Written by Sig Silber
Updated at 8:30 p.m. Friday December 20, 2019 to reflect the updated Week 3 – 4 Forecast which sort of confirms the precipitation forecast but not the temperature forecast.
Here is the December 19, 2019 NOAA 15-month forecast for CONUS and Alaska including the Early Outlook for January 2020 and forecasts out through March 2021. There are only slight changes since the forecast last month. For the three months January, February and March, the Northern Tier wet anomaly (not including the West Coast) has expanded to the south a bit. Thus the Southern Tier dry anomaly has also been forced further south and is fragmented, no longer including the Gulf Coast. On balance, it is a slightly wetter forecast for February and March as compared to January. More importantly, the wet anomaly for the three months is very different than for January – this implies that the difference will be magnified for February and March if the three-month forecast is to be correct.
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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 January, 2020. It is called the Early Outlook because it will be updated at the end of Decenber. Only the January 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 January 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 January*. For Temperature, it is mostly EC but warm in Alaska, the Northwest and in southern Texas and Florida. There is a large cool anomaly from Montana to Maine and as far south as South Dakota at the western end and New Jersey at the eastern end of the cool anomaly. With respect to precipitation, western Alaska is wet but the Panhandle is dry and that seems to extend down to the coast of the Northwest. There is a large wet anomaly stretching from eastern Texas to the Mid-Atlantic coast but not including Florida.
* 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 December (so they are less useful for this purpose) and the third map only extends the coverage through the first thirteen days of January The Seasonal Outlook was issued fairly early this month since the third Thursday fell on December 19, 2019.
Perhaps we should have waited a day to publish this article but there were two NOAA releases today so we had 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, December 20. At that point, we will have all but fourteen days covered by the shorter-term period forecasts. That is still not a solid basis for doing this visual consistency testing.
First Temperature
 |  |  |
| The new monthly forecast is to the right. Does it appear to be reflective of the parts of the month for which we have forecasts? → |
| ↑ ← The full month forecast does not seem to fit well with the Week 3 – 4 forecast which now covers seventeen days of January as of today’s Week 3 – 4 update. We will also revisit this question at the end of December when the January forecast is updated. |
And then Precipitation
 |  |  |
| The new monthly forecast is to the right. Does it appear to be reflective of the parts of the month for which we have forecasts? → |
| ↑ ← The full month forecast does seem to fit better with the Week 3 – 4 forecast which now covers seventeen days of January as of today’s Week 3 – 4 Update. We will also revisit this question at the end of December when the January forecast is updated. |
Now we consider the three-month Outlook.
Notice that the three-month periods are abbreviated e.g. January/February/March is shown as JFM. You will see such abbreviations often in this report.
Prior Temperature Outlook for JFM 2020
New Temperature Outlook for JFM 2020
Prior Precipitation Outlook for JFM 2020
New Precipitation Outlook for JFM 2020
Now let us focus on the long-term situation.
First Temperature
Prior 14 Month Temperature Outlook: JFM 2020 – DJF 2020/2021
New 14 Month Temperature Outlook: FMA 2020 – JFM 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: JFM 2020 – DJF 2020/2021
New 14 Month Precipitation Outlook: FMA 2020 – JFM 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 December 19, 2020. 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 (January), the new NOAA Summary for JFM, and finally the remainder of the 15-Month Forecast.
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
Oceanic observations indicate that ENSO-neutral conditions persist. The Nino3.4 index value peaked at +0.8 degrees C during the fall, but this was largely related to the Madden-Julian Oscillation (MJO). This index value has recently decreased to around +0.4 degrees C. Positive anomalies remain the largest (near 1.0 degrees C) in the westernmost Nino-4 region [Editor’s Note: This is what JAMSEC refers to Modoki-like], while SST indices were near average across the eastern equatorial Pacific. The equatorial subsurface temperature anomalies (averaged across 180 to 100 degrees W) returned to near zero during the past month. OLR anomalies were generally small throughout the equatorial Pacific, consistent with ENSO-neutral conditions.
Positive SST anomalies remain across the higher latitudes of the northeast Pacific. However, the magnitude of these anomalies have weakened recently due to an upper-level trough over this region. Extratropical SST anomalies can change rapidly with any increase in mid-latitude storm tracks. The strong Indian Ocean Dipole (IOD) is beginning to show signs of weakening with the negative SST anomalies waning near the western Maritime Continent. As the IOD weakens, the MJO is expected to strengthen during the remainder of December. Recently, upper-level divergence has finally propagated east from the western Indian Ocean. A strengthening MJO, entering the West Pacific, could play an increasing role in the longwave pattern over North America and result in a colder outcome later in January.
PROGNOSTIC DISCUSSION OF SST FORECASTS
The CPC SST consolidation forecast, which includes three statistical forecasts along with the CFS model, predicts a continuation of ENSO-neutral conditions through the early spring before the CFS and statistical models slightly diverge. The North American Multi Model Ensemble (NMME) ensemble mean forecast for the Nino-3.4 SST anomaly is near 0.5 degrees C during the winter and then decreases closer to zero thereafter. Based on the latest observations and model forecasts, the CPC/IRI ENSO outlook favors ENSO-neutral conditions to persist through the spring 2020.
30-DAY OUTLOOK DISCUSSION FOR JANUARY 2020
The temperature and precipitation outlooks for January 2020 are based on a variety of statistical and dynamical models , expected influence of the Madden Julian Oscillation (MJO) and Indian Ocean Dipole (IOD), historical temperature and precipitation trends , and current sea-surface temperatures. Current ENSO-neutral conditions offer little help in creating the January outlooks, and were therefore not considered.
Temperature
The January 2020 temperature outlook favors below normal mean temperatures across the northern tier of the Lower 48 states from western Montana to the Northeast/Upper Mid-Atlantic regions. This anomalous cold is supported by the latest Week-3/4 CFS and ECMWF 2-meter temperature forecasts, and a predicted deep, anomalous 500-hPa trough over central and eastern Canada. The most recent 6 days of CFS ensemble runs promote an extensive area of forecast colder-than-normal temperatures over the northern tier of the contiguous U.S., though there are differences in predicted spatial coverage from day to day. Additional support for the favored below normal temperatures across the northern tier comes from the MJO and IOD. The enhanced convective phase of the MJO is presently located over the eastern Indian Ocean (Phase 3 in RMM phase space), having propagated eastward from the western portion of the basin in the past week to ten days. The MJO signal is now destructively interfering with a broad region of subsidence associated with the positive phase of the IOD, and the MJO remains weak. A general consensus of MJO forecasts brings the enhanced phase of the MJO across the Maritime Continent (Phases 4 and 5) and out over the western Pacific (Phase 6) during the next two weeks. Once the subseasonal signal moves beyond the broad region of convective suppression across the eastern Indian Ocean, it is expected to increase in amplitude over the western Pacific. Using the western Pacific (Phase 6) as the region on which to base U.S. lagged temperature composites for this time of year indicate an expansive area of anomalous cold over most of the Lower 48 states. However, the favored area of anomalous cold on the official map designates where the CFS and ECMWF solutions agree. Much of the cold signal depicted over the West by some tools was not included in the official outlook, being offset by pronounced warm trends at this time of year, and resulting in a forecast of EC.
The lagged composites also support elevated odds of above normal temperatures over most of Alaska, with the greatest uncertainty over the Panhandle region. This scenario also has the support of the most recent CFS runs. Conceptually, this temperature pattern is consistent with the prediction of a large anomalous 500-hPa ridge centered over the northern Gulf of Alaska. Relatively mild onshore flow west of the mean ridge axis results in elevated odds of above normal temperatures for most of Alaska. Continental offshore flow east of the mean ridge axis suggests below normal temperatures, though due to conflicting indications, Equal Chances (EC) appears to be the better bet across the Alaska Panhandle. Above normal temperatures are favored over the Pacific Northwest, northern portions of California, and northern and central portions of the Intermountain Region, as supported by the CFS and the Constructed Analog on Soil Moisture (CAS). The area of favored above normal temperatures in Florida is supported by the Week-3/4 CFS and ECMWF temperature forecast guidance, and the most recent CFS runs valid for January. There is also some support from both models for elevated odds of warmer-than-normal temperatures in southern Texas.
Precipitation
The January 2020 precipitation outlook favors increased chances of above normal precipitation from southern portions of the Mid-Atlantic and Southeast westward across the Tennessee Valley, Gulf Coast states, Lower Mississippi Valley, and eastern portions of the southern Plains. The exception is Florida, which is indicated as EC. This favored region of relative wetness is supported by the Week-3/4 and monthly CFS forecasts, the Week-3/4 ECMWF precipitation forecast, and most of the climate model constituents of the North American Multimodel Ensemble (NMME). This broad band of favored above normal precipitation may be related to a persistent mean frontal boundary. Over western North America, above normal precipitation is also favored over western Alaska, while below normal precipitation is favored over the Alaska Panhandle, and much of Washington and Oregon. As mentioned earlier in the temperature section, these areas are associated with the prediction of an anomalous ridge centered over the northern Gulf of Alaska, and related onshore and offshore flow patterns, respectively. This scenario is also generally supported by the Week-3/4 CFS and (especially) ECMWF precipitation forecasts, and the NMME (though the area of favored drier-than-normal conditions is predicted to be shifted somewhat westward, from south-central Alaska to the northern Panhandle region). For remaining areas of the United States, which constitutes a significant portion of the country, there are either conflicting or weak precipitation signals , warranting a forecast of EC.
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS (With a focus on JFM)
ENSO-neutral conditions continue across the equatorial Pacific Ocean, as represented in current oceanic and atmospheric observations. The official CPC ENSO forecast indicates that ENSO-neutral is most likely through the Northern Hemisphere winter 2019-20 (70 percent chance) and spring 2020 (near 65 percent chance).
Temperature
The January-February-March (JFM) 2020 temperature outlook favors above-normal temperatures across the southern tier of the CONUS and along the West Coast. Increased chances for below-normal temperatures during JFM are forecast across the northern Great Plains, upper Mississippi Valley, and much of the Great Lakes. Equal chances (EC) of above, near, or below normal temperatures are indicated across the remainder of the CONUS. Above-normal temperatures are favored throughout Alaska.
Precipitation
The JFM 2020 precipitation outlook indicates enhanced probabilities of above-normal seasonal total precipitation amounts for the northern Rockies, northern Great Plains, Missouri River Valley, middle to upper Mississippi Valley, Midwest, mid-Atlantic, and much of Alaska. Below-normal seasonal precipitation amounts are slightly favored across southern California, parts of the Southwest, Rio Grande Valley, and the Florida Peninsula. Equal chances (EC) are forecast among areas where seasonal precipitation amounts are expected to be similar to climatological probabilities.
BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
The temperature and precipitation outlooks for JFM 2020 were based on dynamical model guidance and statistical tools that include global SST anomaly patterns and a canonical correlation analysis that uses the evolution of SST and sea-level pressure as predictors. During the next four leads (FMA through MJJ 2020), the seasonal outlooks were based largely on the calibrated probabilistic forecasts from the NMME and a consolidation forecast of dynamical and statistical tools. Long-term climate trends were considered for all leads but were relied more heavily from the summer 2020 through the next winter 2020-21.
PROGNOSTIC DISCUSSION OF OUTLOOKS – JFM 2020 TO JFM 2021
TEMPERATURE
Increased chances of above-normal temperatures during JFM 2020 are forecast along the West Coast and extending from the Southwest eastward to the Gulf Coast States and Southeast. This favored area of above-normal temperatures is supported by the calibrated probabilistic NMME forecast and also long-term trends throughout the southwest quarter of the CONUS. Although the seasonal mean temperature is favored to be above normal in these areas, a variable temperature pattern is likely during this three-month period given the ENSO-neutral conditions. Subseasonal variability such as the MJO and Arctic Oscillation (AO) are expected to influence the circulation pattern and temperatures this winter. Away from the West Coast, Southwest, and southern tier of the CONUS, the calibrated probabilistic NMME forecast indicates a large area with little to no signal, implying poor model skill and/or a highly variable pattern. Therefore, equal chances (EC) of below-, near-, or above-normal temperatures are forecast for a relatively large area of the CONUS. Below-normal temperatures during JFM 2020 remain favored for the northern Great Plains, upper Mississippi Valley, and much of the Great Lakes, based on statistical tools such as the CCA and ENSO-OCN tools. Also, this area of favored below normal temperatures is consistent with the January 2020 outlook. Increased chances of above-normal temperatures are forecast throughout Alaska although probabilities are lowest in southeast mainland Alaska and the Alaska Panhandle, based on recent dynamical model guidance.
The temperature outlook for FMA 2020 (compared to the previous month release) reveals a slightly warmer solution along the East Coast, based on the latest consolidation tool. During the spring (MAM) 2020, support for below-normal temperatures across the north-central U.S. diminishes. During AMJ and MJJ 2020 (compared to the previous month release), probabilities for above-normal temperatures were increased across the West which is supported by the latest calibrated NMME and long-term trends . The remaining temperature outlooks through next winter 2020-21 closely resemble long-term trends .
PRECIPITATION
Despite an active southern stream through late December 2019 and potentially into early January 2020, precipitation tools during JFM 2020 favor near or below-normal precipitation across the southern tier of the CONUS. The consolidation tool (statistical and dynamical inputs) is most bullish with the dry signal, but probabilities of below-normal precipitation across southern California, the Southwest, and parts of Texas and Florida are only modest based on the calibrated NMME forecast. The tilt in the odds for below-normal precipitation across these areas is consistent with ongoing SST gradients in the tropical Pacific and broad-scale suppressed convection at the Date Line. Compared to the previous month, model guidance is more widespread with the wet signal across the central and eastern U.S. through MAM 2020. Nearly all the tools support increased chances of above-normal precipitation (winter and spring 2020) throughout the Missouri River Valley and Corn Belt. Enhanced odds of above-normal precipitation are also forecast across much of Alaska through the spring 2020, although coverage and probabilities vary with time.
Coverage of favored areas for anomalous precipitation decrease during the summer as forecast confidence diminishes with a weakening signal among tools and convective precipitation becomes more dominant. The favored areas of below or above normal precipitation at later lead times are based largely on historical trends .
ENSO Considerations
Since the ENSO phase is not likely to change very much and since NOAA does not make it clear which forecasts for the NOAA Phase they rely on, we have decided to greatly abbreviate our coverage of that topic for the time being but it is discussed well in the NOAA Discussion so you can read their thoughts on the matter there. We are going to show the latest IRI-CPC computer model forecast of the probabilities and what is called the plume of forecasts.
C
B. Conclusion
There were a number of fairly minor changes. The dynamic models do the best job of forecasting the next month so the new outlook issued each month is better able to forecast the next three months which last month was months 2, 3 and 4. There is always a lot of uncertainty in the forecasts and we see a lot of switching back and forth from month to month which probably is more related to how the conflicting or weak model results are resolved in the forecast rather than true changes in the forecast. So we may be seeing certain changes in the forecast maps which really reflect how the conflicting information is resolved that month rather than true changes in the forecast.
This month the thinking is that the MJO might become more active and this month the discussion addressed the AO and last month it was the NAO.so these may reflect slight changes in the projected Walker Circulation.
All in all the forecast basically has not changed.
