Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* Sunshine, Warmth to Replace Cloudy, Raw Weather Starting This Weekend *

1:00 p.m. Friday, September 27, 2023: 

The remnants of Tropical Storm Ophelia dumped 1.5-3.0" of beneficial rain across southeastern PA, northern MD and the Lower Susquehanna Valley last weekend (see below). Due to the prolonged and drawn-out nature of the event, flooding was essentially a non-issue except in low-lying and poor-drainage areas. From Saturday-Sunday, Millersville picked up 1.97" of rain, and Lancaster Airport received a similar amount (1.93"). Despite Ophelia's remnants having moved back out to sea early this week, low-level easterly flow off the Atlantic has kept cloudy, damp and dreary conditions in place. A sprawling high pressure system over eastern Canada has been to blame for our extended stretch of miserable weather. Air flows clockwise around areas of high pressure, so winds along the southern periphery of these systems are traditionally east-to-northeasterly. Unfortunately, this type of flow is "no bueno" for residents along and east of the Appalachians. Essentially, the persistent flow off the Atlantic Ocean draws moisture farther west and "dams" it up against the eastern slopes of the Appalachians. The result is days of cloudy, raw and breezy conditions with below-average temperatures and periods of mist/drizzle.. the complete antithesis of weather typically associated with the first few days of autumn. Yuck!

On a positive note, monthly rainfall totals stand at 6.12" at Millersville and 5.83" at Lancaster Airport through September 26th. Most parts of the Lower Susquehanna Valley typically receive about 4" of rain during the entire month of September. This month's rainfall surplus has certainly put a dent in the drought, but the Drought Watch remains in effect due to the abnormally dry conditions from May through August. In fact, a Drought Warning was issued for York County about 10 days ago, and Ophelia's rain did not change that status. In order for drought concerns to be completely quelled, we will need above-average rainfall again in October and perhaps even November.

There will be a slight improvement in the weather this afternoon through tomorrow. A pocket of drier air rotating around the southern periphery of the Canadian high pressure system will promote a continuation of gradual clearing across south-central PA through the mid-afternoon hours (see below). Due to more sunshine, highs this afternoon will be slightly higher than the last 4 days, or generally in the mid-to-upper 60s. However, temperatures should drop quickly after sunset under mainly clear skies and ultimately bottom out in the upper 40s to low 50s early Thursday morning.

The aforementioned high pressure system will gradually shift off the southern New England coastline later Thursday and "camp out" there through Friday. At the same time, a broad, upper-level disturbance moving slowly eastward from the Ohio Valley will combine with the disorganized remnants of Ophelia still lingering off the North Carolina coastline to "re-energize" the system. Ophelia's leftover, ragged low pressure system will become better organized again as it tracks back to the north several hundred miles east of the Delmarva Peninsula. Fortunately, it should remain over the open waters of the western Atlantic and fail to reacquire tropical characteristics. However, it may still track close enough to the coast for showers or a period of light rain to sneak into southeastern PA and parts of Lancaster and Lebanon Counties late Thursday night into Friday. Easterly flow off the Atlantic will also become somewhat more pronounced again late this week and aid in drawing some of the system's moisture into the region. As a result, clouds will return later tonight, and mostly cloudy skies should then "rule the roost" through the end of the week. Pockets of mist and drizzle are a "good bet" again Thursday night, as well, prior to Friday's potential for more showery conditions. Despite the clouds, highs on both Thursday and Friday should be similar to today. At this point, I don't expect more than 1-2 tenths of an inch of additional rainfall through Friday evening across the Lower Susquehanna Valley. Higher amounts of 0.5-1.5" should be confined to far southeastern PA, DE, and NJ. If the coastal storm trends westward at the last second, then steadier/heavier rain could impact the eastern half of the Lower Susquehanna Valley. In addition, highs on Friday would be several degrees below current expectations and only in the low 60s. However, this outcome only has about a 20% chance of coming to fruition.. at least in my opinion..

Looking ahead into the weekend and through all of next week, our abysmal weather pattern is finally going to break down and, in fact, do a complete 180! Vast improvements are on tap beginning this Saturday, and we'll be treated to an extended stretch of mostly sunny skies, light winds, and pleasantly warm conditions from Sunday through at least the end of next week. After a horrible stretch of weather to round out September, I couldn't be more ready for the impending, spectacular start to October! The high pressure system will actually retrograde back to the south and west over the weekend, ultimately becoming centered over the Ohio Valley and mid-Atlantic States by Sunday. It will then remain in control of our weather for the entirety of next week. The coastal storm will move farther offshore later Friday night into Saturday morning, and gradual clearing should occur during this time with mostly sunny skies on tap for Saturday afternoon. A gradual warming trend will take place from Saturday through early next week with highs rising from the mid 70s to the low-to-mid 80s by Tuesday. Dewpoints will generally be in the mid-to-upper 50s through next Friday, so overnights lows will also drop into the comfortable mid-to-upper 50s. Normal highs in early October fall into the upper 60s to low 70s with lows in the upper 40s, so temperatures will average some 5-10 degrees above normal next week. High temperatures may very well reach or exceed the 80-degree mark each afternoon next week, and there won't be a drop of rain within several hundred miles of south-central PA. For outdoor enthusiasts, it'll be a dream come true and a satisfying reward for having to endure a downright nasty end to September. Bring it on! -- Elliott

 

2023 ATLANTIC HURRICANE AND SUMMER OUTLOOKS ISSUED JUNE 1, 2023:

Not only does June 1st mark the beginning of meteorological summer, but it's also the start of the 2023 Atlantic Hurricane Season. Due to a developing and perhaps strengthening El Niño, wind shear.. or the change in wind direction and speed with height above the ground.. should be higher than normal in both the Atlantic and Pacific Basins this season. In El Niño patterns, the southern branch of the Jet Stream typically becomes dominant over the northern branch. As a result, easterly trade winds in the tropics weaken and can even become westerly in the mid- and upper-levels of the atmosphere. Unlike severe thunderstorms, wind shear is detrimental to tropical storm and hurricane formation. Thus, I expect a near- to slightly-below average Atlantic Hurricane Season with only 10-14 named storms and 4-6 hurricanes. Of those, 1-3 could become major hurricanes. I expect most of these systems to "recurve" back out into the open waters of the Atlantic with a lower-than-normal chance of a significant U.S. landfall.. and that's good news! Fingers crossed.. 🤞

As for my 2023 summer outlook, things look relatively bleak in the rainfall department. We're still in a transition phase from La Niña to El Niño, and it will take the atmosphere several more months to respond to these changes. Both the northern and southern branches of the Jet Stream are currently quite weak and should remain that way through August. Put simply, there is just not enough energy available in the atmosphere to spawn significant storm systems or potent cold fronts, and I don't foresee many changes until autumn. Thus, I expect drier-than-normal conditions this summer across much of the mid-Atlantic region. In ENSO-neutral (neither La Niña nor El Niño) summers, there tends to be a general lack of rainfall in south-central and southeastern PA. I do not expect record dryness this summer, but overall rainfall should end up below average by a few to several inches. Given that we're already experiencing abnormally dry conditions, continued drier-than-normal weather will only exacerbate the situation. As for heat, the worsening drought should promote an above-average number (about 25-35) of 90-degree days yet again this summer. There is often a correlation between drought and the core of the heat during summer months. This year, I expect the hottest conditions (relative to average) to extend from the Plains through the Midwest, Ohio Valley, and mid-Atlantic States. After a near- to perhaps slightly-above normal June, I expect several heat waves in July and August with above-normal odds for a 100-degree day or two. In aggregate, I expect temperatures from June through August to average 1-3°F above normal. Unlike many summers, our heat this season should be primarily of continental origin and come from "over the top" instead of from the western Atlantic or Gulf of Mexico. Fortunately, this means that a lot of our heat should be accompanied by low humidity. Regardless, any temperatures in the mid 90s to 100°F are dangerously high and make practicing heat safety essential. -- Elliott