Cold Front Pressing forward:
After afternoon temperatures near 50 degrees, a return (once again) to the ever absent "normal" weather is in the offings for the region. A powerful cold front, associated with a developing (and intensifying low) near the US/Canada border, will sweep across the Ohio River Valley this evening, before setting its sites on the metro region overnight.

After the cold front axis passes, you will notice (If you're up at say 4 or 5 AM) the winds quickly begin to ramp upwards. This is caused by a weather phenomenon known as the Pressure Gradient Force, which is defined as:



Therefore, as the spacing between isobars (lines of equal pressure) decrease over a distance, the PGF increases, a figure that is correlated to wind speed. For example: in the image above, the PGF over the Mid Atlantic is something like 1 mb per 100 km, not a very strong one, and therefore, we'd expect generally light winds in the region. However, behind the cold front, the PGF ramps up to about 4 mb per 100 km (rough estimate), and we'd anticipate wind speeds to be significantly higher to the west of the cold front.

So, as the front passes, the PGF will gradually increase, incrementally forcing the surface winds higher as air moves more quickly over a specific region. On top of all this (as if it weren't enough) the release of solar energy as the sun rises has a stark effect on wind speeds. By 7 or 8 AM, the overnight inversion or increase in temperature with height to about 1000 feet, erodes as the surface warms. This allows any quickly moving air in the upper levels to be easily transferred to the surface, further increasing the wind speed. With this in mind, wind gusts to 40 or 45 mph are anticipated tomorrow afternoon.

That's your lesson for the day...

Temperatures should warm above average once again by this weekend.