918
FXUS06 KWBC 151903
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EDT FRI SEPTEMBER 15 2023
6-10 DAY OUTLOOK FOR SEP 21 - 25 2023
THE 6 TO 10 DAY HEIGHT FORECAST MAINTAINS TWO STRONG POSITIVE HEIGHT ANOMALY
CENTERS OVER AND NEAR NORTH AMERICA. THE FIRST, A RELATIVELY FLAT RIDGE,
CENTERED NEAR THE ALEUTIANS AND STRETCHING ACROSS MUCH OF THE NORTH PACIFIC.
THE SECOND, MORE MERIDIONAL, OVER THE HUDSON BAY EXTENDING SOUTH INTO THE GREAT
LAKES AND NORTHEAST. IN THE WESTERN CONTIGUOUS U.S. (CONUS) WEAKLY NEGATIVE,
ALTHOUGH STRONGER THAN YESTERDAY, 500-HPA HEIGHT ANOMALIES LEAD TO SLIGHT
TROUGHING IN THE REGION. NEAR TO BELOW NORMAL 500-HPA HEIGHTS STRETCH INTO
PARTS OF THE SOUTH-CENTRAL AND SOUTHEASTERN CONUS. IN ALASKA, POSITIVE 500-HPA
HEIGHTS ARE FORECAST ACROSS MUCH OF THE STATE. RELATIVE TO PRIOR FORECASTS,
500-HPA HEIGHTS HAVE INCREASED SUBSTANTIALLY ACROSS MUCH OF THE STATE.
THE TEMPERATURE OUTLOOK FOR THE PERIOD IS VERY SIMILAR TO PREVIOUS FORECASTS.
ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS MOST OF THE CONUS EAST OF THE
CONTINENTAL DIVIDE. EXCEPTIONS ARE IN PORTIONS OF GEORGIA AND THE CAROLINAS
WHERE NEAR-NORMAL TEMPERATURES ARE FAVORED. IN THE WESTERN CONUS, BELOW-NORMAL
TEMPERATURES REMAIN FAVORED AS THE NEGATIVE 500-HPA HEIGHT ANOMALIES LOOK
STRONGER RELATIVE TO YESTERDAY. RAW AND BIAS-CORRECTED TOOLS ARE SUPPORTIVE OF
ENHANCED CHANCES FOR BELOW-NORMAL TEMPERATURES ACROSS MUCH OF THE WESTERN
CONUS. REFORECAST TOOLS INDICATE SLIGHTLY LOWER CHANCES ALONG THE PACIFIC COAST
AND CANADIAN BORDER. IN ALASKA, REFORECAST TOOLS HAVE WARMED SIGNIFICANTLY
RELATIVE TO YESTERDAY’S FORECAST GUIDANCE. HOWEVER, RAW AND SHORT TERM
BIAS-CORRECTED TOOLS ARE STILL RELATIVELY COOL, PARTICULARLY ALONG THE SOUTH
COAST OF ALASKA. THEREFORE, MUCH OF THE STATE IS FAVORED TO SEE NEAR-NORMAL
TEMPERATURES WITH BELOW-NORMAL TEMPERATURES BEING SLIGHTLY FAVORED IN PARTS OF
SOUTH-CENTRAL AND SOUTHEAST ALASKA.
ABOVE-NORMAL PRECIPITATION IS FAVORED ACROSS MUCH OF THE WESTERN CONUS INTO THE
ROCKY MOUNTAINS, PLAINS AND MISSISSIPPI VALLEY DURING THE 6 TO 10 DAY PERIOD
AHEAD OF THE 500-HPA TROUGH ACROSS THE WESTERN CONUS. ENSEMBLE TOOLS INDICATE
THAT AN AREA OF LOW-PRESSURE MAY EJECT OUT OF THE ROCKY MOUNTAINS AND TRACK
NORTHEAST THROUGH THE PLAINS BRINGING ENHANCED CHANCES FOR ABOVE-NORMAL
PRECIPITATION. BENEATH THE STRONG POSITIVE 500-HPA HEIGHT ANOMALIES ACROSS THE
GREAT LAKES AND NORTHEAST, BELOW-NORMAL PRECIPITATION IS FAVORED. ENSEMBLES
CONTINUE TO INDICATE ABOVE-NORMAL PRECIPITATION ACROSS THE SOUTHERN ATLANTIC
STATES ASSOCIATED WITH A STATIONARY BOUNDARY. IN THE SOUTHWEST, BELOW-NORMAL
PRECIPITATION IS FAVORED WITH FEW CHANCES FOR ANY GULF OF CALIFORNIA SURGE
EVENTS AND A SUBTROPICAL RIDGE TO THE SOUTH LIMITING MOISTURE INTO THE REGION.
IN ALASKA, MUCH OF THE MAINLAND IS SLIGHTLY FAVORED TO SEE ABOVE-NORMAL
PRECIPITATION WITH ONSHORE FLOW INTO WESTERN ALASKA FROM THE BERING SEA AND
POTENTIAL LOW PRESSURE SYSTEMS TO TRACK NORTH OF THE HIGH PRESSURE CENTERED
SOUTH OF THE ALEUTIAN ISLANDS. HOWEVER, ALONG THE SOUTH COAST AND INTO THE
SOUTHEAST, ONSHORE FLOW LOOKS WEAKENED RELATIVE TO YESTERDAY AND NEAR-NORMAL
PRECIPITATION IS FAVORED.
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 15% OF TODAY'S 0Z GFS
ENSEMBLE MEAN CENTERED ON DAY 8, 20% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED
ON DAY 8, 10% OF TODAY'S OPERATIONAL 6Z GFS CENTERED ON DAY 8, 25% OF TODAY'S
0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8, 10% OF TODAY'S OPERATIONAL 0Z
ECMWF 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, GOOD
CONFIDENCE IN THE HEIGHT ANOMALY CENTERS ACROSS THE HUDSON BAY AND NORTH
PACIFIC IS OFFSET BY CONCERN OVER THE PATTERN IN THE WESTERN CONUS.
8-14 DAY OUTLOOK FOR SEP 23 - 29 2023
THE WEEK-2 HEIGHT FORECAST IS SIMILAR TO THE 6 TO 10 DAY PATTERN. TWO POSITIVE
500-HPA HEIGHT ANOMALIES REMAIN CENTERED NEAR THE ALEUTIAN ISLANDS AND THE
HUDSON BAY. THE POSITIVE 500-HPA HEIGHT ANOMALY CENTERED ACROSS THE HUDSON BAY
IS STRONGER RELATIVE TO THE EARLIER PERIOD AND EXTENDS ACROSS MUCH OF THE
EASTERN CONUS. MEANWHILE, THE 500-HPA HEIGHT ANOMALY AREA CENTERED ON THE
ALEUTIAN ISLANDS IS SLIGHTLY WEAKER RELATIVE TO PRIOR FORECASTS AND THE 6 TO 10
DAY PERIOD. THE WEAK TROUGH ACROSS THE WESTERN CONUS IS FORECAST TO BE SLIGHTLY
MORE AMPLIFIED RELATIVE TO PRIOR FORECASTS AND HAS RETROGRADED SLIGHTLY TO BE
CENTERED OVER COASTAL BRITISH COLUMBIA. NEAR-NORMAL 500-HPA HEIGHTS ARE FAVORED
ACROSS MOST OF ALASKA.
BELOW-NORMAL TEMPERATURES REMAIN FAVORED ACROSS THE WESTERN CONUS DURING THE
WEEK-2 PERIOD BENEATH A NEGATIVE 500-HPA HEIGHT ANOMALY. ACROSS MUCH OF THE
EASTERN CONUS, ABOVE-NORMAL TEMPERATURES ARE FAVORED. THE STRONGEST
PROBABILITIES ARE CENTERED ACROSS THE GREAT LAKES NEAREST STRONG POSITIVE
500-HPA HEIGHT ANOMALIES OVER THE HUDSON BAY. WEAKER PROBABILITIES REMAIN ALONG
PORTIONS OF THE SOUTHERN ATLANTIC STATES WHERE LINGERING COOLER AIR AT THE
ONSET OF THE PERIOD AND FORECAST ABOVE-NORMAL PRECIPITATION REDUCES CHANCES FOR
ABOVE-NORMAL TEMPERATURES. MEANWHILE, IN ALASKA, REFORECAST TOOLS CONTINUE TO
OSCILLATE BETWEEN WARMER AND COLDER SOLUTIONS ACROSS THE STATE. A BROADER AREA
OF NEAR-NORMAL TEMPERATURES IS THEREFORE FAVORED. BIAS-CORRECTED AND RAW
FORECAST TOOLS REMAIN ON THE COOLER SIDE WHILE REFORECAST TOOLS HAVE WARMED
CONSIDERABLY RELATIVE TO PREVIOUS FORECASTS.
DUE TO THE PRIOR MENTIONED TROUGH OVER MUCH OF THE WESTERN CONUS RETROGRADING
SLIGHTLY NORTHWEST, STRONGER ONSHORE FLOW IS FORECAST ACROSS THE PACIFIC
NORTHWEST, INCREASING CHANCES FOR ABOVE-NORMAL PRECIPITATION INTO THE REGION.
THIS ENHANCED MOIST PACIFIC FLOW MAY ALSO HELP TO ENHANCE MOISTURE AND
PRECIPITATION ACROSS PORTIONS OF THE NORTHERN AND CENTRAL PLAINS WHERE
ENSEMBLES CONTINUE TO INDICATE THE POTENTIAL FOR AN AREA OF LOW-PRESSURE TO
EJECT OUT OF THE ROCKY MOUNTAINS. IN THE SOUTHEAST, ABOVE-NORMAL PRECIPITATION
IS FAVORED ALONG THE ATLANTIC COAST WHERE A STATIONARY BOUNDARY MAY REMAIN
STALLED DURING PARTS OF THE PERIOD. NEAR-NORMAL PRECIPITATION IS FAVORED ACROSS
PARTS OF THE NORTHEAST AHEAD OF THE 500-HPA RIDGE AXIS. IN THE SOUTHWEST, NEAR
TO THE SUBTROPICAL HIGH, BELOW-NORMAL PRECIPITATION IS FAVORED. IN ALASKA, DUE
TO THE RETROGRADING TROUGH, ENHANCED ONSHORE FLOW MAY RELAX SLIGHTLY ACROSS THE
SOUTHEAST, LEADING TO A SLIGHT TILT TOWARDS BELOW-NORMAL PRECIPITATION BEING
FAVORED. ABOVE-NORMAL PRECIPITATION IS SLIGHTLY FAVORED ACROSS PARTS OF THE
INTERIOR WHERE THE STORM TRACK MAY SET UP NORTH OF THE STRONGEST ABOVE-NORMAL
500-HPA HEIGHT ANOMALIES.
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 15% OF TODAY'S 0Z GFS
ENSEMBLE MEAN CENTERED ON DAY 11, 15% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED
ON DAY 11, 40% 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, GOOD
CONFIDENCE IN THE HEIGHT ANOMALY CENTERS ACROSS THE HUDSON BAY AND NORTH
PACIFIC IS OFFSET BY THE FORECAST PATTERN ACROSS ALASKA AND THE EASTERN CONUS.
FORECASTER: RYAN BOLT
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
SEPTEMBER 21.
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:
19620925 - 20060908 - 20010923 - 20090911 - 19870921
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:
19620924 - 20090826 - 20010921 - 19870921 - 20060907
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 21 - 25 2023
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON B A OREGON B A NRN CALIF B A
SRN CALIF B N IDAHO B A NEVADA B A
W MONTANA B A E MONTANA B A WYOMING B A
UTAH B A ARIZONA B B COLORADO B A
NEW MEXICO A B 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 A LOUISIANA A N WISCONSIN A A
ILLINOIS A A 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 B NEW HAMP A B MAINE A B
MASS A B CONN A B RHODE IS A B
PENN A B NEW JERSEY A B W VIRGINIA A B
MARYLAND A N DELAWARE A N VIRGINIA A N
N CAROLINA A A S CAROLINA N A GEORGIA N N
FL PNHDL A N FL PENIN A A AK N SLOPE N A
AK ALEUTIAN N N AK WESTERN N A AK INT BSN N A
AK S INT N A AK SO COAST N N AK PNHDL N N
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 23 - 29 2023
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON B A OREGON B A NRN CALIF B A
SRN CALIF B N IDAHO B A NEVADA B A
W MONTANA B A E MONTANA N A WYOMING B A
UTAH B N ARIZONA B B COLORADO A A
NEW MEXICO A B N DAKOTA A A S DAKOTA A A
NEBRASKA A A KANSAS A A OKLAHOMA A A
N TEXAS A N S TEXAS A N W TEXAS A N
MINNESOTA A A IOWA A A MISSOURI A A
ARKANSAS A A LOUISIANA A N WISCONSIN A A
ILLINOIS A A MISSISSIPPI A N MICHIGAN A A
INDIANA A A OHIO A N KENTUCKY A A
TENNESSEE A N ALABAMA A N 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 A N
MARYLAND A N DELAWARE A N VIRGINIA A N
N CAROLINA A A S CAROLINA A A GEORGIA A N
FL PNHDL A N FL PENIN A N AK N SLOPE N N
AK ALEUTIAN N N AK WESTERN N A AK INT BSN N N
AK S INT B N AK SO COAST B N AK PNHDL B 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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