Winter Storm Warning issued for Montgomery, Bucks, Philadelphia counties ahead of weekend system

A Winter Storm Warning has been issued for Montgomery and Bucks counties as a powerful winter system is expected to bring heavy snow, ice, and dangerous cold from Saturday night through Monday afternoon, according to the National Weather Service.

Forecasters said the storm could produce 8 to 12 inches of snow in Montgomery County, along with ice accumulations near three-tenths of an inch, while Bucks County could see 10 to 15 inches of snow with lighter icing. 

The warning is in effect from 7 p.m. Saturday through 1 p.m. Monday.

The National Weather Service warned that a combination of heavy snow, sleet, and freezing rain could make travel very difficult to nearly impossible, particularly during the Monday morning commute. 

Significant ice buildup on power lines and tree limbs may lead to widespread and prolonged power outages, especially in areas closer to the Interstate 95 corridor, according to the NWS.

Meteorologists said confidence continues to increase that the storm will bring major impacts across southeastern Pennsylvania, as a low-pressure system moves northeast along the East Coast while bitterly cold air settles into the region from Canada, according to the NWS. 

Snow is expected to begin Saturday evening, with a period of mixing or freezing rain possible Sunday before temperatures plunge again.

In addition to snowfall, the region is expected to experience dangerously cold temperatures and wind chills lasting well into next week. Wind chills in the single digits or below zero are possible overnight, increasing the risk of hypothermia and frostbite during prolonged exposure.

No flash freeze is expected with this event. Snow and ice covered surfaces will be slow to melt, with well below freezing temperatures through most of next week, the NWS said.

Officials urged residents to avoid unnecessary travel, prepare for possible power outages, and keep emergency supplies on hand. Drivers who must travel were advised to carry extra food, water, and a flashlight in their vehicles.

Road conditions can be checked by dialing 511, and residents were encouraged to monitor local forecasts and municipal alerts as conditions evolve.

How can there be sleet with 20-degree surface temperatures?

The NWS said precipitation falls through a warm layer of air temperatures, just above freezing, about 6,000 to 9,000 feet above ground. This is enough to melt snow, despite a surface air temperature of 23 degrees, the NWS said.

The melted snow then falls back through a deep layer of well below-freezing air temperatures, refreezing into sleet. According to the NWS, sleet has a much lower liquid ratio, about 3:1,  and is much more dense compared to snow, at around 10 to 15:1, which is why sleet results in lower accumulation totals than pure snow.

Storm timeline and evolution

The NWS Friday morning briefing shows this is a long-duration, multi-phase winter storm, not a quick hitter.

• Saturday night (after 7 p.m.)
  • Snow overspreads eastern Pennsylvania, New Jersey, Delaware, and eastern Maryland.
  • Conditions deteriorate quickly after sunset as temperatures fall below freezing.
  • Roads may initially become snow-covered, then increasingly icy as mixed precipitation develops.
    
    
• Overnight Saturday into Sunday
  • Periods of heavy snow continue.
  • For Montgomery County especially, snow mixes with sleet and freezing rain at times, increasing ice accretion.
  • Travel conditions worsen overnight and remain hazardous into Sunday morning.
    
    
• Sunday
  • Snow, sleet, and freezing rain persist through much of the day.
  • Ice accumulation becomes a primary concern, particularly on trees and power lines.
  • Plowing effectiveness may be limited due to ongoing precipitation and falling temperatures.
    
    
• Sunday night into Monday morning
  • Wintry precipitation tapers off from west to east.
  • Conditions remain dangerous due to untreated roads, refreezing, and power outage risks.
  • The Monday morning commute is expected to be significantly impacted, even after precipitation ends.

 Temperature and cold-air concerns

The NWS emphasized that the storm is followed by bitter cold, which compounds impacts:

• Temperatures remain well below freezing throughout the event.
• Wind chills between -10°F and 0°F are expected across much of the region.
• In higher elevations nearby, wind chills could drop below -20°F.
• Brief temperature rises may occur during mixed precipitation phases, but not enough to melt ice.
• After the storm exits, refreezing becomes a major hazard, extending travel issues well into Monday and Tuesday.

We will continue to update the community on the storm throughout the weekend.