what causes storms to backbuild??

i was watching the radar just north of milwaukee earlier and i noticed how the storms stopped at a point just northwest of milwaukee.......the whole line stopped but for 3 hours now storms in the oskkosh area just keep backbuilding over the exact same area seems like 20 miles west of Oshkosh hasnt received a drop of rain while the city has been drenched for hours now, is this some outflow boundary that acts like a blowtorch to the east???? i was just wondering if anyone could explain or if they can send me to a link that does..........


thanks

dan
 
It's not that 'a' storm is backbuilding, but in this case that's where the LLJ is feeding in and new updrafts / cells are forming in the preferred area. They move off to the southeast, another cell forms and the pattern repeats.
 
i was watching the radar just north of milwaukee earlier and i noticed how the storms stopped at a point just northwest of milwaukee.......the whole line stopped but for 3 hours now storms in the oskkosh area just keep backbuilding over the exact same area seems like 20 miles west of Oshkosh hasnt received a drop of rain while the city has been drenched for hours now, is this some outflow boundary that acts like a blowtorch to the east???? i was just wondering if anyone could explain or if they can send me to a link that does..........

Thunderstorms require three ingredients:

1. Moisture. There must be sufficient water vapor (typically measured as dewpoint) to produce unstable air.

2. Unstable air. Thunderstorms almost always form in a "conditionally unstable" airmass. That is, the air parcel is warmer than its environment after being lifted above its "Level of Free Convection (LFC)". Unstable air is typically denoted by a stability index or positive CAPE values.

3. A lifting mechanism. This lift is necessary to lift air parcels to their Level of Free Convection (LFC). Surface heating often acts to decrease the amount of lift necessary for air parcels to reach their LFC, but some lift is almost always required. The source of lift is usually mesoscale, but is sometimes synoptic scale: Fronts, frictional convergence (around lows and troughs), upslope wind, gust fronts, outflow boundaries (generated by previous storms), drylines, sea-breeze fronts, lake breeze circulations, and valley breeze circulations.

Virtually all thunderstorms consist of more than one cell (even supercells). All three of these ingredients must be met for new cell growth and the continuation of the thunderstorm. If not, the thunderstorm will die.

It appears to me the reason thunderstorm cells continued to "backbuild" over Oshkosh, WI was because moist, unstable air was lifted by a warm front at the intersection of a low level jet stream.

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Chris,

I didn't read your entire response, but you did ask if anybody had archived the obs. Plymouth State keeps a metar archive here:

http://vortex.plymouth.edu/sa_parse-u.html

To get a (somewhat) full set of US metars, just set the indent=all in the link that displays in the address bar after making your button selection - all available observations will be retrieved.

Pat
 
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