Severe Weather Discussion for Sunday, July 6th

Severe weather is possible on Sunday, July 6.

SPC

The Storm Prediction Center has highlighted portions of Wisconsin, Minnesota, Iowa, Illinois, Indiana, and Missouri for severe weather on Sunday. Within the aforementioned regions, northwest Illinois, Wisconsin, northeast Iowa, and extreme southeast Minnesota look to have the highest severe weather potential.

Twisterdata

Projections of convective available potential energy (CAPE), a measure of how unstable the atmosphere is projected to be for Sunday night, give away the reason the aforementioned states have an elevated risk. We see CAPE values exceeding 5000 j/kg over Iowa and Wisconsin, nearly encompassing the entirety of that 30% severe weather risk area. It is apparent that high instability will be the focal point of Sunday's severe weather event. While the highest threat should remain over IA/IL/WI, I'm seeing continued high instability readings across Missouri and Illinois, areas that should also see some active weather tomorrow.

I am concerned that convection in northern Illinois and southern Wisconsin may not be fully realized after analyzing projected atmospheric soundings. Soundings valid for Sunday evening show that temperatures needed for thunderstorms to form in northern Illinois will need to break into the low 90s, even though the high temperature in Chicago is projected to be 88. I do believe active weather will go through these regions, but I wanted to voice my concerns of a potential letdown, per se, of any potential severe weather in these areas.

Andrew

Potentially Dangerous Tornado & High Wind Discussion for Monday, June 30

This discussion will focus on the anticipated tornado and high-wind threat on Monday, June 30.

SPC

The Storm Prediction Center has issued a Slight Risk of severe weather on Monday in the 15% shading, which extends from Oklahoma into Kansas, Missouri, Iowa, Illinois, Wisconsin, and into Michigan. An enhanced risk of severe weather exists from eastern Kansas into southeast Iowa, northern Missouri, much of Illinois and portions of Indiana and Wisconsin. This enhanced area is where we are watching for potentially significant severe weather on Monday, June 30, which may include tornadoes and a swath of damaging winds.

WPC

Short range analysis from the Weather Prediction Center, valid for Monday morning, shows multiple features relevant to tomorrow's expected severe weather outbreak. We see a decaying mesoscale convective system (MCS) progressing across Illinois, moving eastward as it does so. This complex of thunderstorms will have formed today (Sunday) out to the west, and will have produced additional severe weather in those areas (see Sunday's severe weather discussion here). We also see a stationary front draped across Nebraska, Iowa, and Wisconsin, which is the focus of some early-day convection in northwest Iowa per this forecast graphic. However, the main concern here is if the morning MCS over Illinois will limit convection later in the day due to the MCS-associated cloud cover.

COD

If we look at the forecasted relative humidity values at the 500mb level of the atmosphere from the NAM, valid in the early hours of Monday, we see only limited moisture across Illinois and Indiana, despite the expected presence of the decaying MCS. This tells me that while we can expect cloud cover in the aforementioned regions due to the thunderstorm complex moving east, the cloud deck shouldn't be thick or extensive enough to severely limit convection later in the day, and this is what makes me believe we are looking at a potentially more explosive environment on Monday afternoon.

COD

By Monday afternoon, we see extensive instability has developed over the Midwest, focused in on the areas projected to receive severe weather. We see a swath of 4000 j/kg CAPE (convective available potential energy) stretching from Oklahoma to Illinois, with a pocket of 5000 j/kg CAPE existing in south-central Iowa and northern Missouri, likely the initialization point of Monday's convection.

There is ample concern that Monday's event could produce tornadoes. This stems from a very dynamic wind field in the upper, middle, and lower levels of the atmosphere, thanks in part to the dominant upper level low in southern Canada. These dynamic wind fields then create ample wind shear, a necessary ingredient for tornadoes. With the aforementioned extreme instability, tornadoes are very possible with the initial cells that form Monday afternoon out in Iowa and northwest Illinois, prior to coagulation into a cluster of thunderstorms. From there, a potentially dangerous damaging wind threat may be expected to evolve. You can stay tuned to our Facebook Page and Twitter account for more frequent updates on the situation.

Andrew

Severe Weather Outbreak Discussion for Sunday, June 29

A severe weather outbreak is expected today, June 29.

SPC

The Storm Prediction Center has posted a Moderate Risk of severe weather for southeast Nebraska, northeast Kansas, northern Missouri, and the southern half of Iowa in advance of severe weather expected today. Current discussions indicate ongoing convection over Iowa will be clearing later on in the day, paving the way for diurnal heating to develop and destabilize the environment to provide a breeding ground for severe thunderstorms.

COD

The NAM model indicates deep instability will develop over Iowa and Nebraska later on this evening, where convective available potential energy (CAPE) values look to exceed 3000 j/kg in spots. The development of this instability depends severely on the morning convection over the same areas right now. If cloud cover tends to linger over the area, we could see a reduced severe weather risk, as destabilization will be limited. However, if cloud cover can clear quickly enough, such CAPE values will be easy to come by.

TwisterData

When the storms do form, it looks like they will have decent potential to be originally tornadic. The NAM model places over 50 knots of shear near Iowa, increasing the likelihood that these initial cells that form may have a tornadic component to them. With such deep instability and shear, it is no wonder the Storm Prediction Center elected to go for a higher-level tornado threat for this Moderate Risk area. As the night progresses, the initial cells are expected to come together to form a mesoscale convective system (MCS), also known as a body of severe thunderstorms, that will be moving to the east.

To summarize, those in the Moderate Risk area today should prepare for:
• Damaging winds in eastern Iowa
• Tornadoes and very large hail in central Iowa into Missouri with the initial cells
• General poor weather conditions across the Plains and Midwest

Andrew

Severe Weather Discussion for Monday, June 30

This is a discussion for potentially significant weather on Monday, June 30.

HOOT OU

Model guidance indicates a shortwave trough will extend southward across the Plains and Midwest from a parent upper level low centered in south-central Canada. This shortwave trough is expected to be the firing mechanism for the anticipated severe weather, as it shifts eastward amid strong mid-level winds and a steadfast zonal flow. This chart shows the aforementioned mid-level winds at speeds of over 50 knots in a wide swath of land across the north Plains, supporting the zonal flow regime due to a slightly suppressed ridge along the Gulf Coast. It is this zonal flow that makes me concerned for a severe damaging wind event, possibly to the extent of a derecho.

COD

A zoomed-in view of upper level winds over the Plains and Midwest shows a band of intense winds rounding the base of the upper level low in Canada, and these winds look to push down as far south as southern Minnesota and Wisconsin, per the NAM model. I am using the NAM model primarily due to observed convective feedback issues in the GFS model immediately prior to Monday's event. These convective feedback issues have been slowly eroded today, but due to their continued presence, I feel more comfortable sticking with the NAM. The presence of these strong upper level winds tells me that we are likely looking at a continued supportive environment for a severe wind event.

Let's now analyze the typical characteristics of a damaging wind environment.

This image is from an academic journal, and shows a screenshot of a tornado environment setup on the top panel, with a "typical" damaging wind environment displayed on the bottom. The area where storms are favored to form is outlined in the hatched region. For the bottom panel, we see that the average damaging wind environment has the polar jet (the primary jet stream for all intents and purposes) shooting northeast, mainly over the northern portion of where storms are anticipated to form, eastward of the cold front. We also see the lower level jet stream shooting more north-northeast into the southern portion of the storm formation region, eventually coming together later on down the road.

If we compare the aforementioned factors with the ones we've already gone over, we can see the jet stream winds slanting northeast across the Midwest, north of where storms are expected to form on Monday (they are expected to form in Iowa/Illinois/Wisconsin). A glance at the frontal boundaries on Monday shows a cold front in a similar stance to the west of IA/WI/IL (shown below) as the bottom panel above.

HPC
Forecasted frontal boundaries on Monday morning

Let's now move on to an analysis of the projected instability values for Monday evening to try and identify any other boundaries that may ignite storms.

Twisterdata

The NAM's forecasted convective available potential energy (CAPE) is quite impressive for this event. We see the band of elevated CAPE ahead of the cold front in the north Plains, but the real story is the swath of 3000+ j/kg of instability from Oklahoma to Ohio, and it is this area of instability we will focus on. When taking into account that storms are expected to form in Iowa, Wisconsin and Illinois, we look that way and find what looks to be a boundary of sorts over northern Illinois. This appears to be defined by a steep drop-off in CAPE values from the tip of Lake Michigan to the WI/IL border. This makes me wonder if storms could fire along that potential boundary there, though the long range format of this forecast tells me to wait and watch for this particular feature. Nonetheless, it is apparent that ample instability will be present for this event.

SPC

The final item to look over is the idea of analog forecasting. This method involves analyzing past conditions, and choosing dates with conditions that best match up with forecasted conditions. In this case, the SLU CIPS program was utilized to see what dates had the most similar conditions as those forecasted to be present on Monday. The top analog that came up was June 18, 2010, and the storm reports for that day are shown above. It is quite apparent that this top analog greatly favors a damaging wind environment, as we've already evaluated for ourselves with the two-panel graphic earlier in this post. In this top analog, the damaging wind swath extended from Illinois and Wisconsin, as well as Iowa, into Indiana and Michigan. This is actually quite similar to what I think may happen if current forecasted predictions are to verify, and this must be watched closely.

To summarize, a potentially significant severe weather event is projected for Monday, with damaging winds being a primary threat. The areas affected look to be Iowa, Illinois and Wisconsin. More information will be delivered as it becomes available.

Andrew

Severe Weather Discussion for Sunday, June 29

Sunday is being monitored for potentially significant severe weather.

SPC

The Storm Prediction Center has highlighted portions of the Plains and Midwest for severe weather on Sunday. The Slight Risk covers eastern Nebraska, northern Kansas, northwestern Missouri, Iowa, southeast South Dakota, much of Missouri, Wisconsin, and the Upper Peninsula of Michigan. The most elevated risk inside this overall outlook area extends from eastern Nebraska to west-central Wisconsin.

Instant Weather Maps

Projected instability values off of the NAM model show figures in excess of 4000 j/kg situated from Kansas to Iowa, which should be more than enough to fire off these storms as a disturbance propagates eastward across the northern Plains. Shear from the surface to the 500mb layer looks to grow to upwards of 60 knots across the northern Plains and Upper Midwest, with spots of 70 knots also being found. It does appear that the initial storms that fire look to have some substantial tornado potential, with the aforementioned instability and shear present. As the night wears on, the expectation is for these cells to coagulate into a mesoscale convective system, which will then likely shift off to the east overnight. A strengthening nocturnal lower level jet stream should enable this eastward progression to continue.

Andrew