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Prognostic Meteorological Discussion (PMD)

Issued by National Weather Service (NWS)

                            
000
FXUS06 KWBC 221918
PMDMRD
Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks
NWS Climate Prediction Center College Park, MD
300 PM EDT Thu August 22 2019

6-10 DAY OUTLOOK FOR AUG 28 - SEP 01, 2019

Today's GFS, ECMWF, and Canadian ensemble means are in good agreement with 
their predictions of the 500-hPa flow pattern throughout most of the forecast 
domain during the 6-10 day period. The manual 500-hPa height blend is based on 
the ensemble means of the three models noted earlier, and features a mid-level 
trough over the Bering Sea and Aleutians, a closed trough northeast of Alaska, 
and a trough centered over the Upper Mississippi Valley/Upper Great Lakes 
region. Mid-level ridges are predicted near the West Coast and the Canadian 
Maritimes. Maximum mid-tropospheric heights associated with both of these 
anomalous ridges are predicted to exceed 120 meters above normal, which is 
fairly strong for this time of year.

There are enhanced probabilities of above normal temperatures across most areas 
west of the Continental Divide, extending eastward across southern Texas. 
Upper-tercile temperatures are also favored over the East Coast states and 
southern and western portions of Alaska. Maximum probabilities for 
upper-tercile temperatures top 80% in and near the Willamette Valley in western 
Oregon. These favored areas of warmer-than-normal temperatures are due to 
mid-level ridging, near to above-normal 500-hPa heights, and (in the case of 
Alaska) coastal sea surface temperatures. In contrast, lower-tercile 
temperatures are favored across most areas of the contiguous U.S. between the 
Rockies and the Appalachians, and over northeastern Alaska. Maximum chances for 
colder-than-normal temperatures exceed 80% over the Northern Plains and 
adjacent parts of the Upper Mississippi Valley. These favored areas of 
anomalous cold are associated with mid-level troughs and near to below normal 
500-hPa heights. The official temperature outlook is also based on the 
automated temperature forecast, the consolidated temperature forecast, and GEFS 
and ECMWF calibrated Reforecast temperatures.

Predicted above normal heights and ridging leads to enhanced probabilities of 
near to below normal precipitation for much of the CONUS west of the Divide, 
which extend eastward over the Northern Plains and much of Minnesota. The 
exception is over southern California, and much of Nevada and Arizona, where 
odds slightly favor above normal precipitation due to the monsoon. The area of 
favored near to below normal precipitation also includes the southern Alaska 
coast from the Alaska Peninsula to the Panhandle, and most of the Mainland 
south of the Brooks Range. In contrast, there are elevated odds of above normal 
precipitation over the North Slope, the Aleutians, and nearly all remaining 
areas east of the Continental Divide. This is associated with frontal activity, 
cyclonic curvature, near to below normal heights, and 500-hPa troughs. The 
official precipitation outlook is also based on the automated precipitation 
forecast, the consolidated temperature forecast, and GEFS and ECMWF calibrated 
Reforecast precipitation.

The official 6-10 day 500-hPa height blend consists of 25% of Today's 0z GFS 
Ensemble Mean centered on Day 8, 25% of Today's 6z GFS Ensemble Mean centered 
on Day 8, 30% of Today's 0z European Ensemble Mean centered on Day 8, and 20% 
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 
good agreement between models on the predicted 500-hPa height pattern, and 
among the temperature and precipitation forecast tools.

8-14 DAY OUTLOOK FOR AUG 30 - SEP 05, 2019 

During Week-2, the predicted 500-hPa circulation pattern is fairly similar to 
the pattern predicted for the 6-10 day period. Most of the longwave features 
are forecast to weaken during Week-2, except for the large trough over the 
Bering Sea which is expected to strengthen and dig southward over the 
North-Central Pacific.

The Week-2 temperature outlook differs slightly from the 6-10 day temperature 
outlook in that it depicts reduced spatial coverage of favored anomalous cold 
over northeastern Alaska, and shows a slight eastward displacement in the 
anomaly pattern across the eastern CONUS. The official temperature outlook is 
based on the automated and consolidated temperature forecasts, and GEFS and 
ECMWF calibrated Reforecast temperatures.

The Week-2 precipitation outlook shows significant differences from the 6-10 
day period. Onshore flow in advance of the Bering Sea trough tilts the odds 
towards above normal precipitation over most of Alaska, though most of the 
Panhandle region is still favored to be drier-than-normal. Marginally enhanced 
monsoonal moisture across the Southwest and central and southern Intermountain 
Region warrants a slight tilt in the odds for wetter-than-normal conditions 
there. Anomalous wetness is also favored over much of the High Plains, 
attributed to periods of southerly and easterly upslope flow coinciding with 
the western fringes of cold fronts. Ahead of the mid-level trough predicted to 
be centered in the vicinity of 85W longitude, upper-tercile precipitation is 
generally favored. In contrast, lower-tercile precipitation is favored over 
portions of the Middle and Lower Mississippi Valley and lower parts of the Ohio 
and Tennessee Valleys, and over portions of the northwestern CONUS. 
Incidentally, the 12z GFS run has recently predicted the development of an area 
of low pressure over the eastern Gulf of Mexico during the last few days of 
August, which strengthens and heads west towards the Texas coast. This single 
run of the GFS model predicts this system may develop into a tropical cyclone, 
reaching Texas around Labor Day. This area of unsettled weather will be 
monitored for further developments tomorrow, and if necessary, an update will 
be made to the eastern Texas precipitation forecast. The official precipitation 
outlook is also based on the automated and consolidated precipitation forecasts 
and the GEFS and ECMWF calibrated Reforecast precipitation.

The official 8-14 day 500-hPa height blend consists of: 25% of Today's 0z GFS 
Ensemble Mean centered on Day 11, 25% of Today's 6z GFS Ensemble Mean centered 
on Day 11, 30% of Today's 0z European Ensemble Mean centered on Day 11, and 20% 
of Today's 0z Canadian Ensemble Mean centered on Day 11 


FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Near average, 3 out of 5, due to 
generally good agreement between models on the predicted 500-hPa height 
pattern, but offset somewhat by differences among the temperature and 
precipitation forecast tools.

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 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: 
19800904 - 20030803 - 19660810 - 19730814 - 19770824


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: 
19800904 - 19660811 - 19910806 - 19770826 - 20030803


6-10 DAY OUTLOOK TABLE
Outlook for Aug 28 - Sep 01, 2019

STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN   
WASHINGTON  A    B     OREGON      A    N     NRN CALIF   A    N     
SRN CALIF   A    A     IDAHO       A    B     NEVADA      A    A     
W MONTANA   B    B     E MONTANA   B    B     WYOMING     B    B     
UTAH        A    B     ARIZONA     A    A     COLORADO    B    A     
NEW MEXICO  A    A     N DAKOTA    B    B     S DAKOTA    B    N     
NEBRASKA    B    A     KANSAS      B    A     OKLAHOMA    B    A     
N TEXAS     B    A     S TEXAS     A    A     W TEXAS     B    A     
MINNESOTA   B    N     IOWA        B    A     MISSOURI    B    A     
ARKANSAS    B    A     LOUISIANA   B    A     WISCONSIN   B    A     
ILLINOIS    B    A     MISSISSIPPI B    A     MICHIGAN    B    A     
INDIANA     B    A     OHIO        B    A     KENTUCKY    B    A     
TENNESSEE   B    A     ALABAMA     B    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  N    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  N    A     
AK ALEUTIAN A    A     AK WESTERN  A    N     AK INT BSN  N    N     
AK S INT    A    B     AK SO COAST A    B     AK PNHDL    A    B     
 
                           

8-14 DAY OUTLOOK TABLE
Outlook for Aug 30 - Sep 05, 2019

STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN   
WASHINGTON  A    B     OREGON      A    N     NRN CALIF   A    N     
SRN CALIF   A    A     IDAHO       A    N     NEVADA      A    A     
W MONTANA   A    N     E MONTANA   B    A     WYOMING     B    A     
UTAH        A    N     ARIZONA     A    A     COLORADO    B    A     
NEW MEXICO  N    A     N DAKOTA    B    A     S DAKOTA    B    A     
NEBRASKA    B    A     KANSAS      B    A     OKLAHOMA    B    N     
N TEXAS     B    N     S TEXAS     N    N     W TEXAS     N    A     
MINNESOTA   B    N     IOWA        B    A     MISSOURI    B    B     
ARKANSAS    B    B     LOUISIANA   B    N     WISCONSIN   B    A     
ILLINOIS    B    N     MISSISSIPPI B    N     MICHIGAN    B    A     
INDIANA     B    N     OHIO        B    N     KENTUCKY    B    N     
TENNESSEE   B    N     ALABAMA     B    N     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        N    A     NEW JERSEY  A    A     W VIRGINIA  B    A     
MARYLAND    A    A     DELAWARE    A    A     VIRGINIA    N    A     
N CAROLINA  A    A     S CAROLINA  N    A     GEORGIA     N    A     
FL PNHDL    N    A     FL PENIN    A    N     AK N SLOPE  A    A     
AK ALEUTIAN A    N     AK WESTERN  A    N     AK INT BSN  N    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.

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