Measuring Precipitation

How?

• Raingauges

• Radar

• Snow pillows

• Hail pads

• Precipitation patterns

Measuring Rain w/ Standard GaugeMeasuring Rain w/ Standard Gauge

Figure 8.27Figure 8.27

Standard rain gauge uses a funnel Standard rain gauge uses a funnel to collect rain and then stores it in to collect rain and then stores it in a narrower tube, so that the gauge a narrower tube, so that the gauge detection is amplified 10-fold.detection is amplified 10-fold.

The 50 cm long tube, when filled, The 50 cm long tube, when filled, represents only 5 cm of total represents only 5 cm of total rainfall.rainfall.

Measuring Rain w/ Recording GaugeMeasuring Rain w/ Recording Gauge

Tipping bucket and weighing rain gauges record precipitation rate Tipping bucket and weighing rain gauges record precipitation rate at shorter time intervals, providing rain intensity data.at shorter time intervals, providing rain intensity data.

Snow intensity can be measured with depth recorders, or Snow intensity can be measured with depth recorders, or accumulated totals with measuring sticks.accumulated totals with measuring sticks.

Figure 8.28Figure 8.28

NEXRAD -- The WSR-88D

A radar

WSR-88D Specifications

• Weather Surveillance Radar commissioned in 1988 with Doppler capability.

• The radar tower is 98 feet high and has an antenna that is 28 feet in diameter.

• It has a beamwidth of 0.95 degrees and rotates at a rate of 36 degrees per second.

                                                                                        

                                                        

Radar RainfallRadar Rainfall

Figure 8.29AFigure 8.29A

Doppler radar uses microwave transmission and reception to Doppler radar uses microwave transmission and reception to measure backscatter intensity, or reflectivity for large geographic measure backscatter intensity, or reflectivity for large geographic areas.areas.

This signal is converted into maps of precipitation intensity.This signal is converted into maps of precipitation intensity.

Figure 8.29BFigure 8.29B

Rain gauge

Snow Pillows

• Measure the weight of snow accumulated on the pillow

• Problems with drifting

Snow depth

• Snow can be measured as an actual depth by sticking a measuring stick into it

• This is not reliable as the depth will change the next place you measure

• Depth will depend on the type of snowflakes that fall (how fluffy they are)

Equivalent rain water depth

• Usually more useful to know how much rain the snow would be equivalent to if it melted

• Can use a heated raingauge

• Or convert from snowdepth to rain water equivalent

Equivalent rain water depth

• Usual conversion is 10 to 1

• 10cm of snow = 1cm of rain– (or 10” snow = 1” rain)

• But very variable and depends on type of snow and how long it’s been settling

Hail pads

• Measure the force with which a hailstone impacts the pad

• Can calculate hail size

• Small and unrepresentative

• Hail reports usually from spotters

Annual Precip

Annual hail incidence

Annual snowfall