Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* Onslaught of Winter Storms through mid-February *

1:45 p.m. Tuesday, February 4, 2025:

Punxsutawney Phil saw his shadow Sunday morning, and that means six more weeks of winter according to groundhog lore. Unfortunately, I agree with the rodent's call. After a topsy-turvy February with wild temperature swings and multiple mixed precipitation events, March may also turn out quite chilly and unsettled. Despite above-average snowfall (11.1"), January concluded as the 6th-driest on record at 无忧短视频 (see below). Moderate-to-severe drought continues to plague northern MD and southeastern PA, but odds favor a much more active pattern and vanquishing of the drought over the next 1-2 months.

A "gradient pattern," or one involving a large, north-to-south difference in temperature, is now present across the Lower 48 and will remain in place through most if not all of next week. A quasi-stationary frontal boundary will stretch from the Central States to the Eastern Seaboard and separate spring-like warmth from wintertime chill. In fact, only a few hundred miles will separate temperatures in the 70s from those in the 20s and 30s. The clash of air masses along the boundary will create and be indicative of a highly-unstable environment. As a result, the boundary will serve as the focal point for several storm systems over the next 7-10 days. The systems will ride east-to-northeastward along the boundary, and residents along and north of their track will face bouts of mixed precipitation and dangerous travel conditions. I won't be able to fine-tune the details of each system more than 2-3 days in advance, but it's shaping up to be a wild period of winter weather (see below). The first of these systems will impact the mid-Atlantic States from Wednesday night into Thursday morning. Beforehand, today and tomorrow will essentially be the "calm before the storm." A cold front moved through the region early this morning, but temperatures will remain above average this afternoon despite mostly cloudy skies and a 12-25 mph northwesterly breeze. The colder air behind the front will finally arrive tonight into tomorrow and set the stage for the impending winter storm. Skies should stay mostly cloudy through Wednesday afternoon prior to the arrival of the icy mix. Temperatures will bottom out in the 20s tonight and only reach the low-to-mid 30s tomorrow afternoon. They'll slide back into the 28-30°F range during the late-afternoon and early-evening hours and then hover there throughout the night. 

Turning my attention to our first winter storm, the primary low pressure system will actually track from the Upper Midwest into southeastern Canada spanning Wednesday night to Thursday night. However, a secondary low will form along the Delmarva or New Jersey coastline early Thursday morning and "cut off" warmer air to the south. As a result, a wedge of cold air near the ground will get dammed up against the eastern slopes of the Appalachians, but a narrow tongue of warmer air will intrude the mid-levels of the atmosphere. This type of vertical temperature configuration is almost always present during mixed precipitation events, and this case will be no exception. Sleet and freezing rain will, therefore, be the predominant precipitation types across northern MD, southeastern PA and the Lower Susquehanna Valley. The icy mix should overspread the region from southwest-to-northeast between ~7-11 PM Wednesday evening, continue overnight, and then taper off between ~8-11:30 AM Thursday morning (see below). Liquid equivalent precipitation amounts should range from 0.40-0.70", but much of that will likely fall as sleet. Sleet-to-liquid ratios are typically around 2:1, and ice-to-liquid ratios are often around 0.3:1. Thus, I expect a coating to 2" of sleet and 0.05-0.15" of ice accretion across most of the region. Less sleet and higher freezing rain amounts (0.20-0.40") are likely in northwestern VA, the WV Panhandle, western MD and south-central PA. Temperatures may creep above 32°F, especially in areas south/east of I-76 and Route 15, just before precipitation ends, but any period of plain rain should be very brief.

Unfortunately, salt and other roadway treatment chemicals are not very effective at melting sleet and freezing rain, so the Thursday AM commute will be downright dangerous. Tires cannot gain proper traction on icy roadways, so motorists are urged to avoid all unnecessary travel Wednesday night and Thursday morning. Travel will be snarled on both treated and untreated roadways during this time, and driveways and sidewalks will also turn into virtual ice skating rinks. Most schools and businesses will be closed or have a delayed opening on Thursday. Isolated power outages may also occur, and they'll be more widespread in the aforementioned regions with higher freezing rain amounts. The safest course of action will be to just stay inside, if possible, from Wednesday evening through Thursday morning. Fortunately, temperatures should rise into the 40s Thursday afternoon, so most of the sleet and freezing rain will melt off roadways after midday. A cold front trailing southward from the primary low pressure system will then sweep through the Commonwealth from northwest-to-southeast Thursday night. In its wake, west-to-northwesterly winds of 15-30 mph will usher another batch of chillier air into the region late this week. However, the cold air will lag behind the front by several hours or more.. much like today. Thus, temperatures should remain above freezing Thursday night south/east of I-81 and still reach the upper 30s to mid 40s on Friday. Roadways will quickly dry out on account of the gusty winds, and travel conditions will be much improved from Thursday. Wind chills may only be in the 20s or low 30s throughout most of the day, but at least the sun will be shining again. Just make sure to dress and layers and bundle up! 

A bubble of high pressure will briefly settle over the Commonwealth Friday night and promote lighter winds, mainly clear skies and seasonably cold conditions (20s). Unfortunately, the sub-freezing temperatures will set the stage for another mixed precipitation event later Saturday into Saturday night. A second storm system will develop in the lee of the Colorado Rockies Friday night and zip east-northeastward along the quasi-stationary frontal boundary over the weekend. The system should reach Missouri Saturday afternoon, pass through the Ohio Valley and eastern Great Lakes region Saturday night, and ultimately exit the New England coastline late Sunday morning. For residents of northern MD, southeastern PA and the Lower Susquehanna Valley, impacts from the event may be very similar to Wednesday night/Thursday AM. However, there will only be one area of low pressure with the weekend storm, and the center of that low should pass between I-80 and I-90. As a result, the heaviest precipitation should fall along and north of I-80 with lower sleet/freezing rain amounts farther south. The system is still 4-5 days away, so any subtle shift in its track can have big implications on precipitation types and amounts. At this point, a coating to 1" of snow/sleet and trace to 0.10" of ice accretion are good starting points Saturday afternoon/evening prior to a changeover to plain rain later Saturday night. A southward shift in the storm track would mean similar amounts to Wednesday night/Thursday AM, while a northward shift would mean less and a low-impact event.

Regardless of the eventual outcome, another trailing cold front will sweep through the mid-Atlantic States Saturday night, and Sunday's weather should eventually be a carbon copy of Friday's. Much like Friday night, another high pressure system will likely settle over the region on Sunday night and Monday. My bets are, therefore, on a partly-to-mostly sunny, dry and seasonably cold start to next week with highs in the mid 30s to perhaps low 40s Monday afternoon. However, the quiet weather probably won't last into the middle of the week as the quasi-stationary boundary lifts back to the north and yet another storm system forms along it. Odds favor the boundary being farther south next week in comparison to this week, so the chances of an "all-snow" event north of I-70 will be much greater. Buckle up! The coldest weather of the 2024-2025 winter season is behind us, but an onslaught of wintry precipitation lies ahead. Check back Friday for an update on the weekend system and its impacts! -- Elliott