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Sunday Forecast Update
Updated Sat 9:21 PM — No major change in the the forecast. Sunny skies. High 66° with temperatures around 63° with winds NNW around 7-10 mph for the start of the Eagles game.
Weather and Daylight Savings Time-> Standard Time
Twice a year, I feel compelled to talk about Daylight Saving Time and how it negatively affects timely access to updated evening weather model data before bedtime for those of us on the east coast.
Frankly, I love Daylight Saving Time and the extra hour of daylight we get in the late afternoon. The problem for us weather people is that major weather models are run worldwide at “00z” (Coordinated Universal Time or what used to be called Greenwich Mean Time). This corresponds to 7 PM Eastern Standard Time, but 8 PM Eastern Daylight Time. That hour makes a difference.
Since numerical weather models take 2-5 hours to ingest data, compute and process, many of the major models become available too late in the night to be any use for us on the East Coast for planning our activities the following day.
When you hear “tune back in at 11″, you’re not going to see any change in the 5 day forecast at 11PM and likely to see little change in the next day forecast; new model data simply hasn’t become available yet.
So for us weather people, the return to Eastern Standard Time makes a big difference for last minute evening updates about snow storms.
Here’s some of the changes in some model availability (eastern time) :
Oh, I just remembered, I have a forecast for Saturday and Sunday!
An upper air disturbance and a very weak trough will move through to our north on Saturday. The disturbance is visible in satellite water vapor imagery—
5 PM Friday satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine white contours) and superimposed MRMS radar. (Click on image for a larger view.)
Previously Posted Fri 8:27 PM —
Saturday
A mix of mid level clouds with some breaks of sun possible and some bright spots. Somewhat thicker clouds in the early afternoon, clearing late afternoon towards sunset. No rain. (The Canadian HRDPS has less cloudiness than our NOAA models and my forecast reflects that.)
High temperature 59º ( NBM model— location Blue Bell, PA) High temperature 61º ( NBM model— location Philadelphia, PA) uncertainty ± 2.6º (somewhat more spread than average)
Sunday
Mostly sunny. Light winds.
High temperature 62º ( NBM model— location Blue Bell, PA) High temperature 64º ( NBM model— location Philadelphia, PA) uncertainty ± 1.7º (less uncertain than average)
Updated Thu 11/02 @ 8:33 PM — It looks like a weak upper trough will affect our area on Saturday with more cloudiness than previously forecast, especially during the afternoon hours.
So while Saturday will be milder than Friday (Friday’s highs are expected to be upper 50s, just short of 60º in most places), the highs on Saturday will only reach about 61º-(62)º in some places, somewhat less than previously forecast due to the increased cloud cover. These highs may be different by Saturday.
NBM high temps for Saturday (Click on image for a larger view.)
Forecast Change for Saturday
Updated Thu 11/02 @ 6:21 PM — A quick update; I haven’t reviewed today’s models in detail. It appears on the latest GFS that a weak cold front tries to approach on Saturday with an increase in clouds. This was not previously forecast. I’ll update later with some new models.
Canadian RGEM shows cloudiness on Saturday. (Click on image for a larger view.)
Thursday through Sunday Outlook
Updated Wed 11/01 @ 8:27 PM — The cold weather expected tonight is being somewhat hyped on TV/radio, in my opinion. It’s going to be cold, but it’s already November and guess what, it sometimes gets pretty cold in November.
In case you missed it, here’s the low temperatures expected tonight (with an uncertainty of ± 2º) —
There isn’t much else to talk about regarding the weather. A sprawling area of cold high pressure will affect our weather for the next several days, with moderating temperatures over the weekend.
Next chance for rain is Monday into Tuesday.
Wednesday Outlook
Updated Tue 10/31 @ 7:53 PM — Some showers may move in later tonight (Tuesday), especially from the city eastward.
The cold temperatures expected for tonight have been well-advertised. Here’s the 18z NBM model forecast lows—
NBM low mean temperatures for Tuesday night into Wednesday morning. Some uncertainty with the above standard deviation around ± 2ºF (Click on image for a larger view.)
Clouds linger in the morning. There’s uncertainty with the degree of clearing we get on Wednesday. The GFS, HRRR, HREF all show low clouds until noon to 2 PM. The Canadian models have clearing with partly to mostly sunny skies. I’m going with the Canadian models with more sun than clouds mid day into the afternoon.
Tuesday Wednesday Outlook Update
Updated Tue 10/31 @ 9:47 AM — Perhaps you’ve noticed that the forecasts have been less than consistent in recent days? There have been larger than average spreads in the model forecasts since the weekend. Luckily, the model forecasts have begun to come closer together.
The models guidance forecasts low pressure development in the western Atlantic and the position and track are close enough for some moisture and clouds to be thrown back towards us later today, Tuesday and early Wednesday.
I get a kick out of everyone thinking the European model (ECMWF) is so great. The ECMWF runs on Sunday and Monday had the low pressure system too far away to affect us. Kudos to the Canadian model (and to some extent our GFS ) that had forecast the low consistently closer to the coastline.
Sometimes I wonder if the TV forecasters put too much stock in the ECMWF forecasts. (They’re paying thousands of dollars a year to get the ECMWF; maybe they figure they have to use it?)
The ECMWF model data has been available for free as a reduced resolution and limited parameter format for about a year and a half. It’s been very nice to have, but so far, I haven’t been that impressed with its forecasts. Our GFS, GEFS combined with the Canadian models have provided better guidance for these forecasts, in my opinion.
For longer term forecasts, the NAEFS (which combines the GEFS and Canadian Ensembles) has been more useful for these forecasts.
Tuesday: Some cloudiness moves back in from the east about 4 PM today and some showers are possible late Tuesday night into Wednesday morning.
Wednesday: Some cloudiness and even some widely scattered showers linger from Philadelphia and eastward into mid afternoon Wednesday as a weak surface low develops near us.
Today’s latest 06z NAEFS forecast for Wednesday 2 PM shows a low pressure in the western Atlantic with a weaker low over our area Wednesday. Slow clearing Wednesday, especially from Philadelphia and eastward.
Forecast Update
Updated Mon 10/30 @ 5:23 PM — The question for this week is how much will the developing low pressure system in the western Atlantic affect our area?
It appears now that the answer is that some clouds may spill up into our area later on Tuesday and some shower activity is possible in eastern areas on Wednesday, especially early Wednesday morning. Here’s the latest NAEFS—
Today’s 12z NAEFS model has some showers possibly brushing the Philadelphia area early Wednesday. Not all models are on board with this forecast. The ECMWF has the system further eastward. The latest GFS is close to the NAEFS.
Monday Update
Update Mon 10/30 8:30 AM — The fog many areas are encountering this morning was forecast by last night’s models, but not yesterday afternoon’s models. It appears that we’ll move from fog to mostly cloudy today. The front is moving slowly, even more slowly than forecast yesterday, with the actual front now expected to move through early to mid afternoon (instead of this morning.)
Due to the slow movement, another weak low pressure system is forecast to develop along the front and affect us with rain showers starting about 4-5 PM.
Monday
Previously Posted Sun 8:09 PM —
A cold front is to our northwest and its energy and associated rain is sliding up past us to our northwest—
Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine white contours) and superimposed MRMS radar. Most of the energy will move up to our northwest missing us. The upper trough visible over North Dakota will move eastward and be over us by Wednesday with much colder temperatures. (Click on image for a larger view.)
The actual front moves through our immediate area late morning on Monday. Ahead of the front, some additional showers are forecast to break out from the city and southeastward before daybreak Monday, but most of the energy with this front is moving up to New England.
Early morning sunshine will be replaced by cloudy conditions later in the morning and windy and gusty conditions as the front moves slowly through our immediate area.
By Wednesday, the trough will move moving over us, as low pressure develops in the western Atlantic.
GEFS forecast for Wednesday 5 AM shows the trough moving closer to us as low pressure develop too far off the coast to directly affect us. Temperatures in the 30s expected Wednesday night. (Click on image for a larger view.)
