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Fourthcast: Flash Flood Watch

Overview

You won’t find any jokes in this fourthcast, because it sucks.

An unusually wet weather pattern is arriving, and it won’t change for the next several days.  This will be like a tropical system, full of moisture and thunderstorm chances. Strong to severe thunderstorms cannot be ruled out at any time over the next several days.

But the main story will be rain.  A lot of rain.

Tonight

Rain will be close by. Weather models keep the rain in East Tennessee, but extend it as far west as I-65. This may be our last dry night for a while.

Fourthcast

Our NWS has issued a Flash Flood Watch effective beginning at 12 a.m. Thursday morning through Friday at 7 p.m.

...HEAVY RAINFALL AND FLASH 
FLOODING POSSIBLE THROUGH 
FRIDAY...

.A DEEP SOUTHERLY FLOW OF 
TROPICAL MOISTURE WILL MOVE 
ACROSS MIDDLE TENNESSEE 
THROUGH FRIDAY. THE HIGH 
LEVELS OF MOISTURE COMBINED 
WITH AN UNUSUALLY STRONG 
UPPER LEVEL JET STREAM OVER 
THE REGION WILL PRODUCE 
WIDESPREAD AND PERSISTENT 
SHOWERS AND THUNDERSTORMS 
TONIGHT THROUGH FRIDAY 
EVENING. WIDESPREAD 
RAINFALL TOTALS OF 2 TO 4 
INCHES ARE EXPECTED...WITH 
SOME LOCATIONS SEEING UP 
TO 6 INCHES OF RAIN.

The shaded counties are included in the Watch. Remember, a Watch means conditions are favorable for flash flooding. A Warning means flash flooding is occurring or imminent.

From our NWS:

All weather models forecast rain for us. Let’s just look at the Hi-Res NAM’s “four hour streaks,” which displays (thanks to weatherbell.com) hourly radar images from 1 p.m., 2 p.m., 3 p.m., and 4 p.m. all at once:

Here it is during fireworks:

Notice we’re still sitting on the edge of this system. There may be periods of dry weather at various times on the Fourth. We anxiously await the arrival of the “moisture axis” which will help identify whether we will see an “all-day washout” or “off-on” showers and storms.

There is also a small chance rainfall rates could be excessive. The greatest risk is in East Tennessee, but we are included in the western fringe of the risk area:

Forecast rainfall totals through the Fourth (actually, through 1 a.m. Friday morning) are close to 2″.

Friday – Sunday

Rain is expected to continue. It won’t be a continuous rain, but most of the weekend will be wet. Here are forecast totals through Monday at 7 a.m.:

Note these are estimates — the amounts and locations are subject to change. We will be closely monitoring river heights for flooding concerns. If these totals verify, it would still be WAY below the totals received during the historic May 2010 flood; nevertheless, flooding is statistically among the most dangerous forms of severe weather. Respect flooded roadways – do not drive through them.

Next Week

This anomalous weather pattern continues. Above normal rain is expected next week.

Additional updates and more timely information can be found on Twitter @NashSevereWx.

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