Monday, March 19, 2012

Complex Storm System Brings Flooding/Severe Threat

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6:50 PM Monday update... Not much has changed with my thinking on how this unfolds.  The rain is already coming down across eastern Oklahoma with numerous reports of flooding.  I still think this area of rain will slowly creep to the east and will not arrive in central Arkansas until Tuesday afternoon or evening.  There could be a few showers here and there, but the bulk of the heavy rain will wait until that time.  Western Arkansas continues to be the target for the flooding rainfall starting tonight into Tuesday.  I have read some reports that a few campsites have been temporarily closed anticipating the flooding threat.  I think that was a very smart move.  As the WeatherNinja and I have been talking about, the campers and hikers really need to pay attention to the weather or just plan a trip some other time.

Here are a few of the latest maps from Monday afternoon.

The afternoon run of the NAM shows the highest amounts of rain for western Arkansas with a very sharp gradient the further east one goes.  It's really amazing to see how strong it is.  While some places could receive more than 5'', just 50-100 miles to the east may only get an inch or two.

The afternoon run of the GFS shows heavy rainfall all the way into central Arkansas.  If this looks like it could verify, the NWS would more than likely extend flash flood watches to the east.


HPC's latest rainfall forecast indicates more than 5'' across a large area of western, central, into southwestern Arkansas.  This is total rainfall through the entire event.

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To say this storm system is complex with uncertainties is an understatement!!!! As you know by reading this blog, "cut-off" lows are tricky to predict and it's important we get this as right as possible when it comes to forecasting due to the potential for very high amounts of rainfall.  These lows wobble around when they are cut off and the models handle them poorly.  The one thing we are confident in right now is the high risk for flash flooding across northeast Texas, eastern Oklahoma, into western Arkansas.

Remember, we talked about the rainfall gradient?  The data continues to show there will be a very significant one across the state. This means there will be a very noticeable difference in rainfall amounts over a very short distance from west to east.

While we could get a few showers in central Arkansas today and Tuesday, the heavy and steady rain may WAIT until late Tuesday into Wednesday morning in the metro.  The timing and and placement of these storm systems are tricky so this can change.

There's also the severe element that I'll watch.  Early Monday morning, the Storm Prediction Center placed a very small portion of western Arkansas under a moderate risk for severe weather.  The main threat will be hail and wind, but an isolated tornado will be possible.  The main threat to the remainder of western Arkansas will be heavy rain.

This is spring break.  Please get the word out to anyone spending it outdoors in western Arkansas that they need a NOAA weather radio or maybe even rearrange their plans.  Late this week into the following week, we'll watch rivers rise as water drains out of eastern Oklahoma into Arkansas.  It will be interesting to watch the Arkansas River here in Little Rock and downstream.

Check out the maps below to see all the complexities with the data.

This is the overnight run of the GFS.  Look at the 5''+ amounts across the western half of the state through Thursday.  Also, notice the very sharp rainfall gradient.  The GFS shows it over central and eastern Arkansas while other models have it further west.  The higher elevations of western Arkansas will get the brunt of the rain meaning runoff will be high into creeks, rivers, and streams.  Campers and hikers beware!

The NAM out to Thursday shows the highest rainfall amounts further west over western Arkansas and eastern Oklahoma.  Totals, according to this model, will decrease significantly according to this model so you see the uncertainties.
Our own model, Futurecast, also shows the complexities and uncertainties.  The one thing all the models agree on are the high rainfall amounts across western Arkansas.  This shows 5-7'' in that area of the state.  However, look how much they drop off the further east.  REMEMBER, THESE ARE MODELS AND NOT FORECASTS!!!!!!!!!!!!!!!!!!!!!!!!!!!!
The SPC has placed a very small portion of western Arkansas under a moderate risk for severe weather.  This includes towns like Mena and DeQueen.  The main threat will be hail and wind, but an isolated tornado can't be ruled out later Monday into early Tuesday morning.
This is courtesy of the National Weather Service office in North Little Rock.  This is their thinking right now which is in line with some of the model data I posted above.  Here's a link to their site.  http://www.srh.noaa.gov/lzk/

1 comment:

jimmylee42 said...

Winter time in Ironwood Michigan in the UP. 79 degrees at 1PM. Matches their all time high for the Month of March. Incredible heat for this early all through the upper Midwest. Snowpack is gone. The webcam at Porcupine Lodge in the UP showing only snowpiles left. They had 22 inches only two weeks ago. Marquette Mich has lost their 44 inches of snowpack.