Ok , I’m still up. It’s 11:45 and the GFS has almost identical QPF as the NAM and a bit colder. It’s looking like at least12 inches in PHL and immediate surrounding suburbs north and west.
The latest NAM data has become available and it has reverted back to a somewhat warmer, but more intense storm.
Latest QPF value has increased to 1.30 inches water.
For the Philadelphia area and immediate suburbs, it shows about 6-8 inches by daybreak, BUT it shows that temperatures in the upper atmosphere warm up so that a several hour mix of sleet and freezing rain is possible in PHL and immediate suburbs, from 6 am to 9 am before a return to all snow, ending about 1-2 pm.
The GFS model data won’t be available tonight until after my bedtime 🙂
Still too early to try to pin down storm totals. I’ll be updating tomorrow, so check back.
Sunday 6PM Update: This afternoon’s NAM and GFS model runs continue with a significant snowstorm for us starting after 1 AM Tuesday and continuing through at least late morning on Tuesday. Total QPF is about 0.80 (NAM) and about 1.00 inch (GFS) for Philadelphia. With a 12:1 ratio, we’re talking about 9-12 inches of snow as a current estimate. It’s expected to be very windy as well. Updates about 10:30 tonight.
Just a quick update:
The NAM has joined the GFS with a slightly more eastern track for the storm, putting us in the cold sector. The storm looks like it will be a faster mover and not linger into Tuesday afternoon.
Current QPF values are about 0.75 inches water for the NAM and about 1.00 inches water for the GFS. With a 12:1 ratio, we’re taking at least 8-10 inches for PHL, mostly occurring before daybreak and very early morning Tuesday. Effects of the March sun through the clouds won’t be a factor for much of the precipitation, but will allow for faster melting on roadways once the snow ends. Temperatures remain below freezing.
The details really can’t be nailed down until Monday evening. I’ll update later tonight. (The updates will be after 10:30 PM and will only be for the NAM, with the GFS data coming out an hour later.)
As has been the case this past season, forecasts of snow have changed in the short term and that’s beginning to appear to be the case with the upcoming snowfall for this Tuesday in Philadelphia. Here are the current trends–
The snow arrives earlier than previously predicted, now starting sometime Monday evening.
The NAM is much warmer than the GFS in Philadelphia with a further west track.
It’s unclear whether the warmer NAM is correct.
Heavy rain is expected in PHL by daybreak Tuesday according to the latest NAM limiting snowfall totals ( 4 inches). Heavy snow (15 inches) is expected if the GFS is correct in the immediate PHL area.
As a result of these trends, snowfall estimates continue to be uncertain in the Philadelphia area.
Expect further changes with this forecast. Stay tuned.
[stbpro id=”info” caption=”Weather Tidbit”] With the switch to Daylight Saving Time, model data becomes available one hour later. Early data previously available by 9:10 (NAM) and 10:25 -10:35 (GFS) now become available at 10:10 (NAM) and 11:35 (GFS) eastern daylight time.
So, when you watch the 10pm and 11pm news/weather on TV, keep in mind that their forecasts cannot be based on the latest GFS model runs; it’s simply not available at broadcast time when Daylight Saving Time is in effect. [/stbpro]
