IT'S ALL ABOUT TIMING...
When it comes to severe weather in early Spring, it's all about timing! Moisture and heating are critical ingredients and it's challenging to to get that combination in abundance as we're still transitioning from winter. Occasionally those ingredients do come together and then you are in the game. However, to hit the home run for a severe weather outbreak, you need the forcing and wind shear to coincide with the instability the warmth and moisture can generate. As happened with the last two significant weather events (one in December, the other in March), it looks like those factors come together over western Iowa Tuesday afternoon leaving my area on the outside looking in. (Most of you are happy about that)!
As it stands now, the Storm Prediction Center has an enhanced risk outlook in place for much of central and western Iowa.
That area looks prone to all forms of severe weather as a deep low pressure tracks toward NW Iowa Tuesday afternoon. As the surface low approaches it will draw a warm front into Iowa during the afternoon. Moisture will increase substantially with dew points climbing into the low 60s. That and highs in the upper 60s and 70s will generate substantial instability. The HRRR shows this for CAPE (convective available potential energy). Easily the highest we've seen so far this year.
Additionally, near the warm front and triple point backed winds will lead to significant shear. That allows for rotating thunderstorms or mesocyclones. These can generate all forms of severe weather and are the primary producers of tornadoes. Here's the supercell index.
The significant tornado parameter is also at high levels and supportive a few long tracked tornadoes. No guarantee but certainly threatening in parts of WC and NC Iowa. Despite some of these parameters being high further east in my area (eastern Iowa and much of NW and WC Illinois), there is no forcing to generate storms until late night. By then much of the instability has weakened due to nighttime cooling. A few active storms could reach my western counties well after midnight but may not make it to the Mississippi by daybreak, that's if they even hold together. There's a pretty healthy line going into central Iowa around 10:00pm but little if anything left by the time they reach the western Illinois border.
So for my area, timing is the saving grace as we are unlikely to see any severe weather here Tuesday or Wednesday. The primary action stays west Tuesday and kicks up again to the east in southeast Illinois Wednesday. There is a chance a few storms could just catch my counties southeast of the Quad Cities Wednesday afternoon but data is pretty conflicting in that regard. With this set-up we may not see much in the way of rain as it splits due to the late night and early morning timing. Here's what models are indicating.
The 3k NAM
In a nutshell, it looks like Tuesday should be relatively quiet here with only a chance of a shower or storm in the north during the afternoon (mainly north of HWY 30). Temperatures will remain mild with the EURO showing this for highs after a cool morning start.
Once rain moves out of my counties east of the Mississippi Wednesday afternoon, the remainder of the week looks chilly and dry as we come under the influence of high pressure. The GFS shows average temperature departures for the 5 day period April 13th-17th to be back below normal after our newfound warmth departs early Wednesday.
By the way, Easter Sunday despite being one of the latest possible is not looking warm. Clouds are expected to be on the increase and highs may not get out of the 40s in all but the extreme south. So far the day looks dry but I'm not completely convinced a rain or snow shower might not pop up, especially late in the north. The GFS shows this for highs.
Here's the temperature departures for Easter which are at least 15 degrees below normal. Sigh.
The late season chill looks to be around for much of April. These are the departures the EURO depicts April 18-23rd
We may not be done with snow yet! Both the EURO and GFS are still showing snow over much of the central and northern Midwest between April 17th through the 28th. I stress not to look at the numbers as they are low confidence, particularly at this time of year. However, snow of any magnitude is a trend none of us want to see. Here's what's on the table.
Well, I guess that's enough pain for one post. We'll keep an eye on storm development late Tuesday and Tuesday night but right now it looks like severe activity should be just off to the west. Have a good one and roll weather...TS