Prognostic Meteorological Discussion
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FXUS06 KWBC 281920
PMDMRD
Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks
NWS Climate Prediction Center College Park, MD
300 PM EDT Wed July 28 2021

6-10 DAY OUTLOOK FOR AUG 03 - 07 2021

Todays numerical model solutions from the GEFS and ECMWF forecast suites
depict fairly substantial differences relative to yesterday on the mean 500-hPa
height pattern across much of the forecast domain, particularly over the
eastern and southern CONUS. A persistent and anomalously strong closed 500-hPa
low is predicted over the western Bering Sea. A split-flow pattern, and a weak
closed low, is predicted downstream of the closed low over the Bering Sea,
leading to favored 500-hPa ridging across central and eastern Alaska and
troughing forecast farther to the south off the coast of the Pacific Northwest.
The long-wave pattern over the CONUS shows a continued retrogression today,
relative to yesterday`s forecast. Subtropical ridging is expected to dominate
much of the west-central CONUS during the 6-10 day period. An anomalously
strong trough is expected across the eastern CONUS. The southern extent of this
trough is forecast to continue to push farther southward into the Southeast in
todays model solutions, relative to yesterdays. The manual 500-hPa height
blend, based on the ensemble means from the GEFS and ECMWF models, supports
below-normal heights across much of the eastern CONUS, the southeastern Alaska
Panhandle, the Aleutians, and near the west coast of Mainland Alaska. Near to
above-normal 500-hPa heights are expected elsewhere across the forecast domain.

Above normal temperatures are generally favored across much of Mainland Alaska
and the Alaska Peninsula, associated with a mean mid-level ridge ahead of a
closed low forecast over the western Bering Sea. With subtropical ridging
expected to dominate much of the western CONUS, above-normal temperatures are
favored across the West Coast, Great Basin, and the Northern Rockies, extending
eastward to the Great Lakes, with enhanced probabilities over the Northern
Plains. Over the eastern CONUS and Southern Plains, enhanced probabilities of
below-normal temperatures are forecast, associated with a deepened mean trough,
relative to yesterday`s 6-10 day forecast. Over the southern Florida Peninsula,
above-normal temperatures are favored ahead of a mean frontal boundary.

Ahead of the closed upper level low predicted over the western Bering Sea,
above normal precipitation is favored over southwestern Mainland Alaska and the
eastern Aleutians. Over eastern Mainland Alaska and the central and northwest
Panhandle, ridging to the north of the split mid-level flow over the Northeast
Pacific increases odds of below-normal precipitation. Troughing to the south of
the split mid-level flow favors above-normal precipitation in the Pacific
Northwest. Surface high pressure is expected to dominate across much of the
eastern two-thirds of the CONUS, leading to below-normal precipitation
probabilities across the Eastern Rockies, Northern and Central Plains, much of
the Mississippi and Ohio Valleys, the Great Lakes, and Northeast. Along a mean
frontal boundary across the Southeast and Gulf Coast, above-normal
precipitation is favored. Over the Desert Southwest and Four Corners Region,
the retrogression of the long-wave pattern shifts the mean ridge axis into a
more favorable position for an enhanced Southwest Monsoon. However, the center
of the mean mid-level high pressure is predicted to be shifted farther
southward, suppressing any major northward moisture surges in the Southwest and
Great Basin. This favors a weak tilt toward below-normal precipitation for
parts of the Southwest, with near-normal precipitation favored south of the
highest mean mid-level height center.

The official 6-10 day 500-hPa height blend consists of 45% of Today`s 6z GFS
Ensemble Mean centered on Day 8, and 55% of Today`s 0z European Ensemble Mean
centered on Day 8


FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Below normal, 2 out of 5 due to
large inconsistencies among the model guidance and forecast tools with respect
to the temperature and precipitation fields across much of the forecast domain.

8-14 DAY OUTLOOK FOR AUG 05 - 11 2021

During the Week-2 period, numerical model guidance depicts a generally similar
500-hPa flow pattern to that predicted for the 6-10 day period in terms of
phasing, but having a lower amplitude. A strong upper low is forecast to
persist well into Week-2 over the Bering Sea continuing an active pattern for
western  and interior Alaska. Downstream, ridging is forecast to continue over
eastern Alaska and a weak trough is forecast farther to the south off the coast
of the Pacific Northwest. Subtropical ridging close to climatological strength
is predicted across much of the CONUS. A trough is forecast to persist early in
Week-2 across the Great Lakes and Northeast and weaken as time progresses.
Despite mean troughing in the East, mean 500-hPa heights are forecast to be
near to above-normal over the CONUS. Above-normal heights are favored for
eastern Alaska while below-normal heights are likely over southwestern Alaska
and the Aleutians near the persistent upper level low over the Bering Sea.

In Alaska, enhanced onshore flow to the east of the mean mid-level low over the
Bering Sea favors increased odds for below-normal temperatures over the
Southwest Mainland and eastern Aleutians. Above-normal temperatures are favored
for the eastern Mainland, associated with mid-level ridging ahead of the mean
trough forecast over the Bering Sea. Above-normal temperatures are favored for
the western and northern CONUS, with enhanced above-normal temperature
probabilities over the Northern Plains, exacerbated by ongoing drought. Over
the Southeast, westward to the Southern Plains, increased probabilities of
below-normal temperatures are predicted behind a mean frontal boundary. Ahead
of the mean front, above-normal temperatures are weakly favored over the
southern Florida Peninsula, as there is some uncertainty regarding the
southward progression of the front during the Week-2 period.

With the persistent upper level low forecast over the Bering Sea, an active
wetter-than-normal pattern is forecast to continue well into Week-2 across
western Alaska, interior Mainland, and eastern Aleutians. Above-normal
precipitation probabilities extend southeastward to the Pacific Northwest,
ahead of a mean trough to the south of mean split mid-level flow. Below-normal
precipitation is favored for much of the interior West, extending eastward to
the Mississippi River, associated with the mean subtropical ridging across the
west-central CONUS. In the Great Lakes, odds tilt toward above-normal
precipitation, in favor of decent model agreement in the potential for
short-wave energy to propagate through the region during Week-2. Above-normal
precipitation is also favored over parts of the Southeast and Gulf Coast, along
a mean frontal boundary. Similar to the 6-10 day period, the positive mid-level
height anomaly center over the Four Corners Region is favored to be shifted
farther southward, which would tend to suppress any major northward surges of
monsoonal moisture, increasing odds for below-normal precipitation northward
from the Mexico border.

The official 8-14 day 500-hPa height blend consists of: 50% of Today`s 6z GFS
Ensemble Mean centered on Day 11, and 50% of Today`s 0z European Ensemble Mean
centered on Day 11


FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Below normal, 2 out of 5, due to
large uncertainty among the model guidance and forecast tools.

FORECASTER: Adam Hartman

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
August 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:
19800725 - 19780726 - 20030713 - 19720728 - 19850709


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:
19800724 - 19780726 - 19570707 - 19790803 - 20030713


6-10 DAY OUTLOOK TABLE
Outlook for Aug 03 - 07 2021

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



8-14 DAY OUTLOOK TABLE
Outlook for Aug 05 - 11 2021

STATE      TEMP PCPN   STATE      TEMP PCPN   STATE      TEMP PCPN
WASHINGTON  A    A     OREGON      A    N     NRN CALIF   A    N
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  N    B     N DAKOTA    A    B     S DAKOTA    A    B
NEBRASKA    A    B     KANSAS      A    B     OKLAHOMA    B    B
N TEXAS     B    N     S TEXAS     B    N     W TEXAS     B    N
MINNESOTA   A    N     IOWA        A    B     MISSOURI    N    B
ARKANSAS    B    N     LOUISIANA   B    A     WISCONSIN   A    N
ILLINOIS    A    N     MISSISSIPPI B    A     MICHIGAN    A    A
INDIANA     A    N     OHIO        A    N     KENTUCKY    N    N
TENNESSEE   B    N     ALABAMA     B    A     NEW YORK    A    N
VERMONT     A    N     NEW HAMP    A    N     MAINE       A    N
MASS        A    N     CONN        A    N     RHODE IS    A    N
PENN        A    N     NEW JERSEY  A    N     W VIRGINIA  N    N
MARYLAND    N    N     DELAWARE    N    N     VIRGINIA    N    N
N CAROLINA  B    N     S CAROLINA  B    A     GEORGIA     B    A
FL PNHDL    B    A     FL PENIN    A    N     AK N SLOPE  N    N
AK ALEUTIAN B    A     AK WESTERN  B    A     AK INT BSN  N    A
AK S INT    N    A     AK SO COAST B    A     AK PNHDL    A    N

                           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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