Tuesday, April 09, 2013

SPC Outlook for April 9th and 10th

The Storm Prediction Center is a branch of NOAA and the NWS that issue outlooks on severe weather, severe weather watches, discussions on ongoing severe weather (MDs), and fire outlooks. Before I wanted to go the television route, this was my dream job. Maybe I'll do that when I grow up.

Let's first talk about the Day 1 outlook for today, April 9th. This is an animation showing the probability of hail, probability of damaging wind, probability of a tornado, and the actual Day 1 outlook:
Notice there is a moderate risk (red) for parts of Texas and Oklahoma. We talked about this possibility last night at 10:00. The probabilities of severe weather dictate the outlooks. Look at this conversion chart from the SPC:
 So, by looking at this chart, the reason that parts of OK/TX are in a moderate risk are not specially because of the tornado threat (10%) and not specifically for damaging winds (30%), but for large hail, with a 45% hatched area. That means that there is a 45% chance of severe hail (1"+) with 25 miles of any given point in that area. The "hatched" area means there is a 10% or greater chance of significant, severe hail of 2" or greater! The Day 1 outlook is broken down to the three forms of severe weather: hail, wind, and tornadoes.

The Day 2 outlook combines all three for the probability and the conversion chart is different. Here's the Day 2 outlook and probability of severe weather:

If you notice, there is a large area with a 45% probability of severe weather. The conversion table is different on the Day 2 outlooks. Here is the chart:
  So, why is there not a moderate risk on the Day 2 outlook? WELL, while there is a 45% probability of severe weather, it is not a HATCHED area (yet) for significant, severe weather. This Day 2 outlook is the closest to a moderate risk without being a moderate risk that I have seen from the SPC. But, their reasoning make perfect sense.

If SPC still thinks there is a 45% chance of severe weather tomorrow, there will at least be a moderate risk for Region 8. We will wait and see.

Have a great day. More on the severe weather threat later today here and online.... and on Twitter at @ryanvaughan throughout the day!


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