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