Fall is here again with winter also fast approaching. The new Daylight Savings Time regulations have been put in place and the days are rapidly becoming shorter. Welcome to fall and thank you for picking up a copy of the OFFICIAL Kenny Weather Winter Outlook for the 2007-2008 season. Following you will find a short introduction with a few notes about what to expect inside this outlook.
This year, I am including more data and maps in an effort to provide scientific data to backup my findings and predictions. It should be noted that long-range forecasting is still quite inaccurate at times and can sometimes yield very large errors. Nonetheless, advancements in technology and techniques allow many more capabilities compared to decades ago let alone year’s ago.
I hope that you take the time to read this outlook in its entirety and should you have any questions or comments, please do not hesitate to drop me an email using the contact information contained towards the back of this packet.
La Nina will no doubt play a large role in the overall pattern for this winter. This will be analyzed further within the meat and potatoes of this publication. Once again, I would like to thank you for taking the time to at least look over my winter outlook for the 2007-2008 season. Please enjoy!
Winter 2006-2007 Recap
Last fall, there were several storm systems that occurred late in the season that brought chilly rains to much of the Mid-Atlantic and Northeastern United States. This led many to believe that the pattern had a chance of continuing and bringing large quantities of snowfall or other winter precipitation to the region later in the winter. However, it turned out this was not the case. Winter started off on quite a mild note with little snowfall if any. In fact, the real notable snowfall events held off until late January and February when several interesting storms brought snow and ice accumulation to the DC area.
In my mind, the most notable storm was the snow, sleet and ice storm that impacted a large portion of the region on the week of Valentines Day. Most hard hit was areas just to the southeast of Washington, DC where freezing rain accumulated up to ¾ of an inch in some areas. This type of ice accumulation can easily cause power outages. Farther to the north, snow fell at the beginning of the event followed by a prolonged period of sleet and freezing rainfall. By the end of the storm, several inches of crusty, frozen and slippery precipitation had fallen area wide.
There were several smaller snowfall events that produced anywhere from 1-4 inches of snowfall depending on the location. In the end, the winter was deemed as fairly exciting, despite its rather late entrance. One of the factors that led to the lack of cold and snow early in the season was the existence of an El Nino weather pattern. An El Nino occurs when there is an abnormal warming of the waters in the Pacific Ocean. As you will learn shortly, this year there is the opposite (La Nina), where an abnormal cooling of the water in the same location occurs.
Winter 2007-2008 Data/Analysis and Outlook
[img width=150 height=150]http://img444.imageshack.us/img444/1008/tempanomweaktomodninagw6.th.gif[/img]The above maps show average temperature anomalies for years where there was a La Nina weather pattern in place. Stronger La Nina’s are shown using the map on the left while weaker La Nina’s are showing using the path on the right. You can clearly see that no matter what the case is, many of the year’s that contained La Nina weather patterns had above normal temperatures.
Areas that had negative anomalies in the temperature department were confined to the far northern United States where significant anomalies were recorded in some cases.
The year’s used for the weak to moderate La Nina dataset were: 1950-51, 1956-57, 1964-65, 1970-71, 1971-72, 1974-75, 1998-99, and 2000-01.
The year’s that were used for the moderate to strong La Nina data set were: 1950-51, 1955-56, 1964-65, 1970-71, 1973-74, 1975-76, 1988-89, 1998-99, and 2000-01.
The months that were used for both data sets were November through February. Therefore, the data spans two year’s.
It is suspected that the higher temperatures shown for a weaker La Nina is due to a smaller dataset and therefore, less data to work with. In reality, both maps should probably be more similar. The exception would be in the southern states where more positive departures would be likely under a strong La Nina weather pattern.
[img width=150 height=151]http://img512.imageshack.us/img512/1233/precipanomweaktomodninavp7.th.gif[/img][img width=150 height=153]http://img112.imageshack.us/img112/1925/precipanommodtostrongnihc6.th.gif[/img]
Above you will find the precipitation anomalies for different types of La Nina years. Once again you will find that they are quite similar. On the left the weak to moderate La Nina years are shown while on the right the stronger La Nina years are shown.
Notable differences include a relatively wetter area in PA during stronger La Nina years. Another difference is the overall less dry pattern during a strong La Nina than during a weaker La Nina. Again, due to less quantity within the right dataset, the data could be skewed slightly.
For the DC area, near normal precipitation is indicated during both strong La Nina winters as well as weaker La Nina winters.
The year’s used for the weak to moderate La Nina dataset were: 1950-51, 1956-57, 1964-65, 1970-71, 1971-72, 1974-75, 1998-99, and 2000-01.
The year’s that were used for the moderate to strong La Nina data set were: 1950-51, 1955-56, 1964-65, 1970-71, 1973-74, 1975-76, 1988-89, 1998-99, and 2000-01.
The months that were used for both data sets were November through February. Therefore, the data spans two year’s.
It is interesting to note that although precipitation during these months is near normal over most of the United States, the Palmer Drought Severity Index using average anomalies shows areas of drought for the Mid-Atlantic. This would fit in well with the pattern we are currently seeing this fall with drought conditions persisting and at times worsening.
[img width=150 height=149]http://img256.imageshack.us/img256/2505/pdsiweaktomodninack6.th.gif[/img][img width=150 height=151]http://img212.imageshack.us/img212/8185/pdsimodstrongninaln0.th.gif[/img]
Above, are the Palmer Drought Severity Index maps for select La Nina years. On the left are the weak to moderate La Nina years and on the right are the moderate to strong La Nina years. It is clear that the Mid-Atlantic Region and parts of the southeast United States are in drought from these maps. With the exception of the positive departures in MS/AL/TN and similar areas, these maps are very similar to the pattern we are in now (2007-2008).
Given the above, I would say that the moderate to strong La Nina is the better match for the current pattern. This is due to the similarities in drought areas across the above mentioned areas. Both datasets range from November to February. Therefore, it would be anticipated that the drought could persist throughout the winter season. However, due to the current severity of the drought, and based on the PDSI anomalies shown in the maps, some fairly significant improvement could occur sometime between now and winter.
Nonetheless, the drought may indeed persist for months and become a long term drought. It should be noted once again that exceptions do occasionally occur, which may yield a different outcome than is suggested by the analogs.
The year’s used for the weak to moderate La Nina dataset were: 1950-51, 1956-57, 1964-65, 1970-71, 1971-72, 1974-75, 1998-99, and 2000-01.
The year’s that were used for the moderate to strong La Nina data set were: 1950-51, 1955-56, 1964-65, 1970-71, 1973-74, 1975-76, 1988-89, 1998-99, and 2000-01.
The months that were used for both data sets were November through February. Therefore, the data spans two year’s.
North Atlantic Oscillation
In the next week or two, the NAO is expected to move into a negative phase. CPC ensemble charts show that the models are in good agreement with this dip into the negative zone. This could bring cooler temperatures into the eastern United States. There has certainly not been a lack of warmth across the east this fall. After the fall to the negative phase, models diverge somewhat on what the NAO will do. However, a line-of-best-fit placed on the charts indicate the NAO returning to a positive phase towards the end of October or early November. Warmer than average temperatures could be the result in the east, while cooler temperatures evolve in the west.
Given the above, it is possible that by the time winter rolls around, the NAO will be moving into another negative phase. As previous studies have shown, large east coast winter storms have a tendency to form during periods where the NAO is moving back towards the positive range. Therefore, there could potentially be a winter storm for parts of the east coast sometime early in the winter. However, that is all speculation at this point. In addition, the NAO is not the sole predictor in weather for North America.
Pacific-North American Teleconnection
If you are a snow-lover on the east coast, a positive PNA is what you should be rooting for. Typically, when the NAO is in a negative phase, the PNA is in a positive phase and vice versa. When the PNA is in a positive phase, heights are higher than average around Hawaii, as well as in the intermountain region of North America. Meanwhile, the southeast United States receives lower heights.
Therefore, at times when the NAO is forecasted to be negative, the PNA is generally forecast to move into the positive range. The opposite also holds true.
Pacific-Decadal Oscillation (PDO)
The PDO is a multi-decade climate variability. It is linked to ENSO in that ocean temperatures are the driving factor in its changes and cycles. During a +PDO ocean temperatures in the western Pacific cool while the eastern Pacific waters warm somewhat. During a –PDO the opposite holds true.
NOTE ABOUT ABOVE - I will add more teleconnections as I do more analysis and get more data.
2007-2008 Winter Outlook
Many weather enthusiasts and experts alike have released winter outlooks or are planning to release them soon. Based on the outlooks that I have seen and read so far this fall, there seems to be a good consensus to a warmer than normal winter with less precipitation than normal as well. Following, you will find my official predictions for this winter. Of course, they may be updated as new data becomes available and there is no guarantee of accuracy with long range forecasting. Maps are included on the following page.
I expect the drought to continue over areas of the Mid-Atlantic and Southeastern United States throughout the winter. Precipitation should be below normal over much of this region. However, there may be several opportunities for storm systems to dump some beneficial rainfall during the late fall and winter months. Given the fact that there is the potential for the NAO to tank negative early in the winter, there could be an early season snowfall or at least wintry precipitation event sometime in mid to late December. The Farmers Almanac forecasts an early season snowfall in November.
If you want colder than normal temperatures, it may be wise to take some trips into the northern part of the United States and into Canada where I am forecasting slightly below normal temperatures. It should also be noted that this forecast is primarily for areas on the eastern half of the United States.
I have also noticed that several forecasters have brought to attention the potential for a few icing events. I agree with this potential and will include that in my outlook as well.
I will call a colder pattern for the beginning of the winter followed by above normal temperatures as the winter presses on. Snowfall over the eastern United States may come close to normal if not reach normal over New England while snowfall deficits will likely be realized in the Mid-Atlantic region. However, in the end precipitation as a whole may come close to near normal as some precipitation events could occur during warm periods. Median snow to rain conversion is 1 inch of rain to every 10 inches of snow. However, this can change given certain conditions.
On the following page(s) you will find maps detailing the regions I have mentioned above. After the map section there will be a short conclusion and contact information. Please feel free to submit your questions and comments! Have a great fall! This outlook will be updated as needed or in late November.
[img width=150 height=123]http://img181.imageshack.us/img181/7310/tempdecembertn4.th.gif[/img]
[img width=150 height=123]http://img104.imageshack.us/img104/1759/tempfebruaryhs0.th.gif[/img]
[img width=150 height=123]http://img237.imageshack.us/img237/6476/precipwinterof9.th.gif[/img]
DC Area Focus
Given all of the data that has been presented in this outlook as well as some data not presented, I would anticipate that the Washington and Baltimore Region will have a colder start to winter, followed by positive temperature departures later in the winter. Snowfall will likely not reach normal seasonal values but may come close in the far western parts of the area. It is important to remember that the entire season’s snowfall could come in one storm or in several storms.
In addition, there could be some icing events for the DC/Baltimore areas given the forecast storm track (inland). It will be especially important to look for storm development when the NAO is negative and moving to positive while the PNA is positive. See below for the possible storm tracks for this winter. Note that the inland route is more likely for this winter with only some storms transferring energy to the coast. Miller B type systems will be more likely (energy transfer to coast from inland runner). Miller A type storms are certainly still possible (storms that move from Gulf of Mexico to coastal areas of east.
Normal snowfall is between 20-25 inches in the Montgomery County of Maryland. It drops off significantly as one moves south and east and it gains a lot when one moves toward the north and west. Snowfall should be around 10-15 inches for this winter. However, icing events are not included in that total and there could be 1-2 icing events.
Updates will be made to this outlook should more data become available in the coming weeks as we approach winter. Please see the next page for contact information and credits.
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This is my first try at a winter outlook and therefore there are certainly things I will need to improve. This is just my first try at one. I had a lot of help from some of the pro mets on here as well as some other sources. Thanks to all that aided!
Constructive criticism is welcomed but please don't come in here just to bash me.
~Kenny (Kmlwx)