AllSky - Buyer Beware

All Sky Layer Cape looking funky with some discontinuities around KS? Why?



A quick look at the Data Type product (below) shows only GFS being used in these suspect areas. Major caveat emptor!



All right, time to look at storms around Bismark.

#MarfaFront

ProbSevere Potential Gotcha

A potential "gotcha" and/or training issue...
I initially loaded a 4-panel with 0.5 Reflectivity and ProbHail overlaid, 0.5 SRM and ProbTor overlaid, and 0.5 Vel and ProbWind overlaid, but I had not loaded the full ProbSevere Model in any of the 4 panels. I then noticed that there was a 29% ProbTor (which was erroneous with bad dealiasing), but my attention wasn't called to it because the 2nd circle around the storm only appears on the full ProbSevere. It would seem like a good idea to either always have the full ProbSevere displayed or if folks prefer to load the threats separately, perhaps need to add a second circle around the ProbTor object.


ProbSevere 4 Panel - Upper Left: 0.5 Reflectivity + ProbHail, Upper Right: 0.5 SRM + ProbTor, Bottom Right: 0.5 Vel + ProbWind, Bottom Left: NMDA + ProbSevereModel

-Tempest Sooner

Differences between Observed Sounding and NUCAPS

Compared KBIS observed 19z Skew-T to NUCAPS 20z Skew-T

Key points:
Lapse rate differences: Between 1-1.5C/km difference through all levels
SFC and MU CAPE was 500J/kg higher on the NUCAPS
Vertical profile is markedly different and is a much more saturated on the observed Skew-T



To further confuse matters the NUCAPS forecasted SFC CAPE values for the same location and time is 400J/kg...which is closer to the observed sounding than to the NUCAPS sounding.

---Desmond---

GLM Event Density - Livin' on the Edge with GOES 16 and 17

Looking north of the ND/MT state up in Canada. Green (Red) is  Event Density from GOES-16 (GOES-17) and yellow is ENTLN cloud to ground strikes. Remarkably good agreement in position, although the data smearing is evident and parallax isn't much of an issue (yet?) given the shallow convection.

#MarfaFront

NUCAPS Gradients of CAPE

The 12Z Bismarck sounding was quite dry and and the surface observation at Bismarck was around 32F. Low level moisture has quickly rebounded this afternoon across central and western ND, however it remains dry across eastern ND. Dewpoints have come up into the upper 40s to near 50F and temperatures have climbed into the upper 70s. The AllSkyLAP CAPE loop clearly shows that instability is increasing across portions of ND with values topping out around 900 J/KG at 1930z, though most of the retrievals are GFS based because of cloud cover lingering in the area.

AllSkyLAP CAPE Loop

I decided to look at the NUCAPS soundings across the area to see if the CAPE values were similar. What I found was in the areas of low level moisture, the NUCAPS modified and unmodified sounding had similar MLCAPE values. However, as I checked NUCAPS soundings further east into the drier air, the un-modified soundings showed MLCAPE values that were far to high (should be near zero based on other observations), but the modified soundings were pretty spot on regarding the surface observations (especially Td, T may be slightly low), and thus MLCAPE values appeared to be more reasonable.



NUCAPS Swath. Soundings in quesiton are located just northwest of Bismarck, just northeast of Bismarck, and 2 dots east of Bismarck.

The next six images are the comparisons between the non-modified and modified NUCAPS soundings at three different locations. The first is near the peak in instability northwest of Bismarck, the second is east-northeast of Bismarck near the gradient, and the third is farther east into the drier air.


NOAA 20 Non-Modified NUCAPS Sounding just northwest of Bismarck
NOAA 20 RTMA Modified NUCAPS Sounding just northwest of Bismarck
NOAA 20 Non-Modified NUCAPS Sounding just ENE of Bismarck.

NOAA 20 Modified NUCAPS Sounding just ENE of Bismarck.
NOAA 20 Non-Modified NUCAPS Sounding 2 Dots East of Bismarck.
NOAA 20 Modified NUCAPS Sounding 2 Dots East of Bismarck.

With that said, the modified soundings seemed to do a decent job capturing the gradient in CAPE. The values appear to be a bit high compared to the AllSkyLAP CAPE (1183 vs 750 J/KG around the same time), and high also compared to the SPC Meso Analysis Page (around 500 J/KG).

GLM usability in heavily parallaxed locations

It's pretty clear to me that both the GOES-west and GOES-east are having a lot of trouble detecting lightning (GLM) in the northwest U.S. with accuracy of location or frequency due to parallax, spatial resolution, and GOES tilt sampling of storms. Below is an animation specifically over southwest Montana where the GLM displaces the FED significantly (side note: TOE was very similar for these, so FED is shown for best example), and also has trouble picking up in-cloud pulses. The ENTI is overlaid in pink to show the differences in GLM vs ENTI. If you watch closely, the first frame depicts an ENTI in-cloud lightning flash & pulse in the far southwest portion of the screen, where no GLM FED (or TOE; not shown here) was even detected. There is also some instances where the GLM places lightning pixels where the ENTI or NLDN does not show anything in the same time frame (also making it hard to verify both products).

Below is a separate example where the FED does not show what I would expect it to show for a central Wyoming storm (differentiating intensity as well as location and timing). The GOES-east is the first to detect, then the GOES-west detects thereafter. GOES-east and GOES-west did not detect at the same time in any frame. Both products are loaded as a 5min-1min update.



Now here's a case farther south in New Mexico where a storm cell is of comparable intensity as the northern examples. The GLM detection seems more accurate than the MT case, but the last frames here show that the GLM also has trouble with keeping FED on the cell core of interest.



Interestingly enough, the TOE (shown below) does a better job here  in NM with spatial coverage than it did up north in MT, but still has displacement issues comparing to ENTI and MRMS storm cores. I find that the TOE (especially with GOES-west) does a better job at recognizing the spatial extent of a flash here than the FED product did. (See above vs. below).     

-shearluck



Now the question is, is the parallex better in the south-central U.S.?  And what if we look at higher resolution products like the group centroid density GLM product? While comparing the satellite GLM, with Day-Land-Cloud-Convection RGB, and with the ENTI/GLD/NLDN strikes (overlaid in pink) in SE Missouri.....it's clear that a forecaster should not solely rely on GLM for core lightning locations:

Another Marginal Day in the HWT

Continuing the theme of the week, today figures to be another day with few storms across the country producing some severe reports. Today we are operating across the slight risk area in North Dakota in the Bismark and Grand Forks CWAs where convection should initiate across central North Dakota this afternoon and into the evening. A third group will also be operating in the Memphis CWA looking for redevelopment behind a morning MCS along a trailing outflow boundary which could produce some marginally severe hail and wind across northeast Arkansas and into western Tennessee.



-Michael

Area Discussion Prior to Severe Wx Kickoff

Area discussion for the Dakotas: Lower heights area located over western S Dakota and stacks from 700-500mb and will make its way easterly throughout the day. 850mb winds from the south at 30Kts.
METSAT shows low/mid clouds moving into ND from the west with clearing over the center of the states where wx is expected. Upstream surface observations support this clearing as they show dry air advecting into the area from the south.

Radar shows weak convective activity to the north moving into Canada. Models and the SREF are in agreement that the majority of thunderstorm development happen around 1-3z.

Merged TPW Composite total PW values over the center of the N/S Dakota states where convection is expected according to SPC outlook is less than 1” with values between .80-.95” and AllSkyLAP 900mb PW is even lower at .30”.



NUCAPS fcst Sfc CAPE overlay CAPE values range between 400-500/kg but there are quite a few gaps in coverage.



Meanwhile AllskyLAP CAPE shows 900-1500J/kg, and NAM models show extremely high CAPE values of 3000-4500J/kg.



Local TAFs show no thunderstorms or even rain while the SPC continues to carry SLGT over the Dakotas. It’ll be interesting to see how this scenario plays out as the day progresses.

--DESMOND--

ProbSevere

Overall impressed with the performance of Prob Severe today. Quick way to distinguish between weak/strong/severe storms. In this example from the high plains of Wyoming, there was an organized storm that Prob Hail spiked to 90% about an hour before the 1.5" hail report, and remained at elevated to 75% at the time of the hail report. Don't mind the low (3%) threshold for the ProbTor outline, as it is an easy way to keep that important piece of information quickly viewable by the warning forecaster.



-- warmbias --

Mexican Severe Storm

A strong low level moisture gradient showed up on the Sfc- 0.9sigma AllSkyLAP image early in the afternoon south of the Big Bend region in Mexico. This could serve as an initiating boundary later in the afternoon.

Low Level AllSkyLAP and Low Level IR/WV top, mid level AllSkyLAP and IR/WV bottom

A look at the NUCAPS Forecast CAPE from the ~21Z pass showed over 3000 J/KG of CAPE at the 03Z Forecast hour. Earlier forecast hours (00-02Z) were missing data, however, if you interpolated between available data points, it seemed as though there was a maxima of CAPE in the area. It was noted that a storm developed around 21Z.

NUCAPS Forecast 03Z Forecast

To gain more detail, I clicked on a NUCAPS modified sounding east of the low level moisture gradient in the vicinity of the storm. It's clear this is a very unstable sounding, capable of producing (at least) large hail. This clued me  in on how fast the storm could become severe. Certainly would not have had a special 19-20Z sounding in this area without NUCAPS and would have solely relied on model forecast soundings.


NUCAPS sounding from Mexico ahead of low level moisture gradient at 20Z

Even though it is far away from the KCRP radar, prob severe quickly showed the developing storm ramp up and have very high severe hail (and wind) probabilities (roughly within 15 minutes of initiation). If the NUCAPS forecast is right, this storm would likely continue into the evening given the abundant instability.

Prob Severe from KCRP looking in Mexico

-Tempest Sooner