Timing Out The Heavy Rain
By Steve MacLaughlin on August 8, 2012, 5:00pm
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We are still on track for a stormy end to the workweek and a stormy start to the weekend here in Connecticut and for much of the East Coast and Northeast.
The image above is the GFS weather model showing 700mb heights and relative humidity. We use this level to determine the moisture field and to also see the upper-level wind patterns to see where that moisture is headed.
The time frame for this image in Saturday morning at 2am when the heart of the storm will be on top of Connecticut.
The first feature that really jumps out is the smallest, closed circle over the Great Lakes. This is the center of the upper-level low pressure system that will be driving our unsettled weather. Because the flow around low pressure is always counter-clockwise in the northern hemisphere and because the solid, black lines show the main movement of air from west to east across the United States, you can see that the air will start in Canada, then swing south underneath the area of low pressure toward the Gulf of Mexico, then turn back up to the north along the east coast right into Connecticut.
As we know, when we get into a southwesterly flow, that means a surge of humidity and moisture from the Gulf. This is confirmed by looking at the green shading which shows the moisture field. Notice how the green shading over CT extends all the way to the Gulf...the origin of our humidity.
Also, notice that at this point we not only have the lighter green shading, but also the darker green. That is an indication of some very heavy rain late Friday into early Saturday.
Rainfall totals still look like 1-2" on average, but with the heavier downpours late Friday into Saturday, some isolated areas could see between 2-4".
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