Wednesday, September 23, 2015

Fall is Here! (Sort of)

Public weather briefing

Today is the Autumnal Equinox, but it sure felt quite a bit like summer. The beautiful weather we have had this week is likely to continue over the next couple of days, and we should remain rain-free as we head into the weekend. Storms over the Great Plains could send clouds our way on Thursday, but these should clear up by Friday morning.  Low temperatures tonight may fall a bit below normal, and there is a good chance that it will become very humid overnight.  However, daytime highs in the next few days are likely to reach the mid 70's, exceeding the average temperature by a sizable amount and reducing the relatively humidity to a comfortable level.  Although Autumn is technically here, you can plan on keeping the fall sweaters packed away at least until next week.


Tonight. Clouds rolling in from the West. Lows in the low 50's.

Thursday. Partly cloudy AM, breaking up later in the day. High around 76.

Thursday night. Warm and humid.  Low in the upper 50's.

Friday. AM clouds and PM sun. High near 75. Low in the mid to low 50's.

Saturday. Mostly sunny. High near 76. Badger football kickoff temperature around 68.

Outlook for Sunday through Tuesday. Warm temperatures remain through Monday, with highs in upper 70's. Winds to pick up late Sunday, coming from the southwest.  Cooler and partly cloudy on Tuesday, with a chance of rain and a low in the mid 50's.  [CONFIDENCE: MEDIUM]

Forecast Discussion

A surface low pressure system over Nebraska and South Dakota is expected to weaken as it moves toward a relatively stronger high pressure center over western Ontario.  This should keep any precipitation well north of Madison on Thursday.  In addition, an 850mb high centered over the eastern Great Lakes looks to remain stationary over the next two days, providing Wisconsin with the sustained warm temperatures we are likely to experience at the surface.

Convergence of 850mb geostrophic wind over northern Wisconsin on Monday could force a tighter temperature gradient and produce a thermally direct circulation over the northern half of the state and into Ontario.  The cold air forced downward is likely to result in a (somewhat weak) cold front at the surface, leading to slightly cooler temperatures in Madison on Tuesday. 

Steven Fons

1 comment:

  1. Very good post, Steven! You were definitely right that it stayed unseasonably warm last week. Notes about the humidity were a nice detail to add. In the forecast discussion, remember that the geostrophic wind is nondivergent (on an f-plane which is reasonable for the span of Wisconsin (or a few states, really)). So maybe your first sentence in the second paragraph could describe the full wind instead. You continue with a very interesting diagnosis related to the forecast, although discussing such details 6 days out can be a little risky, particularly with weaker systems that are less structured. Altogether great job!


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