Monthly Archives: January 2018

Philadelphia Area Weather Forecasts

Philly Weekend Weather Forecast

An arctic airmass with windy conditions from a strong pressure gradient caused by the exiting nor’easter will bring cold temperatures for Saturday and Sunday.

Saturday morning will have some low level instability stratocumulus clouds, that should dissipate by the afternoon.  It will be windy and very cold. High temperature about 17.

After low temperatures near zero Saturday night, Sunday will start sunny, but mid-level cloudiness is expected during the afternoon as milder air moves in aloft ahead of a warm front approaching late Monday. High temperatures near 23.

Attention will turn to late Monday as a warm front type precipitation event will occur late Monday into Monday night.

A snow to freezing rain/sleet event is likely Monday night into Tuesday.

Updates

Final Snow Update- 12 PM

The continuous snow will be ending between 1-2 PM or so in the city.

This morning’s model runs had both the GFS and NAM nearly identical, with a QPF of 0.33 between 7 AM and 1 PM, then ending.

Snow totals in my area (just northwest of the city limits) has been 4 inches at 12:00 noon.  Still a bit to go.

Snow totals measured and recorded by NWS can be found at http://forecast.weather.gov/product.php?site=NWS&issuedby=phi&product=PNS

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.

Updates

Snow Update 7AM

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.