Sun 2:33 PM Forecast Review — Some sunshine with increased instability from upper air disturbances gave us the showers. Some moved through an hour earlier than forecast by the HRRR. Cold air aloft resulted in some of the precipitation coming down as a frozen form called “graupel“.
NEXRAD radar at 2:15 PM with 500 mb wind streamlines (red). The radar image above looks remarkably similar to the NBM simulated radar forecast graphic just below (Click on image for a larger view.)
Update Sun @ 8:49 AM — Last night’s models are on-board with some sun and clearing about noontime followed by the development of an area of showers that moves through between 2-4 PM along with an increase in WIND. The showers will be from an upper/mid-level area of vorticity swinging through.
09z NBM simulated radar forecast for 3 PM Sunday (Click on image for a larger view.)
Update Sat @ 9:57 PM — This afternoon’s and tonight’s early models continue to show clouds and showers in the morning Sunday, but with breaks of sunshine moving in between 11 AM and 1 PM.
Despite intervals of sunshine, periods of clouds and widely scattered showers are predicted during the afternoon, the result of instability and several upper/mid-level air disturbances, especially in the 2-5 PM time frame.
The latest HRRR shows an area of significant showers around 3 PM or so. The air aloft will be very cold and some of those showers may fall frozen as graupel. Areas south of the city will have the most sunshine. It will become WINDY in the afternoon.
Tonight’s 00z NBM cloud forecast (shades of grey) and simulated radar (multi-colored concentric contours) at 2PM Sunday. Notice the areas of little to no clouds interspersed between scattered showers. (Click on image for a larger view.)
Update Sat @ 10:14 AM — Reviewing this morning’s early models along with last night’s models, it appears that Sunday will have showers in the morning, with additional showers AND some sunny breaks in the afternoon. The showers in the morning due to low pressure; the showers in the afternoon due to high instability and ‘self-destructive sunshine’, with a secondary low developing off the coastline. Windy.
Despite the occasional sunny breaks, the amount of showers forecast may put a damper on outdoor activities.
Today’s 12zNAM-NEST Simulated Radar and cloud forecast for 1 PM Saturday. Just a snapshot of a very changeable situation. But most of the area has clear skies despite the showers occurring in some areas. (Click on image for a larger view.)
Update Fri @ 9:44 PM — Just reviewed the ECMWF and tonight’s latest NBM. There’s more uncertainty regarding Sunday’s forecast, specifically how long the showers linger into the afternoon and how much clearing and sunny breaks we’ll see. The Sunday forecast posted below is currently on the optimistic side of things. I’ll update tomorrow.
High pressure builds in for Saturday. A low pressure system over the Great Lakes pulls an upper trough through on Sunday.
GFS model forecast for 8 AM Sunday morning. Showers and clouds will break for a mix of clouds and sunshine. The upper trough (as outlined in the red 540 thickness line) will cause instability clouds and widely scattered showers in the afternoon. (Click on image for a larger view.)
Saturday
A sunny but cool as high pressure moves in. Average seasonal high temperatures are 59-60º, but our high will be 54.6º sd 1.4º NBM model Blue Bell.
Previously Posted Fri 5:26 PM —
Sunday
An upper trough moves through with a weak cold front. Clouds and showers in the morning will break for a mix of clouds and sun in the afternoon. Instability widely scattered showers possible in the afternoon. WINDY in the afternoon. High temperature 54.6º (again!) sd 1.6º NBM model Blue Bell.
Winds
NBM wind forecast for Blue Bell, PA (Click on image for a larger view.)
2 thoughts on “WEEKEND WEATHER FORECAST”
Hello
Why is the Philadelphia area so windy? I don’t remember it being so windy. It seems to always be extra windy,
Frank
That’s a question and an observation that I’ve received before. Wind is the result of pressure differences. Pressure differences are the result of temperature differences, whether they occur between different regions or at different vertical heights. From basic physics, by definition, temperature is a measure of the average kinetic energy of a gas (air). With average temperatures having increased in the past 50 years, there’s more energy, expressed as an increase in winds.
On a more meteorological level, it could be that the average position of the jet stream is different, as a result of the larger extent of warmer air in the tropics. A search in the American Meteorological Journals (AMS.org) should provide a more answers and perhaps confirm your suspicion about wind increases.
Hello
Why is the Philadelphia area so windy? I don’t remember it being so windy. It seems to always be extra windy,
Frank
That’s a question and an observation that I’ve received before. Wind is the result of pressure differences. Pressure differences are the result of temperature differences, whether they occur between different regions or at different vertical heights. From basic physics, by definition, temperature is a measure of the average kinetic energy of a gas (air). With average temperatures having increased in the past 50 years, there’s more energy, expressed as an increase in winds.
On a more meteorological level, it could be that the average position of the jet stream is different, as a result of the larger extent of warmer air in the tropics. A search in the American Meteorological Journals (AMS.org) should provide a more answers and perhaps confirm your suspicion about wind increases.