GRG333C / Severe and Unusual Weather Surface and Upper Air Station Models

200MB : -57C / Air Height (Prefix 1,Suffix 0): (Appx 39,000' 4C Point Depression 12130 Meters MSL) (-61C / Temperature) 12 Hour Height Change: : 250 Degrees / 110 Knots + 20 Meters

Center Circle: Blackened - Dew Point Depression is 5C or Less

250MB: -45C / Air Temperature Pressure Height (Prefix 1, Suffix 0): (Appx 34,000' 4C Dew Point Depression 10670 Meters MSL) (-49C / Dew Point Temperature) 12 Hour Height Change: Wind: 250 Degrees / 110 Knots) + 10 Meters

Center Circle: Blackened - Dew Point Depression is 5C or Less

300MB: -37C / Air Temperature Pressure Height (Suffix 0): (Appx 30,000' 1C Dew Point Depression 9440 Meters MSL) (-38C / Dew Point Temperature) 12 Hour Height Change: Wind: 250 Degrees / 100 Knots + 20 Meters

Center Circle: Blackened - Dew Point Depression is 5C or Less

500MB: -14C / Air Temperature Pressure Height (Suffix 0) (Appx 18,500' 27C Dew Point Depression 5720 Meters MSL) (-41C / Dew Point Temperature) 12 Hour Height Change: Wind: 250 Degrees / 55 Knots) - 10 Meters

Center Circle: Not Filled - Dew Point Depression is > 5C

700MB: 1C / Air Temperature Pressure Height (Prefix 2 or 3) (Appx 9,600' 23C Dew Point Depression 3097 Meters MSL) (-22C / Dew Point Temperature) 12 Hour Height Change: Wind: 270 Degrees / 25 Knots + 20 Meters

Center Circle: Not Filled - Dew Point Depression is > 5C

850MB: 6C / Air Temperature Pressure Height (Prefix 1) (Appx 4,600' 12C Dew Point Depression 1525 Meters MSL) (-6C / Dew Point Temperature) 12 Hour Height Change Wind: 010 Degrees / 10 Knots +20 Meters

Center Circle: Not Filled - Dew Point Depression is > 5C

CONSTANT HEIGHT CHART NOTE (FOR STATION MODELS ABOVE): “x” in the Dew Point Depression Position Indicates Dew Point Depression of > 29C Dew Point Depression is Not Plotted on Some Constant Height Charts When Air Temperature is < -41C

SURFACE: 77F / Air Temperature Surface Pressure 5 Miles / Rain (Add Decimal Point Before Last #, 71F / Dew Point Temperature Prefix with 9 or 10 to Bring Whole Number Closest to 1000.0) Center Circle: Coverage 999.8 Millibars 3 Hour Pressure Change/Tendency Cloud Types / Bases -0.3 Millibars

GRG333CSurfaceUpperAirStationModels.wpd GRG333C / Severe and Unusual Weather Constant Height (Upper Air) Charts - What They Tell Us

850 MB Constant Height (Upper Air) Chart - Approximately 4,800 ASL (Constant Height Contours Drawn Every 30 Meters)

Strongly affected by heating and cooling of Earth.

Represents near surface conditions although this is not considered to be in the boundary/friction layer which is only found up to 2,000 to 3,000 feet AGL (more during the heating of the day).

Low level moisture: Watch for relative above 60% (to be drawn in green)

Warm / Cold air : Watch for height contours being perpendicular to isotherms (indicating advection)

Fronts: Watch for frontal boundaries at 850 mb

Forecast tools: (1) In summer, take 850 mb temperature overhead and add 15 C / 27 F to approximate day’s high (2) In winter, take 850 mb temperature overhead and add 9 C / 16 F to approximate day’s high (3) In winter, 850 mb temperature overhead must be 0 C or lower for to transition from liquid to frozen

700 MB Constant Height (Upper Air) Chart - Approximately 9,800 ASL (Constant Height Contours Drawn Every 30 Meters)

Mid Level Dry Air Intrusion at this level in severe situations

Air Mass (Single Cell) are steered by at this level

Thunderstorm Development: When air temperature at 700 mb is 14 degrees C / 57 degrees F or higher, this tends to preclude thunderstorm development (indicating a mid or “inversion” in the atmosphere; warmer air aloft)

500 MB Constant Height (Upper Air) Chart - Approximately 18,500 feet ASL (Constant Height Contours Drawn Every 60 Meters)

One half (1/2) the mass or weight of the Earth’s atmosphere is located below/above this spot (considering that the average (or standard) is 1013.2 millibars at the surface.

Find troughs and ridges (leading to convergence and divergence in our middle and upper atmosphere)

Surface weather systems are steered by 500 mb directional flow but at only 1/4 to 1/2 of the wind speed found at 500 mb.

300 MB / 200 MB Constant Height (Upper Air) Chart - 300 MB Approximately 30,000 feet ASL, 200 MB Approximately 38,500 feet ASL (Constant Height Conrours Drawn Every 120 Meters)

Good for detecting: upper air divergence / upper air convergence, jet streams (polar jet streams around 30,000 ASL, subtropical jet streams around 35,000 to 40,000 feet), jet streaks. Isotachs are plotted to denote jet streams/jet streaks.

Directional / Speed Divergence aloft is favorable for surface convergence below and for cyclogenesis

Stronger winds aloft help to ventilate developing thunderstorms so that continue to strengthen and become supercells; also it assists in causing a slight tilt in the cumulonimbus tower in order to keep the updraft and downdraft of a strom separate making it longer lasting.