Summer Weather:
Convection Information & Safety

 

  General  Hazards  Current Threat  Seasonal Products  Safety  
 

Summer Severe Weather Products
Severe Weather Products | Follow-up Products | Summary and Near-Severe Products

 

Severe Weather Products:

Product
Product Description
Severe Thunderstorm Warning
Forecast offices should issue Severe Thunderstorm Warnings (SVRs) when there is radar or satellite indication and/or reliable reports of wind gusts equal to or in excess of 50 knots (58 mph) and/or hail size of one inch (U.S. quarter-size) diameter or larger. Forecast offices may issue SVRs for a convective squall with little or no lightning that otherwise meet or exceed hail or wind warning criterion.
Tornado Warning
Forecast offices should issue Tornado Warnings (TORs) when there is radar or satellite indication and/or reliable reports of a tornado or developing tornado.
 Flash Flood Warning
 A flash flood warning (FFW) will be issued for a geographical area defined by a polygon in a Forecast office's county warning area when:
  • Flash flooding is reported; and/or
  • A dam or levee failure is imminent or occurring; and/or
  • A sudden failure of a naturally-caused stream obstruction (including debris slide, avalanche, or ice jam) is imminent or occurring, and/or
  • Precipitation capable of causing flash flooding is indicated by radar, rain gages, and/or satellite; and/or
  • Precipitation as indicated by radar, rain gages, satellite and/or other guidance is capable of causing debris flows, particularly (but not only) in burn areas; and/or
  • Local monitoring and prediction tools indicate flash flooding is likely; and/or
  • A hydrologic model indicates flash flooding for locations on small streams, or
  • A previously issued flash flood warning needs to be extended in time, or
  • Flash flooding is imminent or occurring in a geographical area currently not under a valid flash flood warning. Note: since flash flood warnings cannot be extended in area, a new flash flood warning should be issued for adjacent areas when flash flooding in imminent or occurring in those areas.
If a reliable source has reported that flooding has ended in all of the warned area and a flash flood warning is still in effect, a flash flood statement should be issued canceling or expiring the warning rather than allowing the product to expire on its own.
 Areal Flood Warning
 An areal flood warning will be issued for a geographical area defined by a polygon in a WFO’s CWFA when:
  • Flood monitoring and forecasting tools indicate an over 80 percent likelihood of flooding over an area which cannot be quantified by a flood warning for forecast points; and/or
  • Flooding is reported over a wide area which cannot be quantified by a flood warning for forecast points; and/or
  • A previously issued areal flood warning needs to be extended in time; or
  • Flooding is imminent or occurring in a geographical area currently not under a valid areal flood warning. Note: since areal flood warnings cannot be extended in area, a new areal flood warning should be issued for adjacent areas when flooding in imminent or occurring in those adjacent areas.
The following are special issuance and cancellation criteria:
  • An areal flood warning does not have to be issued if river/stream flooding is adequately accounted for by one or more flood warnings for forecast points.
  • If a reliable source has reported that flooding has ended in all of the warned area and an areal flood warning is still in effect, a flood statement should be issued cancelling or expiring the flood warning rather than allowing it to expire on its own.


Severe Weather Followup Products

Product
Product Description
Severe Weather Statement Forecast offices (WFOs) should issue a Severe Weather Statement (SVS) to provide notice an SVR or TOR has been canceled for all or portions of the warning polygon. WFOs should issue SVSs at least once during the valid time of an SVR or TOR. WFOs may issue an SVS to provide notice that an SVS or TOR has expired. WFOs should issue an SVS to notify users that erroneous counties included in the original SVSs or TORs have been removed
Flash Flood Statement Flood statements will be issued to follow up areal flood warnings when:
  • Information needs to be provided to update or supplement a previously issued areal flood warning, and/or
  • Cancellation or expiration of all or part of a flood warning needs to be announced.
If a reliable source has reported that flooding has ended in all of the warned area and an areal flood warning is still in effect, a flood statement should be issued cancelling or expiring the flood warning rather than allowing it to expire on its own.
Areal Flood Statement Areal advisories will be issued for a geographical area defined by a
polygon in a WFO’s CWFA when:
  • Elevated stream flow or ponding of water occurs or is more than 80 percent likely to occur which warrants public notification.
  • An advisory needs to be issued for a geographical area currently not under a valid flood advisory.
    Note: since flood advisories cannot be extended in area, a new flood advisory should be issued for adjacent areas when deemed necessary by a forecaster.
  • Updated hydrometeorological information needs to be provided on an existing advisory.
If a reliable source has reported that elevated streamflow or ponding of water has ended in all of the advisory area and an areal flood advisory is still in effect, a flood statement should be issued cancelling or expiring the flood advisory rather than allowing it to expire on its own.

Summary and Near-Severe Products

Product
Product Description
Special Weather Statement Forecast offices (WFOs) may issue Special Weather Statements (SPSs) for ongoing or imminent weather conditions less than warning or advisory criteria. WFOs should issue SPSs to report funnel clouds which are not expected to touch ground and become tornadoes.
Short-Term Forecasts Forecast offices should issue Short Term Forecasts to discuss the evolution of convective and stratiform precipitation, winter weather, tropical cyclone landfall events, marine events, fog, significant winds, blowing dust, and extreme temperatures (excessive heat or cold) within their geographic area of responsibility.
Local Storm Reports Forecast offices (WFOs) will issue Preliminary Local Storm Reports (LSRs) for severe weather events such as tornadoes,waterspouts, large hail, thunderstorm/marine wind gusts and flash floods. WFOs should issue LSRs for other events listed in Appendix B. LSRs should be issued for events that meet or exceed applicable warning criteria. Other events may be included. LSRs should be issued as close to real time as possible. WFOs should issue LSRs to “summarize” a list of reports during and/or at the end of an event (e.g. severe weather outbreak, winter storm). Events reported more than seven days after occurrence will be included in monthly Storm Data reports instead of LSRs.
Public Information Statement Forecast offices may issue a Public Information Statement to provide additional summary information from a past weather event. This may include rainfall amounts, hail sizes, wind and wind gust speeds and other assorted information.
 
             

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.