Synthetic ABI brightness temperatures are being generated
at CIMSS and CIRA using output from the 00 UTC NSSL-WRF
4-km model simulations. Discussions have been held during
the past several days describing how infrared imagery can
be used to quickly evaluate the structural evolution of
the simulated thunderstorms and other cloud features as
well as to examine the overall accuracy of model
forecasts. Simulated IR imagery provides a powerful means
to quickly evaluate model output since various
characteristics such as cloud top height, water vapor
distribution, and thunderstorm coverage and intensity can
be inferred from a single image rather than having to look
at many different fields. As an example, the synthetic
imagery was used today to determine how quickly a
low-level stratus cloud deck present over the high plains
of NE Colorado and SE Wyoming would dissipate this
morning. Real GOES imagery indicated that the cloud cover
was not dissipating very quickly, which raised some
concerns that this would reduce surface warming and impede
the development of thunderstorms later in the day. A
quick examination of the synthetic 11.2 micron imagery,
however, quickly showed that this cloud cover would
dissipate by late in the morning. This provided greater
confidence that a risk for severe thunderstorms was
warranted over that region. The clouds did indeed
dissipate during the morning and several severe
thunderstorms, including one near the Denver airport,
developed during the afternoon.
-Jason Otkin
Thursday, May 27, 2010
Wednesday, May 26, 2010
SATCAST within Aviation Applications
The GOES-R Convective Initiation algorithm being developed by the University of Alabama in Huntsville within the GOES-R Algorithm Working Group Aviation Applications Team. Nowcasting convective initiation is very important to aviation interests for airport operations and airline planning. If there is a good indication that a storm will develop 30 minutes to 1 hour, the airlines can plan for a particular aircraft takeoff/landing route to close causing an airport to reduce capacity for take-offs and landings or shutdown airport operations. The airlines would be able to hold back some aircraft at other airports, preventing a backlog at a particular airport and cause airplane diversions which can be costly.
In addition, knowledge of thunderstorm growth can help airport operators plan for the potential of lightning strikes and clear the ramp preventing any possible injury/deaths from lightning strikes.
There were significant airmass thunderstorm development over Illinois, eastern TN, and over the Atlanta area today. Below is an example of SATCAST over the Atlanta region which is a major Delta and Airtran Airline hub.
SATCAST Nowcast valid 1702 UTC
Radar valid 1709 UTC
Radar valid 1903 UTC
Radar valid 2000 UTC
Below are examples over the Ohio valley. Notice the convection which developed over central Illinois and around the southern eastern KY area.
SATCAST Nowcast valid 1732 UTC
Radar valid 1733 UTC
Radar valid 1811 UTC
Radar valid 1830 UTCGOES-R Proxy products used in archive mode from 24 May 2010
The four forecasters split into two groups, one group focused on real-time storm development in western Oklahoma area while the other is looking at GOES-R proxy GLM lightning, convective initiation, overshooting-top, and enhanced-V signal from May 24, 2010 convective outbreak in Oklahoma area to take advantage of OKC LMA data. The figure below shows pseudo GLM (upper left), UW convective initiation (upper right), UW cloud top cooling (lower left), and visible lower right. This allowed forecasters to access GOES-R GLM proxy cloud-to-cloud lightning in conjunction with GOES imager based convective initiation/cloud-top cooling within AWIPS. Cloud-to-cloud lightning was shown to first occur at first indication of cloud-top cooling in this case.
Pseudo-GLM Archive Case: 24 May 2008
Looking backward at 1754, noticed CTC+CI, along with first lightning, simultaneously at 1702.
At this point, we hadn't noticed that GLM was slaved to satellite imagery updates, so GLM may have shown up prior to the CTC/CI.
No MRMS with this case (forecaster inquired about availability).
Might be helpful to have a suggested best practice for combining products in a display at outset of the case (ltng overlay w/satellite, ltng overlay with radar, etc). Careful to not slave GLM to satellite 15 min updates when doing overlay. Load GLM first.
18:16 - 50 dBZ core in cell in NE major county, 29-30kft
18:23 - "Blaine county going up quick" - based on <>
18:25 - CG activity dropped off in northern cell after initial flurry after initiation. IC modulating but holding steadeier than CG.
"Lightning data helpful for nowcasting - can but thunder in short term statements if there are just showers forecast. Don't have to rely on just CG data for thunder."
Blaine probably not going quite as quickly as initially thought.
18:30 - 64 dBZ 16kft in NW Garfield cell.
18:38 - Querying for mesocyclone signatures in radar on Major/Garfield storm. pulled up OK mesonet to look at low level inflow (very backed, just S of E)
18:34 - Blaine elevated core > 50 dBZ
CG data dropout at 18:20, restored by 19:00
Blaine remains of interest at 18:42- most vigorous updraft. Determined from radar. First GLM 18:43.
18:53 - Garfield storm has meso. 1855 - 60 dBZ to 20kft. Lightning picked up on southern storm a bit.
18:57 - storm top divergence on Garfield
19:01 - began to issue severe + tor in ctrl/western Garfield
18:30-18:35 - GLM showed increase right where core went up at same time.
19:05 - issuing svr on Blaine/Kingfisher storm
Screen real-estate an issue. Careful interrogation of radar means limited space for other data (e.g., GLM). Requires conscious context switch to notice any trends in lightning.
19:07 - noted that core growth in blaine was commensurate with jump in lightning activity
SPC mesoanalysis from the archives would be helpful to have on right screen during WES cases. (needs plugin though)
19:13 - "46 dBZ to 52kft on northern storm. huge overhang"
Just after 19Z spike to over 100, pulse to 125 at 1922-24 in northern storm.
19:27 - media report of tornado 2 W Lacey in Kingfisher county (southern storm).
19:39 - tornado lifted
19:45 - another reported tornado NE of Lacey
Lightning rate dropped from 80->40 in the 5 min before 1927 tornado.
19:56 - second tornado lifted
Northern storm noted to have eased off on lightning rate (to <>
20:07 - tornado report in the southern storm
EWP daily briefing and thermal couplets
24-hour thermal couplet detections and severe reports for 25 May 2010In today's EWP daily briefing, Wayne Feltz and I showed the 24-hour thermal couplet and severe storm reports maps from the UW-CIMSS website. The thermal couplet locations correlated well to locations of reported tornadoes, especially along a track through western KS (see above). The thermal couplet detection product has been brought in to the N-AWIPS system for the SPC and EFP as of yesterday, but we still have yet to be able to provide it within the EWP's AWIPS system. We attempted to make the changes today, but a power outage thwarted our efforts and has yet to be restored. We will be monitoring this throughout the evening and hope to have this working by tonight.
The plan for the day is to start with a pseudo-GLM archive case for two of the forecasters, while the other two monitor real-time weather in OK. We will adjust for interesting weather as is occurs...
Severe hail probability forecasts hail over central US
The severe hail probability product was examined this morning to determine what characteristics of what it showed following yesterday's widespread severe weather across most of the country. We noticed that the product performed well in forecasting the occurrence of severe hail over IA/IL/WI/AR earlier in the day, with probabilities exceeding 2% hours in advance of severe hail reported on the ground. Along the dryline in NM/TX/CO/KS toward the evening, the probabilities also were seen 1-2 hours in advance of severe hail reported on the ground, including one report of 3" along the CO/KS border. (see above images) The lead time slightly decreased along the dryline region where storm growth was much more explosive. This helps explain the decrease in lead time over this region as the product may not be able to detect these storms as far in advance.
SATCAST Identifies Severe Storms in Texas Yesterday
Yesterday, a line of convection developed over the Texas, New Mexico border. SPC issued a Severe Thunderstorm Watch at 3:05pm CDT over the region.
SPC Severe Thunderstorm Watch Issued 3:02pm CDT
SATCAST identified a line of growing clouds in New Mexico at 2:15pm CDT (1915 UTC). The convection grew into severe storms.
SATCAST output at 2:15pm CDT (1915 UTC)
The radar images from the region showing no convection within that region at 2:13pm CDT.
Radar image at 2:13pm CDT (1913 UTC)
Radar image at 2:51pm CDT (1951 UTC)
Radar image at 3:34pm CDT (2034 UTC)
SATCAST provided a lead-time of approximately 45 minutes before achieving a 35 dBZ radar reflectivity and the line of storms was identified for initiation approximately 45 minutes before the issue time of the SPC watch. This shows the utility of SATCAST in nowcasting possible severe convective weather and highlight areas of development up to an hour in advance.
Tuesday, May 25, 2010
Visible/IR blended imagery of enhanced V in AWIPS
The above image taken by the Amarillo, TX forecaster group shows multiple enhanced-V signatures on severe storms located in the TX panhandle at 0015 UTC in the visible. Blended on top in the IR brightness temperature image. These enhanced-V signatures, clearly observed on visible imagery near sunset, were not detected by the thermal couplet detection product because of the coarseness of the IR data. We can see the higher level cirrus above the main anvil, associated with the overshooting tops, possibly being the source of the warmer temperatures detected downstream of the overshooting top in the typical IR representation of an enhanced-V signature seen in case studies. Since the cirrus is associated with an overshooting top, which is likely penetrating into the lower stratosphere, the warmer stratospheric temperatures may be the cause of the warmer downstream temperatures.
A storm without lightning strikes?
During operations earlier this afternoon, a forecaster noted a storm in the northern Texas panhandle with an extensive 60 dBZ radar reflectivity core but without any lightning strikes reported by the National Lightning Detection Network (NLDN). The forecaster expected that such a mature this storm would be a lightning producer. And some storms are indeed prolific in-cloud lightning producers while rarely producing channels that strike ground. Many storms with high cloud flash ratios were observed during the STEPS field program (Lang et al. 2004).
The GOES-R Geostationary Lightning Mapper (GLM) would have been able to confirm lightning with this storm. The storm unfortunately was not over one of the ground-based Lightning Mapping Arrays that, like GLM, provide real-time total ground + cloud flash rates. Had it been, we would have examined flash rate tendencies associated with modulation in the storm's mixed phase updraft as a complement to radar indications of updraft processes that together provide situational awareness about the likelihood of severe weather threats.
Forecasters monitoring consistent overshoots during IOP
The Amarillo, TX forecaster group are monitoring consistent overshooting top detections above a storm slowly entering the southwest edge of their CWA (see image above)... They are preparing to issue warnings as soon as it enters. The consistency of the overshooting top detections are providing them with strong confidence that the storm is continuing to maintain its intense updraft and thus telling them that it is still severe. The magnitude of the overshooting tops, or difference between the temperature of the overshooting top relative to the cloud around it, has been slowly increasing from 4 K to above 9 K over the past few satellite scans. Note that these values may be diluted since the contours are smoothed, so the actual magnitudes are probably higher. Nonetheless, this may be saying that the updraft is strengthening. The forecasters are also noticing trends in the overshoot magnitude as severe weather occurs. There was a report of a tornado with this storm following the intensification, but that has yet to be verified. I mentioned that a total disappearance of the overshoot may indicate the occurrence of severe wind or hail at the surface as the updraft collapses.
The Pueblo, CO group have also been monitoring the overshooting top magnitudes, but for a different purpose. They have a cluster of storms and are using the overshoots to detect the regions of renewed intensification on satellite, since it is one large thick cirrus shield over the area and the radar signatures look somewhat similar.
Subscribe to:
Posts (Atom)