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Precipitation Chances In The Next
Three Hours

Lightning Chances In The Next Three Hours
About this page: These experimental products
indicate probabilities of rainfall exceeding certain thresholds, a 'best
estimate' peak rainfall amount, and probability of cloud-to-ground (CG)
lightning. Rainfall forecasts are for the highest rainfall amounts within
square regions 40 km (~20 miles) on a side. Lightning forecasts are for the
probability of two or more strikes within the same regions. Probabilities are
for 3-hour rainfall exceeding 0.1, 0.5, 1, and 2 inches (approximately 2.5,
12.5, 25, and 50 mm). Rainfall amount forecasts are for rainfall in the
categories 0.1-0.49, 0.5-0.99, 1-1.99, and 2+ inches. The algorithm that
generates the forecasts is slated for implementation within the National
Weather Service's Advanced Weather Interactive Processing System (AWIPS), which
is used at field offices and national forecast centers. Input to the products
includes a national radar composite, infrared satellite imagery,
cloud-to-ground lightning strike observations, and numerical weather prediction
model forecasts. All data are input to an extrapolative/statistical algorithm
that analyzes the intensity, position, and short-term movement of rainfall and
convective systems, and general atmospheric conditions (humidity, stability,
and vertical motion) conducive to rain. The probabilistic output takes the form
of color-filled contours on county-state map backgrounds. Categorical amount
forecasts take the form of color-filled boxes. The box format accounts for the
fact that the rainfall amount forecasts refer to the maximum rainfall values
anywhere within the entire box, not the amount at any one place. Forecasts are
updated at approximately 0:55 each hour, and cover the succeeding 3-hour
period.
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