Roger Smith

and it was 70 F two days later. In this case, more like 55 F to 60 F?

That NAM fiasco is due to the low running 200 miles further north, it's north of Erie PA on the map instead of somewhere near the WV-OH border into sw PA. It's over the left guardrail into the Walmart parking lot.

I think your outcome is mainly sleet and freezing rain bands with snow northeast of Baltimore possibly, but there is probably a one in ten chance this becomes your snowstorm at the last moment, the low is definitely going to have considerable energy from the high dew points it will encounter over the mid-section of the country, while right now it is just dealing with dry air masses over the Rockies (freezing fog in Miles City MT is about all it is producing so far). When it gets into Iowa and Illinois it will have a lot more moisture available and bands of sleet and freezing rain will develop around s WI and MI, then snow will develop over s ON and nw PA, w NY. If this turns hard right over w PA you could get a semi-surprise snowfall into DC and most of MD. Looking at all guidance the solutions are further apart than usual at 36h-48h lead time. But if I had to choose I think the GFS is probably nearest to reality at this point and its snow axis is ne PA to n/c NJ. Thundersleet around mid-day Friday is possible for s PA into ne MD.

Reggie slid into the left guardrail and some of the other guidance is up against the right fence, but GFS sailing down the actual intended path, this model run reminds me of rush hour in Salt Lake City (stay behind a truck in the middle lane and you'll survive it perhaps) ... I believe so anyway. Low is now in n.e. WY and air mass cold enough to snow (with just freezing fog) is in Montana and North Dakota. It's sunny and mid-70s in e CO and most of KS, but foggy and low 50s in s IA into central IL, this is the moisture available to this storm basically, so it should begin to drop moderate amounts of sleet and freezing rain in WI and MI tonight into Christmas Day, transition to snow will start over ne OH, w NY and s ON Christmas night into early 26th. I can't see it missing south, too much development taking place before the transfer to a C Hat coastal low. Axis of heaviest snow seems likely to be ne PA into n/c NJ. Northeast winds off LI Sound should help with banding and accumulations.

A more general answer about outcomes for heavy snowfall Decembers in the past ... 40 Decembers have seen 8.0" or more (of 157 incl 2025 so far) 29 Decembers have seen 10.0" or more. There were only four seasonal totals below 30 inches in these forty winters, and only one below 20 inches. All of those were well back in the record, the more recent snowy Decembers have generally surpassed 40 inches in seasonal totals. Of course, the snowier the December, the less extra snow is required to break any given target, but as a general rule it appears that you can triple to quaadruple total December snowfall to get a reasonable estimate of most winter totals. I noticed a typo in the NWS discussion, they say 8-10 inches is a worst case scenario, we all know they meant best case scenario. (merry Christmas) I will stick to my first call of 3 to 6 inches for the region in general and 8 to 12 inch local banding near Raritan Bay into areas like New Brunswick and Somerville NJ.

I suspect there will be a convergence zone near the 28F isotherm in n/c NJ with enhanced totals similar to that event last winter (?) (or was it two winters back now?) ... 3 to 6 inches might be a good general forecast with this narrow band of 8 to 12 inches possibly somewhere like Long Branch - Sayreville-NB-Somerville NJ. That convergence zone would represent the southern boundary of unmodified arctic air, a second boundary further south would limit the mixed precip zone across parts of central NJ and e PA. That one would likely run through n DE and ne MD into the PA/MD border region. These two frontal zones would both likely stall for several hours then drift south near end of event, so mixing north of the strong convergence zone might be negligible.

1947 was 26.4" (26.1" on 26th) and 2010 was 20.0" (12.2" 26th + 7.8" 27th). That 7.8" portion is the daily record for the 27th. The 12.2" on 26th would have been a daily record on every day of December except the 15th (12.7" fell in 1916), the 20th (15.5" fell in 1948), but even without 1947, not the 26th .... 18 inches fell in 1872 on Dec 26th during a very cold spell. Boxing Day seems good for snow, I think Don showed it was the most likely date in December to see measurable snow, and other significant falls include 7.0" in 1890, and 11.2" in 1933. In 1969 there was 6.3" over the 25th and 26th. The three largest December totals for two days all include the 26th.

2 inches for CPK, I'll believe that when I see 0.5" posted in the climate summary. My take on this one is, light coatings of snow grains, mixed with drizzle, not a great road scenario because it won't slow down traffic very much while adding the hazards of slushy partly frozen crud. Could drop 1-3 inches on colder northern suburban areas though. Widespread black ice the following morning.

Warm ridge in central US is slowly retrogressing and this Friday (possibly into Saturday as per CMC) wave is sliding down the retreating forward edge, a good scenario as it will lock in cold on northeast side of the wave. Also there's a good 50/50 type low forming as the Tuesday minor event explodes into a deep low south of NS and heads for s.e. Newfoundland. That locks in the cold high. I could see this being an over-performer and giving the NYC region 8 to 12 inches of snow. Mixing issues will be way south, like PHL to DCA. I expect the timing may begin to shift a bit towards Friday overnight into Saturday morning. Looks like it is followed by a slight warming trend before extreme cold descends after the arctic vortex amplifies over the Lakes. That could lead to another 1-2 inches of snow from outer edges of rapidly developing coastal near Cape Cod. This is an oddball if not unique pattern setting up so analogues won't be very helpful.

Probably the way models are trending, it's becoming a question of whether the milder air ever makes it past central NJ but I think temps will spike at around 45F for a few hours late Christmas Day, then slide down into high 20s setting up a solid wall of icy resistance when the Friday wave drops southeast, could lead to a much heavier snowfall than forecasts are currently saying (can't say record because it's 78 years after 12-26-1947). A few days ago it was looking like a very mild two days 24th-25th and now it's looking more like a couple of hours of slight warming. Encouraging when the models bust on the warm side.

I would bet when it warms up slightly for Christmas Eve into the 25th, it will get very foggy until the warm sector is suppressed south. Foggy and 48-52 F temps, Santa will not find every house. Oh right, I'm supposed to pretend Santa doesn't exist. Forgot about that.

Tracking anomalies and projected end of month ... _____________________________ DCA _NYC _BOS __ORD _ATL _IAH ___DEN _PHX _SEA _____ (anom 1-16) __________ -9.2 _ -8.7 _ -7.7 __-10.7 _-4.9 _-3.2 __+8.3 _ +5.1 _ +6.4 _____ (p anom 1-31) ________ -5.0 _ -4.5 _ -4.0 __-6.0 _-2.5 _-1.0 __+6.0 _ +3.5 _ +2.5 (17th) _ A more variable regime will cut into large negative anomalies in eastern and central regions. It will stay generally mild in the western regions but SEA will have a larger reversal as arctic air builds in for a while later in the month.

Strong winds also up here, with resultant power failure after trees came down on power lines. Near blizzard conditions in southern Alberta, major highway multi-vehicle pile up north of Calgary. We have lost our thin snow cover during recent mild spell, quite cold in the wind but it cleared up shortly after a couple of brief flurries, still quite windy, 35 F.

Until you see a temp above 47 F, Dec 2025 remains tied with 1917 in first place for lowest max. Sadly that probably won't survive. Today's departure looks like it could push the running anomaly down to around -9 F which will perhaps be the low point for the month. As I was saying yesterday, lots of ups and downs ahead and I would expect this anomaly to be cut in half but -5 to -6 for the month is still possible if there's enough cold in the mix. If the mean after today drops to 32.4 F it will currently be tied with three t-28th coldest Decembers (for the entire month), a finish closer to 36 F seems likely, and the median of all 157 (if below 36.5) will be 36.5 F so there is some chance of the month being in the lower half of all Decembers, something that only happens two or three times a year in the modern and urban-warmed climate. A total of 26 Decembers had a mean at or below 32.0, the only recent ones being 1989 and 2000. By decades it is fairly easy to see the warming of the climate but about half of this is likely due to urban heat island increases. (27th was 1892 at 32.2 and the three at t-28th 32.4 are 1909, 1944 and 1995). Three more (1902, 1921, 1980) were tied at 32.5 F. DECEMBERS WITH MEANS 32.0 OR LOWER (listed by 30-year intervals slightly modified, 1869-1900 (8), 1901-30 (7), 1931-60 (6), 1961-90 (4), 1991-2024 (1). 1871 (29.2), 1872 (28.3), 1876 (24.9), 1880 (26.5), 1882 (30.6), 1883 (32.0), 1886 (29.6), 1890 (29.9) 1903 (31.5), 1904 (30.3), 1910 (30.0), 1914 (31.6), 1917 (25.0), 1919 (30.2), 1926 (28.9) 1935 (30.0), 1942 (31.1), 1945 (31.0), 1955 (29.7), 1958 (29.4), 1960 (30.9) 1962 (31.5), 1963 (31.2), 1976 (29.9), 1989 (25.9) 2000 (31.1)

ORD anomaly for 1st to 15th is -11.3 F.