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06/09/2018

Severe Threat With Sunday Storms

The Storm Prediction Center has put our entire area in a Marginal Risk for severe weather Sunday.  That is the lowest category - level 1 out of 5.  Below we analyze timing and threats by what ingredients are present and which are lacking.

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INGREDIENTS

Heat and humidity both remain high tomorrow.  High temperatures will be in the upper 80s to near 90 around the area with dewpoints in the lower and middle 70s.  That is certainly ample moisture to spark storms at any point during the day.

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CAPE values are a bit tricky given the potential timing of more than one wave of storms.  There will be sufficient energy for storms to tap in to, but we will discuss the impact of that in the timing section below.  These factors support another day of hail potential and gusty wind inside the storm, in addition to the heavy rain and thunder/lightning. 

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Notably missing is any mention of ingredients for spin or a tornado threat.  There are no strong indicators or a tornado threat Sunday based on storm ingredients.  We could have 20-30 knots of bulk shear maximum, but without other forcing or wind support higher in the atmosphere, I don't see a strong tornado threat. 

TIMING

Models all agree that our storms will be driven by a southward propagating MCS (mesoscale convective system) like the one you see below.  The issue is exactly when this gets to our area and if we will see more than one. 

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Storm-wise we will be pretty quiet through the morning, but the clouds you see here pose a problem.  More clouds through the morning means less sun which means less heat.  Fewer clouds gives us more heat, increasing storm potential later. 

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The latest model updates, factoring in the storms we saw Saturday, show the potential for more than one round of storms.  By early afternoon you see one such "line" approaching from the north. 

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We will have nearly maximum heating and humidity at this point, but most models agree this early wave could break apart as it moves through our WDRB counties.  While it will still bring some strong storms (see below), it potentially won't hold together very well for our southern counties. 

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The consistent part of the forecast is the storm chance later that night.  We have seen this for a day or two at this point.  Another southward propagating MCS is shown below just before sunset. 

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Based on model guidance and the consistency over the last day, this second wave might hold together better.  That means stronger storms will be possible farther south.  That will be especially true if earlier storms break apart before getting that far south, as the earlier AdvanceTrak images suggest.  Remember the higher CAPE numbers in our southern counties? 

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Please note that storms, potentially some strong ones, continue through the early morning hours Monday.  It is possible we will see strong storms during sleeping hours, so make sure you have a way to receive weather alerts while you are asleep (something that could wake you up in the event of severe weather).  If you need suggestions, use the links at the bottom of this post to connect with me on social media, and I can help! 

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Two rounds of strong storms seems unlikely given the potential timing mid-afternoon and late evening.  For the late night threat to materialize, we either need to give the atmosphere time to destabilize again or keep it unstable all day by skipping the earlier round of storms.  Two rounds of storms is still possible (likely - in fact), but I doubt they would both be strong/severe even though that's what the models are showing at the moment. I expect the earlier round to be much more isolated.

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I'll walk you through these storm chances hour-by-hour during the news tonight at 10, and Katie will have the latest updates for you during WDRB in the Morning from 6-9 Sunday. 

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-Hannah Strong

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