Strong Storms Possible Monday & Tuesday
by Angela Schilling, Meteorologist
March 25, 2012 12:00 AM
Potential is still there to see a few scattered showers and thunderstorms Sunday night, some of them could produce some small hail, but we’re not looking at anything severe. Around 5:30pm Sunday afternoon we did get some reports of penny-sized hail in Spink county, but the storms didn’t last long and are weakening as they move east. As we progress into the overnight hours a low level jet will move north, possibly sparking a few more showers and storms, but again we’re not looking anything too strong Sunday night. If we get any rain in the Sioux Empire over the next 48 hours it will probably be late Sunday night into Monday morning, as the low level jet moves north. The image below shows water vapor, the green color over the Rockies shows an increase in moisture…notice how it’s moving in our direction.
By Monday afternoon a potent area of low pressure will be much closer, and central South Dakota will be in a much more favorable environment for storms to thrive. Some of the storms tomorrow afternoon could be severe, with a slight risk for large hail and damaging winds. The image to below shows a slight risk from Bismarck, North Dakota to just south of Chamberlain.
(Monday) Slight Risk = cities shaded in orange...Non Severe Storms = yellow
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You can think of a severe weather event as a recipe with certain ingredients required. Some recipes require more of one ingredient than others, and sometimes the recipe doesn’t pan out like you planned. Along with an early start to spring/summer comes an early start to severe weather season in the Northern Plains. A potent area of low pressure will make its way eastbound beginning Sunday night and exiting the region by Wednesday morning. Some of the storms could be on the strong to severe side, especially on Monday and Tuesday. Monday’s event calls for the following ingredients: a warmfront lifting northward, an area of low pressure moving east, plenty of moisture, and lots of wind.
A warmfront is just what it sounds like, the leading edge to a warmer air mass. Get behind the warmfront and you’re in what’s known as the warm sector. While in the warm sector, our winds typically come out of the south or southeast, not only drawing in warmer air but also moisture (higher dewpoints). With a warmfront overhead, we will have enough fuel to keep storms developing throughout the day on Monday.
An area of low pressure will make its way eastbound over the next several days, with a cold front swinging through by Tuesday afternoon. Once the cold front swings through the majority of the moisture or fuel for the storms will have dissipated. Out ahead of the cold front conditions will be favorable for storms to develop. The low itself will act as a forcing mechanism to help get storms going, and possibly getting them to rotate. Besides an unstable atmosphere you also need shear for strong storms to occur. With an area of low pressure, or shortwave heading in our direction, it will create a decent amount of shear over the Northern Plains. You can think of shear as a change in wind direction/speed with height. On Monday our winds will be coming out of the west aloft and out of the east southeast at the surface, before switching to out of the south by Monday evening. Positive vorticity or “spin” is a term meteorologists often use to forecast rain…positive vorticity advection can cause uplift or get rain to occur. You can think of advection as transferring something into another area, so as an area of low pressure travels east it is advecting positive vorticty into that area. As a result it is not when the low is overhead that we see rain, rather it is when the low is approaching.
During severe weather season a dryline is another way to get storms to form. A dryline simply separates dry air from humid air. By Monday afternoon a dryline will set up just to the east of the cold front, triggering a few storms as it moves from the west to east.
When pinpointing severe weather you want to look for boundaries. Whether that means a separation between dry air and humid air or high cape values to low cape values, all boundaries are key when it comes to forecasting severe weather. By Monday afternoon, the highest cape values will be found in central South Dakota, it is around there severe storms are most likely to fire up. The main threats will be damaging winds, large hail, and possibly even a few tornadoes.
Regardless if we get severe weather or not, winds will be quite strong, coming out of the east out ahead of the warm front on Sunday, before transitioning to out of the south by Monday night. Wind speeds will be anywhere between 20 and 40 miles per hour, with gusts upwards of 50 on Monday.
Make sure to stay tuned to KDLT and KDLT.com for the very latest.