Category Archives: Winter Storm Outlook

Winter Storm Outlook

Heavy Snow for Tuesday still not a certainty in PHL

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]

Winter Storm Outlook

Thursday Snow Update

Tonight’s NAM model data has become available.  Here are the trends– the NAM has reverted back to its forecast from a day ago. The storm is a bit less developed and a bit faster.  Total QPF values about 0.70 inches water with the heaviest snow ending about 8-9 AM Thursday.

Based on temperature profiles, the precipitation starts as rain or rain mixed with snow about midnight Wednesday and changes to snow sometime between 3-4 AM, then continues as snow until 8-9 AM.  Warm surface temperature before the storm will reduce snowfall accumulations. Best guess is about 4 inches in the immediate PHL area, up to 6-8 inches north and west, less in southern NJ.

This afternoon’s GFS had much higher QPF values and greater intensification of the storm. ( Tonight’s GFS model data won’t be available until later tonight.)

Will update tomorrow morning, but we won’t really have a handle on this storm until Wednesday evening’s model runs.

A quick 11 pm  update- the latest GFS is similar to the NAM – QPF similar (0.89)  and ending earlier  about 7-8 AM