrance over our area, which could create more vertical forcing for precipitation.

Daniel Knuth
Rebecca Schultz


  1. I was just looking at the 3z Tuesday GFS model at the 250mb level and that jet stream you mention has dives all the way to Louisiana! The jet there takes an extreme left turn and comes all the way back to Canada virtually right next to the jet that has winds heading south! Also at that same time I noticed huge amounts of vorticity just to the north of Louisiana as it makes that left turn. Not all that much is seen in the vertical velocity right now though.

  2. Interesting observation, Ryan! Any thoughts on why there may not be much vertical velocity despite the strong trough to the west or the maximum in vorticity?

  3. Overall, our forecast and discussion went well. We accurately predicted the conditions throughout the weekend (clear skies becoming cloudy/rainy on Monday). Our forecasted "moderate chance" for rain Monday turned out to be an underestimate, as moderate and at times heavy rain persisted throughout the entire day and into Tuesday. Given our low levels of experience and the variability of a 4 day forecast, we are generally satisfied by our recognizing of the incoming precipitation. Hopefully with more practice we can more accurately diagnose the severity and duration of weather systems such as this.

  4. Becky and Dan - I'd say that there are definitely some great elements to your forecasts over this two-day period. I think you make a decent effort to integrate some of the dynamics/thermodynamics pertinent to southern Wisconsin over the period in your forecast discussion. For example, you do a great job of discussing the elements necessary for frost early in the period and you do well to consider what may be happening at upper-levels. I'd challenge you to provide additional details related to these processes, however. If you diagnose a trough axis to the west, what processes are responsible for the diagnosed divergence? Or, discuss where specifically southern Wisconsin is located with respect to the jet entrance region. These details are definitely important when considering the vertical motions that can be expected. Finally, I think you do a nice job pinpointing that the precipitation was more than you expected Monday into Tuesday, but discuss some of the factors that contributed to this. Nevertheless, there is some nice work here for this first take and I am a huge fan of posting forecast headlines from the NWS. Keep thinking critically about ways to integrate more dynamical diagnosis into your forecasts and you'll be in great shape for the next time!


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