5-44 OTHER WATCH INFORMATION...CONTINUE...WW 646...
DISCUSSION...THUNDERSTORMS WILL CONTINUE TO INCREASE ACROSS WATCH AREA WHERE AIR MASS HAS BECOME STRONGLY UNSTABLE AND UNCAPPED.
VEERING SHEAR PROFILE SUPPORT STORMS EVOLVING INTO SHORT LINE
SEGMENTS ENHANCING WIND DAMAGE POTENTIAL AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM MOTION VECTOR 33025.
...NAME
5.6.2.3 Public Tornado Watch Notification Message.
The SPC issues a Public Tornado Watch Notification Message when forecasting two or more tornadoes or any tornado that could produce EF2 or greater damage. The forecast event minimum thresholds are at least 2 hours over an area at least 8,000 mi2. Below these thresholds, the SPC, in collaboration with affected NWS offices, may issue for smaller areas and for shorter periods of time when conditions warrant, and for Convective watches along coastlines, near the Canadian border, and near the Mexican border.
A Public Tornado Watch Notification Message contains the area description and axis, watch expiration time, the term “damaging tornadoes,” a description of the largest hail size and strongest thunderstorm wind gusts expected, the definition of the watch, a call-to-action statement, a list of other valid watches, a brief discussion of meteorological reasoning, and technical information for the aviation community.
The SPC may enhance a Public Tornado Watch Notification Message by using the words “THIS IS A PARTICULARLY DANGEROUS SITUATION” when there is a likelihood of multiple strong (damage of EF2 or EF3) or violent (damage of EF4 or EF5) tornadoes.
The SPC includes the term “adjacent coastal waters” when the watch affects coastal waters adjacent to the Pacific/Atlantic coast or the Gulf of Mexico.
Adjacent coastal waters refers to a WFO’s near-shore responsibility (out to 20 NM for oceans), which include portions of the Great Lakes.
The SPC issues a watch cancellation message whenever it cancels a watch prior to the expiration time. The text of the message will specify the number and area of the canceled watch.
5.6.2.3.1 Format of a Public Tornado Watch Notification Message.
The format for a Public Tornado Watch Notification Message is the same as the Public Severe Thunderstorm Watch Notification Message.
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5.6.2.3.2 Example of a Public Tornado Watch Notification Message.
A Public Tornado Watch Notification Message contains three bulleted blocks of information:
• The geographic area of the watch,
• The valid time of the watch, and
• A description of the primary threats anticipated within the watch.
A plain text summary is included beneath the bulleted information.
(Note this is a fictitious example) WWUS20 KWNS 050550 (communication header) SEL2 SPC WW 051750
URGENT - IMMEDIATE BROADCAST REQUESTED TORNADO WATCH NUMBER 243
NWS STORM PREDICTION CENTER NORMAN OK 1250 AM CDT MON MAY 5 2011
THE NWS STORM PREDICTION CENTER HAS ISSUED A * TORNADO WATCH FOR PORTIONS OF
WESTERN AND CENTRAL ARKANSAS
SOUTHERN MISSOURI
FAR EASTERN OKLAHOMA * EFFECTIVE THIS MONDAY MORNING FROM 1250 AM UNTIL 600 AM CDT.
...THIS IS A PARTICULARLY DANGEROUS SITUATION...
* PRIMARY THREATS INCLUDE
NUMEROUS INTENSE TORNADOES LIKELY NUMEROUS SIGNIFICANT DAMAGING WIND GUSTS TO 80 MPH LIKELY NUMEROUS VERY LARGE HAIL TO 4 INCHES IN DIAMETER LIKELY THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 100 STATUTE MILES EAST AND WEST OF A LINE FROM 15 MILES WEST NORTHWEST OF FORT LEONARD WOOD MISSOURI TO 45 MILES SOUTHWEST OF HOT SPRINGS ARKANSAS. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).
REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA.
PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING
WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS.
OTHER WATCH INFORMATION...THIS TORNADO WATCH REPLACES TORNADO WATCH NUMBER 237. WATCH NUMBER 237 WILL NOT BE IN EFFECT AFTER 1250 AM CDT. CONTINUE...WW 239...WW 240...WW 241...WW 242...
5-46 DISCUSSION...SRN MO SQUALL LINE EXPECTED TO CONTINUE EWD...WHERE
LONG/HOOKED HODOGRAPHS SUGGEST THREAT FOR EMBEDDED SUPERCELLS/POSSIBLE TORNADOES. FARTHER S...MORE WIDELY SCATTERED
SUPERCELLS WITH A THREAT FOR TORNADOES WILL PERSIST IN VERY STRONGLY DEEP SHEARED/LCL ENVIRONMENT IN AR.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 4 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM MOTION VECTOR 26045.
.
..NAME To see a dynamic representation of this, please go to the following website:
http://www.spc.noaa.gov/products/watch/2017/ww0020.html.
5.6.3 Traffic Flow Management (TFM) Convective Forecast (TCF).
The TCF is a high-confidence graphical representation of forecasted convection meeting specific criteria of coverage, intensity, and echo top height. The TCF graphics are produced every 2 hours and are valid at 4, 6, and 8 hours after issuance time. Areas of convection in the TCF include any area of Convective cells containing (at a minimum):
1. Composite radar reflectivity of at least 40 decibels (dBZ);
2. Echo tops at or above FL250;
3. Coverage (1 and 2) of at least 25 percent of the polygon area; and
4. Forecaster confidence of at least 50 percent (high) that criteria (1, 2, and 3) will be met.
Lines of convection in the TCF include any lines of Convective cells having (at a minimum):
1. Composite radar reflectivity of at least 40 dBZ having a length of at least 100 NM;
2. Linear coverage of 40 percent or greater;
3. Echo tops at or above FL250; and
4. Forecaster confidence of at least 50 percent (high) that criteria (1, 2, and 3) will be met.
All four of the threshold criteria listed above for both areas and lines of convection are required for inclusion in the TCF. This is defined as the minimum TCF criteria.
The TCF domain is the FIR covering the CONUS and adjacent coastal waters. It also includes the Canadian airspace south of a line from Thunder Bay, Ontario to Quebec City, Quebec.
From March 1st through October 31st, the TCF is collaboratively produced by meteorologists at the AWC in Kansas City, MO, and embedded at the FAA Air Traffic Control System Command Center (ATCSCC) in Warrenton, VA; at the CWSU
5-47 embedded at the FAA’s ARTCC; at various airlines; and by other authorized participants.
Automated routines will continue to make the TCF available from November 1st through February 28th.
The TCF is issued 24 hours a day, 7 days a week at 30 minutes prior to the indicated issuance time. The issuance time supports the FAA’s Strategic Planning (SP) Webinar, which occurs 15 minutes following odd hours Eastern Time (ET). The Canadian portion of the forecast is available from April 1st through September 30th. However, Nav Canada may request the issuance of each forecast as early as March 1st and as late as October 31st.
All available Canadian forecasts are incorporated into the TCF. During times the forecasts are not available for Canadian airspace, the TCF graphics will be annotated with “No Canadian TCF.”
The TCF is intended to be used as an SP tool for air traffic flow management. It aids in the reduction of air traffic delays, reroutes, and cancellations due to significant convection. It is not intended to be used for tactical air traffic flow decisions, in the airport terminal environment, or for pilot weather briefing purposes. The graphical representation is subject to annual revision.
Figure 5-25. TFM Convective Forecast (TCF)—Example
5-48 Figure 5-26. TFM Convective Forecast (TCF)—Example
5.6.3.1 Issuance.
The TCF is issued by the AWC.
The TCF is issued every 2 hours. The TCF product issuance time is approximately the bottom of the hour preceding the FAA ATCSCC’s SP telecom (i.e., the 1600 UTC issuance would be available at ~1530 UTC for the 1615 UTC SP telecom). The product can be found on https://www.aviationweather.gov.
5.6.3.2 Content.
Data graphically displayed on the TCF consist of coverage of convection within a defined polygon, maximum tops, and confidence of Convective occurrence meeting the TCF minimum criteria.
Additiona l information on the TCF product is available on the TCF website form under the INFO tab, on https://www.aviationweather.gov.
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5.6.3.3 Coverage.
The Convective coverage within the forecast polygon is represented by the amount of fill within the polygon (see Figure 5-27, TCF Product Legend). The polygon is then assigned as a sparse or medium coverage.
• Medium coverage, defined by medium fill, indicates 40 to 100 percent of the polygon is forecast to contain convection.
• Sparse coverage, represented by sparse fill, means 25 to 39 percent of the polygon is forecast to contain convection.
Figure 5-27. TCF Product Legend
5.6.3.3.1 Confidence.
The TCF is a high confidence (50 to 100 percent) graphical representation of forecasted convection that denotes the forecasters’ confidence that the represented convection will meet the minimum criteria. Confidence is not to be associated with probability of occurrence.
5.6.3.3.2 TOPS.
The word “TOPS” is used to depict the forecast maximum echo tops, in thousands of feet MSL, specified by four selected layers listed in Figure 5-27.
The heights of the forecast echo tops must cover at least 25 percent of the polygon. The exact location of the highest echo top within the polygon cannot be determined.
5.6.3.4 Use.
The TCF is an SP tool for air traffic flow management in the 2- to 8-hour forecast period.
The TCF does not include a forecast for all convection. If the convection does not meet the threshold criteria, it is not included in the TCF. The TCF is not intended to be used as a tactical short-term decision product.
The product is not intended to be used as a pilot weather briefing product;
however, TCF is available to pilots and aircraft dispatchers as an additional product for SP.
5-50
5.6.4 Extended Convective Forecast Product (ECFP).
The ECFP planning tool (see Figure 5-28, ECFP Example) is a graphical representation of the forecast probability of thunderstorms and is also intended to support the long-range planning for Convective constraints in the National Airspace System (NAS). The product identifies graphically where thunderstorms are expected through the next 72 hours over the CONUS. Although the ECFP uses TCF-style graphics to facilitate ease of interpretation, the ECFP does not forecast TCF criteria.
The development of the ECFP planning tool was a response to FAA and industry needs in planning for weather hazards, specifically convection, 1 to 3 days in advance. To meet these planning needs, the ECFP provides traffic planners and collaborators a quick look at where the probability of convection is greatest. By utilizing TCF-style graphics, users familiar with TCF can easily determine where traffic constraints are most likely to occur over the next 3 days.
5.6.4.1 Issuance.
The ECFP is an automated forecast product issued by the AWC. It is issued four times a day at approximately 0100, 0700, 1300, and 1900 UTC.
Figure 5-28. ECFP Example
5.6.4.2 C ontent.
This automated graphical forecast is created from the Short Range Ensemble Forecast (SREF) Calibrated Thunderstorm guidance. Probability of thunderstorm contours are depicted at 40, 60, and 80 percent probabilities, using TCF-like shading. Hashed areas represent 40 to 59 percent probability,
5-51 solid lined areas represent 60 to 79 percent probability, and solid, blue-filled areas represent greater than 80 percent probability.
5.6.4.3 Use.
The ECFP is intended for FAA traffic managers at ARTCC, FAA ATCSCC, airline and aviation industry dispatch and flight planners, as well as commercial weather information providers supporting airlines and the FAA.
5.6.5 National Convective Weather Forecast (NCWF).
The NCWF is a near real-time, high-resolution display of current and 1-hour extrapolated forecasts of selected hazardous Convective conditions for the CONUS. The NCWF may be used in conjunction with the report and forecast information contained within Convective SIGMETs. The NCWF is available for use by General Aviation (GA), aircraft dispatchers, and Traffic Management Units (TMU).
5.6.5.1 Issuance.
The NCWF is issued by the AWC and is updated every 5 minutes. The product is available at the Convection Web page on https://www.aviationweather.gov.
5.6.5.2 Content.
The NCWF displays current Convective hazard fields (detection), 1-hour extrapolated forecast polygons (see Figure 5-29, NCWF Example), forecast speed and directions, and echo tops. Past performance polygons can also be select ed for display.
5-52 Figure 5-29. NCWF Example
5.6.5.2.1 NCWF Hazard Scale.
The Convective hazard scale uses six hazard levels (see Figure 5-30, NCWF Hazard Scale) to characterize hazardous convection conditions.
The six hazard levels are determined by two factors:
• Intensities and maximum tops of WSR-88D reflectivity data; and
• Frequencies of cloud-to-ground lightning.
Higher hazard levels are associated with higher radar reflectivity intensities and higher frequencies of lightning strikes.
The six hazard levels are reduced to four-color codes for display on the NCWF.
5-53 Figure 5-30. NCWF Hazard Scale
5.6.5.2.2 One-Hour Extrapolated Forecast Polygons.
One-hour extrapolated forecast polygons are high-resolution polygons outlining areas expected to be filled by selected Convective hazard fields in 1 hour. Extrapolated forecasts depict new locations for the Convective hazard fields based on their past movements. Extrapolation forecasts do not forecast the development of new Convective hazard conditions or the dissipation of existing conditions. Forecasts are provided only for Convective hazard scale Levels 3 or higher. The forecast polygons do not depict specific forecast hazard levels. In Figure 5-29, the light blue polygon denotes the location of the 1-hour forecast Convective hazard field.
5.6.5.2.3 Forecast Speed and Direction.
Forecast speed and direction are assigned to current Convective hazard fields having a 1-hour extrapolated forecast. A line (or arrow on the AWC JavaScript product) is used to depict the direction of movement. The speed in knots is depicted by the first group of two numbers located near the current Convective hazard field. The second group of three numbers identifies echo tops.
Forecast speed and direction is only updated every 10 minutes. The larger update time interval (compared to five-minute updates for the NCWF) smooths erratic forecast velocities. In Figure 5-29, the forecast direction (depicted by an arrow) is pointing to the southeast, and the speed is 25 kts.
5.6.5.2.4 Echo Tops.
Echo tops are assigned to current Convective hazard fields having a 1-hour extrapolated forecast. Echo tops are depicted by a group of three numbers located near the current Convective hazard field and are plotted in hundreds of feet MSL. In Figure 5-31, NCWF One-Hour E xtrapolated Forecast Polygon, Forecast Movement Velocity and Echo Tops—Examp le, the echo tops are 45,000 ft MSL.
5-54 Figure 5-31. NCWF One-Hour Extrapolated Forecast Polygon, Forecast Movement Velocity and Echo Tops—Example
5.6.5.2.5 Past Performance Polygons.
Past performance polygons are magenta polygons displaying the past hour’s extrapolated forecast polygons with the current Convective hazard fields. A perfect forecast would have the polygons filled with Convective hazard scale Levels 3 or higher data. Levels 1 and 2 would be outside the polygons. The display of past performance polygons allows the user to review the accuracy of the past hour’s forecast.
Figure 5-32, NCWF Past Performance Polygons—Example, depicts current Convective hazard fields and past performance polygons (magenta) valid at 1500Z. The past performance polygons are the 1-hour extrapolated forecasts made at 1400Z. Although the polygons do not perfectly match the current Level 3 and higher hazard fields, the forecasts are still fairly accurate.
Newly developed Convective hazard Levels 3 and higher do not have past performance polygons. Extrapolated forecasts do not forecast developing hazardous Convective.
5-55 Figure 5-32. NCWF Past Performance Polygons—Example
5.6.5.3 St rengths and Limitations.
5.6.5.3.1 Strengths.
Strengths of the NCWF include:
• Convective hazard fields that agree very well with radar and lightning data;
• Updates every five minutes;
• High-resolution forecasts of Convective hazards; and
• Well-forecasted long-lived Convective precipitation.
5.6.5.3.2 Limitations.
Limitations of the NCWF include:
• Initiation, growth, and decay of Convective precipitation are not forecast;
• Short-lived or embedded convection may not be accurately displayed or forecast;
• Low-topped convection that contains little or no lightning may not be depicted;