Climate Prediction Center - 6-10 and 8-14 Day Prognostic Discussions

Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks 
NWS Climate Prediction Center College Park, MD 
300 PM EDT Fri August 07 2020 
 
6-10 DAY OUTLOOK FOR AUG 13 - 17 2020 
 
Today’s model guidance is in good overall agreement on the predicted   
mid-tropospheric circulation pattern over North America and adjacent oceanic    
areas during the 6-10 day forecast period. Troughs are forecast over the  
western Aleutians as well as over Western North America from western Canada to  
the West Coast of the CONUS. Broad subtropical riding is forecast over the  
Southwest and the Southern High Plains, extending through the southeastern  
CONUS. A weakness in the subtropical ridge is noted near the western Gulf Coast  
Region. Ridging is forecast farther to the north over eastern Canada, favoring  
above normal heights from the north-central to the northeastern CONUS. Today's  
manual 500-hPa height blend weights the ECMWF ensemble mean slightly greater  
than the NCEP GEFS and Canadian ensemble means, due to recent model skill.  
 
Anomalous ridging over eastern Canada leads to enhanced probabilities of above  
normal temperatures for the north-central and northeastern CONUS. The greatest  
likelihood of above normal temperatures (greater than 70 percent) is indicated  
for parts of the Great Lakes and Upper Mississippi Valley where positive height  
anomalies are forecast to be the most pronounced. Above normal temperatures are  
also favored across the Great Plains and parts of the Southwest, ahead of a  
trough forecast over western North America. Probabilities of above normal  
temperatures are relatively weaker across the southeastern CONUS, due to  
predicted weak height anomalies and the prospect of increased cloudiness and  
precipitation. Below normal temperatures are likely for the northwestern CONUS  
extending northward to the Alaska Panhandle near the predicted mean trough  
axis. Enhanced probabilities of above normal temperatures are indicated for  
parts of western Mainland Alaska, the Alaska Peninsula, and much of the  
Aleutians due in large part to above normal SSTs noted in adjacent waters.  
 
The forecast position of the mean subtropical ridge over the Southwest is  
generally not conducive to an enhanced Monsoon. Therefore, a continuation of a  
dry pattern is likely across the Southwest. Enhanced probabilities of below  
normal precipitation extend northward across much of the Great Basin and  
eastward across the Central and Southern Rockies to much of the Great Plains,  
consistent with both ECMWF and GEFS ensemble guidance. The combination of a  
forecast weakness in the subtropical ridge and the potential for shortwave  
troughs lead to enhanced probabilities of near to above normal precipitation  
from the Western Gulf Coast Region and Mississippi Valley eastward to much of  
the Southeast and Mid-Atlantic States. Below normal precipitation is favored  
farther to the north, across much of the Northeast, due to predicted mean  
surface high pressure. There are enhanced odds of above normal precipitation  
from the Pacific Northwest eastward along the CONUS/Canadian Border to the  
Northern Plains, near and ahead of a mid-level trough predicted over western  
North America. A predicted 500-hPa trough over the western Aleutians and areas  
of surface low pressure increase chances of near to above normal precipitation  
across southern Alaska. Below normal precipitation is favored for much of  
northern Mainland Alaska, farther away from the predicted mean storm track.  
 
The official 6-10 day 500-hPa height blend consists of 10% of Today's 0z GFS  
Ensemble Mean centered on Day 8, 15% of Today's 6z GFS Ensemble Mean centered  
on Day 8, 10% of Today's operational 6z GFS centered on Day 8, 45% of Today's  
0z European Ensemble Mean centered on Day 8, 10% of Today's operational 0z  
ECMWF centered on Day 8, and 10% of Today's 0z Canadian 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 model circulation forecasts offset by some differences  
among the temperature and precipitation tools.  
 
 
8-14 DAY OUTLOOK FOR AUG 15 - 21 2020  
 
During the week-2 period, model solutions begin to diverge as the ECMWF  
ensemble mean generally forecasts a less amplified and more progressive pattern  
relative to the GEFS. The predicted circulation pattern features a persistent  
but weakening trough over western North America from southeastern Alaska to  
near the west coast of the CONUS. Slightly above normal 500-hPa heights are  
forecast ahead of this trough from the southwestern CONUS to the Plains.  
Anomalous ridging is expected to persist across eastern Canada, continuing to  
favor above normal 500-hPa heights across the north-central and northeastern  
CONUS. Slightly below normal heights are favored for the Gulf Coast Region due  
to a predicted weakness in the subtropical ridge. Weakly cyclonic flow and near  
normal heights are forecast across the Bering Sea. Slightly above normal  
heights are favored ahead of this trough across much of western Mainland  
Alaska. The ECMWF ensemble mean was weighted most in the manual blend of  
500-hPa height forecasts, due to recent model skill.   
  
The 8-14 day temperature outlook is very similar to the temperature pattern  
forecast for the 6-10 day period. Below normal temperatures continue to be  
likely for parts of the northwestern CONUS, under a predicted trough and  
negative 500-hPa height anomalies. Above normal temperatures continue to be  
favored from much of the southwestern CONUS northeastward to the Northern  
Plains, Great Lakes and Northeast, under continued positive 500-hPs height  
anomalies and ridging. The region of enhanced above normal temperature  
probabilities is expanded west relative to the 6 to 10 day period to include  
most of California, as the trough over western North America is generally  
forecast to weaken. Below normal temperatures are likely for the Alaska  
Panhandle, under predicted below normal 500-hPa heights, while above normal  
temperatures are favored for the Aleutians and coastal southwestern Mainland  
Alaska in association with above normal SSTs. 
 
Above normal precipitation is likely from the Alaska Panhandle to parts of the  
Pacific Northwest, under a predicted mid-level trough. Near to below normal  
precipitation continues to be favored across most of the western and central  
CONUS, associated with mean ridging and consistent with ECMWF ensemble  
guidance. However, confidence is low across parts of the Southwest Monsoon  
Region as the potential for tropical activity over the Eastern Pacific may  
promote moisture transport into the area. Positive 500-hPa height anomalies and  
mean surface high pressure increase probabilities of below normal precipitation  
over the northeastern CONUS. Above normal precipitation probabilities are  
increased from the Mid-Atlantic States and Southeast westward to the Central  
and Western Gulf Coast Region due to a predicted weakness in the mean  
subtropical ridge. Above normal precipitation probabilities are also enhanced  
for parts of the Upper Mississippi Valley and Great Lakes underneath mean  
southerly low-level flow. Below normal precipitation is likely for much of  
northern Mainland Alaska, consistent with guidance from the GEFS and ECMWF  
ensembles.  
 
The official 8-14 day 500-hPa height blend consists of: 15% of Today's 0z GFS  
Ensemble Mean centered on Day 11, 15% of Today's 6z GFS Ensemble Mean centered  
on Day 11, 40% of Today's 0z European Ensemble Mean centered on Day 11, and 30%  
of Today's 0z Canadian Ensemble Mean centered on Day 11  
 
 
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Average, 3 out of 5, due to good  
overall forecast consistency with the preceding 6 to 10 day period offset by  
increasing model differences between the ECMWF and GEFS ensemble solutions.  
 
FORECASTER: Scott H 
 
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  
August 20. 
 
 
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:  
19700720 - 19920805 - 19800814 - 20030815 - 19920815 
 
 
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:  
19700720 - 19970718 - 19820809 - 19920804 - 19930815 
 
 
6-10 DAY OUTLOOK TABLE 
Outlook for Aug 13 - 17 2020 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  B    A     OREGON      B    A     NRN CALIF   N    N      
SRN CALIF   N    N     IDAHO       B    A     NEVADA      B    B      
W MONTANA   B    A     E MONTANA   B    N     WYOMING     B    B      
UTAH        B    B     ARIZONA     A    B     COLORADO    A    B      
NEW MEXICO  A    B     N DAKOTA    A    A     S DAKOTA    A    N      
NEBRASKA    A    B     KANSAS      A    B     OKLAHOMA    A    B      
N TEXAS     A    B     S TEXAS     A    N     W TEXAS     A    B      
MINNESOTA   A    A     IOWA        A    A     MISSOURI    A    A      
ARKANSAS    N    A     LOUISIANA   N    A     WISCONSIN   A    A      
ILLINOIS    A    A     MISSISSIPPI N    A     MICHIGAN    A    A      
INDIANA     A    A     OHIO        A    A     KENTUCKY    A    A      
TENNESSEE   A    A     ALABAMA     A    A     NEW YORK    A    B      
VERMONT     A    B     NEW HAMP    A    B     MAINE       A    B      
MASS        A    B     CONN        A    B     RHODE IS    A    B      
PENN        A    A     NEW JERSEY  A    N     W VIRGINIA  A    A      
MARYLAND    A    A     DELAWARE    A    A     VIRGINIA    A    A      
N CAROLINA  N    A     S CAROLINA  N    A     GEORGIA     A    A      
FL PNHDL    A    N     FL PENIN    A    N     AK N SLOPE  N    B      
AK ALEUTIAN A    N     AK WESTERN  A    B     AK INT BSN  N    B      
AK S INT    N    N     AK SO COAST N    N     AK PNHDL    B    A      
  
                            
 
8-14 DAY OUTLOOK TABLE 
Outlook for Aug 15 - 21 2020 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  B    A     OREGON      N    N     NRN CALIF   A    N      
SRN CALIF   A    B     IDAHO       B    B     NEVADA      N    B      
W MONTANA   B    N     E MONTANA   B    B     WYOMING     B    B      
UTAH        A    B     ARIZONA     A    B     COLORADO    A    B      
NEW MEXICO  A    B     N DAKOTA    A    N     S DAKOTA    A    B      
NEBRASKA    A    B     KANSAS      A    B     OKLAHOMA    N    B      
N TEXAS     N    B     S TEXAS     A    A     W TEXAS     A    B      
MINNESOTA   A    A     IOWA        A    N     MISSOURI    A    N      
ARKANSAS    N    A     LOUISIANA   N    A     WISCONSIN   A    A      
ILLINOIS    A    A     MISSISSIPPI N    A     MICHIGAN    A    A      
INDIANA     A    A     OHIO        A    A     KENTUCKY    A    A      
TENNESSEE   N    A     ALABAMA     N    A     NEW YORK    A    B      
VERMONT     A    B     NEW HAMP    A    B     MAINE       A    B      
MASS        A    B     CONN        A    B     RHODE IS    A    B      
PENN        A    A     NEW JERSEY  A    N     W VIRGINIA  A    A      
MARYLAND    A    N     DELAWARE    A    N     VIRGINIA    A    A      
N CAROLINA  N    A     S CAROLINA  N    A     GEORGIA     A    A      
FL PNHDL    A    N     FL PENIN    A    N     AK N SLOPE  N    B      
AK ALEUTIAN A    N     AK WESTERN  A    B     AK INT BSN  N    B      
AK S INT    N    N     AK SO COAST A    N     AK PNHDL    B    A      
  
                           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. 
 
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