Heat Wave Expands to the East Coast; Flash Flooding Likely in the Central Plains into the Midwest; Severe Thunderstorms in the Northeast

Dangerous, prolonged heat is ongoing in the Mid-South to Mid-Mississippi Valley and heat expands into the Northeast for a brief period today. Widely scattered instances of flash flooding due to heavy rains are forecast from northeast Kansas to much of Indiana. Scattered strong to severe thunderstorms are possible across parts of New England, northern Mid-Atlantic, and North Dakota. Read More >

X-Band

A frequency band of microwave radiation in which radars operate.

X-Ray Background

In solar-terrestrial terms, a daily average background X-ray flux in the 1 to 8 angstrom range. It is a midday minimum designed to reduce the effects of flares.

X-Ray Burst

In solar-terrestrial terms, a temporary enhancement of the X-ray emission of the sun. The time-intensity profile of soft X-ray bursts is similar to that of the H-alpha profile of an associated flare.

X-Ray Flare Class

In solar-terrestrial terms, rank of a flare based on its X-ray energy output. Flares are classified by the order of magnitude of the peak burst intensity (I) measured at the earth in the 1 to 8 angstrom band as follows:

Class	Intensity (in Watts/m²)
B	I < 10^-6
C	10^-6 <= I < 10^-5
M	10^-5 <= I < 10^-4
X	I >= 10^-4

X-Rays

Very energetic electromagnetic radiation with wavelengths intermediate between 0.01 and 10 nanometers (0.1-100 Angstroms) or between gamma rays and ultraviolet radiation. Essentially all X-Rays from space are absorbed in the Earth's upper atmosphere.

XBT

Expendable Bathythermograph

XCITED

Excited

XCPT

Expecting

XPC

Expect

XSEC

Cross Section

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