Written by Sig Silber
Updated at 6:00 p.m. EST November 22 to reflect the new Week 3-4 Forecast which raises serious questions about the Early Outlook for December.
Here is the November 21, 2019 NOAA 15-month forecast for CONUS and Alaska including the Early Outlook for December and forecasts through February 2021. There are only slight changes since the forecast last month. The precipitation forecast is a bit drier for the Southern Tier early in the forecast. The Early Outlook for the single month of December may change when it is updated at the end of November nine days after the current NOAA release. The forecast of a negative North Atlantic Oscillation might lead to a reduction in the Northern Tier temperature forecast.
Please share this article – Go to the very top of the page, right-hand side for social media buttons.
A. Focus on the NOAA Update
A note about terminology; the deviations from climatology/normal are color-coded but also labeled “A” for more than (above) normal and “B” for less than (below) normal. The area designated EC means Equal Chances of being more or less than normal. In my comments For the shorter-term maps, NOAA uses “N” instead of “EC” as they believe they can be more definitive with respect to shorter timeframes. So the words “warm”, “cool”, “wet”, “dry” should be generally interpreted as being relative to climatology/normal for that location and time of year.
First, we will take a look at the NOAA Early Outlook for December, 2019. It is called the Early Outlook because it will be updated at the end of November. Only the December Outlook will be updated at that time.
Temperature
Precipitation
We have nothing to compare these maps with as NOAA does not in their Update provide a forecast for each of the subsequent two months separate from their three-month forecast. Thus I do not have forecast maps for December from the previous NOAA Report to compare against. And the current month is not over so we can not really compare the forecast for next month against the actual for this month. It is probably best to just try to understand what NOAA is trying to convey about December*. For Temperature, it is warm to cold from west to east in Alaska and mostly warm for CONUS but EC for part of the Northern Tier. As you move from the Northwest to the Southeast, the probability of being warmer than climatology increases. For precipitation, Northwest Alaska is wet and CONUS Northwest is wet extending to the south and east down to and including the Four Corners area. There is a small dry anomaly in extreme South Texas.
* compared to normal/climatology for the indicated time of the year.
Visual Consistency Testing.
It is useful to see how the month forecast fits with the set of shorter forecasts that we have. The first two maps cover November (so they are less useful for this purpose) and the third map only extends the coverage through the first thirteen days of December. The Seasonal Outlook was issued fairly late this month since the third Thursday fell on November 21, 2019.
Perhaps we should have waited a day to publish this article but there were two NOAA releases today so we day to decide which to publish today and which tomorrow. I wanted our readers to get the new forecast ASAP. We will update this Visual Consistency Testing after the Week 3 – 4 forecast is issued on Friday, November 22. At that point, we will have all but eleven days covered by
First Temperature
 |  |  |
| The new monthly forecast is to the right. Does it appear to be reflective of the three parts of the month for which we have forecasts? → |
| ↑ ← The full month forecast does seem to fit at all well with the Week 3 – 4 forecast which now covers twenty days of December as of the update of the Week 3-4 Forecast. We will revisit this question at the end of November when the December forecast is updated. |
And then Precipitation
 |  |  |
| The new monthly forecast is to the right. Does it appear to be reflective of the three parts of the month for which we have forecasts? → |
| ↑ ← The full month forecast does not seem to fit at all well with the Week 3 – 4 forecast which now covers twenty days of December as of the release of the new Week 3 – 4 Forecast. We will revisit this question at the end of November when the December forecast is updated. |
Here is the discussion released with the updated week 3 – 4 Forecast
Week 3-4 Forecast Discussion Valid Sat Dec 07 2019-Fri Dec 20 2019
Guidance exhibits reasonably good consistency for the upcoming Weeks 3-4 period, although the mechanisms by which they arrive at their solutions varies. In terms of background context, the Madden-Julian Oscillation (MJO) remains active, albeit at a fairly rapid phase speed, with the current envelope approaching the Indian Ocean at present. The ongoing Indian Ocean Dipole event remains robust, and is likely to mask any higher frequency signal from the MJO over the coming days. El Nino-Southern Oscillation conditions are anticipated to remain neutral, with an associated unremarkable atmospheric footprint at present. Model guidance is hinting at some displacement of the polar vortex in the extended range period, although typical impacts over North America in such events are not robust and instead more focused across Eurasia. The resulting forecast outlook is based primarily on dynamical model guidance with other consideration given predominantly to the evolution from the Week-2 pattern in addition to some deference for long-term trends.
The general theme for the evolution of the circulation pattern from Week-2 to Week 3-4 appears to be rising mid-level heights across the country after a period of anomalous troughing, except for the Southeast where anomalous ridging is favored throughout. The CFS model has the most interesting pattern, with a strong projection on the positive phase of the North Pacific Oscillation-West Pacific pattern resulting in cross-polar flow of Arctic air into the Central U.S. and bitter cold temperatures. The ECMWF features a north-south dipole of above- and below-normal heights, while the JMA persists the Week-2 troughing across the West into Week-3. By Week-4 the CFS features anomalous ridging across the CONUS, while the ECMWF and JMA maintain some semblance of weak troughing across the West. The Subseasonal experiment (SubX) multimodel ensemble (MME) features mean ridging across the Yukon with troughing over eastern Canada.
The resulting Week 3-4 temperature outlook slightly tilts toward below-normal temperatures across the Great Basin and Rockies with an eastward extension through the Great Lakes and Northeast. The rationale for this is consistency with the Week-2 forecast pattern before a possible pattern change by Week-4, with rising 500-hPa heights across much of the country. Anomalous ridging consistently forecast across the Southeast results in above-normal temperatures being favored across much of Texas eastward into the Mid-Atlantic, with the highest probabilities focused along the Gulf Coast and Florida Peninsula. A broad strip of equal chances exists between these two areas, resulting from uncertainty regarding the timing of the transition and strength of the initial cold and resulting warm air masses. Equal chances also exist across much of the West Coast, given mixed treatment among model guidance. Above-normal temperatures are favored across coastal portions of Alaska and western parts of the state tied to the possibility of forecast ridging in addition to above-normal SSTs and/or below-normal sea ice coverage.
While the temperature outlook would imply a mean baroclinic zone extending east-northeastward from West Texas through the Capital Region, no accompanying above-normal precipitation forecast exists here given the anticipated transitory nature during the forecast period. Instead, the most consistent signals for precipitation tilt below-normal across the Northern and Central Plains (likely anomalous northerly flow early, with proximity to the ridge axis late) and above-normal for the Eastern U.S. (lying east of the trough axis early before possibly drying out by Week-4 as ridging builds) and parts of the Desert Southwest (models imply the possibility of tropical moisture making it into the region). Equal chances are given elsewhere across the CONUS given the mixed guidance signals. Western Alaska appears likely to tilt toward below-normal precipitation given proximity to the ridge axis.
Persistent above normal SST anomalies surrounding Hawaii indicates that above normal temperatures are likely for Hawaii with probabilities exceeding 90 percent. Above median precipitation is predicted to be likely for the Hawaiian Islands by the ECMWF and SubX MME.
Now we consider the three-month Outlook.
Notice that the three-month periods are abbreviated e.g. December/January/February is shown as DJF. You will see such abbreviations often in this report.
Prior Temperature Outlook for DJF 2019 – 2020
New Temperature Outlook for DJF 2019-2020
Prior Precipitation Outlook for DJF 2019-2020
New Precipitation Outlook for DJF 2019-2020
Now let us focus on the long-term situation.
First Temperature
Prior 14 Month Temperature Outlook: DJF 2019/2020 – NDJ 2020/2021
New 14 Month Temperature Outlook: JFM 2020 – DJF 2020/2021
To compare maps from one release to another, one needs to remember that the new release drops one three-month period and adds a later one. So to make the comparisons one has to shift the new maps to the right one position and that makes the map on the right drop down to become the left-most map in the next level. I do not have a computer software tool for doing that for you so you have to do it mentally. When I do the comparison, I print the two sets of maps and put them side by side and number the same three-month maps 1, 2, 3,…..,11 in both sets of maps to make it easier for me to easily compare the same three-month period in the new with the previous forecast. One uses the same procedure to compare the precipitation maps. Based on this procedure, I conclude that:
Now Precipitation
Prior 14 Month Precipitation Outlook: DJF 2019/2020 – NDJ 2020/2021
New 14 Month Precipitation Outlook: JFM 2020 – DJF 2020/2021
If you want larger versions of each map (temperature and precipitation) you can find them here. And then each of those maps can be clicked on to further enlarge them.
Sometimes it is useful to compare the three-month outlook to the forecast for the first of the three months. It shows how much the pattern changes over the three-month period.
One can mentally subtract the First-Month Outlook from the Three-month Outlook and create the Outlook for the last two months in the three-month period.
*The concept is that the probabilities of a deviation from climatology in the First Month and the combined Month Two and Three forecast that one derives must average out to the probabilities shown in the three-month maps.
Below is the NOAA Discussion (slightly reorganized) released by NOAA on November 21, 2019. Headings that are “Initial Cap” only rather than all caps were added by the Author of this Update Report for clarity. Also, we have organized the sequence of the sections of NOAA Discussion to first present the Atmospheric and Oceanic Conditions and then the Initial Month (December), the new NOAA Summary for DJF, and finally the remainder of the 15-Month Forecast.
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
As noted in the summary, oceanic and atmospheric indicators show current ENSO-neutral conditions. The most recent weekly Nino3.4 index value has spiked to +0.8 degrees C, but this is largely due to tropical subseasonal activity associated with the MJO. Broadly positive SST anomalies are now observed over nearly the entire equatorial Pacific. A review of the ocean sub-surface reveals shoaling of a downwelling Kelvin wave in the eastern Pacific, as expected from last month’s outlook. The overlying atmospheric circulation is unremarkable, consistent with ENSO neutral conditions. The SOI has been consistently negative over the past three months, but the equatorial SOI has hovered near zero.
Two other areas of ocean anomalies need to be watched in the coming couple of months. One is a large area of positive SST anomalies ranging from 1-3 degrees C north of 20 N in the northeast Pacific Ocean. Extratropical SST anomalies, although often impressive in scale, can change rapidly due to mid-latitude wave activity and the associated variation in mean storm tracks. Extratropical SSTs of this magnitude, however, may play a small role in the coming seasons.
Also, a strong Indian Ocean Dipole (IOD) is currently in place with above-normal SSTs in the western Indian Ocean and below normal SSTs in the eastern Indian Ocean and waters in proximity to the Maritime continent. The atmosphere has responded to this boundary forcing with stationary enhanced convection observed for several weeks across Africa and the western Indian Ocean with stationary suppressed convection observed over the eastern Indian Ocean and Maritime Continent. It is unclear how this forcing affects the forecast circulation over North America, though the various coupled model systems do indicate some wave train propagating away from this source region.
PROGNOSTIC DISCUSSION OF SST FORECASTS
The CPC SST consolidation forecast, the NMME ensemble mean forecast and the official CPC / IRI probabilistic ENSO outlook for Nino3.4 all favor continued ENSO-neutral conditions through the upcoming winter 2019-2020 and spring 2020. There is, of course, considerable spread across the various model forecasts (statistical and dynamical) over the next 6 months. A few dynamical models favor a tendency toward bordering on weak La Nina (as characterized by Nino3.4) by late winter while the majority remain in ENSO-neutral territory or tend toward borderline weak El Nino over the same period. The expectation of ENSO-neutral conditions was utilized in making this month’s seasonal outlook package.
The various dynamical and statistical tools weaken the strong IOD signal over the coming months, and maintain the strongly positive SST anomalies over the Northeast Pacific.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
The temperature and precipitation outlooks were based on currently depicted, organized, large scale SST anomaly patterns (i.e., ENSO-neutral, IOD, northeast Pacific SSTs, and near Alaska SSTs), both temperature and precipitation long term climate trends , bias-corrected and calibrated dynamical model forecasts from several sources, statistical forecast tools including the Constructed Analogue (CA) tool using near global SSTs as the primary predictor and an objective, historically skill weighted consolidation of (1) statistical tools only and (2) both statistical and dynamical forecast tools. Since ENSO is unlikely to provide a major influence on the mid-latitude circulation pattern, long term climate trends were weighted more heavily than normal during early and middle forecast leads.
Experimental, empirical forecasts of the North Atlantic Oscillation (NAO) and North Pacific Oscillation-West Pacific pattern (NPO-WP) are utilized to support the consensus of the statistical tools especially during later winter and early Spring. These forecasts utilize SST, sea ice coverage, and stratospheric circulation as predictors in a multiple regression model. This model predicts negative phases of both the NAO and NPO-WP for the upcoming winter, with stratospheric predictors driving the NAO forecast and Pacific SST patterns driving the NPO-WP forecast.
30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2019
Temperature
The December 2019 temperature outlook is based on Week-2 model guidance, Weeks 3 to 4 outlooks from the CFS and ECMWF models, recent daily CFS model output, consideration of influences from the Madden-Julian Oscillation (MJO), and long-term trends . Near to above-average sea surface temperatures were observed across the east-central tropical Pacific Ocean during October and early November. However, suppressed convection continued near the Date Line. The oceanic and atmospheric observations reflect ENSO-neutral conditions which are likely to persist through December.
The Madden-Julian Oscillation (MJO) strengthened in late October and its enhanced phase quickly propagated east across the Western Hemisphere during early to mid-November. The MJO is likely to constructively interfere with the ongoing positive Indian Ocean Dipole (IOD) through the remainder of November into the beginning of December. It is unclear how this constructive interference between the MJO and IOD and the resultant enhanced convection across the western Indian Ocean will influence the mid-latitude circulation pattern. Lagged MJO composites are consistent with Week-2 model solutions that feature upper-level ridging south of the Aleutians and a downstream trough over the western U.S. The ECMWF ensemble mean maintains this anomalous ridge/trough pattern through Week-3 (early December) and then indicates a retrogression of the longwave pattern by mid-December. This evolving longwave pattern favors a relatively cold start to the month across the northern Rockies and northern Great Plains before a moderating trend or transition to above-normal temperatures occurs by mid-December. Downstream of the upper-level trough over the West, anomalous subtropical ridging is expected to result in a relatively warm start to the month across the Southeast and Gulf Coast States. The highest confidence (albeit limited at a half-month lead) in the temperature outlook across the CONUS exists for these areas due to the likely warm start to the month and good model consensus. Forecast confidence decreases north of the 40th parallel across the central and eastern U.S. since the GFS and ECMWF ensemble means continue to feature anomalous 500-hPa ridging over the Davis Strait and Greenland persisting into the first week of December. Given the persistence of this ridging at high latitudes, forecast confidence in the temperature outlook is low across the Great Lakes and New England.
Precipitation
The precipitation outlook for December is based primarily on recent daily runs of the CFS model and the calibrated North American Multi-Model Ensemble (NMME). The area with enhanced odds for above normal precipitation across the Pacific Northwest, interior West, and central to northern high Plains is supported in part by the likelihood of an amplified upper-level trough forecast over the Rockies or near the West Coast during early December. The slight tilt in the odds for below normal precipitation forecast for south Texas is consistent with the seasonal precipitation outlook. A large area with equal chances for below, near, or above normal precipitation throughout much of the central and eastern U.S. is necessary due to weak signals among precipitation tools along with low predictability inherent with a monthly outlook at this time lead. Revisions to the December temperature and precipitation outlooks are likely with the November 30 release.
The amplified upper-level ridge (trough) over the North Pacific (western North America) is forecast to become established by the end of November and likely continue into early December. This longwave pattern favors at least a slight tilt in the odds for below-normal temperatures across eastern mainland Alaska. The highest probabilities (above 60 percent) for above-normal temperatures are forecast for areas of the state adjacent to the Bering and Chukchi Seas where sea surface temperature anomalies are averaging as high as 2.5 degrees C above normal. The favored area of above normal precipitation across Alaska is consistent with the likelihood of enhanced onshore flow during early December and supported by many of the precipitation tools.
BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS (focus on DJF)
Oceanic and atmospheric conditions in the equatorial Pacific Ocean reflect an ENSO-neutral state and these conditions are forecast to continue through the winter and spring of 2019-2020. Additional details regarding tropical conditions are provided below.
Here we focus on a summary of the first 3-month seasonal outlook for temperature and precipitation for the December-January-February (DJF) season. Additional information related to the forecast for this season and subsequent 3-month overlapping seasonal outlooks through DJF 2020-2021 are also given below.
Temperature
The DJF 2019-2020 temperature outlook favors above-normal seasonal mean temperatures for Alaska and most of the western and southern contiguous U.S., with modest probabilities in favor of above-normal temperatures extending up the Eastern Seaboard. Equal-chances (EC) is indicated over a large swath of the north-central U.S. where climatological odds for either of the three categories (below-, near- or above-normal) are forecast.
Precipitation
The DJF 2019-2020 precipitation outlook favors above-normal seasonal total precipitation amounts for Alaska (especially the Southwest portion of the state) and much of the northern tier of the contiguous U.S. Smaller areas of favored below-normal seasonal precipitation amounts are highlighted for parts of California and the Southwest, as well as the western Gulf Coast and lower Mississippi Valley. Remaining areas of the forecast domain denote Equal-Chances (EC) where climatological odds for either of the three categories (below-, near- or above-normal) are forecast.
PROGNOSTIC DISCUSSION OF OUTLOOKS – DJF 2019 TO DJF 2020
TEMPERATURE
The DJF 2019-2020 temperature outlook is informed by the objective consolidation, but heavily adjusted to account for the latest CFSv2 runs, the international model suite, and the empirical NAO and NPO-WP guidance. This has the effect of reducing above-normal temperature probabilities over the north-central CONUS, Midwest, and Great Lakes to equal-chances (EC). In JFM through MAM seasons, the statistical guidance is more heavily utilized to depict enhanced probabilities of below-normal temperatures across parts of the northern tier of the CONUS. This is especially apparent in the SST constructed analog, but also consistent with the CCA and ENSO-OCN tools. The latest CFSv2 runs (initialized over the past 10 days) depicts a colder solution relative to long-term trends centered over eastern Canada and the northernmost parts of the Northeast CONUS for the DJF through FMA seasons, more consistent with the international model blend and less so with the NMME. [Editor’s Note: This only shows up slightly in the forecast so it may show up a bit more for December when the Early Outlook is updated at the end of November]
In many ways the forecast temperature evolution is similar to the long-term trends as assessed by the optimal climate normals. This seems appropriate given the conflicting signals between the dynamical models and the statistical models on many key features, including the seasonal phase of the NAO.
The remaining forecasts throughout 2020 across the CONUS and Alaska are largely derived from an objective, skill-weighted combination of statistical forecast tools and support large coverage of favored above-normal temperatures for most, if not all, of the forecast domain over the period. Long-term temperature trends become less dominant heading into late fall and winter 2020-2021.
PRECIPITATION
The DJF 2019-2020 precipitation outlook depicts above-normal seasonal total precipitation amounts for all of Alaska and most of the northern tier of the CONUS. Modestly elevated odds for below-normal precipitation are depicted for small regions of the southern West Coast and western Gulf Coast. For Alaska, dynamical model guidance, long term positive precipitation trends and overall warmer, more open waters (potentially wetter, stronger cyclones) around the state support the forecast. Across the CONUS, strong climate signals for precipitation departures from climatology were few. Statistical-dynamical guidance consolidation and long-term precipitation trends are the primary basis for the forecast over the entire forecast period. These are consistent with the consensus of dynamical model guidance through spring 2020, which may be related to forecast SST gradients in the tropical Pacific being associated with suppressed convection near and east of the Date Line.
The majority of forecast tools support expansion of favored below-normal precipitation from Texas to the Southwest by JFM 2020. The remaining outlooks are based on long term precipitation trends in the absence of more clear, reliable climate signals such as a confident ENSO prediction. These trends appear consistently across the statistical forecast suite and, during the warm season, favor a tilt toward dry (wet) across parts of the western (eastern) CONUS.
New Drought Forecast
ENSO Considerations
We covered this only slightly in our November 14 article on the Economic Impacts of Weather which can be read here. So I am not going to go into a lot of detail tonight. The NOAA Atmospheric and Oceanic Conditions section in the NOAA Discussion is excellent. We will be discussing any differences between the NOAA assessment of ENSO and JAMSTEC in our Sunday night article.
Here is the NOAA proprietary model.
And just to look ahead to our discussion for Sunday night, here is the JAMSTEC one-year forecast
Here is what is called the Plume of Forecasts.
First, we look at the CPC-IRI Probability Analysis which we believe was utilized in the forecast last month. This is not forecasting the level of the Nino 3.4 Index but rather the propability of the Index being equal to or greater than +0.5C (El Nino) or equal to or less than -0.5C (La Nina) or between +0.5C and – O).5C (ENSO Neutral).
Then we look at the new forecast
B. Conclusion
There were a number of fairly minor changes mostly related to factors other than the Phase of ENSO but rather the IOD, NAO, NPO-WP and the MJO. That is why those changes in the forecast show up early in the forecast. NOAA does not mention the El Nino Modoki that JAMSTEC has correctly in our opinion observed. JAMSTEC believes this will have an impact into early Winter. We shall discuss this more in our Sunday Night article but the NPO-WP and the MJO may be surrogates for what JAMSTEC has observed so NOAA may be taking this into account but not using the same terminology as JAMSTEC.
