Sunday, March 18, 2012

Spring Breakers Deal With A BIG Wet Weather Maker!

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We're all going to have to deal with this, but I really want to communicate the message to anyone who has outdoor plans that this could turn into a serious situation.  Thanks to the WeatherNinja for pointing this out to me Saturday.  There will be many campers, hikers, etc across the state that need to have a NOAA weather radio or even consider other plans.  It appears the heaviest rain will fall across western Arkansas which as you know is a very hilly area of the state.  This will contribute to more runoff into streams and rivers causing a possible rapid rise in water levels.

As we have talked about here on the Arkansas Weather Blog for more than a week now, this intense storm system means business.  It will be a very slow mover as it cuts off from the main jet stream flow.  This slow movement will produce copious amounts of rain over the same areas over a 2 day period.  We are hoping this system speeds up and limits the amount of rainfall, but these cut off lows are often difficult to pinpoint the exact track and speed. Even at this time, there are still disagreements with various models as to where the axis of heaviest rainfall will set up.

There will also be a severe element to this storm system, but I think the flooding threat is much higher.  The Storm Prediction Center has placed portions of Arkansas under a slight risk for severe weather and I'll explain below.

We are not expecting this rainfall to start until Monday night into Tuesday and Wednesday.  Remember, turn on your NOAA weather radios and/or sign up for WeatherCall 7.

Below are a few maps explaining the situation.  I'll keep you updated!

The NAM model is much slower and shows total precipitation amounts more than 5'' in some sections of western Arkansas.  Notice the very sharp gradient between the heavy rain and lighter amounts.  This is the only model I have seen doing this, but it's worth watching.  If you believe the NAM, rain won't really start in central Arkansas until Tuesday afternoon.

This is the midday Saturday run of the GFS showing the axis of heaviest rainfall across eastern Oklahoma into western Arkansas.   However, this shows several inches in central and eastern Arkansas as well.  So you see there are some disagreements in the short range at this point.

The late Saturday run of the GFS shows the axis further to the east with 5'' + across the majority of Arkansas.  The GFS is having a tough time with each run pinpointing how much rain will fall.  Like I have said, it's not a matter of if it will rain, but how much?
The next run of the GFS Sunday morning shows the axis back over eastern Oklahoma into western Arkansas with a sharp gradient across central sections.  Lighter amounts are forecast the further east you go, but it could still be significant.  Once you have examined all the data, you can clearly see the consistency of heavy rainfall for western Arkansas.  That's the area that concerns me.
This is the official guidance from HPC showing 8'' + for western Arkansas over the next 5 days.
The Storm Prediction Center has outlined the western half of Arkansas, including Little Rock, for a slight risk of severe weather late Monday into Tuesday.  The main threat will be hail and wind.
The threat continues into Tuesday, especially for portions of central and southern Arkansas.  Remember, it's only slight.  The area is much smaller with hail and wind the main threat.  As I said above, I really think heavy rainfall will be the bigger story.  I'll keep you updated!

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