308
FXUS06 KWBC 171940
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 17 2024
6-10 DAY OUTLOOK FOR SEP 23 - 27 2024
A STRONG ANOMALOUS RIDGE STRETCHING FROM NORTHEASTERN CANADA SOUTHWARD INTO
MUCH OF THE EASTERN CONTIGUOUS UNITED STATES (CONUS) IS EXPECTED TO REMAIN IN
PLACE THROUGH THE 6 TO 10 DAY PERIOD AND GRADUALLY WEAKEN. 500-HPA HEIGHT
ANOMALIES ARE FORECAST TO AVERAGE AT LEAST +30 DM OVER SOUTHERN BAFFIN ISLAND,
AND THE CANADIAN OPERATIONAL MODEL SHOWS A 582 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 LOW, WITH A BROAD ARRAY OF POSSIBILITIES SHOWN IN THE
ENSEMBLES. MEANWHILE, A MID-LEVEL TROUGH OVER WESTERN NORTH AMERICA SHOULD
DRIFT EASTWARD. SLOW WEAKENING IS EXPECTED, BUT TODAY’S GUIDANCE HANGS ON TO
THIS FEATURE LONGER THAN YESTERDAY, TRACKING IT INTO THE EASTERN CONUS BEFORE
IT FADES LATE IN THE PERIOD. THE ENSEMBLE MEANS ARE NOT IN GOOD AGREEMENT ON
THE EVOLUTION OF THIS WEAK MID-LEVEL TROUGH, SO A COMPROMISE OF THE GUIDANCE
WAS USED. THERE ARE ADDITIONAL INCONSISTENCIES FARTHER WEST. ALL GUIDANCE SHOWS
A STRONG TROUGH OVER OR NEAR ALASKA ON DAY 6. THEREAFTER, THE GEFS BROADENS THE
TROUGH AND PUSHES IT EASTWARD, BRINGING BELOW-NORMAL 400-HPA HEIGHTS INTO
WESTERN CANADA AND THE NORTHWESTERN CONUS. IN CONTRAST, THE CANADIAN AND
EUROPEAN ENSEMBLE MEANS KEEP A STRONGER TROUGH GENERALLY IN PLACE, WHICH HELPS
TO BUILD POSITIVE MID-LEVEL HEIGHT ANOMALIES DOWNSTREAM, RESULTING IN BROAD
MID-LEVEL RIDGING WITH AN AXIS FROM THE SOUTHWEST THROUGH THE NORTHERN ROCKIES.
THE GEFS IS MORE CONSISTENT WITH YESTERDAY, BUT THE PREPONDERANCE OF THE
GUIDANCE FAVORS RIDGING IN THE WESTERN CONUS, AND THE OFFICIAL FORECAST HAS
BEEN SHADED IN THIS DIRECTION, ALTHOUGH THE GEFS SOLUTION IS NOT DISCARDED.
OVERALL, THESE CHANGES ARE EXPECTED TO RESULT IN A SLIGHTLY LESS AMPLIFIED
PATTERN ACROSS NORTH AMERICA BY DAY 10, 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
PATTERN WITH NEAR- TO ABOVE-NORMAL 500-HPA HEIGHTS IS FORECAST FOR HAWAII, WITH
HIGH SURFACE PRESSURE TO THE NORTH KEEPING CONSISTENT EASTERLY WINDS ACROSS THE
ISLAND CHAIN, CONSISTENT WITH MOST GUIDANCE.
DESPITE UNCERTAINTIES IN THE EVOLUTION OF UNSETTLED WEATHER IN THE SOUTHEAST
AND THE POTENTIAL MID-LEVEL RIDGING IN THE WESTERN CONUS, THE TOOLS DERIVED
FROM THE ENSEMBLE MEANS ARE IN FAIR TO GOOD AGREEMENT, BUT WITH SOME NOTABLE
EXCEPTIONS. IN ADDITION TO DIFFERENCES IN THE MODEL SOLUTIONS, ADDITIONAL
UNCERTAINTY COMES FROM DIFFERENCES BETWEEN THE RAW AND BIAS-CORRECTED
TEMPERATURE AND PRECIPITATION OUTPUT 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. WITH THE OFFICIAL FORECAST FAVORING THE DEVELOPMENT OF A BROAD
MID-LEVEL RIDGE OVER THE INTERIOR WEST, CHANCES FOR ABOVE-NORMAL TEMPERATURES
ARE INCREASED FROM YESTERDAY IN THE NORTHWEST. MEANWHILE, NEAR- OR BELOW-NORMAL
TEMPERATURES ARE FAVORED IN PARTS OF THE EASTERN SEABOARD. 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 ALSO CONSIDERABLE
UNCERTAINTY ACROSS ALASKA, WHERE RAW AND BIAS-CORRECTED NUMBERS SHOW COLDER
THAN NORMAL CONDITIONS COVERING MOST OR ALL OF THE STATE WHILE THE REFORECAST
AND CALIBRATED OUTPUTS LEAN TOWARD WARMER THAN NORMAL WEATHER IN SOUTHEASTERN
ALASKA AND THE EASTERN MAINLAND. 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 STRONG STORMS ARE EXPECTED
TO IMPACT EASTERN ALASKA, BUT BECAUSE OF UNCERTAINTIES IN THE EVOLUTION AND
ORIENTATION OF SURFACE LOW PRESSURE, VARIABLE TEMPERATURES WILL LIKELY END UP
NEAR NORMAL AVERAGED ACROSS THE PERIOD. WARMER THAN NORMAL WEATHER IS FAVORED
OVER THE NORTHWESTERN HALF OF HAWAII, CONSISTENT WITH THE CANADIAN ENSEMBLE
MEANS, THE GEFS, AND THE CONSOLIDATION. THE EUROPEAN ENSEMBLE MEAN SHOWS COOLER
WEATHER ACROSS THE ISLANDS, BUT THIS IS NOT CONSISTENT WITH THE EXPECTED
MID-LEVEL PATTERN.
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 60 PERCENT IN SOUTHERN
FLORIDA, WHERE GUIDANCE IS IN GOOD AGREEMENT SHOWING UNUSUALLY HEAVY RAIN.
ENHANCED CHANCES FOR WETTER THAN NORMAL WEATHER EXCEED 50 PERCENT FARTHER NORTH
ALONG THE SOUTH ATLANTIC COAST. CHANCES FOR UNUSUALLY HEAVY PRECIPITATION ALSO
EXCEED 60 PERCENT 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, ENHANCED CHANCES FOR SURPLUS
PRECIPITATION HAVE BEEN REMOVED IN A SWATH FROM THE NORTHWEST TO THE NORTHERN
GREAT PLAINS DUE TO THE MID-LEVEL RIDGE EXPECTED TO BUILD ACROSS THE REGION,
WHICH SHOULD INHIBIT PRECIPITATION LATER IN THE PERIOD. BELOW-NORMAL
PRECIPITATION IS FAVORED OVER NEW ENGLAND CLOSEST TO THE GREATEST 500-HPA
POSITIVE HEIGHT ANOMALIES AND ACROSS THE SOUTHERN PLAINS AND MUCH OF THE WEST
OUTSIDE OF THE DESERTS UNDER THE DEVELOPING RIDGE. THE CENTRAL GULF COAST IS AN
AREA OF UNCERTAINTY. RAW ENSEMBLE MEAN OUTPUTS FAVOR LIGHTER THAN NORMAL
RAINFALL WHILE REFORECAST TOOLS CALL FOR WETTER CONDITIONS. SINCE THIS AREA
COULD BE AFFECTED IF ONE OR MORE STORMS IMPACTING THE SOUTHEAST TRACK FARTHER
WEST, THE FORECAST SPLITS THE DIFFERENCE, FAVORING NEITHER PRECIPITATION
EXTREME. ENHANCED CHANCES FOR ABNORMALLY DRY CONDITIONS ALSO COVER WESTERN
ALASKA, WHICH WILL BE UNDER OR UPSTREAM FROM THE MEAN 500-HPA TROUGH.
MEANWHILE, WEAK CYCLONIC MID-LEVEL FLOW INCREASES THE ODDS FOR SURPLUS
PRECIPITATION OVER CENTRAL AND WESTERN HAWAII.
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 50% OF TODAY'S 6Z GFS
ENSEMBLE MEAN CENTERED ON DAY 8, 15% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN
CENTERED ON DAY 8, 20% OF TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8, AND
15% OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON DAY 8
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: AVERAGE, 3 OUT OF 5, WITH LESS
AGREEMENT ON THE EVOLUTION OF THE MID-LEVEL PATTERN THAN YESTERDAY, AND
SIGNIFICANT AREAS WHERE THE DISPARATE TEMPERATURE AND PRECIPITATION TOOLS ARE
IN POOR AGREEMENT.
8-14 DAY OUTLOOK FOR SEP 25 - OCT 01, 2024
TODAY, MODELS SHOW MORE DEAMPLIFICATION OF THE MID-LEVEL PATTERN LATER WEEK-2
THAN WAS INDICATED YESTERDAY, BUT IN THE MEAN, MID-LEVEL FEATURES SHOULD REMAIN
APPROXIMATELY IN PLACE WHILE HEIGHTS SLOWLY MOVE CLOSER TO NORMAL. DUE TO THE
MAGNITUDE OF THE CHANGES FORECAST BY THE DETERMINISTIC MODELS, THE
DEAMPLIFICATION SHOWN BY THE MODELS PROBABLY REFLECTS A PATTERN ADJUSTMENT, AND
AREN’T JUST AN ARTIFACT OF GROWING UNCERTAINTIES INHERENT TO LONGER-RANGE
ENSEMBLES. BY THE END OF WEEK-2, NONDESCRIPT FLOW IS SHOWN BY MOST
DETERMINISTIC MODELS THROUGHOUT NORTH AMERICA, WITH WIDESPREAD NEAR- OR
ABOVE-NORMAL 500-HPA HEIGHTS. MID-LEVEL TROUGHING IS EXPECTED TO WEAKEN
SIGNIFICANTLY NEAR ALASKA OVER THE COURSE OF WEEK-2 WHILE FARTHER EAST,
VESTIGES OF MODERATE TO STRONG MID-LEVEL RIDGING SHOULD RESULT IN POSITIVE
500-HPA HEIGHT ANOMALIES BEING SLIGHTLY HIGHER IN NORTHEASTERN CANADA AND JUST
NORTH OF THE AMERICAN ROCKIES THAN IN SURROUNDING AREAS, ALBEIT WITH MUCH LOWER
MAGNITUDE. STILL, THE FAVORABLE SET-UP FOR STORM DEVELOPMENT WILL CONTINUE IN
THE SOUTHEAST, INCLUDING POSSIBLE TROPICAL OR SUBTROPICAL CYCLONE DEVELOPMENT.
THIS PATTERN SHOULD KEEP ABOVE-NORMAL TEMPERATURES OVER MOST OF THE CONUS
OUTSIDE THE SOUTH ATLANTIC REGION AND ADJACENT AREAS, WHERE UNSETTLED WEATHER
SHOULD KEEP DAYTIME TEMPERATURES CLOSER TO NORMAL. MEANWHILE, 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
CENTRAL AND WESTERN ALASKAN MAINLAND NEAR OR UPSTREAM OF A DEAMPLIFYING
MID-LEVEL TROUGH.
ENHANCED CHANCES FOR WET WEATHER CONTINUE IN BOTH SOUTHEASTERN ALASKA
DOWNSTREAM FROM A MID-LEVEL TROUGH, AND IN THE SOUTHEASTERN CONUS WHERE TOOLS
CONTINUE TO DEPICT 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, WHICH SEEMS SLIGHTLY MORE LIKELY THAN YESTERDAY. MEANWHILE, DRIER
THAN NORMAL WEATHER IS FAVORED ACROSS A LARGE AREA COVERING MOST OF THE CENTRAL
AND WESTERN CONUS UNDER WEAKENING MID-LEVEL RIDGING AND NONDESCRIPT 500-HPA
FLOW. SLIGHTLY INCREASED ODDS FOR HEAVIER THAN NORMAL RAINFALL REMAIN IN PLACE
OVER WESTERN HAWAII.
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 55% OF TODAY'S 6Z GFS
ENSEMBLE MEAN CENTERED ON DAY 11, 15% OF TODAY'S OPERATIONAL 6Z GFS CENTERED ON
DAY 11, 15% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 11, AND 15% OF
TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON DAY 11
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: BELOW AVERAGE, 2 OUT OF 5, DUE THE
INHERENT UNCERTAINTIES INVOLVED IN FORECASTING A MID-LEVEL PATTERN CHANGE,
ALONG WITH CONTINUED AREAS OF DISAGREEMENT AMONG THE 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 - 20070930 - 19880919
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:
20070922 - 20040921 - 20070927 - 20050904 - 19850916
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 23 - 27 2024
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON A B OREGON A B NRN CALIF A B
SRN CALIF A N IDAHO A B NEVADA A B
W MONTANA A B E MONTANA A N WYOMING A B
UTAH A B ARIZONA A B COLORADO A N
NEW MEXICO A B N DAKOTA A A S DAKOTA A A
NEBRASKA N A KANSAS N A OKLAHOMA A A
N TEXAS A N S TEXAS A B 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 N
INDIANA A A OHIO A A KENTUCKY A A
TENNESSEE A A ALABAMA N A NEW YORK A N
VERMONT A B NEW HAMP A B MAINE A B
MASS N N CONN N N RHODE IS N N
PENN A N NEW JERSEY N A W VIRGINIA A A
MARYLAND N A DELAWARE N A VIRGINIA N A
N CAROLINA N A S CAROLINA N A GEORGIA N A
FL PNHDL N A FL PENIN A A AK N SLOPE B N
AK ALEUTIAN B N AK WESTERN B B AK INT BSN B A
AK S INT B A AK SO COAST N A AK PNHDL N A
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 25 - OCT 01, 2024
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON A N OREGON A B NRN CALIF A B
SRN CALIF A N IDAHO A B NEVADA A B
W MONTANA N B E MONTANA A B WYOMING A B
UTAH A B ARIZONA A B COLORADO A B
NEW MEXICO A B N DAKOTA A B S DAKOTA A B
NEBRASKA A B KANSAS A B OKLAHOMA A B
N TEXAS A B S TEXAS A B W TEXAS A B
MINNESOTA A B IOWA A B MISSOURI A B
ARKANSAS A N LOUISIANA A N WISCONSIN A B
ILLINOIS A N MISSISSIPPI A A MICHIGAN A B
INDIANA A N OHIO A N KENTUCKY A A
TENNESSEE A A ALABAMA N A NEW YORK A A
VERMONT A N NEW HAMP A A MAINE A N
MASS A A CONN A A RHODE IS A A
PENN A A NEW JERSEY A A W VIRGINIA A A
MARYLAND N A DELAWARE N A VIRGINIA N 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 B AK WESTERN B B AK INT BSN N A
AK S INT B A AK SO COAST B 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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