Storm Prediction Center Update: 7/26/17

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

Day 1:  Marginal Risk

There are three Marginal Risks in place for this evening and the early morning hours.  One of these risks is over the Intermountain West region, one is over the Southern High Plains, and one is over the Middle Mississippi River Valley.

The Marginal Risk over Nevada and California is due to an approaching shortwave trough and a large pocket of damp mid-level air.  The movement of this trough and other factors have raised the deep-layer shear, meaning that gusty downdraft winds are possible.

There is another patch of moisture, and some steep lapse rates across the Southern High Plains, hence the Marginal Risk in this region.

There are currently heavy rains and the potential for flooding associated with the storms that are affecting Illinois at this time.

All three threat areas have a tornado risk of less than 2%.


Day 2: Marginal Risk

Day 2 shows two Marginal Risk areas, one of which is covering a large swath of the South, and the other is over the High Plains.

The High Plains is expected to adequate deep-layer shear to support rotating storms (supercells).  While lapse rates are not expected to be particularly steep, afternoon convection that fires in this region will be well-ventilated.

In the South and Mid-Atlantic, there will be deep moisture, with high Precipitable Water values, in a region of adequate deep-layer shear to support rotating storms.  The major variable is that there is an ongoing Mesoscale Convective System (MCS) that will provide outflow boundaries, but may limit diurnal heating.  The models do not have a good, converging solution on severe storm development, based on this MCS.


Day 3:  Slight Risk

There is a Slight Risk area through much of the South.

As the trough and associated cold front move into the South, storms will form in an area of adequate deep-layer shear.  The moist air mass will also remain over the southern states, meaning that there will be moisture and shear for severe storm development.  However, because the models diverge on the MCS, there is some uncertainty added to this forecast from Day 2.


Day 4-8:  Predictability Too Low

The cold front is expected to move into the Atlantic by Day 4.  A few storms are possible in the Mid-Atlantic Region ahead of its departure.  Storms will be less likely in this region after the frontal boundary passes.

Another low-amplitude shortwave trough may move into the Intermountain West region again by Day 5, but there is some disagreement in the models, leading to the “Predictability Too Low” statement.

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.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s