Thursday, December 19, 2013

Increasing Flooding Threat & Possible Severe Wx


The Storm Prediction Center has upgraded most of Western Kentucky and NW Tennessee to the Moderate Risk outlook for severe weather, including the threat for damaging winds and tornadoes. Here is the latest map from SPC:
Storm Prediction Center Outlook for Severe Storms on Saturday
The National Weather Service in Paducah, KY has posted this very informative web video discussing the timing and threats associated with storms headed our way this afternoon along with flooding details.

A WEATHER AUTHORITY ALERT DAY has been declared starting Friday night running through Sunday Morning.

Projected rainfall totals are holding pretty tight and havent changes a whole lot since yesterday. Below is a little more refined map updated Fri evening concerning total rainfall expected from Friday night ending Sunday morning. Isolated areas of 5-6" will be possible, especially with heavier thunderstorms. The severe weather threat is still a feature of this storm system that we are concerned about. We remain in the Slight Risk outlooked area issued by the Storm Prediction Center for Saturday. A Moderate Risk is outlined immediately to our SW in Arkansas and Tennessee. Severe storms cannot be rulled out Saturday afternoon and evening as the cold front approached the Local 6 area. Tornadoes will be isolated but winds are a higher threat with any severe storms. Flooding continues to be our highest risk and concern.

Severe weather update from the Storm Prediction Center as of Friday morning. This storm system continues to show a dual threat of flooding and strong storms. See my blog post below. 

It is not very often that you see signal in the weather models, DAYS OUT, that suggests an extreme weather event is about to unfold. Since last Friday, we were looking at a rather potent system that would bring warmer temps, heavy rain, and maybe even strong storms. That signal is still holding in every model run and seems to be focusing the heaviest of rain right over the Lower Ohio Valley, the WPSD Local 6 area.

Projected Rainfall Totals, 12Z Thu GFS Model Data

Scattered showers are expected to begin Friday with under 0.5" of accumulation. The heavier rain is expected to make its arrival by very late Friday night and last into the day on Saturday. From the graphic above, you can see that generally 2-4" of rainfall is likely. If you factor in any additional rain that could fall Sunday, we could easily see totals closer to 3-5" area-wide.

The National Weather Service has issued a Flood WATCH for the Local 6 area to being Friday evening to run through Saturday night. To the left is a map of included counties as of 3pm Thursday. Scattered showers will cross the area during the day on Friday and should amount to about .25-.05". Heavy periods of rain will then begin to move into the Local 6 area by midnight Friday and continue for much of the day on Saturday. A brief break in the heavy rain is possible Saturday late afternoon, especially across Western Kentucky, West Tennessee, and the Missouri Bootheel. This area will be monitored closely for strong to severe thunderstorm development that will likely impact these areas into the late evening. Severe weather is conditional upon the track of the low pressure center over Missouri/Illinois. If it passes further south than expected, rain will likely be continuous, resulting in the higher end of accumulations. Look for additional hour by hour details on WPSD Local 6.

Observed Precipitation since July 1, 2013 (Climate Prediction Center) with a
grid selection of SEMO, SIL, NWTN, and WKY
Flood and flash flood preparations are particularly important with this rain event for a couple of reasons. Over the course of 2013 conditions have been wetter than average for the Lower Ohio Valley and parts of the Mid South. While we have been relatively dry since the winter storm in early December, temperatures have been below normal and a thin layer of frozen ground has persisted. These conditions have kept the soil saturated and with quick melting taking place over the past 3 days, runoff water will become an issue. Low lying and usually flood prone areas are at high risk. Flat residential and commercial areas are also at risk if rainfall rates exceed 1.5" per hour.
Much of this heavy rainfall will occur during dark hours. Water covered roadways can be deceiving depth-wise and whether or not a road has been eroded away. This is why we reinforce The National Weather Service's campaign, "Turn Around, Don't Drown." It only takes 6 inches of flowing water to move a vehicle. Be sure to know alternative routes in case flooding cuts off your primary road networks.
WPSD Local 6 Reporter Robert Bradfield shows how local road crews are preparing for impending heavy rain and the preventative measures they are using to protect properties.

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