Wednesday, October 7, 2015

A warm Sun(ny)day ahead

Public weather briefing

Settled and mild weather has been present for a reasonably long period now, with high temperatures in the high 60's and low 70's, as well as mostly sunny skies. This looks likely to end on Thursday as showers and thunderstorms are of high possibility. Over the next few days there will be a good variation in temperatures - Friday will see temperatures below the average for this time of year, whilst on Sunday temperatures will reach the high 70's, much higher than normal for this time of year.


Tonight. Partly cloudy with light easterly winds, becoming more southerly into early Thursday morning. Low around 50F.

Thursday. High possibility of showers and thunderstorms in the late morning and early afternoon. Cloudy throughout the day with a moderate southwesterly wind and strong gusts. High around 74F.

Thursday night. Cloudy and mild, with a small chance of showers in the early evening. Low in the lower 50's.

Friday. Mostly cloudy but brightening up as the day progresses. Light northwest wind. Cooler temperatures, with a high of 59F. Over night will be relatively clear, making for a cold night, with temperatures dropping to around 42F.

Saturday. Mostly sunny conditions. High near 64F, low over night around 51F.

Outlook for Sunday through Tuesday. Sunny and much warmer temperatures for Sunday, reaching around 77F. Monday will be windy, still warm temperatures for this time of year, with a high in the high 60's. Mostly clear on Tuesday. High in the mid 60's. Lows will be in the high 60's over Sunday night and in the mid 40's over Monday and Tuesday night. [CONFIDENCE: MEDIUM]

Forecast Discussion

 Surface high gradually moving east of Madison gives rise to winds becoming light and southerly over Wednesday night. A surface low moving eastward behind it will reach MN by Thursday morning, bringing precipitation ahead of it as warm air advection occurs, with rain expected over Madison by Thursday midday.
 On Thursday evening southern Wisconsin is in the right entrance region of the upper level jet, causing weak upper divergence and upward motion, giving rise to the possibility of precipitation. As the low pressure system moves eastward, away from the area, cold air advection will drag cold air from Canada over Madison. This results in much cooler temperatures on Friday.
 By Friday afternoon the upper level trough axis is to the southeast of Wisconsin, resulting in upper convergence and downward motion. This will bring clearer skies and settled conditions.
 By Friday evening the center of the surface high is across Madison and upper level divergence is neutral. This allows for clear skies overnight, causing strong radiative cooling over night.
 Strong warm air advection is present on Saturday and the upper level jet becomes zonal over southern Canada. A southern flow, along with continued warm air advection for Sunday gives higher than average temperatures for this time of year.
 An upper level shortwave trough is present over northern Wisconsin and strengthens in the early part of next week. Conditions will be settled.

Rich Johnson

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