Prognostic Discussion for Monthly Outlook 
NWS Climate Prediction Center College Park MD 
300 PM EDT Mon Sep 30 2019 
 
 
30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2019 
 
The updated October 2019 temperature and precipitation outlook builds upon some 
of the factors outlined in the mid-September discussion below and is modified 
by the latest suite of dynamical model guidance from the short-range, 
medium-range, extended-range and complete monthly forecast integrations. 
 
The start of October is anticipated to see an amplified pattern across the 
CONUS with a strong trough-ridge pattern oriented across the CONUS. Over the 
first 7 days or so, this pattern is favored to shift eastward, become less 
amplified and then make a transition to a more zonally oriented flow over the 
CONUS. During the second week of October, a warmer pattern is favored to 
develop for the eastern two-thirds and Southwest CONUS as a result of this more 
zonal oriented flow and increasing coverage of positive 500-hPa height 
departures along the southern tier and eastern CONUS. Residual troughing is 
favored to remain across the Pacific Northwest. 
 
A number of factors point to elevated odds for above-normal temperatures for 
most of the CONUS for the second half of October. First, long term trends  are 
positive in nearly all areas of the forecast domain, ongoing MJO activity 
favors above-normal temperatures for most of the central and eastern CONUS and 
Southeast Canada and Week 3-4 dynamical model guidance from the CFS, ECMWF and 
JMA favor above-normal temperatures for much of the second half of October. 
Also, short-term or regime based bias corrections (i.e., based on past 45 days) 
 show that some model forecasts for below-normal temperatures across the CONUS 
have been overestimated to some degree. 
 
Forecast of favored below-normal temperatures for October are focused over some 
areas of the Pacific Northwest to the northern High Plains. These depictions 
only show modest increases in odds as compared to climatology and are related 
to early in the month cold air intrusion during the first week of October that 
may potentially keep mean October temperature anomalies below the lower 
one-third of the historical range. 
 
High odds for above-normal temperatures are depicted for the Southeast, lower 
Appalachians and lower mid-Atlantic - a result of nearly all information 
primarily pointing to above-normal temperatures and also where flash drought 
conditions are ongoing and favored to continue to deteriorate during the first 
10 days of October. 
 
The updated October precipitation outlook is able to increase forecast coverage 
from very low areal numbers released in the mid-September initial outlook. The 
general themes, to first order, are maintained with the forecast coverage for 
above-normal precipitation depicted in the initial outlook along the northern 
tier of the CONUS increased with modest odds depicted for the Pacific Northwest 
and Northeast and greater probabilities depicted over the northern Plains, 
upper Mississippi Valley and western Great Lakes. This area of favored 
above-normal precipitation is extended southward in the updated outlook as a 
plume of moisture from the sub Tropics is likely to spread northward and 
eastward around anticipated ridging located over the Southeast and then 
interact with troughing and the general westerlies along the Canadian border. 
 
Above-normal precipitation remains most likely for areas of the Southwest 
associated with potential influence from eastern Pacific tropical disturbances 
or cyclones that may increase moisture at times during the month. These odds 
are on modestly increased from climatology. 
 
Forecast guidance for the first week in October indicates very little 
precipitation for much of the Southeast from Texas to the lower Atlantic 
seaboard. Week 3-4 forecast tools, long term trends  and MJO impacts do not 
indicate with any consistency or reliability, robust signatures for 
above-normal precipitation during the second half of October. Based on this 
combined information below-normal precipitation is depicted for this region. 
Elevated odds for above-normal precipitation remain forecast for parts of the 
Florida Peninsula, however. There is high uncertainty for Alaska so the initial 
outlook was modified to now favor enhanced odds for above-normal precipitation 
for the west coast of Alaska. 
 
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** Previous discussion from mid-month outlook made in mid-September is below ** 
******************************************************************************* 
 
 
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. 
 
FORECASTER: Jon Gottschalck 
 
The climatic normals are based on conditions between 1981 and 2010, following 
the World Meteorological Organization convention of using the most recent 3 
complete decades as the climate 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. 
 
The next monthly outlook...for Nov ... will be issued on Thu Oct 17 2019 
 
These outlooks are based on departures from the 1981-2010 base period. 
$$