Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT Sat Oct 31 2020


30-DAY OUTLOOK DISCUSSION FOR NOVEMBER 2020

The updated November 2020 outlook is based on the November outlook released in 
mid-October adjusted using the current WPC outlooks for week 1 and CPC outlooks 
for the extended range and week 3-4, while considering current climate 
conditions, including an ongoing La Nina, and following the most recent 
subseasonal and monthly integrated dynamical model guidance. The influence of 
ongoing La Nina conditions is apparent in both the prior half-month lead 
November outlook and the updated November outlook, increasing the chances of 
above normal temperatures and below normal precipitation across much of the 
southern CONUS, while increasing the chances of below normal temperatures and 
above normal precipitation for parts of the northern CONUS. 

The updated November temperature outlook has only small changes relative to the 
prior outlook, most notably increasing the area of likely above normal 
temperatures in the Pacific Northwest to include Oregon and southwestern 
Washington, while increasing the probabilities of above normal temperatures 
over parts of the Central Plains to be over 50 percent. Dynamical models 
predict an amplified 500-hPa ridge over the western CONUS and a 500-hPa trough 
over the eastern CONUS at the start of November, with the ridge expected to 
progress eastward while the trough lifts to the northeast during the first week 
of the month. This pattern increases the probabilities of above normal 
temperatures for much of the western CONUS in the monthly outlook, while 
decreasing probabilities over the southeastern CONUS. Above normal temperatures 
remain likely for almost the entire CONUS in the updated November outlook, with 
the exception of parts of the Northern Rockies extending to the Northern 
Plains, where equal chances of above, near and below normal temperatures are 
forecast. During the second week of November, a trough is predicted to amplify 
over the western CONUS, and the week 2 outlook calls for high probabilities of 
below normal temperatures over parts of the west that are consistent with areas 
showing equal chances in the November outlook. Probabilities of above normal 
temperatures were increased over parts of the Northeast, where the outlooks for 
week 2 and week 3-4 indicate greater chances of above normal temperatures. 
Small adjustments were made in the area of likely above normal temperatures in 
western and northern Alaska, consistent with current dynamical model forecasts. 

The updated November precipitation outlook has a similar pattern to the prior 
outlook, predicting enhanced probabilities of below normal precipitation across 
a large area of the southern CONUS from the Southwest region across the Central 
and Southern Plains into the Southeast region from the southern Ohio Valley and 
Mid-Atlantic region to the Gulf Coast. The area of enhanced probabilities of 
above normal precipitation has expanded over the Pacific Northwest into 
Northern Plains, supported by dynamical model forecasts and precipitation 
outlooks for weeks 1 through 4. Chances of below normal precipitation have 
decreased and equal chances of below, near and above normal precipitation are 
predicted in the November update for parts of California, Arizona and Nevada, 
where the climatology is relatively dry and there is uncertainty in the 
precipitation outlook for early November and only weak probabilities of below 
normal precipitation are predicted in the week 3-4 outlook. Probabilities of 
below normal precipitation have increased for parts of the Southeast, where 
likely below normal precipitation is predicted for the week 2 and week 3-4 
periods. An area of enhanced probabilities of above normal precipitation over 
Alaska shifted somewhat to be over northwestern Mainland Alaska and the North 
Slope, consistent with current dynamical model forecasts for November. 

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********** Previous Forecast discussion from mid-October is below ************
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The November 2020 monthly temperature and precipitation outlooks are based 
primarily on dynamical model forecast guidance in the context of ongoing and 
likely strengthening La Nina conditions as we progress through the autumn 
months. In addition, some areas of the forecast domain consider current land 
surface states and nearby ocean surface temperatures.

The MJO was considered but played a lesser role in the outlook, as the MJO 
signal over the Maritime Continent is not expected to lead to significant 
subtropical impacts. Due to expected interaction of any eastward propagating 
MJO convective signal with suppressed convection over the west-central 
equatorial Pacific, related to La Nina, it is unclear if a coherent MJO 
enhanced convective phase over the Pacific will alter tropical-subtropical 
interactions. Also, statistically significant impacts on higher latitudes from 
the MJO are small during November, compared to winter months. 

The November 2020 temperature outlook favors above-normal monthly mean 
temperatures for nearly all of the forecast domain except for areas in 
southeast mainland Alaska,  the Alaska Panhandle, and from the Pacific 
Northwest to the Northern Plains, where Equal Chances (EC) is forecast. 
Dynamical model forecast guidance and typical temperatures observed during 
November under La Nina conditions support this outlook. Decadal temperature 
trends along with dry surface conditions enhance probabilities for above-normal 
temperatures for parts of the southwestern CONUS into the Southern Plains 
states. Strong negative decadal trends in sea ice coverage and thickness and 
warmer than normal ocean surface temperatures near the coasts of Alaska also 
increase chances for above-normal temperatures for parts of western and 
northern Alaska. 

La Nina conditions tend to favor near to below-normal temperatures in parts of 
the Pacific Northwest, southeast Alaska and the Alaska Panhandle, but with 
positive decadal trends in some of these areas counteracting this generally 
weaker La Nina signal in autumn, EC is forecast for these areas. Decadal 
positive temperature trends, dynamical model forecast guidance, and to a lesser 
extent warm coastal ocean surface temperatures and dry land surface conditions 
support increased chances for above-normal temperatures for the Northeast.

For precipitation, consistent dynamical model forecast guidance and typical La 
Nina impacts in autumn favor below-normal precipitation stretching from 
Southern California across the Southwest region and south-central Rockies 
eastward to include the Central and Southern Plains, the Lower Mississippi 
Valley, and the remainder of the Southeast region, excluding the southern 
Florida Peninsula. 

The consensus of dynamical model forecast guidance favors above-normal monthly 
total precipitation amounts for parts of the southern Alaska Panhandle and a 
small area of the Pacific Northwest centered around northeastern Washington. La 
Nina conditions increase the chances of below-normal precipitation along the 
south coast of mainland Alaska and the northern Alaska Panhandle later in 
autumn and in winter, where EC is forecast for November. La Nina conditions and 
warm ocean waters near the coast support above-normal precipitation for the 
west coast of Alaska, as does the consensus of dynamical model guidance.

FORECASTER: Dan Collins

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 Dec ... will be issued on Thu Nov 19 2020

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