Severe Weather Today: 6/25/15

The Storm Prediction Center (SPC) has issued an Enhanced Risk today for a corner of the High Plains.

Associated with this risk is a 2% Tornado Threat Ring. There is a 5% Tornado Threat Ring over the Mid-Atlantic, and I’m sure some of my storm chaser friends in MD/VA/DC will be out chasing today. I, however, will focus on the High Plains threat instead.

What’s So:

The visible satellite imagery shows clear skies over the area of tornado threat. To the northwest, there are some clouds in a mountain wave pattern, which are ahead of the Front Range and an existing Mesoscale Convective System (MCS). To the southeast, there is some clustered clouds from another MCS.

The infrared imagery shows that both of these MCS have high, cool tops, with the system over northwestern Nebraska having higher and cooler tops.

The water vapor imagery shows an approaching shortwave dipping through the Four Corners area.

Zooming into a higher resolution image, there is a dry pocket that extends from Denver, CO, along I-76, then along I-80 through Nebraska.

The 12Z upper air sounding from North Platte, NE, shows that there is a capping inversion present from 850 mb to 600 mb, which is driving the high Convective Inhibition (CIN). There was 87 J/kg of Convective Available Potential Energy (CAPE) this morning.

The 12Z hodograph from North Platte, NE, shows 17 kts of low-level shear, which is enough to support tornadoes, and 21 kts of deep-layer shear.

At Denver, CO, the 12Z upper air sounding showed no CAPE at all, and had similar shear. There was a large temperature inversion present as well.

The SPC Mesoscale Analysis surface observations map shows no distinct dryline; dewpoints are in the low 60s throughout the region, except near either MCS. The surface winds are generally from the southwest, with the exception of a cyclonic flow pattern centered just northwest of Dodge City, KS.

This cyclonic flow pattern corresponds to an elongated 1012 mb low pressure system, shown on the surface pressure map.

The surface-based CAPE map is showing a bull’s eye of 4000 J/kg south of Burlington, CO, with no CIN.

The CAPE roughly corresponds to an area of -9 Lifted Index (LI).
Both the LI and the CAPE are south of the 2% Tornado Threat Ring, currently.

The Lifted Condensation Level (LCL) heights are high, with the lowest values being around 1750 m. High LCL heights are correlated with lower tornado threat.

Currently, the shear is weak over the 2% Tornado Threat Ring.

However, by 1Z, the shear is expected to exceed 40 kts, which is enough to support rotating storms.

Analysis:

Overall, I think there is a lot of energy present to form storms. 4000 J/kg is plenty. However, given the shear is still low, but the capping inversion has almost eroded away, I expect the storms will have fired and congealed before the full potential of this system could be realized.

This is an example of where timing is everything: if the shear was good enough and then diminished, storms could form and then continue rotating through their own momentum. Instead, storms will fire and quickly lose their discrete nature.

The high LCL heights would also reduce the tornado potential. I would expect high-based storms that morph into a mess very quickly.

The low LI (-9) and high CAPE mean that updrafts will be strong. This, plus the low freezing levels (due to the higher altitude) lead me to believe that there will be some large hail. This region is known for more hail days than anywhere else, and I think today may be one of those hail days.

However, with two MCS producing precipitation, there might be some enhanced shear at the storm scale that could produce a brief spin-up or two.

Overall, it looks like a gustnado, severe wind and large hail type of day, rather than a tornado outbreak.

If I were already in the Great Plains today, chasing storms, I would probably hang out near Burlington, CO, and wait for towers to start forming. I think the higher tornado threat will be farther north, but the high CAPE to the south (and equal shear at the moment), has me thinking of going farther south than the 2% Tornado Threat Ring.

The trick today would be to get on the storms very quickly after initiation. Storms will quickly morph into a mess, and will begin to use that 4000 J/kg CAPE quickly, as every updraft has equal access to it, due to the eroded capping inversion.

Thank you for reading my post.

The Severe Weather Outlook is from the Storm Prediction Center website.
The satellite imagery is from the NOAA Satellite and Information Service.
The surface observation and upper level charts are from Unisys Weather.

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About highplainschasing

This blog is about my tales in storm chasing. My name is Seth Price and I am an instrumentation instructor at New Mexico Tech. My amateur radio call sign is N3MRA.
This entry was posted in Practicing Concepts, Predictions, Satellite Imagery and tagged , , , , , , . Bookmark the permalink.

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