HPC Mission

The Hydrometeorological Prediction Center (HPC) provides forecast, guidance, and analysis products and services to support the daily public forecasting activities of the NWS and its customers, and provides tailored support to other government agencies in emergency and special situations. 

We are here to assist and be a resource for you. We are available 24 hours a day, 7 days a week to alert you to the potential for significant weather events dealing with heavy rainfall or snowfall, to discuss quantitative precipitation forecasts and model differences relating to general weather and precipitation forecasts, and to provide forecast guidance into the medium range period (days 3 to 7). Most of the forecasters at the HPC have extensive experience at quantitative precipitation, heavy snow and medium range forecasting. 

Quantitative Precipitation Forecasts (QPFs)

Forecasters at the HPC [and its predecessor organizations, NMC's Meteorological Operations Division, Heavy Precipitation Branch (HPB) and the Quantitative Precipitation Branch (QPB)] have been issuing QPFs since 1960. All QPFs incorporate the latest surface and upper air analyses, radar data, satellite data, and model guidance from the Eta, NGM, AVN, meso-Eta, and RUC displayed on N-AWIPS workstations. The FOB also works in conjunction with meteorologists in NESDIS's Synoptic Analysis Branch (SAB) to obtain information regarding satellite trends, precipitation and moisture availability estimates. This collocation and collaboration between SAB and HPC is bureaucratically known as the National Precipitation Prediction Unit (NPPU). 

An FOB Senior Branch (lead) Forecaster (SBF) is on shift at all times. He or she is responsible for producing the 24 hour precipitation forecasts, coordination of all HPC products (both internally and with other NWS offices), and center administrative operations after business hours. In addition to normal duties, the SBF participates in the East Coast winter storm and NHC hurricane conference calls regarding heavy precipitation, the NWS PRE-MARD Initiative, occasional unscheduled FEMA conference calls and numerous media interviews. 

24 Hour QPFs

Isohyets of expected basin average rainfall of 0.01,  0.25 inch, 0.50 inch, 1 inch, and 1.50 inch and greater (in inch increments) are drawn for the 24 hour forecast period ending at 1200Z on both days 1, 2, and 3. 

An electronically generated bulletin, which describes the location of the forecast isohyets using latitude and longitude points, is transmitted at the end of the qpf discussion for the Day 1 through Day 3 finals. 

Example: 
 0.25 350731 349761 349789 347803 340819 327837 310854 297864 284874
 0.50 404072 395071 390076 387081 389084 395085 402082 404076 404072

The first field is the value of the contour (in this case...0.25" or 0.50"). The following fields are the latitude/longitude pairs for the contour. The first three digits of the pair are the degrees of latitude (in tenths of degrees North latitude). The last three digits of the pair are the degrees of longitude (in tenths of degrees West longitude).  If the fourth digit is less than 5, a leading "1" is added to indicate longitudes greater than or equal to 100° W. From the above message, the following table gives the decoded lat/long pairs:
 
 

Value: 0.25"	Value: 0.50"
35.0N, 73.1W	40.4N, 107.2W
34.9N, 76.1W	39.5N, 107.1W
34.9N, 78.9W	39.0N, 107.6W
34.7N, 80.3W	38.7N, 108.1W
34.0N, 81.9W	38.9N, 108.4W
32.7N, 83.7W	39.5N, 108.5W
31.0N, 85.4W	40.2N, 108.2W
29.7N, 86.4W	40.4N, 107.6W
28.4N, 87.4W	40.4N, 107.2W

6 Hourly QPFs
 

These forecasts depict isohyets of accumulated precipitation of 0.01, 0.25, 0.50, and 1 inch expected in each six hour period. The SBF generates the six-hourly forecast for Day 1. The QPF forecaster, known as the Day 2/3 six-hourly forecaster, generates the Day 2 and Day 3 six hourly products during 2 shifts per day (~9am-5pm/9pm-5am EST), issuing QPFs for eight consecutive six-hourly periods ending on synoptic hours.

Excessive Rainfall Potential

This product outlooks the potential for flash flooding based on current flash flood guidance issued by RFC's. The graphic and discussion are issued 3 times a day, at 0615Z, 1430Z, and 1815Z for the current 24 hour period ending at 12Z. Special rainfall discussions (NFDQPFSRD) and an updated graphic (94E) are issued after 1930Z if significant changes to the flash flood outlook are necessary before the next scheduled issuance time. 
 

Three categories are used to indicate flash flood threat:

An Exceeding area outlines a geographical area to the right of a solid arrow drawn using station identifiers as anchor points where conditions are favorable for rainfall to exceed flash flood guidance values. 

An Approaching area is generally used in winter-time or for synoptic-scale situations where flash flood guidance values are relatively high but accumulated precipitation amounts from a larger scale system may lead to run off problems. It outlines an area with a dashed arrow and labeled "APCHG".

An Isolated area is mainly intended for use in the Western U.S. where events tend to be more isolated than over the rest of the conterminous U.S. It is drawn with a dashed-dotted line and labeled with "ISOLD". 
 

Other labels on the Excessive Rainfall Graphic: 

"SEE FOUS 30/CCCQPFERD" over the area affected or with an arrow pointing to the general area of concern indicates that there is not sufficient cause or confidence to draw an area, but that the QPFERD discussion talks about the situation. 

If the forecasters feel that the potential exists for 5 inches or more within the remainder of the outlook period it is depicted on the graphic with a hatched area. 

If conditions are not favorable or are not expected to become favorable for flash flooding then "Rainfall Not Expected To Exceed Flash Flood Guidance" is appended to the graphic. 

QPF Forecast Verification:

6-hourly precipitation forecasts are verified using a point (station) method while 24 hour forecasts are verified using an areal method. Current graphs depicting HPC verification scores are available on the HPC Verification page. For more details about the verification of HPC precipitation forecasts, read the article by Olson, Junker and Korty in Weather and Forecasting.Volume 10, 1995, pgs. 498-511. 

Medium Range/Extended (3-7 days)

The medium range forecast products include: 1) surface pressure patterns, circulation centers, and fronts for days 3, 4, and 5 into the future, 2) daily maximum and minimum temperatures and anomalies for days 3-7, 3) daily precipitation probabilities for days 3-7, and 4) total 5-day precipitation for days 1 through 5. These products are issued once per day along with a written discussion. Separate forecasts, similar to the 5-day mean products, are prepared for Hawaii. 

Two meteorologists work this once a day shift. One produces 4-5 day pressure systems/fronts, 4-5 day precipitation, and 3-5 day POP progs while the other produces the 3-7 day temperature and 6-7 day POP progs. They routinely use output from the MRF, ECMWF, and UKMET medium range models and also consider the Canadian, the Navy's NOGAPS model, the MRFX, a semi-operationally run experimental version of the MRF, and ensembles. 

During hurricane season, at 1200 noon EDT, on a daily basis since June 1, 1997, the medium range pressure forecaster participates in a conference call with the NHC via the Hurricane Hotline to discuss current and potential tropical activity in the Atlantic and Eastern Pacific oceans and how the medium range models are handling the situation.

Model Diagnostics

Surface Analysis Products

The following chart indicates the approximate issuance and web posting schedule for the HPC Surface Analysis. This product depicts the analysis of synoptic and sub-synoptic/mesoscale surface features including highs, lows, fronts, troughs, outflow boundaries, squall lines, and drylines. The analysis domain covers most of North America, the Western Atlantic and Eastern Pacific oceans, and the Gulf of Mexico.

PLEASE NOTE:  The Pacific Ocean analyses (East and West Pacific) are prepared by NCEP's Ocean Prediction Center. 

Probabilistic Heavy Snow/Icing Forecasts

From mid-September through mid-May the HPC routinely issues heavy snow/icing outlooks and accompanying discussions for heavy snow out to 54 hours. They cover two separate 12 hour forecast periods, 06 to 18 hours (93S) and 18 to 30 hours (94S) and a 24 hr period, 30-54 hours (98S). The HPC has decided to modify its current heavy snow guidance product in an effort to make it more useful to those making decisions based on this forecast. This is described in the Public Information Statement. The confidence levels used can be considered comparable to the probability of occurrence of the forecasted parameter.

Risk Criteria:
LOW - 20% to 30% chance of occurrence within the outlined area.
MODERATE (MDT) - 31% to 70% chance of occurrence within the outlined area.
HIGH - greater than 70% of occurrence within the outlined  area. 

At times the forecasters may use only one or two isolines for the forecast. This simply implies low or low to moderate forecaster confidence in the occurrence of the forecasted parameter. One should expect the confidence to lower as the forecast is extended out in time. To gain further insight into this forecast, please read the Heavy Snow/Icing Discussion (HSD) that accompanies this graphical product. 

Short Range Forecasts (1-2 days)

The "Basic Weather" forecaster is responsible for preparing the 12, 18, 24, 30, 36 and 48 hour surface progs (forecasts). These progs are issued twice a day based on output from the 00Z and 12Z model runs. Emphasis is placed on the subjective modification of numerical guidance, especially with regard to timing and placement of coded fronts, high and low pressure systems, and instantaneous precipitation (coverage and type). The primary aim is to accurately depict the evolution of major weather systems that will affect the continental U.S. during the next two (2) days. 

* Please note that the transmission space limits the NFDPMDSPD narrative to 40 lines, thus this message is necessarily short and sometimes may not discuss significant weather conditions over the entire continental U.S. in detail and may not be able get into as much technical detail as users may like. 

International Desks

Selected Cities/Travler's
 

Description	Selected Cities Product
Part 1 (Abilene, TX to Columbus, OH)	SCS9 / WMO: FPUS20 KWNH
Part 2 (Concord, NH to Lexington, KY)	SCS10 / WMO: FPUS21 KWNH
Part 3 (Lincoln, NE to  St. Thomas, V.I.)	SCS11 / WMO: FPUS22 KWNH
Part 4 (Salem, OR to Yuma, AZ)	SCS12 / WMO: FPUS23 KWNH

The Selected Cities Summary is a highly visible product that is issued two times per day at 0100 and 1300 UTC. It includes a tabular array of the previous day's maximum and minimum temperatures along with temperature and weather forecast for the next two days. The Selected Cities Summary covers 158 cities in the United States, Puerto Rico, and the Virgin Islands. It is composed of four parts with the last part including the observed maximum and minimum temperatures from around the nation. Forecast data is obtained from your CCFs. 
 
 

The Travelers Forecast Bulletin is an abbreviated version of the Selected Cities Bulletin. The Travelers Forecast, like the Selected Cities is transmitted two times per day, one hour before the Selected Cities, for thirty (30) cities in the U.S. The Travelers Forecast consists of three parts which contain the weather and high and low temperature forecasts extracted from your CCFs. 

Other HPC Products

Storm Summaries are issued by the HPC after any named tropical or sub-tropical cyclone has moved inland and public advisories are no longer issued by the National Hurricane Center (NHC). In addition, storm summaries are issued for any major winter storms that produce widespread snow or ice.  The Storm Summaries will continue to be issued as long as there is a threat of severe weather or flash flooding from the storm or its remnants. They are numbered sequentially (continuing from the last numbered advisory issued on the storm by the NHC for tropical systems).  Storm Summaries are transmitted four times a day at or before 0300Z, 0900Z, 1500Z, and 2100Z.