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Predicting Water Levels - Weather

Weather Appendix to Steve Ettinger’s Capital Canoeing & Kayaking Whitewater Guide

1  Three Key Sites

2  River Predictions

3  Precipitation Forecasts

4  Fast Local Weather Predictions

5  Local Precipitation Gauges

6  Quick Access - including USGS Water Alerts

1.  THREE KEY SITES:      Steve Ettinger says: “I tend to rely on this site:

The QPF:  Quantitative Precipitation Forecast gives rainfall predictions for the next 5 days. [see para. 3, below]    "Then I keep tabs on the  


Sterling Loop: It tells you how much rain has actually fallen during the current rainstorm.  I line that up with my maps, and figure out which basins have gotten the most rain, etc.” [see para. 4.A, below]


And New NOAA Rainfall Site:

This site displays rainfall in the last 3, 6, 13, 24 hours – for details, see para 5, below.

But if you like it complicated, try the following:


2.  RIVER PREDICTIONS      NEW     (This is only good for the Big Stuff - >200 sq mi)  Works for the mid and lower Potomac, James, Shenandoah, Appomattox, Conococheague, Brandywine, Youghioheny, and Antietam.   For the Potomac just below the dams at Barnum WV (Bloomington) and the Savage R, see the CoE's 3-day release schedules in the relevant Stream-Finder tables - #14, and #15.  Add the two volumes.  Or here:  For Savage and Bloomington.


The easiest source is the USGS state polka-dot maps measuring current streamflow.  Open the Stream-Finder to the Whitewater Gauge Tables and open one.  Click on the blue state name above the actual chart:  Here are the links to copy and paste:

Maryland - 
Virginia -
West Virginia -
Pennsylvania -

Then click on a gauge on your (big) river.  On the ensuing pop-up's top bar, choose "Forecast."  Click anywhere on the tri-color chart to enlarge it.  For a forecast in feet & volume (cfs) put the stylus on the relevant square point on the right side of the chart.  Click on it to get a detailed table.,   Note that all readings are in UTC = GMT = Standard [not DST = daylight time, for which you must add one hour.]  END NEW 

Your go-to source is NOAA’s Middle Atlantic River Forecast Center – MARFC  (copy & paste in browser - the link doesn't work), DEAD LINK which isthe lead-in website referenced on the Monocacy Canoe Club’s “River Levels” page. It features under “Forecast River Conditions / Current River Forecasts” a regional (Delaware R down to the Appomattox) map with (usually) green and dark gray circles and squares along the rivers on which you click to link to a hydrograph, an eight-day line graph showing the past (5 days) and predicted (2-4 days) river levels. Click on the graph’s main line to get the precise volume data in cfs. Over thirty of these sites are in our frequently-paddled area (CC&K’s two-hour radius from Washington), but it has nothing in the Tidewater or immediately NE of Washington, where the Balto area brooks are too short or dam-infested to make any long term prediction possible.



For regional maps predicting cumulative rainfall for the next three days, with detail – breaking down those days into six-hour segments, again go to MARFC.  - TRY THE ABOVE. which starts with the caption “Gridded Precipitation Forecast Maps.” These are subdivided into unlabeled counties, so you must know their shapes and locations.

Then scroll down to the “Basin Average Precipitation Forecast Maps” and then to the southern MARFC Area, in the Piedmont west of Washington and below the Mason and Dixon Line – for the Potomac, Rappahannock, James, and Appomattox watersheds. Click on any of the six-hour rainfall boxes, the daily totals, or the 72-hour total to bring up a river-basin map carved into NE-SW aligned portions of river valleys colored by intensity of rainfall – ascending from light green (0-¼”) to blue, red, and orange.  Again, you must know your geography, for this map has no state or county lines; however, the 40-odd basins are identified by three-letter abbreviations based on a prominent USGS gauge location (e.g., HNK, REM, DAW) in each.  Some are difficult, so unlimber your imagination.

Regional Precipitation Forecast Map: The QPF - Quantitative Precipitation Forecast

This useful tool is at “NWS Weather Prediction Center.” Scroll down to the QPF (on the left) – The map is of the USA – Lower 48 and Canada, showing the major rainfall zones lying over clear state lines, this time (to keep you on your toes) a different color sequence, ascending from light green through the blues, then purple to red, then orange and yellow. Go figure.


4.  FAST LOCAL WEATHER PREDICTIONS  For very local weather:


On the left of the QPF page – type in the nearest City and State – or zip code, and up come nine little pictures of weather happening in that town – under which is your “Detailed Forecast.”  Over on the right is the RADIO & SATELLITE IMAGES  - with the map with the Sterling Loop – and the HOURLY WEATHER GRAPH  -  rich with wind, temperature, precipitation, relative humidity, chance of precipitation, and even wind chill data – as it says, by the hour.  Pass your stylus over the chart to the time of day you want, and you will see the values also displayed below the several charts.  On the chart two days worth of data are displayed – for farther into the future, above and to the left of the charts - at “48-Hour Period Starting:” click on the “Submit” button.  Or at the top right, it offers tabs saying “Forward 2 Days” and “Back 2 Days.” You can also display these numbers in tabular form.  Go one table below this for the vertical green bars predicting rainfall by the hour – and summing up how many inches may fall in a certain period.

Or: DC-Area NWS Page - Go to for the National Weather Service office for the Baltimore-Washington (Sterling, Va) area [LWX] and click on the map on the desired locale (even where there’s no town shown) for a full local (e.g., Harpers Ferry) NWS prediction. On the lower right side for each locale is an Hourly Weather Forecast Graph with detailed temperatures, wind speed and direction, and possibility of precipitation - all searchable four days in advance. Below that under “Detailed Forecast” is a prose day by day presentation of the local weather. is very similar.

A  The Sterling Radar Loop [LWX],

This tells current weather. Note the bar at the bottom, where you can dial up if you want your display to show counties, rivers, cities, etc: (Steve’s favorite site, mentioned above)

“Storm Total Precipitation” – the preceding 12-or so hours – in an oval centered on Sterling, Va. “Sterling, Va Radar – Base Reflectivity Map” This is one of the three fundamental quantities that a Doppler radar measures. Reflectivity is related to the power, or intensity, of the reflected radiation that is sensed by the radar antenna. Base reflectivity, expressed on a logarithmic scale [on the map’s right-hand scale] in units called dBZ, is related to rainfall intensity (e.g., drop size and rainfall rate) and hail size.


B  The Big Picture – Large CONUS Map – Mosaic Loop:                                                  What’s coming our way.

C  Aviation Weather Center Forecast: Another way to get to the loop [LWX] or to similar maps for other parts of the country.

D  Washington-Area Airports - Map  Has quick info if you hover over the “+” at individual airports – click for lots more: esp. immediately-past precipitation. (watch out: ZULU time)

5.  LOCAL PRECIPITATION GAUGES (what actually fell) –


A   New NOAA “Hourly Precipitation Analysis” Site

This site displays rainfall in the last 3, 6, 13, 24 hours (and the past 2 through 120 days), opening with the whole continental USA. Drill down to the desired locale and then go below the map to “Available Precipitation Images” – which are the above listed time-periods. The amount of precipitation is in different colors – see the codes in the vertical bar on the right. This may obviate going to the individual (idiosyncratic and often nonexistent) state and county rainfall gauges, listed below.


B  USGS Cumulative Precipitation Gauges

These are the easiest and best such gauges, as they graphically show the cumulative amounts of rainfall and precisely when it fell over the last hours or days – you set the parameters. Usually carried as an extra table at an existing USGS stream gauge, they are rare in our area, but are ubiquitous in Pennsylvania. Here are eight useful ones for the Washington/ Baltimore/ Cumberland area: Fourmile Run (Alexandria, VA), Lovettsville (N of Leesburg, VA), Markleton on the Casselmans (SW PA), Indian Rock Dam (upper Codorus, near York, PA), Chadds Ford on the Brandywine (PA + Del), Petersburg on the Potomac So Br, North Fork (WVa), and Hendricks on the Dry Fork of the Cheat (WVa).  In the tables (last column) they are in BOLD.


These gauges appear in Steve’s book, but his link to them on page 14 via AFWS (Automated Flood Warning System) no longer works.  Instead one should go directly to IFLOWS – the Integrated Food Observation and Warning System.


For Virginia:

Drill down into your area using the blue “+” sign at the top left of the screen. Wait until it loads; counties and their names will appear. Click on any green square or triangle in your target county, and a table of all of the rain and stream gauges in it will appear. These show precipitation in the past ¼, ½, 1, 3, 6, 12, and 12 hours, as well as the county’s USGS river gauges – these latter in stage readings in feet, not cfs.


For West Virginia:

A different system from Virginia’s. The map that appears is small – click on it to get detail. Then click on one of the squares – and the same table of rain gauges over the past day.


For Pennsylvania:

For SW Penna: the Pittsburgh region - different again. Click on the map to have it expand.

For center-south Penna: Gives rainfall in the area south of State College between Morgantown on the Md-WVa line and Lancaster.

Additionally, about 100 USGS steam gauges in Pennsylvania also measure rainfall.


For Maryland:

The AFWS System in Maryland has but eight gauges, all to the W and SW of Baltimore. Same view as for Penna – green and grey clouds, each with a single rainfall table. Odd, since the system was built for Appalachia.

Many AFWS websites appear to have been discontinued in March 2013 – and that Service is unresponsive to attempts to telephone and e-mail it. It is under NOAA, and apparently under NWS, the National Weather Service. IFLOWS appears not to be an agency, but a program that has been hived off to the states. Therefore, the different formats described.


D  New Multi-Purpose International Data

This website based in Europe is useful: It gives a refreshingly new set of graphics, and the geographic (and other) settings can be changed – also for places abroad, like Chile and Mexico. It gives each day in 3-hour intervals and its 14-day forecast shows both the chance of rain and predicts the amount thereof (in millimeters; sorry, I did say it was European.)




- Sign up for your special streams by going to your target gauge and entering the minimum point at which you want the Service to ping your e-mail or cell ‘phone. For example, I have set 17 Water Alerts for the following minimum cfs:


VA            Passage Ck 200                   Battle Run 80           Accotink - 2.8 ft = 100

WV          SoFk, SoBr, Potomac (Brandywine) 400 - 200     Great Cacapon - for Lost R - 1,300

                SoFk, NoBr, Potomac (Cabins) 500

MD-DC    Rock Ck  300                       Little Patuxent - 125           Patapsco - 200                    Seneca Ck – 2.5’ = 200

                GPF, upper  100                  Lower Savage – 250           Upper Savage – 300            Upper Catoctin (Middle Ck) – 300                Goose Ck - 180

PA           Codorus  180                      Bermudian Ck – 90              Chadds Ford for Brandywine – 700


To sign up, look below and to the right of each USGS gauge table for the “Water Alert” link. If you’re asked to enter your minimum reading not in cfs, but in feet, you’ll have to go to the two-column table for that gauge and obtain that equivalent for your desired minimum cfs figure.

A   QPF Quantitative Precipitation Forecast


B   MARFC Mid Atlantic Regional Forecast Center

C   LWX Sterling Loop Storm Total Precipitation

D   WX for the Locale - the Weather Channel

McLean Weather Forecast and Conditions Virginia (22101)

E   AW - American Whitewater (Mid Atlantic – “What’s Running”)

F   USGS Waterwatch

USGS Real-Time Water Data for the Nation (the colored dots – Pick MD, VA, etc)

This appendix will progress only if you, gentle reader, will show me how to improve it, correct my errors, and keep me abreast of the protean weather web-sites.  For as you have probably noticed from the above disparate websites, the weather side of the house is far different from the stream-gauges – which are run by a single agency using a single format.  Please send comments and updates to me at


rev. 15 Feb 2018