With convective initiation just starting, I wanted to to a comparison of the All Sky CAPE with the SPC mesoanlysis of SBCAPE and MLCAPE. Let’s start with the SBCAPE (all images at 19Z on 5/22).
A very sharp gradient in SBCAPE can be seen in the mesoanalysis above, with values ranging from essentially nil in the northwestern part of the state to values over 4000 J/Kg in the southern third of the state.
The MLCAPE, as one would expect during maximum surface heating, is somewhat less, with values greater than 2500 J/kg running roughly from Tulsa to Norman, and values in excess of 3500 J/kg along the Red River.
Finally, let’s look at the All Sky CAPE. These values are running about 500 J/Kg lower than the SPC MLCAPE in the Tulsa to Norman corridor, and as much as 1000 J/Kg lower near the Red River. However, it does nicely indicate the “shape” of the area that has MLCAPE, and emphasizes the area with the maximum values. This indicates the product is very helpful in a qualitative sense, but specific values need to be used with caution.
A comparison of the All-Sky LAP derived PWATs with 12z RAOBs shows that the LAP product is depicting PWAT quite well.
The PW retrievals were done mostly in clear skies (blue colors):
A four-panel plot of total PW and PW at different layers from 12-18Z shows rapid low-level moistening over OK and AR (upper right and bottom left panels).
The moisture return, in combination with diurnal heating, is resulting in a rapid increase in CAPE as suggested by the all-sky LAP product:
The AllSky Layer Precipitable Water clearly shows the moisture return this morning into southern Texas and Central Oklahoma. PWATs across the Red River were ~0.5 inches early this morning and have now increased to ~1.5 inches this afternoon.
This product is a great situational awareness tool to survey the pre-storm environment. -Atlanta Braves
The northern extent of a line of storms that has produced sporadic wind damage is approaching the LSX CWA from the south. One of these storms has good reflectivity structure with a tight front reflectivity gradient and a rear inflow notch. However, these storms appear to be entering a more stable airmass. This is reflected in the ProbSevere probabilities of the storm in question compared with one just a bit further north:
The northernmost storm with the cool contours has only a 22% ProbWind and is in an environment of only 715 J/kg MLCAPE (per the sampling feature). Meanwhile the storm in question to the south in the warmer contours has a 90% ProbWind with 1220 J/kg MLCAPE. These storms are moving to the northeast toward the more stable air. Incidentally, the All-Sky LAP CAPE does not depict as sharp of a gradient in the CAPE compared with the RAP-derived ProbSevere values:
I am not sure which is more accurate but I suspect the model-derived values are more accurate in this situation.
Furthermore, a weakening trend in the Flash Extent Density is observed on the northern end of the line:
This storm still deserves a warning, but we will see how quickly it weakens.
The Blended TPW product (top left) shows promise in creating an all-observations precipitable water product in AWIPS. The polar-orbiter PW data in cloudy areas produces artificial gradients and inaccurate values compared to modeled fields (GFS top right and HRRR bottom left), but its attempt to generate an all-observational PW product is successful. I am unsure of how to suggest improvements in the cloudy areas but would encourage these model-free fields continue to be developed.
The AllSky PW product (bottom right) looks really good. The inclusion of GFS data in cloudy areas is a neat idea and the partly cloudy areas seem to be well-computed. This is a tool I will definitely use for situational awareness. -Atlanta Braves
Radar image of a severe QLCS in NW Arkansas at 1923Z. This line has been producing wind damage and a few spin up tornadoes. Next I’m going to diagnose column moisture and instability downstream, across north-central Arkansas using satellite and satellite-model merged products.
The GOES-16 AllskyLAP showed a deep plume of moisture extending from the Gulf of Mexico northward into Arkansas and Missouri. Specifically, in north-central Arkansas, sampled PWATs were around 1.60 inches and MUCAPE was near 700-800 J/kg. Skies were mainly clear in this area, which resulted in a relatively smooth appearance in the PWAT and CAPE plots. Interestingly, and not plotted here, the 700-300mb AllskyLAP PWAT had lower values or drier conditions to the east of the approaching QLCS. This presence of mid-level dry air may be conducive for severe weather over north-central and northeast Arkansas over the next 1-3 hours — especially for damaging winds.
Merged TPW data at 19Z estimated PWATs near 1.50 inches into north-central Arkansas. However, there was a sharp discontinuity from 1.50 to 1.00 into the northwest part of the state where widespread cloud cover was present and the data originated from polar orbiting satellites (some of which could have been advected in). The SPC mesoanalysis did not display a sharp gradient in PWATs in this area, but rather had a gradual decrease to 1.30 inches.
Not the best satellite pass with my area of concern on the far western fringe of the NUCAPS data. Surprisingly, the sounding data on the edge in northern Arkansas was nearly identical to the SPC mesoanalysis data with values near 1200 J/kg! It likely helped that skies were mainly clear at the time of the pass. The GOES-16 AllskyLAP data was underdone in comparison. As mentioned, only up to 700-800 J/kg.
NUCAPS 700-500mb lapse rates in northern Arkansas are close to model forecasts. The NUCAPS in this pass was indicating lapse rates around 6.2 C/km. Model data was generally a little bit lower around 5.8 C/km. The SPC mesoanalysis was on the high end near 6.5 C/km. Roy
The AllSky products seem to do a really good job of providing timely and relevant environmental data with higher spatiotemporal resolution than other means. Representative model soundings and the SPC Mesoanalysis page are nice tools, but the AllSky products add a helpful third point to interrogate environmental evolution. Perhaps the most helpful application is tracking of fronts and boundaries. As the dry line advances it is easy to see its eastward extent. In addition, the extent of the warm air is very clear as it pushes into Missouri.
This 4 panel display with cloud type in the lower right is a useful tool for identifying potential causes for inconsistent data from pixel to pixel. I like these products and look forward to their operational implementation at the end of this month! -Atlanta Braves
I was taking a first look at AllSky products this afternoon and put together a four-panel procedure. I expected to see some noise/sharp gradients in the data because differing pixel population methodology, but viewing a loop revealed an interesting artifact:
There appears to be an artifact in northern Arkansas that looks a little bit like a dinosaur head. This artifact is visible in parcel Lifted Index (to 500 mb), all PWAT products, and CAPE, but not in Total Totals, K Index, or Showalter Index fields. The artifact does not appear to be dependent on the Cloud Type field. Perhaps this artifact is associated with terrain in Arkansas but warrants further investigation. -Atlanta Braves
One of the forecast problems of the day for the LSX forecast area is determining how far north the reservoir of instability will extend. It may be useful to monitor the all-sky LAP CAPE product in concert with surface obs to assess the destabilization throughout the day. Looking at a comparison of the product with selected 12Z RAOBs, the product appears to have a reasonable representation of CAPE values so far.
The ILX RAOB is in the stable air well north of the warm front:
Although the MLCAPE at SGF is zero, the LAP CAPE produce is indicating around 400 J/kg of CAPE, which appears to reflect the MUCAPE in the sounding:
The LAP CAPE product underestimated the CAPE at LZK, but still gets the general idea:
While some of the details may not be correct, and it is blocky in places, the LAP CAPE product appears to be doing a reasonable job at depicting the reservoir of instability over the southern Plains. By 18Z, it showed the northward spread of instability in concert with the northward advancing warm front:
Looping the AllSky LAP CAPE product, moisture and instability is noted spreading northward toward the LSX CWA, which remains to the north of a warm front. One thing I noted is the western edge of the instability plume across eastern Texas jumps back and forth when looped. Not sure if this associated with the product itself or some other issue, but it was noteworthy. Otherwise the product seems to do a nice job depicting the instability plume spreading northward.