The updated climate outlooks from the NOAA Climate Prediction Center (CPC) reflect the unusual climate pattern that has developed the past few months. Previous outlooks predicted a tendency towards warmer and perhaps drier across the northern plains, but the outlook issued on November 15 2012 portend a difference. The updated outlooks reflect unusual changes in the climate signals that have developed since late summer. Key among these changes include the weakening (cooling) of the El Nino / Southern Oscillation (ENSO) signal in the Equatorial Pacific. During the spring and summer of 2012, La Nina was fading and El Nino was developing. The forecast then called for a weak, possibly moderate El Nino during the 2012/2013 Northern Hemisphere Winter. However, during the summer of 2012 an unexpected cooling of the Tropical Pacific began. Although rare, such events have been noted infrequently in the past 60 years of data. This reversal of the temperature patterns in the Pacific is not clearly understood, but may in part be tied to the larger scale Pacific Decadal Oscillation (PDO).
Looking at the historic record, there are only a handful of years where the Pacific Ocean began to exhibit the El Nino (warming) signal during the spring and summer, only to stall or cool slightly during the fall. These include 1953, 1969, 1987 and 1993 - only 4 years of 62 years of historic record. It is important to note that in each of the following winter seasons the Pacific, while technically "ENSO Neutral" was warmer than normal. Taken in aggregate, the winters listed above tended towards cooler and slightly wetter than median. However, each winter listed represent wide swings in temperature and precipitation as other, shorter term climate signals influenced our weather .
Below are the images from the CPC and are the Official Outlook issued November 15 2012.
The next set of images represent the "average" departure from normal temperature and precipitation across the northern plains during December - February, for the 4 winters listed above. It is crucial to note these are simple analogs and not outlooks, representing historical weather based on similar events in the Pacific during the previous 6 to 9 months.
Average Departure from normal Temperature (left) and precipitation (right) based on alaog years 1953/54, 1969/70, 1987/88 and 1993/94. Click on image for a larger version.
"Image provided by the NOAA/ESRL Physical Sciences Division, Boulder Colorado from their Web site at http://www.esrl.noaa.gov/psd/"
Based on the historical precedence of the few previous El Nino events that weakened or stalled, the following winter seasons exhibited a significant amount of variability in temperature, with brutal cold snaps followed by rapid warm ups. One example is seen in December 1993. The high temperatures recorded at the University of North Dakota Climate station were in the upper 20s to lower 30s from December 8th to the 19th; a shift in the pattern sent a cold front through the area just before Christmas. High temperatures failed to get above zero on Christmas day 1993 or the next two days, with lows to -20F. A similar temperature roller-coaster is noted in the data for the other years listed as well. From the snowfall and liquid totals, those winters were generally within the normal climatic range for "normal" across the region, perhaps indicating a bias towards above median precipitation over the southern Red River Valley and western Minnesota Lakes Country.
The upshot then: With the El Nino weakening, it's influence will be muted. Although it has weakened, the Equatorial Pacific forecast to remain [weakly] warmer than normal; that will still have an influence as sub-seasonal signals such as the MJO and AO fluctuate.
Some of the climate signals that can have a significant impact on our "weather" are listed below.
Madden-Julian Oscillation (MJO)
The Madden-Julian Oscillation is a relatively short term climatological event on the order of 45 to 60 days in length. An MJO is essentially a wave of relatively warm water that translates from the Indian Ocean, across the tropical Pacific to the west coast of South America. There is typically an upper level wave of energy associated with the MJO that has an effect on tropical weather in the Atlantic basin as well. Recent research indicates that these upper level waves dampen hurricane activity in the Atlantic Basin. For our weather, a strong MJO serves to modulate the strength of a preexisting El Nino or La Nina. At this time there is limited skill at predicting the MJO strength, therefore it does not have a significant impact on the seasonal outlooks. However, shorter term forecasts such as the 8 to 14 day outlook consider MJO influences.
El Nino Southern Oscillation
Fluctuations in sea surface temperatures (SST) across the tropical Pacific Ocean are part of the El Nino/Southern Oscillation (ENSO). The warm phase of the ENSO is called El Nino and the cool phase is called La Nina. During a strong El Nino, warmer than normal winter weather generally prevails across the northern plains, as the polar jet stream is displaced north into Canada, preventing incursions of arctic air. The primary storm track is across the southern states, resulting in drier than normal conditions across our region. During La Nina, the storm track is more variable, resulting in intervals of cold and warmth and the potential for significant winter storms. An important aspect of forecasting the winter weather in the northern plains region is having the ability to predict the location and magnitude of the largest SST anomalies in the tropical Pacific Ocean. Warm ocean water leads to thunderstorm formation (called convection) and large clusters of thunderstorms that form over the tropical Pacific have a major influence on the pattern of the jet stream. This can influence the location of the storm track and where the areas of warmer and colder weather will prevail across North America. If the most persistent convection in the western Pacific is close to the South American coast, this usually results in frequent and persistent cold air outbreaks over the upper plains. If the most persistent convection is closer to the International Date Line, warmer than normal weather usually prevails across our region. Last winter featured above normal sea surface temperatures west of the International Date Line and near to below normal sea surface temperatures east of the Date Line.
Since August 2012, water temperatures west of the Date Line have been a bit above normal, indicative of a warm phase ENSO. However cooler water below the surface has been 'upwelling' which has kept the El Nino from becoming as strong or as widespread as originally expected..
Pacific Decadal Oscillation (PDO)
The Pacific Decadal Oscillation (PDO) is a larger, longer time scale oscillation than ENSO. The PDO affects the ocean temperature anomalies over the Pacific Ocean, with a time span of decades. Since the PDO affects most of the Pacific Ocean, and ENSO is primarily a tropical Pacific Ocean temperature anomaly, the PDO modulates the strength of ENSO. When the PDO is in the positive phase, as it was from 1978 to 1998, El Nino conditions dominate the tropical Pacific Ocean and strong El Nino conditions like the 1982-83 and 1997-98 events are more likely. La Nina events, the negative phase of ENSO, are weaker and less frequent. During the negative phase of the PDO, the opposite is true. The PDO was in the negative phase from around 1947 until 1977. During that time, the Valley Region saw generally colder than normal winters. Drier than normal weather is also more prevalent over the northern plains, with greater than 60% of our dry years occurring since 1950 occurring during the negative phase of the PDO. Given the 20 to 30 year cycle of the PDO, we would expect the PDO to trend towards the negative phase over the next decade. The PDO has mostly been in the negative phase since1998, with brief weaker positive peaks between 2002 and 2007. So what phase will it be in this winter? Based on the current trend, the negative phase seems likely. Based on that alone, it would seem that a colder and drier than normal winter would be indicated for the Valley Region.
NAO One of the most significant atmospheric variables to affect the winter weather over the northeast third of the United States is the phase of the North Atlantic Oscillation (NAO). The negative phase of the NAO results in cold and snowy weather, as was the case during December of 2000, when Grand Forks had 19 inches of snow and averaged 11.8F below normal. The following month the NAO went into the positive phase, which typically results in warm and dry weather over our region. January 2001 in Grand Forks was 9.1F above normal with only 3.3 inches of snow! Unfortunately, it is difficult to predict changes in the phase of the NAO, meaning that sharp changes in the winter weather pattern like those of December 2000 to January 2001 can occur without much warning. Recently the NAO has been strongly negative which favors colder than normal weather across the northern plains. AO Another significant atmospheric variable is the Arctic Oscillation (AO). The AO is a measure of the difference in pressure (at sea level) or 500-hpa height (in the middle troposphere) between the northern polar region and middle latitudes. When pressures and heights are above (below) average at high latitudes and below (above) average at middle latitudes - the AO is defined as negative (positive) and is associated with below (above) average temperatures over middle latitudes - including the United States. The AO can swing rapidly and dramatically from one phase to the next in a matter of days, then remain in a strong positive or negative phase for weeks or months. An example of how the AO can negatively influence the ENSO includes the 2009/2010 winter, when a moderate, borderline strong El Nino was expected to bring us a very mild and dry winter. The AO dropped to record low (negative) levels during December 2009 – February 2010. This completely disrupted the El Nino signal, resulting in a slightly cooler and wetter winter – more like a La Nina. In particular, the AO and NAO are difficult to predict beyond a few days or weeks. Improvements in computer models have shown promise this skill may be extended to several months, and indeed the CPC has used one of these computer models - the Climate Forecast System Version 2 - to help modify this outlook. For additional information contact the NWS in Grand Forks. Mark Ewens, Climate Services Focal Point 701-772-0720 x327 / Mark.Ewens@noaa.gov The Climate Prediction Centers Long-Lead Seasonal Outlook Non Technical Discussion is repeated below PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830AM EST THURSDAY NOV 15 2012
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS
THE MAIN FACTORS WHICH USUALLY INFLUENCE THE SEASONAL CLIMATE OUTLOOK INCLUDE:
1) EL NINO AND LA NINA - WHICH TOGETHER COMPRISE EL NINO/SOUTHERN OSCILLATION
OR ENSO. IMPACTS OF THESE EVENTS ARE SUMMARIZED BY SEPARATING 3-MONTH
OBSERVATIONS FROM 3 OR MORE DECADES INTO EL NINO, NEUTRAL, AND LA NINA SETS,
AVERAGING EACH SEPARATELY, AND THEN COMPUTING ANOMALIES. THESE ARE CALLED "ENSO
COMPOSITES", WHICH ARE USED AT TIMES TO SUBJECTIVELY MODIFY THE FORECAST.
2) TRENDS - APPROXIMATED BY THE OCN TOOL AS THE DIFFERENCE BETWEEN THE MOST
RECENT 10-YEAR MEAN OF TEMPERATURE OR 15-YEAR MEAN OF PRECIPITATION FOR A GIVEN
LOCATION AND TIME OF YEAR AND THE 30-YEAR CLIMATOLOGY PERIOD (CURRENTLY
3) THE TROPICAL 30-60 DAY OSCILLATION - SOMETIMES CALLED MADDEN JULIAN
OSCILLATION (MJO) - AFFECTS CLIMATE VARIABILITY WITHIN SEASONS.
4) THE NORTH ATLANTIC OSCILLATION (NAO) AND THE PACIFIC NORTH AMERICAN (PNA)
PATTERNS - WHICH AFFECT THE TEMPERATURE ANOMALY PATTERN ESPECIALLY DURING THE
COLD SEASONS. THESE PHENOMENA ARE CONSIDERED LESS PREDICTABLE ON A SEASONAL
TIMESCALE THAN ENSO.
5) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE
VARIABILITY AFFECTING THE TROPICS AND THE NORTH PACIFIC AND NORTH AMERICAN
REGIONS, BUT WHICH VARIES ON A MUCH LONGER TIME-SCALE THAN ENSO.
6) PERSISTENTLY DRY OR WET SOILS IN THE SPRING AND SUMMER AND SNOW AND ICE
COVER ANOMALIES IN THE WINTER. THESE FACTORS TEND TO PERSIST FOR LONG PERIODS
AND ACT AS A KIND OF MEMORY IN THE CLIMATE SYSTEM.
7) STATISTICAL FORECAST TOOLS - CANONICAL CORRELATION ANALYSIS (CCA), SCREENING
MULTIPLE LINEAR REGRESSION (SMLR), CONSTRUCTED ANALOGUE (CA) AND ENSEMBLE CCA
8) DYNAMICAL FORECAST MODELS - INCLUDING THE NCEP CLIMATE FORECAST SYSTEM
(CFS). THE UPGRADED PARALLEL VERSION OF THE CFS (CFSV2) BECAME OPERATIONAL IN
LATE MARCH OF 2011. BOTH VERSIONS OF CFS ARE CURRENTLY RUN IN PARALLEL. AN
EXPERIMENTAL MODEL FORECAST SYSTEM, THE NATIONAL MULTI-MODEL ENSEMBLE,
COMPRISED OF SEVERAL MODELS AND DESIGNATED NMME, MAY ALSO BE USED
EXPERIMENTALLY AND SUBJECTIVELY UNTIL IT IS INCLUDED INTO THE CONSOLIDATION. AN
INTERNATIONAL MODEL ENSEMBLE DESIGNATED IMME IS ALSO AVAILABLE.
9) CONSOLIDATION (CON) - AN OBJECTIVE, SKILL WEIGHTED COMBINATION OF THE OCN,
CCA, SMLR, ECCA, AND CFS FORECASTS IS USED AS A FIRST GUESS IN PREPARING THE
FORECAST MAPS. THIS TECHNIQUE MAKES OPTIMUM USE OF THE KNOWN SKILL OF OUR
ENSO NEUTRAL CONDITIONS ARE FAVORED THROUGH THE WINTER 2012-13 AND THE LATEST
OBSERVATIONS AND MODEL PREDICTIONS EMPHASIZE A HIGH DEGREE OF UNCERTAINTY IN
SOME AREAS OF THE UNITED STATES FOR THE UPCOMING WINTER AND SUBSEQUENT SEASONS.
THE DJF 2012-13 TEMPERATURE OUTLOOK INDICATES ENHANCED CHANCES FOR ABOVE NORMAL
TEMPERATURES FOR MUCH OF THE WESTERN CONTINENTAL U.S. STRETCHING ACROSS THE
SOUTH CENTRAL GREAT PLAINS TO THE WESTERN GULF COAST. BELOW NORMAL TEMPERATURES
ARE FAVORED FOR PARTS OF THE NORTHERN GREAT PLAINS AND WESTERN GREAT LAKES AND
THE FLORIDA PENINSULA. FOR ALASKA, THERE ARE ELEVATED ODDS FOR ABOVE-NORMAL
TEMPERATURES ALONG THE NORTH SLOPE AND BELOW NORMAL TEMPERATURES FOR THE
SOUTHEAST AND ALASKA PANHANDLE.
THE DJF 2012-13 PRECIPITATION OUTLOOK FAVORS ABOVE-AVERAGE PRECIPITATION FOR AN
AREA IN THE TENNESSEE VALLEY AND BELOW-AVERAGE PRECIPITATION FOR PARTS OF
CALIFORNIA, NEVADA, SOUTHEAST ALASKA AND THE ALASKA PANHANDLE.
IN LOCATIONS WHERE THE LIKELIHOODS OF SEASONAL MEAN TEMPERATURES AND SEASONAL
PRECIPITATION AMOUNTS ARE SIMILAR TO THE CLIMATOLOGICAL PROBABILITIES, EQUAL
CHANCES (EC) OF BELOW, NEAR, AND ABOVE-AVERAGE TEMPERATURE AND PRECIPITATION
BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS
NOTE: FOR GRAPHICAL DISPLAYS OF THE FORECAST TOOLS DISCUSSED BELOW SEE:
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
EQUATORIAL PACIFIC SSTS ALONG THE EQUATOR REMAIN NEAR TO ABOVE-AVERAGE (UP TO
+1.5 DEGREES C) WEST OF ABOUT 120W AND THESE HAVE INCREASED DURING THE MONTH OF
OCTOBER. NEAR AVERAGE SSTS ARE CURRENTLY EVIDENT ACROSS THE EAST PACIFIC
EASTWARD OF THIS LONGITUDE. THE UPPER OCEAN HEAT CONTENT REMAINS ABOVE-AVERAGE
ACROSS MUCH OF THE CENTRAL AND EASTERN PACIFIC AT A DEPTH GENERALLY RANGING
FROM 50 - 150 M EAST OF THE DATE LINE. WHILE THE SUBSURFACE AND SURFACE PACIFIC
OCEAN HAS RECENTLY WARMED, THE TROPICAL ATMOSPHERE REMAINED LARGELY CONSISTENT
WITH ENSO-NEUTRAL. UPPER- AND LOWER-LEVEL WINDS WERE NEAR AVERAGE, AND THE
STRENGTH OF ANOMALOUS CONVECTION DECREASED OVER THE PAST MONTH. OCEAN SURFACE
TEMPERATURES ARE ALSO BELOW AVERAGE IN PARTS OF THE NORTH PACIFIC OCEAN, GULF
OF ALASKA AND OFF THE SOUTHEAST U.S. COAST.
PROGNOSTIC DISCUSSION OF SST FORECASTS
ENSO-NEUTRAL CONDITIONS ARE FORECAST THROUGH THE NORTHERN HEMISPHERE WINTER
2012-13. THE CPC SST CONSOLIDATION FORECAST FOR THE NINO3.4 REGION AND ALL OF
ITS MODEL COMPONENTS FORECAST ENSO NEUTRAL THROUGH NORTHERN HEMISPHERE SUMMER
2013. THE CFSV2 HAS THE LOWEST FORECAST SSTS DURING THE WINTER MONTHS AND HAS
VALUES SLIGHTLY BELOW ZERO UNTIL LATER SPRING. MOREOVER, ENSEMBLE MEANS OF
FORECASTS FROM BOTH THE NMME AND IMME FOR THE NINO3.4 REGION FORECAST
ENSO-NEUTRAL INTO AT LEAST THE SUMMER 2013 PERIOD, ALTHOUGH SOME MEMBERS OF THE
MODELS USED IN EACH OF THESE SYSTEMS DO FORECAST ANOMALIES ABOVE 0.5 DEGREES C
DURING THIS PERIOD. THE IRI NINO3.4 FORECAST PLUME ALSO TELLS A SIMILAR STORY
WITH A MAJORITY OF MODELS INDICATING ENSO NEUTRAL INTO SUMMER 2013.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
FORECASTS WERE MADE WITH THE EXPECTATION OF ENSO NEUTRAL CONDITIONS DURING THE
WINTER AND SPRING MONTHS GIVEN THE LATEST OBSERVATIONS AND SST FORECASTS CITED
EARLIER. THE FORECASTS WERE BASED ON DYNAMICAL MODEL OUTPUT FROM THE CFSV2,
NMME AND IMME AS WELL AS INPUT FROM SOME STATISTICAL FORECAST TOOLS, LONG-TERM
TRENDS AND THE CON WHERE DEEMED HELPFUL. LONGER LEAD OUTLOOKS WERE BASED ON THE
CON FROM MJJ 2013 ONWARDS. ENSO-NEUTRAL COMPOSITES DURING NEGATIVE PDO PERIODS
WERE CONSIDERED. AS ALWAYS, A SIGNIFICANT WILDCARD IN THE UPCOMING WINTER
OUTLOOK IS THE UNCERTAINTY ASSOCIATED WITH THE PHASE OF THE ARCTIC OSCILLATION
(AO) WHICH THE MAJORITY OF THE CURRENT LITERATURE INDICATES LOSES
PREDICTABILITY QUITE RAPIDLY BEYOND A FEW WEEKS.
PROGNOSTIC DISCUSSION OF OUTLOOKS - DJF 2012 TO DJF 2013
THE DJF 2012-13 TEMPERATURE OUTLOOK INDICATES ENHANCED ODDS FOR ABOVE NORMAL
TEMPERATURES FOR MUCH OF THE WESTERN CONTINENTAL U.S. STRETCHING ACROSS THE
SOUTH CENTRAL PLAINS TO THE WESTERN GULF COAST AND WAS PRIMARILY BASED ON
REASONABLE AGREEMENT AMONGST DYNAMICAL MODEL OUTPUT FROM THE CFSV2, THE NMME
AND THE IMME. BELOW NORMAL TEMPERATURES ARE FAVORED FOR THE FLORIDA PENINSULA
CONSISTENT WITH THE PREVIOUS OUTLOOK AND IS SUPPORTED BY LONG-TERM TRENDS,
NEARBY CURRENT BELOW-NORMAL SSTS AND SOME DYNAMICAL MODEL OUTPUT. THE ENHANCED
LIKELIHOOD FOR BELOW-NORMAL TEMPERATURES ACROSS THE NORTHERN PLAINS AND WESTERN
GREAT LAKES IS PRIMARILY BASED ON CONSISTENT SIGNATURES IN CLIMATE MODEL OUTPUT
FROM THE CFSV2, NMME AND IMME FORECASTS. FOR ALASKA, THERE ARE ELEVATED CHANCES
FOR ABOVE-NORMAL TEMPERATURES ALONG THE NORTH SLOPE CONSISTENT WITH RECENT
POSITIVE TRENDS IN THIS AREA AND FURTHER SUPPORTED BY LONG-RUNNING AND
CONSISTENT FORECASTS FROM DYNAMICAL MODELS OVER THE LAST FEW MONTHS. ENHANCED
ODDS FOR BELOW NORMAL TEMPERATURES ARE ALSO INDICATED FOR PARTS OF SOUTHEAST
ALASKA AND THE ALASKA PANHANDLE.
AREAS HIGHLIGHTED FOR BELOW NORMAL TEMPERATURES ACROSS THE NORTH CENTRAL CONUS
AND ALASKA ARE CONSISTENT WITH NEGATIVE PDO PHASE COMPOSITES. THE LACK OF A
STRONG ENSO SIGNAL, ALWAYS-PRESENT UNCERTAINTY IN THE PHASE AND PERSISTENCE OF
THE AO OVER THE ENTIRE WINTER SEASON, CONSIDERABLE DIFFERENCES IN DYNAMICAL
CLIMATE MODEL OUTPUT MAKE EC OR EQUAL CHANCES FOR ABOVE-, NEAR- OR BELOW-NORMAL
TEMPERATURES THE APPROPRIATE CHOICE FOR MUCH OF THE EASTERN U.S..
AS WE MOVE FORWARD TOWARDS SPRING 2013, ABOVE NORMAL TEMPERATURES ARE FAVORED
ACROSS MUCH OF THE WEST. THIS HIGHLIGHTED AREA FIRST SPREADS EASTWARD ALONG THE
SOUTHERN TIER OF THE U.S. WITH TIME AND THEN EXPANDS EASTWARD AND NORTHWARD TO
INCLUDE MUCH OF THE LOWER 48 BY AMJ 2013. THIS IS PRIMARILY BASED ON NMME AND
IMME MODEL OUTPUT GIVEN UNCERTAINTY WITH ENSO AS WE MOVE FORWARD INTO 2013.
BELOW-NORMAL TEMPERATURES REMAIN FAVORED FOR JFM 2013 ACROSS PARTS OF THE
NORTHERN PLAINS. THIS AREA IS THEN TRANSITIONED TO EC DURING FMA 2013.
ELEVATED ODDS FOR BELOW NORMAL TEMPERATURES ARE INDICATED FOR A SMALL AREA OF
THE PACIFIC NORTHWEST FOR MAM AND AMJ 2013 SUPPORTED BY THE CCA, LONG-TERM
TRENDS AND THE CON. THE TEMPERATURE OUTLOOKS FROM MJJ 2013 ONWARDS ARE BASED ON
THE CON TOOL, DOMINATED BY LONG-TERM TRENDS, GIVEN WEAK OR UNCERTAIN CLIMATE
FORCING DURING THIS PERIOD.
IN AREAS WITHOUT STRONG OR RELIABLE CLIMATE SIGNALS, EQUAL CHANCES FOR
BELOW-NORMAL, NEAR- NORMAL, OR ABOVE-NORMAL SEASONAL MEAN TEMPERATURES IS
GIVEN ENSO NEUTRAL CONDITIONS AND CONSIDERABLE SPREAD AND VARIABILITY IN
CLIMATE DYNAMICAL MODEL FORECASTS, ESPECIALLY THE CFSV2, ONLY A FEW NON-EC
AREAS ARE HIGHLIGHTED ON THE DJF 2012-13 PRECIPITATION OUTLOOK. AREAS WHERE
SOMEWHAT MORE CONSISTENT SIGNALS WERE INDICATED INCLUDE AN ENHANCED LIKELIHOOD
FOR ABOVE-MEDIAN PRECIPITATION IN THE TENNESSEE VALLEY AND BELOW-MEDIAN
PRECIPITATION FOR PARTS OF CALIFORNIA, NEVADA, SOUTHEAST ALASKA AND THE ALASKA
PANHANDLE. THESE AREAS ARE LOCATIONS WHERE THERE WAS SOME CONSENSUS IN CFSV2,
NMME AND IMME MODEL OUTPUT AND CONSISTENT WITH TYPICAL NEGATIVE PDO CIRCULATION.
THE ABOVE-MEDIAN PRECIPITATION SIGNAL ACROSS THE TENNESSEE VALLEY CONTINUES
THROUGH FMA 2013 IN LINE WITH NMME AND IMME FORECASTS. ENHANCED ODDS FOR
BELOW-MEDIAN PRECIPITATION HIGHLIGHTED IN DJF 2012-13 EXPANDS EASTWARD ACROSS
THE SOUTHWEST TO PARTS OF THE SOUTHERN PLAINS DURING THE COURSE OF SPRING 2013
AND CONTINUES FOR PARTS OF THE SOUTHWEST AND SOUTHERN PLAINS ONLY DURING AMJ
AND MJJ 2013. THESE FORECASTS ARE BASED ON THE DYNAMICAL MODEL CONSIDERATIONS
AND THE CON FORECAST.
IN AREAS WITHOUT STRONG OR RELIABLE CLIMATE SIGNALS, EQUAL CHANCES FOR BELOW,
NEAR, OR ABOVE-MEDIAN SEASONAL PRECIPITATION AMOUNTS IS PREDICTED.
FORECASTER: JON GOTTSCHALCK
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING
THE WORLD METEROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3
COMPLETE DECADES AS THE CLIMATIC REFERENCE PERIOD. THE PROBABILITY ANOMALIES
FOR TEMPERATURE AND PRECIPITATION BASED ON THESE NEW NORMALS BETTER REPRESENT
SHORTER TERM CLIMATIC ANOMALIES THAN THE FORECASTS BASED ON OLDER NORMALS.
FOR A DESCRIPTION OF OF THE STANDARD FORECAST TOOLS - THEIR SKILL- AND THE
FORECAST FORMAT PLEASE SEE OUR WEB PAGE AT
(USE LOWER CASE LETTERS)
INFORMATION ON THE FORMATION OF SKILL OF THE CAS FORECASTS MAY BE FOUND AT:
HTTP://WWW.CPC.NCEP.NOAA.GOV/SOILMST/FORECASTS.HTML (USE LOWERCASE LETTERS)
NOTES - THESE CLIMATE OUTLOOKS ARE INTENDED FOR USE PRIOR TO THE START OF THEIR
VALID PERIOD. WITHIN ANY GIVEN VALID PERIOD OBSERVATIONS AND SHORT AND MEDIUM
RANGE FORECASTS SHOULD BE CONSULTED.
THIS SET OF OUTLOOKS WILL BE SUPERSEDED BY THE ISSUANCE OF THE NEW SET NEXT
MONTH ON DEC 20 2012
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011
One of the most significant atmospheric variables to affect the winter weather over the northeast third of the United States is the phase of the North Atlantic Oscillation (NAO). The negative phase of the NAO results in cold and snowy weather, as was the case during December of 2000, when Grand Forks had 19 inches of snow and averaged 11.8F below normal. The following month the NAO went into the positive phase, which typically results in warm and dry weather over our region. January 2001 in Grand Forks was 9.1F above normal with only 3.3 inches of snow! Unfortunately, it is difficult to predict changes in the phase of the NAO, meaning that sharp changes in the winter weather pattern like those of December 2000 to January 2001 can occur without much warning. Recently the NAO has been strongly negative which favors colder than normal weather across the northern plains.
Another significant atmospheric variable is the Arctic Oscillation (AO). The AO is a measure of the difference in pressure (at sea level) or 500-hpa height (in the middle troposphere) between the northern polar region and middle latitudes. When pressures and heights are above (below) average at high latitudes and below (above) average at middle latitudes - the AO is defined as negative (positive) and is associated with below (above) average temperatures over middle latitudes - including the United States. The AO can swing rapidly and dramatically from one phase to the next in a matter of days, then remain in a strong positive or negative phase for weeks or months. An example of how the AO can negatively influence the ENSO includes the 2009/2010 winter, when a moderate, borderline strong El Nino was expected to bring us a very mild and dry winter. The AO dropped to record low (negative) levels during December 2009 – February 2010. This completely disrupted the El Nino signal, resulting in a slightly cooler and wetter winter – more like a La Nina.
In particular, the AO and NAO are difficult to predict beyond a few days or weeks. Improvements in computer models have shown promise this skill may be extended to several months, and indeed the CPC has used one of these computer models - the Climate Forecast System Version 2 - to help modify this outlook.
For additional information contact the NWS in Grand Forks. Mark Ewens, Climate Services Focal Point 701-772-0720 x327 / Mark.Ewens@noaa.gov
The Climate Prediction Centers Long-Lead Seasonal Outlook Non Technical Discussion is repeated below
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS