NUCAPS 850mb Theta-E: A rough comparison to SREF and RAP13 850mb Theta-E

There's isn't really a good "real data" comparison one can make for 850mb Theta-E values (at least, not that I know of). It would be easier to make the comparison at the surface, but I don't believe NUCAPS allows this (it doesn't really do too well in the boundary layer). So...I did a rough comparison of NUCAPS 850mb Theta-E (top left) to both the SREF 850mb Theta-E (top right) and RAP13 850mb Theta-E (bottom left). I say "rough" because with the pass occurring just after 19Z, that's when the NUCAPS data are valid, but the SREF data are valid for 18Z and the RAP13 data are valid at 20Z.

There is, naturally, some disagreement within the model data regarding 850mb Theta-E values, so the NUCAPS data don't match up "perfectly" with either model in many locations around the country. (The amount of cloud cover and the reliance on microwave retrieval may also be playing significant roles, since there were a lot of "yellow" sounding dots.) Still, there are areas where it is close, especially where the values are lower in non-/fewer-cloud areas, such as across N MN, E WI, MI, and down into E IL, IN and OH. (Perhaps somewhat due to a dry bias, per the developer.)

As Theta-E numbers get higher, there will obviously be more moisture in the atmosphere, so the satellite signal is probably being scattered, etc. a bit more, leading to some skewing to the numbers. Areas where clouds are abundant and/or thick are actually pretty easy to discern as they show up as some anomalously low Theta-E values, such as what is observed in NE MT, NW ND and cntrl MN. Other areas where there are cu fields or where there is patchy cloud cover (such as across NE), are not so easy to discern within the Theta-E values.

At this point, my recommendation for the NUCAPS 850mb Theta-E product is: "Use with extreme caution" as more testing needs to be accomplished on this product.

- Thomas Bell

Warning Decision

My severe t-storm warning (2nd one) was about to expire with the storm on the edge of severe.  MESH was .97.

I decided to extend it for another 30 mins.  Even though the ProbSevere values were low..I haven't been able to go off those values this time.  GLM still showed a higher value on Event Density and Total Energy.  So I went with a warning.  (warning box was too long..I forgot to change the shape!)

 

Just after I issued all values dropped a bit again.  The GLM data starting to slighting decrease too but in the 5 minute scan the lightning data still looked strong enough that the storm might pulse up again.

The ProbSevere values have been too low in this area of the country and in this scenario.  (Billings WFO)  I keep putting more weight on the MESH with GLM data and dbz values.


-Penny Gardens

NUCAPS Sounding CAPE/PWAT/LCL/LI Modified vs. Reduced Latency

[23:00 UTC] Even with storm activity in full-force at this hour, decided to take a more in-depth look at NUCAPS as it related to our environment early this afternoon (approximately 19 UTC). Especially wanted to gauge the modified sounding vs. the reduced latency sounding as it related to other derived environmental parameters.

SBCAPE:
NUCAPS Modified Sounding- 1430 j/kg
NUCAPS Reduced Latency Sounding- 1022 j/kg
SPC Mesoanalysis  - about 1500 j/kg

PWAT:
NUCAPS Modified Sounding - 0.74 inches
NUCAPS Reduced Latency Sounding - 0.74 inches
SPC Mesoanalysis  - about 0.80 inches

SBLCL Height:
NUCAPS Modified Sounding - 928m
NUCAPS Reduced Latency Sounding- 841m
SPC Mesoanalysis  - about 1200m

Sfc LI:
NUCAPS Modified Sounding - -4
NUCAPS Reduced Latency Sounding- -3
SPC Mesoanalysis - about -3.5

Overall, the modified sounding seemed to be slightly better (closer to SPC mesoanalysis) than did the reduced latency sounding, although both were in fairly good agreement with SPC mesoanalysis, particularly in an area that was being closely watched for convective initiation and expansion. There was not much cloud debris from upstream convection that would have potentially contaminated the sounding data to some degree. Overall, very impressed by the NUCAPS soundings in an environment that likely would not have had actual RAOBs to look at.

Rosie Red

Aviation T-storm Forecasting/Warning: GLM Avg Flash Area vs CWA and SIGMET sizes

One thing that GLM data is going to change for aviation forecasters at the Aviation Weather Center, CWSUs, etc. is Convective SIGMET (C-SIG) and CWA size. As it is now, some aviation forecasters may tend to get a little too "cute" with C-SIG and CWA size, considering C-SIGs and CWAs can be valid for up to 2 hrs or so. As GLM data becomes available to aviation forecasters, I think it is going to open some eyes as to just how much areal extent to lightning there can be in individual t-storms & t-storm clusters/lines/line segments. Consider the following example, which compares GLM average flash area to a C-SIG (again, valid for up to 2 hrs) in NE/KS/N OK. Clearly, the areal coverage of the lightning will extend beyond the boundaries of the C-SIG soon:

GLM avg flash area (w/composite radar) at 2158Z:

C-SIG a few mins later:

- Thomas Bell

GLM Aided In Confidence For Early Warning Issuances

[22:00 UTC] Storm strength has really increased over the past hour or so in the Billings area with several intense updrafts having developed: a few in Rosebud County and one in central Yellowstone County. Test warnings were issued based on sudden and rapid increases in several of the GLM products (most notably total energy and extent density). Interestingly though, review of ProbSevere and ProbHail showed percentages that were a little lower than would be expected, especially as MESH was near and in excess of 1.5" with several of the storms. Most notably, a test warning was issued for the storm in central Yellowstone County about 30 minutes before a TBSS signature appeared on the 3.1 and 4.0 elevation scans from KBLX.

GLM data proved to be beneficial in analysis of the storms and issuance of the ensuing warnings. In fact, the sudden jumps in data provided more of a "head-start" in this afternoon's environment than did the ProbSevere products.

Rosie Red & Penny Gardens

GLM Group Centriod Density

We are on the edge the domain and the GLM data is very pixilated and stretched out.  Also seems displaced from the storms.  This is the Group Centroid Density snapshot.  I noticed yesterday in New Mexico & TX these looked more like dots.

-Penny Gardens

21:30 UTC Billings MT mid-afternoon MD

[21:30 UTC] Storm initiation is well underway across central portions of the Billings CWA and enhancement of multiple updrafts/storm cores has been noted over the past hour as increasing low level destabilization combines with relatively modest deep layer shear to support increasing storm development and potential organization. Still expect most of the widespread coverage this evening to work into our area from the south, but ongoing storms will still need to be watched, especially as they near the frontal boundary draped across our north. Do think that these storms will gradually transition from mainly a hail threat now to more of a damaging wind threat later. Additionally, cannot completely rule out an isolated funnel or tornado given low level turning.

Rosie Red

Warning Issued

The MESH jumped up to 0.94 along with the dbz & flash on the storm NE of the radar site.  I issued the warning just before the MESH jumped up to 1.58.  The ProbHail seemed a tad low.

***34 minutes later the NWS issued a warning

-Penny Gardens

UNR - SVR issued off of ProbSevere. Not a great idea!!

2125Z: Strong/Severe storms continue to move from SE WY into the UNR CWA as expected so took after quickly glancing at GLM/ProbSevere after a blog post, decided to issue a SVR based on ProbSevere & MESH values. WHen I first noticed the storm it was nearing the CYS/UNR CWA boundary & had a ProbHail of 77%, ProbWind of 53%, & MESH of 1.68". Loopping through the last 10 minutes of data I noticed an increasing trend for all values so issuing a quick warning for golf-ball sized hail based on MESH & ProbHail values seemed like a no-brainier to me. Furthermore GLM total energy showed relatively high values compared to other storms in the area so far this afternoon.

Unfortunately... after spending time on a blog post I committed the cardinal sin of warning operations & lost my situational awareness before issuing the warning. The storm began to weaken almost immediately after I issued my warning ProbHail values quickly dropping to less than 10% & GLM lightning data showing a clear decreasing trend as well. SPC mesoanalysis clearly showed these storms moving into a poor environment in NE WY with less than 500 J/kg MLCAPE, less than 30 kts effective bulk shear, & less steep lapse rates as well. I looked at the all-sky CAPE post warning as well but it was not useful in depicting the CAPE gradient from south-north in eastern WY.

Obviously it goes without saying but situational awareness & a proper analysis of the near-storm environment is essential in a warning environment. ProbSevere cannot be used by itself in a vacuum for warning decision making but rather as part of a package with other storm interrogation techniques.

ProbSevere/GLM 4 panel animation:

2030Z all-sky CAPE:

Peter Sunday

ProbSevere Polygon

The ProbSevere Polygon picked up a couple separate cells south of the severe cell we warned.  This is misleading.  In the latest update the highest values took over, when in reality it only represents the northernmost storm in this scattered line that's trying to form.

-Penny Gardens