Thursday, March 22, 2012

Heavy cloud, no rain?
- Sting in Ten Summoners Tales

1:10 PM EDT 3/23/12 (Forecaster Jason M.) Earlier this week, a deep upper level trough over the Southwest separated from the main jetstream into a cutoff upper level low. Over the past couple of days, the low has tracked into the southern Plains. A surface reflection of this low is also present over the Southern Plains, making this system a “vertically stacked low” as shown below in the 8:00 AM upper level conditions output from NOAA's Global Forecast System (GFS). 


What is a "cutoff low"? Cutoff lows are notorious for moving unusually slow, and this one is no exception. With the slow and erratic movement of cutoff lows, there is often a relatively high degree of uncertainty in regards to their track and axis of heaviest rainfall. However, most model guidance suggests a large portion of the Southeast will be affected Thursday and Friday, with the system moving into the Mid Atlantic Saturday.

What's expected to happen? A deep feed of moisture in all levels of the atmosphere allowed for torrential rain over portions of Texas and Louisiana Wednesday. This low will weaken over the next couple days as it slowly moves towards the north and east, and as a result the threat for heavy rain may diminish. Nevertheless, localized flooding will be a concern for portions of the Deep South and Mid Atlantic. Thus, this "heavy cloud" is likely to produce a lot of rain, regardless of how it first looks on the radar and satellite loops.

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