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 April 26 2024 
 
6-10 DAY OUTLOOK FOR MAY 02 - 06 2024 
 
Model solutions depict a persistent longwave pattern into the beginning of May.  
The GEFS along with the ECMWF and Canadian ensemble means feature a 500-hPa  
trough of varying amplitude near the West Coast, a broad ridge over the central  
contiguous U.S. (CONUS), and a trough across the western Atlantic. Positive  
500-hPa height anomalies support increased above-normal temperature  
probabilities from the Rockies to the East Coast. However, recent model  
guidance shows at least a brief period of cooler-than-normal temperatures  
affecting the Great Plains and Upper Mississippi Valley and this is reflected  
in the ECMWF reforecast tool. Also, a cooling trend is forecast for the  
Northeast and Northern Mid-Atlantic from day 6 to 10. Therefore, above-normal  
temperature probabilities are lower today in portions of the central and  
eastern CONUS. Anomalous mid-level troughing and enhanced onshore flow favor a  
slight tilt towards below-normal temperatures across parts of the Pacific  
Northwest and California.  
 
An upstream trough along the West Coast generally favors a wetter-than-normal  
outcome for much of the western and central CONUS. This is supported by the  
GEFS and ECMWF reforecast tools. Enhanced onshore flow leads to increased  
above-normal precipitation probabilities from the Pacific Northwest and  
northern California eastward to the northern Rockies. Near normal precipitation  
is forecast for the Great Basin and climatological dry areas of the Southwest.  
Downstream of a mid-level ridge axis, near to below-normal precipitation is  
favored across the eastern CONUS.  
 
A 500-hPa trough over the Bering Sea favors above-normal precipitation for much  
of Alaska. The uncalibrated model output is colder than the GEFS and ECMWF  
reforecast tools. Given the lower 500-hPa heights in today’s manual blend and  
expectation for more widespread cloudiness and increased chances of  
precipitation, near normal temperatures are forecast for the southern  
two-thirds of Alaska. Good model agreement continues on the favored  
below-normal temperatures across the North Slope.  
  
Based on the GEFS and ECMWF ensemble means, near normal temperatures and  
precipitation are favored across much of Hawaii.  
 
The official 6-10 day 500-hPa height blend consists of 35% of Today's 6z GFS  
Ensemble Mean centered on Day 8, 35% of Today's 0z European Ensemble Mean  
centered on Day 8, and 30% of Today's 0z Canadian Ensemble Mean centered on Day  
8  
  
 
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Average, 3 out of 5, due to good  
model agreement on the longwave pattern offset by increasing forecast  
uncertainty across the eastern CONUS.  
 
8-14 DAY OUTLOOK FOR MAY 04 - 10 2024  
 
The GEFS, ECMWF, and Canadian ensemble means maintain the persistent longwave  
pattern with 500-hPa troughs near both coasts of North America and a broad  
ridge centered over the central CONUS. By the second week of May, the ensemble  
means indicate a retrogression of the longwave pattern over North America with  
a 500-hPa ridge axis shifting from the Mississippi Valley to the Rockies and an  
amplifying trough closer to the East Coast. The Northeast and Mid-Atlantic is  
vulnerable to backdoor cold fronts and cold air damming during the spring and  
model guidance continues to show an increased chance for this to occur. A  
slight lean towards below-normal temperatures is forecast for southern New  
England and the coastal Northeast. Compared to yesterday,  
coverage/probabilities for above-normal temperatures are reduced across the  
eastern CONUS. The ridging aloft and associated positive 500-hPa height  
anomalies favor above-normal temperatures from the Rockies to the Appalachians.  
Conversely, a mid-level trough and negative 500-hPa height anomalies supports  
slightly elevated below-normal temperature probabilities for southwest Oregon  
and California. 
 
The mid-level longwave trough upstream yields a relatively wet outlook across  
much of the western and central CONUS. Forecast confidence is not high though  
since the GEFS reforecast tool indicates weak probabilities. In addition, as  
the ridge axis shifts westward to the High Plains, that would lead to a drier  
pattern across the Great Plains later in week-2. Due to the amplifying trough  
near the East Coast, a cold front may shift south and become stationary across  
the southeastern CONUS. This could provide a focus for precipitation which  
tilts the outlook towards the wet side for parts of this region. Farther to the  
north across the eastern Great Lakes, Mid-Atlantic, and much of the Northeast,  
below-normal precipitation is slightly favored and supported by the GEFS and  
ECMWF reforecast tools.  
 
A broad 500-hPa trough over the Bering Sea and western Mainland Alaska supports  
increased above-normal precipitation probabilities nearly statewide for Alaska.  
Similar to the 6-10 day period, the likelihood for enhanced precipitation and  
cloudiness supports near normal temperatures for a majority of Alaska.  
 
The GEFS ensemble mean features a mid-level trough lingering over the Central  
Pacific. This is expected to promote cooler-than-normal temperatures for Hawaii  
and increased chances of above-normal precipitation except for the Big Island.  
 
The official 8-14 day 500-hPa height blend consists of: 35% of Today's 6z GFS  
Ensemble Mean centered on Day 11, 35% 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: Below average, 2 out of 5, due to  
a predicted retrogression of the longwave pattern and weak signals among the  
precipitation tools.  
 
FORECASTER: Brad Pugh 
 
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 1991-2020 base period means as reference in  
the climate outlooks. 
 
The next set of long-lead monthly and seasonal outlooks will be released on May  
16. 
 
 
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:  
19660425 - 19900507 - 20040416 - 19900418 - 19740429 
 
 
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:  
20040415 - 19640407 - 19740428 - 19900418 - 19900508 
 
 
6-10 DAY OUTLOOK TABLE 
Outlook for May 02 - 06 2024 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  N    A     OREGON      B    A     NRN CALIF   B    A      
SRN CALIF   N    N     IDAHO       A    A     NEVADA      A    A      
W MONTANA   N    A     E MONTANA   A    A     WYOMING     A    N      
UTAH        A    N     ARIZONA     A    N     COLORADO    A    N      
NEW MEXICO  A    A     N DAKOTA    A    A     S DAKOTA    A    A      
NEBRASKA    A    A     KANSAS      A    A     OKLAHOMA    A    A      
N TEXAS     A    A     S TEXAS     A    A     W TEXAS     A    A      
MINNESOTA   A    A     IOWA        A    A     MISSOURI    A    A      
ARKANSAS    A    A     LOUISIANA   A    N     WISCONSIN   A    N      
ILLINOIS    A    A     MISSISSIPPI A    A     MICHIGAN    A    N      
INDIANA     A    N     OHIO        A    N     KENTUCKY    A    N      
TENNESSEE   A    A     ALABAMA     A    A     NEW YORK    A    B      
VERMONT     A    B     NEW HAMP    A    B     MAINE       A    N      
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    N     FL PENIN    A    B     AK N SLOPE  B    A      
AK ALEUTIAN N    A     AK WESTERN  N    A     AK INT BSN  N    A      
AK S INT    N    A     AK SO COAST N    A     AK PNHDL    N    A      
  
                            
 
8-14 DAY OUTLOOK TABLE 
Outlook for May 04 - 10 2024 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  N    A     OREGON      N    A     NRN CALIF   B    A      
SRN CALIF   B    N     IDAHO       A    A     NEVADA      N    A      
W MONTANA   A    A     E MONTANA   A    N     WYOMING     A    N      
UTAH        A    N     ARIZONA     A    N     COLORADO    A    N      
NEW MEXICO  A    A     N DAKOTA    A    A     S DAKOTA    A    A      
NEBRASKA    A    A     KANSAS      A    A     OKLAHOMA    A    A      
N TEXAS     A    A     S TEXAS     A    A     W TEXAS     A    A      
MINNESOTA   A    A     IOWA        A    A     MISSOURI    A    A      
ARKANSAS    A    A     LOUISIANA   A    N     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    A     NEW YORK    N    B      
VERMONT     N    B     NEW HAMP    N    N     MAINE       N    N      
MASS        B    N     CONN        B    B     RHODE IS    B    N      
PENN        A    B     NEW JERSEY  B    B     W VIRGINIA  A    B      
MARYLAND    N    B     DELAWARE    N    B     VIRGINIA    A    B      
N CAROLINA  A    N     S CAROLINA  A    N     GEORGIA     A    A      
FL PNHDL    A    N     FL PENIN    A    N     AK N SLOPE  B    A      
AK ALEUTIAN N    A     AK WESTERN  N    A     AK INT BSN  N    A      
AK S INT    N    A     AK SO COAST N    A     AK PNHDL    N    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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