Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* Spring in "Full Bloom" Through Sunday, But Colder Air Returns Thereafter *

1:00 p.m. Friday, March 15, 2024, Update:

The weather since Monday has been absolutely glorious across northern MD, southeastern PA, and the Lower Susquehanna Valley! In fact, you really couldn't ask or hope for better weather during mid-March. Mostly sunny skies and relatively light winds have accompanied high temperatures some 15°F to as much as 30°F above average. The mercury soared to 78°F yesterday at Millersville University. It was the warmest day since October 28, 2023 (81°F) but still well below the March 14th record high of 83°F from 1990. On account of the unseasonable warmth, early-spring flowers such as daffodils, forsythia, crocuses, and dogwoods burst into full bloom this week (see below). Some magnolia, cherry, and Bradford pear tree blossoms have also made an early appearance this year. Sadly, the beautiful weather will be a distant memory by the start of next week, and near- or perhaps sub-freezing overnight lows could spell the end for some of these early bloomers. Fortunately, we'll first get to enjoy relatively nice weather over the weekend prior to the pattern change.

A cold front will slice through northern MD, southeastern PA, and the Lower Susquehanna Valley this afternoon and clear the I-95 corridor by 6-7 p.m. However, no more than a brief shower or two will accompany the frontal passage. Expansive cloud cover from last night's convection has stabilized the atmosphere and will result in a near-absence of shower and thunderstorm activity across the region. It will be a different story south of the Baltimore/Washington metro. areas, but we'll "dodge a bullet" with this one. Ahead of the front, high temperatures will still reach the upper 60s to low 70s across most of the region early this afternoon before slowing falling late in the day. Behind the front, winds will shift to the northwest overnight and usher cooler air into the Commonwealth. However, the post-frontal air mass will still be quite mild for mid-March, and temperatures should only bottom out in the upper 30s to low 40s by daybreak. Winds will quickly shift back to the west- and southwest by Saturday afternoon and remain westerly on Sunday, so highs should still reach the low-to-mid 60s areawide tomorrow and range from the mid-to-upper 50s north/west of I-81 to the mid 60s along the I-95 corridor Sunday. A secondary cold front will traverse the mid-Atlantic States from northwest-to-southeast from Saturday night through Sunday morning. Much like today's front, it will be starved for moisture and reach areas east of the Appalachians during the late-night and morning hours. Instability is at a minimum during these times of the day, so I expect no more than a stray shower late Saturday night or Sunday morning. Westerly winds will increase behind the front and may gust up to 30-35 mph at times Sunday afternoon, but they won't be nearly strong enough to cause power outages or downed tree limbs. Overall, pleasant weather will be the theme of the weekend with a good amount of sunshine on both days. Get outside and enjoy! 

Regarding next week's weather, a major pattern change featuring a large ridge, or northward bulge in the Jet Stream, across western North America and a deep trough, or southward dip in the Jet Stream, over the eastern United States will promote blustery and much colder conditions just in time for the official start of spring. After a mainly clear and seasonable Sunday night with lows in the low-to-mid 30s, the core of the cold air mass will settle over the mid-Atlantic States during the beginning of next week. Some smaller disturbances will round the base of the larger, Jet Stream trough from Monday-Wednesday, and a few flurries or snow showers cannot be ruled out each afternoon and evening. They won't be nearly as widespread or intense as this past Sunday, and no accumulation is expected on either grassy or paved surfaces. However, any talk of snow on the first day of spring is a "loss" for a warm-weather lover like myself. Partly-to-mostly cloudy skies and dry conditions should prevail most of the time, but persistent, northwesterly winds of 12-25 mph with gusts as high as 35-40 mph are a virtual "lock" on Monday and possible again on Tuesday. Factor in temperatures some 5-10°F below average (highs in the 40s with lows in the upper 20s to low 30s), and it's going to feel more like the first day of winter on the first day of spring. In fact, wind chills may only be in the teens early Tuesday morning and fail to exceed the low-to-mid 30s during the afternoon hours. Needless to say, you'll be trading in this week's shorts and t-shirts for winter coats and gloves early next week. Yuck!

It now appears that the colder air will have more "staying power" than previously anticipated. Wednesday may turn out similar to Tuesday with highs in the 40s, winds in the 15-30 mph range, wind chills in the 20s/30s, and a few flurries or snow showers in the air. The pocket of cold air should finally lift back northward into eastern Canada late next week, allowing temperatures to moderate back into the 50s on Thursday and Friday. However, Wednesday night could be the coldest night of the week. A bubble of high pressure may settle over the Commonwealth from Wednesday night into Thursday. If so, then mainly clear skies and light winds would promote the ideal setting for efficient, radiational cooling Wednesday night prior to Thursday's warmup. In the worst case scenario, low temperatures could bottom out in the low-to-mid 20s, effectively killing many early-blooming flowers. The cold air will penetrate into the Deep South and Tennessee River Valley, as well, potentially endangering or killing apple, pear, and peach blossoms. No matter what the eventual outcome, late-season cold shots aren't ideal. Instead, they're one of the dangers that come with an "early spring." A storm system is expected to drop southward out of western Canada and into the northern Plains and Rocky Mountains next Wednesday and Thursday. By Friday and/or Saturday, it should make the trek into the eastern United States and bring the next threat for rain back to the mid-Atlantic States. Precise details are nebulous at this distance, but the possibility of another soaking rainfall certainly exists. Check back in next Tuesday for an update, and enjoy the nice weather while it lasts.. -- Elliott


12:45 p.m. Tuesday, March 12, 2024:

In terms of wild weather, this past weekend had it all! Following Saturday's 1-2" of rain, a vigorous, upper-level low traversed the mid-Atlantic States on Sunday and triggered widespread snow showers and squalls. Most parts of northern MD, southeastern PA, and the Lower Susquehanna Valley received little if any accumulation from the squalls, but up to 1" of snow fell in places hit repeatedly by heavier squalls. Visibility was reduced to near zero at times, and some roadways briefly turned slippery and slushy. Factor in howling, northwesterly winds with gusts up to 55 mph, and Sunday could be considered one of the most miserable days so far this year. The storm system responsible for Saturday's soaking departed into the Canadian Maritimes on Monday. In its wake, skies rapidly cleared late Sunday night into Monday morning, but strong winds continued through Monday afternoon due to the large pressure gradient, or difference in pressure, between the storm system and an area of high pressure over the Deep South. Fortunately, the rest of this week will be virtually uneventful in terms of active weather. Instead, it will feel like spring is in "full bloom" with a ridge, or northward bulge in the Jet Stream, in control of the weather across the eastern United States (see below). By the end of the week, early-spring flowers such as daffodils, forsythia, dogwoods, and perhaps even Bradford pear and cherry trees may indeed be in "full bloom" with temperatures averaging some 15-25°F above normal through Friday. 

The aforementioned high pressure has moved into the Carolinas today and will shift into the southwestern Atlantic tomorrow. It will then remain positioned over or just southwest of Bermuda through Friday. On its backside, the combination of westerly winds and abundant sunshine has already boosted temperatures into the low 60s early this afternoon. They'll climb a few more degrees by 4-5 p.m. and peak in the mid-to-upper 60s. Needless to say, it will be an absolutely perfect day to get outside despite a lingering 12-25 mph breeze. West-to-southwesterly flow will persist through the end of the week and usher even warmer air into the mid-Atlantic States from Wednesday-Friday. Skies will remain partly-to-mostly sunny through Thursday, and high temperatures will soar into the upper 60s to low 70s tomorrow and climb an additional 2-3°F on Thursday. Average highs in mid-March are generally in the low-to-mid 50s across northern MD, southeastern PA, and the Lower Susquehanna Valley, but record highs are generally in the low-to-mid 80s. Thus, the unseasonable warmth won't be in record-challenging territory but instead considered "pleasant" by most people. Overnight lows are typically around freezing (32°F) in mid-March, but they'll be in the upper 30s to low 40s tonight, low-to-mid 40s Wednesday night, and low-to-mid 50s Thursday night. Temperatures in the highest elevations may even remain a few degrees above these ranges at night. There will essentially be a "nil" chance of rain through Thursday, and wind speeds will only be in the 7-14 mph range the next two days. Shorts and t-shirts will be the attire of choice for most through Friday, and it could even be warm enough for some to sunbathe. Needless to say, I will definitely fall victim to "spring fever" this week and am perfectly OK with that! 🔥😎

By Thursday night, skies will turn mostly cloudy again in advance of an approaching cold front. The low pressure system associated with the front will track eastward along the NY/PA border and into southern New England spanning Thursday night to Friday. The trailing cold front will traverse the Commonwealth from northwest-to-southeast on Friday, but temperatures should reach the low-to-mid 70s for the second day in a row south and east of I-78/81. Not until the afternoon or evening hours should the front move through the I-81 and I-95 corridors, so temperatures will have a chance to spike quickly ahead of it. Scattered showers will accompany the frontal passage, and a few rumbles of thunder cannot be ruled out in the event of enough pre-frontal sunshine. Most areas will receive less than one quarter of an inch of rain, but brief, heavy downpours are certainly possible in a few spots during the afternoon commute. Behind the front, winds will shift to the northwest and usher cooler air into the region. Despite this, temperatures will still be at least 5-10°F above normal over the weekend. Saturday should turn out partly sunny, somewhat breezy, and mild with highs in the upper 50s to low 60s. A weak bubble of high pressure will move through the mid-Atlantic States later Saturday into Saturday night and shift into the western Atlantic on Sunday, so southwesterly flow should briefly return for the second half of the weekend. However, a secondary cold front is expected to move through the mid-Atlantic States and trigger a few more showers. Fortunately, most of the day should turn out dry, and the showers should be more isolated than on Friday. I certainly wouldn't cancel or postpone any outdoor plans this weekend, but you might want to keep an umbrella handy on Sunday in the event of a brief shower. With partial sunshine in between the showers, high temperatures should once again reach the upper 50s to perhaps mid 60s closer to the I-95 corridor. Overall, this weekend's weather won't be as nice as today through Thursday but still MUCH better than this past Saturday and Sunday.

Looking ahead into early next week, a major pattern shift.. featuring a northward bulge in the Jet Stream across western North America and a deep trough across the Northeast and mid-Atlantic States.. will be responsible for much colder conditions from Monday-Wednesday. Behind Sunday's cold front, winds will shift to the northwest again and continue to drive the colder air mass southward through Tuesday. Sadly, another round of gusty winds seems inevitable with gusts of 40-45 mph a "good bet" both Monday and Tuesday. Temperatures may still be "near normal" on Monday with highs in the upper 40s to low 50s, but the core of the cold air will move overhead Monday night through Wednesday morning. As a result, the first day of astronomical spring (Tuesday, March 19) will feel more like the first day of winter with highs in the low-to-mid 40s, wind chills in the 20s and 30s, and even a few flurries or snow showers possible. I don't expect the snow showers to be nearly as widespread or intense as on Sunday, but any snow on the first day of spring is NOT ideal for warm-weather lovers like myself. Talk about a stark turnaround from this week's warmth.. hard pass! The good news is that the cold shot will be short lived and already on its way out by the middle of next week. That's been the theme of the entire winter, and the upcoming case will be no exception. A storm system will likely drop southward out of western Canada and into the northern Plains and Rocky Mountains next Wednesday and Thursday, and this will force the Jet Stream back north over the eastern United States. Wednesday could very well be a "transition day" with highs back in the upper 40s to low 50s before above-average warmth (60s?) returns late next week. Overnight lows on Tuesday and Wednesday nights will probably dip below freezing, so that could spell the end for some early-blooming flowers. Then again, what else is new? Seems to be the norm in recent years.. sigh! -- Elliott