The 1930 UTC GOES-R Convective Initiation image on May 13, 2014 depicted yellow  (65%), green (58%), light blue (46%), and several darker blue pixels (less than 40%) across northwest Ohio ahead of a line of storms.  There was a small cell that developed near the green pixel at 1945 UTC (third image below) moved northeast at 1958 UTC (fourth image below).  A cell developed and moved into the yellow and light blue pixel areas at both the 1945 UTC and 1958 UTC images below.
This product seems to do a good job highlighting higher potential areas for convection initiation (if 50% or greater) compared to lower chances (50% or less).

Michael Scotten

Overall, the vLAPS is performing a bit better today.  It’s still a bit too slow with the linear band of convection, again likely not catching the cold pool that has accelerated east with the convection in reality.  But it does hint at storm structure, with generally a disorganized line with some embedded bowing structures, some of which have been severe given decent low-level lapse rates and inverted-v soundings. So overall, it’s done pretty well and certainly useful in an operational setting.

Just a quick blog update to show how the NSSL simulated satellite imagery is behaving.  It is not doing all that well, unfortunately.  It seems well overdone across central Indiana, where outflow from earlier storms has undercut convection and largely caused it to die out.  In our area of the day (Detroit CWA), the convection is well underdone.  We have ongoing strong to  locally severe storms, that the model does not have a handle on at all.

-Deitsch

Here is a screen shot from 19z focused on the DTX CWA. In this four-panel the upper left image is the 1 hour forecast from the 18z run of the vLAPS 1km Surface Layer Max Base Reflectivity, lower left is the 1 hour forecast for the 18z HRRR 1km AGL reflectivity and the upper right is 19z observed reflectivity from DTX. Overall the vLAPS is comparable with the HRRR in the placement of the stronger convection along a line extending south across eastern lower Michigan but the vLAPS is quite noisy with developing convection ahead of the main line that was not been observed by DTX Radar.

Shawn Smith

The CIMSS Probability Severe Model indicated low probability for severe storms 5-10% for a fast moving line of storms over eastern Michigan (northern part of line moving 50-60 mph) at 1928 UTC on May 13.  It seems to be a good idea to include DCAPE as a displayable variable in addition to MUCAPE, EBShear, MESH, Vertical Growth Rate, and Glaciation Rate and use this variable for calculating SVR PROBs.  The low probabilities are likely due to MESH values well below 1 inch (closer to 0.25 to 0.50 inch) as well as EB Shear generally 20-25 kt.

Michael Scotten

On Monday afternoon, a line of storms developed and propagated eastward, essentially bisecting Missouri by late afternoon. Here’s a look at the base reflectivity for the radar at KLSX (St. Louis) at 22Z (about 4pm):

In the same timeframe, the CIMSS NearCast model was projecting a fairly high Theta-e lapse rate.

The box in the top right corner shows this GOES- derived Theta-e difference of around 20-21K in an area west of St. Louis. Interestingly enough, this ΔTheta-e maximum is aligned with the area of convection, seen in the radar imagery above. Will the storm cells continue to propagate eastward and will they actually strengthen as they enter this area of higher instability?

By 23Z, We’re starting to see some individual storm cells develop out ahead of the bow echo.

This would indicate that the area of high instability on the NearCast model is starting to produce some convectively-driven storms. The highest value I found in this image in the newly-formed cells was 56dBZ. So in the near term, it appears the NearCast is correctly predicting convective initiation through the ΔTheta-e product. How about at 0Z itself?

The stronger line behind the pop-up cells has accelerated and swallowed up the smaller individual cells! That is a straight line of storms if I’ve ever seen one. I suppose the ΔTheta-e could be used in this situation to predict that this storm line would evolve in this way. More cases will have to be examined in order to see if this parameter is consistently usable for this purpose!

The GOES-R CI product did a fine job depicting convection growing in northern Illinois. The top image at 2145 UTC depicting values around 74% and the second image at 2200 UTC depicting 89%.  The radar images below at 2203, 2222, and 2240 UTC depicted a few developing showers and storms near the CI values below.   The product gave 15-45 minutes of storm lead time.  These storms did not become severe.

Michael Scotten

Monday, May 12, 2014 Mike Smith

Two situations worthy of note:

I “issued” a special weather statement for Winnebago Co. At 2:47pm for 3/4 inch hail and gusts to 40 kts. Using ONLY surface obs and 1-minute satellite data.

At 2:59pm, I issued a severe thunderstorm storm warning for the same county, based on a Fujita U with overshooting then collapsing top in 1-minute data.

NWS issued severe at 2:56pm (unknown to me). Both warnings verified with 1.75” and 2.0” hail reports.

I observed a downburst south of Sullivan, WI and based on the right moving cell, I thought the RFD would intensify at 4:12pm for Walworth Co. Predicted 55 kt and 2” hail. Unknown if it verified.

The right mover got more pronounced and at 4:22pm, I issued a tornado warning for the southeast third of Walworth Co. This was due to the wrapping pattern of the outflow air (into RFD), the 1-minute satellite U and collapsing top, the persistent right movement and high spectrum width in the inflow. NWS issued a tornado warning for the same area at 4:45pm. While a pronounced hook formed, it never quite formed a tight couplet.

The ProbSevere Model is doing a great job highlighting the strongest cells. In this image from 2208z the ProbSevere Model is overlaid on top of the MRMS reflectivity above the -20C isothermal level. The cells annotated with an arrow across eastern IA, southern WI, and north-central IL have 50dBz echoes above the -20C isotherm and the model indicates an 80+% prob of severe.

There were hail reports from three of the four cores highlighted. The lower left produced Quarter sized hail in Henry county IA with the MESH indicating 2.5in, The upper left storm produced reported penny sized hail in Johnson county IA with MESH of 0.89in and the upper right storm produced nickel sized hail in Racine county WI with a MESH of 1.13in. The MESH product is overdone in this example.

Shawn Smith

The Super Hi-Resolution Visible Satellite Imagery below depicted a differential heating boundary over northern Illinois, denoted by the green line.  Very little cumulus was observed north of the green line where cirrus cloud cover was thicker, while enhanced cumulus congestus was occurring south of the green line.  With low level south to southwest flow, cumulus that developed south of this boundary had a tendency to dissipate when moving north of the green line/boundary. A severe storm denoted by the orange circle in southeast Iowa was moving east northeast and seems to be moving along this boundary.  It will be interesting to see if this storm will continue to be severe over the next few hours.

Michael Scotten