Mid-Week Flood & Severe Weather Threat

We have gone from worrying about the drought to now worrying about flooding, all in about a 2 week period. The pattern has finally shifted to a more typical spring time pattern with active storms every 3-4 days. The next storm looks really similar to the last storm over the weekend but maybe slightly stronger dynamically with a wrinkle at the end. Lets get right to the nuts and bolts of this thing.

Flood threat

With the recent rains from last week and this weekend the ground is saturated especially across the mountains and foothills. It will take very little rain to cause rapid rises in creeks and streams late Wednesday into Thursday. Below is the Flash Flood Guidance basically how much rain in 3 hours it would take to cause flash flooding. It ranges from 1.8”-2.25” across our area.

2011-03-08_1011

Here’s a look at what the NAM model rainfall looks like out to 84hours. Notice the mountains and foothills receive 2-3”.

2011-03-08_1035

The HPC forecast for the amount of rain matches up very similarly what the model have as well.

p120i12

Severe Weather Threat

day2otlk_0700The storm prediction center has most of the severe weather threat confined to the Gulf Coast. That’s where the most instability will be present. Further north into the Carolinas a wedge of cool air will keep us stable for a while but when the warmer air moves north watch out! This is our typical case of a high shear and low CAPE event. We have loads of wind energy for severe weather but very little instability. It won’t take much warm surface air to cause problems.

 

           Wind Shear Thursday AM                                              CAPE

2011-03-08_10232011-03-08_1024

You can see how much shear there is but at the same time such little CAPE. This is something to watch closely because even very small amounts of CAPE moving north into the area could cause quick tornado spin ups and lots of straight line wind damage. Even without the surface CAPE some elevated thunderstorms could mix down strong winds to the surface. Another interesting thing about this system is the very strong 500mb trough that moves in on the back side. This is a potent trough with very cold air aloft which could cause hail or graupel behind the front. Or likely even some very wet snow even east of the mountains. The snow should be confined to the mountains but something that bears watching.

                        GFS 500mb                                                     NAM 500mb

2011-03-08_10212011-03-08_1022

Notice how cold the air is at 850mb well below 32°F or 0°C. All that dark blue is cold enough for snow if there is any precipitation falling under this trough.

2011-03-08_1022_001

Conclusion and timing:

Look for all of this to start as a cold and rainy Wednesday with temperatures in the upper 40s to low 50s. Then rain picks up late Wednesday into Thursday morning as warmer air tries to move in from the south. The worst of the rain and severe weather threat will be early Thursday. Stay tuned…..

  • Hi Brad

    This is Lee up in Watauga County. With the possibility of snow at the end of this big rain event. Do you think this may be a repeat of last Sunday’s snow. It was basically a dusting in downtown Boone to about a inch were I’m at, which is 4000 ft elev. I’m more worried about flash flooding than snow, but there was a lot of black ice during the snow last Sunday.

    Thanks again
    Lee

  • wxbrad

    Lee, pretty good just like Sundays storm snow levels drop fast behind the front. 3500′ and above will see some wet snow.