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000
FXUS06 KWBC 251902
PMDMRD
Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks
NWS Climate Prediction Center College Park, MD
300 PM EDT Thu April 25 2024

6-10 DAY OUTLOOK FOR MAY 01 - 05 2024

Model solutions depict a persistent longwave pattern into the beginning of May.
The GEFS along with the ECMWF and Canadian ensemble means feature a 500-hPa
trough of varying amplitude near the West Coast, a broad ridge over the central
contiguous U.S. (CONUS), and a trough across the western Atlantic. Positive
500-hPa height anomalies and southerly surface flow support increased
above-normal temperature probabilities from the Rockies to the East Coast.
5-day temperatures are expected to be more variable across the Northeast with
above-normal temperature probabilities lower in this region. Anomalous
mid-level troughing and enhanced onshore flow favor below-normal temperatures
across the Pacific Northwest and much of California.

The highest forecast confidence in the 6-10 day precipitation outlook exists
for the Great Plains and Upper Midwest where above-normal precipitation is
favored. This wet start to May is due to the upstream mid-level trough and
enhanced low-level moisture from the Gulf of Mexico. Above-normal precipitation
probabilities are tempered though due to uncertainty on where the heaviest
convective rainfall occurs. Enhanced onshore flow leads to increased
above-normal precipitation probabilities from the Pacific Northwest and
northern California eastward to the northern Rockies. Near normal precipitation
is forecast for the Great Basin and climatological dry areas of the Southwest.

A 500-hPa trough over the Bering Sea favors above-normal precipitation for much
of Alaska. The uncalibrated model temperature output is colder than the
reforecast GEFS and ECMWF tools. The 6-10 day temperature outlook hedged
towards the reforecasts, but there is a notable trend the past few days for
less coverage of increased above-normal temperature probabilities.

Based on the GEFS and ECMWF ensemble means, near normal temperatures and
precipitation are favored across much of Hawaii.

The official 6-10 day 500-hPa height blend consists of 35% of Today`s 6z GFS
Ensemble Mean centered on Day 8, 35% of Today`s 0z European Ensemble Mean
centered on Day 8, and 30% 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
a persistent longwave pattern and good agreement among the temperature tools
throughout the CONUS.

8-14 DAY OUTLOOK FOR MAY 03 - 09 2024

The GEFS, ECMWF, and Canadian ensemble means maintain the persistent longwave
pattern with 500-hPa troughs near both coasts of North America and a broad
ridge centered over the central CONUS. The 6-10 and 8-14 day temperature
outlooks are quite similar with a majority of the CONUS favored to have
above-normal temperatures due to the broad ridge centered over the Mississippi
Valley. The Northeast is vulnerable to backdoor cold fronts and cold air
damming during the spring and there seems to be an increasing chance for that
to occur during early May with an amplified trough over the northwestern
Atlantic. A comparison between the manual 500-hPa height blend from the past
two days shows the trough over the western Atlantic closer to the East Coast
which would increase the potential for a cooler outcome for the Northeast.
Although the reforecast tools continue to favor above-normal temperatures
across the Northeast, near normal temperatures are forecast for this region due
to the colder uncalibrated model output and the analog tool. The 500-hPa trough
with negative height anomalies along with enhanced onshore flow favor
below-normal temperatures for California and parts of the Desert Southwest and
Pacific Northwest.

The mid-level longwave trough to ridge pattern from the West Coast to the
Mississippi Valley yields a relatively wet (dry) outlook across the western and
central (eastern) CONUS. Forecast confidence is not too high though since the
reforecast tools indicate weak probabilities overall and the ECMWF ensemble
mean predicts a retrogession of the longwave pattern late in week-2. One small
change from yesterday’s outlook was a reduction in the coverage of increased
below-normal precipitation probabilities across the eastern CONUS. This is
based on the GEFS and ECMWF reforecasts  and the analog tool derived from the
manual 500-hPa blend. These precipitation tools imply the potential for a
stationary front to develop across the Southeast or southern Mid-Atlantic which
could be a focus for precipitation.

A broad 500-hPa trough over the Bering Sea and western Mainland Alaska supports
increased above-normal precipitation probabilities nearly statewide for Alaska.
Temperature tools continue to differ and a consensus between the GEFS and ECMWF
reforecasts favor below (above)-normal temperatures for the North Slope
(southeastern Alaska).

The GEFS and ECMWF ensemble means feature a mid-level trough, near the West
Coast, extending southward to the Central Pacific. This is expected to promote
cooler-than-normal temperatures for Hawaii and increased chances of
above-normal precipitation except for the Big Island.

The official 8-14 day 500-hPa height blend consists of: 35% of Today`s 6z GFS
Ensemble Mean centered on Day 11, 35% of Today`s 0z European Ensemble Mean
centered on Day 11, and 30% of Today`s 0z Canadian Ensemble Mean centered on
Day 11


FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Average, 3 out of 5, with good
model agreement on the 500-hPa height pattern offset by uncertainty in the
temperature and precipitation outlooks for the eastern CONUS.

FORECASTER: Brad Pugh

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 1991-2020 base period means as reference in
the climate outlooks.

The next set of long-lead monthly and seasonal outlooks will be released on May
16.


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:
19900507 - 19900417 - 19810417 - 19770406 - 20000410


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:
19510404 - 19520404 - 19530404 - 19540404 - 19550404


6-10 DAY OUTLOOK TABLE
Outlook for May 01 - 05 2024

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



8-14 DAY OUTLOOK TABLE
Outlook for May 03 - 09 2024

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

                           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.

$$