Last Updated 1 day ago

Updated based on tonight’s NAM data just available.

Those reading my posts over the past few days know that this weekend’s weather will be be influenced by a closed upper low, a situation where the models have trouble in placement of precipitation and timing of areas of vorticity that rotate around the upper low causing instability showers to develop. As a result, this forecast is lower than average confidence.

For Saturday, the general trend has been for the main precipitation to end mid morning west of the city and later east into NJ.

Low clouds thin around noon and some sun through high clouds is likely in the afternoon. High 69-72. It will be windy.

Sunday will have a mix of clouds and sun. Instability in the mid afternoon may allow clouds to redevelop with light scattered showers possible, especially in western suburbs.  Highs 66-69. Light winds.

Last Updated 1 week ago

The model forecasts have changed for this weekend, especially for Sunday.

But, let me start with Saturday’s forecast:

The warm front that is moving through tonight (Fri) will bring heavy rain during the nighttime hours.  The models have been consistent with the rain ending between 6 and 8 AM Saturday.   There will be slow clearing by late morning and some sun is expected during Saturday afternoon. Winds will be light.  High temp 74-76, but the EKDMOS has us near 80!

The big change is Sunday’s forecast, where the models (NAM, GFS) are delaying the heavy rain until late in the afternoon and Sunday evening/night.

There’s  uncertainty whether there will be some light widely scattered showers earlier in the day.  The statistical models (MOS) have a low chance of any precip during much of the daytime hours, however the NAM has some light, widely sprinkles/showers in the morning and afternoon.

It will be windy on Sunday.  With less sun, it will be cooler with a high of 72, still above average for the middle of April.

 

 

Last Updated 2 weeks ago

Low pressure will slowly depart overnight. Showers should end before daybreak Saturday.

The models, particularly the GFS, maintains significant low level moisture for the morning and at times during the afternoon on Saturday.  So, while the model cloud algorithms have the clouds dissipating slowly in the morning, it’s possible we may see lingering low level clouds into the afternoon. High temperatures between 65 and 67, depending upon the cloud cover. Winds will be light from the W-NW

Sunday will start sunny and it will be milder.  Clouds move in during the afternoon. High 68.  Winds light, but become southerly and increasingly gusty in the later afternoon.

Last Updated 3 weeks ago

from Friday evening…

A diffuse warm front that gave us the [unpredicted] light showers today will slowly move north by Saturday afternoon. (The models didn’t pick up on this until just a few hours before the showers started.)

For Saturday- A southeasterly flow of warm air will bring unseasonably warm temperatures, along with enough mid and high level moisture aloft to create high and mid-level cloudiness.  High temperatures are forecast in the 70-73º F range for the Philadelphia area, despite this cloud cover layer which may at times be significant during the day.  Winds light from the southeast in the morning, shifting to the south and increasing somewhat after the warm front passes in the early afternoon.

[A cold front approaches later on Saturday night into Sunday morning.  The cold front is expected to bring showers to our area between 9 AM and 3 PM on Sunday as it moves through.   It will be cloudy for much of the day, possibly clearing late in the afternoon. There is some uncertainty about the timing of the showers ending, as low pressure developing along the front may cause the light showers to linger.  Total rainfall is currently expected to be less than 0.20 inches water.

High temperatures will be early in the day Sunday, before the frontal passage and will fall through the 50s during the afternoon, reaching the 40s by evening and near freezing by Monday morning.