Tuesday, September 16, 2014

Warm Wednesday, cooler Thursday, then an even warmer week's end . . .

Public weather briefing

The last of our unseasonable cool night will occur this evening as clear skies and light winds provide favorable conditions for cooling off. Tomorrow will be mostly sunny and warmer than today as westerly winds transport warmer air into the southern Wisconsin. Thursday, a shift in winds from the north and east will herald the arrival  of cooler temperatures and some low clouds before westerly winds resume and warm air from the south and west transports in warmer temperatures. Rain showers are expected late Saturday before temperatures dip to below seasonal normals on Monday.


Tonight. Clear with light  winds. Lows around 40.

Wednesday. Mostly sunny with light winds. High around 69.

Wednesday night. Partly cloudy.  Winds become easterly by dawn on Thursday. Low in the mid 40's.

Thursday. Mostly cloudy and cooler. Clearing late. Winds east 5-9 mph. High near 60. Low upper 40's.

Friday. Sunny. High near 68.

Outlook for Saturday through Monday. Partly cloudy Saturday with rain and rain showers in the afternoon and night; clearing, breezy and cooler Sunday.  Highs in the upper 70's Saturday and low 70's Sunday and upper 60's Monday. Lows in the upper 50's to lower 60's Saturday and Sunday morning and in the lower to mid 50's on Monday. [CONFIDENCE: MEDIUM]

Forecast Discussion

With full sun, the high temperatures on Wednesday will easily rebound into the upper 60's.  The passage of a weak but dry front late Wednesday will keep temperatures cooler over the state as another anticyclone builds west and south over the area from southern Canada. As the anticyclone moves east on Friday, warm thickness advection will boost temperatures up to and beyond daily normals for the week's end (average daily high temperature for later in the week 70F; low 49F).

The only wrinkle in an otherwise dry forecast for the week, is the overall fate of Tropical Storm Odile located on Tuesday late afternoon over the central Baja Peninsula of Mexico.  The remnants of the cyclone (primarily the water vapor) are forecast by the GFS to move into the southwestern US and then northeast to the midwest by week's end. If this moisture gets entrained into the broad southwesterly flow ahead of a cyclone moving through northern Wisconsin on Saturday, a wet Saturday afternoon and evening is possible for southern Wisconsin. Clearing conditions will follow in the cyclone's wake on Sunday. After a brief period of cold advection Sunday, warm advection returns Monday afternoon before another Canadian anticyclones builds into the state.

Michael C. Morgan

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