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NOUS41 KWBC 011530
PNSWSH
SERVICE CHANGE NOTICE 26-75
NATIONAL WEATHER SERVICE HEADQUARTERS SILVER SPRING MD
1130 AM EDT TUE SEP 1 2026
TO: SUBSCRIBERS:
-NOAA WEATHER WIRE SERVICE
-EMERGENCY MANAGERS WEATHER INFORMATION NETWORK
-NOAAPORT
OTHER NWS PARTNERS, USERS AND EMPLOYEES
FROM: KATHRYN GILBERT, DEPUTY DIRECTOR
WEATHER PREDICTION CENTER
SUBJECT: EXPERIMENTAL PROBABILISTIC PRECIPITATION PORTAL WILL
TRANSITION TO OPERATIONAL STATUS ON OR ABOUT OCTOBER 1, 2026
THE NATIONAL WEATHER SERVICE (NWS) WILL TRANSITION THE
EXPERIMENTAL PROBABILISTIC PRECIPITATION PORTAL (PPP) TO
OPERATIONAL STATUS ON OR ABOUT OCTOBER 1, 2026.
THE PPP IS A WEBSITE DESIGNED AND MAINTAINED BY THE WEATHER
PREDICTION CENTER (WPC) TO BE A CENTRALIZED LOCATION OF NWS
PROBABILISTIC WINTER PRECIPITATION FORECAST (PWPF) AND
PROBABILISTIC QUANTITATIVE PRECIPITATION FORECAST (PQPF)
INFORMATION. PPP GRAPHICS ARE CREATED ACROSS THE CONTIGUOUS
UNITED STATES (CONUS), ALASKA, HAWAII, AND PUERTO RICO, AND ARE
ALSO DISPLAYED ON NWS WEATHER FORECAST OFFICE (WFO) LOCAL WINTER
FORECAST PAGES AND LOCAL QPF FORECAST PAGES. THE UNDERLYING
ENSEMBLE INFORMATION USED BY THE PPP IS THE LATEST OPERATIONAL
VERSION OF THE NATIONAL BLEND OF MODELS (NBM).
THE PPP PRODUCES 10% AND 90% EXCEEDANCE PERCENTILES,
REPRESENTING A LOW END AMOUNT (A 90% CHANCE OF HIGHER
SNOWFALL/ICE/QPF) AND A HIGH END AMOUNT (A 10% CHANCE OF HIGHER
SNOWFALL/ICE/QPF) TO COMPLEMENT THE EXISTING NWS DETERMINISTIC
SNOWFALL/ICE/QPF FORECASTS (THE EXPECTED AMOUNT). NARROW RANGES
BETWEEN THE MINIMUM AND MAXIMUM SNOWFALL/ICE/QPF TOTALS INDICATE
HIGHER FORECAST CERTAINTY, WHILE LARGE RANGES BETWEEN MINIMUM
AND MAXIMUM TOTALS INDICATE LOWER FORECAST CERTAINTY. IN
ADDITION, 25%, 50%, AND 75% EXCEEDANCE PERCENTILES WILL ALSO BE
DISPLAYABLE ON THE WEBSITE.
THE PPP PRODUCES THE PROBABILITY OF EXCEEDING THE FOLLOWING
AMOUNTS OF SNOW: 0.1", 1", 2", 4", 6", 8", 12", AND 18", THE
FOLLOWING AMOUNTS OF QPF: 0.01", 0.1", 0.25", 1", 2", 3", 4",
6", 8", AND 12", AND THE FOLLOWING AMOUNTS OF RADIAL ICE
ACCUMULATION: 0.01", 0.1", 0.25", 0.50", 0.75", 1.0", 1.25", AND
1.50".
THE EXPECTED AMOUNT IS THE DETERMINISTIC NDFD FORECAST. THE PPP
WILL ALSO ALLOW A FORECASTER TO SHOW THE EXPECTED AMOUNT AS A
RANGE OF TWO VALUES (THE 25TH TO 75TH PERCENTILE AMOUNTS) IN AN
IMPACT-BASED DECISION SUPPORT SERVICES GRAPHIC. GRIDS ARE VALID
FOR 6-, 12-, 24-, 36-, 48-, AND 72-HOUR PERIODS OUT TO 72 HOURS
FOR PWPF AND PQPF FROM 0000 COORDINATED UNIVERSAL TIME (UTC) DAY
1 BEGINNING WITH THE 2200 UTC ISSUANCE. THEY ARE VALID FROM
1200 UTC DAY 1 BEGINNING WITH THE 1100 UTC ISSUANCE AND ARE
UPDATED ONCE PER HOUR.THE SNOW PERCENTILE VALUES ARE ALSO SENT
AS GRIDS TO THE NATIONAL DIGITAL FORECAST DATABASE (NDFD).
THE PPP CAN BE ACCESSED HERE:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/PROB_PRECIP
THE PPP SNOW, ICE, AND QPF DATA WILL BE AVAILABLE FOR DOWNLOAD
IN GRIB2 FORMAT FOR ALL TIMEFRAMES AND ALL TYPES OF DATA
(DETERMINISTIC AMOUNTS, EXCEEDANCE PROBABILITIES, AND EXCEEDANCE
PERCENTILES). EXCEEDANCE PERCENTILES OF 5% AND 95% ARE ALSO
CREATED. THE DATA WILL BE AVAILABLE FOR DOWNLOAD IN KML AND
SHAPEFILE FORMAT AT THE 24-, 36-, 48-, AND 72-HOUR PERIODS OUT
TO 72 HOURS. THIS DATA WILL BE ACCESSIBLE FOR END USERS VIA
FILE TRANSFER PROTOCOL (FTP) AT:
HTTPS://FTP-WPC.NCEP.NOAA.GOV/PROB_PRECIP_PORTAL/CO/ FOR CONUS
HTTPS://FTP-WPC.NCEP.NOAA.GOV/PROB_PRECIP_PORTAL/AK/ FOR ALASKA
HTTPS://FTP-WPC.NCEP.NOAA.GOV/PROB_PRECIP_PORTAL/PR/ FOR PUERTO
RICO
HTTPS://FTP-WPC.NCEP.NOAA.GOV/PROB_PRECIP_PORTAL/HI/ FOR HAWAII
NOTE THAT THIS FTP SITE MAY NOT BE FULLY POPULATED UNTIL ON OR
AROUND THE PPP OPERATIONAL IMPLEMENTATION DATA OF OCTOBER 1,
2026.
FOR ADDITIONAL INFORMATION, PLEASE SEE THE PPP SERVICE
DESCRIPTION DOCUMENT (SDD) AT:
HTTPS://NSDESK.SERVICENOWSERVICES.COM/API/G_NOA/NWSPC/RES2/2527D
BE9CF3E43503452F7F42F851CA3
FOR ADDITIONAL COMMENTS/QUESTIONS, PLEASE CONTACT:
WPC SERVICES
WEATHER PREDICTION CENTER
RIVERDALE PARK, MD
WPCSERVICES@NOAA.GOV
NATIONAL SERVICE CHANGE NOTICES ARE ONLINE AT:
HTTPS://WWW.WEATHER.GOV/NOTIFICATION/
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