8-TO-14-DAY OUTLOOKS FOR OCT 6 - OCT 12 2000
CLIMATE PREDICTION CENTER NCEP
NATIONAL WEATHER SERVICE WASHINGTON DC
3 PM EDT THURSDAY SEP 28 2000
TODAYS 6 TO 10 DAY MEAN 500 MB FORECASTS FROM THE MRF...
ECMWF...MRF ENSEMBLE MEAN...AND PRC ARE IN GOOD AGREEMENT OVER
MOST OF THE NORTHERN HEMISPHERE...BUT DISAGREE SOMEWHAT OVER THE
EASTERN PACIFIC AND NORTH AMERICA. ALL THE MODELS AGREE ON
FORECASTING A VERY STRONG BLOCKING RIDGE OVER NORTHERN EUROPE.
THIS FEATURE TELECONNECTS WITH POSITIVE HEIGHT ANOMALIES OVER THE
SOUTHEASTERN HALF OF THE U.S. AND NEGATIVE ANOMALIES OVER THE
NORTHWESTERN HALF. THIS AGREES BETTER WITH THE SOLUTIONS OF THE
PRC AND ENSEMBLE MEAN THAN THOSE OF THE MRF AND ECMWF.
MODEL SOLUTIONS FROM THE MRF...MRF ENSEMBLE MEAN...AND PRC
FOR THE D+11 MEAN PERIOD SHOW EVEN MORE DIFFERENCES THAN FOR THE
6 TO 10 DAY PERIOD WITH THE PRC HOLDING ONTO ITS WELL TELECONNECTED
PATTERN OF BELOW NORMAL HEIGHTS OVER THE NORTHWESTERN HALF OF THE
LOWER 48 STATES AND WEAKLY ABOVE NORMAL HEIGHTS OVER THE SOUTH-
EASTERN HALF WHILE THE MRF AND THE ENSEMBLE MEAN COVER ALL BUT THE
EAST COAST WITH ABOVE NORMAL HEIGHTS...ALTHOUGH THE ENSEMBLE MEAN
HAS SMALLER ANOMALIES THAN THE MRF INDICATING DISAGREEMENT AMONG
THE ENSEMBLE MEMBERS WITH THE HIGH RESOLUTION MRF RUN. OVER ALASKA
THERE ARE ALSO BIG DIFFERENCES WITH THE MRF AND ENSEMBLE MEAN
CALLING FOR A MEAN TROUGH WHILE THE PRC FORECASTS A RIDGE.
THE TEMPERATURE OUTLOOK FOR THE LOWER 48 STATES IS BASED ON
A MIX OF THE KLEIN AND NEURAL NETWORK SPECIFICATIONS FROM A BLENDED
HEIGHT PROG CONSISTING OF 30 PERCENT OF TODAYS ENSEMBLE MEAN D+11
PROG AND 70 PERCENT OF TODAYS PRC SOLUTION CENTERED ON DAY 11.
THE PRECIPITATION FORECAST IS BASED ON THE NEURAL NET PROBA-
BILITY DISTRIBUTION FROM THE INDIVIDUAL ENSEMBLE MEMBERS AND NEURAL
NETWORK SPECIFICATIONS FROM THE BLENDED WEEK 2 HEIGHT PROG.
THE ALASKAN SURFACE TEMPERATURE AND PRECIPITATION FORECASTS
ARE LARGELY BASED ON NEURAL NET SPECIFICATIONS FROM THE PRC.
SSTS SURROUNDING THE HAWAIIAN ISLANDS ARE SLIGHTLY BELOW NORMAL.
THE 500 MB HEIGHTS ARE FORECAST BY THE BLENDED HEIGHT PROG TO BE
BELOW NORMAL IN ASSOCIATION WITH A MEAN TROUGH NORTH OF THE ISLANDS.
HILO 5 BELOW CLIMATOLOGY
KAHULUI 5 BELOW 5 ABOVE
HONOLULU 5 BELOW CLIMATOLOGY
LIHUE 5 BELOW 5 ABOVE
FORECASTER - R. MARTIN
notice notice notice notice notice notice notice notice notice
On October 2- 2000- CPC will begin issuing operational 6-10 day and 8-14 day
temperature and precipitation outlooks- daily- in a probabilistic format.
Operational ensembles of forecasts from the MRF model make this change
possible. Computing technology that allows automated production and
dissemination - on the one hand - but permits intervention by the forecaster
- on the other hand - has made this feasible. With this change we are
greatly increasing our service to users of our outlooks by:
- Increasing the information content of the 6-10 day outlook through the use
of a probabilistic format
- Adding a new operational outlook for 8-14 days
- Increasing the frequency of the 6-10 day outlook to daily
while maintaining accuracy of the forecasts.
The forecasts will be expressed in 3 categories Above normal- Near normal and
Below normal- which are equally likely at any given location over thirty years-
for a given calendar forecast period. The total probability will be shown.
This means the 33.33% contour forms a boundary separating Near normal - on one
side - from either Above normal or Below normal- on the other side. The 33.33%
contour will be drawn thicker than the others.
When the 33.33% contour lies between Near normal and Below - it - and all the
contours on the Below side of the line - will be colored blue.
When the 33.33% contour separates Near normal and Above - it - and all the
contours on the Above side of the line - will be colored red.
Near normal contours will be colored green. To further clarify the map - the
letters B - N and A will mark the highest values of the favored category on the
Because the climatological likelihood of each category is 33.33%- when the total
probability of the A or B category exceeds 66.67% - the likelihood of the
opposite category approaches zero - while the likelihood of extreme values
increases. Regions where probabilities exceed 66.67% on the new outlook maps
will often correspond closely to the much above or much below normal categories
on the old outlook maps.
In the Southwest and other climatologically dry regions- there will be a greater
than 33.33% 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 light blue dashed contours on the map are the climatological normal (30 year
average) temperature and precipitation totals for the forecast period- expressed
in degrees Fahrenheit and tenths of inches - respectively.
A single text bulletin (NMCPMDMRD FXUS06 KWBC) will accompany both the 6-10 day
and 8-14 day outlooks. Two tables of U.S. State forecasts - one for the 6-10 day
one for the 8-14 day outlook - will appear in the body of the bulletin. On
Saturday and Sunday - the tables only will appear in the bulletin. Likewise - on
weekend days the forecasts will be fully automated and objective - while on
weekdays forecasters may intervene in the content of the forecast maps. Also on
weekdays - the bulletin will contain a prognostic discussion of the 6-10 and 8-14
day outlooks written by the forecaster.
A sample of a set of 6-10 day maps in the new format may be viewed at: