764
FXUS06 KWBC 191915
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EDT TUE SEPTEMBER 19 2023
6-10 DAY OUTLOOK FOR SEP 25 - 29 2023
TODAY’S GFS, ECMWF, AND CANADIAN ENSEMBLE MEAN 500-HPA HEIGHT FORECASTS ARE IN
EXCELLENT AGREEMENT OVER THE FORECAST DOMAIN DURING THE 6-10 DAY FORECAST
PERIOD. THE MANUAL 500-HPA HEIGHT BLEND DEPICTS A TROUGH EXTENDING FROM THE
BERING SEA AND WESTERN ALASKA SOUTHEASTWARD OVER THE GULF OF ALASKA, WITH WELL
BELOW-AVERAGE HEIGHTS (AT LEAST -150 METERS) INDICATED OVER THE EASTERN GULF OF
ALASKA. A FAIRLY FLAT, LOW-AMPLITUDE RIDGE IS FORECAST SOUTH OF THE ALEUTIANS.
THE FLOW PATTERN SPLITS OVER WESTERN NORTH AMERICA, WITH THE NORTHERN BRANCH OF
THE WESTERLIES MOVING UP AND OVER AN AMPLIFIED MID-LEVEL RIDGE OVER MOST OF
CANADA, AND THE SOUTHERN BRANCH OF THE WESTERLIES EVOLVING INTO A
TROUGH/RIDGE/TROUGH PATTERN ACROSS THE LOWER 48 STATES. EARLY AUTUMN IS THE
TIME OF YEAR WHEN THE ATMOSPHERIC CIRCULATION TYPICALLY BECOMES MORE ENERGETIC,
AND FASTER-MOVING SHORTWAVE TROUGHS EMBEDDED IN THE MEAN FLOW BECOME MORE
CHALLENGING TO FORECAST.
THE CALIBRATED-REFORECAST TEMPERATURE TOOLS FROM THE ECMWF AND GFS ENSEMBLE
MEANS ARE IN MUCH BETTER AGREEMENT TODAY, DEPICTING NEAR TO BELOW NORMAL
TEMPERATURES FOR MOST AREAS WEST OF THE CONTINENTAL DIVIDE, AND ABOVE NORMAL
TEMPERATURES FOR PRACTICALLY ALL AREAS EAST OF THE CONTINENTAL DIVIDE. THE
CANADIAN REFORECAST TEMPERATURE TOOL DIFFERS PRIMARILY IN THAT IT PREDICTS A
BROAD EXTENSION OF NEAR NORMAL TEMPERATURES FROM PARTS OF THE WEST EASTWARD
ACROSS MOST OF THE ROCKIES, CENTRAL PLAINS, AND MIDDLE MISSISSIPPI VALLEY. IN
ALASKA, ODDS FAVOR ABOVE NORMAL TEMPERATURES ACROSS NORTHEASTERN PORTIONS OF
THE STATE, ASSOCIATED WITH THE LARGE ANOMALOUS RIDGE OVER CANADA. BELOW NORMAL
TEMPERATURE CHANCES ARE ENHANCED OVER SOUTHWESTERN ALASKA, IN PROXIMITY TO A
MID-LEVEL TROUGH AND ANOMALOUSLY COOL SEA-SURFACE TEMPERATURES. THE MANUAL 6-10
DAY TEMPERATURE OUTLOOK IS HEAVILY BASED ON THE CONSOLIDATED TOOL (WHICH IS A
SKILL-WEIGHTED MEAN OF GEFS AND ECMWF REFORECAST TEMPERATURES) AND THE
AUTO-TEMPERATURE TOOL.
THERE ARE ELEVATED CHANCES OF ABOVE NORMAL PRECIPITATION OVER THE PACIFIC
NORTHWEST, THE NORTHERN INTERMOUNTAIN REGION, THE NORTHERN ROCKIES, AND
APPROXIMATELY THE NORTHWESTERN TWO-THIRDS OF CALIFORNIA AND NEVADA, IN
PROXIMITY TO A MID-LEVEL TROUGH, BELOW NORMAL 500-HPA HEIGHTS, AND CYCLONIC
CURVATURE. THE CONSOLIDATED AND AUTOMATED PRECIPITATION TOOLS DEPICT BELOW
NORMAL PRECIPITATION CHANCES OVER THE CENTRAL AND SOUTHERN ROCKIES, FAR ENOUGH
REMOVED FROM ANY EXPECTED STORM ACTIVITY. A LOW PRESSURE SYSTEM OVER THE
CENTRAL PART OF THE COUNTRY EARLY IN THE 6-10 DAY PERIOD TILTS THE ODDS
SLIGHTLY TOWARDS ABOVE NORMAL PRECIPITATION FOR MUCH OF THIS REGION. THE LARGE
ANOMALOUS RIDGE OVER CANADA AND ASSOCIATED POSITIVE 500-HPA HEIGHT ANOMALIES
FAVOR BELOW NORMAL PRECIPITATION CHANCES ACROSS THE NORTHERN GREAT LAKES REGION
AND NORTHERN NEW ENGLAND. ANOTHER LOW PRESSURE SYSTEM, THIS ONE OF POSSIBLE
SUBTROPICAL ORIGIN, IS PREDICTED TO MOVE UP THE EAST COAST EARLY IN THE
FORECAST PERIOD, ENHANCING ODDS FOR ABOVE NORMAL PRECIPITATION FOR THE
MID-ATLANTIC AND SOUTHERN NEW ENGLAND. SURFACE HIGH PRESSURE OVER THE WESTERN
ATLANTIC OCEAN LATER IN THE 6-10 DAY PERIOD IS PREDICTED TO BRING AN EXTENDED
PERIOD OF MOIST, EASTERLY FLOW TO THE EASTERN GULF COAST REGION, ALSO
INCREASING THE CHANCES FOR ABOVE NORMAL PRECIPITATION TO THAT AREA. IN ALASKA,
ODDS FAVOR BELOW NORMAL PRECIPITATION OVER WEST-CENTRAL PORTIONS OF THE STATE,
WHICH IS SUPPORTED BY THE AUTOMATED AND CONSOLIDATED PRECIPITATION FORECASTS.
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 33% OF TODAY'S 0Z GFS
ENSEMBLE MEAN CENTERED ON DAY 8, 34% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN
CENTERED ON DAY 8, AND 33% 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
EXCELLENT AGREEMENT IN THE ENSEMBLE MEAN 500-HPA HEIGHT FIELDS, GOOD AGREEMENT
AMONG THE TEMPERATURE TOOLS, BUT OFFSET BY NOTABLE DISCREPANCIES AMONG THE
PRECIPITATION TOOLS.
8-14 DAY OUTLOOK FOR SEP 27 - OCT 03, 2023
THE PREDICTED WEEK-2 500-HPA CIRCULATION PATTERN IS SIMILAR TO THAT ANTICIPATED
DURING THE EARLIER 6-10 DAY PERIOD, THOUGH SLIGHTLY MORE PROGRESSIVE AND
DE-AMPLIFIED. A MID-LEVEL TROUGH IS FORECAST OVER THE BERING SEA AND WESTERN
ALASKA, WITH FAST WESTERLY FLOW ACROSS MUCH OF THE NORTH PACIFIC OCEAN. AN
UPSTREAM TROUGH NEAR THE KAMCHATKA PENINSULA IS EXPECTED TO HELP CARVE OUT A
NEW TROUGH OVER THE BERING SEA AND WESTERN GULF OF ALASKA. TROUGHING IS
EXPECTED JUST OFF THE WEST COASTS OF CANADA AND THE LOWER 48 STATES, WITH THE
FLOW BEGINNING TO DIVERGE OVER WESTERN NORTH AMERICA. THE NORTHERN BRANCH HEADS
UP INTO CANADA, WHILE THE SOUTHERN BRANCH EVOLVES DOWNSTREAM ACROSS THE
CONTIGUOUS U.S. (CONUS) INTO A TROUGH-RIDGE-TROUGH PATTERN DISPLACED SLIGHTLY
EASTWARD OF ITS ANTICIPATED 6-10 DAY POSITION. ACROSS THE SOUTHWESTERN CONUS,
THE CLIMATOLOGICAL MONSOON SEASON IS DRAWING TO A CLOSE. A MAJOR CONTRIBUTOR TO
THE MONSOON IS THE SUBTROPICAL RIDGE, WHICH IS NOW SHIFTED WELL SOUTHWARD OVER
MEXICO AND ADJACENT PORTIONS OF THE EASTERN PACIFIC.
BELOW NORMAL TEMPERATURES ARE FAVORED FOR MOST AREAS WEST OF THE CONTINENTAL
DIVIDE AND OVER SOUTHWESTERN ALASKA, CONSISTENT WITH THE WEEK-2 CONSOLIDATED
TEMPERATURE FORECAST AND THE PROXIMITY OF MID-LEVEL TROUGHS AND CYCLONIC
CURVATURE. ABOVE NORMAL TEMPERATURE CHANCES ARE ENHANCED FOR PRACTICALLY ALL
AREAS EAST OF THE CONTINENTAL DIVIDE, AND NORTHEASTERN ALASKA. THIS IS
SUPPORTED BY MID-LEVEL RIDGING, NEAR TO ABOVE NORMAL 500-HPA HEIGHTS, AND/OR
ANTICYCLONIC CURVATURE.
ABOVE NORMAL PRECIPITATION CHANCES ARE INDICATED FROM WASHINGTON, OREGON, AND
APPROXIMATELY THE NORTHWEST HALF OF CALIFORNIA EASTWARD ACROSS THE NORTHERN AND
CENTRAL ROCKIES, THE GREAT PLAINS AS FAR SOUTH AS OKLAHOMA, AND ADJACENT PARTS
OF MINNESOTA AND IOWA. THIS IS ATTRIBUTED TO THE MID-LEVEL TROUGH OVER THE WEST
AND ASSOCIATED SHORTWAVE ACTIVITY. THERE ARE INCREASED ODDS FOR BELOW NORMAL
PRECIPITATION FOR NEW MEXICO, CENTRAL AND SOUTHERN TEXAS, CONTINUING NORTHEAST
ACROSS THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS TO THE UPPER GREAT LAKES
REGION, THOUGH THERE IS CONSIDERABLE UNCERTAINTY AMONG THE VARIOUS
PRECIPITATION TOOLS REGARDING THIS FORECAST ANOMALY. THE LARGE CANADIAN RIDGE
AND SIGNIFICANTLY POSITIVE 500-HPA HEIGHT ANOMALIES FAVOR BELOW NORMAL
PRECIPITATION FROM THE PREVIOUSLY NOTED UPPER GREAT LAKES REGION EASTWARD
ACROSS NORTHERN NEW YORK STATE, AND NORTHERN NEW ENGLAND. THE POSSIBILITY OF
ANOTHER LOW PRESSURE SYSTEM DEVELOPING OFF THE SOUTHEAST COAST EARLIER IN
WEEK-2 TILTS THE ODDS TOWARDS ABOVE NORMAL PRECIPITATION FOR THIS AREA AND THE
SOUTHERN MID-ATLANTIC REGION. ABOVE NORMAL PRECIPITATION CHANCES ARE ALSO
ELEVATED OVER THE EASTERN MAINLAND OF ALASKA AND THE PANHANDLE REGION,
COINCIDENT WITH A SUSPECTED WESTWARD SHIFT OF SOME OF THE ENERGY ASSOCIATED
WITH THE GULF OF ALASKA TROUGH, IN RESPONSE TO THE NEW TROUGH PREDICTED TO
APPROACH THE BERING SEA REGION. BELOW NORMAL PRECIPITATION CHANCES ARE SLIGHTLY
ENHANCED OVER PORTIONS OF THE WEST COAST OF ALASKA.
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 33% OF TODAY'S 0Z GFS
ENSEMBLE MEAN CENTERED ON DAY 11, 34% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN
CENTERED ON DAY 11, AND 33% 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 AMONG THE VARIOUS 500-HPA HEIGHT FORECASTS AND SURFACE
TEMPERATURE GUIDANCE, BUT OFFSET BY SIGNIFICANT DISCREPANCIES IN THE
PRECIPITATION 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 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:
19870915 - 20090928 - 19590901 - 19960920 - 19870910
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:
20090927 - 19870914 - 19590901 - 19830903 - 19960919
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 25 - 29 2023
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON N A OREGON B A NRN CALIF B A
SRN CALIF B N IDAHO N A NEVADA B A
W MONTANA A A E MONTANA A N WYOMING A B
UTAH A N ARIZONA A N COLORADO A B
NEW MEXICO A B N DAKOTA A N S DAKOTA A N
NEBRASKA A N KANSAS A N OKLAHOMA A N
N TEXAS A N S TEXAS A N W TEXAS A N
MINNESOTA A N IOWA A N MISSOURI A N
ARKANSAS A N LOUISIANA A N WISCONSIN A N
ILLINOIS A N MISSISSIPPI A N MICHIGAN A N
INDIANA A A OHIO A A KENTUCKY A A
TENNESSEE A N ALABAMA A A NEW YORK A A
VERMONT A N NEW HAMP A A MAINE A B
MASS A A CONN A A RHODE IS A A
PENN A A NEW JERSEY A A W VIRGINIA A 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 N AK N SLOPE A N
AK ALEUTIAN B N AK WESTERN N N AK INT BSN N N
AK S INT N N AK SO COAST N N AK PNHDL N N
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 27 - OCT 03, 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 N A E MONTANA A A WYOMING A A
UTAH N N ARIZONA N N COLORADO A N
NEW MEXICO A B N DAKOTA A A S DAKOTA A A
NEBRASKA A A KANSAS A N OKLAHOMA A N
N TEXAS A N S TEXAS A B W TEXAS A N
MINNESOTA A N IOWA A N MISSOURI A N
ARKANSAS A N LOUISIANA A B WISCONSIN A B
ILLINOIS A B MISSISSIPPI A B MICHIGAN A B
INDIANA A B OHIO A N KENTUCKY A N
TENNESSEE A N ALABAMA A N NEW YORK A N
VERMONT A B NEW HAMP A N MAINE A B
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 A
N CAROLINA A A S CAROLINA A A GEORGIA A N
FL PNHDL A N FL PENIN A A AK N SLOPE A N
AK ALEUTIAN N N AK WESTERN B B AK INT BSN N N
AK S INT N N AK SO COAST N N AK PNHDL N 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.
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