usedtobe Posted July 17, 2012 Share Posted July 17, 2012 There have been comments that I cancelled winter for NYC and BOS in my talk. In reality I never made a forecast for either city. I usually make any such calls for DCA to Phl as you don't need quite the same pattern to get snow over NE as you need for farther south. That said, I did include slides for NYC. We'll start with two tables, one showing the 10 top snow seasons since 1950 (courtesy of D Sutherland) and one of the bottom 10 snow years (left table). Red indicates El Nino years and Blue La Nina years. 5 of 10 of big snow years were El Nino years and only 2 were La Nina years. However those two were NYC's two biggest snow years. NYC shared 6 top ten showy seasons with DCA and six with BOS but only 3 of the six (underlined) were big years for all three cities. Obviously, El Nino's can be good years but, the table of the left shows that 4 of the worst 10 were also nino years. Ninos can be real good or sometimes real bad. If you composite the 500 anomaly patterns for those same years you fine marked differences between the two. The good years (on left) have a nice east coast trough along with a negative AO and NAO (note all the red over greenland and canada) while also having some ridging over the western US. Remember that a negative AO has two impacts, one is to keep pressures high over Canada and since air moves from high to lower pressure that keeps cooler air filtering into the U.S. north of the storm track which is typically suppressed south of its normal location. By contrast, the crappy snow year composite shows lower than normal heights and pressures across canada and greenland and higher heights to the south which helps bottle up the cold air. Also, note that the bad years have lower than normal heights over Ak and above normal just north of Hawaii, that a positive EPO. The composite also shows below normal heights poking into the western US where you want above normal heights. Trials, Snow88 and CT Blizz would probably be unruly in such years. The next table looks at the El Nino seasons giving the 3.4 temp anomaly for NYC, snowfall (blue is below average snowfall, red above) , and the number of months the AO was below -.5, the NAO was below -.5 and the PNA was positive during the 4 month period December-March. While there are years like 1986-1987 where the AO was mostly negative and the PNA positive where both NYC and BOS got below normal snowfall (DCA got 3 KU storms), most years where the OA was strongly negative even in EL NIno years ended up being bad in terms of snow for all 3 cities. The next slide shows the el nino snowy years for NYC and DCA (left) and the years when all three big cities got below normal snowfall (right). Note how different the Pacific is in the two cases. Oddly enough, I looked at the tropical forcing in the Pacific and didn't many differences between the two composites. Anyway, the NAO and PNA seem to be important. I also composited the 500 anomalies for 24 hrs or so prior to NYC getting a foot of snow (certainly not a complete data base) and compared it to cases where DCA got at least 8 inches. The composites are pretty similar. NYC does better with Miller Bs but still needs the 50 50 low. I also discussed how there were a number of things that correlated with the AO, for example OCtober Eurasian snowcover, Atlantic SSTA, Solar and Bboy's AP index, November stratospheric winds near 60N and stratospheric warming but the correlations were generally too weak to use by themselves to forecast the winter AO. I also mentioned the QBO which tends to act differently on the pattern based on ENSO and the solar cycle and that stratospheric warming events last year were misused badly. I didn't make a forecast but I did for DCA in 2009-2010 at least by early December and did call for a snowy season. I'm not always negative. So far I'm neutral about the winter but wish the Glaam would rise a tad. Link to comment Share on other sites More sharing options...
Isotherm Posted July 17, 2012 Share Posted July 17, 2012 Great stuff Wes. Really want to make it to a conference one of these years. I think the NAO/AO/PNA are very important for the entire I-95 corridor, but for NYC southward, ENSO becomes more important as well. Once into the southern mid atlantic and SE US, the ENSO is probably a bigger factor than the other teleconnections wrt snowfall. I hear you re the GLAAM - we don't want a 65/66 or 06/07 type strange acting Nino with the negative AAM. Plenty of time for change. Link to comment Share on other sites More sharing options...
uncle W Posted July 17, 2012 Share Posted July 17, 2012 Thanks Wes...Great post...I looked up precipitation maps for those years...the good years had more coastal events while the bad years had more inland runners... Link to comment Share on other sites More sharing options...
usedtobe Posted July 17, 2012 Author Share Posted July 17, 2012 Thanks Wes...Great post...I looked up precipitation maps for those years...the good years had more coastal events while the bad years had more inland runners... Thanks, that's what I would have thought. Link to comment Share on other sites More sharing options...
uncle W Posted July 17, 2012 Share Posted July 17, 2012 Great stuff Wes. Really want to make it to a conference one of these years. I think the NAO/AO/PNA are very important for the entire I-95 corridor, but for NYC southward, ENSO becomes more important as well. Once into the southern mid atlantic and SE US, the ENSO is probably a bigger factor than the other teleconnections wrt snowfall. I hear you re the GLAAM - we don't want a 65/66 or 06/07 type strange acting Nino with the negative AAM. Plenty of time for change. they are OK if you like warm Decembers and little snow before the middle of January...I'll take those two over last years debacle... Link to comment Share on other sites More sharing options...
uncle W Posted July 17, 2012 Share Posted July 17, 2012 Thanks, that's what I would have thought. two el nino winters that went wrong were 1972-73 and 1997-98...both had plenty of precipitation but had little cold air to work with... Link to comment Share on other sites More sharing options...
usedtobe Posted July 17, 2012 Author Share Posted July 17, 2012 two el nino winters that went wrong were 1972-73 and 1997-98...both had plenty of precipitation but had little cold air to work with... 1972-1973 had a positive OA most of the month. !997-1998 had everything except we never could get the 50 50 low so the cold air never held in. It had really nice storm tracks. Link to comment Share on other sites More sharing options...
Neblizzard Posted July 17, 2012 Share Posted July 17, 2012 1972-1973 had a positive OA most of the month. !997-1998 had everything except we never could get the 50 50 low so the cold air never held in. It had really nice storm tracks. There is definitely a coorelation between +Enso and east coast storms. I remember 97-98 featured at least ten coastal storms thruout the winter but the El Niño flooded the CONUS with too much warm air. What was the state of the NAO that year? Link to comment Share on other sites More sharing options...
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