Additional GRIB Tables

Element Encoding Characteristics

      Binary Scale Factor Decimal Scale Factor  
Weather Element Original NDFD Units GRIB2-encoded Units CONUS 5 km CONUS 2.5 km CONUS 5 km CONUS 2.5 km Primary Missing Value Substitute
MaxT Fahrenheit Kelvin 0 2 1 1 9999
MinT Fahrenheit Kelvin 0 2 1 1 9999
PoP12 Percent Probability Percent Probability 0 0 0 0 9999
T Fahrenheit Kelvin 0 2 1 1 9999
Td Fahrenheit Kelvin 0 2 1 1 9999
Sky Percentage
Total sky coverage
Percentage
Total sky coverage
0 0 0 0 9999
Wind Speed Knots ms-1 0 2 1 1 9999
Wind Direction degrees true Degrees true 0 0 0 -1 9999
Weather N/A N/A 0 0 0 0 9999
QPF Inches kgm-2 0 0 2 2 9999
Snow Amount Inches Meters 0 0 3 3 9999
Wave Height Feet Meters 0 0 1 1 9999
Apparent Temperature Fahrenheit Kelvin 0 2 1 1 9999
Relative Humidity Percent Percent 0 0 0 0 9999
Wind Gust Knots ms-1 0 2 1 1 9999
Tropical Wind Speed Probabilities 
(34, 50, 65 kts)
Cumulative and Incremental
Percent Probability Percent Probability 0 0 0 0 9999
Convective Outlooks/Fire Wx Outlooks Categorical Categorical 0 0 0 0 9999
Hazard Probabilities Percent Probability Percent Probability 0 0 0 0 9999
Climate Outlook Probabilities Categorical Categorical 0 0 0 0 9999
Ice Accumulation Inches kgm-2 0 0 2 2 9999
MaxRH % % 0 0 0 0 9999
MinRH %   0 0 0 0 9999
Hazards N/A N/A 0 0 0 0 9999
Daily FRET Inches kgm-2 NA 0 NA 2 9999
Daily FRET Departure Inches kgm-2 NA 0 NA 2 9999
Total Weekly FRET Inches kgm-2 NA 0 NA 2 9999
Tropical Cyclone Storm Surge Threat Categorical Categorical NA 0 NA 0 9999
Tropical Cyclone Flooding Rain Threat Categorical Categorical NA 0 NA 0 9999
Tropical Cyclone Wind Threat Categorical Categorical NA 0 NA 0 9999
Tropical Cyclone Tornado Threat Categorical Categorical NA 0 NA 0 9999
PPI Percent Probability Percent Probability 0 0 0 0 9999

 

NDFD Grid Location and Sizes (by geographic region/sector)

Lambert Conformal

Sector Name Item Value
CONUS    
5 km Nx 1073
  Ny 689
  La1 2019199
  Lo1 2384459
CONUS    
2.5 km Nx 2143
  Ny 1375
  La1 2019199
  Lo1 2384459
Central Great Lakes    
  Nx 173
  Ny 219
  La1 3876136
  Lo1 2715378
Central Mississippi Valley    
  Nx 197
  Ny 187
  La1 3409910
  Lo1 2646187
Central Plains    
  Nx 223
  Ny 187
  La1 3469884
  Lo1 2550276
Central Rockies    
  Nx 254
  Ny 185
  La1 3510457
  Lo1 2462040
Eastern Great Lakes    
  Nx 187
  Ny 192
  La1 3925241
  Lo1 2735126
Mid-Atlantic    
  Nx 194
  Ny 200
  La1 3139028
  Lo1 2742057
Northeast    
  Nx 187
  Ny 229
  La1 3869834
  Lo1 2812826
Northern Plains    
  Nx 252
  Ny 239
  La1 3968270
  Lo1 2546129
Northern Rockies    
  Nx 306
  Ny 228
  La1 3944028
  Lo1 2439814
Pacific Northwest    
  Nx 313
  Ny 212
  La1 3949451
  Lo1 2341168
Pacific Southwest    
  Nx 312
  Ny 252
  La1 2926025
  Lo1 2368744
Southeast    
  Nx 243
  Ny 201
  La1 2407851
  Lo1 2691026
Southern Mississippi Valley    
  Nx 199
  Ny 184
  La1 2860611
  Lo1 2640133
Southern Plains    
  Nx 314
  Ny 275
  La1 2510639
  Lo1 2528770
Southern Rockies    
  Nx 267
  Ny 190
  La1 3031159
  Lo1 2451204
Upper Mississippi Valley    
  Nx 245
  Ny 270
  La1 3818489
  Lo1 2597956

 

Polar Stereographic

Sector Name Item Value
Alaska    
  Nx 825
  Ny 553
  La1 4053010
  Lo1 1814290

 

Mercator

Sector Name Item Value
Puerto Rico    
  Nx 339
  Ny 227
  La1 1697739
  Lo1 2919721
  La2 195445
  Lo2 296016
  LaD 2000000
Hawaii    
  Nx 321
  Ny 225
  La1 180726
  Lo1 1984750
  La2 230877
  Lo2 206131
  LaD 2000000
Guam    
  Nx 193
  Ny 193
  La1 1234988
  Lo1 1436865
  La2 1679439
  Lo2 1482800
  LaD 2000000
Oceanic    
  Nx 2517
  Ny 1793
  La1 -30419200
  Lo1 129906005
  La2 80010000
  Lo2 10710000
  LaD 2000000

 

NDFD Hazard Keys

Code Phenomenon/ Significance Code Phenomenon/ Significance Code Phenomenon/ Significance Code Phenomenon/ Significance
AF.W Ash Fall Warning GL.A Gale Watch <None> No Hazard WC.W Wind Chill Warning
AF.Y Ash Fall Advisory GL.W Gale Warning RB.Y Small Craft Advisory for Rough Bar WC.Y Wind Chill Advisory
AS.Y Air Stagnation Advisory HF.A Hurricane Force Wind Watch RP.S Rip Current Statement WI.Y Wind Advisory
BH.S Beach Hazard Statement HF.W Hurricane Force Wind Warning SB.Y Snow and Blowing Snow Advisory WS.A Winter Storm Watch
BS.Y Blowing Snow Advisory HI.A Hurricane Wind Watch SC.Y Small Craft Advisory WS.W Winter Storm Warning
BW.Y Brisk Wind Advisory HI.W Hurricane Wind Warning SE.A Hazardous Seas Watch WW.Y Winter Weather Advisory
BZ.A Blizzard Watch HS.W Heavy Snow Warning SE.W Hazardous Seas Warning ZF.Y Freezing Fog Advisory
BZ.W Blizzard Warning HT.Y Heat Advisory SI.Y Small Craft Advisory for Winds ZR.Y Freezing Rain Advisory
CF.A Coastal Flood Watch HU.A Hurricane Watch SM.Y Dense Smoke Advisory ZY.Y Freezing Spray Advisory
CF.S Coastal Flood Statement HU.S Hurricane Statement SN.A Snow Advisory    
CF.W Coastal Flood Warning HU.W Hurricane Warning SR.A Storm Watch    
CF.Y Coastal Flood Advisory HW.A High Wind Watch SR.W Storm Warning    
DS.W Dust Storm Warning HW.W High Wind Warning SS.A Storm Surge Watch    
DU.Y Blowing Dust Advisory HZ.A Hard Freeze Watch SS.W Storm Surge Warning    
EC.A Extreme Cold Watch HZ.W Hard Freeze Warning SU.W High Surf Warning    
EC.W Extreme Cold Warning IP.W Sleet Warning SU.Y High Surf Advisory    
EH.A Excessive Heat Watch IP.Y Sleet Advisory SV.A Severe Thunderstorm Watch    
EH.W Excessive Heat Warning IS.W Ice Storm Warning SV.W Severe Thunderstorm Warning    
EW.W Extreme Wind Warning LB.Y Lake Effect Snow and Blowing Snow Advis. SW.Y Small Craft Advisory for Hazardous Seas    
FA.A Areal Flood Watch LE.A Lake Effect Snow Watch TI.A Tropical Storm Wind Watch    
FA.W Areal Flood Warning LE.W Lake Effect Snow Warning TI.W Tropical Storm Wind Warning    
FA.Y Areal Flood Advisory LE.Y Lake Effect Snow Advisory TO.A Tornado Watch    
FF.A Flash Flood Watch LO.Y Low Water Advisory TO.W Tornado Warning    
FF.W Flash Flood Warning LS.A Lake Shore Flood Watch TR.A Tropical Storm Watch    
FG.Y Dense Fog Advisory LS.S Lake Shore Flood Statement TR.S Tropical Storm Advisory    
FL.A Flood Watch LS.W Lake Shore Flood Warning TR.W Tropical Storm Warning    
FL.W Flood Warning LS.Y Lake Shore Flood Advisory TS.A Tsunami Watch    
FL.Y Flood Advisory LW.Y Lake Wind Advisory TS.W Tsunami Warning    
FR.Y Frost Advisory MA.S Marine Weather Statement TS.Y Tsunami Advisory    
FW.A Fire Weather Watch MA.W Marine Weather Warning TY.A Typhoon Watch    
FW.W Fire Weather Warning MF.Y Dense Fog Advisory TY.S Typhoon Statement    
FZ.A Freeze Watch MH.Y AshFall Advisory TY.W Typhoon Warning    
 FZ.W  Freeze Warning MS.Y Dense Smoke Advisory UP.A Heavy Freezing Spray Watch    
        UP.W Heavy Freezing Spray Warning    
        UP.Y Heavy Freezing Spray Advisory    
        WC.A Wind Chill Watch    

Explanation of Tropical Cyclone Categorical Threat Values

All Tropical Cyclone Categorical Threat parameters have values of 0, 4, 6, 8, or 10 that should be mapped to the threat labels as described below for each hazard. There are five levels to describe each threat (all threat levels are based on the reasonable worst-case scenario):

Wind Threat

Values are based on the official NDFD wind grids created from the official hurricane center forecast along with a measure of uncertainty provided by the official tropical cyclone wind speed probabilities.

  1. Grid value 0 – Wind less than 39 mph
  2. Grid value 4 - Potential for wind 39 to 57 mph
  3. Grid value 6 – Potential for wind 58 to 73 mph
  4. Grid value 8 - Potential for wind 74 to 110 mph
  5. Grid value 10 - Potential for winds greater than 110 mph

Storm Surge Threat

Is computed based on the probabilistic storm surge guidance. The guidance used will be the same the National Hurricane Center uses to determine the range of values used in their public advisories.

  1. Grid value 0 - Little to no storm surge flooding
  2. Grid value 4 - Potential for storm surge flooding greater than 1 ft above ground
  3. Grid value 6 - Potential for storm surge flooding greater than 3 ft above ground
  4. Grid value 8 - Potential for storm surge flooding greater than 6 ft above ground
  5. Grid value 10 - Potential for storm surge flooding greater than 9 ft above ground

Flooding Rain Threat

Is computed using a combination of the official NDFD QPF forecasts, flash flood guidance from the river forecast centers, and the Excessive Rainfall Probabilities and Probabilistic QPF products from the Weather Prediction Center (WPC). In simplest terms, threat levels are described as follows:

  1. Grid value 0 - Little to no potential for flooding rain
  2. Grid value 4 - Potential for localized flooding rain
  3. Grid value 6 - Potential for moderate flooding rain
  4. Grid value 8 - Potential for major flooding rain
  5. Grid value 8 - Potential for major flooding rain

Tornado Threat

Is computed for the event analyzing SPC Tornado Probabilities for day 1 and severe weather probabilities as a proxy for tornado threat for days 2 and 3 (in case event falls in days 2 or 3), In simplest terms, threat levels are described as follows:

  1. Grid value 0 - Tornadoes not expected
  2. Grid value 4 - Potential for a few tornadoes
  3. Grid value 6 - Potential for several tornadoes
  4. Grid value 8 - Potential for many tornadoes
  5. Grid value 10 - Potential for an outbreak of tornadoes

NDFD