The ultra short range models (HRRR and LAMPS) haven’t been doing too well predicting the morning showers today (Saturday) in Philadelphia. A line of showers/thunderstorms went to our north through Bucks county and another area of showers is fallling apart to our south.
The actual warm front boundary is very diffuse, but based on dew points, it’s just to our west and south. The GFS-based LAMPS still maintains a chance of showers between now and 4 PM, but it’s hard to hang your hat on that forecast.
If the warm front passes through and we get breaks of sunshine, instability alone could trigger scattered showers, but predicting location is going to be even more difficult than this morning’s forecast when we had a distinct trigger.
Sunday is still looking to be sunny, hazy, hot, humid and dry.
The models are are showing the warm front to move through early Saturday morning, accompanied by showers and maybe a thunderstorm. After the showers and morning cloudiness, there should be breaks of sunshine by the afternoon, as temperatures rise towards 90 with dewpoints in the uncomfortable low 70s.
High pressure that has been dominating our weather Thursday and today, Friday, will move off to the east today, allowing a weak warm front to pass over Friday night. An increase in humidity and clouds will be noticeable tonight and Saturday.
Saturday will be affected by the lingering weak warm front boundary, diffuse weather features, and a moist flow of air from the south. Considerable cloudiness is expected on Saturday; there will likely be bright spots and breaks of sun mid-day, but an increasing chance of showers/thunderstorms is likely later Saturday afternoon and evening. Most of Saturday will be rain-free, but wherever scattered thunderstorms do develop, heavy downpours are possible. There won’t be any distinct location-predictable triggers for the showers much in advance.
It will be very warm and very humid Saturday (dewpoints in the low 70s) but the cloudiness is expected to reduce high temps to about 88. If we get more sun, temps may raise above 90.
Sunday currently looks to be be partly sunny, hot and very humid. High in the low 90s and dewpoints in the uncomfortable 70s. Scattered showers and thunderstorms possible, but much of the day rain-free.
The weak summer pressure pattern has caused the model forecasts to have been anything but consistent for this coming weekend’s weather, (even this past week’s forecasts have been less than stellar). Expect changes in the forecast each day. A lower than ususal confidence forecast this weekend.