THE MADNESS OF MARCH...
We're setting up for what looks to be a wild week of weather around the Midwest. Near record temperatures, severe thunderstorms, and a return to wintry weather conditions potentially featuring snow and much colder conditions . It all adds up to March Madness in the weather office. Let's dig in.
SPRING STORM SATURDAY...
After a "noticeable" cool-down Thursday, warmer air surges back into the region Friday and especially Saturday. The system seems to be behaving about as expected with low pressure emerging over Colorado Friday and tracking into NC Iowa Saturday evening. That puts my area in the warm sector of the storm Saturday and in a position where showers and thunderstorms can be expected. Here's the EURO surface depiction at 6:00pm Saturday indicating the surface low over NC Iowa. A cold front and dry line trails through central Iowa into Missouri. A couple bands of thunderstorms are shown in the warm sector ahead of the front in Iowa
The EURO's flash density product indicates plenty of lightning in the two bands.
The K index, which is a measure of thunderstorm potential based on vertical temperature lapse rates, and the amount and vertical extent of low-level moisture in the atmosphere is 30-36. That implies scattered to numerous thunderstorms.
Two issues to keep and eye on regarding the overall strength of any storms are moisture and temperatures. Those will be key to how much instability will be in place for the front to act on when it arrives late Saturday. Dew points are forecast to reach the mid to upper 50s. That's good for March 5th but no where near summertime levels which reach well into the 70s, (even low 80s on occasion). If these numbers increase into the low 60s by Saturday that would enhance instability.
Additionally, sunshine of any magnitude would raise temperatures. Current highs are generally in the range of 62 to 70 from north to south. Highs more in that 70-75 range would also raise instability levels. The satellite below does show some holes in the clouds around mid-day Saturday. If the openings are more significant that would drive up temperatures. On the other hand, if there is more cloud cover than indicated cooler readings would diminish the severe weather potential. No matter what, temperatures in my southern counties could peak close to record levels which are indicated below for some of my communities. Three of these records go back over 100 years.
RECORD HIGHS FOR SATURDAY MARCH 5TH...
The Quad Cities (Moline) 69, 2009
Cedar Rapids 72, 1921
Dubuque 69, 1921
Burlington 73, 1910
As it is, projected warmth and moisture results in marginal CAPE values less than 1,000 j/kg. That's meager by severe weather standards but it could be all some areas need with low level shear sufficient for rotating storms and perhaps a brief tornado threat, especially closer to the surface low and triple point in central Iowa. This appears to be more of QLCS type tornado threat where fast moving bows within a line produce spin ups, somewhat similar to what happened December 15th. Saturday's system is not near as strong so this would be on a much smaller scale of intensity and coverage.
The Storm Prediction Center has much of Iowa currently under a slight risk of severe storms. At this point, I think the greatest threat looks to be just west of my area, perhaps a few of my counties in eastern Iowa might get in on a strong storm or two. It's still too early to say for sure but that's what my gut is telling me. Friday's data should confirm my thoughts. I also think there will be many dry hours Saturday with some spots in the SE avoiding rain entirely until Saturday evening. That means time to enjoy those unseasonably mild temperatures! Here's what the EURO and GFS indicate for rainfall totals.
A SNOW SYSTEM MONDAY?
Showers and storms will depart later Saturday night setting the stage for colder weather to return. While Sunday will be dry, it will be breezy and cool with highs ranging from the low 40s north to the upper 40s south. As the cold deepens it sets up a boundary for the next system to ride northeast on Monday. This time my area is in the cold sector and any part of my area impacted by the storm will see snow.
As always seems to be the case, we have some large disparity among models regarding the track and intensity of the system. The EURO is more amplified, stronger, and further north with the system indicating several inches of snow for most of my area. The GFS is flatter and less phased with a weaker surface reflection. That limits the snow band to my far southeastern counties. I can't say with certainty but I feel the more amplified solution of the EURO is more likely to verify. At any rate, here's what models are currently showing. These are not forecasts, just raw model guidance used to determine trends and later forecasts.
The 12K NAM
After this disturbance passes, the upper air pattern remains in a favorable position to allow plenty of cold air access to the nation. The GFS 10 day temperature departures March 9th to the19th shows the majority of the nation with well below normal temperatures.
The EURO looks particularly cold March 13th with departures as much as 40 degrees colder than the norms. Ugh! Hopefully that trend eases in coming days.
Whether the snow materializes or not, it's looking pretty likely we won't be seeing these spring-like temperatures we've enjoyed much of this week after Saturday for some time. However, it was nice while it lasted and it should give us all encouragement that the sun is getting stronger and stronger and there's better days in the not so distant future. Happy Friday and roll weather...TS
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