Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks 
NWS Climate Prediction Center College Park, MD 
300 PM EDT Tue September 22 2020 
 
6-10 DAY OUTLOOK FOR SEP 28 - OCT 02, 2020 
 
Today's models show good agreement predicting an amplified circulation pattern  
across the forecast domain. An amplified trough is forecast over the North  
Pacific, with below normal 500-hPa geopotential heights to extend over the  
eastern Aleutians. A ridge is expected over parts of eastern Alaska, western  
Canada, and the western CONUS, favoring positive 500-hPa height anomalies over  
Mainland Alaska, the Alaska Panhandle, and much of the western CONUS. Over the  
last two days, models continue to predict an amplified trough over the central  
and eastern CONUS, leading to negative 500-hPa height anomalies over much of  
the eastern CONUS. Positive 500-hPa height anomalies over northern New England,  
associated with a predicted ridge over the North Atlantic, are expected to only  
last through the start of the 6-10 day period as the trough progresses slowly  
eastward. 
 
Near normal temperatures are favored for southwestern Mainland Alaska and the  
Aleutians underneath predicted near to slightly below normal 500-hPa heights.  
Above normal temperatures are favored for most of Mainland Alaska and the  
Alaska Panhandle, under positive 500-hPa height anomalies and anomalous  
southerly flow. Enhanced probabilities of above normal temperatures are  
predicted for the western half of the CONUS, under a  ridge and positive  
500-hPa height anomalies. Below normal temperatures are likely across much of  
the eastern half of the CONUS, in association with the trough over the central  
and eastern CONUS. Above normal temperatures are favored for parts of the  
Northeast, where positive 500-hPa height anomalies are expected early in the  
period, and over the southern Florida Peninsula, supported by both the ECMWF  
and GEFS model forecasts. 
 
In association with the predicted trough over the North Pacific, above normal  
precipitation is favored for central and eastern areas along the south coast of  
Alaska, southeastern Mainland Alaska, and the northern Alaska Panhandle. Below  
normal precipitation is favored over western areas of Mainland Alaska and parts  
of the Aleutians, to the west of the mean trough axis. Enhanced probabilities  
of below normal precipitation are predicted for much of the western and Central  
CONUS into the Southeast Region, under and ahead of an amplified ridge. Above  
normal precipitation is likely from the Great Lakes region southward into the  
Ohio Valley and eastward into the Mid-Atlantic and Northeast, ahead of the  
trough. The greatest probabilities for above normal precipitation exceed 50  
percent for parts of the Northeast.  
 
The official 6-10 day 500-hPa height blend consists of 40% of Today's 6z GFS  
Ensemble Mean centered on Day 8, and 60% of Today's 0z European Ensemble Mean  
centered on Day 8  
  
 
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Above average, 4 out of 5, due to  
good agreement among the model 500-hPa circulation forecasts on an amplified  
flow pattern, offset by some differences among forecast tools for temperature  
and precipitation.  
 
8-14 DAY OUTLOOK FOR SEP 30 - OCT 06, 2020  
 
For the week-2 period, the 500-hPa circulation pattern forecast is similar to  
the 6-10 day period forecast with some slight eastward progression and  
deamplification, predicting a trough over the North Pacific, a ridge over  
eastern Alaska and the western CONUS, and a trough over the eastern CONUS. All  
ensemble means indicate some deamplification of the circulation pattern  
relative to the 6-10 day period forecast, with the ECMWF ensemble mean showing  
weaker 500-hPa height anomalies overall compared to the GEFS ensemble mean.  
Troughing over the eastern CONUS in particular is lower in amplitude in the  
ECMWF ensemble mean than that in the GEFS.  
 
Anomalous southerly flow and above normal 500-hPa heights lead to enhanced  
probabilities for above normal temperatures over Mainland Alaska and the Alaska  
Panhandle. Near normal temperatures are favored for the western Aleutians,  
under rising midlevel heights. The predicted ridge over the western CONUS  
increases chances of above normal temperatures across the western half of the  
CONUS. Enhanced probabilities of below normal temperatures are predicted across  
most of the eastern CONUS, under the amplified trough, with probabilities  
exceeding 70 percent over parts of the Southeast. Above normal temperatures  
continue to be likely for parts of northern New England, under anomalous  
southerly flow and positive 500-hPa height anomalies early in the period. 
 
Probabilities for above normal precipitation continue to be elevated in week 2,  
for eastern Mainland Alaska and the Alaska Panhandle, ahead of the trough,  
along with continued below normal precipitation over parts of western Alaska.  
Elevated probabilities for below normal precipitation are predicted for almost  
the entire western, central, and southeastern CONUS under the ridge, outside of  
climatologically dry regions of the Southwest where near normal precipitation  
is favored. As the trough begins to deamplify and progress eastward, above  
normal precipitation continues to be likely for a smaller area of the  
Northeast.  
 
The official 8-14 day 500-hPa height blend consists of: 40% of Today's 6z GFS  
Ensemble Mean centered on Day 11, and 60% of Today's 0z European Ensemble Mean  
centered on Day 11  
 
 
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Above average, 4 out of 5, due to  
good agreement among the model 500-hPa circulation forecasts on an amplified  
flow pattern, offset by some differences among forecast tools for temperature  
and precipitation.  
 
FORECASTER: D Collins 
 
Notes: 
 
 
Automated forecasts are issued on Saturday and Sunday. Occasionally manual  
intervention is necessary to address quality control and consistency issues. In  
these cases, forecasts are manually drawn but a full discussion is not issued. 
 
 
The notation for the categorical forecast indicated on the maps is the same as  
that in the tables: A-above   N-near normal   B-below 
 
 
The temperature map shows regions with > 33% chance of being warmer (orange,  
"A"), colder (blue, "B"), or close to (unshaded, "N"). Historical average  
values for the calendar period of the forecast (dashes, "f").  Labels on the  
shaded lines give the probability (> 33%) of the more likely category (B or A).  
 Probability of N is always < 40%. 
 
 
The precipitation map shows regions with > 33% chance of being wetter (green,  
"A"), drier (tan, "B"), or close to (unshaded, "n"). Historical median values  
for the calendar period of the forecast (dashes, "inches").  Labels on the  
shaded lines give the probability (> 33%) of the more likely category (B or A).  
 Probability of N is always < 40%. 
 
 
In the southwest and other climatologically dry regions - there will be a  
greater than 33.3% chance of no precipitation and occasionally even a normal  
(i.e. Median) value of zero - especially during the dry seasons.  In such cases  
a forecast of near normal is effectively a forecast of little or no  
precipitation. 
 
 
The climate prediction center uses 1981-2010 base period means for  
temperature...precipitation...and 500-hpa heights as reference in the climate  
outlooks. 
 
The next set of long-lead monthly and seasonal outlooks will be released on  
October 15. 
 
 
Analogs to the 5 day mean observed pattern centered 3 days ago (D-3) 
for the region from 20N to 70N latitude and 175E to 60W longitude 
include the 5 day periods centered on the following dates:  
19630919 - 19620925 - 19820906 - 19920929 - 20041006 
 
 
Analogs to the 7 day mean observed pattern centered 4 days ago (D-4) 
for the region from 20N to 70N latitude and 175E to 60W longitude 
include the 7 day periods centered on the following dates:  
19920928 - 19630920 - 19551005 - 19620925 - 20070902 
 
 
6-10 DAY OUTLOOK TABLE 
Outlook for Sep 28 - Oct 02, 2020 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  A    B     OREGON      A    B     NRN CALIF   A    N      
SRN CALIF   A    N     IDAHO       A    B     NEVADA      A    B      
W MONTANA   A    B     E MONTANA   A    B     WYOMING     A    B      
UTAH        A    B     ARIZONA     A    B     COLORADO    A    B      
NEW MEXICO  A    B     N DAKOTA    B    B     S DAKOTA    B    B      
NEBRASKA    B    B     KANSAS      B    B     OKLAHOMA    B    B      
N TEXAS     B    B     S TEXAS     B    B     W TEXAS     A    B      
MINNESOTA   B    B     IOWA        B    B     MISSOURI    B    B      
ARKANSAS    B    B     LOUISIANA   B    B     WISCONSIN   B    A      
ILLINOIS    B    B     MISSISSIPPI B    B     MICHIGAN    B    A      
INDIANA     B    A     OHIO        B    A     KENTUCKY    B    A      
TENNESSEE   B    B     ALABAMA     B    B     NEW YORK    N    A      
VERMONT     A    A     NEW HAMP    A    A     MAINE       A    A      
MASS        A    A     CONN        A    A     RHODE IS    A    A      
PENN        B    A     NEW JERSEY  N    A     W VIRGINIA  B    A      
MARYLAND    B    A     DELAWARE    B    A     VIRGINIA    B    A      
N CAROLINA  B    A     S CAROLINA  B    B     GEORGIA     B    B      
FL PNHDL    B    B     FL PENIN    A    B     AK N SLOPE  N    B      
AK ALEUTIAN N    B     AK WESTERN  A    B     AK INT BSN  A    A      
AK S INT    A    A     AK SO COAST A    A     AK PNHDL    A    A      
  
                            
 
8-14 DAY OUTLOOK TABLE 
Outlook for Sep 30 - Oct 06, 2020 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  A    B     OREGON      A    B     NRN CALIF   A    N      
SRN CALIF   A    N     IDAHO       A    B     NEVADA      A    N      
W MONTANA   A    B     E MONTANA   A    B     WYOMING     A    B      
UTAH        A    B     ARIZONA     A    N     COLORADO    A    B      
NEW MEXICO  A    B     N DAKOTA    B    B     S DAKOTA    B    B      
NEBRASKA    B    B     KANSAS      B    B     OKLAHOMA    B    B      
N TEXAS     B    B     S TEXAS     B    B     W TEXAS     A    B      
MINNESOTA   B    B     IOWA        B    B     MISSOURI    B    B      
ARKANSAS    B    B     LOUISIANA   B    B     WISCONSIN   B    B      
ILLINOIS    B    B     MISSISSIPPI B    B     MICHIGAN    B    N      
INDIANA     B    B     OHIO        B    N     KENTUCKY    B    B      
TENNESSEE   B    B     ALABAMA     B    B     NEW YORK    B    A      
VERMONT     B    A     NEW HAMP    N    A     MAINE       A    A      
MASS        N    A     CONN        B    N     RHODE IS    N    N      
PENN        B    N     NEW JERSEY  B    B     W VIRGINIA  B    B      
MARYLAND    B    B     DELAWARE    B    B     VIRGINIA    B    B      
N CAROLINA  B    B     S CAROLINA  B    B     GEORGIA     B    B      
FL PNHDL    B    B     FL PENIN    B    B     AK N SLOPE  A    N      
AK ALEUTIAN N    B     AK WESTERN  A    N     AK INT BSN  A    A      
AK S INT    A    A     AK SO COAST A    A     AK PNHDL    A    B      
  
                           LEGEND 
TEMPS WITH RESPECT TO NORMAL     PCPN WITH RESPECT TO MEDIAN 
A - ABOVE   N  - NEAR NORMAL     A - ABOVE   N - NEAR MEDIAN 
B - BELOW                        B - BELOW 
  
THE FORECAST CLASSES REPRESENT AVERAGES FOR EACH STATE. NORMAL 
VALUES - WHICH MAY VARY WIDELY ACROSS SOME STATES - ARE 
AVAILABLE FROM YOUR LOCAL WEATHER SERVICE FORECAST OFFICE. 
  
FOR ADDITIONAL INFORMATION SEE MESSAGE FXUS06 KWBC - ON AWIPS AS 
PMDMRD. 
 
$$