Some interesting observations about upcoming weather for the Philadelphia area—
The rain now expected Thursday into Friday morning was not really picked up by the models until two days ago. The exception was the new FV3-GFS, which predicted the coastal storm almost two days before the other models jumped on board. (The ‘exclusive forecast’ from one of the TV stations was predicting a full week of dry weather just last weekend.)
This upcoming weekend, especially Friday through Saturday, will be anything but Spring-like. Windy conditions and unseasonably cold temperatures are expected, especially on Saturday.
The FV3-GFS is predicting a very cold outbreak Monday night into Wednesday next week. Included is a possible changeover from rain to snow late Monday into Monday evening. Maybe an outlier of a forecast, but something to watch, considering the model’s success this week.
The medium range model forecast for the weekend sems to be in flux as details of the development of several systems seem to have changed over the past few days – a storm expected to develop Friday into Saturday is now forecast for Saturday into Sunday. It appears that we will get rain from this system. I would not be surprised if the timing changes again.
There’s also a small impulse forecast for this Thursday into Friday which keeps changing intensity and track.
So a very uncertain weather outlook for this weekend in Philadelphia.
The models are consistent in the appearance of a deep dive in the jet stream for much of next week caused by arctic high pressure. As a result, well below average temperatures are likely for much of next week. Storm development with this jet dip is expected to be off-shore, but that could change.
For snow lovers, it looks like there’s disappointment in the forecast. Those several disturbances mentioned to move along the flat jet stream are still coming through, but not with much if any snow. Here’s the latest–
The Saturday disturbance still looks like it will miss us to our south.
The Sunday evening disturbance looks to be less organized with a mix of rain and maybe some wintery mix.
The Wednesday disturbance currently appears to move slightly to our north, giving us mostly rain.
Previous prediction of 200 mb winds
Current prediction of 200 mb winds
The flat jet usually doesn’t allow much if any development and shape of the jet is now anticyclonic vs cyclonic. Furthermore, it moved from a position to our south (cold for us) to a more northern position which allows warmer air to move in.
Just a quick note that the first of the impulses expected to move along the fast jet stream track will approach on Saturday. It appears that this most likely misses us to our south, according to the ECMWF.
This afternoon’s GFS gives us a light 1 inch accumulation on Saturday, as does the Canadian CMC.
Another impulse moves by Sunday afternoon. The GFS is more aggressive with this second system and gives us a QPF of about 0.30 inches water. The forecast for these systems is low confidence at this time.
We’re almost done with the current storm. The “cold air damming” proved to be more persistent than any of the models had forecast; the cold low level temperatures and the mixed precip remained somewhat longer than expected.
We’re continuing in an active weather pattern. The high level wind flow will act as a fast highway for moisture and disturbances to transit across the country–
We’ll be seeing a chance for precipitation almost every 36-48 hours! Note that the track is just to our south. There are several more chances for snow and mixed precipitation over the next week. Details are uncertain, but I’m keeping an eye on it. Stay tuned.