With the storms moving out of La Crosse’s CWA, I’ve got a bit of time to finally take a look at the Optical Flow Winds. I’m intrigued by the product to say the least.
Here is a still image of the GOES-East Meso1 sector today with the string of supercells ongoing (and tail-end charlie in NE Iowa). One thing I was curious about was how well this could detect storm top divergence. The radar data was pretty noisy in AWIPS so it was hard to see this in those products.
Here is what the “base” product shows.
Now let’s overlay the upper-level winds as detected by this product (roughly the 100-50 hPa layer although I wouldn’t be surprised if some storm tops are going above this:
A user can also overlay lower layer wind fields to see what could be happening in those areas. The key thing was though to see what the storm-top divergence may look like:
And that’s pretty impressive for an optically derived wind field! Individual turrets may be showing up where there are enhanced area of convergence/divergence couplets not the ones on the edge of the cloud detection). It isn’t perfect though:
There is a lot of variability from scan to scan on the strength of the divergence field but there is enough of a signal to figure out where the strongest couplets could be and which storm tops they could be associated with. We couldn’t overlay radar data or the 3.9 micron “Red/visible” channel with a divergence product to make a 1:1 comparison; something to consider would be a grid that could be overlaid on a different ABI image to do a visual comparison to this product.
– Hank Pym
With a busy day still underway across Wisconsin, the use of the Optical Flow Winds, GLM, Prob Severe, and NUCAPS soundings were a big help in looking at the pre-convective storm environment and in warning operations.
When it came to looking at sounding data we had a NOAA-20, and AQUA pass for the polar orbiting satellites, that we could then compare to the special observed sounding from GRB.
By 2200z, a strong cluster of storms was ongoing in northwestern Minnesota ENE of the KMVX RDA while moving northeast. Below are a set of 4 figures showing the divergence at the cloud top of the ongoing cell, with a cyan circle outlining the updraft area.
Here is a comparison of the Optical Flow Winds divergence versus storm top divergence provided by traditional means:
OFW – STD
>100 – ~115 kt
~80 – ~105 kt
>100 – ~150 kt
> 100 – ~130kt
PHS and NUCAPS
At 2144Z the Prob Severe V2 tornado jumped to 21% while V3 only went to 6%.
PHS CAPE values increase from north to south over Fort Stockton. This correlated well with RAP mesoanalyzed SB CAPE on SPC webpage. Storms actively going up along this gradient as an outflow boundary pushed south during the early afternoon from overnight convection over Oklahoma.
PHS CAPE 18Z 1 hour forecast for 19Z
PHS CAPE 18Z 2 hour forecast for 20Z.
Storms developing over Fort Stockton via Day Cloud Phase Distinction on GOES 17 Mesosector
We showed above that the north side of the outflow would contain more instability – which is directly related to the moisture from the morning MCS outflow. The Gridded NUCAPS provides additional insight using the 850mb moisture fields from both AQUA and NOAA20 respectively – validating our hypothesis.
We double checked since there was a dust advisory/dust in the forecast and yes – Dust
Don’t warn if pop = 0
Convection was skirting the northeast portion of the CWA so we’ll use the recent pass of NOAA-20 to view the potential for convection redevelopment to the west and affecting the forecast in our CWA. Here are the Modified NUCAPS soundings:
The top image is for the sounding in Jones county, below is Scurry – which shows a capping inversion still in place.
Weak winds aloft and throughout the atmosphere have contributed to very little in the way of storm motion. Hence, locally heavy rainfall may begin to evolve, even over an area that has received very little rainfall in the last 6 months.
Optical Flow Winds in the 200-100 mb level.
Day Cloud Phase valid 2041Z.
Day Cloud Phase valid 2141Z.
PHS depicts this plume of moisture and associated instability will back into New Mexico this evening. Could it play a part in tomorrow’s severe weather risk?
Here is what happened at El Paso when the front backed into the area – Dewpoint jumped from 30F to 50F
– David Spritz
– Mr. Bean
Optical Flow Winds
A comparison of NUCAPS at 19Z with observed/analysis products from SPC showed good comparison for both modified and unmodified data. Below shows the unmodified NUCAPS sounding that was “green” over the north-central portion of the ILX CWA. The MLCAPE was around 500 J/kg, with DCAPE around 690 J/kg, freezing levels just below 10,000 feet, and PW’s around 1.1 inches.
A modified NUCAPS sounding for the same location showed an uptick in MLCAPE to around 600 J/kg, along with similar PW’s, DCAPE and freezing level.
A comparison with SPC mesoanalysis at 20Z showed very comparable PW values, between 1.1 to 1.2 inches over north-central IL, and freezing levels between 10 to 11 kft. As for MLCAPE, it appeared that for both modified and unmodified NUCAPS, the observed was higher than NUCAPS, around 1000-1500 J/kg, perhaps not having a high enough surface dewpoint. As for 850 mb temperatures, they were comparable to those observed, in the 12-14 degC range. DCAPE was also comparable in NUCAPS with what the SPC mesoanalysis page was showing, between 600-700 J/kg.
With regards to lightningCAST, ProbSevere, and GLM, around 1932Z, once again the LightningCast was showing good lead time for areas downstream of storms. The main cell at this time I was watching was in the southeast Part of our CWA, which had a nice contour of 75% to the north and east of that cell extending well north of the storm core.
At 20Z, the Optical Flow divergence field appeared to match up well with observed convection at this time. It thus showed quite well with the shear field.
ProbSevere’s time series graph continues to show added value, allowing the forecaster to see the trend in a storm’s severity and probability of severe potential. This image was at 20:40Z.
Around 21Z, I noticed a jump in GLM FED for the area of storms in the northwest part of the CWA. Alongside this, the GLM TOE also increased, along with a decrease in MFA with the same storm cell. This area corresponded with increased flash rates in the EarthNetworks. I modified the GLM FED scale to 20-25 as a maximum to see the activity better, as well as lowering TOE to 50 as a maximum.
Around 22Z, the GLM TOE showed a good correlation with the 3 strongest storms based on dBZ and ProbSevere, one to the north, and two in the far southeast, bordering Indiana. For this display of TOE, I lowered the contours to a max of 50, which seemed to work well.
Around 22:12Z, the LightningCast showed an uptick in probabilities of 75% north of a cell that was starting to show towering CU on the day cloud phase. This was before GLM and ground-based radar showed uptick in lightning activity.
Are the edges of LightningCast contours related to the detection of GLM? See below image…The contours do not close off.
LightningCast & GLM for DSS
Optical Flow Winds
An upper low and cold front is expected to move across the lower MS Valley. As the upper low moves east today, weak shortwaves embedded in southwest flow will lead to a marginal risk of thunderstorms as they form along and ahead of the front over the Memphis region. The main concern was a moderate risk of excessive rainfall for this afternoon/evening.
IR imagery. Upper low located near the OK Panhandle.
Surface analysis map of the surface low and attendant front.
Surface observations as of 4:00PM CDT.
SPC Day 1 Convective placing TN at a marginal risk.
MLCAPE ~500 J/kg.
PHS displaying weak CAPE/LI values and a well-defined dry line just west of AR.
WFO Memphis headlining excessive rainfall outlook.
WFO Memphis headlining marginal risk of severe storms.
Most of the severe storms were east and south of our area of interest shown here with GLM.
GLM overlaid with Radar.
GLM overlaid with satellite imagery.
ProbSevere3 showing a low risk of thunderstorms.
Optical Flow winds show an area of divergence over eastern and southern AR/TN border.