Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* More Tranquil and Much Milder for Last 7 Days of February *

Brief 12:30 p.m. Friday, February 21, 2025, Update: 

As expected, Wednesday's storm was "a swing and a miss" for northern MD, southeastern PA and the Lower Susquehanna Valley. An upper-level disturbance traversed the Commonwealth on Thursday and brought scattered snow showers to the region, but travel impacts were minimal due to very little if any accumulation in most areas. Behind the disturbance, winds increased dramatically Thursday afternoon, and the blustery conditions are still with us today. A tight pressure gradient, or difference in pressure, between the aforementioned storm system (currently centered just south of Newfoundland) and a strong high pressure system over the Central States is to blame for this bout of howling winds. Northwesterly winds will be sustained at 15-30 mph this afternoon with gusts up to 40 mph at times. The Jet stream is also still exhibiting a pronounced, southward dip along the Eastern Seaboard, so high temperatures will be around 10°F below normal this afternoon (low-to-mid 30s) despite mostly sunny skies (see below). Wind chills will be in the teens throughout the day, so dress in layers and bundle up before heading outdoors! In addition, motorists should keep a tight grip on the wheel and be alert for blowing objects/debris on roadways due to the strong winds.

Fortunately, the pressure gradient across the region will decrease/relax significantly over the next 12-24 hours. As a result, winds will gradually subside tonight and then remain light over the weekend (see below). The aforementioned high pressure system will settle into the Southeast, Carolinas and southern mid-Atlantic States this weekend and promote dry, tranquil and more seasonable conditions. To the north of the high, west-to-southwesterly winds will usher noticeably milder air into the Commonwealth and Delmarva Region. The large-scale subsidence, or sinking motion, beneath the high will also support partly-to-mostly sunny skies both days (see below). Overall, this weekend's weather will be a HUGE improvement and welcome change from the recent stretch of windy and bitterly cold conditions. With highs in the low-to-mid 40s on Saturday and mid-to-upper 40s Sunday, it may actually feel "pleasant" outside, especially with a sun angle now equivalent to that of mid-October. You may just need to wear a light jacket or sweatshirt for outdoor activities each afternoon. After one more unseasonably cold night (tonight) with lows in the mid teens to perhaps 20°F, both Saturday and Sunday nights will turn more tolerable with lows generally in the mid-to-upper 20s. I'll take it!

Looking ahead into next week, the relatively tranquil weather and gradual moderating trend should continue. The large-scale pattern will continue to become less amplified as the Jet Stream takes on a "zonal" configuration. Zonal flow supports weak, fast-moving storm systems and "minor" precipitation events, and this case should be no exception. In addition, the trough over the Eastern States will vanish, so temperatures may actually be several or more degrees above normal from Monday-Wednesday. There will still be a mean "ridge" over the western U.S., but westerly flow will direct some of that warmth across the entire nation (see below). A moisture-starved, clipper-type system will zip eastward across southeastern Canada spanning Sunday night to Monday night, but we'll be in the system's "warm sector" and far away from any precipitation. A southwesterly breeze of 12-25 mph may even boost highs into the low 50s Monday afternoon for the first time since January 29th in some spots.

Another fast-moving disturbance may zip through the Commonwealth on Tuesday or remain several hundred miles farther north. In the first scenario, mostly cloudy skies and scattered showers would accompany highs in the 40s Tuesday afternoon. In the second scenario, partial sunshine and gusty, southwesterly winds could boost highs into the mid 50s to perhaps even 60°F due to an absence of any rain showers. Regardless of the eventual outcome, a bubble of high pressure should settle over the mid-Atlantic States on Wednesday and promote mostly sunny and pleasant conditions with highs in the upper 40s to perhaps mid 50s. Temperatures should also be well above normal Monday, Tuesday and Wednesday nights with lows in the "balmy" 30s. Ice on area streams and rivers will melt by the end of next week, and any lingering patches of snow/ice will also be history. A third system and its associated cold front is expected to bring another bout of scattered showers to the region on Thursday, but weekly rainfall totals will be light and on the order of 0.25" or less. High temperatures could reach the 50s again Thursday afternoon before the week concludes on a partly sunny, dry and cooler note behind the frontal passage. After the recent onslaught of winter storms and bouts of frigid air, I couldn't be more excited for the impending warmup! -- Elliott

1:30 p.m. Tuesday, February 18, 2025:

As expected, a widespread 0.75-1.50" of liquid equivalent precipitation fell across northern MD, southeastern PA and the Lower Susquehanna Valley over Presidents' Day Weekend (see below). An initial thump of snow dumped a coating to as much as 3" of snow on the region over a several-hour period spanning late Saturday morning to the middle of the afternoon, but precipitation generally fell as plain rain for the rest of the weekend. A vigorous cold front swept through the mid-Atlantic States Sunday afternoon and was accompanied by a gusty line of showers and embedded thunderstorms. In addition, small hail fell for a few minutes at Millersville University, and some of my students reported hearing a low rumble of thunder. Behind the front, west-to-northwesterly winds of 20-40 mph with gusts of 50-60 mph buffeted the region from late Sunday afternoon through early Monday evening and caused power outages and downed trees and powerlines. Peak gusts on Sunday reached 47 mph at York Airport, 53 mph at Harrisburg International Airport and 58 mph Lancaster Airport. Gusts at the three airports maxed out at 45 mph, 48 mph and 54 mph, respectively, on Monday.

An incredibly tight pressure gradient, or difference in pressure, between the deep storm system over the Canadian Maritimes and a strong, Canadian high pressure system over Saskatchewan was responsible for the howling winds over the past 48 hours (see below). Fortunately, the pressure gradient across the mid-Atlantic States slackened overnight and will continue to do so over the next 12-24 hours. Thus, winds this afternoon won't be as high as yesterday, but they'll still be sustained at 12-25 mph with gusts up to 35 mph at times (see below). A deep trough, or dip in the Jet Stream, over the eastern United States will also remain in place through the end of the week, so unseasonably cold weather will accompany the blustery conditions. Low temperatures bottomed out in the teens early this morning, and minimum wind chills were between 0-5°F in most spots. Despite partly-to-mostly sunny skies, highs will be around 15 degrees below average this afternoon, or generally in the mid-to-upper 20s. Factor in the winds, and it will feel like it's in the high single digits and teens outside. As a warm-weather lover, this stinks.. and stings! 🥶😡

Winds will finally subside tonight, but it will remain bitterly cold with lows in the teens and minimum wind chills between 5-10°F. Wednesday will then turn out mostly cloudy and very cold with high temperatures still around 15°F below normal and within 1-2°F of today's numbers. Winds will be much lighter and on the order of 8-16 mph, but that still places wind chills in the teens. For the third night in a row, temperatures will then bottom out in the teens again early Thursday morning. Due to the frigid conditions, it will be imperative to dress in layers and wear a winter coat and gloves before heading out into the elements this week. Limit time outdoors and cover all exposed skin, as well, during the overnight- and early-morning hours to prevent frostbite or hypothermia. In addition, leave faucets dripping the next two nights to prevent pipes from freezing or bursting.

Last week, I discussed the potential for a major winter storm late this week and outlined three distinct possibilities (a "miss," a "light-to-moderate" event, and a "blockbuster snowstorm"). Contrary to my expectations several days ago, it now appears that the system will be "a swing and a miss" for residents of northern MD and southeastern PA. Over the last 24-48 hours, all major computer models have trended weaker, flatter, less amplified and more strung out in their depiction of the upper-level energy associated with the storm system (see below). For snow-lovers, this is the opposite of what was needed to get a "blockbuster storm." Instead, the system will now remain weak and suppressed, ultimately zipping from the Gulf Coast off the southeastern U.S. coastline spanning Wednesday into Thursday. There is also another issue. The trough will be positively tilted over the Ohio Valley and central Appalachians with its axis oriented from southwest-to-northeast. In order for a low pressure system to rapidly intensify and "hug" the immediate coastline, the trough axis must be neutrally- or negatively-tilted (oriented from southeast-to-northwest). In our situation, the flow will remain west-to-southwesterly ahead of the positively-tilted trough and push the surface low farther out to sea and away from the coast (see below). As a result, it looks like "game, set, match" for the Lower Susquehanna Valley in terms of much if any snow. The upper-level low pressure system will traverse the Commonwealth on Thursday and bring scattered snow showers to the region, but I don't anticipate more than a slippery coating of snow in most spots with amounts generally below one half of an inch. Better luck next time! 

The storm system will ultimately intensify hundreds and hundreds of miles off the Carolina coastline later Thursday into Friday but do so "too late in the game" for us. However, the tight pressure gradient between it and a Canadian high pressure system over the Central States will result in another bout of strong winds later Thursday into Friday. Fortunately, gusts won't be of the "damaging" variety this go around, but they'll still reach 30-40 mph at times during this period. High temperatures should be in the upper 20s again on Thursday and only slightly higher (low-to-mid 30s) on Friday, so wind chills will be in the single digits again Thursday night and the teens both Thursday and Friday afternoon. Be alert for slick spots on Thursday as a result of the snow showers, but I don't anticipate too many travel impacts. Following an overcast Thursday, skies will likely turn partly sunny again on Friday as drier air filters back into the mid-Atlantic States. 

Looking ahead into the upcoming weekend and early next week, the large-scale pattern will "relax" and become less amplified. High-latitude blocking and the large, Jet Stream ridge centered over and to the southwest of Greenland (a west-based -NAO) will vanish, and the northward bulge in the Jet Stream over western Canada will also disappear. As a result, the flow across the Lower 48 will turn zonal (west-to-east). Zonal flow supports weak, fast-moving storm systems and "minor" precipitation events, and I expect this case to be no exception. In fact, winter may very well be "on its way out" after this week. That's not to say we won't get another "light-to-moderate" snowstorm in March, but it would have to be a "thread-the-needle" type of event. Anyhow, the upcoming weekend looks relatively "nice" by late-February standards. The aforementioned high pressure system will shift into the Carolinas and southern mid-Atlantic States and promote lighter winds, partly-to-mostly sunny skies and milder conditions. After a week of brutally low temperatures, highs will finally be back around normal on Saturday (low 40s) and perhaps even a bit above normal by Sunday (mid-to-upper 40s). Overnight lows will also be more tolerable and generally in the 20s. With the sun angle increasing dramatically by the week, it may actually feel "pleasant" outside each afternoon, and you may need to only wear a light jacket or sweatshirt for outdoor activities. I'll take it! The milder conditions should last into early next week, as well, with temperatures near- to slightly-above normal from Monday-Wednesday. A moisture-starved, clipper-type system may zip eastward along the U.S./Canadian border from the Upper Great Lakes region into northern New England spanning Monday to Tuesday, but no more than some sprinkles or a brief shower would impact the southeastern half of the Commonwealth. Overall, the weather pattern looks a lot more temperate and less active after this week. After the recent onslaught of winter storms, we're due for a break, and I'll welcome the "calm" with open arms! -- Elliott