Written by Sig Silber
Here is the September 19, 2019 NOAA 15-month forecast for CONUS and Alaska including the Early Outlook for October and forecasts through Oct – Dec 2020. There have only been a few changes in the forecasts since last month. The Early Outlook for the single month of October may change again when it is updated at the end of September thirteen days after the current NOAA release.
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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 October, 2019. It is called the Early Outlook because it will be updated at the end of September. Only the October 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 October 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 October*. For Temperature, it is warm everywhere but with higher probabilities of being warm for Alaska near water expecially waters that are recently warmer than usual and for CONUS Southwest. For Precipitation, it is a wet SE Alaska and Panhandle and a mostly EC CONUS with four wet anomalies (Northwest, northern Plains, Arizona and neighboring states and central and southern eastern seaboard). There is a dry anomaly in eastern Oklahoma and Arkansas and parts of neighboring states.
* 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 September and early October (so they are less useful for this purpose) and the third map only extends the coverage through the first eighteen days of October. The Seasonal Outlook was issued fairly late this month since the third Thursday fell on September 19, 2019.
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 not seem to fit well with the Week 3 – 4 forecast. We do not have the remainder of the month ( 13 days) in the sequence of maps above. We will revisit this question at the end of September when the October 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 well with the Week 3-4 Map. We do not have the remainder of the month (13 days) in the sequence of maps above. We will revisit this question at the end of September when the October forecast is updated. |
Now we consider the three-month Outlook.
Notice that the three-month periods are abbreviated e.g. September/October/November is shown as SON. You will see such abbreviations often in this report.
Prior Temperature Outlook for OND 2019
New Temperature Outlook for OND 2019
Prior Precipitation Outlook for OND 2019
New Precipitation Outlook for OND 2019
Now let us focus on the long-term situation.
First Temperature
Prior 14 Month Temperature Outlook: OND 2019 – SON 2020
New 14 Month Temperature Outlook: NDJ 2019/2020 – OND 2020
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: OND 2019 – SON 2020
New 14 Month Precipitation Outlook: NDJ 2019/2020 – OND 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.
*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 September 19, 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 (October), the new NOAA Summary for OND, and finally the remainder of the 15-Month Forecast.
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
Oceanic and atmospheric observations across the equatorial Pacific reflected ENSO-neutral conditions during August and early September. The 7-day average sea surface temperature (SST) observations centered on September 11th are below average (-0.5C to -1.5C) over the central and eastern Pacific, and above average (+0.5C to +1.5C) over the west-central Pacific. The latest weekly Nino 3.4 SST anomaly is -0.3 deg C, down from +0.0C one week ago. Subsurface temperatures range from -0.5C to greater than -3.0C below average over much of the central and eastern equatorial Pacific, to a depth of about 175 meters. Outgoing longwave radiation (OLR) anomalies depicted near average convection across the equatorial Pacific from August 16th to September 10th, and suppressed tropical convection over Indonesia. Trade winds during the past month averaged close to normal over the equatorial Pacific. The Madden-Julian Oscillation (MJO) remained weak for at least the past 40 days, with other modes of subseasonal variability (such as Kelvin waves, equatorial Rossby waves and Tropical Cyclones (TC)) influencing convection across the global tropics. Sea surface temperature anomalies of +2.5 to +3.5 degrees C, or higher, persist throughout areas surrounding Alaska. These anomalies and the likelihood for another autumn season with significantly delayed sea ice onset were major factors in the temperature outlook for Alaska this fall.
PROGNOSTIC DISCUSSION OF SST FORECASTS
A substantial spread in the dynamical and statistical model forecasts of SSTs across the equatorial central and eastern Pacific during the fall and winter continues. Statistical model forecasts such as the Canonical Correlation Analysis and the Constructed Analog predict a Nino 3.4 SST anomaly at or slightly above +0.5 degree C through most of winter 2019-2020[Editor’s Note: This is the view of JAMSTEC], with a very slow decline within the upper half of the Neutral category (that is, +0.0C to +0.49C) throughout spring. The CPC SST Consolidation and the NMME (North American Multi-Model Ensemble) predict only slightly reduced anomalies (relative to the tools noted above) throughout the upcoming winter and spring, though the forecast anomalies still range within the upper half of Neutral. The CPC/IRI consensus forecast indicates that ENSO-neutral conditions are most likely through the winter with La Nina the least likely to develop.
[Editor’s Note: This part of the discussion is the weak link in the NOAA Analysis this month. I am sympathetic to the NOAA view that we will be in ENSO Neutral this winter. But given that some of their tools suggest close to El Nino conditions will apply, one might have expanded this discussion so that the variablity in possible outcomes was handled in some manner in their forecast and it was not.]
30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2019
The initial half month lead October monthly outlook always represents a considerable challenge in short term climate prediction. A two week lead monthly outlook during a transition season period, such as October, integrated over only a monthly period, historically is one in which predictability is low.
Reviewing the latest climate conditions and status of major climate modes, there are a few items to note, however. During the summer, we entered ENSO-neutral conditions across the Pacific Basin so that the ENSO phase did not play any role in the October outlook. However, there is coherent subseasonal tropical variability (MJO / atmospheric Kelvin wave activity) ongoing and is considered in preparing the outlook. Although impacts from this subseasonal tropical variability at higher latitudes this time of the year are tenuous and unreliable, this forcing can play a role in October conditions for portions of the southern CONUS – mainly related to potential enhancement of tropical cyclone activity in the East Pacific and Atlantic basins. It is also noted that soil moisture anomalies are substantial in some areas. This includes large soil moisture surpluses in the northern Plains and upper Midwest as above-normal rainfall continued through the summer months. Also, the CONUS devoid of much drought for most of the year, has shown an increase in drought conditions for parts of the Southeast, Texas and Southwest. The soil moisture anomalies, although noteworthy, played a generally minor role when preparing the October outlook.
The October temperature outlook favors above-normal monthly mean temperatures for the entire forecast domain. The largest probabilities are depicted for the western and northern areas of Alaska due to continued well above-normal ocean surface temperatures, feedback due to earlier loss and lower coverage of nearby sea ice extent, as well as dynamical model guidance from a number of sources. Odds for above-normal temperatures are modestly elevated for the southwest corner of the CONUS due to strong positive temperature trends during this time of year, consistent model guidance and to a lesser extent generally drier than normal conditions in some areas. The increase in probabilities for above-normal temperatures from climatological values across the central portion of the country are small. In these areas, there was considerable uncertainty as available forecast tools and dynamical model guidance were in conflict and in locations of historically low skill so that forecast confidence is low. A potential cooler start to October in the Pacific Northwest and northern Rockies along with surpluses in soil moisture in the northern Plains and Upper Midwest tempered above-normal probabilities in these areas as well.
There is high uncertainty, low forecast confidence and so small forecast coverage in the October precipitation outlook. Monthly total precipitation amounts are forecast to be above-normal for small regions of the forecast domain. This includes the Alaska Panhandle and areas of the Pacific Northwest, Southwest, northern Plains and central and southern eastern seaboard. Model guidance indications of northward shifted westerlies support forecasts of above-normal precipitation for the highlighted areas along the northern tier of the CONUS. Long term trends and the potential for an active period of tropical cyclone activity in the Atlantic, consistent with MJO/subseasonal variability noted earlier, tilts the odds for above-normal precipitation for the eastern seaboard from the mid-Atlantic southward. Similar prospects for continued enhanced tropical cyclone activity in the eastern Pacific basin increases the potential for Gulf surges and tropical moisture to enter the far Southwest. Some consistency in dynamical model guidance was the primary basis for the favored below-normal rainfall highlighted area in the southern Plains.
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS (with focus on OND 2019)
Temperature
The October-November-December (OND) 2019 temperature outlook favors above normal temperatures throughout the entire forecast domain, although probabilities vary. The highest regional probabilities for above normal temperatures are forecast across parts of the Southwest, the Northeast, and the North Slope of Alaska. Probabilities for above normal temperatures are lowest from the northern Great Plains and Upper Mississippi Valley to interior portions of the east-central Gulf Coast region, and for interior parts of southern Alaska.
Precipitation
The OND 2019 precipitation outlook indicates that above normal seasonal total precipitation is favored near the Atlantic Coast from Florida to New Jersey, much of the west-central and central CONUS, and Alaska (excluding the Panhandle). Below normal precipitation is favored over the north-central portion of the West Coast.
Equal chances (EC; white areas) of below, near, and above normal are forecast in areas where the likelihood of seasonal mean temperatures or seasonal total precipitation amounts are expected to be similar to their 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 were based on calibrated NMME forecasts, a statistical-dynamical hybrid model combining calibrated NMME forecasts with statistically bridged impacts from NMME Nino 3.4 forecasts (CBaM), and a new Consolidation (CON) tool which uses the CCA (Canonical Correlation Analysis), the CA (Constructed Analog), the NMME, OCN (Optimal Climate Normals) and ENSO phase. The CA-SST (Constructed Analog which uses tropical Pacific SSTs as input) was also utilized. Due to the expectation that ENSO is unlikely to provide a major influence on the mid-latitude circulation pattern at least through earlier lead times, decadal climate trends were weighed more heavily during the fall and winter 2019-2020. Decadal climate trends became the major tool for temperature and precipitation outlooks at the longer leads.
PROGNOSTIC DISCUSSION OF OUTLOOKS – OND 2019 TO OND 2020
TEMPERATURE
Above normal temperatures are favored throughout the forecast domain during OND, based on good agreement among the dynamical models and statistical tools. In Alaska, there is not only good agreement among the models and tools, but SSTs range from +1.5C to +3.5C above average surrounding most of the state, which contributes toward relative warmth in coastal regions. The greatest chances for above normal temperatures (in excess of 70%) are across the North Slope, where there is a strong historical trend during the past two decades for a significant delay in the formation of sea ice over the adjacent waters of the Arctic Ocean and Chukchi Sea.
Over the Lower 48 states, probabilities for above normal mean temperatures exceed 60% over the Southwest, supported by the calibrated NMME, CBaM, historical temperature trends , and the CON tool. Probabilities for above normal (upper-tercile) temperatures exceed 50% over parts of the Northeast based on the CA-SST tool, trends , the calibrated NMME, the CON, and the CBaM. Probabilities for above normal temperatures are tempered across the northern Great Plains where more variability is expected during the three month period, and where the signal is weaker among dynamical models . In addition, the potential for recurving tropical cyclones in the northwest Pacific and their effect on the longwave pattern downstream over North America limits confidence in the temperature outlook across the north-central CONUS. These tempered probabilities for upper-tercile temperatures extend southeastward towards the central and eastern Gulf Coast region, as indicated by CCA, the calibrated NMME, CBaM, and the CON tool. If ENSO-neutral conditions persist through the upcoming winter as expected, subseasonal variability such as the Arctic Oscillation (AO) could play a greater role in determining the seasonal mean temperature pattern.
During the next few leads (NDJ 2019-20 through FMA 2020), probabilities for above normal temperatures are reduced somewhat across much of the domain, with an area of EC (Equal Chances) being favored initially over the north-central CONUS. This area of EC expands across the Great Lakes and Ohio Valley, reaching a maximum spatial extent in JFM 2020 before decreasing in coverage. This area of increased uncertainty is highlighted in the calibrated NMME and CBaM tools, and to a lesser degree the OCN and new CON. As noted earlier, with ENSO-neutral favored to persist through the upcoming winter, the odds of other subseasonal factors such as the AO playing a larger role in the temperature pattern may result in episodic cold air outbreaks across the north-central states in particular.
Temperature outlooks during the spring and summer 2020 were not changed from the previous set of outlooks issued last month, since multi-decadal trends remain the primary tool. During these seasons, above normal temperatures are most likely across Alaska and a majority of the CONUS except for the north-central CONUS. By fall 2020, increased chances of above normal expand to include all of the forecast domain which follows long-term trends .
PRECIPITATION
The OND 2019 precipitation outlook favors above normal precipitation over Alaska (except the Panhandle), much of the west-central and central CONUS, and the Middle and Southern Atlantic Coast states. To various degrees, these areas are based on the CON, CBaM, trends (especially in the Carolinas and Mid-Atlantic), the CA-SST, and to a lesser extent the calibrated NMME. The anticipated delay in sea ice formation just north of Alaska, in addition to anomalously warm SSTs surrounding the state, also contribute to the relatively wet forecast. The Southern Atlantic region is also vulnerable to tropical cyclones, especially during October, as the main formation area returns to the Caribbean and Gulf of Mexico. Parts of the Southwest CONUS are also susceptible to tropical cyclones in October, and resultant Gulf surges with east Pacific tropical storms and hurricanes. Below normal amounts of precipitation are favored over north-central portions of the West Coast. This is supported by the CON tool, the CA-SST, and the CA.
From NDJ 2019-20 to MAM 2020, odds favor above normal precipitation across much of Alaska. For the CONUS, the enhanced odds of above normal precipitation across the Middle Atlantic and Southern Atlantic Coast states gives way to EC, suggestive of a relatively wet month of October. The broad area of favored wetness over the west-central CONUS transitions to the northern CONUS, from about central Montana to the Great Lakes region. Increased odds of below normal precipitation shift southward with time from Oregon and northern California to most of California and Nevada by JFM 2020. Precipitation signals become very weak over the CONUS in FMA and MAM 2020, with EC favored.
At the longer leads, AMJ 2020 through OND 2020, the tilt in the odds towards above normal precipitation across parts of the eastern CONUS is consistent with long-term trends . Also, the favored area for below normal precipitation, beginning with JJA 2020 across parts of the western and north-central CONUS is also related to trends .
ENSO Considerations
We covered this on Monday so I am not going to go into a lot of detail tonight. The ENSO section in the NOAA Discussion is excellent but brief. We will be discussing any differences between the NOAA assessment of ENSO and JAMSTEC in our Sunday night article. For those who wish to review what we presented Monday Night, it can be found here.
And the CPC-IRI Probability Analysis.
B. Conclusion
The only change in the forecast tonight was to OND 2019 and we suspect that really the only change was to October but we can not confirm that. We now have the Early Outlook October forecast but we do not have a prior forecast for October for comparison purposes. We think the change in the October forecast impacted the OND forecast for which we have a prior forecast from last month.
Soon, probably on the evening of Sunday, September 22, 2019, we will compare the NOAA and JAMSTEC forecasts.
Just to get you thinking, below is the JAMSTEC forecast for ENSO or at least the Nino 3.4 Index which is central to any ENSO forecast. It differs slightly from the assumptions about ENSO used by NOAA.
We will provide a more detailed comparison when we compare the NOAA and JAMSTEC forecasts Sunday night.
