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Jason M. Cordeira Graduate Student Webpage

  

2009

Deptartment of Earth and Atmospheric Science
University at Albany - SUNY / ES 318 / cordeira"at"atmos.albany.edu

Precipitable Water
Precipitable Water Imagery:

updated 3 July 2009
   

Global

North America

| Archive | Forecast | Archive + Forecast |

| Archive | Forecast | Archive + Forecast |
 
Plot description:
The precipitable water (PW) imagery incorporates the column integrated PW along with the 925-850-hPa layer-averaged relative vorticity and the 250-hPa geopotential heights. The North America view also plots the 700-hPa wind barbs. Precipitable water is shaded in mm, wind barbs (where plotted) are plotted in knots such that the pennant, barb, the 250-hPa geopotential height is contoured in dam, and half-barb represent 50, 10, and 5 knots, respectively, and the relative vorticity is contoured positive (cyclonic) every 0.5 x 10E-4 beginning at 0.5 x 10E-4.

North America PW imagery was updated to shade to 4 mm and utilize a white contour for the vorticity. The change was implemented with the 1200 UTC run on 3 July 2009.
 
Utility of PW imagery:

Precipitable water is the amount of water in a column of the atmosphere. The PW value is the depth that would be achieved if all the water in that column were precipitated as rain. The PW value can therefore represent the amount of moisture in a given environment and is typically very high near the equator and is low over deserts, higher latitudes, and elevated terrain. The PW is constantly in motion as it is deformed (e.g. advected/diverged/converged/sheared) by atmospheric motions. Because the PW is an integrated quantity, the advective wind is difficult to ascertain. Since a majority of atmospheric moisture is contained in the lowest levels of the atmosphere, a low-level wind, typically 700-hPa or 850-hPa is commonly used. The PW value (in association with the 250-hPa geopotential heights, the low-level relative vorticity, and the 700-hPa winds) is a great tool to visualize tropical cyclones (and their attendant structures such as predecessor rain events; PREs), moisture availability ahead of large-scale troughs in forecasting the possibility of convection, or the filamentary structure of atmospheric rivers commonly found in the warm sector of extratropical cyclones.

 
Model description:

The PW imagery uses the Global Forecast System (GFS) gridded forecast data. The 0 to 84-hour forecast plots utilize the half-degree (latitude by longitude) data, while the 90 to 180-hour forecast plots utilize the one-degree data. Plots are made in GEMPAK using a c-shell script that was programmed in UNIX and called 4xdaily using cron. The cron scheduler begins generating plots at 0530, 1130, 1730, and 2330 UTC from the 0000, 0600, 1200, and 1800 UTC datasets, respectively. Each image takes approximately 90 seconds to generate and is 400 Kb in size. The last plot is typically generated at 56 minutes past the hour mentioned above.
 
Additional imagery:

PW imagery (both forecast and analysis data) can be found from the websites listed below:
CIRA global 5-day loop
CIRA global 30-day loop
AMSR-E 'liquid'-related imagery
Morphed microwave imagery at CIMSS
Ryan Maue [Florida State University]