Weather Station Model

Temperature, pressure, moisture, and wind measurements are reported hourly at the surface (most are usually made 2 meters above the ground).

77: Temperature.

68: Dewpoint.

998: Pressure, to the nearest tenth of a millibar. Add either a 10 or 9 in front based on which would bring the value closer to 1000. The pressure here is 999.8 millibars (mb).

-03: Pressure tendency the last 3 hours, to the nearest tenth of a millibar. The pressure here has fallen .3 mb the last 3 hours.

Middle Circle (filled in w/ mostly black): Cloud cover. It's mostly black showing that this station is mostly cloudy. Technically, this represents a broken sky with 7/8 of the sky covered with clouds.

Black line, extending from circle: Wind barb. It points to where the wind is coming from. The wind here is from the southwest, hence a southwest wind. The two lines extending represent 20 knot winds with each line representing 10 knots.

Symbol between 77 and 68: This is the present weather field and in this case shows that there is a thunderstorm occurring at the station.

Symbol next to -03: That line is the pressure tendency. The 1st hour the pressure was steady, then fell the last two hours.

Triangle (with a dot above it): Previous weather, or the weather one hour ago. In this case it was a light rain shower.

How does the upper air station model differ from the surface station model?

─     Temperature is given in Celsius

─     Dewpoint depression is given not dewpoint temperature

─     Altitude of the pressure surface is given instead of pressure

─     Cloud cover is not noted

─     Circles indicating station locations are often omitted

Physical Principles: Why Cloud Droplets Don't Fall

Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward Aguado, James E. Burt

Physical Principles: The Surprising Composition of Clouds

Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward Aguado, James E. Burt

Forecasting: Why Clouds Have Clearly Defined Boundaries

Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward Aguado, James E. Burt

Forecasting: Dew Point and Nighttime Minimum Temperatures

Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward Aguado, James E. Burt

Supercell Thunderstorms

Ø  Forward and rear flank downdrafts are rapping around the updraft which is occlusion

Ø  Occlusion (pg. 162 – Figure 9.7)

Ø  New updraft will form on the triple point of the occlusion

Ø  V-Notch

̶        Strong updraft

̶        Goes around the updraft

̶        Inflow notch

Ø  Beaver’s Tail

̶        Flat cloud that lines up on the forward flank gust front

̶        Connected to the rain free base

Ø  Tail Cloud

̶        Attached to wall cloud

Ø  SCUD – Scattered Cumulus Under Deck

̶        Cooler air from the forward flank is drawn into the storm and reaches saturation below the cloud’s LCL

̶        Often the wall will lean toward the precipitation

̶        Strong motions are often apparent to the spotter

Ø  HP (High Precipitation)

̶        These storms are difficult to spot for two primary reasons:

1.    Obscuration and misplacement of important features and safety. The best place to spot the tornado is usually in its path

2.    Originally, HP supercells were considered rare. In reality, perhaps half of all supercells are HP

̶        HP supercells are also prolific tornado producers, much more than originally thought.

̶        These are usually big and scary storms.

̶        Great deal more precipitation in the RFD with rain actually falling through the rain free base (not really a rain free base)

̶        2 reasons they are EASY to find

1.    Visual Vault

2.    Beaver’s Tail

̶        Beaver’s tail is INFLOW into the storm

Ø  LP (Low Precipitation)

̶        Storm without a rear flank downdraft

̶        These storms are easy to identify marked by light precipitation in the main downdraft

̶        LP’s tornadic potential is somewhat limited

̶        They do produce damaging hail and can change modes throughout their lifetime

̶        Prolific producers of large hail

̶        IF tornadoes do form the storm may be becoming more like a supercell