OAX: Cloud-Top-Cooling (UW-CTC) Success!

Forecaster comments from EWP blog...

Issued a severe thunderstorm warning strictly off of explosive CTC at 2315 UTC (previous post), with very little showing up on radar at the time.  As would be expected, through the following 15-20 minutes, the storm exploded, with MRMS MESH spiking up to 1″ by 2334 UTC, and a quarter size hail report by 2336 UTC.  This gave us 21 minutes of lead time from the initial warning issuance off of CTC.  Would have likely issued the warning based on traditional base products by 2325 UTC, 10 minutes after the CTC-based issuance.

UAH-CI/UW-CTC Tag Team Leads to Successful Experimental Warning

*** This is a joint post from Chris Jewett and Lee Cronce ***

A forecaster covering the OAX CWA was able to place an experimental severe thunderstorm warning based on the trends recognized in the UAH-CI and UW-CTC products.  This great example shows how the UAH-CI and UW-CTC products can work collectively to create strong forecaster confidence in a severe weather situation.

The initial recognition of severe potential took place at 2302 UTC when the UAH-CI product showed a strength of signal of 80 out of 100 (see Fig. 1).

Fig. 1

The next scan at 2315 UTC had the UW-CTC product exhibiting a strong cooling rate of ~-25K/15 min.  This information combined with what the forecasters have learned/noticed about our product in other situations prompted the forecaster to issue the warning with high confidence that the growing convective element would eventually become severe.  See Fig. 2 for the UW-CTC cooling rate along with the warning polygon created.

Fig. 2

Comparison synthetic-real IR over E-Nebraska

Forecaster comments from EWP blog...

The area over E-Nebraska was monitored for initiation. The synthetic images did a pretty good job in timing of thunderstorm development. The real development occurred only slightly to the north to what the synthetic ones proposed. The model forecast however overestimated the development along the cold front over C/S Kansas, where warm mid-levels prevented DMC of developing until now (although showers finally try to form at 23Z onwards).

Another CTC success case in the OAX CWA

Forecasters shifted their domain of interest to the OAX CWA for the potential of severe convection in the area.  Convection initiated around 2145 UTC with the UW CTC product exhibiting strong cooling for the cu popping up in the area.  The cooling rate was ~-20K/15 min (see Fig. 1).

Fig. 1

About an hour later at 2244 UTC, the cell that the CTC product flagged with the strong cooling rate produced a MESH value of 1.89" (see Fig. 2).   Again, good lead time over the potential of severe hail.

Fig. 2

Simulated Split Window Difference

On Wednesday 5/23, the NSSL-WRF simulated 10.35-12.3 micrometer product showed a local maximum across central Kansas at 21 UTC (see below; the maximum is oriented southwest to northeast and has values approaching +8 K).  This maximum is due to water vapor pooling along the surface cold front in the area, and it preceded convective cloud development along that line.  When real GOES-R data is available, this product will be very useful for forecasters who are interested in the regions where convective clouds, and eventually storms, are likely to form.

Fire in Catron county, New Mexico

Forecaster comments from EWP blog...

Between 2130 and 2145 Z another burst of the extensive smoke plume occurred, which was also captured by the CIMMS Cld Top Cooling product with values mainly below -5K/15 min.

DDC: Initiation in C-Kansas imminent?

Forecasters comments from EWP blog...

Latest VIS imagery indicates a rapid increase in convection along slowly SE-ward progressing cold front, namely over Hodgeman, Ness and Rush counties. UAH-CI product already showed modest probabilities (50-60 %) for CI with no reflectivity yet present in local radar data.

UAH-CI product placed in the upper left corner at 2130 Z

Latest HRRR is a bit more optimistic with SW-ward zipping convection compared to OUN WRF. Still unsure if storms can initiate in that area with warm mid-level tongue partly covering the cold front/dry line. Strong shear now gradually moving in from the west, so increasing storm organization is likely in case of initiation.

WFO ILM-Another Cloud Top Cooling Success!

Forecaster comments from EWP blog...

Here in WFO ILM, we have had some great success with the CIMSS Cloud Top Cooling (CTC) product this afternoon (see our previous post). Here is another success story from Horry County, SC. First we will look at the Cloud Top Cooling product at 1845Z (Top Right panel):

1845Z Cloud Top Cooling (CTC) image from WFO ILM (Top Right Panel).

 

There are two “bull’s eye’s” over SC. Our storm is the northern “bull’s eye”. The CTC showed cooling rates of -21C/15minutes AT 1845Z, which typically correlates to strong convection with significant lead times averaging 45 minutes before Maximum Expected Size of Hail (MESH) exceeds 1″. Now let’s look at some verification. First is the MESH image from 1936Z (lower left panel). This is the first time the MESH exceeded 1″ for a lead time of 51 minutes!

1936Z MESH product for WFO ILM (Lower Left panel).

 

And now for a conventional radar image from 1947Z from the KLTX Radar:

1947Z KTLX Radar image.

 

The cursor readout shows this storm has 60dbz echos up over 28,000ft…which is above even the -30C level from the 12Z CHS sounding (~25,000ft). We finally got verification of quarter size hail in NW Horry County by around 20Z, though the reports seem to have not come from directly beneath the core of the storm so some larger hail was possibly produced. Now let’s examine some NSSL 3DVAR Imagery:

KTLX Base Reflectivity (top left), NSSL 3DVAR Max Divergence (Top Right), NSSL 3DVAR Max Updraft Composite (Lower Left) and NSSL 3DVAR Max Vorticity (Lower Right) at 2005Z.

 

You can easily identify this storm based on the Max Divergence above 8km, Updraft Composite, and Max Vorticity Images as all show local, significant maxima. Today, the CTC product has shown significant value in lead time for severe hail beneath the Southeastern CONUS upper low.

ILM: CTC Lends to Good MESH Lead Time?

Forecaster comments from EWP blog...

In the 1815 UTC vis satellite image (upper right of top 3-panel), cloud-top cooling was on the order of -17C/15min with a developing thunderstorm.  By 1858 UTC, MRMS MESH product reached 1″ hail size (middle image), and just over 2″ hail size by 1906 UTC.  The UW-CTC product lead to 45-50 minute lead time for 1-2″ hail (as estimated by MRMS MESH).  This is one of many instances we’ve noticed the CTC give decent lead time for 1″ or larger hail.

1815 UTC. Rapid convective development as indicated by -17C/15min cloud-top-cooling rates.

1858 UTC. MRMS (multi-radar, multi-sensor) MESH (max estimated hail size) is estimating 1.02" hail, about 45 minutes after rapid CTC.

1906 UTC. MRMS MESH now estimating 2.13" hail, about 50 minutes after initial rapid CTC.

Awaiting initiation over NE Colorado

Forecaster comments from  EWP blog...

Conditions gradually improve for thunderstorm development over NE Colorado although initiation may be delayed until the 23-00 Z time frame. Surface boundary pushed through as lee depression slowly consolidated over W-Kansas. 12Z Denver soundings showed steep lapse rates with a deepening and well mixed boundary layer. Numerous weak caps present (roughly at 700, 600 and 500 hPa).  CIMSS Cld top cooling product revealed numerous spots with moderately cooling tops in the order of -10 to -15 K/15 min with UAHCI CI product showing low to non existent probabilities. This may be the reason for growing updrafts before reaching one of those aforementioned caps, which suppressed further development. For the forecaster however this is already helpful to pinpoint the area, where enhanced cumulus growth occurs and where initiation may be the most likely.

Question now arises if moisture recovered since 12 Z. Surface dewpoints struggle to exceed mid to upper 30s with lower 40s now entering far NE Colorado as winds backs more to NE-erly directions in response to the consolidating lee cyclogenesis. However, products like the 780mb equiv pot temp and the theta-e diff show robust signals for available potential instability over far NE Colorado with an increasing trend during the following hours. In fact, latest HRRR forecast and the tongue of pot. instability seem to overlap nicely. Hence initiation seems possible around and south of a line Steamboat Springs-Denver-Deer Trail during aforementioned time frame. Incoming mid-level speed max pushes DLS aoa 80 kt, which is more than adequate for well organized storms.