Storm Prediction Center Update: 5/20/20

The Storm Prediction Center (SPC) Outlook shows a moderately active week, with a lingering storm system dropping tornadoes this evening.

Day 1:  Slight Risk

The SPC continues to issue two Slight Risk areas:  one for eastern Montana and one for west central Texas.

Associated with the Slight Risks are 2% Tornado threat rings:

The Montana threat is in an area with some instability (CAPE 1500-2500 J/kg).  Shear is directional, at 45 kts in the 0-6 km range, which will support supercells.  Large hail is the primary threat, with damaging winds taking over as storms weaken.

The Texas threat is near the western edge of a corridor of moderate instability (CAPE 2500-3500 J/kg).  There is good shear (50 kts in the 0-3 km), supporting supercells, with hail as the primary threat.  As the sun sets, the cells will become more multicellular, with damaging winds taking over as the primary threat.


Day 2:  Slight Risk

The SPC is calling for a bullseye of Slight Risk over the Texas and Oklahoma Panhandles.

Associated with the Slight Risk is a 2% Tornado Threat Ring:

An upper wave will be moving out of the region, as moderate, mid-level westerlies and southerly surface flow continue in the region.  There is still ample moisture in the region.  Storms are expected to fire over southeastern Colorado and northeastern New Mexico, and move east.  Large hail, damaging winds and a brief tornado are possible.

Day 3:  Marginal Risk

The SPC has issued a Marginal Risk for most of Oklahoma on Day 3.

Moisture will continue to advect northward into this region, raising dewpoints into the 70s F.  Surface troughing, as well as some upper-level perturbations will enhance thunderstorm growth.  It is possible that storms from Day 2 may reintensify in this region.  Storms may start out as supercellular, but they will quickly morph into a complex with embedded supercells.   Large hail and damaging winds will be the primary threats.

Day 4: 15% Probability

The SPC is calling for a 15% probability of severe weather in the Northern Great Plains on Day 4.

A shortwave trough and continued moisture advection will contribute to this threat.  At this time, a likely scenario is that a complex forms and propagates southeasterly, with large hail and damaging winds as the primary threats.


Day 5-8:  Potential Too Low/Probability Too Low

After Day 4, the pattern settles down a little bit.  More zonal, mid-latitude westerlies look to take over, limiting severe weather.  On Day 8, there may be a shortwave trough near the US/Canadian border, which may bring with it the chance of severe weather, but the models are not consistent at this time.

Thank you for reading this post.

All data and images are from the Storm Prediction Center Website, accessed 5/20/20.

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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