30 Day Narrative

034 
FXUS07 KWBC 311900
PMD30D
Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT Sat Aug 31 2019
30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2019
The updated monthly temperature and precipitation outlooks for September 2019 
are based on the latest dynamical model guidance, WPC temperature and 
precipitation outlooks for the first week of September, CPC 6-10 day, week 2, 
and week 3-4 temperature and precipitation outlooks, and GEFS and CFS monthly 
temperature and precipitation forecasts. There is no Madden-Julian Oscillation 
(MJO) currently present, and no MJO is forecast to emerge during the next 
several weeks. Therefore, the MJO is unlikely to impact the mid-latitude 
circulation pattern during September.
Dynamical model forecasts for the month of September, including 700-hPa height 
anomalies from the CFS monthly forecasts, generally predict troughing over the 
Bering Sea, a ridge over western North America, and troughing over northeastern 
North America. Forecasts from the ECMWF and NCEP GEFS ensembles, as well as the 
multi-model consensus of the Subseasonal Experiment or SubX, indicate 
persistence of this circulation pattern overall into weeks 3 and 4, with the 
exception that a trough over the Northeast CONUS early in the month, as 
indicated by the CPC 6-10 day and week 2 outlooks, is predicted to lift 
northeastward, as in the CPC week 3-4 outlook.
The updated September temperature outlook continues to indicate high 
probabilities of above normal temperatures over Alaska and the western CONUS, 
with a persistent ridge and above-normal 500-hPa heights predicted throughout 
the month. Probabilities exceed 70 percent for coastal areas of northern and 
western Alaska, where sea surface temperatures remain anomalously much above 
average. Probabilities exceed 60 percent for areas of the Pacific Northwest and 
Central Rockies, under persistent above normal 500-hPa heights throughout the 
month of September in dynamical model forecasts. Above normal monthly average 
temperatures are likely for the month of September across much of Texas, 
excluding the Texas Panhandle, and the Southeast region, following the CPC 6-10 
day, week 2, and week 3-4 outlooks. Probabilities of above normal temperatures 
are lower over Texas and Louisiana, following guidance for the month of 
September from a tool that merges GEFS and CFS forecasts for weeks 1 and 2 with 
CFS forecasts for the week 3-4 period, and where the GEFS ensemble forecast 
indicates a greater probability of below normal temperatures in the week 2 and 
week 3-4 periods, as does the SubX MME consensus forecast for the week 3-4 
period. Below normal average September temperatures are predicted to be most 
likely for the northern central CONUS from the Northern and Central Plains into 
the Great Lakes region, with troughing and greater probabilities of below 
normal temperatures predicted during the first two weeks of the month, and weak 
probabilities for above normal temperatures indicated in the CPC week 3-4 
temperature outlook. Likely below normal temperatures over the Northeast in the 
WPC forecasts for the first week of September and in the CPC 6-10 day and week 
2 outlooks, with probabilities exceeding 50 percent, give way to likely above 
normal temperatures in the CPC week 3-4 outlook, with probabilities exceeding 
60 percent. Equal chances of above, near and below normal temperatures is 
indicated in the September temperature outlook for most of the Northeast 
region. 
Predicted troughing over the Bering Sea and Aleutian Islands in dynamical model 
forecasts for much of the month leads to continued enhanced probabilities of 
above normal precipitation for western and southern Alaska including the Alaska 
Panhandle. Above normal accumulated precipitation is likely for a large area of 
the western CONUS from the Southwest region into the Central and Northern 
Plains, as indicated by WPC precipitation forecasts for week 1 and the CPC 6-10 
day and week 2 precipitation outlooks, where moisture surges from the Eastern 
Pacific are expected to enhance precipitation over the Southwest. Hurricane 
Dorian is expected to impact Florida and parts of the Southeast Atlantic Coast 
during the first week of September bringing very large precipitation amounts to 
areas along the eventual storm track. Uncertainty in the exact storm track and 
uncertainty in precipitation amounts during the remainder of the month leads to 
moderate probabilities for above normal precipitation for the September monthly 
outlook. Probabilities of above normal precipitation in the September monthly 
outlook exceed 60 percent for the Atlantic Coasts of northern Florida, Georgia 
and the Carolinas. Likely above normal precipitation is indicated over the 
Northeast region in the September outlook, with precipitation predicted in the 
7-day WPC forecast for week 1 and likely above normal precipitation predicted 
in the CPC 6-10 day and week 2 outlooks, along with a potential for Hurricane 
Dorian to follow a northeastward track off of the Atlantic coast enhancing 
precipitation over the Northeast. Although the CPC week 3-4 outlook indicates 
likely below normal precipitation for the second half of the month for much of 
the Atlantic coast and Northeast, there is greater certainty in the 
precipitation outlook for the first two weeks of September. 
----------- Previous message (from August 15) is shown below ------------
The September 2019 temperature and precipitation outlooks are based on 
dynamical model guidance for the month including the North American Multi-Model 
Ensemble (NMME), as well as Week 4 CFS and ECMWF dynamical model forecasts, 
statistical tools based on large-scale sea surface temperature patterns and 
other climate forcings, as well as the influence of current soil moisture 
conditions and coastal sea surface temperatures on regional temperature and 
precipitation, and potential influences from modes of tropical climate 
variability. ENSO-neutral conditions are currently present over the Tropical 
Pacific Ocean. No discernible Madden-Julian Oscillation (MJO) signal is 
currently indicated by MJO indices, and the future emergence of an MJO signal 
is highly uncertain. ENSO and MJO are not likely to influence the longwave 
pattern across the mid-latitudes in the next several weeks. 
Dynamical model forecasts from the CFS and ECMWF indicate a slowly evolving 
longwave mid-level circulation pattern from the end of August into the first 
week of September, with positive 500-hPa height anomalies predicted over Alaska 
and the eastern North Pacific into the Western CONUS. This circulation pattern 
is predicted to persist and influence the September average temperature and 
accumulated precipitation. Negative 500-hPa height anomalies and troughing are 
predicted over the Northern Central CONUS during September, and dynamical model 
forecasts are consistent in predicting positive 500-hPa height anomalies across 
the Southern Plains, over the Southeast, and up the Eastern Seaboard into the 
Northeast region. 
The September 2019 temperature outlook indicates enhanced probabilities for 
above normal temperatures across Alaska and the Western CONUS from the Pacific 
Coast to the Rocky Mountains, under a predicted ridge and consistent with large 
positive decadal temperature trends for Alaska and the Southwest region. 
Probabilities for above normal temperatures exceed 70 percent for coastal 
regions of Alaska, influenced by significantly above normal sea surface 
temperatures around the region. Enhanced probabilities for above normal 
temperatures are predicted across the Southwest region into Texas, as well as 
for the Southeast, from the Appalachian Mountains eastward to the Atlantic 
Coast, and across the Northeast including the northern Great Lakes region. 
Probabilities for above normal temperatures exceed 60 percent for the southern 
Florida Peninsula, influenced by regional above average sea surface 
temperatures, and exceed 50 percent for parts of northern New England where 
decadal climate trends are a significant component of seasonal climate 
variability. Enhanced probabilities of below normal temperatures are indicated 
for parts of the Northern Plains, due to northerly flow under a predicted 
trough early in the month when the circulation is more predictable, and 
supported by the negative feedback between temperature and a forecast of likely 
above normal precipitation. Equal Chances of above and below normal 
temperatures or EC is indicated for a large area of the Northern Central CONUS, 
where cooler air flowing southward from Canada may moderate average September 
temperatures. 
The September 2019 precipitation outlook indicates above normal precipitation 
is likely for coastal regions of Alaska including the Alaska Panhandle, due to 
a predicted trough over the western Aleutian Islands and enhanced by increased 
atmospheric moisture related to above average coastal sea surface temperatures. 
Enhanced probabilities for above normal precipitation are indicated for a 
region of the Northern Central CONUS, as storm systems are likely to develop 
under a mid-level trough. There is a slight increase in the probabilities of 
above normal precipitation extending into parts of Colorado and the Central 
Plains, where the Southwest Monsoon circulation may draw moisture northward 
from the East Pacific. Elsewhere throughout the CONUS, Equal Chances of above 
and below normal precipitation or EC is indicated for the September outlook 
with limited skill in a half-month lead precipitation forecast during the 
summer. The September 2019 precipitation outlook will be reassessed at the end 
of August when uncertainty in the dominant climate signals is reduced at 
shorter lead times. 
FORECASTER: Dan Collins
The climatic normals are based on conditions between 1981 and 2010, following
the World Meteorological Organization convention of using the most recent 3 
complete decades as the climate reference period.  The probability anomalies
for temperature and precipitation based on these new normals better represent
shorter term climatic anomalies than the forecasts based on older normals.
The next monthly outlook...for Oct ... will be issued on Thu Sep 19 2019
These outlooks are based on departures from the 1981-2010 base period.
$$