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Friday November 9, 2018

Assignment: Predict the 24 hr precipitation amount (inches) for Hartford-Brainard, CT (KHFD)

Cold and Wet

With a complex system moving quickly through the Northeast on Friday, cold rain is expected across a wide area, but predicting the amount for a particular site is always a tough challenge. The NWS forecast discussion from New York City says: "The rain could become locally moderate to heavy at times, especially late Fri and Fri eve. Have bumped up rainfall amounts a little, especially in CT where orographic enhancement could result in 1-2 inch amounts." So let's forecast the 24-hr precipitation amount for Hartford, Connecticut.

Question of the Day: What do they mean by "orographic enhancement" of the precipitation?

What Happened?

It looks like somewhat larger precipitation amounts fell to the east of Connecticut, for example Providence, Rhode Island received about 1.5 inches. But in Hartford, the 0.76 inch amount was less than any of the MOS forecasts.

Answer: Orographic lift is the tendency of atmospheric flow to be lifted up as it passes over hills and mountains, often leading to clouds and precipitation. As cold fronts, low pressure centers, etc. move through an area, rising motion occurs over both flat and mountainous areas because of the dynamics of the storm, but the extra orographic lifting in certain areas (depending on which direction the flow is coming from, etc.) enhances, or increases, the amount of precipitation.

Forecasts for Hartford-Brainard, CT (KHFD)
Forecaster Precip24, inches (error) Comment Day Score