As the team has briefed you early this morning about the system that is going to impact the area late tonight and tomorrow, it is time to get down to business, and finalize our prediction. This update will contain finalized timing, an updated accumulation map, and even interstate forecasts so that you can know what to expect on the roads when you need to be out on them.
As the system moves slowly to the northeast, expect precipitation to begin after rush hour and after sunset, with all precipitation being light in nature. However as the system moves Northeast overnight, more precipitation will begin to spread North, and vary significantly in precipitation type. The precipitation looks to first impact Philadelphia region a couple of hours after sunset between 5:30 and 8:00PM. The northward march of the precipitation shield will then reach Allentown in the late evening to midnight (10PM-12AM), and into the early overnight hours, with points North feeling the effects after Midnight, between the hours of 1AM and 2AM in the morning. By daybreak, and the morning rush hour, all of the areas mentioned will have precipitation falling, but the type will vary significantly by geographic location. The event should progress throughout the day, with the gradual end of the precipitation occurring from late afternoon across the southern regions to the evening for the northern regions.
As a result, the National Weather Service has issued Winter Weather Advisories for the counties highlighted below.
“Fragile” Thermal Profiles
This is the result of thermal profiles in the atmosphere being very “fragile”, in a sense. Right now, temperatures throughout the region across the atmosphere seem to be progressing as modeled, but a slight variation of the intensity, track, or mesoscale (small scale) dynamics will alter the forecast across the transition zones, or the areas that are within ten miles of each snow amount tier in the graphic below.
We mention this because there is a warm layer temperature inversion that is prevalent throughout the majority of Southeastern Pennsylvania and Central and Southern New Jersey. This affects the snowflake, as it forms above the warm layer and falls as snow. However as the snowflake reaches the warm layer, the depth and the intensity (how warm the layer is), will determine if the warm layer melts the snow completely, or if it re freezes at sleet as it exits the warm layer and falls through the last couple thousand feet of the atmosphere before reaching the surface.
Not to fear though, as the team will release a nowcast in the evening outlining any new details or features that emerge, however we do not expect any to occur.
Final Snowfall Accumulations
The graphic below indicates the final call for accumulating snowfall across the region when all is said and done. At times during the onset of the precipitation in the areas that are not forecast to receive any measurable snowfall, snow and sleet may mix in, but as the bulk of the precipitation moves Northeast, the layers of the atmosphere will be too warm to support snow, therefore changing the areas to rain. Where the colder air will remain longer, the team has brought the mention of those areas seeing up to a maximum of 1″, with the transition to rain occurring tomorrow morning. Areas that are forecast to see anywhere between 1″-2″ will be predominantly all snow, with sleet and a change of rain mixing in in those living along the southern transition zone between the Mix’1″ and the 1″-2″ accumulation tiers. However, areas that receive all snow will pick up a quick 2″-4″ tomorrow throughout the morning and afternoon, remaining all snow, with higher amounts expected. However, the team will address the “lollipop amounts” in the nowcasting update late this evening.
Morning Interstate Conditions
As you wake up tomorrow, on your commute many interstates may experience different conditions. We have provided a map to alert you what kind of conditions you will be experiencing, and where. The graphic below is valid for the morning rush hour [5AM - 7:30 AM].
Interstate 76 Corridor [I-76]
- Areas and commuters along I-76 will be too far south to pick up substantial snowfall, however may experience a mix of sleet, freezing rain, and rain along the interstate during the morning rush hour. However, as you head towards the Philadelphia Metropolitan Region, all rain is likely to fall. At times, and especially on bridges and overpasses in the northern extent of the corridor, icy conditions are to be expected. Please drive cautious and obey any special speed restrictions on highways.
Interstate 78 Corridor [I-78]
- In the morning along 1-78, snow will be the dominant precipitation type at the start of the rush hour, but throughout will quickly transition to a mix of snow and sleet, with sleet the dominant precipitation type at the end of the rush hour across the southern regions of the corridor. The snow and sleet may be heavy at times, limiting visibility. Please prepare for these conditions.
Interstate 80 Corridor [I-80]
- Snow will fall all throughout the morning commute, and be heavy at times, as certain atmospheric dynamics will cause the rapid accumulation of snow on all surfaces at the onset and throughout the duration of the rush hour. Please prepare for snowy conditions during your commute, and obey all restrictions.
Why Use Our Forecast?
We honor your read and interest. GeoEnvironmental Atmosphere is a universal organization which outputs forecasts for Snow Plowers, Emergency Managers, and the everyday public during daily travels throughout the day. The team uses Science and understanding to not only share with you what the weather will produce but the effect is will have on the “land beneath the clouds”. Later tonight, please check back for the latest as the team will release a nowcasting update.
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