USCAPEWEATHERAF

Pattern change comes in the first week of January 2019, towards a colder and snowier potential and a major coastal storm on January 7th-9th.

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.

I am about to up the ante on the snowfall map for tomorrow, 3-6" is looking nice right now, will await 00z runs before going to change the map.

This is the 12z model update for the clipper snow threat tomorrow into Christmas morning. Big snows don't look likely now, but 2-4" is still possible for the outer Cape.

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.

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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.

First updated map for the threat for snowfall tomorrow. Models are upping the ante and we could be surprised.

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.

With the many arctic shortwaves present in the flow of the northern stream, the Arctic is opened for business but remains extremely hostile for any significant coastal storms to impact the region. With the questions remain about phasing or not phasing streams in the split flow regime spells extreme instability in the model fields. With this in mind, no snow midweek and the next weekend system remains in question and minimal at this time.

Right now all options are on the table. In the next 84 hours, the solutions will vary greatly in detail and overall vigor. The reasoning for why so many options remain open for a blizzard to sunny days remains the unknowns. The unknowns are the strength, wavelength, positioning of the factors at play. One is the Arctic Shortwave, this is either the kicker s/w or the phasing backside s/w that determines if the storm gets whisked out to sea or comes to the benchmark location. IF the phase happens like we all hope it does if you love snow, then the arctic shortwave in question is not fully sampled yet and therefore the models have no idea on the details of this shortwave. Two is the southern stream shortwave, our energetic system for coastal development. This should be sampled shortly within the next 12-20 hours of time on the west coast of the US. Its strength and position have a lot to do with where the storm exists off the East Coast. Right now, models, have it exiting around NC without phasing, this goes east and never hits the Northeast US. If the phasing occurs, we get the storm to hit the benchmark. Those are the questions that need to be answered in the next 84 hours.

00z NAM returned with heavier Precipitation on Saturday morning, could lead to accumulating snows. Stay tuned for further updates later tomorrow afternoon.

There are two kinds of tracks that impact the severity of a New England blizzard, one is the NJ track, where a surface low is west of the Apps and combines with southern energy and develops a coastal storm off the New Jersey Coastline. Normally these primary systems with NJ coastal die off before they reach eastward or northward and combine with the coastal energy to form a monster snowstorm for Cape Cod. The second track of this type of snowstorm is the Cape Hatteras track. Now when the primary low and system in the upper-levels develops and tracks northeastward, it originates in the Gulf of Mexico region and then redevelops off the NC coastline, otherwise known as Cape Hatteras. These tend to be powerful as well, perhaps with more energy involved as they mature and therefore a potentially deeper surface pressures. These tend to be less precipitation type issues and more snow even for Nantucket, MA. Now both tracks have been kind to me on Cape Cod, where I received 30" from both tracking lows. So what are some examples of these type of storms, one the NJ low is the Blizzard of 2005 (35") and the Hatteras track is the Blizzard of 2015 (32").

These five images are the four most reliable guidance models we have in determining a snowstorm its track, intensity and future impacts to New England. What they all agree on is the overall setup and teleconnections featured on December 5th, 2018 their forecast in the next 7 days. The models show a classic El Nino pattern, with a sub-tropical jet cutoff low approaching or over the Baja, CA region, with a large +PNA ridging into Alaska and the NW Canada Territories. The GFS is the furthest north with the sub-tropical cutoff upper-level low. This could have impacts downstream over New England with the main shortwave in question being too far northwest compared to the other three guidance members, this flaw could change within the next run. I will side with the Means for now given the setup is favorable for an east coast snowstorm. They all agree on a developing central based -NAO ridge over eastern Greenland, building westward. As well as in agreement over the -AO polar vortex location which is further northwest in a position of least impact. The 50/50 low is in a good position for a blocking pattern to slow down the duration of the storm's movement allowing a longer duration, while the models don't show it quite yet happening just like that, I will wait until within 96 hours before using any one of the operational guidance as gospel. Once the NAM gets in the range we will narrow down impacts and what not, but once we get in range of the 3KM NAM HIRES guidance, we won't have a great handle on the shortwaves and their interactions. GFS is most amped but that is the operational model, the Means are less amped. Also, another threat seems to take place a few days later. We will keep you posted. Stay Tuned!

The latest ensemble guidance suggests the negative AO stays negative for the next two weeks. This could mean snow or no snow for coastal SNE. Depends upon the location of the vortex.

Could we see snow in the next 6-10 days, I believe so, do not pay attention to individual runs of the operational models, they will have flaws in them run to run, but look at the ensembles and their means and they will show you the way. I found this map on PSU EWALL website, the models are 12z runs of the EURO, GFS and CMC from left to right. They pretty much agree on ridging in Alaska, our -EPO/+PNA feature, along with a ridge in northern Greenland and some ridging in northeastern Canada west of New Foundland. Stay tuned, we could be tackling a major east coast snowstorm in this time frame.