3z SREFs has a mean snowfall of 6.45" over HYA from tomorrow evening through Monday evening. Some members are over 20" of snow and half are about 12"+, so there is a lot of spread in the means, and plus while the 00z EURO didn't show much precipitation over Cape and Islands, the model did up the ante with the upper level low and the surface low strengthening. Also, the HRRR 6z run shows a lot of lightning developing with the surface low as it reaches the coastline, this could impact the surface low track by pushing it more towards the coastline as it ramps up within the upper-level trough.
Models bring a chance at snow after 18z tomorrow afternoon. Right now the NWS has a 20% chance for snow over the area, while I think it is something near 40% right now. I am a little more bullish due to short range guidance getting more amped up in the southern stream disturbance and exiting the northern stream energy faster to the north of the storm. This energy is causing a confluent flow over the northeastern CONUS allowing the DC winter storm to slide out to the southeast of the region, however, latest short-range guidance the HRRR and RAP 23z runs showing a potential for a deformation band to reach the South Coast of RI and MA. Should this happen, amounts could vary through a dusting to as much as 6" or more, all depends upon where that band can setup.
Could Cape Cod see their first accumulating snows of the season tomorrow afternoon into Monday? I think so, latest guidance is edging towards an impact with some snow, the question is how much precipitation does fall over the area? WV suggests that the northern confluence zone and northern stream energy causing the southward movement of the precipitation is actually moving out of Quebec, Canada at a quicker fashion, is it enough to allow the southern stream disturbance to intensify and push precipitation back into SNE? I don't know, but tomorrows short range guidance will get a much clearer idea and I will give an accumulations map if we edge that way tomorrow morning. Let's Go Patriots!
Next week could give SNE our first real shot at accumulating snow threats with at least two upcoming events in the next 10 days to start winter off the right way. The GFS, EURO, and EPS mean all show favorable pattern showing up in the 3-10 day range giving SNE shots at snow finally. With a stout +PNA ridge out west leading to northern stream disturbances diving southeastward out of Manitoba, and Saskatchewan Canada we could get a few timing issues fixed and phased super bombs could be producing rounds of heavy snow even over the Outer Cape Cod and island of Nantucket the next week plus into the end of the month. Stay tuned!
Two storms threaten the New year holiday week. The first one is for December 30-31st 2018 and the second one is for January 1-3rd 2019. Stay tuned, could be heavy snow producers. The odds favor a cold storm scenario with an amplified +PNA ridge out west.
GFS and EURO, as well as the new experimental GFS, show the potential for a clipper on Christmas Eve of next week Monday. Six days until this event, which is not a lot of time to discuss the potential. However, models are not squishing the energy anymore and therefore not shredding the disturbance as it goes through the flow over the eastern US. Time will tell if this event becomes more substantial, but there is potential.
Right now the storm for Sunday and Monday looks rather warm for SNE with a later phased stream bringing mainly rain to eastern SNE, especially the coastline. However, I believe the models are having a problem identifying the +PNA and it is rather stout, +1 standard of deviation in the positive realm, leading to high ridging into Arctic Circle bringing cold air southeastward out of the reaches of central Canada. The northern stream becomes quite amped up but too late on most of the guidance. I will quickly check the short range guidance, the 00z RGEM, WRF ARW, and WRF NMM models. The graphic I have below shows the two main players involved in the weather making this weekend. First, the southern stream disturbance and upper-level low moving over the Mid-Atlantic States tomorrow through Sunday and of the NJ coastline by Sunday afternoon and south of ACK by Sunday night, does this tuck into the elbow of Cape Cod and make a stall or does it head out to the east of Nova Scotia? Right now I would favor the HIRES models and show a path just east of Cape Cod occurring and pummeling Eastern SNE with heavy precipitation mainly snow northwest of Boston to Providence and a mix of snow and rain for the coastal plain. I will have a snow accumulations map out tomorrow morning.
Models are still too progressive with the arctic shortwave moving through Canada and Great Lakes region it is digging southward, not southeastward. This will bode well for potential snowfall for Cape Cod on Wednesday. If this shortwave can produce its own surface low, it will enhance the low-level flow over Gulf of Maine and Cape Cod, producing an inverted trough that can produce rapidly deteriorating conditions in a matter of minutes. This inverted trough could produce up to 3-6" or more depending if it has time to mature and develop. Models might be on target, but I am looking at the nowcast situation, we have a developing surface low east of NC coast, this is in a more northerly position than the models had 18 hours ago, also the precip shield is developing SW to NE and pivoting northward on the front end with a large push of heavy rainfall off the NC coast and into Hatteras, NC. We have an additional energy behind the main arctic shortwave, that is diving through western Ontario, Canada and is pushing the overall momentum of the trough southward not eastward. If this trough energy can dig south of Long Island, NY we can see up to 6"+ from the inverted trough. Again the pivotal point will be tomorrow afternoon 18z observations. Stay tuned! I will issue a snowfall map tomorrow morning.
The latest 18z RGEM shows Cape Cod getting 2-4" in the next three days, or possibly more as the run ends before the event does. Some models are more bullish with the inverted trough and ocean effect snow event on Wednesday. NWS ups the chance for snow around 50% for Wednesday.
Latest 12z GFS digs our northern stream shortwave even further southward now and develops a coastal storm just too far out to sea currently to bring substantial snows to Cape Cod. But trends could continue towards favoring an actual closer to the coastline coastal low that could impact our area with snows. Considering our northern stream is digging more than predicted today, this can bode well for later on mid-week period. We need to watch the trends for today to see what the next week brings. Stay tuned!
Latest 18z NAM brings hope to snow weenies across SE New England for next week. In the TUE/WED time frame an explosive disturbance is running through the northern stream flow and amplifies right on the coastline, now if trends continue to a more amped up disturbance, we could see a much higher impactful storm develop near the benchmark, stay tuned!
Below is the forecasted sounding from the 18z GFS for 111 hours out, which is around Wednesday afternoon. This event for Ocean Effect Snows and inverted trough mix could be quite prolific, like the Lake Erie and Lake Ontario events, why, according to the model, we have a lot of moisture present, NNE winds present from 850mb to surface, 850mb temps dropping below -16C, SSTs around +8-9C, leading to 850mb to surface differentials around +25C leading to high instability, inversion heights near 700mb which mean the surface to 700mb is highly moist as NNE winds favor that environment with dry air gone Cape Cod from Chatham to Plymouth, MA could see high snowfall totals. Ocean induced CAPE values likely to be higher than normal, and normal CAPE values should be around .18 sufficient for the salt nucleus. DGZ near the ground, with lift inside around -12 to -18 units. I favor locations such as Plymouth, Barnstable and Nantucket counties for snow accumulations. Updates will continue to come.
Next Thursday, the 6z GFS has a large arctic shortwave that moves southeastward from James Bay, Canada with extremely cold air mass associated with it and a high north of the region and a storm southeast of the region putting the area in an inverted trough, with northeasterly winds enhancing snowfall from Plymouth, MA to Chatham, MA with up to .5" of QPF in spots. I will wait until the short range models are in range, these systems are quite fickle in location and small in stature leading to close near misses at times. It could produce up to 2' at times depending upon the intensity of the trough and the delta ts and instability present in the trough. However, GFS only forecasting 3-6" at this time, but the air is going to be quite cold.
An ocean effect snow band has developed since 2 pm this afternoon, while staying offshore for most of the afternoon, this evening the band is producing moderate to heavy snow in squalls and perhaps some thundersnows are possible, the band is developing through surface convergence developing as winds are from the northeast to the right and north to the west of the band, this acts as a convergent band allowing lift and perhaps heavy snows developing over the Outer Cape Cod region with DBZs reaching 40 on the reflectiveness. Check out the latest from BOX radar picking this band up below.
Snow flurries or snow showers have a 20% chance of occurring over HYA eastward on the Cape. Winds are currently northwesterly but will become northerly later today into tomorrow night as an ocean storm changes the wind field.
Could there be impacts from a nor'easter on Cape Cod on Wednesday night into Thursday? If there will be, it might be shortlived as snow impacts will be light if it occurs. Judging by the model trends tonight, I am growing more confident of an impact, even though less than an inch would be possible unless something large changes like the storm is at the benchmark. H5 has been trending towards a more amped up through the present with an Arctic jet shortwave on the backside of the longwave trough. If this phases we could get a big storm, but right now the Pacific jet shortwave that causes our nor'easter, is just too fast in the flow. Right now the energy is too stretched out now in the long wave trough, however, models are heading towards sharpening up this shortwave energy more and more each run and also going negative sooner more so over DC and not off the coast like yesterday's runs showed. This is a trend now with the 21z SREFs showing precip chances growing. This is a system that I will notify you of if anything changes in the next 24-48 hours.