November 2025 OBS Discussion

[Sundog]

21 minutes ago, FPizz said:

What is NYC's average high temps for Nov 27-30th?  What does the Euro say those 4 days are supposed to be?  My work comp blocks weatherbell so I can't see it.  I know you're good looking up data though, so can you fill me in?  I was thinking it showed a bit below normal temps but maybe that changed.

The 28th at the park averages 50/39

[Sundog]

0z Euro was pretty cold for Thanksgiving weekend in NYC

Mid 40s for Thanksgiving, low 40s for Black Friday, mid 30s for Saturday. 

[eduggs]

Wow that's an historic trof across the west coast on the 12z CMC in the long range. I've noticed ULLs are forming and deepening right along the west coast this fall and then tracking southward along the full length of the California coastline. If you loop 500mb it's been happening and is forecast to happen over and over. I feel like this tendency was noticed the past two winters. And sure, ULLs getting stuck in the southwest has been going on forever. But this recent propensity seems more pronounced and repetitive than in the past.

Does anyone know why this is happening? Is it some kind of frictional effect or landmass-Ocean interface effect... maybe combined with Pacific Ocean temperatures and a strong Pac Jet? Or is this typical upper- & mid- level behavior and I've just never noticed it before?

[eduggs]

ChatGPT has some interesting theories to explain the repetitive ULLs following the CA coast. Its response was lengthy so I've summarized it below. I can't support or refute the validity of any of these potential mechanisms. ChatGPT further suggested that we are in a quasi-stable continental pattern. And in support of that, to my eye, the forecasted mean jet at day 15 does look roughly similar to its pattern and position over the past few days...

• Persistent Coastal Trough / Blocked Jet Stream

  • A semi-stationary trough off the West Coast creates a “corridor” that repeatedly guides ULLs southward.

  • Blocking patterns upstream (central/west Pacific ridging) prevent the flow from progressing eastward, so the same pathway persists.

• Cutoff Lows + Weak Steering Flow

  • ULLs becoming cut off from the main jet move slowly and tend to drift along the coastline where steering currents are weak but coherent.

  • Once one cutoff forms, subsequent ones often follow similar tracks.

• Coastal Waveguide Effect

  • Sharp land–ocean contrasts and California’s north–south coastline help steer shallow upper-level systems parallel to the coast.

  • The long coastline supports a “channeling” effect for southward-moving lows.

• North Pacific SST / PDO Influence

  • Negative PDO–like SST patterns (colder near CA, warmer farther west) promote troughing off the West Coast.

  • This anchors the mean storm-track/upper-level pattern in a coastal position.

• Weak La Niña Teleconnection

  • Current La Niña is weak, so typical ENSO storm-track signals (often more northerly) are not dominant.

  • With ENSO influence muted, other mid-latitude patterns can take over and become unusually persistent.

• Seasonal Transition Effects

  • Autumn jet-stream reorganization makes the atmosphere more prone to amplified and sticky patterns.

  • Early-season troughs are more likely to become cut off and recur along similar paths.

[SACRUS]

 

Records:

Highs:

EWR: 73 (1931)
NYC: 74 (1900)
LGA: 69  (1991)
JFK: 66 (2020)

Lows:

EWR: 18 (1987)
NYC: 16 (187 9)
LGA: 20 (1987)
JFK: 19 (1987)


Historical:

 

1798 - A four day storm was in progress in the northeastern U.S. The storm dropped a foot of snow on New York City and New Haven, and as much as three feet in Maine and New Hampshire. The snowstorm ushered in a long and severe winter, in some places the ground remained covered with snow until the following May. (David Ludlum)Northeastern States from November 19th to the 21st:
The infamous Long Storm sweeps across the the northeastern US spreading deep snow from Maryland to Maine. The storm dumps a foot of snow on New York City and New Haven, and as much as three feet on Maine and New Hampshire. Storm opens the famous Long Winter of 1978-99 which continues to drop snow on the region as late as May.
(Ref. WxDoctor)

1876: Boston, Massachusetts on the 20th and 21st had 5.43 inches of rain the greatest 24 hour precipitation for November. (Ref. NOAA Boston Weather Events)

1900: 79° the peak of a 6-day heat wave from 18th -23rd at WBO, Baltimore also 79° (Ref. Washington Weather Records - KDCA)

1924: Boston, MA. ended their longest period with no precipitation at 44 days. (Ref. Wilson Wx. History)

1967 - Excessive rains in southern California caused the most severe flooding and the most damaging mmud slidesin 33 years. Downtown Los Angeles received eight inches of rain, and 14 inches fell in the mountains. (David Ludlum)

1977: Arctic high pressure with an upper level trough brought record cold from the northern Rockies to the Pacific Northwest. Record low temperatures for the date included: Hardin, MT: -30° , Boulder, MT: -25°, Butte, MT: -24°, Wisdom, MT: -21°, Billings, MT: -18° (high was only 5 above), Sheridan, WY: -17°, Lander, WY: -14°: Tied, Rapid City, SD: -7°, Yakima, WA: 6°, Salt Lake City, UT: 7°, Olympia, WA: 11° and Seattle, WA: 21°. In contrast, Brownsville, TX set a record high with 89°. (Ref. Wilson Wx. History)

1979: The Upper Plains was hit with heavy snow through the 22nd as the storm raced northeast into Canada. Snowfall totals were in the 6 to 13 inch range with generally lesser amounts across northwest Iowa and southwest Minnesota. Sioux Falls, SD reported the highest storm total at 13 inches. Sioux Falls' 24-hour total through the 22nd of 11.8 inches is the heaviest 24-hour snow total in the month of November on record for the city. Moderate winds of 20 to 35 mph made travel difficult at times, but nowhere near as bad as a classic Dakota ground blizzard. Across the Rockies, some storm totals included: Wheatland, WY: 30 inches, Cheyenne, WY: 25.6 inches, Kimball, NE: 17 inches and 12.8 inches at Scottsbluff, NE. In contrast, on the west coast, Quillayute, WA set a record high with 60°. (Ref. Wilson Wx. History)
 

1985 - Hurricane Kate made landfall during the evening hours near Mexico Beach, FL. Wind gusts to 100 mph were reported at Cape San Blas FL. It was the latest known hurricane to hit the U.S. so far north. (The Weather Channel)

1987 - Squalls in the Lower Great Lakes Region and the Upper Ohio Valley produced 14 inches of snow at Snowshoe WV, and nearly eight inches at Syracuse NY. Eleven cities in the eastern U.S. reported record low temperatures for the date. Record lows included 21 degrees at Pinson AL, 9 degrees at Syracuse NY, and 8 degrees at Binghamton NY. Gale force winds lash the Middle and Northern Atlantic Coast, and the strong northwesterly winds produced wind chill readings as cold as 30 degrees below zero. Winds gusting to 60 mph at Trumansburg NY toppled a chimney onto a nearby truck. (The National Weather Summary) (Storm Data)

1988 - High winds accompanied rain and snow in the northeastern U.S. Caribou ME received eight inches of snow in six hours, and Fort Kent ME was blanketed with a total of fourteen inches of snow. (The National Weather Summary) (Storm Data)

1989 - The storm which produced thunderstorms and high winds in the northeastern U.S. the previous day, produced snow and high winds in New England, with blizzard conditions reported in Maine. Winds gusted to 55 mph at Boston MA, and reached 58 mph at Augusta ME, and hurricane force winds were reported off the coast of Maine. Snowfall totals ranged up to 18 inches at Vanceboro ME, with 17 inches at South Lincoln VT. There were thirty-five sstormrelated injuries in Maine. (The National Weather Summary) (Storm Data)

1992: The November 21st – 23rd tornado outbreak was the 3rd largest outbreak in recorded history and one of the longest continuous outbreaks ever recorded. There was no break in tornado activity from 1:30 pm on the 21st when the tornadoes started in Texas until 7:30am on the 23rd, when the last tornadoes lifted in North Carolina. On this date, severe thunderstorms spawned 6 tornadoes within 70 minutes in the Houston metro area in Texas. At one time, there were three on the ground in Harris County. The strongest, an F4, tracked 20 miles through the eastern suburbs of Houston destroying 200 homes and damaging 1,000 more. In total, 23 tornadoes struck Mississippi and Alabama. An F4 tornado killed 12 people on a 128-mile track through 7 Mississippi counties. The deadliest tornado of 1992, an F4 tornado killed 12 people on a 128 mile track through 7 counties in Mississippi, one of the bodies was blown a quarter mile into a tree. (Ref. AccWeather Weather History)

1996: Brutal cold invaded Montana bringing record low temperatures for the date including: Havre, MT: -27°, Shelby, MT: -25°, Cut Bank, MT: -23°, and Stanford, MT: -18°. In contrast, Corpus Christi, TX set a record high with 91°. (Ref. Wilson Wx. History)

1999: Forests across the east became tinderboxes, with up to 60,000 acres burned in the Appalachians. Moist air from the Pacific shifted farther north than usual, leaving the South and Southwest drier and warmer than normal. Crawfish farmers in Louisiana were feeling the effect as their ponds were drying up. Hunters also reported that waterfowl were bypassing dry central Louisiana in favor of coastal areas. In contrast, the first significant snow of the season struck the Colorado Rockies. Snowfall totals included: Bailey, CO: 16 inches, Evergreen, CO: 13 inches, North Turkey Creek, Genesee, Morrison and Sedalia, CO: 12 inches, Conifer and Evergreen, CO: 11 inches, Louisville, CO: 10 inches, Brighton, Broomfield and Denver, CO: 9 inches and Arvada, Castle Rock and Eldorado Springs, CO with 8 inches. (Ref. AccWeather Weather History)

2004: Southern California from November 21st to 22nd: Up to 3 feet of snow blankets Southern California's San Gabriel and San Bernardino mountains east of Los Angeles. and even whiten nearby desert areas. (Ref. WxDoctor)
 

[donsutherland1]

28 minutes ago, eduggs said:

ChatGPT has some interesting theories to explain the repetitive ULLs following the CA coast. Its response was lengthy so I've summarized it below. I can't support or refute the validity of any of these potential mechanisms. ChatGPT further suggested that we are in a quasi-stable continental pattern. And in support of that, to my eye, the forecasted mean jet at day 15 does look roughly similar to its pattern and position over the past few days...

• Persistent Coastal Trough / Blocked Jet Stream

  • A semi-stationary trough off the West Coast creates a “corridor” that repeatedly guides ULLs southward.

  • Blocking patterns upstream (central/west Pacific ridging) prevent the flow from progressing eastward, so the same pathway persists.

• Cutoff Lows + Weak Steering Flow

  • ULLs becoming cut off from the main jet move slowly and tend to drift along the coastline where steering currents are weak but coherent.

  • Once one cutoff forms, subsequent ones often follow similar tracks.

• Coastal Waveguide Effect

  • Sharp land–ocean contrasts and California’s north–south coastline help steer shallow upper-level systems parallel to the coast.

  • The long coastline supports a “channeling” effect for southward-moving lows.

• North Pacific SST / PDO Influence

  • Negative PDO–like SST patterns (colder near CA, warmer farther west) promote troughing off the West Coast.

  • This anchors the mean storm-track/upper-level pattern in a coastal position.

• Weak La Niña Teleconnection

  • Current La Niña is weak, so typical ENSO storm-track signals (often more northerly) are not dominant.

  • With ENSO influence muted, other mid-latitude patterns can take over and become unusually persistent.

• Seasonal Transition Effects

  • Autumn jet-stream reorganization makes the atmosphere more prone to amplified and sticky patterns.

  • Early-season troughs are more likely to become cut off and recur along similar paths.

Interesting. You should ask it to follow up with links to related scientific papers on which its assessment was based. 

[NorthShoreWx]

28 minutes ago, donsutherland1 said:

Interesting. You should ask it to follow up with links to related scientific papers on which its assessment was based. 

I'd also like to see the original wording of the query, just to further my understanding of how the bot responds.

[eduggs]

6 minutes ago, NorthShoreWx said:

I'd also like to see the original wording of the query, just to further my understanding of how the bot responds.

It was a quick and casual prompt:

ULLs have been following the full coastline of CA, all the way and sometimes past the southern tip. This has been recurring every few days for the past few weeks and current model forecasts out to 15 days into the future show the same recurring feature... I've never seen this feature so repetitive before and I'm trying to figure out why.

...followed by a request to provide a concise summary.

[SACRUS]

 

 

Nov Dep through the 2/3 (20th)

EWR: +0.2
JFK: -0.5
NYC: -1.2
LGA: -1.5

[eduggs]

40 minutes ago, donsutherland1 said:

Interesting. You should ask it to follow up with links to related scientific papers on which its assessment was based. 

It responded that it didn't use any papers.

My earlier responses were based on:

• foundational meteorological knowledge (jet dynamics, cutoff-low behavior, coastal steering, ENSO teleconnections, North Pacific climatology),

• plus the real-time information I retrieved via your previous queries.