Sat 8 AM : Sunday forecast uncertainty: Last night’s model runs show differences between the NAM (cloudy, cooler and windy High low to mid 70s) and the FV3-GFS (A mix of sun and clouds, breezy warm. High near 80. ) Will need to wait for today’s models to have a better handle on Sunday’s weather.
Fri 11 pm: Tonight’s NAM shows considerable cloudiness again for Sunday afternoon. Reduced high temp on Saturday to 81.
Periods of high, thin cloudiness (cirrostratus) will be with us over the weekend, as this moisture high in the atmosphere (34,000 ft) is all that will be able to move towards us from the south. Rain in the Carolinas will be suppressed to our south, as high pressure builds over our area from the northwest, keeping us dry.
Saturday will be similar to today (Friday). Periods of sun and high thin cloudiness. High temperature 84 (EKDMOS) or 81 (NBM model).
Sunday is looking better than it did earlier. While it appeared that there would be more clouds than Saturday, things have changed with today’s models. Periods of sun and high clouds. it appears now that there should be more sun than Saturday! No rain expected. High 81 (NBM) or 78 (EKDMOS model).
Fri AM Update: With significant activity to our south (rain and low pressure development) in the Carolinas, the models are forecasting a layer of thin, high clouds in our area for much of Friday, Saturday and early Sunday before the lower clouds move in late Sunday. I’ll update this evening.
Earlier this week, (Tuesday) I wrote that the weekend looks to be spectacular, only to hedge a bit with an update Wednesday morning that some clouds may move in on Sunday.
Saturday is still looking wonderful, with low humidity and high temperatures in the low 80s. (Much cooler at the shore due to an easterly wind flow.)
Things have changed for Sunday. Low pressure is expected to organize late Sunday off the Caroline coast. Moisture is expected to creep up from the south, in the form of clouds for our area Sunday early to mid afternoon. Rain is [currently] expected to stay to our west and south (affecting Delaware) on Sunday late afternoon. Sunday will be breezy and cooler.
I’m always on the lookout for the best forecast model. (Anyone into weather is probably on this ongoing search.) The issue is that some models do better in different weather patterns.
The only model that got close to predicting the thundershowers last night that affected the northwest suburbs and some of the Philadelphia area was a model that I haven’t until recently focused upon- the WRF with its two variants- the WRF-NMMB and the WRF-AFW.
The WRF (Weather Research Forecast) model is a short range (48 hour) model that has a high resolution. It’s only run twice a day for the US.
It did well last night and also with the storms last week. So let’s see how it does today.
The WRF is forecasting showers and thunderstorms to develop as early as 2:30 PM (earlier far northwest suburbs). Most likely time for Philadelphia is 3-5 PM. High temperature forecast for today is 84-85 before the showers move in.