Tuesday, May 11, 2010

Typical early May pattern changes continue

One thing that can be said about the weather the past couple of weeks - persistence forecasting doesn't work! It seems like every few days another shift is taking place in the atmosphere, taking us from one extreme to the other - from severe weather, to flooding, to 90 degrees and humid, to cloudy, cool, and breezy, and now right back to near 90, followed by scattered afternoon thunderstorms! Just so that you don't start putting the blame on your favorite flavor of climate change, understand that rapid changes in the weather this time of year are perfectly normal. In fact, spring may be the time of year that the phrase was coined, "if you don't like the weather, stick around; it'll change!"

This week, we're coming out of a cooler pattern that brought us nice conditions over the weekend into one more typical of early summer. A warm front is moving through the region today, bringing an end to the cool weather and placing us back in a "warm sector" that will mean increased humidity, southerly breezes, and temperatures well into the 80s. As high pressure builds over the southeast U.S. (see upper-level forecast map below), upper 80s to near 90 temps and dewpoints in the mid 60s will be common. The high dewpoints, mix of clouds, and steady southerly wind will also mean warm overnight lows near 70 in the metropolitan area.

500mb chart valid Wednesday evening (5/12/10) - click for larger image

These conditions will last for a few days before another cold front approaches the area on Friday. Unfortunately, but not atypically, the strength of the high pressure over the southeast will keep that front from moving through quickly, which will result in daily chances of thunderstorms, primarily of the afternoon and early evening variety, Friday through the weekend. Early signs point to a upper-level trough that will move into the Mississippi Valley early next week which would finally push the front away from the region (see upper-level map below and note the differences from the map above). Depending on cloud cover and precipitation, high temps this weekend should be in the mid 80s with overnight lows remaining in the 60s. The average high temperature for this time of year is near 80 with lows typically dropping to near 60.

500mb chart valid Monday evening (5/17/10) - click for larger image

For the latest forecast conditions on a daily basis visit MemphisWeather.net and the MWN Forecast - the most accurate for the Memphis area.

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