Artifact in GLM near 26N

There is a known artifact in the FLM data.  Note the linear feature north of the yellow line (ZMA - Miami CWSU boundary) in the upper left and lower right.  This is near 26N and will always appear here, as it is some boundary in the gridded data that's stitched together (as I understood).  GLM development team is aware and working on getting rid of it.  In the example below there was some convection to the north of the artifact.

-Forrest

NUCAPS Across Iowa and Surrounding Areas

Modified NUCAPS came in just as convection began to initiate today. Repeating what I said yesterday, I appreciate the update Jack made to adjust the surface values of all "green/passed QC" NUCAPS points using RTMA, even if the more intensive adjustment cannot be made. The failure of the more intensive adjustment for passed qc soundings is due to a lack of GOES surface temperature data due to low cloud cover.

Sampling NUCAPS soundings from the central portion of our CWA down through south of our CWA, you can see the trend of increasing moisture and instability. This trend is observed in the three soundings below. Looking at SBCAPE, values less than 500 j/kg in central Iowa increase to around 1500 j/kg in southern Iowa to 2300 j/kg. This general pattern verifies what SPC mesoanalysis is showing, and tells us that instability is increasing from the south to values that will support strong updrafts and development of severe weather.

Soundings in the area of early storm development indicate the -20C level around 20,500 ft. High reflectivity cores reaching this level will be relevant given this will be a preferred hail growth zone.

 

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- Bucky

FED vs GED (Event Density)

Over the course of the week I have been concerned with comparing the consistently low FED values (single digit for most storms) with the other lightning fields including ground-based networks. Visually the low counts per pixel do not grab your attention when looking at a busy scene with storms in a variety of stages of their life cycle. The PIs suggested using Event Density (group extent density) as an alternative with the understanding that it will show higher values. To me the GED compares more nicely with the other GLM products than the FED and also helps in distinguishing core intensity within a storm complex.  It also compares more favorably with the number of events from ENI data for easier transition from one network to another. The example below all shows the striping across Pennsylvania as the pixel sizes are adjusted further away from nader. - SCoulomb

GLM and Convective Inititation

Saw an interesting example of a developing CB (over land at the Haiti/Dominican Republic border) where GLM flashed before development was recognizable on satellite.

First, a longer loop.  Then a shorter loop focused on three frames.  All data is time matched to satellite.  In addition to GLM, ENI is plotted on the upper left (small yellow dots).

Satellite/Lightning 2002-2057Z

At the center of each of the four images is the developing cell.  The first flash occurs on frame 4 of 12.  It's most noticeable on the lower right with VIS and Total Energy.  Then, notice on the upper right the enhanced IR.  The flash seemed to practically come from nowhere, but then the cloud becomes more recognizably convective a couple frames later.

Three framed loop.  Initial flash is frame 2.

Satellite times above are 2012-2017-2022Z, with the initial flash at 2017Z.  Again, notice the upper right enhanced IR with little to see.  Max tops estimated by cloud top temp in the sequence was FL280-FL320 (flash)-FL350.  The cloud top ended up a frame or two later peaking at FL380.  ENI didn't pick this up for a few frames after this loop.

Sequence of GLM product values for the event:

Total Energy:  0fJ - 52 - 0.4
Flash Extent Density:  0 - 1 - 1
Event Density:  0 - 42 - 3
Area Extent.   0km^2 - 1122 - 70.2

Eric happened by while I was checking this out and made an interesting comment.  The intense, single flash was likely seen very clearly from the satellite since the icing/charge must have been restricted to the cloud top.  Thus, GLM can be useful for recognizing convective initiation.

-Forrest

GLM Imitates a Zebra

Notice the GLM data.  At first it appears to be "missing" or "broken".  In actuality, this is an artifact of the location.  The resolution of GLM changes as one gets further away from nadir.  One of lines where the resolution changes happens to be over PA, where this image was taken.

-Kevin

Convective Initiation Product for Des Moines, IA

Convective Initiation (severe) product indicating developing TS across far southern IA late this afternoon. The values indicated look to be running too 'hot' (Figure 1). Base reflectivity 5-10 minutes later verifies what the CI product indicated (Figure 2).

 

Figure 1. Convective Initiation Severe values increasing across far southern IA and far northern MO late this afternoon.

Figure 2. 4 panel of ProbSevere products overlaid with 0.5 degree reflectivity. Top Right: ProbHail; Bottom Right: ProbTor; Bottom Left: ProbWind

NUCAPS Gridded Low-Mid Level T & Td

One of the forecast challenges in Florida is detecting "blobs" of moisture advecting west from the open Atlantic/Bahamas into the peninsula.  These areas of increased moisture can indicate a wind surge, and increase nocturnal showers, or provide additional moisture for increased coverage of sea breeze thunderstorms during the day.

Having additional ways of identifying these features is always welcome.  In addition to the NUCAPS images of H7 and H85 moisture, I've included temperature, and compared with RAP.

NUCAPS H7 Td

RAP H7 Td

NUCAPS H85 Td

RAP H85 Td

At 850mb, prevailing flow today is from the east.  On the RAP and NUCAPS images above at this level, you can see elongated (white-red extending N-S, such as over S FL and over the eastern gulf) areas of moisture, as described above, moving westward.

NUCAPS H7 T

RAP H7 T

NUCAPS H85 T

RAP H85 T

When evaluation NUCAPS temperatures, there is good agreement between NUCAPS and RAP when look at relative values.  This seems to be the better interpretation of NUCAPS data that I've found so far, rather than looking at absolute temps.  We can see from the smoothed out point soundings that literal values are not it's strength.  Rather, "Temps at this level are higher over here, than they are over there" is more NUCAPS strength.  That still has value in situational awareness.

The satellite scene 1830-1915Z during time of NUCAPS data

The satellite scene has some patches of lower level clouds over FL and cstl waters.  There is some cirrus streaming SSE over the eastern gulf.

-Forrest

NUCAPS crosses the Delaware

A look at the environment across the BGM area ahead of the approaching convection confirmed weak instability with MUCAPE <1000 J/kg on the RAP forecast sounding near Mt. Vernon. A NUCAPS sounding in the same location an hour earlier depicted greater available instability (almost 1500 J/kg). Boundary layer temperatures were similar on both but NUCAPS showed a more moist profile. The big difference was the warm layer above 500 mb depicted on the RAP sounding and nearby ALY 12Z run. NUCAPS did not have this warm layer and therefore higher overall CAPE values. - SCoulomb

Mesoscale Analysis in Des Moines

GOES-16 upper-level water vapor imagery reveals a closed upper low advancing east across southern Nebraska early this afternoon.

Visible imagery shows low clouds across much of the CWA, with cu beginning to develop across the far southern portions in the warm sector of the storm system

Morning GOES-16 Derived Motion Winds revealed a 110+ knot 300 mb southwest to northeast oriented jet core across Iowa. This agrees with the GFS depiction of the jet in that area, which has that jet exiting and a jet entrance region poking into southern Iowa later today. Winds in the 750 mb to 850 mb layer are generally 15-25 knots from the south/southeast, with slightly stronger winds advancing towards our south implying increasing LL WAA.

The default LAP products have very little data given low cloud cover over the region.  However, the all-sky LAP products have a lot of cloudy sky retrieval pixels, filling in those gaps, in addition to some clear sky pixels moving north into the CWA. From 1730 to 1900, all sky LAP CAPE has increased from 500 to 700 j/kg, and TPW has increased from around 1.32" to 1.36". CAPE over 1000 j/kg reside just south of our warning area. These trends imply the atmosphere is becoming more favorable for the development of severe storms.

 The LAP Layer PW product, comprised mostly of clear sky and cloudy sky retrievals across the domain, shows some significant features. Clockwise from top left PW sigma layers: sfc - 0.9, 0.9 - 0.7, TPW, 0.7 - 0.3. The two lower layers show fairly high levels of moisture, while the upper level reveals a nose of dryer air advancing toward the CWA. This trend would imply increasing convective instability as we advance through the afternoon.

- Bucky

GLM missed low energy/first flash

A couple of times this week we have noticed in comparison with ENI, missed flashes on GLM. The first flash is typically the most important for IDSS for outdoor venues, especially since the need for lead time grows with increased size of crowds. In order to get the most lead time there likely needs to be a trade-off with higher false detections for GLM to keep up with ground-based networks for the weaker events. It is preferred that GLM has equal or better detection capability for low energy and first flash as the ground-based networks in order for it to be trusted for application in IDSS. The more times flashes are depicted by other sources and not by GLM the less GLM is going to be trusted in a forecast environment despite its other benefits.  Similarly the more ECMWF data shows a faster fropa with arctic outbreaks the less the GFS is going to be used to time shallow fronts.

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