donsutherland1

In the wake of today's rainfall, colder air will again move into the region. However, much milder conditions could return toward the middle of next week before additional cold air returns. With the development of an EPO-/AO-/PNA- pattern following a short-lived rebound in the EPO to positive levels, colder air intrusions could again become more frequent toward mid-December. The potential for snowfall could also begin to increase, as well, as a sustained colder pattern begins to develop, but significant snowfall is not likely during the transition to that colder pattern. The latest guidance suggests that the AO could fall to -3.000 or below during the second week of December. Since 1950, there were 24 cases that saw the AO reach -3.000 or below during December. Mean snowfall for those cases was 6.2" (Median: 6.0"). 50% of such cases saw December wind up with 6.0" or more snow (25% saw 10.0" or more). In contrast, during all other December cases, mean December snowfall was 3.5" (Median: 2.5"). In those cases, 21% of years saw December snowfall of 6.0" or more while 8% saw 10.0" or more snowfall. The ENSO Region 1+2 anomaly was -1.7°C and the Region 3.4 anomaly was -0.8°C for the week centered around November 23. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -1.57°C and the ENSO Region 3.4 anomaly has averaged -0.92°C. La Niña conditions will likely persist through mid-winter. The SOI was +18.32 today. The preliminary Arctic Oscillation (AO) was -1.685 today. On December 1 the MJO was in Phase 8 at an amplitude of 0.473 (RMM). The November 30-adjusted amplitude was 0.953 (RMM).

Some cloud shots near sunset.

Statistically, insight regarding strong AO+ values proved useful in heralding the arrival of AO blocking in late November. A sustained AO- regime commenced on November 23. https://www.americanwx.com/bb/topic/58336-november-2022/?do=findComment&comment=6681570 Statistical trends in the PNA following the most similar December 3 cases suggest that, just as is shown on the dynamical guidance, the ongoing PNA- regime will be slow to breakdown. By the end of the third week in December, values should be less negative than they currently are. However, the development of sustained positive values by that time seems unlikely (not zero, but still a less than one-in-three probability).

Tune in starting at 4:30 pm to find out.

Some winter trends for New York City: Rising winter temperatures, rising seasonal snowfall, fewer but bigger events.

Morning thoughts… Today will be rainy and mild. High temperatures will reach the middle and upper 50s in most of the region. Some locations could reach 60°. Likely high temperatures around the region include: New York City (Central Park): 57° Newark: 59° Philadelphia: 59° Cooler air will return for tomorrow and Monday. A sustained cold pattern could develop around mid-month. Normals: New York City: 30-Year: 48.0°; 15-Year: 48.4° Newark: 30-Year: 48.6°; 15-Year: 49.1° Philadelphia: 30-Year: 49.6°; 15-Year: 50.3°

The PNA was +0.289 on 1/6 and +0.447 on 1/7.

For ease of reference, I've included the AO/PNA charts for 4"+ snowstorms for Baltimore for December, January, and February here.

I will do so. Hopefully, sometime this evening or tomorrow.

A system will then bring warmer conditions and rain tomorrow before colder air returns to the region. Rain will likely overspread the region tomorrow morning. Most of the region will likely see 0.25"-0.50" of rain. With the development of an EPO-/AO-/PNA- pattern, colder air intrusions could become more frequent after the first week of December. The potential for snowfall could also begin to increase especially near or just after mid-month. The latest guidance suggests that the AO could fall to -3.000 or below during the second week of December. Since 1950, there were 24 cases that saw the AO reach -3.000 or below during December. Mean snowfall for those cases was 6.2" (Median: 6.0"). 50% of such cases saw December wind up with 6.0" or more snow (25% saw 10.0" or more). In contrast, during all other December cases, mean December snowfall was 3.5" (Median: 2.5"). In those cases, 21% of years saw December snowfall of 6.0" or more while 8% saw 10.0" or more snowfall. The ENSO Region 1+2 anomaly was -1.7°C and the Region 3.4 anomaly was -0.8°C for the week centered around November 23. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -1.57°C and the ENSO Region 3.4 anomaly has averaged -0.92°C. La Niña conditions will likely persist through mid-winter. The SOI was +15.31 today. The preliminary Arctic Oscillation (AO) was -1.351 today. On November 30 the MJO was in Phase 8 at an amplitude of 0.954 (RMM). The November 29-adjusted amplitude was 1.223 (RMM).

Strong blocking patterns can take time to evolve where ridging and warmth in the East gives way to colder conditions and snowfall. November-December 2010 provides a good illustration:

That’s only December.

Farther north is less dependent on the PNA, as it can benefit from Miller B storms that phase or rapidly develop too late to benefit most of the Mid-Atlantic region.

I’ve added to the Mid-Atlantic subforum.

For reference:

For Washington or Baltimore?

For reference:

EPS temperature anomalies for December 12-19. The following week (lower skill) is also colder than normal in much of the East with near normal precipitation. No severe Arctic cold is currently indicated on the weeklies.

Morning thoughts… It will be partly sunny and cooler. High temperatures will reach the middle and upper 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 45° Newark: 47° Philadelphia: 48° Tomorrow will see some rain, along with noticeably milder temperatures. Normals: New York City: 30-Year: 48.4°; 15-Year: 48.7° Newark: 30-Year: 48.9°; 15-Year: 49.4° Philadelphia: 30-Year: 50.0°; 15-Year: 50.6°

Have a happy birthday.

Tomorrow will be fair but cold. A system will then bring warmer conditions and rain for tomorrow night and Saturday before colder air returns to the region. With the development of an EPO-/AO-/PNA- pattern, colder air intrusions could become more frequent after the first week of December. The potential for snowfall could also begin to increase. The latest guidance suggests that the AO could fall to -3.000 or below during the second week of December. Since 1950, there were 24 cases that saw the AO reach -3.000 or below during December. Mean snowfall for those cases was 6.2" (Median: 6.0"). 50% of such cases saw December wind up with 6.0" or more snow (25% saw 10.0" or more). In contrast, during all other December cases, mean December snowfall was 3.5" (Median: 2.5"). In those cases, 21% of years saw December snowfall of 6.0" or more while 8% saw 10.0" or more snowfall. The ENSO Region 1+2 anomaly was -1.7°C and the Region 3.4 anomaly was -0.8°C for the week centered around November 23. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -1.57°C and the ENSO Region 3.4 anomaly has averaged -0.92°C. La Niña conditions will likely persist through mid-winter. The SOI was +16.81 today. The preliminary Arctic Oscillation (AO) was -0.741 today. On November 29 the MJO was in Phase 8 at an amplitude of 1.228 (RMM). The November 28-adjusted amplitude was 1.590 (RMM).

Snowstorm near Christmas anytime would be nice.

An EPO-/AO-/PNA- pattern is forecast to develop. The transition to sustained cold could occur during the second week of December. Afterward, as mid-month approaches, the PNA is forecast to rise toward neutral levels. The rise in the PNA could coincide with an increase in potential snowfalls. Below is the PNA forecast and statistics for the percentage of days with measurable snowfall and 1" or more snowfall under EPO-/AO-/PNA-, EPO-/AO-/PNA+ and all other patterns for December (1950-2021).

Morning thoughts… It will be partly to mostly sunny, blustery, and cooler. High temperatures will reach the lower and middle 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 44° Newark: 46° Philadelphia: 44° Tomorrow will be fair and continued cool. Normals: New York City: 30-Year: 48.7°; 15-Year: 49.0° Newark: 30-Year: 49.3°; 15-Year: 49.8° Philadelphia: 30-Year: 50.3°; 15-Year: 50.9°