Weather Forecastings
Highs ( H )
It is a high-pressure system (anticyclones) where the regional pressure is higher than in the other regions.
Means that it is fair, stable, with weather conditions and clear skies.
Brings settled, dry weather because the air in the high-pressure system is sinking. And as it descends, it creates warmth, and moisture evaporates (goes away),
Air flows downward from the upper atmosphere and outward (spreads in the low atmosphere). Anticylone Flow = The outward flow motion
Coriolis Effect (Earth’s rotation), the winds in the system flow clockwise direction in the Northern Hemisphere.
They usually have nice and calm winds in the center of the system
The temperature really depends on the season, highs in summer can bring the nice and hot days, but the highs in winter can also bring frigid, clear, cold air.
The light/sinking air can lead to a buildup of pollutants and haze in urban areas, reducing air quality.
Lows ( L )
Shows an area of low atmospheric pressure, with inclement weather, clouds, wind, and precipitation.
Low pressure means unsettled, stormy weather because the air is rising. As it rises, it usually means it is getting colder, and the water vapor condenses to form clouds, and often rains, snow, or storms.
Air flows towards the center of the system and at the low of the surface, then upward into the atmosphere. This is why clouds and precipitation form.
Due to the Coriolis effect, that is why it flows in a counterclockwise direction in the Northern Hemisphere and opposite direction in the Southern Hemisphere.
Winds tend to be stronger around the low-pressure systems, especially when isobars are tightly packed together, showing that steep pressure gradient. Intense low-pressure systems can lead to intense/severe weather events, including thunderstorms, blizzards, or even tropical storms like hurricanes.
Low-pressure means (Seeing an L on the graph) that you can see weather patterns, with a good chance of rain or storms.
Isobars
Lines of equal pressure on maps
Curved lines on a weather map that connect points of equal atmospheric pressure.
A fundamental tool for showing the direction and strengths of the winds
Reading:
Determine the wind speed:
Closely packed isobars show that there is a steep pressure gradient, basically meaning that the pressure changes rapidly over a short distance. Basically means strong, windy conditions
Widely spaced isobars show a weak pressure gradient, meaning the pressure is changing slowly. Calm or light wind.
Determine the wind direction:
The wind generally blows almost parallel to the isobars. In the Northern Hemisphere, it goes clockwise around the high-pressure center and counterclockwise around the low-pressure centers.
Identify Highs and Lows.
Isobars from concentric rings around the high-pressure center (H) and low-pressure centers (L).
Pressure Values
Each isobar is labeled with a numerical value in millibars (mb) or hectopsacals (hPa). Represents the atmospheric pressure along that line.
Reflectivity = Precipitation Intensity
The most common radar product seen by the public. Measures the amount of energy (radio waves) sent out by the radar that bounces back after hitting certain points in the atmosphere, mostlyprecipitationn (rain, snow, hail) is targeted.
The larger the target, the more energy it reflects to the radar. The returned energy is measured in decibels of reflective (dBZ) and displayed in different colors.
Blue and Green Color: Indicate weak returns, typically light rain or drizzle
Yellow and orange colors: Indicate moderate to heavy precipitation
Red and magenta colors: Indicate very strong returns, suggesting intense rains or the presence of hail in severe thunderstorms.
Forecasters use rreflectivityto find the location, movement, and potential for heavy rainfall or severe characteristics like “hook echoes,” which means a potentialthunderstorms.
Radar Velocity = Wind Motion
Velocity data, a feature of the Doppler radar, uses the Doppler effects to measure the motion of targets directly toward or away from the radar antenna.
Green Colors = Indicate motion toward the radar (green = forward)
Red Colors = Indicate motion away from the radar (red = away)
Velocity Couplet = Bright Green and red areas are tightly packed next to each other which is a key indicator of strong rotation within a storm, a primary sign of a potential tornado or mesocyclone.
Meteorologists use velocity data to detect wind shear, the speed of cold fronts, and the internal dynamics of storms to issue timely severeweathers warnings for damaging winds/tornadoes.
Satellite IR = Cloud Top Coldness/Height
Infared (IR) satelity imagery measures the amount of heat energy (infared radiation) radiating from objects on Earth’s surface or within the atmosphere
Warmer objects radiate more heat, while colder radiate less. In the atmosphere, temperature generally decreases with height. Satellite capture this radiation, and this data is converted into images.
White or Bright Color = Represents very cold temperauters, typically the tops of high-altidtue clouds like strong thunderstorm
Gray Colors = Represent warmer temperatures, like mid-level or lower-level clouds
Dark Colors = Represent warm surfaces, such as the ground or water in clear areas.
IR imagery is crucial for montitioring weather systems both day and night (unlike visible satellite which needs sunlight). Forecasters use it to determine the height and intensity of storms (stronger stroms have colder, higher tops), track large-scale weather patterns, and even identity fog or low clouds at night.
NWS (The National Weather Service)
Zone Forecast Product (ZFP)
The zone forecast is for the general public
It provides weather expected weather conditions for a specific geprhapic zone for a 7-day period
Usually county-sized areas with similar terrain and climate charascerists
It includes sky condition, probability and type of preciitpation, temperature (highs/lows of the temperate for that day), wind speed, direction, and visiltilbity restrictions
Intended for general public use, media, and emergency managers
Uses non-techinal, plain language
Issued at least twice daily and updated as conditions change
Special Weather Statement (SPS)
A special weather statement provides information about current or imminent weather hazards that are significat but do not meet the criteria for a formal Watch, Warning, or Advisory.
The special weather statement alerts users to significant but now-warning-level hazards like:
Strong Thuderstorms with winds 50-57 mph or hail less than 1in in diameter
Localized Heavy Snow Bands, black ice inforamtion, or dense fog
High-Impact events like heat indices or winds chills approaching advisiory levels.
Funnel clouds taht are not expecte to become tornadoes
In plain plain language focosuing on the impact of area of concern
Typically used for hazards within 6 hours, though it may alert to major events beyond that timeframe
Forecast Discusion (AFD)
A narrative product that explains the scientific and meteorological reasonsg behind the forecasts in other products like the Zone Forecast. It is primarily a coordination tool for other metorlogist, media, and weather-senseitve officials
Forecasters, media, and the weather-savvy public.
Uses semi-techinlal jargon and meteorological reasoning language.
Ridge = An elongated area of high pressure associate with stable weather. It might say “strong upper-level ridge building in,” leading to dry and warm conditions
Trough = An elongated area of low pressure associated with untsettled weather. It may include “a shortwave trought moving through the region”
Dry Air/Moisture = Forecasters frequently mention the presence of advection (movement) of moisture or dary air to explain potential cloud cover or the lack of preciptaion (“ample low-level mositiere is in place to support conevetoin” or “dry air enterinemtn will limit storm potential”)
Models = Forecsster will dicsssu the difference between various computer models like GFS, NAM and which one they are following and why
Synptic Situion = A brief review of the large-scale weather pattern
Advisory (Requires Caution)
Advieros are for weather condition that can be a problem or incvonence to our daily life, which are not threatening if we take simple precaiton. The lowest level of threat
Action Needed
Excersie caution, alter travel plans if necessary, but gerneall life can proceed mostly as normal with some mindfulness for the weather.
Example:
Wind Advisory: Sustained Winds of 26 to 39 mph, or gust of 40 to 57 mph
Dense Fog Advisory: Visibility reduce to ¼ miles of less
Watch (Be prepared)
A watch is issued when the poteentioal exists for a significant hazardous event to happen. It means that while the specific timing and location might be uncertain, all the atmospheric ingredient are present for dangerous sition to devlop
Action Needed
Review safety plans, gather supplies, stay informed of the latest forecast, and be ready to act quickly if a Warnig is issued. Preparation Phase.
Example:
Tornado Watch: Condition are faborbal for multiple tornadoes to develop in teh spcfied are over the next 4-8 hours
Winter Storm Watch: There is a potential for heavy snow or ice accumulations in the next 12 - 48 hours
Flash Flood Watch: Conditions are favorable for flash flooding in and around the specified area.
Warning (Take Action Immediately)
A Warning is the most urgent NWS products. It means that the dangerous weather is currently happening, or it will be happening withing minutes. The threat is specfic, imminetn and life-threatning
Action Needed: immediat action is required to protect life and property
Examples
Tornado Warning: A tornado has been spotted by a trained observer or detected on radar (Get to a SHELTER NOW)
Flash Flood Warning: Flash flooding is happening or imminent in a specific location (eg. a river basin)
Temperature Line vs Dew Point Line
These are the two of the most important lines on the chart, usually drawn in different colors (eg. red for temperature, green for dew points)
Termperature Line = Shows how the actual air temperature changes with altitude (pressure)
Dew Points line = Shows the the dew point temperareu (the temperature at which the air becomes saturated) changes with altitude
Key Concept:
The closer the lines are together, the higher the relative humidity and the greater the moisture content of the air at the altitude.
Where the lines meet: This is the altitude where the air is saturead (100% relative humidity), which is typically where a cloud base forms
The further apart the lines are: The drier the air is at the level
Wind Bars Up Each Level
On the side of the diagram (on the right), there is a vertical column of wind barbs corespoindng to different pressure/altidtude levels
Each Barbs indactres wind direction (the “stick” points where the wind is coming from (North/West/East/South)) and speed
Half Barb = 5 knots
Full Barb = 10 knots
Flag (Triangle) = 50 knots
Analyzing the change in wind speed and direction with height (wind shear) is vital for identifying favrobale conditions for severe weather, parctrucltih supercell thunderstorms and tornadoes
Inversions
When tempereuare increases with height, which is the opposite of the normal atmospheric condition (where air cools as you go higher)
On the Skew - T: The temperuater line bends sharply to the right
Inversions create an extremely stable layers of air that acts like a “cap” forming. If the cap is broken, the subsequent thunderstorm can ber very severe because energy has been allowed to build up beneath the inversion
LCL + Cloud Base Prediction
Lifted Condestion Level (LCL)
Official term for the altidte where a parcel of air, if liftend from the surface, would become saturated and from a cloud
It’s the point where the rising termpereure of a lifted surface air parcel (following specific dry/moist adiabtifc lines on the chart) intersects the dew point line
The LCL provides the cloud base prediction. Meetlosist calculate this level to forecast how high the bottom of the cloud will be. Lower LCl often suggest a higher probability of tornadoes if a strom forms, as the thunderstorm base is closer to the ground.
⬇ SKEW-T Diagram Example ⬇
CAPE vs Stablity
CAPE (Convective Avaliable Potenetial Energy)
Is a mesure of the insatliby of the atmosphere. It represent the potential energy available for a thunderstorm to use for a vertical development.
High CAPE: A large shaded area on the Skew-T diagram indicates high instalbity and the potential for strong, explosive thunderstorms
Low CAPE: Indicates a more stable atmosphere where storms are unlikely or will be weak.
Stability
Is a the atmosphere’s resistance to vertical motion
Stable: Air tends to return to its original posion after being displaced
Unstable: Air tends to continue moving upward after being displaced, which fuels strom growth.
In simple a Skew-T diagram allows meoroloist to visually assess all the ingredients needed for a strom – Moisture (dew point line) , Lift (wind analysis), instability (CAPE), and an “uncorking” mechanism (breaking an inversion).
HRRR (High Resoltion Rapid Refresh)
Short-term, high resolution
The HRRR provides very detailed forecasts of rapdilty evolving short-term weather phenomena. It excels at predicting the immediate timing and location of things like thunderstorms, snow bands, or sudden winds shafts.
Resolution: Very high (around 3km grid spacing)
Forecast Range: Very short (updated hourly, forecast out 18-48 hours)
Nowcasting sever weather, avation forecasting, and idneifiyin loxalizne heav =y rain or snow events happening today or tomorrow morning.
NAM (North American Mescale)
Regional (North America)
the NAM is a robust regional model that provides a balance between detail and forecasts range. Coverst the entire contine but provides more resolution and detail than global models like the GFS
Resolution: High to Moderate (typically run at 12km resolution)
Forecast Range: Medium (updated every 6 hours forecasts out to 48 hours)
Best for: Detailed forecasts of regional weather systems, indeftying frontal boundaries, and providing a solid 2-3 days outlook.
GFS (Global Forecast System)
Global (Cover the whole Earth)
The GFS is the U.S. government’s primary global modeling tool. Because it has to process data for the entire planet, it sacrifice resolution for rage. It is the workhorse for medium to long-range forecasting.
Resolution: Lower resolution tahn the HRRR or NAM (around 13km)
Forecast Range: Long-term (updated every 6 hours, forecasts out to 16 days)
Best for: Tracking large synoptic patterns like global high/low pressure systesm, jet stream patterns, hurricane forming over oceans, and provind gextend range forecasts (Day 5 to Day 16)
MODELS SUGGEST, THEY DO NOT GUARANTEE
1. Initial Donciton are never prefect
2. Physical are simplified
3. Resolution Limits
Heat Index = Humidity Makes Heat Worse
Heat index is the temperature during hot weather. It is a measure of apparent temperature that combines the actual air temperatures with relative humtidity.
Human sweat and since sweat evaporates our body it increase the humidity level. High humidity slows down this evaporation process significantly. The higher the humidity, the less effective sweating is at cooling you down. That is why your body temepare remains high creating extreme heat symptoms.
NWS issues Heat Advisory or Excessive heat warnings based on calculated heat index values, not just the actual air temperature.
Wind Chill = Wind Makes Cold Worse
The Wind Chill is the temperature during cold weather. It is the measure of apparent temperature that combine teh actual air temperature with wind speed.
A thin layer of warm air is sitting on your skin (the boundary level). Wind blows this layer off and keeps on repeating it with cold air from the environment. This rapid removal is called convection. Windeire the environment the faster your body loses its heat making it more colder. This can lead to eventual frostbite.
The NWS issues Wind Chill Advisories or Wind Chill Warnings based on tehse values, often apparent temperature drop into potential danger single digits or below 0 F
Heating Degree Days (HDD) = Heating Demand
Heating Degree Days (HDD) are cumaltitive index used by energy companies, metorliost and engineers to quantify demand for energy need to heat a building over a period.
Calculated based on how far the average daily outdoor temperature falls below the baseline comfort temperature, usually set at 65 F
Higher HDD values means more colder weather and greater need for heating energy
Lower HDD values means milder weather and less heating demand.
Use: TO predict customer billings
Cooling Degree Days (CDD) = AC demand
Cooling Degree Days (CDD) are the counterpart to HDD. Cumulative Index used to quantify the demand for energy neeed to cool a building
It is calculated based on how far the average daily outdoor temperature rises above the same baseline comfort temperature, usually 65 F
Higher CDD values means hotter weather and greater need for air conditioning
Lower CDD values means milder weather and less cooling demand
This metrics helsp forecast summer energy demands and asses climate change trends over a time.