Category Archives: Philadelphia Weather Outlook

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#weather #paweather #wx #pawx #philadelphia

Update Tue 3/14 8:44 AM — Snow flurries/snow showers have developed, as predicted. Last night’s HRRR and RAP models have the likelihood of even greater snow shower coverage during the afternoon.

NEXRAD Radar at 7:54 AM today. Courtesy of WeatherTAP.com

Update Mon 3/13 7:20 PM — This afternoon’s models are predicting surface temperatures to drop to freezing just outside of the city Tuesday morning. There’s the chance of some icy conditions early that should dissipate by the mid morning in most areas.

Most of the precipitation still expected to be east of us, but wrap around moisture will cause snow showers during the day with high winds. Much of the snow shower activity may be later in the afternoon.

NBM temperatures and precipitation type at 7AM. Note the 32º line. The standard deviation is 1.6º meaning that there’s uncertainty where the freezing line is. It could be closer to the city, it could be further. Blue indicates increasing chance of snow showers. (Click on image for a larger view.)

Mon 03/13 @ 11:27 AM — Added wind meteogram below—

The NBM (which tends to be low with winds) is forecasting wind gusts in the 45-50 mph range for our area on Tuesday. (Click on image for a larger view.)

There has been an eastward trend to the storm track with the latest models. (Background on this storm can be found here.) This translates into lower total precipitation in our area to just 0.20 to 0.30 inches of precip (meaning rain or “snow water equivalent”.)

Here’s the latest NAM-NEST total precip forecast for this storm —

This morning’s 12z NAM-Nest shows the majority of the precip will be east of us and into New England. (Click on image for a larger view.)

With the reduction of total precipitation, the possibility of any accumulating snow here has been even further reduced to close to zero. The NAM-NEST shows almost nothing, the CMC HRDPS has a small accumulation near Doylestown.

For today, Monday, the rain doesn’t really get started here until 3-4 PM, moving in from the southeast.

The NBM shows this well—

Today’s 12z NBM forecast for 4 PM Monday. Rain moves in from the southeast as the storm intensifies in the Atlantic. Black is cloud cover. (Click on image for a larger view.)

As for the change of rain showers to snow showers, the NBM is showing the transition to occur early morning hours Tuesday. Most of Tuesday will be non-accumulating snow showers. The snow showers will linger until about 8 PM.

NBM shows an 81% chance of snow showers at 4 PM Tuesday. (Click on image for a larger view.)

Stay tuned for any additional changes.

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#weather #paweather #wx #pawx #philadelphia

Deep Storm Monday Through Tuesday

Update Sun 3/12 7:39 PM — Several of this afternoon’s higher resolution models show enough cold air being brought in to this system by early Tuesday morning that the precipitation will be falling here as snow. Surface temperatures above freezing will limit or prevent accumulation. Solar effects (insolation) through clouds and high March sun angle will further prevent accumulation on dark roadways.

Still a very dynamic system that needs to be watched.

Previously Posted Sun 4:38 PM —

This week’s weather will start out with a coastal storm that is expected to first give us rain Monday through at least early Tuesday as it moves northward. This storm is then expected to retrograde toward Cape Cod and undergo “explosive cyclogenesis“. (yes, the “bombogenesis” as they like to call in on TV.)

Extremely low central surface pressure with blocking high pressure in the North Atlantic will result in very high winds and heavy rains and inland snow to New England. We will be indirectly affected by this storm in it’s advanced form.

It appears that the light rain tonight will move in later tonight (Sun), after midnight. Monday will be increasingly rainy and windy.

Here’s the NAEFS forecast for 11 PM Monday night —

Today’s 12z NAEFS model forecast for Monday night. Coastal low (1) will sling back rain into our area on easterly winds. The upper level low (2) will pull the surface low to the coast as its normal northeastward movement will be blocked by strong high pressure ridge (3) in the North Atlantic.

By Tuesday evening, the low has retrograded close to the Massachusetts coastline and undergone the extreme cyclogenesis. Notice it’s still raining here!

NAEFS model forecast for Tuesday evening show the surface low (1) and the upper low-blue (2) have become almost vertically stacked. Strong cyclonic flow around this storm (white arrows) will bring cold windy conditions with continued rain. Notice the 32º surface line (white on my maps) is well west of us in central PA. keeping it rain for us. (Click on image for a larger view.)

By Wednesday, things dry out here and it will become milder towards the end of the week. Another rainstorm, faster moving, affects us next weekend.