Storm Prediction Center Update: 7/5/17

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

Day 1: Slight Risk

There is a Slight Risk over the Northern Great Plains.

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

High dewpoints (60’s F and low 70’s F) and favorable shear conditions led to some supercell development.  At the latest update, there was a cumulus field developing vertically and some storms were beginning to fire.  Forcing has been weak, but the CAPE and shear have been adequate to support discrete cells.


Day 2: Enhanced Risk

Day 2 shows an Enhanced Risk over most of Wisconsin.

A shortwave trough will push southeast out of the Dakotas into to Enhanced Risk area tomorrow.  Associated with this trough is a cold front, which will provide some forcing for storm development.  Dewpoints in the upper 60’s and lower 70’s (F) will occupy the same area as veering deep-layer shear profiles tomorrow over Wisconsin.  The decaying Mesoscale Convective System (MCS) over Iowa will drop a few outflow boundaries that may increase the risk for storms in Wisconsin, depending on their strength and tracks.   Storms will start out discrete ahead of the cold front, but will evolve into a linear complex into the evening hours.  Large hail, strong winds and a few tornadoes are possible with this setup.


Day 3:  Slight Risk

There are two Marginal Risk areas for Day 3:  one over the Ohio River Valley and one over the High Plains.

The Ohio River Valley threat is based on the same parameters as Day 2.  However, the shear will not be as strong in this region (25-35 kts) and lean towards multi-cellular clusters instead of supercells.  The severe threat will be a little lower based on the weaker, uni-directional shear.

The High Plains threat is based on the movement of a surface high pressure system that will begin to funnel moist air back into the Great Plains from the southeast.  As it does, a little upslope flow may lead to the development of a few isolated thunderstorms.  Given the limited moisture, dry, gusty downburst winds will be the primary threat.


Day 4-8:  Predictability Too Low

The cold front will continue east, though it will eventually cut off the warm, moist air, limiting storm potential.  By Sunday and Monday, there will be some Warm Air Advection (WAA) into the Great Plains again, moving in behind the surface high pressure as it drifts east, and between the thermal low developing over the southwestern states.  This increased moisture may increase the chances of scattered thunderstorms.  However, under the northwesterly flow aloft, storms will have a tough time reaching severe limits.  There may be an impulse or two aloft that causes a few storms to become stronger than others, but the models diverge on these impulses.

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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