Weather Analysis I

GEOG-2505: Week II Homework: Quiz I and Problem Set I due S, 9/30 @ 23:59. GEOG-2505: Day VI Friday, August 31 Forecasting Vertical Motion in the Atmosphere Notes: Weather Sayings - “Crickets are accurate thermometers as they chirp faster when warm and slower when cold.” o This is TRUE; the Old Farmer’s Almanac determined that a formula for determining the actual air temperature is: ¿ of chirps ∈ 14 seconds + 40 = temperature ∈ ℉ . Correct ± 1 ℉ usually. o The temperature must be over 40 ℉ for this to work. The 3-Dimensional Atmosphere - We must look at the conditions above the surface to truly gain insight into forecasting. - Abnormalities in the weather usually mean the atmosphere is unbalanced; somebody is going to pay for it… via a storm . - Buoyancy: the ability of air to rise through the atmosphere. - Positively buoyant air is less dense than its surroundings and can rise vertically (driven by density differences which is influenced by temperature). - Heating creates expansion in gaseous mediums which decreases density (and increases positive buoyancy). Think of Prof. Carroll’s bike in the winter. Cooling does the opposite. - Identify locations where strong vertical motion may occur and determine the extent and intensity of vertical movement, you can identify where significant weather may occur. - “The higher the cloud tops, the more severe the resulting weather.” The Atmosphere - SCF/1000 mb = where we live! - 850 mb = 5,000 feet ABL o Height of the planetary boundary layer (PBL) : friction influences winds below this height. In the winter, it is critical for determining wintery precipitation. o Anything colder than freezing at 850 mb will likely be wintery precipitation. o Typically, high enough to get above most variations in topography (except mountainous areas) and features. The air at this height gives us a better idea for what’s actually going on. o Parking lots and forests will have typically different temperatures, so go ~850 mb to detect upward or downward motion (cold air advection and warm air advection). - 700 mb = 10,000 feet ABL (above sea level) o Vertical motion can provide inside into the potential and strength of precipitation. o Cloud-bearing layer. - 500 mb = 18,000 feet ABL - 300 mb = 30,000 feet ABL

GEOG | 2505 | Weather Analysis I | lecture notes | GEOG-2505: Week II Homework: Q

1 Daniel T. Eisert GEOG-2505 Lecture 7 – The Atmosphere September 05, 2018 (Week 3) Class Business Quiz I is due Sunday, September 30 at 11:59 P.M. Problem Set I is due Sunday, September 30 at 11:59 P.M. Atmosphere Layers - SCF/1000 mb = where we live! - 850 mb = 5,000 feet ABL o Can be above the planetary boundary layer (PBL) : friction influences winds below this height. In the winter, it is critical for determining wintery precipitation. o Away from ground influence—parking lots and forests will have typically different temperatures; go 850 mb to detect upward or downward motion (cold air advection and warm air advection). o Anything colder than freezing at 850 mb will likely be wintery precipitation—rain/snow line in the winter. o Typically, high enough to get above most variations in topography (except mountainous areas) and features. The air at this height gives us a better idea for what’s actually going on. - 700 mb / UVV (upward vertical velocity) / omega (upward motion) = 10,000 feet ABL (above sea level) o Vertical motion can provide inside into the potential and strength of precipitation. o Middle of the cloud-bearing layer. - 500 mb = 18,000 feet ABL o The mid-point of our atmosphere. It is often the “steering level” for weather systems  where the storms are going to go next. o Can indicate the potential surface low development and storm initiation. o Vorticity ( a mass of whirling ﬂuid or air, especially a whirlpool or whirlwind) is maximized here.  Air converges below 500 mb and diverges above 500 mb (think of an hour class where the air is neither fanning outward or inward)— Area of Nondivergence - 300 mb = 30,000 feet ABL o The jet stream level. Tropospheric Temperature Decrease - Think of a stove where the burner is the Earth’s surface… as you raise your hand, it gets cooler.  Example: 1000’ = 45  F, 2000’ = 40  F, 3000’ = 35  F, 4000’ = 30  F - Environmental lapse rate / sounding temperature / thermal profile / environmental temperature: decrease in temperature with height, increasing distance from heat (the Earth) —this is measured daily by weather balloons  good exam question . - Inversion: layer where temperature increases with height—this is measured daily by weather balloons  good exam question . - Lapse rate: the rate of temperature decrease with increasing height. Adiabatic - Temperature change due to the expansion of air (rising to 850 mb / 5000 feet).

GEOG | 2505 | Weather Analysis I | lecture notes | 1 Daniel T. Eisert GEOG-2505 L

GEOG-2505: Week I Homework: None. GEOG-2505: Day III Friday, August 24 Creating Weather Notes: 9 & 10 Rule: if the first digit [6, 9], then the barometric pressure is in the 900s; else, it is in the 1000s. - Monitoring air pressure is good for weather prediction. Falling air pressure can result in stormy weather moving in. Rising air pressure can result in fair weather. Constant air pressure keeps the existing weather. - Air from the SW is likely warmer and more humid (around here). Air from the NW is likely dryer and colder (around here). - Wind bar ‘penates’ represent 50 knots. Each long bar is 10 knots, short bars are 5 knots. - In GEOG-2505, knots can be treated the same as mi/hr. despite a knot being ~15% greater than a mile. Knots are 6,000 feet. - There are +100 weather symbols (don’t need to memorize all of them). Reference the class handout in Week 2. - Four * (snow) mean heaviest snow—can have 1-4 (same for rain). - Air temperature is recorded in shade , over low grass or vegetation , and 1 ¼ to 2 meters above the ground. Sensors are often surrounded by white plates to shade the sensor, so the station can be out in the open (not good to put near trees  holds extra heat at night). - It will be hotter in the sun. - The center of the weather station is cloud cover percentages: convention is to only show 0 (none), ¼, ½, ¾, or 1 (all). Upper Air Station Models - NOAA Weather Centers put up air balloons twice a day (7:00 A.M. and 7:00 P.M.) - Everything is the same except the barometric pressure. The number in that part is the height above sea level in meters (sea level is approximation —geo-potential heights ). o Last three digits: Add a “1” for 850; add a “2” for 700 in front to get elevation in meters. o First three digits: Add a “0” to the end to get elevation in meters. - Temperatures for upper air station models are CELCIUS, NOT FAHRENHEIT. - The balloon will rise until a preset air pressure level. - 850 mB is approx. 5,000 feet above the surface. - 700 mB is approx. 10,000 feet above the surface. - 500 mB is approx. 18,000 feet; 300 mB is approx. 30,000 feet.

GEOG | 2505 | Weather Analysis I | lecture notes | GEOG-2505: Week I Homework: No

1 Daniel T. Eisert GEOG-2505 Day 19 – Surface Winds October 05, 2018 (Week 7) Class Business Look for Quiz 3 on Canvas; it will be due the day of the next exam. Hydrostatic Balance Isoheights & Thermal Wind The highest air pressures exist closer to the surface of the Earth, and pressure declines with height. This creates a vertical pressure gradient all across the globe; however, we do not have consistantly storming conditions across the globe for these reasons. - Air will begin moving from higher pressure to lower pressure. - The same force that keeps our atmosphere from escaping the earth acts upon the rising air— gravity . - Hydrostatic balance results when the vertical PGF and gravity counter each other. Isoheights represent the pressure height (in meters) in lines. - Note that isobars are the wind barbs. - For example, suppose we have a 500 mB chart. The lines show the actual 500 mB pressure surface as being 5880m and 5760m above the surface. - Air moves from high heights to lower heights according to the PGF. Notice the green arrows. - The Coriolis force makes the wind go to the right. Notice the yellow arrows. - The diﬀering forces eventually balance out which creates wind that blows parallel to the hieght lines. Notice the orange arrows. - The more tightly packed the height lines, the stronger the wind force will be. - Warmer temperatures at lower latitudes cause the atmosphere to expand. This increases the constant pressure heights and creates a pressure gradient from warmer areas (typically south) towards colder regions (typically north). Notice the diagram to the upper- left.  EXAMPLE: See maps on slide 25 in the Unit 3 presentation. Wind Circulation Around Height Pressure clockwise ( negative vorticity ) Pos. Vorticity Neg. Vorticity counterclockwise ( positive vorticity ) Wind Circulation Around Height - Descending air warms due to the compression ( adiabatic heating ), which decreases its relative humidity and evaporates 2 Daniel T. Eisert GEOG-2505 any cloud material. As a result, high pressure systems = clear skies and fair weather.

GEOG | 2505 | Weather Analysis I | lecture notes | 1 Daniel T. Eisert GEOG-2505 D

GEOG-2505: Week I Homework: Review notes for W, 8/22. GEOG-2505: Day I Monday, August 20 Introduction to the Course Notes: Professor D. Carrol Major Williams 101 OH: Daily 10:00-11:00, T/TH until 14:00 View Syllabus GEOG-2505: Day II Wednesday, August 22 Creating Weather Notes: Storms are the result of the atmosphere of being out of balance. - Storms help the atmosphere return to being balanced. - Meteorologists try to identify areas that are “out of balance.” They are tasked with trying to identify the time, coverage, and what the atmosphere will support (type of storm). - A light line of reflectivity (shown as light ran) denotes incoming strong winds before a storm. This is visible in the sky with a “shelf cloud.” - When the atmosphere is unbalanced, upward vertical motions (sometimes very subtle) are developed (which forms storms of ALL types). Meteorologists try to identify features to predict storms. Only need about 1/5 mph of upward motion to get a blizzard. Thunderstorms often have higher speeds. - Weather is all about pattern recognition—find those areas of upward motion! - The stronger the upward motion, the stronger/more intense the storm will be. - Downward motion denotes high pressure—calm/fair weather. Creating Weather - Unequal heating of gases surrounding the planet promote both horizontal and vertical circulation (making weather). - There are many variables such as ice cover, grass, parking lots, etc. prohibit equilibrium from occurring. - Horizontal motion drives air masses through different regions on the surface. - WAA = warm air advection (horizontal motion of warmer air moving in) - CAA = cold air advection (horizontal motion of cooler air moving in) - Vertical motion creates cloud cover and precipitation. - The larger the temperature gradient from one region to another, the stronger the circulation dynamics, and the stronger the resulting weather systems. Think about the tornado season in April ( very cold in the Dakotas and very hot in Texas  major gradiant in the Great Plains).

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