MET 216 Exam 2

What is wind shear? What are the types?

- A rapid change in wind velocity or direction (dV/d(x,y,z,p,etc.)) Types: 1) Horizontal (normal/lateral and along-stream (speeds up/slows down along a line)) 2) Vertical 3) Cyclonic (polar side of jet) 4) Anticyclonic (equator side of jet)

What is the Rapid Refresh Model (RAP)? Describe it.

-"nowcasting" numerical guidance; originally introduced as the RUC in 1994 -provides hourly 21-hour forecasts -50 layers; 1:00 data cutoff -uses a wide variety of data sources, including aircraft obs -uses sigma coordinates -13 km horizontal grid spacing/50 vertical levels -initialized by 6-hourly NMM-WRF model output -used for hourly SPC Forecast Tools products

What is divergence?

-A change in area of a parcel -Made of two components: stretching and difluence -Stretching: How the speed increases (divergence) or decreases (convergence) -Difluence: How the flow spreads out along the stream -Confluence: How the flow comes together along the stream -Difluence tends to dominate in a trough, which can indicate that you'll be seeing divergence -Stronger difluence normally means stronger divergence (think of a tornado outbreak in the spring from difluence or a strong blizzard in the winter) -Generally speaking, speed diverging means confluence and speed converging means difluence

What is a wind profiler? What information does it provide? What are its benefits?

-A clear-air Doppler radar designed to measure the vertical profile of the horizontal winds from near the surface (500m) to above the tropopause -It can detect small variations in density due to small variations in temperature and moisture -Reliable observations come from a fixed, phased array antenna and a minimum number of moving parts -Uses 3 beams: vertical, 16.3*N, 16.3*E -Must assume that there is uniformity of flow across the beams -Compared to Doppler weather radars, it has a much lower power (6000W), longer wavelength (74cm), and a higher PRF (>5000/s) -Systems are located in remote, flat areas to reduce radio interference and side lobe reflection -It generates observations every 250m beginning at 500m (AGL); the wind speed accuracy is within 1m/s -It can operate reliably and unattended in nearly all weather conditions (saves time and money!) -Deployment began in 1990, and there are currently 32-35 of them -Their network is maintained by NOAA FSL in Boulder, CO -Some profilers are equipped with RASS to gather vertical temperature profiles as well

How does a parcel move through a jet stream/streak? How does the energy convert? What is the four quadrant model?

-A parcel will move through, not with, a jet streak -To do so, it must speed up (increase its KE and decrease its PE) -To speed up, the parcel will move "downhill" (decreasing its PE) -Once the parcel moves through the streak, it will move "uphill" to increase its PE and decrease its KE -The four quadrant model explains parcel motion through a jet. The upper left is the left entrance where convergence occurs. The lower left is the right entrance where divergence occurs. The upper right is the left exit where divergence occurs. The lower right is the right exit where convergence occurs. At the entrances, PE decreases and KE increases. At the exits, PE increases and KE decreases.

What is the North American Mesoscale (NAM) model? Describe it.

-A regional mesoscale forecast model based on the Nonhydrostatic Mesoscale Model (NMM) and operational version of the Weather Research and Forecasting (WRF) model -Forecasts out to 84 hours -Runs 4 times a day: 00Z, 06Z, 12Z, and 18Z -Uses an early data cutoff (1:15 past the model) -12 km horizontal grid spacing (not resolution!) -60 vertical levels, maximized resolution near surface and near 250 mb -objective, site-specific guidance produced via NAM Model Output Statistics (MOS) or MET, derived via regression at station locations -still cannot resolve thunderstorms ... need convective parameterization!

What is a Mesonet?

-A regional network of automated weather observing sites designed to diagnose mesoscale phenomena and operating at a finer spatial and temporal scale than synoptic observations -Can be fixed or mobile

What does ASOS stand for? When was it deployed? What are some benefits? What are some of the weather-related nuances?

-ASOS = Automated Surface Observing System -A joint venture between the NWS, FAA and DOD -Deployment began in 1991; over 1500 units nationwide Benefits: -Replaces a basic weather watch with a continuous weather watch -Frees up humans to do other tasks, which saves money -Allows for obs in remote places where people are not or can not be stationed (mountain tops, deserts, etc.) -Allows for standardized visibility measurements Nuances: -Visibilities over 10 miles are not detected -Does not observe weather until it is over the sensors -Precipitation rates < 0.01"/hr are not detected -Clouds above 12,000 feet are not detected -Observations can be manually augmented with human observer input

What is atmospheric stability? What are the types?

-Atmospheric stability: Defined as the degree to which the atmosphere is able to resist or suppress vertical or (less commonly) horizontal accelerations in the direction of the displacement Several variations, including: -Hydro(static): conditional vs. absolute -Convective (potential) -Inertial -Symmetric Absolute stability: 1) Vertical motion in inhibited (if clouds form, they will be shallow, layered clouds like stratus) 2) Γd > Γm > Γe - Γd is the dry adiabatic lapse rate (10°C km-1) - Γm is the moist adiabatic lapse rate (6°C km-1) - Γe is the environmental lapse rate 3) T(e) is always larger than T(sp) and T(up) at any level - Hence, an unsaturated or saturated parcel will always be cooler than the environment and will sink back down to the ground -T(up): the temperature of an unsaturated parcel -T(sp): temperature of a saturated parcel -T(e): environmental temperature 4) Inversion layers are always absolutely stable Absolute instability: The condition for absolute instability is: Γe> Γd> Γm • Hence, an unsaturated or saturated parcel will always be warmer than the environment and will continue to ascend Conditional instability: The condition for conditional instability is: Γd> Γe> Γm • The unsaturated parcel will be cooler than then environment and will sink back to the ground • The saturated parcel will be warmer than the environment and will continue to ascend This link is a great review for stability (much of this information comes from here): https://www.weather.gov/media/zhu/ZHU_Training_Page/clouds/stability_clouds/stability_clouds.pdf

What is atmospheric thickness related to? Why is atmospheric thickness important?

-Atmospheric thickness, the depth between two isobaric surfaces, is proportional to the mean temp and (to a much lesser extent) moisture in the layer (T(v): virtual temperature) -Temperature itself, though, has 97% of the effect -The 1000 to 500 mb thickness is a function of two properties, (1) the average temperature of the air between 1000 and 500 millibars and (2) the average moisture content of the air between 1000 and 500 millibars. -Thickness will INCREASE if the average virtual temperature increases (either temperature increasing or moisture content increasing or both). Thickness will DECREASE if the average virtual temperature decreases (either temperature decreasing or moisture content decreasing or both). Thickness will increase due to WAA or diabatic warming (solar heating). Thickness will decrease due to CAA or diabatic cooling (longwave cooling, evaporational cooling, etc.). The thickness values will be higher in the lower latitudes and the thickness values will be lower in the high latitudes. The thickness lines will be packed close together where there is a large temperature gradient in the atmosphere. -The density of air changes with temperature. As the temperature of air cools in becomes more dense and thus more compacted (takes up less volume). Thus, as air cools the height lowers since the air is becoming more dense. Air will cool when it rises, thus a trough can be found where there is a lifting of air. A trough can also be found in a region dominated by a very cold air mass. This troughing will be most pronounced in the upper levels. A ridge is a region with relatively higher heights. A broad region of sinking air or a deep warm air mass will both lead to ridging. Since air is often sinking within a ridge they tend to bring warmer and drier weather. -Fronts can be identified by analyzing the thickness gradient

What does balanced flow mean? What are the different types of balanced flows (including the forces they involve)?

-Balanced flow means no net acceleration -Geostrophic (Coriolis and PGF): The direction of geostrophic flow is parallel to the isobars, with the high pressure to the right of the flow in the Northern Hemisphere, and the high pressure to the left in the Southern Hemisphere. -Gradient (Coriolis, centripetal/centrifugal, and PGF): A geostrophic wind becomes a gradient wind when the wind begins flowing through curved height contours. The gradient wind occurs aloft (no friction) within curved height contours. The wind stays parallel to the height contours throughout the curve. -Cyclostrophic (Centripetal/centrifugal and PGF): occurs when the horizontal pressure gradient and centrifugal forces push equally in opposite directions. This balance describes situations in which the turning of the wind, not the Earth, is the dominant effect. -Inertial (Coriolis and centripetal/centrifugal): Frictionless flow in a geopotential surface in which there is no pressure gradient. The centrifugal and Coriolis accelerations must therefore be equal and opposite.

What does baroclinic mean? Equivalent baroclinic? Barotropic?

-Baroclinic: involving wind shear; you cannot have a front without wind shear -Equivalent baroclinic: winds only change speed with height, no change in direction -Barotropic: There is no or almost no wind shear present, hence no fronts

What is CIN? What is CAPE? What are some other common stability indices?

-CIN: Convective Inhibition; the amount of energy that has to be supplied to get a parcel to the LFC; negative area on a Skew-T -CAPE: Convective Available Potential Energy; the positive area when the parcel is warmer than the environment after hitting the LFC; the greater the CAPE, the greater the vertical velocity, the greater the chance/potential for severe weather (but a large CAPE value and a large CIN value can counteract each other as well); generally more accurate in estimating instability than the LI "If you want to rise up, you must overcome your CIN" K Index: a measure of thunderstorm potential; the index harnesses measurements such as "vertical temperature lapse rate, moisture content of the lower atmosphere, and the vertical extent of the moist layer; describes only static stability; used only for forecasting non-severe convection (like showers and thunderstorms); higher if moist at 700mb; derived for and most applicable to the western U.S. Lifted Index (LI): the temperature difference between the environment Te(p) and an air parcel Tp(p) lifted adiabatically at a given pressure height in the troposphere of the atmosphere, usually 500 hPa (mb); When the value is positive, the atmosphere (at the respective height) is stable and when the value is negative, the atmosphere is unstable; allows for the effects of surface heating

What are CVA and AVA and why do we care?

-CVA: Cyclonic Vorticity Advection; in the region of cyclonic vorticity advection (CVA) in front of the trough axis, parcels are diverging -AVA: Anticyclonic Vorticity Advection; parcels entering the backside of the trough, in a region of anticyclonic vorticity advection (AVA) (that is, vorticity values are becoming more cyclonic along the flow) are having to converge -Simply put: AVA implies convergence and CVA implies divergence -AVA implies height rises, whereas CVA implies height falls. When systems are not deepening or filling rapidly, their movement is associated with vorticity advection

What is a cut-off low? What is Henry's Rule?

-Characterized by a low poleward of the jet and a high equatorward of it -Results from baroclinic wave amplification -Henry's Rule: A shortwave trough that is 2,200 km or less away from a cut-off low will influence that cut-off low

Comparing speed and slope, how fast do cold and warm fronts move and lean?

-Cold fronts tend to more more quickly and have a steeper slope than warm fronts

What is the Conveyor Belt model?

-Describes the three-dimensional structure of a cyclone in terms of the interactions of three airstreams: the warm conveyor, the cold conveyor and the dry conveyor or dry airstream. In relation to the frontal model, the cold front results from the interaction of the warm conveyor and the dry conveyor; the warm front concerns interactions of the warm and cold conveyors and the occluded front includes influences from all three. -Behind the cold front is the dry conveyor which moves upward and along the cold front, wrapping counterclockwise -Ahead of the cold front is the warm conveyor which moves upward and along the cold front, wrapping clockwise -The cold conveyor enters from the east/southeast and moves upward in altitude while making its way west and then wrapping back to continue rising and moving east -This model explains why most fronts come with comma-shaped clouds

What is the geostrophic wind? What assumptions do we make with the geostrophic wind? What are the types of geostrophic wind?

-Equation: 𝐕𝐠=(𝐠/𝐟*𝛛𝐳/𝛛𝐧)=[(−𝟏)/𝛒𝐟*𝛛𝐩/𝛛𝐧] -F (Coriolis parameter, also called earth's vorticity) = (2Ωsinɸ) = 7.292 x 10^(-5)*(s^-1) -The direction of geostrophic flow is parallel to the isobars, with the high pressure to the right of the flow in the Northern Hemisphere, and the high pressure to the left in the Southern Hemisphere. Assumptions: 1) F is constant 2) No acceleration 3) Straight contours 4) Frictionless -Flow is subgeostrophic in troughs and supergeostrophic in ridges

What is the Global Forecast System (GFS) model? Describe it.

-Forecasts out to 384 hours for synoptic systems in support of aviation and forecasting interests -Runs 4 times a day: 00Z, 06Z, 12Z, 18Z -Spectral (spherical harmonic basis function) representation -Later data cutoff (2:45 past the model) -Initialized with global observations and data from satellites -Uses sigma coordinates; domain extends to .2mb -64 levels -The Regional Spectral Model (RSM) can be run on a desktop -The Climate Forecast System (ver. 2) is based on the GFS

What are Convective Allowing Models? Describe them.

-Includes the NAM-Nest and HRRR -both are regional models with have 3 km grid spacing -former is run every 6 hours (out to 84 hours) and the latter every hour (out to 18 hours)

What occurs in areas of fronts?

-Large vertical shear

To form an air mass, what is required?

-Large, homogeneous land/sea surface, weak winds, and long residence times -Hence why the United States is considered to be a battleground for fronts rather than a place for formation; Canada, Mexico, and the Tropics are all common areas for air mass formations

What is vorticity?

-Rotation/spin in the atmosphere -The equation relates curvature and shear -Relative vorticity includes only curvature and shear, whereas absolute vorticity includes curvature, shear, and the Coriolis parameter (f) -In the Northern Hemisphere, positive vorticity indicates cyclonic rotation, and negative vorticity indicates anticyclonic rotation -The Coriolis parameter is always positive (NH) or negative (SH), but relative vorticity can be positive or negative in either hemisphere

What promotes surface high formations? What promotes surface low formations?

-Surface high: upper-air convergence downwind of a ridge -Surface low: upper-air divergence ahead of a trough; troughs aloft are good indicators for the formation of a strong surface low, especially troughs with negative tilt

What is the Margules formula?

-The Margules formula shows that fronts will tilt toward the colder air with height; it also determines the slope at which the front will tilt

What is deformation?

-The change in shape of a fluid element -Two components: shearing and stretching -For example, a parcel of air moving through an area of difluence will start to stretch out to fit that larger area. A parcel moving through an area of confluence will start to compress to fit that small area. -Normally happens around fronts -Deformation explains why heavy snow happens on the NW side of a cyclone

What is advection?

-The horizontal transport of a quantity/property by the wind; velocity (wind) acting on a gradient. -Example: wind blowing from warm to cold areas (velocity acting on a temperature gradient)

What is the thermal wind? How does the thermal wind relate to layer thickness?

-Thermal wind is defined as the vertical shear of the geostrophic wind -This vector extends from tip of lower level wind to the tip of the upper level wind -Magnitude is proportional to the strength of the thickness gradient (the depth of air between two layers) -Cold air (lower thicknesses) is to the left of the thermal wind vector in the NH (to the left of the direction of flow of the thermal wind) -Warm-air advection (WAA) in the layer is indicated by winds veering with height -Veering: Clockwise rotation with height in the Northern Hemisphere -WAA can induce upward motion, and it warms you -Cold-air advection (CAA) in the layer is indicated by winds backing with height -Backing: Counterclockwise rotation with height in the Northern Hemisphere -CAA can induce downward motion, and it cools you -The thermal wind vector is parallel to thickness contours; the stronger the thermal wind means the more tightly packed the thickness contours are -Note: This information does not always apply to the boundary later (1000-850mb), so you can't use them there!

What is unbalanced flow? What is an example of unbalanced flow?

-Unbalanced flow is when acceleration occurs (when the different parameters within the balanced flows, for example, are not equal and opposite) -Isallobaric flow is an example. Another way to look at this is that the wind will be geostrophic until the height or pressure gradient increases or decreases. Then the wind will be out of geostrophic balance and the wind will flow down or, actually, up the pressure gradient again (since the pressure gradient acceleration will be out of balance with the Coriolis acceleration until the wind is in geostrophic balance again).

What are some of the basic thermodynamic parameters?

-Vapor pressure (e) and saturation vapor pressure (es) es ice does not equal es water -This statement above shows that you need more water vapor around water to be saturated air compared to the amount needed to become saturated around ice (and this only matters when below freezing). If this difference were not true, we would never have snow. But, because of this, the Bergeron-Findeisen process exists (water drops shrink at the expense of snowflakes growing) es flat does not equal es curved -This statement above shows that as drop diameter increases, the curvature decreases, so it is easier for the drop to attract water vapor e is the portion of total atmospheric pressure due to water (about 0-40mb) -Mixing Ratio (w) w = ρv / ρd = mv / md ρv is called absolute humidity; w ≈ q (specific humidity) The ratio of the mass of water vapor to the mass of dry air (hence it is expressed with unit g/kg) -Relative humidity (RH) RH = e / es = w / ws -Dew point (Td) -point at which you reach saturation -better indicator of saturation than RH -Wet bulb temperature (Tw); Td < Tw < T -point at which water evaporates into the air -the lowest temperature to which a volume of air at constant pressure can be cooled by evaporating water into it -Virtual Temperature (Tv); Tv = T(1 + 0.609w) -shows that the air temp not only changes due to density, but that moisture can change air temp as well

Describe vertical motion. What is the Level of Nondivergence?

-Vertical motion is related to the change in pressure with time (w = dp/dt) as well as the velocity (∂ω/∂p=−[∂u/∂x+∂v/∂y], don't worry about the equation) -Relates convergence and divergence through the surface and aloft -Level of Nondivergence (LND): The switchover point between convergence and divergence; typically aloft at 500mb (but this is the average). At the LND is when vertical motion is normally at a maximum, and convergence stops increasing here. To note, at the LND, the convergence units do not just disappear. Rather, they diminish as they move further from the LND until the units hit 0.

What do vertical soundings do? What do we plot them on?

-Vertical soundings by radiosonde sample T, w, u and v as a function of pressure, with superior resolution and accuracy to satellite soundings -Skew-T diagram is most common thermodynamic diagram (area is proportional to energy)

How are CAPE and vertical motion (w) related?

-We can convert the potential energy (CAPE) into the kinetic energy of vertical motion per unit mass (½w^2) CAPE = (½wmax)^2 (unit = J/kg = m^2/s^2) wmax = (2*CAPE)^(½) (unit = m/s) -But, due to other natural factors like precipitation loading, entrainment, etc., the equation actually is: wmax ≈ 0.6(2*CAPE)^(½)

What is zonal flow? What is meridional flow? How often does flow switch between these two types?

-Zonal: general flow pattern along latitudinal lines; when the upper level winds are parallel or nearly parallel to the lines of latitude the wind pattern is termed zonal. -Meridional: general flow pattern along longitudinal lines; when the winds cross the latitude lines at a sharp angle, the wind pattern is termed meridional; serves to equalize uneven heating on globe; may develop into or coincide with blocking (Rex, omega, etc.) -In a meridional pattern, the jet stream will have highly amplified troughs and ridges -Low pressure systems tend to move faster (west to east) when associated with a zonal flow -A highly meridional flow can cause atmospheric blocking and spells of much below and much above normal temperatures. A meridional pattern, which its highly curved flow, generates more vorticity than that associated with a zonal flow (hence why zonal flow tends to amplify after a short period of time due to the increased curvature added to the environment) -Flow often flip-flops between these every few weeks at irregular intervals -Wave propagation speed is a function of wavelength

What is a Real Time Mesoscale Analysis (RTMA)?

-designed to provide a "quick look" real-time gridded analysis

What are the Hurricane Models? Describe them.

-includes the HMON and the Hurricane Weather Research Forecast (HWRF) models -both run four times per day (on demand from NHC): 00Z, 06Z, 12Z, 18Z -both have 43 levels (HMON) and 42 levels (HWRF)

What is the Short Range Ensemble Forecast (SREF)? Describe it.

-produces ensemble forecasts from 21 members -four runs per day: 03Z, 09Z, 15Z, and 21Z -output in three hour increments out to 87 hours

What is the Global Ensemble Forecast System (GEFS)? Describe it.

-uses 20 ensemble members -four runs per day: 00Z, 06Z, 12Z, 18Z -output every six hours out to 384 hours

What are the four main coordinate systems used in meteorology?

1) Height (z): simplest, but not used much 2) Pressure/isobaric (p): most common; derived from aviation demands 3) Sigma (σ = p/psfc): terrain-following 4) Isentropic (θ): most realistic (but, the math behind this system is difficult)

What are the three ways that data on weather charts is derived?

1) visually observed phenomena (clouds, etc.) 2) directly sensed data (T, p, etc.) 3) derived data (vorticity, stability, etc.)

What is Numerical Weather Prediction (NWP)?

A broad term to describe the use of objective analysis and complex computer programs to forecast the state of the atmosphere

What is a streamline analysis?

A snapshot of the velocity field at any point in time

What is the definition of kinematics (related to meteorology)?

A term that broadly describes atmospheric motions without reference to mass or the forces responsible for the motion

What is a jet stream?

An elongated maximum in contour packing and hence, wind speeds; a jet streak is a propagating isotach max ("core" of the jet stream)

Why should we care about a thermodynamic diagram, like a Skew-T?

Atmospheric properties that can be diagnosed on a thermodynamic diagram include: -Temperature of air mass -Moist and dry layers -Precipitation type (ex: >400m subfreezing layer needed above surface for sleet) -Elevation and depth of cloud layers -Layer(s) stability (lapse rates defined as positive for cooling with height) -Fronts / inversions (subsidence, frontal, radiation, advection) / tropopause -Vertical wind distributions (veering/backing; hodographs) -Know how to perform a thermodynamic analysis of a Skew-T (characteristics of the sounding, stability characteristics, identifying fronts, etc.)

What is the CCL? CT? LCL? LFC? EL? Potential temperature (theta)?

CCL: Convective Condensation Level; the height to which a parcel of air heated from below will rise adiabatically until it is just saturated. It is the height of the base of a cumulus type cloud if convection is caused by surface heating. CT: Convective Temperature; the surface temperature that must be reached to start the formation of convective type clouds LCL: Lifting Condensation Level; the height at which a parcel of air lifted dry adiabatically would become saturated. The LCL is always found at or below the CCL LFC: Level of Free Convection; the height at which a parcel of air, when lifted, becomes warmer than its surroundings and thus convectively buoyant. The parcel is lifted dry-adiabatically until saturated (at the LCL) and then moist-adiabatically thereafter. EL: Equilibrium Level; the level at which a parcel of air lifted moist adiabatically from the LFC Potential temperature (theta): The temperature a parcel of air would have if brought dry adiabatically to a reference level of 1000 mb

Why do cyclones tend to form on the east side of upper-level troughs? Why do anticyclones tend to form on the west side of upper-level troughs? How do these two show the relation between jets and fronts?

Cyclone: The low pressure system forms to the east of the upper-level trough of the jet stream. Air rises in low pressure systems because of the convergence of air at the surface and diverging air aloft which forms clouds. For the cyclone to intensify, the diverging air aloft has to be greater than the converging air at the surface. This essentially pulls more air upwards and the surface pressure of the system drops, intensifying the cyclone. Latent heat is also released within the clouds of the low pressure system. This warms the air and causes instability which further intensifies the mid-latitude cyclone. Other factors that intensify the storm are vertical wind shear and convection. Anticyclone: A high pressure area usually forms within the ridge that is to the west of the upper-level trough. The sinking air over the high pressure system allows a circulation of air throughout the vertical structure of the high and low pressure systems. This deepens the upper-level trough, which increases the winds both aloft and at the surface. This is why jets and fronts are strongly related! Weather forecasters often use the location of the jet streams and their troughs and ridges to predict weather. For instance, a jet-stream trough (low pressure) just west of your location is often associated with locally bad weather (clouds, precipitation, strong winds often from south-east through south-west). But a jet-stream ridge (high pressure) just west of your location is associated with good weather (light winds from the north-west through north-east), mostly clear skies).

What are grid points?

Elements of an array containing weather data

How do we identify and label hemispheric flow?

Hemispheric flow is identified by the number of lows currently occurring. There are typically 3-5 lows at a time. So, a Wave #5 Pattern means that there are 5 lows around the hemisphere.

What is an ensemble method? Why is it good?

It produces a set of forecasts rather than one individual forecast. Different parameters are slightly changed within the models to see how much the forecast is affected. Ensembles are good to use because the more the outputs coincide, the more assured we are of the forecasts. If the outputs drastically range, then we cannot be sure of the forecasts.

What is the Courant-Friedrichs-Lewy (CFL) criterion?

It relates grid space to time step (how quickly you integrate forward in a model). Air parcels can't move more than one grid space in a time step (if you attempt this, it creates numerical instability)

What is the headquarters for NWP in the U.S.?

NCEP (National Centers for Environmental Prediction)

What is objective analysis? What is subjective analysis?

Objective: The plotting and analysis of weather data by computer Subjective: When humans do the analysis

What are some common types of inversion? Describe them.

Subsidence: demonstrates very dry air aloft; caused by sinking motion; the Skew-T will look like a wavy goal post Frontal: Lifting occurs with moisture flowing upward, causing saturation aloft; the Skew-T will have nearly identical T and Td shapes (but offset from each other) Radiation: caused by low-level cooling at night Advection: Indicative of potential severe outbreaks; normally caused by mT air mass below and a cT air mass above

What is spectral analysis?

The use of Fourier coefficients (or spherical harmonics on a sphere) instead of grid points in the objective analysis process

What is the first guess method?

The use of model data to "fill in" or substitute for observations in data sparse regions

What is a trajectory analysis?

Traces the motion of fluid parcels over a finite time interval

What are boundary conditions?

What you have happen in the model when it hits its boundary points