The majority of deterministic and ensemble guidance within the 12Z
model suite favor less phasing of these upper level features leading
to a progressive and weaker area of low pressure. This has resulted
in a continued downward trend in QPF with the Sunday night/Monday
system and lower snow totals. Despite both upper level features now
likely well sampled by the dense RAOB network of North America...
the northern stream wave is still at a relatively high latitude and
the satellite parallax effect can contribute to poor sampling
of the northern wave possibly leading to the waffling seen in
some model solutions. For example the NAM, which has been there
more amplified model, continues to show with a corridor of 6+
inches shifting back and forth between the mountains to the
coast with the majority of model solutions now suggesting the
highest snowfall could fall closer to the coast rather than in
the foothills and mountains. At this time there remains enough
confidence in near warning level snowfall to occur, and with the
onset time still 30 hours out will plan on holding onto the
current Winter Storm Watch as is with the take away message that
this system looks weaker and the magnitude of impacts has
trended downward.
Still, Fgen forcing on the NW side of the low will lead to strong
lift within the DGZ along with good saturation that could produce
snowfall rates of 0.5 to 0.75 inches per hour for several hours
Sunday night. This will lead to the best accumulating snowfall to
occur Sunday night into early Monday morning leading to another
difficult commute Monday morning. In addition to moderate snowfall
impacting the morning commute, depending on the ultimate track of
the low there will be potential for a corridor of mixed
precipitation including possibly some freezing rain. The current
consensus is for this corridor to set up along the coast and
southern NH and possibly pushing inland for a few hours to the
foothills. Overall expectations are for the wintry mix to be less of
an impact with less than a tenth of ice accretion and the most
likely result will be lower snowfall totals. Again, the main take
away is this system has trended weaker with max snowfall amounts
topping out in the 6 to 8 inch range and winds becoming less of an
issue Sunday night with more details about winds in the long term
section as the system pulls away Monday.
The weaker low at the surface has been pronounced today starting at 12z, If this goes back to a stronger SLP and a partial phase, Its going to go back to a NW track, We will see over the next 24hrs or so.
The majority of deterministic and ensemble guidance within the 12Z model suite favor less phasing of these upper level features leading to a progressive and weaker area of low pressure. This has resulted in a continued downward trend in QPF with the Sunday night/Monday system and lower snow totals. Despite both upper level features now likely well sampled by the dense RAOB network of North America... the northern stream wave is still at a relatively high latitude and the satellite parallax effect can contribute to poor sampling of the northern wave possibly leading to the waffling seen in some model solutions. For example the NAM, which has been there more amplified model, continues to show with a corridor of 6+ inches shifting back and forth between the mountains to the coast with the majority of model solutions now suggesting the highest snowfall could fall closer to the coast rather than in the foothills and mountains. At this time there remains enough confidence in near warning level snowfall to occur, and with the onset time still 30 hours out will plan on holding onto the current Winter Storm Watch as is with the take away message that this system looks weaker and the magnitude of impacts has trended downward. Still, Fgen forcing on the NW side of the low will lead to strong lift within the DGZ along with good saturation that could produce snowfall rates of 0.5 to 0.75 inches per hour for several hours Sunday night. This will lead to the best accumulating snowfall to occur Sunday night into early Monday morning leading to another difficult commute Monday morning. In addition to moderate snowfall impacting the morning commute, depending on the ultimate track of the low there will be potential for a corridor of mixed precipitation including possibly some freezing rain. The current consensus is for this corridor to set up along the coast and southern NH and possibly pushing inland for a few hours to the foothills. Overall expectations are for the wintry mix to be less of an impact with less than a tenth of ice accretion and the most likely result will be lower snowfall totals. Again, the main take away is this system has trended weaker with max snowfall amounts topping out in the 6 to 8 inch range and winds becoming less of an issue Sunday night with more details about winds in the long term section as the system pulls away Monday. The weaker low at the surface has been pronounced today starting at 12z, If this goes back to a stronger SLP and a partial phase, Its going to go back to a NW track, We will see over the next 24hrs or so.
