Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* Cool and Dreary Through Thursday, but a Decent Easter Weekend Follows *

2:15 p.m. Tuesday, March 26, 2024:

Saturday's "Super Soaker" played out as expected across the mid-Atlantic States. Millersville University officially received 1.25" of rain on Saturday. Rainfall totals from Friday evening through Saturday afternoon ranged from 0.75-1.0" in Franklin County to 2-4" along and east of the I-95 corridor (see below). As a result, stream and river flooding was confined to areas south/east of the Lower Susquehanna Valley, but some roadways in low-lying and poor-drainage areas were still covered by standing water. Behind the storm system, another chilly air mass settled over the mid-Atlantic States on Sunday. Despite sunny skies, high temperatures failed to reach the 50-degree mark in most places, and a 10-20 mph northerly breeze made the outdoor air feel even chillier. After a clear and unseasonably cold Sunday night, temperatures bounced back into the mid-to-upper 50s Monday afternoon and are at a similar level this afternoon. However, skies have turned partly-to-mostly cloudy in advance of an approaching cold front, so it's not quite as nice as yesterday. 

Clouds will lower and thicken overnight, and a few showers should reach the Lower Susquehanna Valley in the early-morning hours. However, the heaviest and most widespread showers should not arrive until during the morning commute. A period of steadier rain is possible later Wednesday morning into the early-afternoon hours, but rainfall amounts through Wednesday evening should generally remain below one half of an inch. Showers are expected to shift into northeastern MD and far southeastern PA by or shortly after the Wednesday afternoon commute, but the aforementioned cold front will temporarily stall along or just east of the I-95 corridor from Wednesday night through Thursday afternoon. A wave of low pressure will develop near the tail end of the frontal boundary Wednesday evening and move northeastward along or just off the Carolina coastline on Thursday. Thereafter, it will track east-northeastward and move well out to sea from Thursday nigh into Friday. To the north and west of the low pressure system, rain will expand and intensify across the Carolinas and Delmarva region Wednesday night and should impact the I-95 corridor from D.C. to Philadelphia on Thursday. However, most if not all of the rain associated with the system should remain east of the Lower Susquehanna Valley, and the highest rainfall totals are most likely south/east of I-95. Thus, the flood threat will be minimal, at worst, with this one for areas north and west of the Northeast Megalopolis. There is still some uncertainty surrounding the exact position of the stalled front, but I currently expect rainfall amounts through Thursday evening to range from a few tenths of an inch across central PA and western MD to around or just over 1" along the I-95 corridor (see below). Temperatures will only bottom out in the low 40s tonight but fail to exceed the low-to-mid 50s tomorrow due to the clouds and showers. Unfortunately, low and high temperatures on Wednesday night and Thursday, respectively, will be quite similar.

In the wake of the storm system, winds will turn northwesterly later Thursday through Friday and usher a drier air mass back into the region. As a result, Thursday's cloudy, damp, and cool weather will give way to mostly sunny, breezy, and slightly milder conditions on Friday with highs in the mid-to-upper 50s. Despite winds of 12-25 mph with gusts up to 30 mph, the last week of March will end on a rather pleasant and tranquil note. I then foresee a "decent" Easter Weekend with the only threat for showers coming Saturday afternoon into Saturday night. After a mainly clear and seasonable Friday night with lows in the 30s, clouds should increase on Saturday ahead of a weak and disorganized disturbance. The track of the disturbance is still rather uncertain, but its most likely path will be through the Commonwealth Saturday afternoon/evening and then off the New Jersey coastline Saturday night. Thus, another bout of rain showers is a "good bet" across northern MD, southeastern PA, and the Lower Susquehanna Valley during this time, but amounts should be minimal and generally under one quarter of an inch. High temperatures will likely reach the mid 50s to perhaps 60°F.. essentially "normal" for March 30th.. prior to the showers' arrival, and highs on Easter Sunday may be similar to or perhaps a bit above Saturday's readings. Fortunately, an area of high pressure should settle over the eastern Great Lakes region and northern mid-Atlantic States on Sunday and Sunday night, so I expect partly sunny and dry conditions for the holiday itself. Again, this is "par for the course" in late March, and that's not a bad thing with average highs now in the upper 50s. You'll need to keep an umbrella handy for the first half of the weekend but should be able to leave it at home for Easter Sunday church services and/or family gatherings. No complaints here!

Looking ahead into early next week, another storm system will likely develop over the Central U.S. Sunday night or Monday and reach the mid-Atlantic States during the middle of next week. High and low temperatures, as well as rainfall amounts and exact timing of any wet weather, from Monday-Wednesday will depend on the track, speed, and intensity of the system. However, I won't be able to finesse those details until Friday, so check back then for an update! Predictability in this complex and transitional weather pattern is currently limited to about 3-4 days. Therefore, I'm very hesitant to discuss the pattern beyond the middle of next week. However, the Madden-Julian Oscillation (MJO).. or an eastward-moving wave of convection between the Indian and western Pacific Oceans.. is currently active in phase 1 and will become inactive or progress through phases 2 and 3 through the first week of April. Each "phase" corresponds to a different location between the Indian and western Pacific Oceans, and the location of the convection at any given time can modulate the Jet Stream pattern across North America. During an ENSO-neutral April, phases 1-3 support a trough, or southward dip in the Jet Stream, and below-average temperatures over the eastern United States. Thus, I don't expect persistently warmer weather or 70-degree high temperatures to return until the second week of April. At that point, the MJO should finally reach phase 4 and then move into phases 5 and 6 during the middle of the month. These three phases support a northward bulge in the Jet Stream over the East, so I expect dramatic improvements in our weather and a complete pattern reversal after April 5-7. Until then, high temperatures will primarily be in the 50s with a couple 60-degree days sprinkled into the mix. Oh well.. -- Elliott