FLOOD05189

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Basin: Statewide
• Title: Survey of Thunderstorm Rainfall Characteristics - 1979 to 1988
• Date: 9/1/1989
• Prepared For: CWCB
• Prepared By: Henz Kelly Associates
• Floodplain - Doc Type: Educational/Technical/Reference Information

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APPENDIX A

ATMOSPHERIC VARIABLES - WHAT THEY MEAN

SURPACE TEMPERATURE: Surface temperature coupled with the
dew point (mDisture) is an indication of stability; i.e.,
will the air at the surface be lighter than the surrounding
air SOl that it will be unstable and rise due tD convection.

SURFACE DEW FOINT: Is a measure of the amDunt of low level
moisture. Generally moist air is lighter than dry air and;
therefore, aDre unstable.

SHOWALTER INDEX: The Showalter index is a measure of
stability or instability Df the atmosphere. The index is
computed by the cD.paring the temperaturs of a parcel of air
lifted from the surface Dr IDw levels in the atmosphere to
a pressure Df 500 millibars Dr apprDximately 18,000
feet above MSL to the temperature of the atmosphere at the
same level. SI = TEMPERATURE ATMOSPHERE - TEMPERATURE
LIFTED. If the temperature of the lifted parcel is greater
than the temperature of the atmosphere the index will be
negative and indicate instability. The warmer parcel will
be cDnvectively unstable since it is warmer than the
environment , it will continue to rise.

700 MILLIBAR TEMPERATURE: 700 millibars is apprDximately 10,000
feet MSL. The 700 MB temperature is the temperature of the
atmDsphere at that level and can be cD.pared to the
temperature of a parcel lifted from the surface tD 700MB to
determine stability, i.e., will the lifted parcel cDntinue to
rise ( be unstable) Dr sink back tDward its original
position( be stable).

700 MILLIBAR TEMPERATURE !DEWPOINT DIFFERENCE: The
difference between the temperature and dew point at 700 MB is
a measure of moisture at that level. If the difference is
small the atmosphere is quite mDist and the relative
humidity is quite high. If and as a storm develDps the
difference provides infDrmatiDn such as : whether moist
or dry air will be mixed into the storm at this level,
inputs as to stability at that level, and inputs as
tD thermodynamic processes of cDndensation and evaporatiDn
and the subsequent heat budget at that level.

500 MB, 300 MB, 200 MB TEMPERATURE: The same as described
fDr the 700 MB level except the levels are apprDximately
18,000 , 30,000 and 39,000 feet MSL respectively.

500 MB TEMPERATURE !DEWPOINT DIFFERENCE: The same as
described for the 700 MB level except the level is
approximately 18,000 feet MSL.