Predicting snow totals is anything but easy. The average between the NAM and GFS last night probably gave the best guess for the immediate PHL area. The NBM model probably would have come up short on snow totals.
Last night’s models continue to show the heaviest snow to occur from 7 AM to 1 PM today. That said, the NAM is still showing the heaviest snow (0.40 QPF) while the GFS and the National Blend of Models (NBM) are in the 0.20 QPF range.
I’m beginning to think the NAM is the outlier for PHL and perhaps even more so north and west of PHL. If the NAM is correct, we will get another 4-5 inches of snow on top of what we’ve gotten.
BUT, If the others are correct, we will get only 3 more inches of snow on top of what’s already fallen inthe immediate PHL area.
Areas north and west will get much less, areas south and east, much more.
With such cold/dry air poised to enter from the northwest and the edge/boundary conditions that the models are attempting to get right, the accuracy of the snow depth forecast for this storm may be lower than usual.
This is the first storm where the NBM statistics have become available outside of the NWS research groups. The NBM is a statistical post-processing of multiple “ensemble” (statistical variations) of several models, particularly the GFS and the Canadian. It is touted as being the forecasting approach of the future. We’ll have to see how good it is for this storm. So far, it’s looking good.
As has been the case over the past few weeks, my forecast for sky cover (cloudiness) hasn’t been too spot-on. Yesterday was a good example, where the GFS had cloudiness for much of the afternoon, but we had beautiful sunshine. (I use humidity fields at certain levels to predict cloudiness; something hasn’t been working lately.)
I’ll take another stab at it today. Low level cloudiness (stratocumulus and nimbostratus) lifts by afternoon, but mid-level cloudiness (altocumulus and altostratus) will be with us for the rest of the day. As far as sensible weather, it should just be cloudy. The GFS also shows an ongoing chance of light drizzle through late afternoon. High temp about 63.
The warm front moves through this evening, and winds shift to the southwest.
The low level cloudiness breaks at noon, and temperatures still expected to soar to near or above 80 this afternoon.
A front moves through late Sunday night with some showers. Much cooler weather for the beginning of the week.
Postmortem: Low level clouds never broke for sunshine; this morning’s NAM (available about 10:30 AM) apparently showed this but not the GFS. I posted before the NAM was released. Either way, a poor model forecast. These sort of blown forecasts makes everyone skeptical about weather forecasting.