March 13-26, 2005 Pattern Discussion

Winter Weather Discussion

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donsutherland1
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March 13-26, 2005 Pattern Discussion

#1 Postby donsutherland1 » Fri Mar 11, 2005 10:53 pm

Last week’s discussion raised a number of issues of what one might expect for the March 6-19, 2005 period.

The Mid-Atlantic and Northeastern states are likely to see temperatures moderate this weekend. Temperatures could reach the 40s into New England, especially on Tuesday. The first clipper could bring some rain and snow showers to parts of the Mid-Atlantic tomorrow. Another system will likely bring rain and gusty winds to the East on Monday night and Tuesday (March 7-8). In the wake of this system colder air will likely pour into the East.

The temperature soared to 46° in Boston on March 7. A system bombed out heading north-northeastward on March 8-9, bringing rain changing to briefly heavy snow to the I-95 cities along with very strong winds.

Accumulations included:
Boston: 4.8”
New York City: 1.5”
Philadelphia: 1.0”
Washington, DC: 0.8”

In the wake of the storm, temperatures fell into the teens from Philadelphia to Boston.

The March 9-10 and March 12-13 periods could see snow affect parts of the Mid-Atlantic and Northeast. The first system will likely bring at least some accumulations to Philadelphia, New York City, and Boston. Even Baltimore and Washington, DC have a chance at a light accumulation. Further south, Raleigh could experience perhaps some snow and ice before a possible change to rain/showers on March 9-10. The second system could bring accumulations to Washington, DC, Baltimore, Philadelphia, and possibly all the way to New England.

There was no March 9-10 storm. According to the latest computer guidance, a clipper will develop just south of Long Island and bring some rain and snow to parts of the northern Mid-Atlantic and New England in the March 11-13 period. New York City picked up 0.5” snow on March 11. According to the computer guidance, parts of New England could see a significant snowfall by the end of Saturday.

Throughout the period temperatures will likely average below normal in all the above-mentioned cities.

During the March 6-10 period, temperatures ran below normal as follows:

Boston: 7.2° below normal
New York City: 4.4° below normal
Washington, DC: 3.4° below normal

Colder than normal weather should continue through the duration of the period in the Ohio Valley and Midwest. After some rain in such cities as Chicago and Detroit around March 7, colder air should return. It is not out of the question that these cities see some accumulations of snow before the rain ends. March 8 could mark the start of a prolonged spell of below to much below normal temperatures. March 9-10 could see additional snow in this region. Over the next two weeks, I expect that Chicago will reach and exceed 40” snow for the season.

March 7 saw temperatures average above to much above normal in this region. However, March 8 saw colder than normal air return. Some snow arrived to Detroit and Chicago on March 10. Chicago picked up 1.5” of snow and Detroit received 1.2” on March 10.

In the Central Plains, weekend warmth will likely be replaced by colder temperatures on March 8. On March 6, Omaha could actually see the mercury soar into the 60s. During the March 7-8 timeframe temperatures will likely trend downward.

On March 6, the temperature hit 73° in Omaha. March 8-9, saw temperatures below normal at both Omaha and Kansas City.

Cities such as Omaha, Kansas City, St. Louis, and Bismarck will likely all receive some accumulations of snow during the period. The March 9-11 period offers one such opportunity for accumulating snow at least some of these cities.

This period saw a trace of snow in Bismarck, Kansas City, and Omaha. St. Louis received 0.1” snow on March 11.

The Pacific Northwest looks to remain warmer and drier than normal through the duration of the period. Temperatures at Seattle should be trending higher by March 7. The March 10-12 period offers the potential for temperatures to soar into perhaps the middle 60s or above at Seattle. Afterward, somewhat cooler air should begin to filter back into the region and some showers could occur.

Warm and dry weather continued in the Pacific Northwest. During the March 6-10 period, the temperature averaged 10° above normal in Seattle. On March 10, the temperature peaked at 63° in Seattle and on March 11, Seattle tied a record high of 65°. Total rainfall during this period amounted to 0.01”.

The drying process should continue in California for a time. Temperatures will likely trend upward during the weekend in California. Much above normal readings are likely in the March 8-12 timeframe for Los Angeles as the PNA crests then begins to fade. It is not out of the question that Los Angeles sees the temperature soar above 80° on one or more days during the height of the warmth. After the following weekend (March 12-13), the threat of new rainfall could increase.

Los Angeles was warmer than normal. The March 7-10 period saw the mercury reach or exceed 70° each day, including 75° on March 10 and 77° on March 11. There was no rainfall.

The March 13-26 Ideas:

Last week, I noted: Past experience with extreme blocks. Considering the extreme blocks that peaked in the February 15-March 15 timeframe (the 2005 block peaked on February 25), a sustained positive NAO regime typically didn’t arrive until April. 5/6 (83%) cases saw it arrive after April 1 (typically around April 5). 1/6 (17%) case saw it commence on March 24. The latest case saw its arrival delayed until April 18. The NAO has tanked anew (-4.511 on March 11), is progged to rise after mid-month but then possibly fall again. This is consistent with the above-noted information concerning extreme blocks.

Overall, the East should remain generally cooler than normal, though moderation is likely after mid-month.

• Temperatures should remain somewhat below normal through the entire period, on average. After March 24, readings are likely to be running close to normal in the Mid-Atlantic and Northeast. A storm moving off the Mid-Atlantic coast and heading northeastward from there could bring at least some accumulations of snow from Philadelphia to Boston during the 3/17-19 period. Parts of the northern Mid-Atlantic and Northeast could see a significant snowfall.

A shot of colder air should follow the storm before moderation sets in.

• Temperatures will likely average below normal in the Ohio Valley, Midwest, and Great Lakes region. The March 16-18 period could see Chicago, Detroit, and Cleveland receive accumulating snow. The weekend of March 19-20 could be much colder than normal in this region.

• The Central Plains will likely see a mild day on Saturday (March 12) before a new shot of colder air arrives. March 13-17 could see readings run below normal with some light snow perhaps around 3/16-17. After some moderation beginning on the 18th, cooler air could return during or after the following weekend.

• For the most part, warmer than normal, dry weather should persist in Seattle. The March 17-21 period could briefly experience readings falling to near or even somewhat below normal.

• The warmth should ease in Los Angeles after March 13. However, through the duration of the period, readings are likely to remain somewhat above normal. Rainfall should remain below normal.


February PDO: +0.81:

After three consecutive months where the PDO remained below zero, the PDO rebounded to +0.44 in January. In February, the PDO continued its rapid recovery to +0.81. This may have implications both for the coming summer, particularly hurricane season, and following winter. Given the latest PDO, odds increasingly favor the PDO averaging positive during the summer and during Winter 2005-06.

• Summer PDO
January-February PDO +0.625 or Above: 22/31 (71%) cases positive
January-February PDO > 0: 35/54 (65%) cases positive
January February PDO < 0: 32/51 (63%) cases negative

• PDO during following Winter (December-February)
January-February PDO +0.625 or Above: 21/31 (68%) cases positive
January-February PDO > 0: 37/54 (69%) cases positive
January-February PDO < 0: 32/51 (63%) cases negative

In terms of the upcoming hurricane season, the positive PDO reaffirmed the initial idea discussed previously of another active season. In seasons where the MEI averaged less than +0.600 but above –0.500 (which is likely this season) and the PDO averaged > 0, tropical activity averaged as follows:

Named Storms: 12.8
Hurricanes: 7.8
Major Hurricanes: 3.4

In contrast, in seasons where the MEI was the same as noted above but the PDO averaged negative, the following tropical activity was recorded, on average:

Named Storms: 11.3
Hurricanes: 7.0
Major Hurricanes: 3.0

With regard to the PDO, research has found a roughly 15-20-year cycle with turning points in 1924 (PDO-), 1941 (PDO+), 1957 (PDO-), and 1976 (PDO+). Per this cycle, it would appear that the PDO is either in the early stages of a new negative cycle or is transitioning there. However, there may be more to the story. Dr. Yi Chao of NASA’s Jet Propulsion Laboratory and Drs. Michael Ghil and James McWilliams of UCLA have found evidence that the PDO may have a two-part structure. In addition to the shorter-term PDO cycle noted above, there might be a longer-term PDO cycle of up to 70 years, as well. Longer-term PDO+ cycles occurred up to the 1930s and since the 1970s. In between, was a longer-term PDO- cycle.

The convergence of longer-term and shorter-term cycles might well explain the frequency for given annual PDO tendencies. During the 1930-76 period, the PDO averaged negative 66% of the time. However, during the 1944-1975 timeframe, it was negative in 28/32 (88%) years. In contrast, since 1977, it has averaged positive 75% of the time. During the 1977-1998 period, it has been positive in 18/22 (82%) years.

Finally, for those who are interested in greater detail in examining the likely average PDO during the winter (December-February), the following statistics can be helpful:

∙ January-February Average: Positive
∙ September-October Average: Positive
Result: December-February Average Positive 25/28 (89%) cases

∙ January-February Average: Positive
∙ September-October Average: Negative
Result: December-February Average Negative 14/26 (54%) cases

∙ January-February Average: Negative
∙ September-October Average: Positive
Result: December-February Average Positive 13/17 (76%) cases

∙ January-February Average: Negative
∙ September-October Average: Negative
Result: December-February Average Negative 28/33 (85%) cases

Therefore, if one is looking for the likely winter PDO, aside from the statistics noted at the beginning of this section, the September-October average for the PDO could be crucial.

A Look Back: Winter 1884-85 in North Carolina:

The winter in North Carolina was described as follows: “The weather of the past three months has been the severest and most persistent experienced here for many years. There has been an unusual quantity of rain, hail, sleet, and snow, and the frosts have been frequent and severe. Very little outdoor work has been done by the farmers. Plowing that should have been done five weeks ago has just been commenced.”

Source: “The Winter in North Carolina,” The New York Daily Times, April 4, 1885.

Note: Now that winter is nearing an end, this weekly post will also appear in the United States Weather forum.
Last edited by donsutherland1 on Thu Mar 17, 2005 11:11 am, edited 1 time in total.
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Re: March 13-26, 2005 Pattern Discussion

#2 Postby donsutherland1 » Sat Mar 12, 2005 11:05 am

Two quick points:

1) The NAO continues to fall. The March 12 reading was -4.941.

2) The 3/12 0z run of the ECMWF depicts a winter storm along the East Coast Friday into Saturday. Cities including Washington, DC and Philadelphia would pick up at least some accumulations if that run is correct.

More importantly, the 0z run also continued the ECMWF's trend toward colder solutions with each run.
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krysof

#3 Postby krysof » Sat Mar 12, 2005 12:03 pm

could you post the site how to get to the model, i want to see it
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#4 Postby Jrodd312 » Sat Mar 12, 2005 12:19 pm

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#5 Postby Guest » Sat Mar 12, 2005 3:27 pm

Thank you! :P
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W13
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#6 Postby W13 » Sun Mar 13, 2005 5:08 pm

Great discussion, as always, Don. :)
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Re: March 13-26, 2005 Pattern Discussion

#7 Postby donsutherland1 » Sun Mar 13, 2005 9:29 pm

As noted at the beginning of this thread: A storm moving off the Mid-Atlantic coast and heading northeastward from there could bring at least some accumulations of snow from Philadelphia to Boston during the 3/17-19 period. Parts of the northern Mid-Atlantic and Northeast could see a significant snowfall.

Currently, a look at the synoptic situation argues that there remains a good chance that Philadelphia to Boston will see at least some accumulations of snow even as some of the computer guidance has tried to keep the precipitation shield too far to the south.

With the extreme block in place, there will likely continue to be greater model variability than normal. With the PNA progged to be rising immediately prior to the storm's reaching the Mid-Atlantic coast, I believe that the trough will likely be sufficiently sharp so that the storm exits northeastward off the Coast as opposed to heading mainly east out to sea. Consequently, accumulating snow will likely occur into southern New England (including Boston).

I also believe that odds favor Washington, DC seeing some accumulations.
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#8 Postby donsutherland1 » Sun Mar 13, 2005 9:30 pm

Thanks, W13.
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Re: March 13-26, 2005 Pattern Discussion

#9 Postby donsutherland1 » Mon Mar 14, 2005 2:40 pm

Several quick points:

1) The FSU Superensemble remained suppressed through 3/17 0z:

Image

This suggests that the suppressed solution is certainly on the table.

2) However, there remain arguments against such suppression:

• Toward the end of the week, the extreme block will be weakening
• Toward the end of the week, the PNA should be rebounding temporarily. If so, the trough should be sharper.

Right now, the outcome remains highly uncertain. In fact, the models might well be at their "high tide" of suppression and that "tide" could begin to ebb as later runs sense the weakening of the block, rebound of the PNA. At this point in time, it would be premature to rule out the prospect of snowfall for any of the major cities from DCA to BOS. However, given the FSU Superensemble, one should not completely dismiss the more suppressed idea either.

I'll probably have additional thoughts tomorrow night or Wednesday.
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Re: March 13-26, 2005 Pattern Discussion

#10 Postby donsutherland1 » Wed Mar 16, 2005 10:25 am

On Monday, I noted, "At this point in time, it would be premature to rule out the prospect of snowfall for any of the major cities from DCA to BOS. However, given the FSU Superensemble, one should not completely dismiss the more suppressed idea either."

It is now quite clear, the Superensemble's "super suppression" idea will triumph this week as the tale of too many shortwaves contributed to weaker and more easily suppressed systems. Therefore, my early idea of a track farther to the north has proved incorrect.

Finally, the block is now eroding. As stated in a past weekly pattern discussion, once the NAO goes positive, the prospects for a KU snowstorm will likely be all but finished for Winter 2004-05 even if a positive NAO is not sustained early on. Looking even farther ahead, sometime during the first 10 days of April, I continue to believe that a sustained positive NAO regime will lock into place.
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