donsutherland1

With most of the 18z guidance now in, I have no changes from my thinking following the 12z model cycle. In general, the New York City area remains in line for its biggest snowstorm in nearly four or five years. Moreover, the storm will likely reach at least Category 3 on the Northeast Snowfall Impact Scale (NESIS). Further, this could become the first storm since the January 22-24, 2016 blizzard to bring 6" or more snow to all of the following cities: Boston, Baltimore, New York, Philadelphia, and Washington, DC. it appears that a good initial estimate for storm total snow and sleet in New York City and nearby areas will fall in the 6"-12" range. Areas to the south and east of New York City and its nearby suburbs could see 4"-8" amounts. Pockets of 12"-18" amounts are possible well north and west of New York City, most likely in parts of northeastern Pennsylvania, Orange County, Dutchess County, and Sussex County. A reasonable floor for New York City is 5". A reasonable ceiling is 14". There remains a degree of uncertainty concerning mid-level and surface storm evolution and tracks, and a potential primary-secondary storm handoff. Model skill will improve markedly overnight and tomorrow. At that time, there should be convergence toward a consensus among the models. Estimates could be revised based on the subsequent guidance, as needed.

Arctic air is poised to return to the area tomorrow. A frigid weekend lies ahead. That will set the stage for the region's biggest snowstorm so far this winter and perhaps in a number of years. The temperature will likely stay below 20° in New York City and much of the region on Saturday. The last time that happened in New York City was January 21, 2025 when the high was 19°. Snow could arrive on Sunday. A significant snowfall is likely in and around the New York City area and surrounding region, even as a transition to sleet is likely. At present, it appears that New York City and its nearby suburbs are in line for 6"-12" of snow. Higher amounts are likely north and west of the City where ratios will be higher and mixing is less likely. There could be a few pockets of 12"-18" amounts in that region. Lesser amounts, probably in the 4"-8" range appear likely along the central Jersey Shore and across parts of Long Island. The last time New York City saw a 6" or greater snowfall was January 28-29, 2022 when 8.3" fell. Its last 10" or above snowfall occurred during January 31-February 3, 2021 when 17.4" accumulated. There remains uncertainty and it may still be another day or two before the details can be pinned down with high confidence. Very cold air will return to the region as the storm departs. Highs will be in the 20s through at least midweek. Overall, January 20th-February 3rd will likely be the coldest and perhaps snowiest two-week period this winter. The forecast WPO-/EPO-/AO-/PNA+ pattern is typically the coldest pattern in January and among the coldest during the first half of February. A persistently positive PNA will have above climatological risk of moderate or significant snowfalls. For perspective, the coldest two-week period this winter prior to January 20th was January 3-16, 2026 and January 4-17, 2026 with a mean temperature of 30.3°. The snowiest two-week period was December 14-27, 2025 when 7.2" of snow fell. The ENSO Region 1+2 anomaly was -0.3°C and the Region 3.4 anomaly was -0.7°C for the week centered around January 14. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.48°C and the ENSO Region 3.4 anomaly has averaged -0.68°C. La Niña conditions will likely continue into at least late winter. The SOI was -4.52 today. The preliminary Arctic Oscillation (AO) was -2.162 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 98% probability that New York City will have a cooler than normal January (1991-2020 normal). January will likely finish with a mean temperature near 30.6° (3.1° below normal). Supplemental Information: The projected mean would be 2.0° below the 1981-2010 normal monthly value.

That's from NWS New York's Area Forecast Discussion.

https://www.weather.gov/okx/winter

One possible difference of note is that NWS Upton referred to NBM v.5.0 (this is the parallel version that is being tested and will be implemented during the spring) while NWS Mount Holly referenced DESI. DESI uses v4.2. The experimental version has more conservative snow-liquid ratios.

As for the medium-term, I have no change in my thinking from Monday that the WPO-/EPO-/AO-/PNA+ pattern will likely be the biggest driver of North American weather conditions through the remainder of January. That pattern is typically the coldest January pattern for the eastern half or third of the U.S., along with at least southern Ontario and Quebec. One or more lows in the single digits and one or more highs in the teens is possible in New York City. Subzero cold is likely in places like Chicago, Detroit, and Toronto. The predominantly positive PNA comes with a heightened risk, relative to climatology, of moderate or significant snowstorms for the East Coast. With the PNA likely to be mainly positive into or through at least the first week of February, it is likely that at least one or more of the following cities will see at least one 6" or above snowstorm from the remainder of January through the first week of February: Baltimore, Boston, New York, Philadelphia, Richmond, and Washington, DC. The only update is that the ECMWF weeklies have grown colder in the Eastern U.S. through much of February. And the kind of pattern in place is often slow to break down. After mid-February, a PNA- is a better setup for East Coast snowstorms, as wave lengths typically grow shorter.

I suspect most of the discussion is currently occurring in the subforums where a significant-major winter storm is forthcoming.

Monday morning with maybe some snow showers into the afternoon. There are differences on the guidance and those details will become clearer in subsequent model cycles.

My thinking about an upcoming significant snowfall in and around New York City remains intact following the 1/22 12z model cycle. Overall, the City remains on course to see its biggest snowstorm in nearly four or five years. The storm will likely attain a Category 3 or, less likely but still possible, Category 4 rank on the Northeast Snowfall Impact Scale (NESIS). NESIS is based on a combination of the area affected by the storm, population in the affected areas, and snowfall amounts. During the height of the storm, the dedridritic growth zone (DGZ) will have temperatures between -17°C and -12°C as per the soundings from multiple models, which is close to ideal for snow growth. The layers below it will be well-saturated, and surface temperatures will be very cold, reducing the risk of melting/riming. As a result, well-accumulating dendrites will be the predominant snowflake. Ratios during this time will probably range from 12:1 to 15:1. A classic paper can be found here: https://www.wpc.ncep.noaa.gov/research/snow2a/snow2a.pdf Later on, warmer air will push into the mid levels (mainly between 650 mb and 800 mb), which will lead to a transition to lower ratios and then sleet for parts of the New York City area, including the City and nearby suburbs. There's a small chance that the storm could end as some freezing drizzle as it pulls away early Monday. Taking into consideration the DGZ conditions, historic data for snowstorms with 1" or greater QPF, the various 12z model solutions, it appears that a good initial estimate for storm total snow and sleet in New York City and nearby areas will fall in the 6"-12" range. Areas to the south and east of New York City and its nearby suburbs could see 4"-8" amounts. Areas with 12"-18" are possible well north and west of New York City, most likely in parts of northeastern Pennsylvania, Orange County, Dutchess County, and Sussex County. A reasonable floor for New York City is 5". A reasonable ceiling is 14". There remains a degree of uncertainty concerning mid-level and surface storm evolution and tracks, and a potential primary-secondary storm handoff. Model skill will improve markedly within another day. Estimates could be revised based on the subsequent guidance, as needed, but the initial estimate is probably a reasonable starting point. Areas north and west of New York City where ratios could be higher for a longer period of time and mixing could be less of an issue, will likely see higher amounts than New York City.

The sounding at 84 hours.

I don't know the internal logistics.

That kind of defeats the purpose of the flights. That means the 12z model cycle would be ingesting 12z data and a small sample of data that was collected at 0z.

For reference concerning snow-liquid ratios with storms that had 1"-2" QPF, as currently shown on the NBM: So, assuming a ratio of 11:1-13:1 during the height of the storm (0.50"-0.75" QPF), NYC seems in very good shape to see at least 6" of snow and well-positioned for even higher amounts, even if sleet mixes in or a transition to sleet occurs. This storm remains on track to be the biggest storm New York City has seen in nearly 4-5 years.

Setting aside specific snowfall amounts, the 1/22 0z NBM showed a snow-liquid ratio of 16.6 for New York City while the 1/22 12z NBM showed 14.1. With an estimated 1.00" or more QPF ( 12z NBM), the actual ratios will be lower. Moreover, the impact of a closed 700 mb low over the Great Lakes Region will also bring about some warming aloft, likely leading to a mix or change to sleet in New York City and its nearby suburbs. Some statistics for storms with QPF of 1.00" or more: During the height of the storm, peak ratios will probably be 11:1-13:1. Soundings will be crucial once the event draws closer. Assuming 0.50"-0.75" of liquid during that period, one is probably talking about 5.5" to almost 10" of snow. Thus, it seems right now that a 6"+ snowfall in New York City is a good bet with higher amounts possible. Areas to the north and west of NYC (Morristown, Allentown, Middletown, etc.) could have higher snowfall amounts (better ratios and reduced risk of mixing) despite somewhat lower QPF figures. The 12z NAM's soundings could provide some early insight into the push of warm air. That's one area where the model actually does quite well.

I don't think anyone outside of NCEP can answer that, as one has no comparison to a control case (the model solutions without the additional data). Another flight is scheduled for 1/23 0z. 000 NOUS42 KNHC 211739 REPRPD WEATHER RECONNAISSANCE FLIGHTS CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL. 1240 PM EST WED 21 JANUARY 2026 SUBJECT: WINTER SEASON PLAN OF THE DAY (WSPOD) VALID 22/1100Z TO 23/1100Z JANUARY 2026 WSPOD NUMBER.....25-052 CORRECTION I. ATLANTIC REQUIREMENTS 1. FLIGHT ONE - NOAA 49 A. 23/0000Z B. NOAA9 03WSA TRACK66 C. 22/2015Z D. 10 DROPS AS PUBLISHED ON TRACK BEGINNING WITH DROP POINT 3 AND ENDING WITH DROP POINT 2. E. AS HIGH AS POSSIBLE/ 22/2030Z TO 23/0230Z. 2. OUTLOOK FOR SUCCEEDING DAY: POSSIBLE MISSION ALONG TRACK 66 FOR 24/0000Z. II. PACIFIC REQUIREMENTS 1. FLIGHT ONE - TEAL 75 A. 23/0000Z B. AFXXX 12WSE IOP11 C. 22/1830Z D. 25 DROPS APPROXIMATELY 60 NM APART WITHIN AN AREA BOUNDED BY: 35.0N 130.0W, 35.0N 110.0W, 15.0N 110.0W, AND 15.0N 130.0W E. AS HIGH AS POSSIBLE/ 22/2030Z TO 23/0230Z 2. SUCCEEDING DAY OUTLOOK: A USAF WC-130J AIRCRAFT MAY FLY AN ATMOSPHERIC RIVERS MISSIONS OVER THE EASTERN PACIFIC FOR THE 24/0000Z SYNOPTIC TIME. 3. ADDITIONAL DAY OUTLOOK: TWO USAF WC-130J AIRCRAFT MAY FLY ATMOSPHERIC RIVERS MISSIONS OVER THE CENTRAL AND EASTERN PACIFIC FOR THE 25/0000Z SYNOPTIC TIME.

It's my understanding that all the global models and NAM got it. The recon data is pulled into the 4dVAR (GGEM, ECMWF, UKMET, ICON) and FV3 (American models) initialization packages.

It can, but not always.

It’s usually #2 and sometimes #3 in verification.

No. We are in Phase 6.

Nice improvement on the 0z Icon vs. the 18z run for the NYC area and NJ. 0z: 18z:

Yes. For example, on February 12, 2006, 24.1" snow fell with 1.66" precipitation (14.5:1).

Yes. Lake effect snow has very high ratios, because the air mass moving across the lakes is often both frigid.

In general, higher QPF events have lower ratios. Warmer air holds more moisture. Warmer air can result in less favorable snow growth in the atmosphere, riming, etc.

I believe both the December 26-27, and January 1st events were clippers.

It's my understanding that the data should be captured in tonight's 0z model cycle.