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FXUS06 KWBC 161949
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EDT MON SEPTEMBER 16 2024
6-10 DAY OUTLOOK FOR SEP 22 - 26 2024
A STRONG ANOMALOUS RIDGE STRETCHING FROM NORTHEASTERN CANADA SOUTHWARD INTO
MUCH OF THE EASTERN CONTIGUOUS UNITED STATES (CONUS) IS EXPECTED TO PERSIST
THROUGH THE 6 TO 10 DAY PERIOD. 500-HPA HEIGHT ANOMALIES ARE FORECAST TO
AVERAGE AT LEAST +30 DM OVER SOUTHERN BAFFIN ISLAND, AND THE CANADIAN ENSEMBLE
MEAN SHOWS A 579 DM CLOSED 500-HPA HEIGHT CIRCULATION ON DAY 6. TO THE EAST AND
SOUTH, AN AREA OF NEAR- OR BELOW-NORMAL 500-HPA HEIGHTS IS FORECAST OVER AND
NEAR THE SOUTHEASTERN CONUS. INDIVIDUAL MEMBERS OF THE ENSEMBLES SHOW THE
POTENTIAL FOR TROPICAL OR SUBTROPICAL CYCLONE DEVELOPMENT, BUT CONFIDENCE IN
THE PLACEMENT AND TIMING OF ANY SYSTEM THAT MIGHT DEVELOP IS HIGHLY UNCERTAIN,
WITH A BROAD ARRAY OF POSSIBILITIES SHOWN IN THE ENSEMBLES. MEANWHILE, A
MID-LEVEL TROUGH OVER WESTERN NORTH AMERICA SHOULD DRIFT EASTWARD AND DISSIPATE
WHILE A SIMILAR FEATURE REAMPLIFIES OVER OR NEAR WESTERN MAINLAND ALASKA,
PROLONGING UNSETTLED WEATHER IN THE SOUTHEASTERN PART OF THE STATE. OVERALL,
THESE CHANGES ARE EXPECTED TO RESULT IN A SLIGHTLY LESS AMPLIFIED PATTERN
ACROSS NORTH AMERICA, BUT WITH STRONG POSITIVE HEIGHT ANOMALIES STILL CENTERED
IN NORTHEASTERN CANADA, AND A SIGNIFICANT TROUGH AFFECTING ALASKA, WITH ITS
AXIS THROUGH THE WESTERN PART OF THE STATE. A WEAK BUT CLOSED 500-HPA
CIRCULATION IS ANTICIPATED WEST OF HAWAII WHILE ABOVE-NORMAL HEIGHTS PREVAIL
NORTH OF THE ISLAND CHAIN. MOST OF THE GUIDANCE DEPICTS THIS GENERAL SCENARIO,
WITH DIFFERENCES IN THE LOCATION AND AMPLITUDE OF INDIVIDUAL FEATURES INHERENT
TO LONGER-RANGE FORECASTS.
DESPITE THE GOOD MODEL AGREEMENT ON THE MID-LEVEL PATTERN, THE TOOLS DERIVED
FROM THE ENSEMBLE MEANS SHOW SOME NOTABLE DIFFERENCES IN SOME AREAS. MOST OF
THE UNCERTAINTY COMES FROM DIFFERENCES BETWEEN THE RAW AND BIAS-CORRECTED
TEMPERATURE AND PRECIPITATION ON ONE HAND, AND THE CALIBRATED AND REFORECAST
DATA ON THE OTHER. THERE IS GENERAL AGREEMENT THAT ABOVE-NORMAL TEMPERATURES
WILL PREVAIL ACROSS MOST OF THE CONUS, WITH THE BEST CHANCES FOR ABOVE-NORMAL
TEMPERATURES ACROSS PART OF THE GREAT LAKES AND INTERIOR NORTHEAST. MEANWHILE,
NEAR- OR BELOW-NORMAL TEMPERATURES ARE FAVORED IN PARTS OF THE NORTHWEST AND
EAST COAST. THE REFORECASTS ARE WARMER IN THESE AREAS THAN THE RAW AND
BIAS-CORRECTED TOOLS, BUT THE COOLER SOLUTIONS ARE MORE CONSISTENT WITH THE
MID-LEVEL PATTERN. IN ADDITION, CLOUDS AND PRECIPITATION IN AND NEAR THE
SOUTHEASTERN CONUS HAVE THE POTENTIAL TO KEEP TEMPERATURES LOWER THAN ANY OF
THE TOOLS INDICATE. THERE IS CONSIDERABLE UNCERTAINTY ACROSS ALASKA, WHERE RAW
AND BIAS-CORRECTED NUMBERS SHOW COLDER THAN NORMAL CONDITIONS COVER MOST OR ALL
OF THE STATE WHILE THE REFORECAST AND CALIBRATED OUTPUTS LEAN TOWARD WARMER
THAN NORMAL WEATHER. WITH MID-LEVEL TROUGHING AND BELOW-NORMAL 500-HPA HEIGHTS
EXPECTED FOR MOST OF THE PERIOD, THE COLDER SOLUTIONS WOULD BE FAVORED IN
WESTERN ALASKA. FARTHER EAST, ONE OR MORE STORMS ARE EXPECTED TO IMPACT EASTERN
ALASKA, BUT BECAUSE OF UNCERTAINTIES IN THE EVOLUTION AND ORIENTATION OF
SURFACE LOW PRESSURE, CONDITIONS AVERAGING CLOSE TO NORMAL SEEM MOST LIKELY.
WARMER THAN NORMAL WEATHER IS FAVORED OVER THE NORTHWESTERN HALF OF HAWAII,
CLOSER TO POSITIVE MID-LEVEL HEIGHT ANOMALIES AND CONSISTENT WITH THE
CONSOLIDATION.
IN THE SOUTHEASTERN CONUS, THERE IS A LOT OF UNCERTAINTY REGARDING THE
FORMATION AND EVOLUTION OF SURFACE LOW PRESSURE SYSTEMS, INCLUDING THE
POSSIBILITY FOR TROPICAL OR SUBTROPICAL CYCLONE DEVELOPMENT. HOWEVER, MOST
POTENTIAL SCENARIOS WOULD RESULT IN HEAVY RAIN AFFECTING AT LEAST PART OF THE
SOUTHEAST. CHANCES FOR ABNORMALLY WET WEATHER EXCEED 50 PERCENT CLOSE TO THE
SOUTHEASTERN CONUS COAST. SIMILAR CHANCES FOR UNUSUALLY HEAVY PRECIPITATION ARE
FORECAST IN SOUTHEASTERN ALASKA, WHERE THE EVOLUTION OF THE MID-LEVEL HEIGHT
PATTERN FAVORS ONE OR MORE LOW PRESSURE SYSTEMS BRINGING A PROLONGED PERIOD OF
STORMY WEATHER TO THE REGION. ELSEWHERE, CHANCES FOR ABOVE-NORMAL PRECIPITATION
ARE FORECAST IN A SWATH FROM THE NORTHWEST TO THE NORTHERN GREAT PLAINS FROM
THE DISSIPATING MID-LEVEL TROUGH TO THE WEST, AND WEAK CYCLONIC MID-LEVEL FLOW
INCREASES THE ODDS FOR SURPLUS PRECIPITATION OVER WESTERN HAWAII AS WELL. THE
GULF COAST IS AN AREA OF UNCERTAINTY. RAW ENSEMBLE MEAN OUTPUTS FAVOR LIGHTER
THAN NORMAL RAINFALL WHILE REFORECAST TOOLS FORECAST WETTER CONDITIONS. SINCE
THIS AREA COULD BE AFFECTED BY ANY STORM SYSTEMS IMPACTING THE SOUTHEAST, THE
FORECAST SPLITS THE DIFFERENCE, FAVORING NEITHER PRECIPITATION EXTREME.
MEANWHILE, DRIER THAN NORMAL CONDITIONS ARE EXPECTED IN THE GREAT LAKES AND
NORTHEAST UNDER STRONG MID-LEVEL HIGH PRESSURE, AND FROM THE SOUTHWEST TO THE
SOUTHERN GREAT PLAINS UNDER ANTICYCLONIC MID-LEVEL WINDS SOUTH OF A MID-LEVEL
TROUGH. ENHANCED CHANCES FOR ABNORMALLY DRY CONDITIONS ALSO COVER WESTERN
ALASKA, WHICH WILL BE UNDER OR UPSTREAM FROM THE MEAN 500-HPA TROUGH.
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, 13% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8, 24% OF
TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8, AND 13% 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, WITH
VERY GOOD AGREEMENT ON THE EVOLUTION OF THE UPPER-LEVEL PATTERN OFFSET BY AREAS
OF SIGNIFICANT DISAGREEMENT IN TEMPERATURE AND PRECIPITATION BETWEEN THE RAW
MODEL OUTPUT AND THE REFORECAST TOOLS.
8-14 DAY OUTLOOK FOR SEP 24 - 30 2024
THE PATTERN PREVAILING DURING THE 6 TO 10 DAY PERIOD IS EXPECTED TO PERSIST
THROUGH WEEK-2. MOST MODELS SHOW CLOSER TO NORMAL 500-HPA HEIGHTS, BUT THE
LOCATION OF THE PRIMARY MID-LEVEL FEATURES PERSIST. IT IS UNCLEAR WHETHER THE
DEAMPLIFICATION SHOWN BY THE MODELS REFLECTS A PATTERN ADJUSTMENT, OR IS
INDICATIVE OF GROWING UNCERTAINTIES INHERENT IN LONGER-RANGE MODELS FORECASTS.
IN ANY CASE, THE PRIMARY FEATURES AFFECTING NORTH AMERICA REMAIN ESSENTIALLY IN
PLACE, WITH A STRONG TROUGH SLOWLY WEAKENING OVER ALASKA, A STRONG RIDGE IN
CENTRAL NORTH AMERICA WITH A LARGE POSITIVE 500-HPA HEIGHT ANOMALY IN
NORTHEASTERN CANADA, NONDESCRIPT FLOW ACROSS THE WESTERN CONUS AND ADJACENT
CANADA BETWEEN THESE TWO FEATURES, AND A FAVORABLE SET-UP FOR STORM DEVELOPMENT
IN THE SOUTHEAST.
THIS PATTERN SHOULD KEEP ABOVE-NORMAL TEMPERATURES OVER MOST OF THE CONUS,
EXCLUDING ONLY PARTS OF THE NORTHWEST, WHICH WILL BE UNDER THE INFLUENCE OF A
DISSIPATING MID-LEVEL TROUGH FOR THE FIRST DAY OR TWO. THERE ARE REDUCED ODDS
FOR ABOVE-NORMAL TEMPERATURES IN THE SOUTHEAST DUE TO THE EXPECTED UNSETTLED
WEATHER, AND SLIGHTLY ENHANCED ODDS FOR WARMER THAN NORMAL CONDITIONS CONTINUE
OVER THE WESTERN PART OF HAWAII. THE ONLY AREA WITH INCREASED CHANCES FOR
SUBNORMAL TEMPERATURES IS THE WESTERN HALF OF ALASKA NEAR OR UPSTREAM OF THE
MEAN MID-LEVEL TROUGH AXIS.
THE PATTERN SHOULD CONTINUE TO FAVOR WET WEATHER IN BOTH SOUTHEASTERN ALASKA
DOWNSTREAM FROM A MID-LEVEL TROUGH, AND IN THE SOUTHEASTERN CONUS WHERE TOOLS
CONTINUE TO INDICATE THE POTENTIAL FOR UNSETTLED WEATHER, INCLUDING THE
POTENTIAL DEVELOPMENT OF A TROPICAL OR SUBTROPICAL CYCLONE. GUIDANCE REMAINS
INCONSISTENT IN THE CENTRAL GULF COAST REGION, BUT ODDS LEAN TOWARD NEAR- OR
ABOVE-NORMAL PRECIPITATION IN THE OFFICIAL FORECAST DUE TO THE POTENTIAL
INFLUENCE OF STORMS AFFECTING THE SOUTHEAST. MEANWHILE, DRIER THAN NORMAL
WEATHER IS FAVORED FOR PORTIONS OF THE NORTHEASTERN CONUS, AND IN A SWATH FROM
THE SOUTHERN PLAINS TO THE CENTRAL FAR WEST, SIMILAR TO THE 6 TO 10 DAY PERIOD.
THE WEAK BUT PERSISTENT MID-LEVEL CIRCULATION WEST OF HAWAII SHOULD KEEP
SLIGHTLY INCREASED ODDS FOR HEAVIER THAN NORMAL RAINFALL OVER THE WESTERN HALF
OF THE STATE.
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, 25% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 11, AND 25%
OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON DAY 11
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOUT AVERAGE, 3 OUT OF 5, WITH
GOOD MODEL AGREEMENT ON THE OVERALL PATTERN OFFSET BY UNCERTAINTIES IN THE
AMPLITUDE OF THE MID-LEVEL PATTERN AND AREAS WITH INCONSISTENT TEMPERATURE AND
PRECIPITATION TOOLS.
FORECASTER: RICH TINKER
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 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:
20050905 - 20040920 - 20070923 - 19880918 - 20070929
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:
20040921 - 20050907 - 20070927 - 20070922 - 19850916
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 22 - 26 2024
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON B A OREGON A N NRN CALIF A N
SRN CALIF A N IDAHO B N NEVADA A B
W MONTANA N A E MONTANA A A WYOMING N N
UTAH A B ARIZONA A B COLORADO A B
NEW MEXICO A B N DAKOTA A A S DAKOTA A A
NEBRASKA A A KANSAS A A OKLAHOMA A N
N TEXAS A N S TEXAS A B W TEXAS A N
MINNESOTA A A IOWA A A MISSOURI A A
ARKANSAS A N LOUISIANA A N WISCONSIN A A
ILLINOIS A A MISSISSIPPI A N MICHIGAN A B
INDIANA A N OHIO A B KENTUCKY A A
TENNESSEE A A ALABAMA A A NEW YORK A B
VERMONT A B NEW HAMP A B MAINE A B
MASS A N CONN N N RHODE IS N N
PENN A N NEW JERSEY N N W VIRGINIA A A
MARYLAND N A DELAWARE N A VIRGINIA A A
N CAROLINA N A S CAROLINA N A GEORGIA N A
FL PNHDL N A FL PENIN A A AK N SLOPE B A
AK ALEUTIAN B N AK WESTERN B B AK INT BSN B A
AK S INT N A AK SO COAST N A AK PNHDL N A
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 24 - 30 2024
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON N A OREGON A N NRN CALIF A B
SRN CALIF A N IDAHO N B NEVADA A B
W MONTANA N N E MONTANA A N WYOMING A B
UTAH A B ARIZONA A B COLORADO A B
NEW MEXICO A B N DAKOTA A N S DAKOTA A N
NEBRASKA A N KANSAS A N OKLAHOMA A A
N TEXAS A N S TEXAS A N W TEXAS A B
MINNESOTA A N IOWA A N MISSOURI A A
ARKANSAS A A LOUISIANA A N WISCONSIN A N
ILLINOIS A N MISSISSIPPI A A MICHIGAN A B
INDIANA A N OHIO A N KENTUCKY A A
TENNESSEE A A ALABAMA A A 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 A W VIRGINIA A A
MARYLAND A A DELAWARE A A VIRGINIA A A
N CAROLINA A A S CAROLINA N A GEORGIA N A
FL PNHDL N A FL PENIN A A AK N SLOPE N A
AK ALEUTIAN B N AK WESTERN B N AK INT BSN N A
AK S INT N A AK SO COAST N A 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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