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Northeastern U.S. (with additional details for New Haven)

The northeastern U.S. is far from any monsoon region, but forecasts for this region are shown because it is home to Yale University, which hosts this website.  We show additional details for New Haven, Connecticut.

All forecast data is from the Global Ensemble Forecast System (GEFS) of the U.S. National Centers for Environmental Prediction (NCEP).  All forecasts use an initial atmospheric state at the time indicated on the plot (note that 00Z is midnight Universal Coordinated Time, which is 8 pm the previous day in New Haven [EDT]).

Forecast for wind and precipitation

This animation shows the forecast of precipitation (color shading) and horizontal winds at 850 hPa, which is about 1.5 km above sea level.  The precipitation is the accumulation over the previous 6-hour period, in millimeters (1 inch = 25 mm), and winds are measured in m/s (1 m/s = 2.2 miles per hour).  This is from a single deterministic forecast; the ensemble, probabilistic forecast for New Haven (marked by the red dot) are shown below.

Probabilities of precipitation & temperature

A collection, or ensemble, of forecasts are made from different initial conditions several times each day, and the degree to which the ensemble members diverge from each other over time provides information on the likelihood of the future atmospheric state. For New Haven (indicated by the red dot in the above map), the below plot shows how many of the ensemble of 20 forecasts made each morning predict a given amount of precipitation accumulation and maximum surface air temperature.  In other words, each line on this plot is a histogramof the predictions made during the time periods noted in the legend.  In statistical parlance, this is similar to the probability density function (PDF) for the predictors.  For example, if 15 of the forecasts are predicting 10 mm of rainfall between 1-2 days from now, while the remaining 5 forecasts are predicting 15 mm of rainfall, the dark blue line would have a sharp peak at 10 mm/day that tapers off toward zero at 15 mm/day; this would indicate fairly high confidence in a forecast of 10-15 mm/day for that time period (assuming the weather prediction model does not have large errors/bias).

New Haven precipitation forecast PDF

Seasonal rain accumulation

Also just for the city of New Haven, the below plots show the daily rainfall and the total seasonal accumulation of precipitation, compared to the historical average.

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