Thursday, October 22, 2015

Relief from drought as a wetter pattern returns to the Mid-South

The last couple of months in the Mid-South have seen very little rainfall and what rain has fallen has not been well-distributed, leading to lengthy dry periods and the development of "abnormally dry" conditions. "Severe drought" conditions lurk just to our southwest in the Mississippi Delta.

Total rainfall for the past 60 days across the south reveals a lack of precip along the lower Mississippi Valley and back into eastern TX. Graphic courtesy WeatherBell.
Conditions are "abnormally dry" across the metro with severe and extreme drought just to our southwest.

In fact, at Memphis International, after a wet start to August, there have been just a few days with enough rainfall to really matter much, and almost none since mid-September. If you throw out September 9th with just over 1" of rain, less than 0.25" has fallen since September 1 and only 0.03" for the month of October!

Precipitation accumulation (green) since August 1 at Memphis Int'l vs. average (brown). Memphis is now 6" below average for the year.
However, Mother Nature tends to have a way of balancing out over the long haul and this weekend will likely make a dent in the rainfall deficit. Unfortunately for those who count on nice fall weather this time of year for outdoor activities, many could be impacted by the rain.

Weekend outlook

Upper level ridging (or high pressure) that has influenced the Mid-South this week is transitioning to a southwest flow pattern, bringing moisture into the area from Hurricane Patricia off the coast of Mexico. Also, an upper level low that has been over the southwest U.S. begins to lift into the central portion of the country. This combination will mean increasing rain chances a bit as we head into the afternoon and evening hours on Friday. Fortunately the rain appears light.

Friday night into early Saturday could see higher rain chances as an upper level disturbance moves across the area, though scattered showers are the most likely outcome. The Saturday forecast has been the trickiest all week and computer models still don't have a good handle on the situation, leading to lower confidence than I would like in the forecast.  It appears that the heaviest rain could fall just north of the metro, but there's a good chance we'll see more scattered showers or periods of light rain during the day. We're not expecting a complete washout, but there could be multiple periods of rain. Also, mid-level instability will rise a bit on Saturday afternoon so we can't rule out a few rumbles of thunder as well.

National surface map for Saturday evening showing the approaching frontal system and moisture from Texas moving north along the front and across the Mid-South.

Saturday night could be wet as a cold front moves into the region and stalls out, which could lead to periods of rain, perhaps moderate at times. These showers will linger into Sunday as the front remains in the area, though once again computer model data is less than convincing on the amount of rain to expect. The NWS indicates that we could see a total of 1-2" of rain by Sunday evening for much of the area with beneficial (and perhaps too much) rain across much of the drought areas in the Southern Plains and areas west of the Mississippi River.

Forecast rainfall amounts from the NWS through Sunday evening. Flooding will be a concern in TX and southern OK while beneficial rain is expected in the Mid-South. Graphic courtesy WeatherBell.

Remnants of Patricia

Also this weekend, as we're dealing with rain locally, Hurricane Patricia will make landfall in western Mexico with remnants expected to cross northern portions of the country and emerge in the western Gulf of Mexico early next week. After doing so, what could be a subtropical low will strengthen off the Texas coast and move northeast. In doing so, it could very well end up moving across the Mid-South.

Model solutions for the low associated with Hurricane Patricia, indicating a northeast track, possibly right into the Mid-South. Graphic courtesy WeatherBell.
Timing on this system is still TBD, but we'll be keeping an eye on Tuesday and Wednesday fairly closely. Should it track across the region, periods of heavy rain and some gusty wind could well be the result, putting a bigger dent in the lingering rainfall deficit as we close out the month of October. Stay tuned!

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Erik Proseus
MWN Meteorologist

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