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 September 20 2024 
 
6-10 DAY OUTLOOK FOR SEP 26 - 30 2024 
 
The ensemble mean models are in fair agreement today on the predicted mid-level  
circulation pattern over the forecast domain. The manual height blend captures  
the larger-scale features predicted by the ensemble mean models, though  
significant uncertainty remains in forecasted day-to-day timing, location, and  
amplitude of individual weather disturbances during the outlook period. The  
manual height blend depicts mid-level troughing and negative 500-hPa height  
anomalies over western and southern Alaska, and a very weak mid-level trough  
over the southeastern contiguous U.S. (CONUS). A strong mid-level anomalous  
ridge is forecasted to extend from eastern Canada southwestward across the  
Great Lakes and north-central CONUS, with a weak extension of this anomalous  
ridge continuing into the Southwest. Weak positive height anomalies are  
indicated over Hawaii. 
 
For the 6-10 day temperature outlook, above normal temperature chances are  
increased across most of the Lower 48 states, peaking over 80% across parts of  
North Dakota and Minnesota. A relatively small area of favored near normal  
temperatures is depicted from the south-central Mississippi Valley into central  
Tennessee. This area of favored near normal temperatures is embedded within a  
larger region of slightly enhanced chances of above normal temperatures that  
extend from the southern Plains eastward to the Middle Atlantic coast. Raw and  
bias-corrected temperature output from the ensemble mean solutions tend to be  
colder overall than corresponding reforecast-calibrated temperature guidance.  
Below normal temperature chances are elevated over western, central, and  
southern portions of Alaska, associated with a predicted mid-level trough. This  
is consistent with most reforecast-calibrated and bias-corrected temperature  
tools. For Hawaii, a slight tilt towards above normal temperatures is indicated  
for Kauai and part of Oahu, with near normal temperatures favored elsewhere.  
This is generally supported by the auto-temperature and ERF-CON temperature  
tools. 
 
For the 6-10 day precipitation outlook, above normal precipitation chances are  
increased over the Gulf and Atlantic coast states, the Appalachians, the Ohio  
and Tennessee Valleys, the southern half of the Mississippi Valley, and the  
south-central Plains. This is supported by most tools. Odds favoring above  
normal precipitation chances exceed 50% over much of the Southeast. For at  
least the past few days, there has been very large model uncertainty regarding  
future tracks and intensities of potential tropical cyclones in the Gulf of  
Mexico. Residents and mariners within this broad region are advised to keep  
updated with the latest tropical weather information from the National  
Hurricane Center and local news media outlets. For nearly all of the remainder  
of the CONUS, near to below normal precipitation chances are elevated. This is  
consistent with many of the tools, but not all of them. This broad region of  
favored near to below normal precipitation chances is also supported by the  
forecasted proximity of a weakening mid-level ridge and relatively weak  
positive height anomalies. The 500-hPa trough predicted over western Alaska,  
and increased onshore flow, favors increased chances of above normal  
precipitation for eastern and southeastern Alaska during the 6-10 day period. A  
slight tilt in the odds favoring above normal precipitation is also depicted  
for Hawaii, with generally good agreement between the ERF-CON and automated  
temperature tools. 
 
The official 6-10 day 500-hPa height blend consists of 35% of Today's 0z GFS  
Ensemble Mean centered on Day 8, 40% of Today's 0z European Ensemble Mean  
centered on Day 8, and 25% of Today's 0z Canadian Ensemble Mean centered on Day  
8  
  
 
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Below normal, 2 out of 5, based on  
significant variations in the day-to-day model details regarding timing,  
strength, and location of weather features. 
 
8-14 DAY OUTLOOK FOR SEP 28 - OCT 04, 2024  
 
The ensemble mean models are in fair agreement today on the predicted mid-level  
circulation pattern over the forecast domain. Though the anomalous large-scale  
features described in the earlier 6-10 day section are predicted to persist,  
they are expected to be substantially weaker within the framework of a more  
zonal flow pattern. Weak positive height anomalies are indicated over Hawaii. 
 
The 8-14 day temperature outlook favors above normal temperature chances over  
practically all of the CONUS, though with decreased probabilities relative to  
the earlier 6-10 day period. This is consistent with an expected flattening of  
the flow pattern, and the consolidated and automated temperature tools. A  
predicted weakening of the mid-level trough over Alaska favors increased  
variability and a mix of below to near normal temperatures. A consensus of  
Hawaiian temperature guidance favors above normal temperatures for the  
northwestern islands, and near normal temperatures for the southeastern islands. 
  
The 8-14 day precipitation outlook is similar to the earlier 6-10 day  
precipitation outlook, which favors above normal precipitation over much of the  
southeastern quadrant of the CONUS and the Northeast. Large uncertainty  
persists across the Southeast and Gulf of Mexico associated with the potential  
for tropical cyclone development within the period. For most of the remainder  
of the CONUS, odds favor below normal precipitation with weak mid-level  
ridging. Most of Alaska and Hawaii are favored to have above normal  
precipitation during week-2, with the support of most of the objective tools. 
 
The official 8-14 day 500-hPa height blend consists of: 33% of Today's 0z GFS  
Ensemble Mean centered on Day 11, 34% of Today's 0z European Ensemble Mean  
centered on Day 11, and 33% of Today's 0z Canadian Ensemble Mean centered on  
Day 11  
 
 
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Below normal, 2 out of 5, due to  
the same considerations noted in the earlier 6-10 day period, with added  
uncertainty inherent with zonal flow. 
 
FORECASTER: Anthony A 
 
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  
October 17. 
 
 
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:  
20050906 - 20040919 - 20070923 - 19880919 - 19850917 
 
 
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:  
20040918 - 19850916 - 20050904 - 20070922 - 19880918 
 
 
6-10 DAY OUTLOOK TABLE 
Outlook for Sep 26 - 30 2024 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  A    N     OREGON      A    B     NRN CALIF   A    B      
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    N      
NEW MEXICO  A    B     N DAKOTA    A    B     S DAKOTA    A    B      
NEBRASKA    A    N     KANSAS      A    A     OKLAHOMA    A    A      
N TEXAS     A    N     S TEXAS     A    N     W TEXAS     A    N      
MINNESOTA   A    B     IOWA        A    B     MISSOURI    A    A      
ARKANSAS    N    A     LOUISIANA   A    A     WISCONSIN   A    B      
ILLINOIS    A    N     MISSISSIPPI A    A     MICHIGAN    A    B      
INDIANA     A    N     OHIO        A    A     KENTUCKY    A    A      
TENNESSEE   A    A     ALABAMA     A    A     NEW YORK    A    A      
VERMONT     A    A     NEW HAMP    A    A     MAINE       A    A      
MASS        A    A     CONN        A    A     RHODE IS    A    A      
PENN        A    A     NEW JERSEY  A    A     W VIRGINIA  A    A      
MARYLAND    A    A     DELAWARE    A    A     VIRGINIA    A    A      
N CAROLINA  A    A     S CAROLINA  A    A     GEORGIA     A    A      
FL PNHDL    A    A     FL PENIN    A    A     AK N SLOPE  B    N      
AK ALEUTIAN B    N     AK WESTERN  B    N     AK INT BSN  B    N      
AK S INT    B    A     AK SO COAST B    A     AK PNHDL    B    A      
  
                            
 
8-14 DAY OUTLOOK TABLE 
Outlook for Sep 28 - Oct 04, 2024 
 
STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN    
WASHINGTON  A    N     OREGON      A    B     NRN CALIF   A    B      
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    A    B     S DAKOTA    A    B      
NEBRASKA    A    B     KANSAS      A    B     OKLAHOMA    A    B      
N TEXAS     A    B     S TEXAS     A    N     W TEXAS     A    B      
MINNESOTA   A    B     IOWA        A    B     MISSOURI    A    B      
ARKANSAS    A    N     LOUISIANA   A    A     WISCONSIN   A    B      
ILLINOIS    A    B     MISSISSIPPI A    A     MICHIGAN    A    N      
INDIANA     A    N     OHIO        A    N     KENTUCKY    A    A      
TENNESSEE   A    A     ALABAMA     A    A     NEW YORK    A    N      
VERMONT     A    N     NEW HAMP    A    N     MAINE       A    N      
MASS        A    N     CONN        A    N     RHODE IS    A    A      
PENN        A    N     NEW JERSEY  A    N     W VIRGINIA  A    N      
MARYLAND    A    N     DELAWARE    A    N     VIRGINIA    A    N      
N CAROLINA  A    A     S CAROLINA  A    A     GEORGIA     A    A      
FL PNHDL    A    A     FL PENIN    A    A     AK N SLOPE  N    N      
AK ALEUTIAN B    N     AK WESTERN  B    A     AK INT BSN  N    A      
AK S INT    B    A     AK SO COAST B    A     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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