Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
830 AM EDT Thu Sep 19 2019


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.

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.

An updated monthly outlook... for Oct will be issued on Mon September 30 2019

These outlooks are based on departures from the 1981-2010 base period.
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