Storm Prediction Center Update: 8/9/17

The Storm Prediction Center (SPC) Outlook shows some severe threats this week.

Day 1:  Marginal Risk

There are several marginal threat areas for the remainder of the day.  All of them have less than a 2% chance of tornadoes.

All three Marginal Risk areas are in place due to the boundary layer instability and ample moisture in these locations.  Storms have already fired, and will continue into the evening hours.   The northernmost Marginal Risk area is aided by a trough that is digging south just west of the risk area.


Day 2:  Slight Risk

Day 2 shows a Slight Risk over the central High Plains.

A longwave trough dips slightly south into the central Great Plains.  By itself, this is not a weather-producer.  However, a shortwave will pass along the longwave trough like a ripple in the top of a wave, which will add some upper-level energy to the area.

The air mass ahead of the shortwave impulse is damp, and there is a stalled cold front to provide additional lift.  Also, this area is especially prone to upslope flow, so storms are likely.

Given the 40-55 kt deep-layer shear, supercells are possible, and the primary threats will be gusty winds and large hail.


Day 3:  Marginal Risk

There are two Marginal Risks in place for Day 3, one over the central High Plains and one over the deep south.

In the south, an upper-level trough and associated cold front will push into a moist air mass.  While deep-layer shear is expected to be high enough to support marginally-severe storms, the lapse rates are not very high.  With the mediocre lapse rates, storms will be limited, though possible, hence the Marginal Risk.

In the Central High Plains, there will be another moist airmass, with adequate deep-layer shear, but, once again, lapse rates will be the limiting factor.  Unlike the south, however, there is upslope flow in this region, so storms are possible, and storms that form will have gusty downdraft winds and large hail.



Day 4-8:  Predictability Too Low 

Day 4 may upgrade to a Marginal Threat, low-level moisture increases over the central Great Plains and may destabilize due to diurnal heating.  Upper-level flow may increase the deep-layer shear, but no major disturbances are expected.

In the northeast, the upper-level trough may boost some convection, as the associated cold front pushes through a damp boundary layer.

After Day 4, the models begin to diverge significantly.  Another upper-level trough may begin to develop, but there is no converging solution at this time.

Thank you for reading this post.

All data and images are from the Storm Prediction Center Website.


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 Models, Practicing Concepts, Predictions, Severe Weather, SPC 1-7 day and tagged , , . Bookmark the permalink.

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