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.

CTC provides >1 hr lead time on severe hail report

Forecaster comments from EWP blog...

The CIMSS cloud top cooling algorithm first detected cooling rates of approximately -10 C/15 min with a thunderstorm developing across eastern Hoke and western Cumberland counties on the 1815z image. The algorithm continued to show strong cooling rates on the next two images with accumulated CTC values of approximately -30 to -35 C/15 min before the cell was dropped from the display after 1845z. A report of quarter sized hail was received in far southwestern Harnett county with this thunderstorm at 1937z, almost an hour and a half after the algorithm first detected stronger cooling with this storm.

Accumulated CTC values for a cell that produced severe hail.

CTC success in Raleigh, NC WFO CWA

The UW-CTC product is showing good success with convective development in the Raleigh, NC with the storms being flagged exhibiting severe MESH values, and producing supportive hail reports.  At 1715 UTC, the CTC product showed near strong cooling rates of approximately -16.5K/15 min for the initial development of storms along a boundary in eastern NC (see Fig. 1).

Fig. 1

This particular storm had a severe MESH of 1.25" by 1832 UTC (see Fig. 2) [lead time of 1 hour and 17 mintues], and subsequently 1.5" by 1845 UTC (see Fig. 3) [lead time of 1 hour and 30 minutes]. 

Fig. 2

Fig. 3

The CTC product also picked up the storm following directly to the west of the above first storm, with a cooling rate of ~-18.5K/15 min at 1832 UTC (see Fig. 4).

Fig. 4

This storm would also later product a large MESH (not shown).  Additionally, further south and west in the other domain of interest today (Wilmington, SC), another storm started to grow first exhibiting an large intermediate cooling value of ~14K/15 min at 1732 UTC (Fig. 5), and attained a severe MESH value of ~1" at 1832 UTC, meaning a lead time of one hour (Fig. 6).

Fig. 5

Fig. 6

UAHCI Strength of Signal trends

The weak upper level low over the Southeast United States has proven to produce instances of convective initiation that the UAHCI algorithm has captured. Depending on the individual cell, cells rapidly grew which only provided one forecast of CI before initiation. However, for the slower growing storms, multiple forecasts for an object can be produced. In this example, a storm began to grow in Scotland County, NC at 1702 UTC wtih a CI strength of signal forecast of 41.

At 1715 UTC, the UAH CI Strength of Signal grew to 52 as a line of cumulus continued to develop.

At 1732 UTC, the UAH CI Strength of Signal rose to 61 within the cumulus line.

At 1745 UTC, the UAH CI Strength of Signal produced a forecast of 75.

The UAHCI forecast did not produce a forecast at 1802 UTC as the line matured into cumulonimbus. But this is an example of following a slow growing storm can lead to increased confidence in convective initiation.

CI algorithm successes over North Carolina

Forecaster comments from the EWP...

The UAH-CI algorithm displayed two areas with high strength of signal values (64 and 92) across southern Cumberland and western Sampson counties on the 1702z image. These cells intensified quickly into two thunderstorms and a report of penny sized hail was received from the eastern storm at 1823z, more than an hour after the algorithm first detected these thunderstorms.
The CIMSS-CTC algorithm showed cloud top cooling rates of between -10 to -15 C/15min on several images with a thunderstorm developing across Sampson county in North Carolina. The CTC first appeared on the 1715z image and continued to highlight this cell through the 1815z image. As the algorithm continued to show moderate cooling rates with the cell the radar presentation became more impressive and a three body scatter spike developed with the cell. A report of penny sized hail was received with this cell 1823z 5 miles WSW of Newton Grove, NC.

MCS over far SW Texas: synthetic vs real IR

Forecaster comments from EWP blog...

As described in this blog a few hours ago, storms developed S of Pecos due to ongoing diabatic heating in an environment modestly supportive for strong/isolated severe pulsating storms. Thunderstorms rapidly grouped in a loosley organized convective cluster, which gradually approached the NM boarder during the following hours. At 2300 Z, both IR showed the peak of activity/organization of that cluster with a constant weakening trend thereafter. However, the synthetic one caused a rapid decay of that cluster until 0100Z, whereas real time IR data still indicated a large cluster with cloud top temperatures of below -50 degree celsius at that time. Also, lightning activity was still present at 0100Z with that cluster although a rapid decline was also noticed until 0130 Z. So peak strength was captured well with a too fast decline of the cluster’s strength thereafter.

The synthetic IR did also an outstanding job in highlighting the area of initiation (both timing and the region…not shown).

Airmass composite used over N-Dakota

Forecaster comments on EWP blog...

Broad upper low, situated over the far NW US, pushed eastwards during the afternoon hours and onwards. A sharp 100-120 kt high-level jet also translated to the east over the N-C Rockies with the favorable left exit region approaching our area of interest over NW Dakota at 19Z onwards. The airmass composite image was helpful in pinpointing the position of the jet max as a sharp moisture gradient evolved (roughly extending from Oregon to Wyoming). Initiation over far NW Dakota also awaited the approach of the “ozone-rich” airmass (purple) as it overtook the eastward progressing dryline between 19-22Z, fostered by reports of surface dewpoints in the mid 50s beneath rapidly drying mid/upper levels.

The first image captured at 1900Z:

and the second one at 2200 Z with initiation already underway/building SE-wards:

Differences noted in the Simulated/Real-Time IR

Forecaster comments from EWP blog...

CIRA/CIMMS NSSL-WRF Simulated IR Satellite suggested convection would develop across central portions of ND and further south towards the border of SD.

Actual Real-time IR is below.  Placement of the cells is off somewhat.  Biggest discrepancy is across central portions of ND, where convection still hasn’t initiated.

UW-CTC Hits in Florida Panhandle

UW-CTC captured strong storm development in the Florida panhandle that later produced hail up to an 1 3/4".  The original storm development exhibited strong cooling rates in the neighborhood of -24K/15 min at 1855 UTC (See below).

The first severe hail was reported at 2000 UTC, giving the CTC a leadtime of one hour and five minutes.  The following SPC image shows the collection of hail reports in the panhandle.

Secondary storm development at 1955 UTC, immediately following behind the first storm, was also captured by the UW-CTC product.  Cooling rates near -27K/15 min were observed with this growth (See below).

The first severe hail report from this storm was made at 2110 UTC with a size of 1 3/4", meaning CTC had a leadtime over the severe hail by one hour and 15 minutes.