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Prognostic Meteorological Discussion (PMD)

Issued by National Weather Service (NWS)

                            
000
FXUS06 KWBC 181902
PMDMRD
Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks
NWS Climate Prediction Center College Park, MD
300 PM EDT Wed September 18 2019

6-10 DAY OUTLOOK FOR SEP 24 - 28 2019

Today's model solutions depict a mainly transient 500-hPa geopotential height 
pattern across the U.S. for the 6-10 day period. However, the projected 
downward trend in the Pacific-North American pattern to a negative phase toward 
the end of September favors an amplified pattern developing over the CONUS by 
the end of the period. There are some timing differences between the 00z ECMWF 
ensembles and the 06z GEFS. The ECMWF ensembles build the ridge in the East 
faster, while the GEFS delays this development until further into week-2, and 
depicts more troughing in the East for the 6-10 day period. This forecast 
favors the ECMWF due to its consistency. For the 6-10 day period overall, 
positive 500-hPa height anomalies are favored for parts of the Eastern Plains, 
Mississippi Valley, Tennessee Valley, and the Ohio Valley. Negative 500-hPa 
height anomalies are favored over northern New England and parts of the Pacific 
Northwest and Inter-mountain region.

Near to above normal temperatures are favored across most of the CONUS. Very 
warm temperatures are anticipated over the East, especially early in the 
period. Some cooler temperatures are possible depending on how troughing 
evolves over the East. The 00z deterministic ECMWF shows a period of troughing 
as well, but not as robust as in the GEFS. However, any cooling does not appear 
to last with temperatures increasing once again toward day 10 as the pattern 
begins to amplify. Despite the negative 500-hPa height anomalies over New 
England, both the GEFS and ECMWF reforecast tools show increased above normal 
temperature probabilities over the region. Over parts of the Pacific Northwest, 
the Inter-mountain region, and the Desert Southwest, below normal temperatures 
are forecast. The ECMWF reforecast tool continues to show higher probabilities 
of below normal temperatures over these areas than the GEFS tool. Given the 
forecast for increased cloudiness and rainfall, the cooler solution of the 
ECMWF is favored. Above normal temperatures are forecast for parts of 
California where higher 500-hPa heights are anticipated. Above normal 
temperatures are favored for western and southern mainland Alaska, the 
Aleutians, and the Panhandle as a result of increased Pacific flow and 
anomalously warm sea surface temperatures.

There remains increased probabilities for above normal precipitation over the 
much of the West due to the increase in Pacific flow and troughing forecast 
over the region. Forecast precipitation over climatologically dry areas also 
favors elevated probabilities for above normal precipitation. Tropical Storms 
Lorena and Mario, both off the coast of Mexico, are forecast to track 
northwestward, and may bring increased moisture into parts of the Southwest 
early in the period. To the east, frontal activity over parts of the Plains and 
Mississippi Valley favors increased precipitation chances. Therefore, 
probabilities for above normal precipitation are increased over these areas. 
Below normal precipitation is forecast along the East Coast from Southern New 
England through Florida, and also for southern Texas, as these areas are 
anticipated to be far enough displaced from significant upper level dynamics. 
Above normal precipitation is favored for Alaska due to troughing to the west 
over the Bering Sea and an active storm track forecast for the state.

The official 6-10 day 500-hPa height blend consists of 20% of Today's 6z GFS 
Ensemble Mean centered on Day 8, 10% of Today's operational 6z GFS centered on 
Day 8, 60% of Today's 0z European Ensemble Mean centered on Day 8, and 10% of 
Today's operational 0z ECMWF centered on Day 8 
 

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Average, 3 out of 5, due to a 
forecast transitional pattern, but increasing confidence of greater 
amplification toward the end of the period.

8-14 DAY OUTLOOK FOR SEP 26 - OCT 02, 2019 

For week-2, an amplified pattern is forecast to develop over the CONUS with 
ridging in the East and troughing in the West. The ECMWF ensembles have 
consistently shown this scenario, and the GEFS has been trending toward this 
pattern as well. Above normal 500-hPa heights remain favored for the eastern 
half of the CONUS. Near to below normal 500-hPa heights are forecast for the 
West. The northward expansion of the East Pacific ridge favors positive 500-hPa 
height anomalies over Alaska.

Above normal temperatures are forecast across much of the CONUS east of the 
Rockies, with seasonably warm weather anticipated to end September. Conversely, 
increased probabilities of below normal temperatures are shown over the West 
underneath negative 500-hPa height anomalies and forecast troughing. Increased 
above normal temperature probabilities are favored over Alaska due to forecast 
higher 500-hPa heights and weaker troughing relative to the 6-10 day period.

Above normal precipitation is favored for much of the western two-thirds of the 
CONUS. Troughing over the West favors increased chances of precipitation over 
climatologically dry areas. Further east across the Plains and Mississippi 
Valley, frontal activity downstream of the trough favors increased 
precipitation chances. The highest chances of precipitation are across the 
northern half of these regions, where a stronger temperature gradient is 
anticipated. Below normal precipitation is forecast over the East Coast 
underneath forecast ridging and surface high pressure. Although a trend toward 
higher 500-hPa heights is forecast over Alaska, weak troughing is projected to 
remain in place over the Bering Sea, favoring a continuation of an active 
weather pattern across the state. Therefore, probabilities of above normal 
precipitation are forecast for most of Alaska excluding the Panhandle. Below 
normal precipitation probabilities are favored for the Panhandle due to a 
projected northward shift in the mean storm track.

Of note is that tropical activity is increasing in the Atlantic Basin. Tropical 
Storm Jerry is located in the Central Atlantic and forecast to strengthen into 
a hurricane in the coming days. Most dynamical models currently favor an 
out-to-sea track, but there is a great deal of uncertainty in forecasting 
tropical cyclone tracks beyond a week. Two other disturbances in the Atlantic 
are also being monitored by the National Hurricane Center for possible 
development. Interests along the East and Gulf Coasts should pay close 
attention to forecasts from the National Hurricane Center related to Jerry and 
any other disturbances that may develop in the next couple of weeks. 

The official 8-14 day 500-hPa height blend consists of: 20% of Today's 6z GFS 
Ensemble Mean centered on Day 11, 5% of Today's operational 6z GFS centered on 
Day 11, and 75% of Today's 0z European Ensemble Mean centered on Day 11 


FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Average, 3 out of 5, due to model 
agreement on the pattern becoming more amplified, offset by uncertainty in 
timing.

FORECASTER: Thomas Collow

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 
September 19.


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: 
20040918 - 19770921 - 19970914 - 19600901 - 19850914


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: 
20040919 - 19600902 - 19770920 - 19850914 - 19940911


6-10 DAY OUTLOOK TABLE
Outlook for Sep 24 - 28 2019

STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN   
WASHINGTON  B    A     OREGON      N    A     NRN CALIF   A    A     
SRN CALIF   N    A     IDAHO       B    A     NEVADA      N    A     
W MONTANA   N    A     E MONTANA   A    A     WYOMING     A    A     
UTAH        N    A     ARIZONA     B    A     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     A    A     S TEXAS     A    N     W TEXAS     A    A     
MINNESOTA   A    A     IOWA        A    A     MISSOURI    A    A     
ARKANSAS    A    A     LOUISIANA   A    N     WISCONSIN   A    A     
ILLINOIS    A    A     MISSISSIPPI A    B     MICHIGAN    A    A     
INDIANA     A    A     OHIO        A    N     KENTUCKY    A    N     
TENNESSEE   A    B     ALABAMA     A    B     NEW YORK    A    N     
VERMONT     A    N     NEW HAMP    A    N     MAINE       A    A     
MASS        A    N     CONN        A    B     RHODE IS    A    N     
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  A    A     
AK ALEUTIAN A    A     AK WESTERN  A    A     AK INT BSN  N    A     
AK S INT    A    A     AK SO COAST A    A     AK PNHDL    N    N     
 
                           

8-14 DAY OUTLOOK TABLE
Outlook for Sep 26 - Oct 02, 2019

STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN   
WASHINGTON  B    A     OREGON      B    A     NRN CALIF   N    A     
SRN CALIF   B    A     IDAHO       B    A     NEVADA      B    A     
W MONTANA   B    A     E MONTANA   B    A     WYOMING     B    A     
UTAH        B    A     ARIZONA     B    A     COLORADO    A    A     
NEW MEXICO  A    A     N DAKOTA    N    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    N     LOUISIANA   A    N     WISCONSIN   A    A     
ILLINOIS    A    A     MISSISSIPPI A    N     MICHIGAN    A    A     
INDIANA     A    A     OHIO        A    N     KENTUCKY    A    B     
TENNESSEE   A    B     ALABAMA     A    B     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    B     GEORGIA     A    B     
FL PNHDL    A    N     FL PENIN    A    N     AK N SLOPE  A    A     
AK ALEUTIAN A    A     AK WESTERN  A    A     AK INT BSN  A    A     
AK S INT    A    A     AK SO COAST A    A     AK PNHDL    A    B     
 
                           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.

$$