323
FXUS06 KWBC 211902
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EDT THU SEPTEMBER 21 2023
6-10 DAY OUTLOOK FOR SEP 27 - OCT 01, 2023
THE 0Z/6Z GEFS AND 0Z ECMWF ENSEMBLE MEANS ARE IN GOOD AGREEMENT DEPICTING AN
AMPLIFIED 500-HPA TROUGH SHIFTING INLAND OVER THE WEST, WHILE THE 0Z CANADIAN
ENSEMBLE MEAN IS LESS AMPLIFIED WITH THIS TROUGH. GIVEN THEIR GOOD AGREEMENT
AND CONTINUITY, THE GEFS AND ECMWF MODEL SOLUTIONS ARE PREFERRED. A BROAD RIDGE
WITH LARGE POSITIVE 500-HPA HEIGHT DEPARTURES IS FORECAST OVER THE MIDDLE TO
HIGH LATITUDES OF EASTERN NORTH AMERICA. THIS LONGWAVE PATTERN FAVORS BELOW
(ABOVE) NORMAL TEMPERATURES ACROSS THE WESTERN (CENTRAL) CONTIGUOUS U.S.
(CONUS). THERE IS MORE UNCERTAINTY IN THE TEMPERATURE OUTLOOK FOR THE EASTERN
CONUS. MODEL SOLUTIONS CONTINUE TO FEATURE A MID-LEVEL TROUGH ACROSS THE
SOUTHEAST AND MID-ATLANTIC. THIS TROUGH ALONG WITH EASTERLY SURFACE FLOW
SUPPORTS NEAR NORMAL OR SLIGHTLY ELEVATED BELOW-NORMAL TEMPERATURE
PROBABILITIES FROM GEORGIA AND SOUTH CAROLINA NORTH TO SOUTHERN NEW ENGLAND.
FARTHER AWAY FROM THE INFLUENCE OF THIS MID-LEVEL TROUGH, ABOVE-NORMAL
TEMPERATURES ARE MORE LIKELY FOR NORTHERN NEW ENGLAND AND FLORIDA.
THE AMPLIFIED TROUGH FAVORS ABOVE-NORMAL PRECIPITATION ACROSS THE NORTHERN HALF
OF THE WESTERN CONUS WITH THE LARGEST PROBABILITIES (MORE THAN 60 PERCENT)
ACROSS THE PACIFIC NORTHWEST. DOWNSTREAM OF THIS TROUGH, SURFACE LOW
DEVELOPMENT IS LIKELY ACROSS THE HIGH PLAINS DURING THIS 5-DAY PERIOD. THIS
SURFACE LOW ALONG WITH A TRAILING COLD FRONT SUPPORTS ELEVATED ABOVE-NORMAL
PRECIPITATION PROBABILITIES ACROSS MUCH OF THE GREAT PLAINS, WITH A TRANSITION
TO NEAR NORMAL PRECIPITATION BECOMING MORE LIKELY FOR TEXAS. THE HIGHEST
UNCERTAINTY IN THE 6-10 DAY PRECIPITATION OUTLOOK EXISTS FROM THE MISSISSIPPI
VALLEY TO THE EAST COAST WHERE THE REFORECAST GEFS (DRIER) AND ECMWF (WETTER)
DIVERGE. BASED ON THE LARGE SURFACE HIGH ACROSS EASTERN NORTH AMERICA AND
UNCALIBRATED MODEL OUTPUT, THE DRIER GEFS REFORECAST TOOL IS PREFERRED.
HOWEVER, IN RESPONSE TO A SHORTWAVE TROUGH, THERE IS AN INCREASED POTENTIAL FOR
SURFACE LOW DEVELOPMENT OVER OR OFFSHORE OF THE CAROLINAS ON DAYS 6 AND 7 WHICH
FAVORS NEAR TO ABOVE-NORMAL PRECIPITATION ACROSS PARTS OF THE SOUTHEAST AND
SOUTHERN MID-ATLANTIC.
ABOVE NORMAL PRECIPITATION PROBABILITIES ARE SLIGHTLY ELEVATED FOR MUCH OF
ALASKA DUE TO THE 500-HPA TROUGH OVER THE EASTERN BERING SEA. ENSEMBLE MEAN
SOLUTIONS DEPICT NEAR NORMAL TEMPERATURES FOR MUCH OF ALASKA, ALTHOUGH
BELOW-NORMAL TEMPERATURES ARE FAVORED FOR SOUTHWESTERN ALASKA AND THE ALEUTIANS
CLOSER TO THE TROUGH AXIS.
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, AND 50% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO
GOOD AGREEMENT AND CONTINUITY BETWEEN THE GEFS AND ECMWF ENSEMBLE MEANS ON THE
LARGE-SCALE LONGWAVE PATTERN.
8-14 DAY OUTLOOK FOR SEP 29 - OCT 05, 2023
THE 0Z/6Z GEFS AND 0Z ECMWF ENSEMBLE MEANS REMAIN IN GOOD AGREEMENT WITH AN
AMPLIFIED TROUGH (RIDGE) OVER WESTERN (CENTRAL AND EASTERN) NORTH AMERICA. THE
MANUAL 500-HPA BLEND DEPICTS THE LARGEST POSITIVE HEIGHT DEPARTURES ACROSS THE
HIGHER LATITUDES OF CENTRAL AND EASTERN NORTH AMERICA. THIS LONGWAVE PATTERN
FAVORS BELOW-NORMAL TEMPERATURES ACROSS THE WESTERN THIRD OF THE CONUS, WHILE
ABOVE-NORMAL TEMPERATURES ARE LIKELY ALONG AND TO THE EAST OF THE CONTINENTAL
DIVIDE. PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES DECREASE ACROSS THE
MID-ATLANTIC AND SOUTHEAST DUE TO EASTERLY SURFACE FLOW, ESPECIALLY EARLY IN
WEEK-2.
THE AMPLIFIED TROUGH OVER THE WEST ENHANCES ABOVE-NORMAL PRECIPITATION
PROBABILITIES THROUGHOUT MUCH OF THE WEST AND GREAT PLAINS. THE ONE EXCEPTION
IS THE SOUTHWEST WHERE THE STORM TRACK IS WELL TO THE NORTH AND PRECIPITATION
ASSOCIATED WITH THE MONSOON ENDS. ALTHOUGH DIFFERENCES CONTINUE BETWEEN THE
REFORECAST GEFS (DRIER) AND ECMWF (WETTER) TOOLS FROM THE MISSISSIPPI VALLEY TO
THE EAST COAST, UNCALIBRATED MODEL OUTPUT AND STATISTICAL TOOLS ARE IN BETTER
AGREEMENT WITH ELEVATED CHANCES OF BELOW-NORMAL PRECIPITATION FOR THE GREAT
LAKES, OHIO VALLEY, NORTHEAST, AND A MAJORITY OF THE SOUTHEAST.
THE NATIONAL HURRICANE CENTER IS MONITORING A TROPICAL WAVE TO THE WEST OF THE
CABO VERDE ISLANDS AND A TROPICAL CYCLONE (TC) IS LIKELY TO DEVELOP ACROSS THE
MAIN DEVELOPMENT REGION OF THE ATLANTIC DURING THE NEXT WEEK. ALTHOUGH NEARLY
ALL OF THE GFS AND ECMWF ENSEMBLE MEMBERS RECURVE THIS POTENTIAL TC NORTHWARD
ACROSS THE CENTRAL ATLANTIC DURING WEEK-2, MANY OF THE GFS ENSEMBLE MEMBERS
HAVE IT TRACKING NEAR OR OVER THE U.S. VIRGIN ISLANDS AND PUERTO RICO LATER
NEXT WEEK.
A MEAN 500-HPA TROUGH AXIS IS FORECAST TO EXTEND FROM THE BERING STRAIT TO THE
ALEUTIANS WHICH SUPPORTS MODEST ONSHORE FLOW AND SLIGHTLY ELEVATED
PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION FOR A MAJORITY OF ALASKA.
TEMPERATURE TOOLS ARE IN GOOD AGREEMENT WITH A SLIGHT LEAN TOWARDS BELOW
(ABOVE) NORMAL TEMPERATURES ACROSS SOUTHWESTERN ALASKA AND THE ALEUTIANS
(NORTHEASTERN ALASKA).
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, AND 50% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 11
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO
GOOD MODEL AGREEMENT ON AN AMPLIFIED, WELL-ESTABLISHED LONGWAVE PATTERN.
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
OCTOBER 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:
20091001 - 19960919 - 19870915 - 19960924 - 20050905
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:
19960923 - 20090928 - 19880918 - 20091003 - 19960918
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 27 - OCT 01, 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 A A WYOMING A A
UTAH A A ARIZONA A B COLORADO A N
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 N W TEXAS A N
MINNESOTA A A IOWA A A MISSOURI A N
ARKANSAS A B LOUISIANA A N WISCONSIN A B
ILLINOIS A B MISSISSIPPI A N MICHIGAN A B
INDIANA A B OHIO A B KENTUCKY A B
TENNESSEE N B ALABAMA A N NEW YORK A B
VERMONT A B NEW HAMP A B MAINE A B
MASS A B CONN N B RHODE IS N B
PENN N B NEW JERSEY N B W VIRGINIA N B
MARYLAND B B DELAWARE B N VIRGINIA N N
N CAROLINA B A S CAROLINA N A GEORGIA N N
FL PNHDL A N FL PENIN A N AK N SLOPE N N
AK ALEUTIAN B N AK WESTERN B N AK INT BSN N A
AK S INT N N AK SO COAST N N AK PNHDL N N
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 29 - OCT 05, 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 A A WYOMING A A
UTAH B A ARIZONA B B 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 N S TEXAS A N W TEXAS A A
MINNESOTA A A IOWA A A MISSOURI A N
ARKANSAS A B LOUISIANA A B WISCONSIN A N
ILLINOIS A B MISSISSIPPI A B MICHIGAN A B
INDIANA A B OHIO A B KENTUCKY A B
TENNESSEE A B ALABAMA A B 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 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 N AK N SLOPE N N
AK ALEUTIAN B N AK WESTERN N A AK INT BSN N A
AK S INT N A AK SO COAST N A AK PNHDL N 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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