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 Wed May 12 2021 
 
6-10 DAY OUTLOOK FOR MAY 18 - 22 2021 
 
The GEFS, ECMWF, and Canadian dynamical models are in good agreement today with  
regard to the 6-10 day 500-hPa geopotential height pattern over North America.  
Troughing is predicted over the Bering Sea and across the western CONUS, while  
ridging is forecast across the eastern U.S. 
 
Increased probabilities of near to above normal temperatures are highlighted  
over the Southern Florida Peninsula, Northeast and central CONUS, extending  
southwestward to parts of the interior western CONUS, underneath near to above  
normal mid-level heights and low level southerly flow. Below normal  
temperatures are forecast over parts of the Pacific Northwest and Alaska  
Panhandle, consistent with the consolidation forecast tool. Above normal  
temperatures are favored across much of Mainland Alaska and the Aleutians, due  
to forecast enhanced southerly surface and mid-level flow ahead of a mean  
trough forecast over the Bering Sea. 
 
Near to below normal precipitation is favored over parts of the eastern CONUS  
and Great Lakes, underneath above normal 500-hPa heights. Predicted southerly  
flow and frontal activity significantly increase odds of above normal  
precipitation over the Mid and Lower Mississippi Valleys and parts of the  
Central and Southern Plains. Below normal precipitation is favored for parts of  
the Northern High Plains, Northern Rockies and  the western CONUS , consistent  
with the consolidation forecast tool. Over central and southern Alaska, an  
active storm track is forecast on the northern periphery of the mean Pacific  
ridge, leading to increased odds of above normal precipitation. Below normal  
precipitation is slightly favored for parts of western Mainland Alaska,  
consistent with the consolidation forecast tool. 
 
The official 6-10 day 500-hPa height blend consists of 15% of Today's 6z GFS  
Ensemble Mean centered on Day 8, 15% of Today's GFS Superensemble Mean centered  
on Day 8, 10% of Today's operational 6z GFS centered on Day 8, 30% of Today's  
0z European Ensemble Mean centered on Day 8, 10% of Today's operational 0z  
ECMWF centered on Day 8, and 20% of Today's 0z Canadian Ensemble Mean centered  
on Day 8  
  
 
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Average, 4 out of 5, due to good  
agreement in the model precipitation and temperature forecasts, offset by  
differences among the forecast tools in the predicted temperature and  
precipitation fields. 
 
8-14 DAY OUTLOOK FOR MAY 20 - 26 2021  
 
The predicted 500-hPa height pattern during the Week-2 period depicts mean  
mid-level troughing and near to below normal heights across the western CONUS.  
Positive height anomalies are predicted elsewhere over the CONUS, underneath  
mean ridging and anticyclonic mid-level flow. Over Alaska, near to below normal  
500-hPa heights are predicted for the region, associated with mean troughing  
over the Bering Sea and western Alaska. 
 
Near to below normal temperature probabilities are increased across parts of  
the Pacific Northwest and Alaska Panhandle, associated with forecast troughing  
over the region and northerly surface flow. As predicted high pressure shifts  
eastward across the eastern CONUS throughout the period, return flow from the  
Gulf of Mexico favors increased probabilities of near to above normal  
temperatures for the remainder of the CONUS. Mean southerly to southwesterly  
flow favors above normal temperatures across most of Mainland Alaska and the  
Aleutians. 
 
Odds tilt toward below normal precipitation for much of the Northeast and parts  
of the Great Lakes, underneath forecast above normal heights. Increased odds of  
above normal precipitation in most of the Central CONUS and parts of the  
Southeast are associated with southerly flow and moisture advection from the  
Gulf of Mexico behind surface high pressure predicted over the Southeast, and  
ahead of a mean mid-level trough forecast over the West. Despite the mean  
trough over the Western CONUS, energy crossing the northwestern CONUS and  
southern High Rockies is not expected to amplify until it reaches the Plains,  
leading to enhanced below normal precipitation probabilities in most of the  
northwestern CONUS and Northern High Plains. Above normal precipitation chances  
continue to be increased over most of Alaska due to troughing forecast over the  
Bering Sea and western Mainland Alaska, and the ridging over the eastern  
Pacific, favoring an active storm track across much of Alaska. 
 
The official 8-14 day 500-hPa height blend consists of: 15% of Today's 6z GFS  
Ensemble Mean centered on Day 11, 15% of Today's GFS Superensemble Mean  
centered on Day 11, 10% of Today's operational 6z GFS centered on Day 11, 40%  
of Today's 0z European Ensemble Mean centered on Day 11, and 20% 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  
day-to-day consistency in the dynamical model guidance, offset by continued  
uncertainty in dynamical model forecast precipitation and temperature fields  
over the CONUS and Alaska. 
 
FORECASTER: Y. Fan 
 
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 May  
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:  
20080520 - 19710424 - 19800508 - 19660509 - 19780503 
 
 
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:  
20080520 - 19710425 - 19520516 - 19540509 - 19990421 
 
 
6-10 DAY OUTLOOK TABLE 
Outlook for May 18 - 22 2021 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  B    A     OREGON      B    B     NRN CALIF   N    B      
SRN CALIF   A    N     IDAHO       N    N     NEVADA      A    N      
W MONTANA   N    N     E MONTANA   A    N     WYOMING     A    N      
UTAH        A    N     ARIZONA     A    N     COLORADO    A    A      
NEW MEXICO  A    A     N DAKOTA    A    A     S DAKOTA    A    A      
NEBRASKA    A    A     KANSAS      A    A     OKLAHOMA    A    A      
N TEXAS     N    A     S TEXAS     N    A     W TEXAS     N    A      
MINNESOTA   A    N     IOWA        A    A     MISSOURI    A    A      
ARKANSAS    A    A     LOUISIANA   N    A     WISCONSIN   A    B      
ILLINOIS    A    N     MISSISSIPPI N    A     MICHIGAN    A    B      
INDIANA     A    B     OHIO        A    B     KENTUCKY    A    B      
TENNESSEE   A    N     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    B     NEW JERSEY  A    B     W VIRGINIA  A    B      
MARYLAND    A    B     DELAWARE    N    B     VIRGINIA    A    B      
N CAROLINA  N    B     S CAROLINA  N    B     GEORGIA     N    N      
FL PNHDL    N    N     FL PENIN    A    A     AK N SLOPE  A    N      
AK ALEUTIAN A    N     AK WESTERN  A    A     AK INT BSN  A    A      
AK S INT    N    A     AK SO COAST N    A     AK PNHDL    B    A      
  
                            
 
8-14 DAY OUTLOOK TABLE 
Outlook for May 20 - 26 2021 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  B    B     OREGON      N    B     NRN CALIF   A    B      
SRN CALIF   A    N     IDAHO       A    B     NEVADA      A    B      
W MONTANA   A    B     E MONTANA   A    N     WYOMING     A    N      
UTAH        A    N     ARIZONA     A    N     COLORADO    A    A      
NEW MEXICO  A    N     N DAKOTA    A    N     S DAKOTA    A    N      
NEBRASKA    A    A     KANSAS      A    A     OKLAHOMA    A    A      
N TEXAS     A    A     S TEXAS     N    A     W TEXAS     N    A      
MINNESOTA   A    N     IOWA        A    A     MISSOURI    A    A      
ARKANSAS    A    A     LOUISIANA   A    A     WISCONSIN   A    N      
ILLINOIS    A    N     MISSISSIPPI A    A     MICHIGAN    A    B      
INDIANA     A    N     OHIO        A    B     KENTUCKY    A    N      
TENNESSEE   A    N     ALABAMA     A    N     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    B     NEW JERSEY  A    B     W VIRGINIA  A    B      
MARYLAND    A    B     DELAWARE    A    B     VIRGINIA    A    B      
N CAROLINA  A    B     S CAROLINA  A    N     GEORGIA     A    N      
FL PNHDL    A    A     FL PENIN    A    N     AK N SLOPE  A    N      
AK ALEUTIAN A    A     AK WESTERN  A    A     AK INT BSN  A    A      
AK S INT    A    A     AK SO COAST N    A     AK PNHDL    B    N      
  
                           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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