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arrival, followed by arrival and passage of the plasma cloud and frozen-in-flux magnetic field. More intense levels of geomagnetic storming are favored when the CME enhanced IMF becomes more pronounced and prolonged in a south-directed orientation. Some CMEs show predominantly one direction of the magnetic field during its passage, while most exhibit changing field directions as the CME passes over Earth. Generally, CMEs that impact Earth’s magnetosphere will at some point have an IMF orientation that favors generation of geomagnetic storming. Geomagnetic storms are classified using a five-level NOAA Space Weather Scale. SWPC forecasters discuss analysis and geomagnetic storm potential of CMEs in the forecast discussion and predict levels of geomagnetic storming in the 3-day forecast.*Images courtesy of NASA and the SOHO and STEREO missions National Oceanic and Atmospheric AdministrationNational Weather ServiceNational Centers for Environmental PredictionSpace Weather Prediction Center325 Broadway, Boulder CO 80305DisclaimerPrivacy PolicyAbout NOAA's National Weather ServiceCareers in WeatherHOMEABOUT SPACE WEATHERImpactsEarth's ClimateElectric Power TransmissionGPS SystemsHF Radio CommunicationsSatellite CommunicationsSatellite DragPartners and StakeholdersCommercial Service ProvidersFederal AgenciesInternational OrganizationsInternational Service ProvidersSpace Weather ResearchPhenomenaAuroraCoronal HolesCoronal Mass EjectionsEarth's MagnetosphereF10.7 cm Radio EmissionsGalactic Cosmic RaysGeomagnetic StormsIonosphereIonospheric ScintillationRadiation BeltsSolar EUV IrradianceSolar Flares (Radio Blackouts)Solar Radiation StormSolar WindSunspots/Solar CycleTotal Electron ContentAdditional InfoNOAA Space Weather ScalesCustomer Needs & Requirements StudyPRODUCTS AND DATAForecasts27-Day Outlook of 10.7 cm Radio Flux and Geomagnetic Indices3-Day Forecast3-Day Geomagnetic ForecastForecast DiscussionPredicted Sunspot Numbers and Radio FluxReport and Forecast of Solar and Geophysical ActivitySolar Cycle ProgressionSpace Weather Advisory OutlookUSAF 45-Day Ap and F10.7cm Flux ForecastWeekly Highlights and 27-Day ForecastReportsForecast VerificationGeoalert - Alerts, Analysis and Forecast CodesGeophysical AlertSolar and Geophysical Event ReportsUSAF Magnetometer Analysis ReportModelsAurora - 30 Minute ForecastCTIPe Total Electron Content ForecastD Region Absorption Predictions (D-RAP)Geospace Geomagnetic Activity PlotGeospace Ground Magnetic Perturbation MapsGeospace Magnetosphere MoviesNorth American (US Region) Total Electron ContentNorth American Total Electron ContentRegional Geoelectric (1D)Geoelectric Field 1-Minute (Empirical EMTF - 3D Model)Geoelectric 3D-1D ComparisonRelativistic Electron Forecast ModelSEAESRTSTORM Time Empirical Ionospheric CorrectionWSA-Enlil Solar Wind PredictionWAM-IPEObservationsBoulder MagnetometerGOES Electron FluxGOES MagnetometerGOES Proton FluxGOES Solar Ultraviolet Imager (SUVI)GOES X-ray FluxLASCO CoronagraphPlanetary K-indexReal Time Solar WindSatellite EnvironmentSolar Synoptic MapSpace Weather OverviewStation K and A IndicesSummariesSolar & Geophysical Activity SummarySolar Region SummarySummary of Space Weather ObservationsAlerts, Watches and WarningsAlerts, Watches and WarningsNotifications TimelineExperimentalACE Real-Time Solar WindSolar TErrestrial RElations Observatory (STEREO)Data AccessDASHBOARDSAviationElectric PowerEmergency ManagementGlobal Positioning SystemRadioSatellitesSpace Weather EnthusiastsMEDIA AND RESOURCESEducation and OutreachGlossaryNews ArchiveNewsroomSUBSCRIBEANNUAL MEETINGFEEDBACK