Storm on the Potomac

Moderate instability and good deep-layer shear produced a line of storms near a surface trough in northern Virginia. ProbWind v3 was handling the severe threat better than v2, with a probability of 41% vs. 3%, seven minutes before reports of trees down. PWv3 increased by over 20% at 17:00 UTC, due to increases in the MRMS VIL and 0-3 km lapse rate, with the MRMS azimuthal shears and composite reflectivity also contributing. Forecasters at the HWT have noted this week that PWv3 seems to be better calibrated to the wind threat than its predecessor.

ProbWind in northern Alabama

At the HWT, forecasters working the warning desk in Jackson, MS noted an arc of storms in northern Alabama where ProbWind v3 was much higher than its v2 counterpart. They shared that the greater ProbWind probabilities and the fact that they received sub-severe LSRs, (~40 kt gusts) gave them more confidence that there could be severe-level reports soon. The NWS in Huntsville, AL issued a severe thunderstorm warning at 21:18 UTC and there were indeed trees down at 21:49 UTC, near Athens, AL.

Figure 1: ProbSevere v3 contours, MRMS MergedRef, and official NWS severe weather warnings for storms in northern AL.

Figure 2: ProbSevere time series for the storm highlighted in Figure 1.

ProbWind v3 produced greater and more consistent probabilities than v2 for this storm. A post-mortem analysis showed that the top-5 contributing predictors were:

1. MRMS VIL (23.6 J/kg)
2. 0-3 km lapse rate (7.6 C/km)
3. MRMS 0-2 km AzShear (7 x 0.001 /s)
4. MRMS 3-6 km AzShear (7 x 0.001 /s)
   
5. ABI+GLM intense convection probability (ICP; 69%).

The ProbSevere team has been in active discussions with HWT forecasters regarding explaining and conveying model predictions in AWIPS in near-realtime. 

ProbWind with report Leesburg VA

We had given some thought about operating in Kentucky or Virginia with one group today, so we have been paying a bit of attention in the eastern US.  One storm west of Washington DC had ProbSevere, specifically ProbWind rapidly rise this afternoon, while most storms had ProbWind remain 5% or less.  The figure below shows the rapid increase of ProbWind (blue, upper left) and the black line at 1905 UTC represents a wind report of trees down blocking a road.

ProbSevere time series from the ProbSevere website.  The upper left panel show the time trends of the various ProbSevere models.  Note how ProbWind rapidly increases between 1845 and 1900 UTC.  A report of trees down blocking a road was received at 1905 UTC.

-J. Sieglaff

Prob wind - two cases with unexpected results.

Here are two cases where ProbWind produced surprising results. In the case above, a very strong wind signature descended from a linear storm segment. BV data near 80 knots in the lower 3 scans, however ProbWind was only at 71%. I would have likely issued a warning here without ProbWind, however the ProbWind data made me question mid-level winds within the thunderstorm complex.



In this case, a storm well behind the main outflow is identified. Prob wind is slightly higher here, at 74%, however the storm had no signs of imminent high wind in any of the lower tilt data. This case may have been a result of stronger mid level winds aloft affecting the prob output.

-Dusty Davis

High ProbWind values with severe reports!!

The storm cluster across N TX began to gust out late in the afternoon. Line motion was ~43kt as the storms surged across Montague county just south of the Red River. There was a report of wind damage in Texas (power poles blown down) and in Oklahoma (estimated 60-70 mph winds) associated with the storm cluster.  ProbWind was as high as it has been the past couple of days in the 92-95% range during this time. Of note, the Flash Rate was very high with the identified object, at times nearing 150 fl/min and the AzShear was 'strong'. This combined with the environmental parameters helped increase the wind probs throughout the life of this cluster as it moved ENE. ProbWind was equally high with other objects to the northeast and southwest of the featured storms yet no wind reports were received from them. Interestingly though, ProbTor was ~30% with the Montague county object at this time helping draw attention to it.


Low Level AzShear (UL), Mid Level AzShear (UR), ProbHail (LL), ProbWind (LR)

DLH - Warning Issued based on ProbSevere

2030Z: I issued a warning on a storm near Hill City, MN primairly based on data from ProbSevere. I was started watching the storm when ProbWind values got above 70%. The storm was in a solid environment & GLM data as well as cloud top cooling trends from IR indicated the storm was steadily maintaining its intensity.  Once ProbWind values showed an increase to 80% & MESH values continued to increase over 1" I decided to issue a SVR for 60 mph wind & 1.5" hail. Shortly after issuing ProbHail & ProbWind both continued to increase & MESH increased up to 1.22"

What I found interesting was that the storm to its north seemed to look stronger with higher values of GLM flash extent density & total power, as well as higher reflectivity values. However, ProbSevere values were much lower with this storm with ProbWind the only field of interest up around 58%.

GLM 4 panel animation:

MRMS RALA/warning animation:

Peter Sunday

ABQ - 2300Z Update

2240Z: Heading into 23Z, ProbSevere indicated a likely severe storm SE of ABQ with ProbWind 88%, ProbHail 76%, & even ProbTor of 21%. MESH values are slightly higher than 1", & the prescence of a mid-level mesocyclone along with -20C reflectivity greater than 50 dBZ all indicating the potential for severe hail.
Interestingly enough, there continues to be little correlation between increasing trends in the GLM fields & increasing storm severity (gif below). This has been noted in past HWTs with western storms which may be a limitation with using GLM products in this region.

Zooming out, GOES-16 IR/VIS data shows some cu development & cooling cloud tops across southern NM.

Looking at the CI fields, not too much is expected with this development with values generally 50% or lower & severe CI probs only around 10%

And finally, little to no increasing trend in GLM Flash Density makes me even more confident in anticipating little to no development of this convection over southern NM

Peter Sunday

CWA TomClemmons RAH 05-10-2018

Synopsis: Well removed from the better upper dynamics/forcing and shear
that will move through the NE US this afternoon and evening,
forcing across central NC will be rather weak, limited to mainly
weak near sfc convergence, as the surface trough crosses the area.
However, strong daytime heating, featuring afternoon temps in the
mid 80s, will result in steep low-level lapse rates. These steep low-
level rates when coupled with with BL dewpoints in the lower 60s,
will fuel moderate instability of 1500-2000 J/Kg that extends well
into the mixed phased region. Despite the deep westerly flow in
place, majority of the CAMS indicate a fairly congealed multi-cell
line segment crossing the area between 18z to 03z. Given 20 to 25
kts of deep layer shear, some of the strongest updrafts will have
the potential to produce severe weather, including, hail and
damaging wind gusts.

Hampered by slow computer systems Tuesday, Wednesday, and Thursday:(

Notice low correlation between  -20 C Isothermal Reflectivity & GLM Total Energy 5min-1min update. Notice storm near the cursor.

In this example the storm is on the northern RAH CWA border, the updraft has pushed 50-60dbz echoes up through the -20 C isotherm, notice this time the GLM Total Energy and the Extent Density (# of Flashes that have crossed a pixel) are both showing high values. This would be a good situation awareness tool during an ongoing severe weather event. This storm was currently producing damaging hail and strong winds.

ProbSevere Wind and Hail:

1.75" hail was reported at 5:25 pm near Bahama.

ProbWind:

3NW of Stovall 2 Trees Down

Splitting of Supercells and Prob Severe/Tor/Wind

A supercell that had been warned on split with the northern storm moving into the more favorable area of instability and the updraft rapidly strengthened to severe. Noticed that Prob Tor has increased to 9% on the northern storm and Prob Hail/Wind are 99%/89% respectively.  Issued a severe thunderstorm warning shortly after the last scan on this animation. Will be monitoring that northern storm for ProbTor. Have seen some upstream storms with strengthening with rotation.

More to come...

Supercell

Severe Storm with All Sky CAPE Prob Severe

Interrogated a storm entering the gradient in instability shown by the All Sky CAPE products and also increasing Prob Hail and Wind Products (cell with SVR box on it). The cell is moving into Garden County Nebraska:

More to come...

Supercell

ProbSevereWindTor with severe storm

Looked at Prob Severe Tor/Wind/Hail with MRMS reflectivity. The Hail probabilities actually increased to 90% prior to warning issuance. MESH values were around 1.56 inches. Prob Wind was a lower (78%) value. Did see where there was a TBSS in the dual pol and reflectivity products indicative of hail. Issued severe thunderstorm warning shortly after the probs showed this. Did notice that Prob Tor was around 1% but monitoring the velocities as the cell is located near the warm front and wind shear is sufficient to support it.

More to come...

Supercell

Prob Severe & Wind Flurry of readouts

Looking at the Probabilistic products during the latest warning operations, if there are 2 or more cells within warnings, it is definitely useful to compare the parameters in the readout and probabilities. It would helpful if the color table for the Prob Severe, Hail, and Wind could have a better gradient in colors from 70% and above. Also, did not find it useful to have MESH in the Prob Wind product readout, nor did I find it useful to have the flash rate especially with the GLM data available for us to use. This image also displays why having so much on the readout for Prob Severe is too much on the screen.

Supercell

ProbWind Underdone and Missed a Warning

Here is a 50 minute loop of 0.5 Velocity data from BGM.  Notice the strong area of winds approaching the radar.  It's around 50 kt a few thousand feet off the surface.  The second image measures 52 kt at 2,500 feet AGL.  But ProbWind reported 1% probability for virtually the entire time.  This is massively underdone.  Why?  50 kt is Severe Thunderstorm Warning criteria.  If this wind a few thousand feet above ground mixes down to the surface, then it's easily SVR criteria.  Yet the ProbWind is only 1%.

So what happened?  At 1927Z (image three) NWS BGM reported tree limbs and wires down on Timberline Drive.  This matches up fairly well with the general location highlighted in image two.  If forecasters were relying solely on ProbWind, they would have missed a warning.  It needs to factor the SRM and Velocity data into the calculations.  Otherwise, forecasters may not be as confident in the ProbWind data.

 

-Kevin

Severe storm outbreak in the Mississippi and Ohio River Valleys

A potent shortwave forced severe storms across the middle of the U.S. yesterday, wreaking havoc from Texas to Ohio. Below is the 850mb analysis from 00Z 04/04/2018 (Figure 1), showing well-defined warm and cold fronts emanating from the low, centered on Lake Michigan. We also see that moisture was well-established in the warm sector and the flow at 850mb was quite strong (30-40 kts).

Figure 1: 850mb analysis from 00Z 04/04/2018.

The NOAA/CIMSS ProbSevere model is experimenting with hazard-specific models: ProbHail, ProbWind, and ProbTor. The ProbHail model did fairly well to capture the initial hail threat along the cold front, with numerous storms exhibiting strong satellite growth from GOES-16.

These storms produced numerous hail reports between 1" and 1.5" in and around the Mark Twain National Forest.

Figure 2: ProbHail for storms in eastern MO, with MRMS MergedReflectivity and NWS severe weather warnings.

With sampling turned on in AWIPS2 (Figure 3), users of ProbHail can see the constituent predictors. Here, the strong satellite growth rate, high MRMS MESH (1.5"), and high Earth Networks® total lightning flash rate (40 fl/min) contributed to a ProbHail of 96%. NWP predictors of effective bulk shear, CAPE between -10C and -30C ("hail cape"), precipitable water (PWAT), and the lowest height of the wetbulb 0C isotherm are also used as inputs in ProbHail.

Figure 3: ProbHail readout for storms in eastern MO, with MRMS MergedReflectivity and NWS severe weather warnings.

Due to very favorable kinematics, the tornado threat was rather high, with the Storm Prediction Center issuing a wide swath of 10% probabilities for tornadoes within 25 mi of a location for their 2000Z outlook (Figure 4).

Figure 4: SPC tornado outlook and verification for 20Z and 12Z, respectively.

A storm that produced numerous reports of significant wind damage in the Dayton, OH metro area also produced a tornado east of the metro. ProbTor captured it's development well (Figure 5).

Figure 5: ProbSevere, MRMS MergedReflectivity, and NWS severe weather warnings for southwest OH.

The time series of this storm's attributes demonstrate that very high MRMS 0-2km AzShear (>20 * 0.001 /s), along with SRH of 300-400 m2/s2 in the 0-1km layer helped spike the ProbTor value to over 90%. In this case, the tornado report came slightly after the time of peak ProbTor. Several wind reports in the Dayton area were significant (e.g., "large debris cloud", "structural damage to homes"), around 20Z when ProbTor was in the 30-50% range. Thus, it's possible there may have been a tornado earlier (a NWS survey should confirm the presence or lack thereof).

Figure 6: Time series of ProbTor (red curve) for this storm with its predictors. The bottom axes show NWS warnings and reports.

The "ProbSevere" value simply uses the maximum of ProbHail, ProbWind, and ProbTor. For this long-lived storm, each model was the maximum at different times. Regardless, the ProbSevere values were mostly over 70% when there was reported severe weather. The MESH and lightning (pink and green curves) show the cycling of this storm nicely. The storm produced hail and wind reports in the Columbus, OH metro and later east of the metro.

Figure 7: Time series of ProbSevere (red curve) for this storm with its predictors. The bottom axes show NWS warnings and reports.

Storms later evolved into big wind-producers, evidenced by these storms in the Nashville, TN area. There were many reports of trees and power lines down in the metro area around 0200-0230Z.

Figure 8: ProbWind, MRMS MergedReflectivity, and NWS severe weather warnings for storms affecting the Nashville metro.

 ProbWind was in the 50-70% range for these storms, owing to a strong MeanWind in the 1-3km layer and moderate 0-2km MRMS AzShear. Note that the ProbWind readout in AWIPS2 now has a "weak", "moderate", and "strong" designation tag for the MRMS AzShear fields (e.g., Figure 9)

Figure 9: ProbWind readout for a storm south of Nashville.

At the end of each day, we make an "accumulation" product, plotting the centroids of storms colored by their ProbSevere value (or ProbTor value), along with the NWS severe weather warnings and SPC preliminary reports. From Figure 10, we see that ProbSevere corresponded with severe weather warnings and reports quite well in MO, AR, IL, IN, OH, KY, PA, and TN, and parts of TX and LA. However, many wind reports were missed (at the 50% threshold) in MS, AL, and GA. Many of these storms had meager reflectivity and lightning flash rates, and no discernible satellite growth. ProbWind was largely 10-30% for these storms, a small improvement over the legacy "all-in-one" ProbSevere product, which had < 10% for most of these storms. We are still working to improve upon probabilistic prediction of storms in this regime, and are open to ideas from the field.

Late December storms

A negatively-tilted shortwave brought some low-level moisture return to the gulf states this week, and with the moisture, some scattered severe storms.

A couple tornadic storms affected portions of east Texas. The NOAA/CIMSS ProbSevere model now incorporates the GOES-16 satellite growth rates, and a storm affecting Cherokee Co., TX, had a strong normalized growth well before it produced severe weather.

Figure 1: AWIPS2 screen captures of MRMS MergedReflectivity, ProbSevere contours, and NWS warnings for a storm near Rusk, Texas.

The ProbWind values vacillated largely between 50% and 75% for this storm, before producing a tornado at 00:56 UTC and multiple wind damage reports in the town or Rusk, TX. The strong GOES-16 vertical growth rate, large ENI flash rate (~30-70 fl/min), and stout kinematic fields (eff. bulk shear ~ 45-50 kts; meanwind 700-900mb ~ 35 kts) combined to produce these moderate-strong ProbWind values. The MRMS MESH remained rather low (~ 0.2 - 0.6 in), signaling that this was not a severe hail situation. ProbTor had a maximum value of 12% before the first tornado report.

This storm featured jumps in ProbWind value (one produced by a large increase in flash rate, indicative of a lightning jump), and being an outlier storm amongst its neighbors, in terms of probability value. Both features in ProbSevere objects have been identified by forecasters as indicating possible severe weather.

A second storm formed further south and later in the night, which also produced a damaging tornado, touching down northeast of Beaumont, TX, and later northwest of Lake Charles, LA, blowing off the roof to a restaurant.

Figure 2: AWIPS2 screen captures of MRMS MergedReflectivity, ProbSevere contours, and NWS warnings for storm heading into southwest Louisiana.

The kinematics for this storm were very favorable, with effective bulk shear of 50 kts, meanwind 700-900mb of 45 kts, and 0-1 km storm-relative helicity near 300 J/kg. The first tornado touched down at 07:41 UTC, when ProbTor was about 30%. ProbTor then jumped from 30% to 50% at 08:00 UTC, the time of the second tornado report. This jump in ProbTor value was coincident with an increase in total lightning (a lightning jump) as well as an increase in low-level rotation.

Figure 3: Time series of ProbTor and predictor values for this storm affecting southeast TX and southwest LA.

A tornado warning was issued at 08:10 UTC, when ProbTor had just increased to 90%. The third tornado reported, at 08:20 UTC, was rated EF1 and destroyed the roof of a restaurant in DeQuincy, Louisiana.

Prob Wind numbers

Series of 3 posts of Prob wind percent high, then low, then high (roughly 70%-30%-70%). The azmuthial shear is roughly similar in each one tho. The base V has a sharp velocity increase at the same time of the lower prob wind (00Z time).