Monday Afternoon Technical Discussion

Monday Afternoon Technical Discussion

Synopsis…

A powerful heavy rain event is expected over the next week, with at least some of the rain associated with the remnants of Tropical Storm Lee. Temperatures will be significantly below average to start the week, before settling closer to normal as we approach next weekend.

Short Term (through Tuesday eve)…

A very deep trough off to our immediate west is setting up a potent rain-making system across the state (and much of the eastern seaboard) over the next few days. A small surface low is currently residing near south-central PA as of 20z, enhancing rainfall associated with a slow-moving cold front draped across central Pennsylvania.

Precipiptable water values from the 12z soundings at KPIT and KIAD are above 1.6 inches, indicating the availability of a large amount of moisture. Some areas likely have even large PWAT values in between those two balloon launch locations. Most operational models are showing a large amount of rainfall being trained across the state. 12z WRF indicates 3 inches or more of rain across the center part of the state by Wednesday around midnight, with indications some areas could see significantly more than that. Most areas will see at least two inches by that time.

Temperatures should remain rather cool on Tuesday, barely reaching past 60 degrees in several locations. MOS temperature plots show temperatures in the mid-60s in the western part of the state on Tuesday, with slightly cooler temps in the central part and slightly warmer air in S/SE PA. This is namely due to a thick cloud deck and north/northwesterly flow dominating surface winds.

Long Term (Wed-Fri)…

As we move past Tuesday, the chance for rain really does not waver. The remnants of former Tropical Storm Lee will move northward slowly, arriving on Pennsylvania's doorstep early Wednesday morning, bringing with it the chance for some heavier rainfall yet again. By this point, the ground should be well saturated; though it remains to be seen how great the chance for flooding is.

While the remainder of the week will improve, this improvement will not be very significant. Guidance suggests heavy rainfall will not be as widespread later in the week, although pockets of heavy showers could remain. The upper-level vort. max to our west expands as the week goes on, but does not appear to really move/dissipate from its home over Ohio, at least through Friday. This should continue to funnel moisture from the south.

Temperatures should warm somewhat as the week goes on. GFS MOS indicates temperatures reaching back into the mid-70s by Thursday. These may be slightly higher than what is expected to occur – we have adjusted our forecast accordingly.

Looking out towards next weekend, 12z GFS takes Hurricane Katia east of the Atlantic coastline. Eastern PA may see some cloud cover associated with her, but little else in the way of rainfall/winds. Also look for at least somewhat of a clearing pattern with temperatures returning closer to normal.

-Devin Boyer