Actual surface temps are still quite cold even if air temps (2M) are not.
EDIT - also, as noted below, dews are still pretty low
And then of course there is this from Mt. Holly:
.NEAR TERM /THROUGH TUESDAY/...
Continued concern for significant icing across portions of eastern
Pennsylvania and northern New Jersey through Tuesday.
After examining the latest global and hi-res model runs, no
significant changes were made to the forecast, with a slight warming
trend leading to slightly lower snow and ice totals. Nudged
temperatures up a touch with the early morning update. Some
scattered rain and mixed precip showers are moving across the
region, but this hasn`t amounted to much at this point. Expect
precip to gradually fill in as the morning progresses, though
the main event still arrives tonight.
One interesting observation has been a slight cold bias across much
of the guidance tonight, which is curious given the appreciable snow
pack across the entire region. Temperatures yesterday tended to also
climb a degree or two above model consensus. This bias was closely
taken into consideration with the latest deterministic model
forecasts. One major discrepancy is that the global models, namely
the CMC and GFS erode the CAD quite quickly tomorrow afternoon and
evening while the NAM, HRRR, and ARW keep the shallow cold air wedge
across the Lehigh Valley and NW New Jersey. I tend to side with this
given past performance in such events. The placement of the dominant
surface high to the north across Canada is not completely favorable
for persistent cold air advection down the lee side of the
Appalachians. Forecast soundings from some of these hi-res models
lead to me to suspect this wedge wont erode until later Monday night
into Tuesday morning for these areas, especially across the Poconos
and Sussex County, NJ.
Went with a highly blended approach with PoP and QPF grids but the
output seems quite reasonable and discussion with surrounding
neighbors increased confidence in the overall thinking. With that,
expect a gradual transition from sleet at the onset today to
freezing rain and then to plain rain from the I-95 corridor east.
Rain will gradually build northwest through the night Monday night
as the CAD erodes with stronger warm advection ahead of the surface
low. There appears that there will be two rounds of precip with the
first this morning and afternoon being the lighter of the two, and
confined mostly to areas west of I-95. A brief lull will see another
round of precip move into the area associated with the main surface
low and associated shortwave. This will be where the greatest icing
occurs as temps hold steady and we lose the solar component
overnight. The resultant ice and snow grids were lowered slightly to
account for the aforementioned details. Again, no headline changes
were made with the feeling that impacts continue to warrant the need
for a warning even if exact ice accumulations don`t completely reach
criteria.
