The October 4-8, 2007 Warm Spell: Quick Thoughts

[donsutherland1]

For several days, the model and ensemble guidance has been pointing to a period of unseasonable warmth for the eastern U.S. and southern Canada for the October 4-8 timeframe. In recent days, the ensemble guidance has grown more adamant with some exceptional anomalies.

Forecast 850 mb anomalies at 120 hours:


The forecast 500 mb pattern for that time closely resembles a composite of three very warm periods in the October 1-10 timeframe (1950-2006). Those warm spells occurred in 1950, 1967, and 1997.

Forecast 500 mb Height Anomalies at 120 hours:


Composite 500 mb Height Anomalies:


The following were the highest temperatures during the three similar outbreaks of warmth for select cities:

October 1-3, 1950:
Boston: 84°
Burlington: 82°
New York City: 86°
Philadelphia: 85°
Toronto: 78° (25.6°C)
Washington, DC (DCA): 87°

October 2-5, 1967:
Boston: 81°
Burlington: 77°
New York City: 86°
Philadelphia: 88°
Toronto: 79° (26.1°C)
Washington, DC (DCA): 91°

October 8-10, 1997:
Boston: 82°
Burlington: 76°
New York City: 82°
Philadelphia: 84°
Toronto: 75° (24.0°C)
Washington, DC (DCA): 87°

Conclusion:
Given the above data, I believe it is likely that New York City, Philadelphia, and Washington, DC will see temperatures peak at or above 85° during the upcoming warm period. Boston and Burlington should both see the highest temperature reach or exceed 80°. Toronto will likely see its temperature peak at or above 25°C (77°F). There is some possibility that Toronto could see a high temperature of 80° (26.7°C) and that Washington, DC might see the temperature approach or reach 90°.

Interestingly enough, for the three periods analyzed above, Toronto saw its first 0°C (32°F) or lower reading 10-14 days after the start of the warm period. As a result, it would not be surprising if Toronto saw its first freeze around October near mid-month, probably October 13-18 to allow for some margin of error.

[Stephanie]

Did those high pressure systems during those analog years also prevent any moisture from coming into those cities? Was there a drought situation along the Mid Atlantic and South East as well?

I'm getting nervous that the drought that has started in the Deep South and has crept up through the Carolinas is now affecting us. We only had .55" of precipitation in September and right now, any front that comes across the country breaks down due to this high pressure system.

[donsutherland1]

Stephanie,

In two cases, the warmth coincided with a dry pattern that came to an end beginning in November.

[Stephanie]

Thanks Don. I guess "the trend is our friend".

I know that the fall is the driest time of the year here, but actually, if it wasn't for that one time back at the end of August where we received 2.5" of rain over a couple of days, we'd really have a problem. August was dry up until that time as well.

[VoodooCadillac]

Thanks Don - I don't know about you, but I'm tired of the hot east coast summer/fall. Is there any change on the horizon? I'd be happy with a return to "normal." That will feel cold after what we've been through recently.

[donsutherland1]

Thanks Don - I don't know about you, but I'm tired of the hot east coast summer/fall. Is there any change on the horizon? I'd be happy with a return to "normal." That will feel cold after what we've been through recently.

I agree. I would most definitely appreciate cooler weather.

[donsutherland1]

In today's heat, Toronto saw its all-time October record go up in steam. On October 5, 1951, that city saw the thermometer reach 87° (30.6°C). Today, the mercury sizzled at 90° (32.0°C), the first-ever occasion on which the temperature reached 90° in October there.

[tropicana]

yes Don indeed you are correct!
not only that, the previous record for today, Oct 8, was set in 1993 of 26.8C 80F. And the mercury has stayed above this temperature for at least 8 consecutive hours.

Additionally, todays 89F 31.6C (updated) reading in Toronto was the 2nd hottest temperature ever recorded after Sept 15 of any year in the weather records. The hottest temp ever recorded after this date was 33.8C 92F set just this past Sept 25, 2007.

-justin-

[Stephanie]

I know that I've been looking forward to cooler weather. However, I can't help but think of the phrase "becareful what you wish for because you just might get it".

There are a lot of leaves falling, but many don't have color - it's more from the stress of the lack of rainfall. It seems strange to see the colors on the trees when it's humid and in the mid-80's.

[donsutherland1]

Correction:

Toronto's high temperature was 89° (31.6°C). This broke the all-time monthly record by 2°.

I regret the error.

[donsutherland1]

Thanks for this info., Justin.

[donsutherland1]

Stephanie,

The same is true up in the NYC area. The trees seem to be stressed by the recent dry spell even as total rainfall through August had been the 2nd highest on record.

[donsutherland1]

Verification:

From October 2, 2007:
Given the above data, I believe it is likely that New York City, Philadelphia, and Washington, DC will see temperatures peak at or above 85° during the upcoming warm period. Boston and Burlington should both see the highest temperature reach or exceed 80°. Toronto will likely see its temperature peak at or above 25°C (77°F). There is some possibility that Toronto could see a high temperature of 80° (26.7°C) and that Washington, DC might see the temperature approach or reach 90°.

The duration of the warm spell was a day longer than I had anticipated. Its magnitude also proved more impressive.

Highest Temperatures:
Boston: 86°, October 4
Burlington: 81°, October 5
New York City: 87°, October 8
Philadelphia: 89°, October 8
Toronto: 89° (31.6°C), October 8 (all-time October record)
Washington, DC (DCA): 94°, October 9