Monday 10 AM
A strong cold front that caused cloudbursts of rain in the Ohio Valley yesterday is moving through the East today. At 10 a.m., the leading edge of the strongest thunderstorms extended from Elmira, N.Y., through Harrisburg, Pa., then on southwest through D.C.'s far western suburbs. A tornado watch was issued this morning in anticipation of these thunderstorms getting severe as they move through the very warm, humid air that has been in place recently. The watch was to be in effect until 5 p.m. for the area shown on this map.
The watch will be rescinded from west to east as the line of thunderstorms moves along. Keep in mind that a watch is an alert saying something could happen. Warnings, however, are focused on small areas based on reported tornadoes and on radar indications of one or more tornadoes. If a warning is issued for your neighborhood, please go the safest place you can find right away. Most places will have a period of very intense rainfall with quick street flooding along with strong gusty winds that do not last long.
Much cooler air follows the front, but the front will stall off the Southeast coast. Some computer models suggest that a low pressure area will form along the front and then fling rain at the Middle Atlantic coast. Meanwhile, milder air will start spreading back across the Midwest.
This map shows the GFS forecast for Monday at 2 p.m. ET. If correct, rain will hold off for the Boston Marathon. However, you can see that any speedup of the rain would prove that idea to be wrong.
Another high pressure area will build over the Northeast during the weekend, so sunshine with mild afternoons can be expected. However, this forecast map for next Monday evening shows how extensive and wide ranging the next storm may be.
These maps show how the US model handles the disturbance now causing rain in Tennessee. On the 1st map (for tomorrow), it is embedded in a southwesterly flow. However the 2nd map (for late tomorrow night) shows it turning more toward the course that would take it out to sea.
In the middle of Pennsylvania, rain ended before daybreak, but rolls of sullen clouds presided during the first hours of daylight. A robin takes in the scene.
... map shows this morning's surface pressure pattern, including a southerly flow of warm air in the East and a northwesterly flow of cooler air behind a cold front that is drawn in blue. Showers accompany and precede the cold front marking the boundary between the two air masses.
Rainfall between today and Friday night will be highly variable between the Midwest and East Coast. Parts of the Ohio Valley, where it has been wet recently, will get more heavy rain; places along the East Coast will generally get less. From New York City to D.C., this weekend may be the nicest so far this year!