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How to get the most from the Internet briefings

How to get the most from the Internet briefings. NWS Boise, Id. Contents. Satellite pictures Soundings (parts, inverted “V” profile, etc) 500mb upper air chart with 700-500mb average RH Sea Level Pressure chart. Satellite Imagery.

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How to get the most from the Internet briefings

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  1. How to get the most from the Internet briefings NWS Boise, Id

  2. Contents • Satellite pictures • Soundings (parts, inverted “V” profile, etc) • 500mb upper air chart with 700-500mb average RH • Sea Level Pressure chart

  3. Satellite Imagery • 3 types of imagery is used, 2 of which are used on the internet briefing: Water Vapor and Infrared. • Water Vapor “sees” the amount of gaseous water in the atmosphere, whereas the infrared “sees” the temperature of the clouds.

  4. Satellite Imagery • Water Vapor is best used to locate areas of high and low pressure, jet streams and sources of moisture (monsoonal). • The mid clouds that appear on a water vapor picture appear as an area of gray and murky cloud group. If seen in the morning prepare for possible thunderstorms by the late afternoon.

  5. Water Vapor • Areas of brown indicate very dry air. • Areas of blue-green indicate deep layers of moisture and may indicate convection.

  6. Water Vapor Pictures Area of low pressure Upper jet Mid level moisture

  7. Water Vapor Imagery

  8. IR Imagery • Things to watch for on IR imagery. Note where thunderstorms are developing. As long as the thunderstorm develops, the cloud tops should continue to cool. When they start warming, thunderstorm is collapsing or weakening (watch for microburst or downdraft winds when this occurs). These downdraft winds can extend outward up to 10 miles and can reach speeds well over 60 mph.

  9. IR Imagery Watch cloud top temperature

  10. IR Satellite Imagery

  11. Question • What is one item that can be found on the water vapor imagery? • Whats so important to monitor thunderstorm cloud top temperatures? • How far out can thunderstorm outflow winds extend?

  12. Answers….. • Lows, Highs, Moisture, Jets, etc • Cloud top temperatures indicate whether the thunderstorm is developing or collapsing; if collapsing, expect strong outflow winds in the next several minutes. • Around 10 miles.

  13. Upper Air sounding (profile) Wind profile Elevation increase going up • Released at least twice daily • Shows temperature, moisture, and wind profile through the depth of the atmosphere. • Can determine stable/unstable layers Moisture profile Temperature Profile

  14. Reference sounding heights • Where the moisture and temperature lines converge implies greater levels of saturation. • Helps calculate the Haines Index. • Used to calculate the mixing heights and transport winds. • Can determine where any inversion (thermal belt) may lie. • Helps to determine if strong winds aloft may filter down to the surface. 500mb = 18,000 ft 700mb =10,000 ft 850mb = 4,000 ft

  15. Upper Air soundingsInverted “V” soundings • If you see this type of sounding…it is imperative to know what weather conditions can be expected. • Dry lower layers transition to a moist layer aloft. How high helps determine with thunderstorms will be wet or dry. • Any thunderstorms that develop will be dry with gusty winds that either mix down from aloft OR due to evaporative cooling. Rain drop that falls evaporates and accelerates down due to that parcel now being cooler than the surrounding air. Saturated air Dry lower layers

  16. Other examples of the inverted “V” Strong winds aloft can filter down to the surface bringing gusty winds to the surface

  17. Upper Air soundings • Note the 24 hr temp change block. • Will indicate how much warming/cooling has occurred in the last 24 hours. Warming aloft implies air mass becoming more stable. Cooling aloft => more unstable.

  18. 500mb Upper air chart • This chart is showing the flow across the middle section of the atmosphere. • Moisture is the average RH from 700mb-500mb (10-18,000ft), or mainly the mid level moisture. Typically during the summer the best moisture may be around 500-600mb (15-18,000ft) layer. So moisture that high would tend to bring better chances of late afternoon dry thunderstorms. • So on those days, the average RH may indicate low RH (<40% )

  19. 500 mb charts • H’s and L’s on the chart are similar to high and low pressure areas on a surface sea level pressure chart. • Lines on the chart are called isoheights or lines of equal height. Flow aloft are parallel to these lines.

  20. 500mb heights 500mb height line 700-500mb ave RH

  21. Compare water vapor with models Note:mid level moisture does not really show up in the 700-500mb layer Mid level moisture

  22. 500mb heights and average 700-500 RH

  23. Sea level pressure chart • Remember from S-290…wind around low pressure goes counter clockwise and clockwise around high pressure systems. • Lines on the chart are called isobars and the closer they are the stronger the wind. • Roughly 10 mbs from PDX-BOI will bring breezy conditions (15 to 25 mph) to the region.

  24. Sea level pressure chart • How to read the “wind barbs”

  25. Sea Level Pressure chart Isobar – lines of equal pressure SW wind at 10 kts. See previous slide for decoding wind speed

  26. Definitions • Online terminology

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