Heat Advisory
2026-07-15T20:00:00-04:00

* WHAT...Heat index values up to 105 expected. * WHERE...Portions of DC, central, north central, northeast, northern, and southern Maryland, and central, northern, and northwest Virginia. * WHEN...From 11 AM to 8 PM EDT Wednesday. * IMPACTS...Hot temperatures and high humidity may cause heat illnesses.

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Virginia

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Heat Advisory
Until 2026-07-15T02:45:00-04:00 • National Weather Service
* WHAT...Heat index values up to 105 expected. * WHERE...Portions of DC, central, north central, northeast, northern, and southern Maryland, and central, northern, and northwest Virginia. * WHEN...From 11 AM to 8 PM EDT Wednesday. * IMPACTS...Hot temperatures and high humidity may cause heat illnesses.

DIFFICULT RUN NEAR GREAT FALLS, VA

Realtime Data • Report • Conditions

14

Discharge (cfs)

2.7

Gauge Height (ft)

USGS 01646000

Streamflow discharge was last observed at 14 cfs, and a gauge height of 2.70 feet. With the % decrease since yesterday, the streamflow average over the past 10 days is 68 .

Weather today, Tomorrow,

The run is also impacted by the nearby Great Falls Dam, which regulates flow downstream. Seasonally, the flow tends to be highest in the spring due to snowmelt and lower in the summer and fall. Interesting facts about the hydrology of this area include its importance as a source of drinking water for the Washington, DC area and its role in providing habitat for a variety of aquatic species, including the threatened eastern hellbender salamander.

July 14, 2026

Elevation	157.0 ft
Last Updated
Gage height, ft	2.7 ft
Nitrate plus nitrite, water, in situ, mg/L as N	0.86 mg/l as N
Streamflow, ft³/s	14.3 ft3/s
Specific conductance, water, unfiltered, microsiemens per centimeter at 25°C	167.0 uS/cm @25C
Dissolved oxygen, water, unfiltered, mg/L	8.0 mg/l
Turbidity, water, unfiltered, monochrome near infra-red LED light, 780-900 nm, detection angle 90 ±2.5°, formazin nephelometric units (FNU)	17.4 FNU
pH, water, unfiltered, field, standard units	7.3 std units
Temperature, water, °C	25.1 deg C
Percent of Normal	47%
Year Over Year Average	31 cfs
24hr Flow Prediction	cfs
Maximum Recorded	8,640 cfs
Geolocation	38.98, -77.25

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Difficult Run Near Great Falls, Va Realtime Data

DIFFICULT RUN NEAR GREAT FALLS, VA

Realtime Data • Report • Conditions

14

Discharge (cfs)

2.7

Gauge Height (ft)

July 14, 2026

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Difficult Run Near Great Falls, Va Realtime Data

DIFFICULT RUN NEAR GREAT FALLS, VA

Realtime Data • Report • Conditions

14

Discharge (cfs)

2.7

Gauge Height (ft)

July 14, 2026

Seasonal Comparison

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