NWFS Collaboration Group authors “Northwest Flow Snow Aspects of Hurricane Sandy” in Feb. 2016 Weather and Forecasting

Just a short note to let readers know that several of us who have been collaborating on NW Flow Snow issues in the southern Appalachians now for a number of years have had our manuscript on the northwest flow snow associated with the remnants of Hurricane Sandy (Oct 2012) published in Weather and Forecasting. This will appear in the February issue, and for now is available as an early release version to WaF subscribers here:

http://journals.ametsoc.org/doi/pdf/10.1175/WAF-D-15-0069.1

My sincere appreciation goes to all the co-authors for the hard work in putting this together and final modifications leading to publication: Doug Miller, David Hotz, Pat Moore, Baker Perry, Larry Lee (yes, even in retirement!), and Daniel Martin.

We will likely move on to other NWFS topics for awhile, including HiRes model validation for typical NWFS events, but the opportunity for simulating many of the forcing mechanisms and moisture sources associated with the historic Sandy snowfall is something that some of us may still pursue.

Steve K.

 

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GOES-14 will be in Super Rapid Scan Operations with imagery over the Carolina’s and Virginia’s Today (2/3)

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GOES SRSOR visible satellite loop from 1806-1933 UTC on 20 August 2015

GOES-14 Super Rapid Scan Operations for GOES-R (SRSOR) began on 1 February and will continue for through 24 February, 2016. Super Rapid Scan Operations (SRSO) will provide 1-minute imagery to support multiple research and GOES-R/S user readiness activities. The SRSO domain is usually selected a day or two in advance. The domain schedule along with selected imagery from prior days is available at: http://cimss.ssec.wisc.edu/goes/srsor2016/GOES-14_SRSOR.html#sched_and_movies  Additional background information including training and links to online imagery is available at: http://cimss.ssec.wisc.edu/goes/srsor2016/GOES-14_SRSOR.html

This will be a great opportunity to view the data over our region. NWS forecasters will be able to view some of this data in real-time in AWIPS-2. An example of GOES SRSOR imagery during a test this past June is shown in the image above.

Imagery including visible, infrared, and water vapor is available on the web at the links below…

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December 23, 2015 Severe Weather Potential

Contrary to other potential severe high-shear, low-CAPE (HSLC) setups so far this autumn and winter, tomorrow’s setup appears to have the majority of pieces in place. The main story may be the high-CAPE setup during the afternoon and early evening across the Mississippi and Tennessee Valleys, areas encompassed by the Storm Prediction Center’s Day 2 enhanced risk. However, many signs point to a continued threat overnight extending into the Ohio Valley. While this will again occur west of several of our collaborating WFOs, it will likely be an event worth studying.

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Figure 1. Images from 1200 UTC 22 Dec. 2015 GFS, valid 0000 UTC 24 Dec. 2015: (top left) 500 hPa absolute vorticity and geopotential heights, (top right) 850 hPa isotachs (kt), wind barbs, and geopotential heights, (bottom left) 2-m theta-E and 10-m wind barbs, and (bottom right) 0-3 km energy helicity index.

Figure 1, valid at 0000 UTC December 24th, shows a strong, negatively tilted trough across the Midwest with an attendant 850 hPa closed low and intense low-level jet. A baroclinic zone is evident in the 2-m theta-E field across the Midwest and Ozarks, with a warm sector extending into Great Lakes region. The EHI shows a “reservoir” of favorable values extending from the Ohio River southward into the Deep South. Additionally, SREF mean SHERBS3 (Fig. 2, left) and SHERBE (Fig. 2, right) values remain enhanced across the Tennessee and Ohio Valleys from 00z through 06z, suggesting a continued threat of severe weather during the overnight hours.

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Figure 2. SREF ensemble mean SHERBS3 (left) and SHERBE (right) values valid for 0000 UTC 24 Dec. 2015 (top) and 0600 UTC 24 Dec. 2015 (bottom).

Finally, despite fairly modest lapse rates overnight in the Ohio Valley (Fig. 3) compared to those farther south (Fig. 4), hodographs appear favorable for the development of embedded rotation within an evolving QLCS in both locations.

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Figure 3. 1200 UTC 22 Dec. 2015 NAM forecast sounding valid for 0300 UTC 24 Dec. 2015 in central Ohio.

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Figure 4. As in Fig. 3, but for eastern Tennessee.

Though this may not get a lot of comments due to the holidays around the corner, I wanted to post a brief overview due to the heightened threat. This should be quite an event to watch!

 

Posted in CIMMSE, Convection, CSTAR, High Shear Low Cape Severe Wx, Uncategorized | 3 Comments

CSTAR High-Shear Low-CAPE Conference Call Notes – November 2015

The call was held on Tuesday, November 24th, from 11AM to noon. There were participants from NC State, AKQ, FFC, GSP, ILM, MHX, and RAH.

A recording of the call is available at… https://goo.gl/gtuKbw

1) Research update from Jessica King on the HSLC process study using modeling and emulated radar sampling.   The slide deck is available for downloading at https://goo.gl/r8difO

king•    The CAPE increases among the different cases are all affected differently by changes in the surface temperature, the surface moisture, and changes in the upper level temperature.
•    Non-events typically have small or negative changes in SBCAPE due to changes in surface temperature.
•    We see the most differences in low-level shear between the events and the non-events during the late evening and overnight hours.
•    Events tend to have much higher SHERB-S3 values than the non-events in the simulations.

2) Research update from Dianna on the Predictability with Ensembles and Downscaling project. The slide deck is available for downloading at https://goo.gl/5JSWH1

fanciscoDianna provided a recap of her project which is nicely summarized in her slides that are available at the link above.  In an oversimplification, the project includes 3 steps…
•    Start with a list of parameters – Include all parameters that could affect the development of the severe environment and severe event of interest
•    Next step is the model selection – Program selects the most valuable parameters that give smallest forecast error and assigns coefficients for each parameter
•    Final product is a statistical model that provides a binary answer, it will occur or it will not occur.  Or a probability answer, e.g. probability of tornado.

Dianna is requesting input and she set up a Google document where we all can give suggestions on potential parameters (predictors), and document anything else we think would be useful when creating a predictive equation for specific severe events in HSLC environments.  Spatial and temporal resolution for each parameter is also needed.
https://docs.google.com/spreadsheets/d/1uD4pWDiG3aT_zixlUKKB_5BpwsCFlj3wjShQI5wEdg4/edit#gid=1340224162&vpid=A1

Some items she would like added include…
1)    Add parameters to list
2)    Specific timing that parameter value is important
3)    Spatial and temporal resolution needed
4)    Any additional words of wisdom

3) VORTEX-SE Workshop

Dr Parker provided a summary of the recent VORTEX-SE workshop that was held in Huntsville AL earlier in November.  The goal of the workshop was to develop a roadmap for a larger, more sustained program associated with NOAA/NSF/NASA partners if Congress chooses to fund it in the future. Currently, there was only one year of funding provided which resulted in a somewhat hurried rollout that includes the current funding for 9 projects and a small field campaign in the spring of 2016.

Attendees at the workshop were roughly broken down with 1/3 of participants from the research/academic community, 1/3 from operations including CSTAR participants (Kevin Laws, Steven Latimer, Steve Nelson, Chris Darden, Jeff Waldstreicher, Steve Keighton and Dr Parker among others), and 1/3 from the social science community.

One of the drivers for the project is that fatalities from tornadoes are higher in the Southeast than elsewhere in the country. It is thought that this is the result of meteorological and non-meteorological factors such as a propensity for nocturnal/cool season events with lower SA, quality of building construction, education, etc.  Over 100 pages of meteorological and social science notes were developed during the workshop. The field campaign will take place in the late winter and spring, tethered to the Huntsville AL region with a desire to sample 4 to 6 cases, hopefully including a HSLC case or two.

4) CSTAR Workshop

There was a discussion about a potential CSTAR workshop in the spring. NWS ER SSD is interested in supporting ER participants with travel funds to participate in a combined CSTAR and ER sub regional workshop.  Given the potential involvement of many academic partners in the VORTEX-SE filed project this winter and spring as well as some other organizational needs, it was thought a workshop in May would be preferable.

We are looking for folks to help organize the CSTAR aspect of the workshop. Adam Baker and Keith Sherburn have already offered and we’ll need another ER SOO or two to help with the ER sub regional workshop part of it.

5) Next conference call

Our next call was initially scheduled for Tuesday, December 22nd, but given the holidays along with approaching exams and winter break, call participants opted to hold the next call in January on Tuesday, January 26th at 11am.

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Thoughts on 11 November 2015 HSLC severe event in Midwest

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Figure 1. Verification of SPC’s Day 1 outlooks for 11 November 2015, from earliest (bottom) to latest (top). Credit Dr. James Correia.

On November 11, 2015, a generally well-forecast (Figure 1) high-shear, low-to-moderate CAPE severe event affected portions of the Midwest. Convection initially developed during the late morning in the vicinity of the triple point of an intense surface cyclone across northeastern Kansas and southeastern Nebraska, with some discrete supercells noted early in the event. Over time, convection congealed into a QLCS with embedded supercellular elements as it raced eastward towards the Great Lakes, producing isolated tornadoes and damaging straight-line winds through much of Iowa, northern Missouri, and northwestern Illinois. After dark, convection gradually weakened below severe limits, with the last report of wind-related damage coming just after 8:30 PM in north central Illinois.

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Figure 2. Surface chart from 1900 UTC 11 November 2015. Note a surface cyclone center in southeast Nebraska, a warm front extending into Iowa, a dryline from eastern Kansas through central Oklahoma, and a cold front from central Kansas through the Texas and Oklahoma panhandles. Image courtesy of UCAR.

Aside from one unique feature (a dryline, which can be seen in the surface observations of Figure 2), this setup was very similar to HSLC events across the Southeast and Ohio Valley. Forcing was intense through the depth of the troposphere, with a potent surface cyclone, low-level jet, upstream mid-level vorticity maximum, and upper-level jet streak all present. Additionally, SHERBS3 values were elevated across most of the warm sector, extending from southeast Nebraska and southern Iowa southward through Texas (Figure 3).

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Figure 3. SPC mesoanalysis SHERBS3 values valid at 2000 UTC, approximately the time of first tornado occurrence in western Iowa. Click image for better resolution.

This case could be dissected in several ways, but I wanted to address a few key points that came to mind while watching this event unfold and in the hours after.

First, the SHERBS3, by itself, showed a very large false alarm area across locations where convection struggled to get organized, particularly across the Ozarks. The convection ultimately attaining severe strength developed and persisted in an environment with both favorable SHERBS3 values and intense forcing. Differential divergence, the 300 hPa analysis, and 700-400 hPa differential vorticity advection from the SPC mesoanalysis are shown in Figures 4, 5, and 6, respectively, to illustrate my point.

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Figure 4. SPC mesoanalysis differential divergence valid at 2000 UTC. Click image for better resolution.

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Figure 5. SPC mesoanalysis 300 hPa analysis valid at 2000 UTC. Click image for better resolution.

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Figure 6. SPC mesoanalysis 700-400 hPa differential vorticity advection valid at 2000 UTC. Click image for better resolution.

Second, as forcing (particularly low-level convergence; see Fig. 7) began to wane after dark and the line began to out race the favorable environment (Figs. 8 and 9), convection quickly diminished in intensity. The line was likely sensitive to the fact that favorable forcing and thermodynamics were becoming displaced with time; I suspect this was ultimately the result of the system’s demise, rather than simply losing surface-based instability.

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Figure 7. SPC mesoanalysis differential divergence valid at 0300 UTC, approximately half an hour after the final severe wind report. Click image for better resolution.

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Figure 8. SPC mesoanalysis SHERBS3 valid at 0300 UTC. Note that the convective line is largely east of the SHERBS3 bullseye (cf. Fig. 8) and approaching values of SHERBS3 < 1. Click image for better resolution.

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Figure 9. SPC mesoanalysis 0-3 km CAPE (red contours) and surface vorticity (blue contours) valid at 0300 UTC. Note that the convective line is largely east of the analyzed 0-3 km CAPE bullseye.

Finally, a sounding launched from DVN approximately one hour before the convective line arrived was not all that impressive (Fig. 10). This brings to mind a few considerations; either a) the environment was evolving extremely rapidly ahead of the line, b) given the intense system kinematics, only very weak convection was necessary to mix down significantly severe winds, or c) the sounding is unrepresentative of the local environment given its horizontal displacement after launch (as suggested by Jessica King this morning during a conversation about the event).

dvn

Figure 10. 0000 UTC DVN sounding from the SPC. Click image for better resolution.

All of these are plausible. Jessica’s simulations have revealed rapid destabilization occurring prior to the arrival of HSLC convective lines. Further, areas upstream (e.g., eastern Kansas/northwestern Missouri) were reporting near-severe winds with showers early in the event. Additionally, given the strong winds throughout the profile, DVN’s 0000 UTC sounding was likely in central or eastern Wisconsin by the end of its ascent.

I will leave potential (idealistic) ways to address all of these possibilities in future events for further discussion. For now, please share your thoughts on this recent event!

Posted in Convection, CSTAR, High Shear Low Cape Severe Wx | 5 Comments

CIMMSE Collaborators Participate in the VORTEX Southeast Project

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National Severe Storms Laboratory truck used during a previous field experiment.

This week, several CIMMSE collaborators travelled to Huntsville, Alabama, for the first VORTEX-SE Workshop. The Verification of the Origins of Rotation in Tornadoes EXperiment-Southeast (VORTEX-SE) is a research program to understand how environmental factors characteristic of the southeastern United States affect the formation, intensity, structure, and path of tornadoes in this region. VORTEX-SE will also determine the best methods for communicating forecast uncertainty related to these events to the public, and evaluate public response. In many ways, VORTEX-SE represents a new approach to tornado research in general. The goal of the workshop is to produce a road-map showing specific research projects in the physical and social sciences that could be undertaken in the next few years, as well as the mechanisms for transferring knowledge to operations and applications.

Later this spring in March and April 2016, the first field observing campaign of VORTEX-SE will be held. The current concept is to operate during 4-5 periods of several days each, observing the growth of instability and shear in the atmosphere and the eventual thunderstorm activity, with any associated tornadoes, accompanying the passage of large-scale weather systems. The focus in this campaign will be on the boundary layer evolution during these events.

You can learn more about the VORTEX Southeast Project including topics & impacts, supported research, and the schedule of events at…
http://www.nssl.noaa.gov/projects/vortexse/events/

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An Examination of Preliminary Local Storm Reports during the Historic South Carolina Rainfall Event September 30th, 2015 – October 6th, 2015

1. Introduction

During the historic South Carolina rainfall event of September 30th, 2015 to October 6th, 2015, National Weather Service (NWS) offices at Greenville-Spartanburg (GSP), Columbia (CAE), Charleston (CHS), and Wilmington (ILM) issued a combined 550 Preliminary Local Storm Reports (LSRs) for the South Carolina Counties within their County Warning Areas (CWAs) (Fig. 1). The large scale of this event resulted in at least one LSR for 33 of the 46 South Carolina counties. These LSRs documented nine precipitation and non-precipitation event types from 24 verification sources. This examination will rank the verification sources for all event types and for flood related event types for events that occurred in South Carolina.

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Fig. 1. NWSChat Local Storm Report App for GSP, CAE, CHS, and ILM September 30th, 2015 – October 6th, 2015.

2. Data Analysis

A dataset of the LSRs was obtained and exported in spreadsheet format using the NWSChat Local Storm Report App for GSP, CAE, CHS, and ILM for September 30th, 2015 through October 6th, 2015. The LSRs were filtered to exclude reports from North Carolina and Georgia. This process limited the dataset to LSRs from South Carolina counties, documenting coastal flood, flash flood, flood, heavy rain, high astronomical tides, marine thunderstorm winds, non-thunderstorm wind damage, thunderstorm wind damage, and thunderstorm wind gust. Flood events were limited to LSRs that documented coastal flood, flash flood, flood, and high astronomical tides.

LSRs were provided by 24 verification sources. A few sources were combined to simplify data analysis, reducing the verification sources to 18. The following is a list of the simplified verification sources: 911 call center, broadcast media/media, CoCoRaHS, co-op observer, county official, department of highways, emergency management, fire department/rescue, law enforcement, mesonet, NWS employee, NWS storm survey, official NWS observation/ASOS, other federal/Coast Guard, public, social media, tide gage, and trained spotter/HAM.

3. Results

A comparison of the contributions of verification source for all events and for flood related events is illustrated with a Doughnut graph (fig.2).

Fig. 2. Doughnut graph of percent of reports provided from all events (inner circle) and flood events (outer circle). Note: The legend list from top to bottom corresponds to the graph clockwise, starting at the 12 o’clock position.

Fig. 2. Doughnut graph of percent of reports provided from all events (inner circle) and flood events (outer circle). Note: The legend list from top to bottom corresponds to the graph clockwise, starting at the 12 o’clock position.

A. All Events

Five verification sources provided nearly 75 percent of the 550 precipitation and non-precipitation related LSRs during this historic event (Table 1). The five sources that provided the most reports were law enforcement, emergency management, public, 911 call center, and NWS employee. Law enforcement was the leading verification source, reporting 46 percent of all events.

B. Flood Related Events

Five verification sources provided 80 percent of the 371 flood related LSRs during this historic event (Table 2). The five sources that provided the most reports were law enforcement, emergency management, public, 911 call center, and broadcast media/media. Similar to all events, law enforcement was the leading verification source, reporting 42 percent of reports of flooding. It is interesting to observe that law enforcement cited LSRs outnumbered LSRs from traditional sources (trained spotters and HAMs) by a ratio of 17:1.

Table 1. Percentage, total number, and ratio of reports provided by verification sources for all event types.

Table 1. Percentage, total number, and ratio of reports provided by verification sources for all event types.

Table 2. Percentage, total number, and ratio of reports provided by verification sources for flood events.

Table 2. Percentage, total number, and ratio of reports provided by verification sources for flood events.

4. Summary

Law enforcement provided information that was used in 46 percent of all event LSRs and 42 percent of flood related LSRs during this historic South Carolina rainfall event. The text of the LSRs using law enforcement as the information source indicates that 90% to 95% of these reports are from the South Carolina Highway Patrol (SCHP). The SCHP lists the real-time location, type, and time of traffic related incidents on the South Carolina Department of Public Safety (SCDPS) Web site for the seven troops serving the state.

In the summer of 2011, Mike Jackson and Neil Dixon at NWS GSP, created a script called the SC Highway Patrol Collective (SCHPC). The SCHPC collects reports off the SCDPS Web page that contain keywords (roadway flooding, tree on roadway, closed roads, etc.) and stores them in a 45 day archive. The original script was shared with NWS CAE, CHS, and ILM in the spring of 2014. In the summer of 2015, an updated version of the SCHPC was created by Justin Lane, NWS GSP (fig 3).

Fig. 3. Screen capture of the second version of the SC Highway Patrol Collective.

Fig. 3. Screen capture of the second version of the SC Highway Patrol Collective.

It is likely that the use of the SCHPC, leveraging a human/machine mix, made the collection and dissemination of storm reports more efficient and convenient to the NWS meteorologists. These reports are especially useful during nighttime hours, across rural areas, and locations were emergency managers/911 centers are extremely busy. As a result, the rich supply of real-time information collected by the SCHPC aided in the creation of more informative and timely NWS statements, warnings, and LSRs.

Posted in General Information, Hydrology | Tagged , | 2 Comments