Looking at the 18Z run of the 3km LAPS…the model has a ribbon of north-south oriented CAPE further west into eastern Colorado than the Nearcast model and is much skinner.

Much lower values of CAPE are forecast in far eastern Colorado into western Kansas…and as a result…the storms that fire along the sfc convergence boundary in eastern CO develop quick but quickly die as they move off into the lower CAPE fields along the CO/KS border. This is more or less opposite the Nearcast model.

In a similar fashion…updraft helicity is relativly weak throughout the region although the storm in eastern Yuma county has more persistent helicity field maximized at 58 m2/s2 at 22Z. Composite radar verification at 22z indicates the 18Z LAPS run is slow to move the strongest convection in northwest Kansas to the southeast and is significantly further west with the storms than reality in southeast Colorado. In addition…the LAPS convection is weaker than reality.

Looking at the 21Z run…the CAPE ribbon is a bit further east than the previous run and the model is capturing the return flow of higher instability as moisture is advecting in from the southeast. However…the slower advection of moisture as seen on the surface obs makes me think the LAPS is a bit aggressive with this moisture return.  The reflectivity fields both along the line in northwest Kansas and the weak cluster in southeast Colorado are better analyzed initially although are a bit weaker than reality at 23Z. The 21Z run does however show the cold pool associated with the squall line really well as it traverses southeast across GLD CWA. It also has very good definition of the individual cell’s cold pool boudaries as well.

*see image /bmazur/23ZLAPSanalysis.png

*see image /bmazur/23zcomp.png

I would like to attach an image of the 3km instantaneous updraft helicity as well but am not able to load the data at this time.

An interesting feature showed up at the 2115Z timestep of the 21Z run. A donut of nearly 5000 J/kg of CAPE showed up surrounding a weak isolated cell in Prowers county. This area of high CAPE was then dispersed with time along the CAPE ribbon. Not sure what would cause this in the model but found it to be an interesting feature.

*see image /bmazur/capebomb.png

RJM

A few high based storms have been struggling to develop across southeast Colorado due to abundant dry air and SBCAPE 500-1000 J/kg.

The first image was at 2045 UTC on May 16 where the GOESR UAH CI suggested some potential for convection with a few locations 61-78%, and the CIMSS CTC depicted a maximum of -18C/15 min.  This appeared promising for deep convection.

The next image was at 2115 UTC and continued to depict a few areas 20-62% for CI as well as -16C/15 min along with a few weak cells.  At this point, there still remained hope for some deep convection.The last image was at 2145 UTC respectively with lower CI and CTC values as well as a few non-severe/rather weak cells. So far, these cells have failed to intensify or become severe. Weak forcing aloft in conjunction with the lack of low level moisture may be the main culprits for the poor development of storms.

Storms continue in a linear convective mode across the GLD CWA.  The 18Z run of the LAPS suggested lower instability ahead of the line as it continues to sink south.  Here is the current setup.  As you can see, the storms are maintaining some level of strength as they move into this supposedly more hostile environment.  The mesoscale desk noted that the GOES NEARCAST products maintained higher instability across the CWA and are probably more correct in this scenario.  Just goes to show that no product is right all of the time, or even most of the time!

CL

Held off issuing a severe thunderstorm warning for a developing storm over northern Nebraska due to MESH staying around 0.75 inch and maximum reflectivity of only 55 dBZ at the -20C level.

In addition, the GOESR UAH Convection Initiation Products depicted a few pixels of 10-40% in the hour prior to this storm developing, perhaps suggesting that the environment may not be conductive for explosive storm development.

Playing a bit with the SPoRT flash initiation density product and the evolution of an  updraft. Although it’s not a serious storm, it represents the ongoing pulsating activity very well which could eventually gain strength when entering a more unstable air mass to the east. Below you can find the ‘Flash initiation density product’ at 2035Z and 2040Z, showing a marginal increase in lightning activity. Reflectivity at the same time showed a core with 35-40 dBz and only a few isolated lightning strikes occurred.

At 2055Z, the storm finally strengthened in reflectivity fields (the core peaked at near 60 dBz) . Although that was just a temporal strengthening trend of that storm it is great to see the lead time you get with that lightning product before the updraft eventually strengthens. Helge

Setting up shop in North Platte, NE today. Quite a marginal setup with relatively low instability / higher based storms based upon Nearcast, higher res LAPS, and more conventional data. Enough shear to organize structures into small line segments at present. Here’s a comparison of some of the higher res model Z output and actual Z at 2100Z. Neither have reality nailed perfectly, but it looks like the OUN-WRF has a slightly better idea of the structure, whereas LAPS has more discrete cells.

Actual Reflectivity

OUN-WRF

LAPS

Picca

Setting up in the Goodland KS CWA today.  A small cluster of storms is ongoing and certainly producing a lot of rainfall and lightning…note the 0.5 reflectivity on the upper left.  To the upper right is CTC on top of the visible.  No detections here…likely due to anvil cirrus hinderance.  On the lower left, we have MESH from MRMS.  Nothing at one inch or above here either.  Reports from the area have consisted of small hail lately…0.75″ and less.  This seems to reinforce the marginal nature of the storms depicted by MESH and other experimental products.

CL

The GOES Sounder Air Mass image is very useful in highlighting the different features of interest for today. First of all the compact disturbance which is about to leave NE Colorado to the east/northeast is well visualized by mid-level drying in the image. Weak forcing ahead of that feature already caused some initiation over N/NE Nebraska with another round of storms evolving over extreme NE Colorado. Of interest is a southward extending and weakening vorticity lobe which is about to enter Kansas from the west right now. Also, the dryline is well recognized by that product, showing warm/moist air ahead of the dryline advecting to the north (green-ish colour). This correlates well with mid-level moisture, seen in latest RAP output. A gradual transition from ‘green to blue’ occurs when moving westward (e.g. towards the  TX Panhandle). This corresponds well with some residual low-level moisture f.ex. in the lowest 850 hPa, which gradually mixes out. We will monitor both the dryline and the eastward moving but weakening PVA lobe for some kind of interaction during the following hours and eventually for sporadic CI.  Helge

The following images occurred at 1954 UTC on May 16, one minute before quarter size hail was reported 9 S of Hays Center, Nebraska.  MESH slightly underestimated the hail size with a value of 0.79 inch.  Severe hail probabilities had a maximum of 36%.  The 60 dBZ echo was -13.12 kft below the -20C level, due to possible underestimation due to the lack of nearby radars.  There was a maximum of 57 dBZ at the -20C level.