Written by Sig Silber
Here is the June 20, 2019 NOAA 15-month forecast for CONUS and Alaska. It is not much changed from the forecast last month but a little more optimistic on the staying power of this marginal El Nino. Tomorrow night we will compare it to the JAMSTEC Three-Season forecast which perhaps pays more attention to the western displacement of this El Nino which the Japanese refer to as being a Modoki.
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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 July, 2019. It is called the Early Outlook because it will be updated at the end of June. Only the July 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 previously forecast maps for July 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 July*. For Temperature it is a warm Alaska, both Coasts of CONUS and a cool Greater Central and Upper Mississippi Valley. For Precipitation, it is a mostly wet Alaska, dry Alaskan Panhandle and part of Washington State, a dry Lower Mississippi Valley and a wet anomaly which is sort of like the cool anomaly but shifted to the west a bit and covering a larger area than shown last month.
* 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 June not July and the third map only covers the first through the first two-thirds of July. The Seasonal Outlook was issued fairly late this month since the third Thursday fell on June 20, 2019.
First Temperature
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| 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 seems to fit fairly well with the Week 3 – 4 forecast. We do not have the last third of the month in the sequence of maps above. We will revisit this question at the end of June when the July forecast is updated. |
And then Precipitation
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| 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 well with the Week 3-4 Map. This suggests that NOAA may expect the last part of July to be quite different than the first two-thirds of July. We will revisit this question at the end of June when the July forecast is updated. |
Now we consider the three-month Outlook.
Notice that the three-month periods are abbreviated e.g. July/August/September is shown as JAS. You will see such abbreviations often in this report.
Prior Temperature Outlook for JAS 2019
New Temperature Outlook for JAS 2019
Prior Precipitation Outlook for JAS 2019
New Precipitation Outlook for JAS 2019
More in the NOAA discussion but the evolution of the Southwest Monsoon is always important for this time of the year so here are two more graphics showing this evolution.
| JAS | ASO |
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And here is the new Seasonal Drought Forecast.
Now let us focus on the long-term situation.
Prior 14 Month Temperature Outlook: JAS 2019 – JJA 2020
New 14 Month Temperature Outlook: ASO 2019 – JAS2020
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: JAS 2019 – JJA 2020
New 14 Month Precipitation Outlook: ASO 2019 – JAS 2020
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.
Below is the NOAA Discussion (slightly reorganized and some discussion of methodology removed) released by NOAA on June 20, 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 (July), the new NOAA Summary for JAS, and finally the remainder of the 15 Month Forecast.
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
El Nino conditions continued in the Pacific Ocean during May 2019. Sea surface temperatures (SSTs) across much of the equatorial Pacific Ocean remain above climatological averages, with anomalies ranging from 0 to +1C from 160E to 130W. East of 130W, temperatures are closer to average with smaller scale features evident. [Editor’s Note: This is why JAMSTEC refers to this El Nino as being Modoki-like]. The latest weekly Nino 3.4 SST anomaly is +0.7 degree C. Oceanic heat content, determined from ocean temperature anomalies from the surface to a depth of 300 meters along the near equatorial Pacific from the Date Line to 100W, has increased to about 0.5C since reaching a local minimum during May. Atmospheric conditions, are showing less of a canonical response when looking at monthly average wind anomalies. The drop in oceanic heat content and lack of coherent wind response is likely related to stronger subseasonal variability related to the Madden-Julian Oscillation (MJO) during May and early June. Collectively, these oceanic and atmospheric conditions represent a continuation of weak El Nino conditions as of May 2019. Other boundary conditions relevant to the seasonal outlook are soil moisture anomalies and, in some areas, near-coastal SSTs. Widespread and persistent above normal precipitation for most of the CONUS during recent months has resulted in positive soil moisture anomalies for many areas of the central and eastern CONUS, extending into parts of the Great Basin, with many of these areas exceeding the 99th percentile of climatological soil moisture. Sea ice coverage for the Arctic is at record low amounts and SSTs are above normal near the west coast of Alaska.
PROGNOSTIC DISCUSSION OF SST FORECASTS
The CPC SST Consolidation Nino 3.4 forecast indicates the continuation of an El Nino through 2019. The three statistical models all predict at least a weak El Nino from autumn 2019 into winter 2019-2020, with the CCA predicting a moderate strength El Nino by Dec-Jan-Feb 2019-2020. The CFS dynamical model forecast ensemble mean predicts a slow decline in positive Nino 3.4 anomalies, with the most recent runs indicating a transition to ENSO neutral conditions during the autumn of 2019. The NMME suite of dynamical models shows more spread (implying less certainty in the outlooks through the rest of 2019. Most of the models indicate either a weak El Nino or ENSO neutral. Little possibility of a La Nina event next winter is indicated by statistical and dynamical model forecasts. The probability of a continuation of the current El Nino through the 2019 summer is 66%, with a 50-55% chance of it continuing into the fall and winter.
30-DAY OUTLOOK DISCUSSION FOR JULY 2019
For the month of July, a weak El Nino is predicted to continue. There is a 66% chance of El Nino continuing through Northern Hemisphere summer, and a 50%-55% chance that El Nino will persist through the upcoming fall and winter seasons. For discussion of sea-surface temperature anomalies, as well as subsurface anomalies, lower and upper-level winds, and convective anomalies, please refer to CPC’s Seasonal Outlook message for July-Sept. Following a brief period of interference from westward-moving modes of tropical variability, the Madden-Julian Oscillation (MJO) signal has renewed its eastward propagation and the enhanced convective phase is now over the Maritime Continent. Linkages between the MJO and CONUS impacts are generally weak in July, so the MJO is not forecast to play a significant role in the U.S. monthly temperature and precipitation outlooks. Multiple bouts of heavy rain over the past 30-45 days led to very high soil moisture and flooding over much of the Great Plains and Mississippi Valley. The July 2019 outlooks are based primarily on dynamical and statistical model guidance, the latest available official CPC temperature and precipitation outlooks for Week-2 and Weeks 3/4, the ongoing El Nino, very high soil moisture, heavy rainfall observations during the past 30-days, and July climatology.
Temperature
The monthly temperature outlook indicates that above normal temperatures are favored across Alaska, ranging from 33%-40% odds in the northeast part of the state to over 60% odds in the southwest part of the state. Contributing factors include above normal sea-surface temperatures near the coast, strong historical temperature trends , Week-2 and Weeks 3/4 temperatures, most of the NMME model suite, and available statistical tools. Above normal temperatures are also favored from the West Coast of the contiguous U.S. to near the Continental Divide, and across the Gulf Coast and Atlantic Coast states. Probabilities for upper-tercile temperatures peak between 40%-49%. Support for this relative warmth comes largely from the NMME PAC (Probability Anomaly Calibration), and to a somewhat lesser extent most of the remaining inputs of the NMME dynamical model suite, in addition to the IMME, statistical models including the CAS (Constructed Analog on Soil moisture), historical trends , and the latest Weeks 3/4 temperature outlook. Below normal temperatures are favored across a broad region of the Central CONUS, from Kansas, Oklahoma and northern Arkansas north and east into the Upper Great Lakes region. Probabilities for anomalously cool temperatures peak between 40%-49%. A significant contributor to these predicted below normal temperatures is the very high soil moisture (95th percentile or greater) across this area, with approximately half of this region at or above the 99th percentile. This broad expanse of near-saturated, or saturated, soils has been the result of frequently recurring heavy rainfall. During the past 30-days, rainfall amounts ranged from 2-8 inches or more above normal. Viewed from a slightly different perspective, percent-of-normal precipitation ranged from 150%-400% of normal (locally greater). Lower-tercile temperatures are favored over the Central CONUS by a majority of models and statistical tools, but the exact placement and size of this area of anomalously cool temperatures is uncertain. Elsewhere, Equal Chances (EC) of above, near, and below normal mean temperatures are forecast.
Precipitation
The monthly precipitation outlook indicates that wetter-than-normal conditions are favored from southwestern Alaska northeastward across the Central Interior, with maximum probabilities ranging from 40%-49%. This is supported primarily by a majority of the last 9 days of CFS runs and the uncalibrated NMME, but also the NMME PAC, both GFDL models (FLOR and CM2.1), and to a lesser extent, the latest Weeks 3/4 precipitation outlook. Upper-tercile precipitation is also favored over a large portion of the Central CONUS, as far south as Texas. As was the cas e in Alaska, maximum probabilities range from 40%-49%. Of the statistical tools, the CAS bears the closest resemblance to this predicted pattern of upper-tercile precipitation, which also looks fairly similar to recent observations of both heavy rainfall and very high soil moisture. The CFS precipitation anomaly forecast for July lends some support to this area of anomalous wetness. However, it predicts the lion’s share of the rainfall to be focused farther west, over the Pacific Northwest, the Northern Intermountain Region, and the Northern and Central Rockies. A majority of input models for the NMME generally predict this corridor of wetter-than-normal conditions, though there are variations on the overall theme. The NASA, CMC2 Canadian model, and the IMME also extended the favored area of above normal rainfall farther west as indicated by the CFS. Finally, there is a slight tilt in the odds for drier-than-normal conditions across most of the Alaska Panhandle, and west-central portions of the Gulf Coast region. These areas have modest support from the CFS, CAS (CONUS), NCAR, GFDL FLOR, and the CMC2 Canadian model. July climatology also provides weak support for the relative dryness in the west-central Gulf Coast region. Elsewhere, Equal Chances (EC) of above, near, and below normal precipitation are favored.
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS
The July-August-September (JAS) 2019 temperature outlook indicates that above normal seasonal mean temperatures are most likely for the western third of the CONUS and all of Alaska. The highest odds for above normal temperatures are across Washington and the Alaska Panhandle. Above normal temperatures are also favored for Southern Texas, the Gulf Coast states, and east of the Appalachian Mountains. Below normal temperatures are the most likely category from the Central and Southern Plains to the Upper Great Lakes.
Equal Chances (EC; white areas) of below, near, and above normal seasonal mean temperatures or seasonal total precipitation amounts are where the likelihoods for these three categories are similar to their climatological probabilities. Review of subsequent seasonal outlooks and the scientific forecast basis for all outlooks are given below.
BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS and PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
The temperature and precipitation outlooks were based primarily on dynamical model guidance from the NMME, IMME, and statistical model guidance which includes a statistical forecast of the linear impacts of ENSO combined with decadal climate trends based on the CPC SST Consolidation forecast for Nino 3.4. The potential impacts from a continuation of El Nino conditions were considered for the seasonal outlook period through winter 2019-2020. Soil moisture conditions were strongly considered for the earliest leads, as well as near-coastal SST anomalies. Several statistical and dynamical models , as well as hybrid statistical-dynamical models, along with an objective consolidation of several forecast tools, were also examined in preparation of the seasonal outlooks. Decadal timescale trends were considered for all leads but take a primary role in later outlooks, as uncertainty in interannual climate signals increases. The potential for an out sized influence from subseasonal variability to imprint on the seasonal period was also considered for the early leads, as given a weak El Nino, subseasonal modes of variability can have a larger than normal influence.
PROGNOSTIC DISCUSSION OF OUTLOOKS – JAS 2019 TO JAS 2020
TEMPERATURE
The JAS 2019 through DJF 2019-2020 seasonal mean temperature outlooks utilize the predictability of several climate phenomena, including the ongoing El Nino event and its potential impacts, anomalous land surface and sea surface temperature states, and decadal timescale climate variability or trends . A statistical-dynamical hybrid model combining calibrated NMME temperature forecasts with statistically bridged impacts from NMME Nino 3.4 forecasts (known as calibration, bridging and merging or CBaM) suggest that below-normal temperatures are most likely during JAS over much of the central CONUS. Many of the dynamical models in the NMME suite indicate below normal temperatures. Statistical guidance that emphasizes ENSO and long-term trends indicate that near normal temperatures are most likely for much of the same area, while a pure ENSO response would favor below normal temperatures potentially across the Great Lakes through Aug-Sep-Oct (ASO). Two inputs, summertime ENSO and the relation of temperature to soil moisture, offer less predictability in the autumn, so the SON and OND outlooks largely reflect the model guidance and linear regressions of trend and ENSO. The outlooks beyond OND are largely unchanged from the prior months set as the odds for El Nino to continue arenearly the same as last month. On the seasonal timescale, during the summer and autumn, trends are the dominant mode of variability across Alaska, and trends favor above normal temperatures. The strongest signal is during the months of October and November, and the current outlook reflects strong probabilities for above normal temperatures during the seasons that include those months.
PRECIPITATION
Beginning with the JAS 2019 precipitation outlook, above normal precipitation is forecast for a large region of the CONUS from the interior West to the Mississippi Valley. This pattern is suggestive of a northward shift in the North American Monsoon, and is supported by model guidance and statistical relationships between seasonal precipitation and ENSO. [Editor’s Note: I have some questions about this]. For JAS 2019, some models showed weak signals for below normal precipitation from the Northeast to the Mid-Atlantic, though only the Mid-Atlantic portion of that signal is consistent with ENSO composites/regressions, so the overall signal was not included in the official outlooks. The pattern in the precipitation forecast persists for the ASO 2019 season, though during ASO the signal shifts south to reflect the potential for moisture to surge northward from the East Pacific, an impact typically associated with more tropical cyclone activity. Beyond ASO, the signal gradually shifts southward due to the seasonal evolution of long-term trends and expected ENSO impacts during the winter of 2019-2020. Similar to the temperature outlooks, minimal changes were made to the outlooks covering winter 2019-2020 and spring 2020 as no forecasts of major climate factors have changed since last month. The outlooks for next summer were modified to reflect trends , including the addition of below normal precipitation across the interior Pacific Northwest.
ENSO Considerations
Recent IRI-CDC Analysis
The change in the thinking in a short time is interesting.
Now we look at the NOAA proprietary model. And we are going to look at last month’s forecast and the current forecast
Last Month’s Forecast
This Month’s Forecast
Comparing Last Month to This Month
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And here is the actual (recent history), but it is a weekly average.
Can we make our own forecast?
What about the Southern Oscillation Index (SOI)? The SOI is one measure of the extent to what the atmosphere has been impacted by the Eastern Pacific surface pattern which is measured by the Nino 3.4 Index. After all, we are more interested in the impacts to weather in the atmosphere which impacts populated areas than we are about the temperature distribution of the ocean surface along the Equator in the Pacific Ocean.
B. Conclusion
There has hardly been any change in the forecast this last month. NOAA has changed some of the forecast maps slightly to reflect that which they may not have had sufficient confidence last month to show. But the thinking has not changed very much. The duration of this El Nino and the nature of El Nino is central to making an accurate forecast.
Soon, probably on Sunday June 23, 2019 or if not then most likely the following day, we will compare the NOAA and JAMSTEC forecasts.
