Severe convection currently evolves along the cold front over C Iowa with Cld top cooling product showing impressive cooling rates below -65 K/15 min e.g. over Warren and Polk counties.
Helge
Impressive Cld top cooling rate, Iowa
Month: May 2012
Domain Update
About 2100 UTC we gave up on lightning in the east coast domains (saw a max of 2 flashes / min during our time there) and re-localized to Des Moines, IA (McKinney & Kleinsasser) & La Crosse, WI (Strassberg & Hirsch) with our observers working Pleasant Hill, MO.
Storms are already ongoing with CTC rates as low as -50 C for multiple storms and we expect some SVR warnings shortly.
-K. Calhoun, Week 3 Coordinator
SimSat has problems with tropical low
A weak tropical low moved from Cuba to the NE during the daytime hours and was forecast to affect far SE Florida. Comparing SimSat and real IR/WV data, significant differences can be seen especially regarding the cirrus canopy. The main reason for the differences may be the much stronger development of this depression than expected 21 h ago. NHC also increased probs to 40 %, indicating a consolidating system. This evolution may have resulted in a better defined depression’s center with stronger convective development. Therefore those products may have to be used carefully for tropical lows, which reveal stronger intensification rates compared to what models forecast.
Helge
Iowa CTC Lead Time
The cloud top cooling product in central Iowa indicated nearly 40 C/15 km of cloud top cooling for a storm in Boone and Story counties. This product preceded intense radar reflectivity in the area by nearly an hour. 
WFO MLB-CI/CTC Example
Here is an example of how UAH Convective Initiation (CI) and CIMSS Cloud Top Cooling (CTC) can be used to anticipate convective development. Here in the first image at 1940Z, let’s look at the CI product in the top left panel:
Focus on the Lake/Marion/Sumter County line. There is a maximum in CI there of 80, indicating likely convective development. If we look at the CTC in the same area on the next image (top right panel), we see a developing max CTC over -20C/15min, which is a strong indicator of a developing severe thunderstorm.
Although this did not ultimately become a severe thunderstorm, we did observe a few lightning strikes shortly after this time. This progression from strong CI signal to strong CTC can be a good indicator of a developing thunderstorm.–Gordon Strassberg for WFO MLB
CI along sea breeze over NE Florida
Westward moving sea breeze front helped to spark sporadic showers/thunderstorms during the afternoon hours. We captured the interaction of an already ongoing weak shower, as front moved in from the east.
The southern parts of Nassau and Charlton county and Baker county were monitored. At 1932Z an increase in cloud top cooling was noticed and 8 min later, CI product also had probabilities of 70 % plus for this area. At the same time, a cooling rate of roughly -15K/15 min was detected. Rapid development occurred thereafter with 50 dBz and more seen in the JAX radar side at 1947 Z, which gave a good lead time for focusing on the potential hot-spot over NE Florida. The storm was a pulsating one with rapid weakening thereafter.
Helge
LWX 5/24: UAH-CI Signal Precedes UW-CTC Signal…Both Precede Convective Initiation
The more I look at these products, the more I’m convinced they work very well in tandem with each other. Given an environment that supports convective growth, a strong UAH-CI signal (upper image, top left panel) typically precedes a strong UW-CTC signal (middle image, top right panel). In this case, the strong UAH-CI signal (1615 UTC) preceded the UW-CTC signal (1645 UTC) by about 30 minutes. By 1715-1730 UTC, 30-45 minutes later, deep-moist convection did indeed form as evidenced by the numerous CG strikes (bottom image, bottom left panel). We’ve seen this all week…UAH-CI gives us a heads up that general convection is initially building, then a short time later UW-CTC typically picks up on the stronger convection building. Given a strong cap isn’t present and instability is sufficient, deep-moist convection typically develops 30-60 minutes thereafter.
CI mainly inland across FL peninsula
Latest CI image shows moderately high probabilities for CI along ahead of the westward moving sea-breeze boundary. Best chance for thunderstorms appears to be from the interior counties towards the west coast. Some initiation is possible across Northern Brevard County…though the prospects for lightning are looking slim at this point.
HIRSCH
Overview of sea breeze fronts in Florida
We’re currently monitoring the rapidly inland moving see breeze front over NE Florida with enhanced TCU present along the convergence zone, whereas the west coast see breeze has trouble to move inland within dominant easterly wind regime. Both convergence zones enter an area over N-C Florida where slightly lower dewpoints (lower to mid 60s) are present. With ongoing diabatic heating, cap continues to weaken or has already vanished with isolated initiation possible over N-C Florida in the following hours but ongoing large-scale weak subsidence seems to delay initiation a bit. HRRR quite aggressive with initiation mainly along the western sea breeze front with RUC also showing sporadic storms over N-C Florida. Overall set-up is not impressive and favors only the development of a few thunderstorms. Moderate CAPE and weak shear environment may result in a few strong and slow moving storms.
Neither CI nor Cld top cooling products showing robust signs for initiation … mainly over C Florida. Both products however show more vivid activity offshore over the Atlantic, where mid-levels remain a bit cooler.
Helge
Outlook 24 May 2012: Week 3, Day 4
We’re operating today during the first mod risk of the experiment, however, that is not where we are focusing today… at least not initially.
In order to try and get lightning data into the experiment this week, we’ve initialized in the Sterling, VA and Melbourne, FL domains.
For the FL domain, we’re hopeful that storms will get going as the sea breeze front sets up across the state. Already, the UAH-CI product is flagging cumulus for development (consistently 50-60%) along the line from Sanderson to -Orlando to just northwest of Okeechobee.
For the DC domain, the CI alg is also flagging development generally a bit lower on the probability though. A region of SBCAPE of >1500-2000 J/kg extends from eastern NC to over much of the LWX CWA, so it appears possible that we could at least see some convective development across some of the DC LMA though likely only marginally severe.
Our observers and some PIs are keeping an eye over central WI and the associated moderate risk region for development of surface based storms (as of now all development across Minnesota appears to be elevated). Currently instability is limited across much of the region, but we do expect additional destablization with daytime heating and enhanced lift as the cold front moves in.
-Kristin Calhoun, Week 3 Coordinator