Midwest severe threat taking shape this week

Spring-like temperatures are building in the central US this week, and soon that will lead to spring-like storms from the Upper Midwest to the Southern Plains. The Storm Prediction Center has already issued a Level 2 of 5 risk, a Slight Risk, for Wednesday and Thursday.

Wednesday, storms are forecast to develop rather late in the day. Most of the activity may actually be overnight around the Missouri Valley area from southeast Nebraska through central Missouri. While there is a limited tornado threat, that would wind down drastically after sunset and a large hail threat will take priority.

Hail is especially likely areas along and north of a warm front pushing through the central US Wednesday and Thursday with elevated storms. These elevated hailers could produce hail large than golf balls with the strongest cores.

North American Model forecast for Wednesday.

Global Forecast System forecast for Thursday

Thursday is when things get rather interesting in the Central US. Models differ on the placement of key boundaries including a Warm Front, Dryline and Cold Front. While they may differ 50-75 miles north to south in location, the general idea is about the same.

A tornado threat becomes more pronounced Thursday near the triple point of the Warm Front, Low and Cold Front/Dryline, and this will likely pass through northern Missouri into southern Iowa.

Dewpoints are forecast to reach near 60, which is favorable for severe weather this time of year. The quality of this moisture is one potential limiting factor for the overall severe threat.

Lake Michigan water temperatures

With a strengthening low over the Central Plains, strong easterly winds will develop ahead of it. This wind will cross over the Great Lakes influencing air temperatures. As of Tuesday morning, water temperatures of southern Lake Michigan were in the upper 30s. This will help keep that warm front from surging north.

Given this, I like the idea of the NAM’s more southern placement of the warm front near the Iowa/Missouri border unlike some models pushing it even farther north forwards central/northern Iowa.

NAM forecast Thursday at 6 p.m.

The NAM fires storms by 5-6 p.m. across the Mid-Mississippi River valley Thursday, especially across Missouri which again is likely along/south of the warm front.

CAPE/Instability forecast Thursday at 6 p.m.

With dewpoints in the low 60s, instability should be more than sufficient for severe storms. Mixed Layer CAPE values are forecast off the NAM to be in the 2000j/kg range which is enough for March standards.

0-1km Storm Relative Helicity forecast Thursday evening.

Looking at the low-level spin in the atmosphere, right along and south of the warm front storm relative helicity values should be sufficient for rotating storms along/south of the Iowa/Missouri border. The very high values north of this point is north of the warm front, therefore while hail can be a big concern, a tornado threat would be near non-existent. Important caveat, if the warm front pushes farther north though this changes the outlook drastically for southern Iowa.

This will be a multi-faceted severe weather event this week, and one of the first true spring severe events of the season.

Storm Chase target

If I was storm chasing the above region would be my target area Thursday. Again, while severe weather including large hail and damaging wind could extend up through central Iowa, I think as of this morning’s model guidance the best chance for a tornado would be in southeast Iowa into northeast Missouri.

We get more high-resolution models tonight which should give us a clearer view of the developing severe threat.

-Meteorologist Nick Stewart

Beneficial rain takes aim on central US

The first full week of Meteorological Spring is looking like the part with slightly-above-normal temperatures and a few storm systems which could bring beneficial rainfall to the region - the strongest of which looks to moves through Thursday into Friday.

Rainfall forecast late Monday into Tuesday.

The first storm system will favor areas along and east of I-35 in the Midwest with totals generally under under a half an inch of rainfall. While not a lot, anything is beneficial this time of year heading into the spring plant as widespread drought continues.

Monday’s severe weather risk.

The Storm Prediction Center has added a Level 1 of 5 risk of severe weather, a Marginal risk, to the Central Mississippi River Valley region. The main concern would be large hail and a strong wind gusts with the strongest storms. There is a small chance for a tornado, especially northern Illinois, but as of now the risk is quite low.

Thursday/Friday rainfall forecast.

A second, likely stronger storm system, is forecast to move into the Midwest towards the end of the work week. Late Thursday into Friday, widespread totals could approach 1”+, especially along and south of I-80 across Nebraska, Iowa, Illinois, Kansas and Missouri.

Looking at the combined forecast for rainfall this week is looking pretty good for the region! A large portion of Iowa could pick up over 1” of rainfall, especially south of Highway 20.

February precipitation rankings show much-below-normal precipitation in February. Southwest Iowa was the driest February on record.

The precipitation is needed, especially in areas that are forecast to see the heaviest rainfall. Southern Iowa and northern Missouri into western Illinois saw a top-five-driest February on record based on preliminary data. Southwest Iowa in fact was dead last in 132 years of record.

January precipitation rankings show the region started 2024 on a good note precipitation wise.

The Midwest lost a lot of ground after what was a pretty good January in the region. Much of the Central US was in the top 15 Januarys on record, especially drought-stricken eastern Iowa

There remains timing and location differences in the models to stay tuned to the latest forecast.

-Meteorologist Nick Stewart

Rare Upper Midwest January severe risk Monday

The Storm Prediction Center issued a very rare severe risk area in the Upper Midwest for Monday January 16. The main hazards will be large hail as well as the potential for a few tornadoes.

There are a lot of things that need to go “wrong” for this severe risk to unfold, but there is increasing confidence the instability and moisture will coincide with robust wind shear to allow a few severe thunderstorms to develop.

One key ingredient is the push of very anomalous dewpoint values across the Middle Mississippi River Valley in excess of 50°. Latest high-resolution models are showing just that shaping up, with the trend towards higher dewpoint values in other models as well.

This along with temperatures pushing near 60° will provide rather significant instability given the time of year with very cold temperatures higher up in the atmosphere.

The other key ingredient is sunshine to allow rapid surface heating. Latest models are showing a punch of dry air by late morning into the early afternoon across northern Missouri into Iowa. This surface hating, with dewpoint values in the 50s, is the recipe for thunderstorm development in Iowa.

High-resolution models show thunderstorm development in central and eastern Iowa taking advantage of an environment supportive of supercells.

The potential for severe weather really will not be well known until Monday morning as the clearing and moisture are not of high-confidence at the moment. This is a forecast that will need to be watched closely and further upgrades to severe weather risk areas are possible.