Roger Smith

Lake effect blizzard conditions will develop rapidly across lower MI tonight and SW Ontario by morning. Heavy snow squalls with winds gusting to 55-60 mph will quickly make many highways impassable, unprepared drivers are going to be stranded in dangerous situations. I am not sure how much awareness has been created by public forecasts of these rapidly oncoming changes. Given the way the low is deepening and severe cold phasing into the circulation, and still fairly warm temps Lakes Michigan and Huron, potential for emergency situations is high. This will spread to parts of central ON, nwPA and wNY by late morning and upstate NY by afternoon-evening. Goderich to London ON needs a max alert as NW winds funnel mega-squall conditions directly across the London region. My guess is 401 will be closed or at least impassable from Chatham to Woodstock by 0900h.

Preliminary scoring for December 2025 (version 1, raw scores only) _ note for raw scores in anomalies greater than +5 or -5, error deductions are 1 pt per 0.1 error in range 5.0 to actual, and raw scores are no lower than 0.1 per correct-sign predicted 0.1 deg. When an anomaly exceeds 10.0, scores are then based on a proportional basis, for example, a +5.5 forecast against an +11.0 outcome scores 50 (raw). As another example, a forecast of +0.7 scores 07 if that is higher than the raw score would otherwise be. ... then a max-60 rule is invoked if no raw score is above 60. These max 60 scores are generally in equal increments from zero to 60, adjusted by fairness considerations when compared to the spread of raw scores. I have some objective rules that I try to apply to that adjustment but with contest results perhaps depending on exactly what the details will be (you can see DEN, PHX scores and possibly IAH will need adjustments), I will just give you the raw scores now and will be working out how adjustments affect the overall annual outcome. No idea in advance what that's going to look like (although I can't see potential for outcome to be changed by the max-60 adjustments) ... <<< Raw scores only >>> FORECASTER _____________ DCA_NYC_BOS _ east _ ORD_ATL_IAH _ cent _ c/e_ DEN_PHX_SEA_west_TOT Mercurial ______________________ 00 _ 00 _ 00 _000 _ 30 _ 80 _ 60_ 170 _170_ 00 _ 00 _ 00 _000__ 180 hudsonvalley21 ________________ 00 _ 00 _ 00 _000 _ 52 _ 96 _ 50_ 198 _198_ 04 _ 26 _ 24 _054__ 252 Scotty Lightning _______________ 00 _ 00 _ 00 _000 _ 40 _ 80 _ 40_ 160 _160_ 10 _ 10 _ 40 _060__ 220 ____ Normal ____________________00 _ 00 _ 00 _000 _ 20 _ 70 _ 20 _ 110 _110__ 00 _ 00 _ 30 _030__ 140 wxallannj ______________________ 20 _ 22 _ 26 _068 _ 34 _ 86 _ 54 _174 _242 _ 20 _ 34 _ 80 _134__ 376 DonSutherland1 ________________20 _ 40 _ 40 _100 _ 86 _ 80 _ 52 _218 _318 _ 14 _ 12 _ 32 _058 __ 376 BKViking _______________________24 _ 26 _ 34 _084 _ 54 _ 88 _ 44 _186 _270 _ 13 _ 34 _ 60 _107 __ 377 ___ Consensus ________________26 _ 34 _ 36 _ 096 _76 _ 86 _ 42 _204 _300_ 10 _ 20 _ 40 _070__370 so_whats_happening __________ 28 _ 26 _ 32 _084 _ 72 _ 86 _ 44 _202 _286 _ 11 _ 32 _ 42 _085__ 371 Tom ____________________________38 _ 54 _ 56 _148 _ 98 _ 52 _ 30 _180 _ 328 _ 06 _ 20 _ 52 _078__ 406 RJay ___________________________ 40 _ 40 _ 40 _120 _ 80 _ 94 _ 30 _204_ 324_ 10 _ 20 _ 40 _070__ 394 RodneyS _______________________ 72 _ 60 _ 46 _178 _ 86 _ 20 _ 38 _126 _ 304 _ 13 _ 05 _ 40 _058__ 362 Roger Smith ____________________ 80 _ 76 _ 90_ 246_ 62 _ 04 _ 00 _066 _312_ 00 _ 00 _ 00 _000__ 312 wxdude64 ______________________88 _ 62 _ 66 _ 216 _ 86 _ 20 _ 06 _112 _328_ 00 _ 08 _ 76 _084__ 412 ----------------- (highest and lowest forecasts above are color coded; all forecasts are below normal for ORD) __ Persistence ___(Nov 2025)___ 00 _ 16 _ 10 _026 _ 00 _ 60 _ 72_ 132 _158_ 57 _ 59 _ 72 _188 __346 EXTREME FORECASTS as of preliminary scoring ... DCA _ wxdude would win with lowest forecast NYC, BOS _ Roger Smith would win with lowest forecasts ORD _ currently just outside a win-loss outcome (4th lowest forecast high score) ... outcomes below -4.1 would make it a win-loss (RodneyS, wxdude64 win; Roger Smith loss) IAH, DEN, PHX, SEA _ definitely four wins for wxallannj with high forecasts, Mercurial also (as non-regular entrant for IAH). BKViking ties for PHX. ===================== <<< RAW SCORES for DEN and PHX will need converting to max-60, IAH possibly also but adjustments there would be very small anyway >>> Will adjust around end of month and merge with annual scoring ... given the lead Tom had before this month I cannot see how the raw-score to max-60 adjustments can remove enough of his differential to make much difference to what currently looks like Tom maintaining a 150-200 point advantage over nearest rivals. (actual forecasts) FORECASTER __________________ DCA _NYC _BOS __ORD _ATL _IAH ___ DEN _PHX _SEA Mercurial ______________________ +4.0 _+2.0 _+1.0 __-0.5 _+0.5 _+2.0___ -1.0 _ -3.0 _ -1.5 hudsonvalley21 ________________ +1.3 _+1.4 _+1.0 __ -1.6 _+1.7 _ +1.5 ___ +0.4 _+1.8 _-0.3 Scotty Lightning _______________ +1.0 _+1.0 _+0.5 __ -1.0 _+0.5 _+1.0 ___+1.0 _+1.0 _+0.5 ____ Normal ____________________ 0.0 __0.0 __0.0 ____ 0.0 __0.0 __0.0 ____ 0.0 __0.0 __0.0 wxallannj ______________________ -1.0 _ -1.1 __-1.3 ___ -0.7 _+0.8 _+1.7 ___+2.0 _+2.2 _+2.5 DonSutherland1 ________________-1.0 _ -2.0 _-2.0 ___ -3.3 _+2.5 _+1.6 ___+1.4 _+1.1 _ +0.1 BKViking _______________________-1.2 _ -1.3 _ -1.7 ___ -1.7 _+0.9 _+1.2 ___ +1.3 _+2.2 _+1.5 ___ Consensus ________________ -1.3 _ -1.7 _-1.8 ___ -2.8 _+0.7 _ +1.1 ___ +1.0 _+1.5 _+0.5 so_whats_happening __________ -1.4 _ -1.3 _ -1.6 ___ -2.6 _+0.8 _+1.2 ___+1.1 _ +2.1 _ +0.6 Tom ____________________________-1.9 _ -2.7 _-2.8 ___ -3.9 _-0.9 _+0.5 ___+0.6 _+1.5 _+1.1 RJay ___________________________ -2.0 _-2.0 _-2.0 ___ -3.0 _+1.2 _+0.5 ___+1.0 _+1.5 _+0.5 RodneyS _______________________ -3.6 _-3.0 _-2.3 ___ -4.7 _-2.5 _+0.9 ___+1.3 _+0.5 _+0.5 Roger Smith ____________________-4.0 _-3.8 _-4.5 __ -5.9 _ -3.3 _ -1.5 ___-3.6 _ -2.9 _ -2.4 wxdude64 ______________________-4.4 _-3.1 _-3.3 __ -4.7 _ -2.5 _ -0.7 ___-0.9 _+0.8 _+2.3 ----------------- (highest and lowest forecasts above are color coded; all forecasts are below normal for ORD) __ Persistence ___(Nov 2025)___ +0.4 _-0.8 _-0.5 __+1.1 _+3.5 _+5.4 ___+5.7 _+3.9 _+2.1 =====================

As I was told, ORD did not stay that close to -6 F above normal but they didn't get into the real core of that crazy warmth that is now about to get the boot east ... it has played havoc with my ATL and IAH estimates and DEN has stayed well above +10 just turning cold yesterday. Think the final values now look like being around -5.0 _ -5.0 _ -5.0 __ -4.0 _ +1.5 _ +4.0 ___ +10.0 _ +6.0 _ +3.5 will present some preliminary scoring on that basis, going to need to figure out max-60 mercy rule scoring for the western locations.

There was no storm 14 and barring the unforeseen the above scoring table (ignore the potential scores in brackets) will be FINAL CONTEST SCORING. Congrats to Retrobuc with the highest score 97.5 closely followed by StormchaserChuck (97) and Cardinalland (96.5). Will do it all again in 2026, deus volente.

The way this is rushing in with a spike of warming to follow, I would cut most of those ice accretion forecasts in half and the real problem is likely to be ponding followed by a rapid freeze by late afternoon. It's going to be a nasty mess in many areas by late Monday.

69F at CHW and 73F at HTS in approaching warm sector. Seems likely to peak in low and possibly mid 60s around 0900 EST in MA with squall line potential around 0900-1100h. Could be a brief TRW during fropa.

Correlating 12z GFS to current obs, will estimate peak in temps at 58 F around 10 or 11 a.m., then a steady fall into 30s to 4 p.m., with occasional gusts to 40 mph. Heaviest rain will fall around 11 a.m. and noon. There is a slight chance of a thunderstorm with the cold front. Temps in warm sector currently near 70 F (SDF is 74F) but I think the interaction of air mass with snow cover will fog up the mild air and the warmest portion will be experienced in s NJ where it may reach 65 F. That temperature of 74F at Louisville is a daily record, 70F in 2021 was their previous record. But they had 74F on the 27th in 2021 for yesterday's record. As I posted in storm thread, combined effects of snowmelt and 0.25" rainfall could be localized urban ponding by early Monday afternoon, and eventually any slush left on the ground will freeze Monday night, so Tuesday could be an icy mess in some places. Locations with 6" or more snow on ground will not lose all snow in the melt and what's left will become a frozen ground cover. (I am looking out on that kind of scene after past four days here brought this same sequence, our freeze-up began Friday night). Happy new year, hope the promising January pattern brings some meaningful winter weather.

Nuisance to moderately severe urban ponding is very likely to develop by mid-day Monday as temperatures rapidly rise into low 50s with this expected rain, in particular s CT could see near total melt of existing snow pack but any large snowbanks created by plow operations will survive (partially) and acr as dams for rapidly accumulating meltwater. Some drains will be blocked which will prolong the nuisance. This will be followed by a rapid freeze Monday night and any slushy cover will become solid icy glop. Despite differences in lat-long we have had this same cycle here about three days ahead, first the 4-8 inch snow cover, then the rain and the flash freeze. We lost most of our snow pack even with a peak temp of 40 F in the rainfall. It then fell to 15 F and everything has frozen solid, our partial snow cover looks like snow but is frozen solid, any slush not removed from parking lots or driveways is now a solid frozen mess. Obviously further north into n CT and w/c MA there will be less total snowmelt but there will probably be some urban ponding anyway and a similar cycle will develop without full removal of snow on ground.

Perhaps worthy of a thread, urban ponding type flood situations will develop rather quickly on Monday morning as temperatures of 55-60 F briefly spread in with 0.25" or more rain. An interval of freezing rain is likely to precede this in the late overnight and may be persistent in parts of the LHV where the warmup will be less prolific (to 48 F). All of this will rapidly be replaced by much colder temperatures, remaining slush will freeze hard on Monday night. I am not guessing at this, by a freak of nature we have been going through similar events here about three days ahead and that's what we had here on Friday into Saturday; everything now frozen solid at 15 F (as it was yesterday morning and all day). Wherever plows have made large snowbanks (this is probably more so in LI and CT, LHV) they will act as dams for accumulating meltwater. Clear all drains where possible.

Forecasts for BOS in this thread range from 47" (44" lower end of a range) to 71" which is not a very large spread for a poll with seven responses. Some gave ranges and others gave a single prediction. In order of the mid-range value where a range was used, the forecasts for BOS are in this order from top to bottom ... Torch Tiger _ 71" ... GeorgeBM _ 60" ... dmillz25 _ 53" ... Ginx and Hoth _ 52.5" ... 40/70 BM _ 49" ... Roger Smith _ 47" Don Sutherland made a prediction of 35-45" for BOS in a different thread (his winter forecast in general interest forum). Twelve people including Don and me had a range from 20" to 50.7" in the annual snowfall forecast contest. In general, that group went lower and several were below 40". I can't extrapolate BOS forecasts from two other one-location predictions but they seem consistent with BOS being in this range. Any one of these could turn out best of the bunch, I am not seeing anything to nudge 47" in either direction at this point. (BOS is only at 4.3" to date)

To answer the previous poster's question, these are averages I worked out previously, for each 30-year interval (except I added 1869 and 1870 to the 1871-1900 interval). These are monthly averages for both precip and snowfall ... the general trend for snowfall seems to be that 1991-2020 returned close to the peak value set by the earliest interval, or exceeded it (Feb), and in most cases 1931-1960 or 1961-1990 had the lowest 30-year average. For December however, the peak average was 1931-1960 and the recent rebound was not as robust as for Jan or Feb. Not part of this discussion but it is clear also that average precip has increased considerably for most months in the 1991-2020 interval. It should be added that if one extended 1991-2020 to 1991-2025, it would probably not be as robust a recovery for snowfall, the averages would fall back closer to the lower thirty-year intervals. Month ___ 1869-1900 ____ 1901-30 _______ 1931-60 _______ 1961-90 ______ 1991-2020 ___ all data JAN ______ 3.60 _ 9.0 ___ 3.40 _ 7.4 ___ 3.29 _ 6.1 ___ 3.50 _ 7.6 ___ 3.48 _ 8.7 ____ 3.49 _ 7.8 FEB ______ 3.64 _ 9.0 ___ 3.69 _ 9.4 ___ 2.84 _ 6.8 ___ 3.29 _ 8.5 __ 3.19 _10.2____ 3.33 _ 8.8 MAR _____ 3.75 _ 5.9 ___ 3.76 _ 5.1 ___ 4.01 _ 5.4 ____ 4.13 _ 3.3 ___ 4.29 _ 5.0 ____ 3.99 _ 4.9 APR ______ 3.03 _ 1.1 ___ 3.79 _ 1.3 ___ 3.44 _ 0.9 ___ 4.31 _ 0.4 ___ 4.09 _ 0.8 ____ 3.72 _ 0.8 MAY ______3.13 _ 0.0 ___ 3.50 _ 0.0 ___ 3.67 _ 0.0 ___ 4.45 _ 0.0 ___ 3.96 _ 0.0 ____ 3.73 _ 0.0 (Tr) JUN _______3.12 _ 0.0 ___ 3.74 _ 0.0 ___ 3.31 _ 0.0 ___ 3.69 _ 0.0 ___ 4.54 _ 0.0 ____ 3.67 _ 0.0 JUL _______ 4.60 _ 0.0 ___ 4.45 _ 0.0 ___ 3.70 _ 0.0 ___ 4.35 _ 0.0 ___ 4.60 _ 0.0 ____ 4.34 _ 0.0 AUG ______ 4.42 _ 0.0 ___ 4.42 _ 0.0 ___ 4.44 _ 0.0 ___ 4.16 _ 0.0 ___ 4.55 _ 0.0 ____ 4.40 _ 0.0 SEP _______ 3.59 _ 0.0 ___ 3.45 _ 0.0 ___ 3.86 _ 0.0 ___ 3.95 _ 0.0 ___ 4.31 _ 0.0 ____ 3.83 _ 0.0 OCT _______ 3.51 _ 0.0 ___ 4.02 _ 0.0 ___ 3.14 _ 0.0 ___ 3.56 _ 0.1 ___ 4.38 _ 0.1 ____ 3.72 _ 0.0 (Tr) NOV ______ 3.63 _ 1.8 ___ 2.66 _ 0.2 ___ 3.39 _ 1.1 ___ 4.53 _ 0.4 ___ 3.58 _ 0.5 ____ 3.56 _ 0.8 DEC _______3.07 _ 6.1 ___ 3.77 _ 6.2 ___ 3.25 _ 6.5 ___ 3.91 _ 3.3 ___ 4.27 _ 5.1 ____ 3.65 _ 5.5 year _____43.10 _33.0__ 44.64 _29.6__42.34 _26.9__47.82 _23.5__49.40 _29.9___45.43 _28.6

There could be a few tenths additional snow by end of month, and some might consider the first event (2.9") to be under-measured relative to long-times-past standards, so I have included all Decembers from 6.3" to 9.7" in this table of snowfall analogues ... I included 1869 because it was (regionally) a very cold December and it probably had plenty of snow (Dec 1868) just to make a note of it. Winter ____ OCT _NOV _DEC _JAN _FEB _MAR _APR ___ TOTAL ___ (Year) 1868-69 __ no data Oct-Dec _15.1 __ 9.6 __ 0.8 __ 0.0 _ _ 25.5+ ___ 1873-74 ___ 0.0 __ 2.0 __ 9.3 __ 6.6 _ 19.0 __ 0.3 __ 0.5 _ _ 37.7 ___ 1887-88 ___ 0.0 __ 0.2 __ 9.0 __11.1 __ 3.0 _ 22.2 __ 0.0 _ _ 45.5 ___ 1893-94 ___ 0.0 __ 0.0 __ 8.3 __ 9.4 _ 20.5 __ Tr __ 1.0 _ _ 39.2 ___ 1903-04 ___ Tr ___ 0.0 __ 6.4 __15.6 __ 5.0 __ 5.4 __ Tr _ _ 32.4 ___ 1909-10 ___ 0.0 __ 0.8 __ 9.0 __ 11.1 __ 5.0 __ 1.3 __ 0.0 _ _ 27.2 ___ 1911-12 ____0.0 __ 1.0 __ 8.5 __ 13.0 __ 2.5 __ 4.5 __ Tr __ _ 29.5 ___ 1915-16 ____0.0 __ Tr ___ 8.1 ___ 0.7 __13.1 _ 25.5 __ 3.3 _ _ 50.7 ___ 1916-17 ____0.0 __ Tr __ 14.5 __ 5.8 __ 12.2 _ 11.7 __ 6.5 _ _ 50.7 ___ 1919-20 ____0.0 __ Tr ___ 8.8 __ 8.2 _ 25.3 __ 5.3 __ Tr __ _ 47.6 ___ 1921-22 ____0.0 __ Tr ___ 7.3 __ 9.4 __ 7.2 __ 3.9 __ 0.0 _ _ 27.8 ___ 1922-23 ____0.0 __1.0 __ 8.0 __24.5 __18.8 __ 8.1 __ 0.0 _ _ 60.4 ___ 1932-33 ___ 0.0 __ 0.0 __ 9.4 ___ Tr __12.8 __ 4.8 __ Tr __ _ 27.0 ____ 1935-36 ___ 0.0 __ 2.7 __ 6.6 __12.1 __ 10.3 __ 1.5 __ Tr __ _ 33.2 ___ 1942-43 ___ 0.0 __ Tr ___ 8.5 __ 9.5 __ 4.4 __ 7.1 ___Tr __ _ 29.5 ___ 1944-45 ___ Tr ___ Tr ___ 6.7 __12.3 __ 8.1 __ Tr ___ 0.0 _ _ 27.1 ____ 1952-53 ___ 0.5 __ 1.7 __ 7.5 ___ 4.1 __ 0.4 __ 0.9 ___ Tr __ _ 15.1 ___ 1957-58 ___ 0.0 __ Tr ___ 8.7 __ 9.2 __10.7 _ 15.9 __ 0.2 __ _ 44.7 ___ 1961-62 ___ 0.0 __ Tr ___ 7.7 __ 0.6 __ 9.6 __ 0.2 __ Tr __ _ 18.1 ____ 1966-67 ___ 0.0 __ 0.0 __ 9.1 __ 1.4 __23.6 __17.4 __ Tr __ _ 51.5 ___ 1968-69 ___ 0.0 __ Tr ___ 7.0 __ 1.0 __ 16.6 __ 5.6 __ 0.0 _ _ 30.2 ___ 1969-70 ___ 0.0 __ Tr ___ 6.8 __ 8.4 __ 6.4 __ 4.0 __ Tr __ _ 25.6 ___ 1990-91 ___ 0.0 __ 0.0 __ 7.2 __ 8.4 __ 9.1 __ 0.2 __ 0.0 _ _ 24.9 ___ 1993-94 ___ 0.0 __ Tr ___ 6.9 __12.0 _ 26.4 _ 8.1 __ 0.0 _ _ 53.4 ___ 2005-06 ___ 0.0 __ Tr ___ 9.7 __ 2.0 _ 26.9 __ 1.3 __ 0.1 _ _ 40.0 ___ 2013-14 ___ 0.0 __ Tr ___ 8.6 __19.7 _ 29.0 __ 0.1 __ Tr __ _ 57.4 ___ 2017-18 ___ 0.0 __ Tr ___ 7.7 __ 11.2 __ 4.9 __11.6 __ 5.5 _ _ 40.9 ___ ==================== Quite a few very cold Januaries in this group, and good snowfall winters like 1887-88, 1922-23, 1966-67, 2013-14, 2017-18.

You had the last gasp of the extreme warmth that had been over the Ohio valley up to the early stages of the winter storm that developed over PA. I think Latrobe PA also maxed at around 57 F during the day. As you know it was well above 60 F in KY and parts of s IN-IL for a couple of days leading up to the Boxing Day storm in the northeast. That warmth is going to make one last run eastward on Monday before being suppressed further south. I would expect some parts of the MA to max out in low 60s by Monday afternoon-evening before falling into the high 20s and low 30s on Tuesday.

Can you get sleet from a column with a highest temperature below freezing? Does it depend on actual temperature or potential temperature? How much horizontal shift can there be in falling precip in a winter storm? Can the precip reaching the surface have originated more than a few miles west of where it reached the ground? I would assume it would be 10-15 miles max given wind speeds but I have never studied this detail, has anyone ever studied it? I am interested in what happened in pure physical terms, as I was watching hourly maps of temperatures at 700 and 850 mbs during the sleet phase (in NJ) and it seemed that temps were generally -2 to -4 C at 700 mbs and colder at 850 (and 925) mbs. So does that imply a warmer reading somewhere a little below or above 700 mbs? Or is it possible for sleet to occur from a lower thermal max? (I know what sleet is, that's not the question I am trying to answer, but how and where it forms). Glad to read so many positive outcomes and sad about the negative ones, in hindsight it appears that the GFS miscalculation originated with its track for the surface low, it failed to detect the potential for a double-centered low over w PA with a lingering northern component. As soon as that was absorbed into the southern center (which later transferred to the coastal) the sleet turned back to snow for some parts of n NJ. So I think that was the source of the false snowfall regional depiction at 18-24 hours lead time.

With the new year approaching, I am terminating the 2025 contest thread with the results of Dec 2025 and the annual contest, and moving all new activity over to this thread where you can post Jan 2026 forecasts at any time, as is our custom in January, no late penalties will fall until later into the first week, let's say for sure no penalties before end of Jan 2nd, so take your time and post / edit freely -- if you don't see a table of forecasts you can edit because I only see the forecasts when I make up the table. For anyone new wanting to enter, the forecast contest asks you to predict temperature anomalies at nine locations across the U.S., in F deg relative to 1991-2020 averages. The nine locations are DCA _ NYC _ BOS _ ORD _ ATL _ IAH _ DEN _ PHX _ SEA ... Happy new year ...