We’re about to have a very soggy 24 hours in the Hudson Valley. You can see the current radar loop has rain slowly lifting from south to north through the Hudson Valley. This rain is the product of upper level lift in the atmosphere. On the north side of Ophelia’s remnants will be significant upward motion, that will develop a large area of precipitation, and that area of rain will likely become moderate to heavy at times tonight, into Monday morning. Heaviest amounts are likely to be near and south of I-84… where over 2″ of rain could fall. A very soggy 18 to 24 hours heading our way.
Vertical Motion in Atmosphere Brings Soaking Rain
This is the type of thing we’d LOVE to see if it was the middle of winter. An 18 hour period where the Hudson Valley is north of an upper level low, and intense upward motion of the air results in an extended period of moderate… to at times heavy, rain. The first image shows the projected rainfall between Sunday evening and Tuesday. Location is critical between seeing soaking rainfall, and barely any rainfall. The map shows a narrow band of 2 to 3 inches of rainfall, between I-84 and NYC. While viewers in the Catskills and Upper Hudson Valley (Greene & Columbia counties)… may only see a tenth to a quarter inch of rain. On average… most in the valley will see between 0.5″ and 1 inch of rain. But it would not surprise us if someone sees over 4 inches of rain… especially in the higher elevations of Orange, Rockland & Westchester counties.
WHY IS THIS HAPPENING?
Precipitation falls when the air rises… it cools, and condenses, and then that moisture falls to the ground in the form of rainfall. This process occurs naturally with low pressure systems, which is why we associate rain with low pressure. But sometimes, conditions are much more favorable… and the air rises much faster than normal. The 2nd image shows the vertical velocity of the air (rate of lift) at 700mb (roughly cloud level). The pink and purple colors represent intense lift rates. The Hudson Valley is the focal point for intense upward motion of the air from 8pm until 11am on Monday. This will cause precipitation to develop right over top of us… and become heavy at times. If you watch the radar Sunday night & Monday morning, you will see the same areas seeing rain develop and redevelop right over top of us. You will also notice heavier rainfall rates than surrounding areas. In addition, as long as the Hudson Valley is experiencing these high rates of vertical velocity, it will continue to rain. So our rain likely won’t taper off until after dark Monday night.
A soggy 24 hours ahead… thanks to vertical velocity associated with upper level low pressure. Let’s hope this happens about 4 or 5 months from now.