Storm Prediction Center Update: 5/31/17

The Storm Prediction Center (SPC) Outlook does not show much severe weather action over the next week.

Day 1: Slight Risk

There are two Slight Risks issued today; one is over New England and one is over the central Great Plains.

The New England Slight Risk also has a 2% Tornado Threat Ring:

The threat over New England shows CAPE values exceeding 1000 J/kg and adequate deep-layer shear to support rotating storms this afternoon.  The primary threat will be large hail and some storms may have gusty winds.  Currently, the surface winds are backed near the Hudson River, in which case, an isolated tornado or two is possible.  If the winds shift, this tornado threat will decrease.

Day 2: Marginal Risk

There are three broad Marginal Risk regions:  one over Montana, one near the Red River and one over IA/MO.

The primary threat in all three of these regions will be large hail and gusty winds.

The Montana threat is due to the combination of a shortwave trough and steep lapse rates.  Moisture will be limited, leading to inverted-v  type soundings, perfect for virga bombs and downburst winds.

The IA/MO threat stems from adequate moisture and some weak Warm Air Advection (WAA).  Initial storms may be weak, but new storms could form along the outflow boundaries generated by the initial storms.  This would extend the threat of hail into the overnight hours.

The Red River threat relies on a stalled frontal boundary, ample moisture (70 F+ degree dewpoints) and a weak shortwave trough.  Given the abundant moisture, wet downbursts are the primary threat.  However, ongoing thunderstorms associated with the shortwave may limit convective potential.

Day 3:  Marginal Risk

There is a Marginal Risk extending from the Dakotas into Indiana.

This threat is based on the interaction between a shortwave trough and a surge of moisture (60 F+ degree dewpoints).  There will be adequate deep-layer shear to support rotating storms, though tornadoes are not mentioned as a threat.  Large hail and damaging winds are the primary threats of this setup.

Day 4-8:  Predictability Too Low

On Saturday and Sunday, a trough will deepen through the northern Great Plains, and move east into an area of better moisture.  Also, a cold front will move south into the Ohio River Valley.   Storms that form along this cold front could become severe.  After Sunday, this cold front would continue south into ample moisture.  However, the models begin to disagree on spacial placement of the severe threat.

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.
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