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 Thu April 25 2024 
 
6-10 DAY OUTLOOK FOR MAY 01 - 05 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 and southerly surface flow support increased  
above-normal temperature probabilities from the Rockies to the East Coast.  
5-day temperatures are expected to be more variable across the Northeast with  
above-normal temperature probabilities lower in this region. Anomalous  
mid-level troughing and enhanced onshore flow favor below-normal temperatures  
across the Pacific Northwest and much of California.  
 
The highest forecast confidence in the 6-10 day precipitation outlook exists  
for the Great Plains and Upper Midwest where above-normal precipitation is  
favored. This wet start to May is due to the upstream mid-level trough and  
enhanced low-level moisture from the Gulf of Mexico. Above-normal precipitation  
probabilities are tempered though due to uncertainty on where the heaviest  
convective rainfall occurs. 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.  
 
A 500-hPa trough over the Bering Sea favors above-normal precipitation for much  
of Alaska. The uncalibrated model temperature output is colder than the  
reforecast GEFS and ECMWF tools. The 6-10 day temperature outlook hedged  
towards the reforecasts, but there is a notable trend the past few days for  
less coverage of increased above-normal temperature probabilities.  
  
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: Above average, 4 out of 5, due to  
a persistent longwave pattern and good agreement among the temperature tools  
throughout the CONUS.  
 
8-14 DAY OUTLOOK FOR MAY 03 - 09 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. The 6-10 and 8-14 day temperature  
outlooks are quite similar with a majority of the CONUS favored to have  
above-normal temperatures due to the broad ridge centered over the Mississippi  
Valley. The Northeast is vulnerable to backdoor cold fronts and cold air  
damming during the spring and there seems to be an increasing chance for that  
to occur during early May with an amplified trough over the northwestern  
Atlantic. A comparison between the manual 500-hPa height blend from the past  
two days shows the trough over the western Atlantic closer to the East Coast  
which would increase the potential for a cooler outcome for the Northeast.  
Although the reforecast tools continue to favor above-normal temperatures  
across the Northeast, near normal temperatures are forecast for this region due  
to the colder uncalibrated model output and the analog tool. The 500-hPa trough  
with negative height anomalies along with enhanced onshore flow favor  
below-normal temperatures for California and parts of the Desert Southwest and  
Pacific Northwest.  
 
The mid-level longwave trough to ridge pattern from the West Coast to the  
Mississippi Valley yields a relatively wet (dry) outlook across the western and  
central (eastern) CONUS. Forecast confidence is not too high though since the  
reforecast tools indicate weak probabilities overall and the ECMWF ensemble  
mean predicts a retrogession of the longwave pattern late in week-2. One small  
change from yesterday’s outlook was a reduction in the coverage of increased  
below-normal precipitation probabilities across the eastern CONUS. This is  
based on the GEFS and ECMWF reforecasts  and the analog tool derived from the  
manual 500-hPa blend. These precipitation tools imply the potential for a  
stationary front to develop across the Southeast or southern Mid-Atlantic which  
could be a focus for precipitation.  
 
A broad 500-hPa trough over the Bering Sea and western Mainland Alaska supports  
increased above-normal precipitation probabilities nearly statewide for Alaska.  
Temperature tools continue to differ and a consensus between the GEFS and ECMWF  
reforecasts favor below (above)-normal temperatures for the North Slope  
(southeastern Alaska).  
 
The GEFS and ECMWF ensemble means feature a mid-level trough, near the West  
Coast, extending southward to 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: Average, 3 out of 5, with good  
model agreement on the 500-hPa height pattern offset by uncertainty in the  
temperature and precipitation outlooks for the eastern CONUS.  
 
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:  
19900507 - 19900417 - 19810417 - 19770406 - 20000410 
 
 
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:  
19510404 - 19520404 - 19530404 - 19540404 - 19550404 
 
 
6-10 DAY OUTLOOK TABLE 
Outlook for May 01 - 05 2024 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  B    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    A      
ILLINOIS    A    N     MISSISSIPPI A    N     MICHIGAN    A    N      
INDIANA     A    N     OHIO        A    B     KENTUCKY    A    N      
TENNESSEE   A    N     ALABAMA     A    N     NEW YORK    A    B      
VERMONT     A    N     NEW HAMP    A    N     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    B     GEORGIA     A    B      
FL PNHDL    A    B     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    A    A     AK SO COAST A    A     AK PNHDL    A    A      
  
                            
 
8-14 DAY OUTLOOK TABLE 
Outlook for May 03 - 09 2024 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  N    A     OREGON      B    A     NRN CALIF   B    A      
SRN CALIF   B    A     IDAHO       N    A     NEVADA      N    A      
W MONTANA   A    A     E MONTANA   A    A     WYOMING     A    N      
UTAH        A    A     ARIZONA     N    N     COLORADO    A    N      
NEW MEXICO  A    N     N DAKOTA    A    A     S DAKOTA    A    A      
NEBRASKA    A    A     KANSAS      A    A     OKLAHOMA    A    A      
N TEXAS     A    A     S TEXAS     A    N     W TEXAS     A    A      
MINNESOTA   A    A     IOWA        A    A     MISSOURI    A    A      
ARKANSAS    A    N     LOUISIANA   A    N     WISCONSIN   A    A      
ILLINOIS    A    N     MISSISSIPPI A    N     MICHIGAN    A    N      
INDIANA     A    N     OHIO        A    N     KENTUCKY    A    N      
TENNESSEE   A    N     ALABAMA     A    N     NEW YORK    N    B      
VERMONT     N    B     NEW HAMP    N    B     MAINE       N    B      
MASS        N    B     CONN        N    B     RHODE IS    N    B      
PENN        A    B     NEW JERSEY  N    B     W VIRGINIA  A    N      
MARYLAND    A    B     DELAWARE    N    B     VIRGINIA    A    N      
N CAROLINA  A    N     S CAROLINA  A    N     GEORGIA     A    N      
FL PNHDL    A    B     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 A    A     AK PNHDL    A    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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