824
FXUS06 KWBC 281902
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 28 2023
6-10 DAY OUTLOOK FOR OCT 04 - 08 2023
THERE ARE LARGE DIFFERENCES BETWEEN THE FORECAST GUIDANCE FROM YESTERDAY AND
TODAY. THE GEFS, ECMWF, AND CANADIAN ENSEMBLES FORECAST A STRENGTHENING AREA OF
POSITIVE 500-HPA HEIGHT ANOMALIES OFF THE WESTERN CONTIGUOUS U.S. CONUS DURING
WEEK-1. THIS HAS IMPACTED THE FORECAST FOR THE 6 TO 10 AND WEEK-2 FORECASTS
ACROSS MUCH OF NORTH AMERICA. THE STRONGER MID-LEVEL HIGH PRESSURE IS ABLE TO
BREAK AN OMEGA-LIKE BLOCK THAT HAS BEEN CENTERED OVER NORTH AMERICA AND
INTRODUCES A MORE PROGRESSIVE FORECAST RELATIVE TO YESTERDAY. THEREFORE, DURING
THE 6 TO 10 DAY PERIOD, AN AREA OF POSITIVE 500-HPA HEIGHT ANOMALIES IS
FORECAST OVER THE WESTERN CONUS, THE NORTHEAST, AND MUCH OF ALASKA DURING THE 6
TO 10 DAY PERIOD. NEAR TO BELOW-NORMAL 500-HPA HEIGHTS ARE FORECAST IN THE
CENTRAL PORTIONS OF THE CONUS.
AS WITH THE HEIGHT FORECAST, THERE ARE SIGNIFICANT DIFFERENCES IN THE
TEMPERATURE FORECAST ACROSS THE COUNTRY. THE BIGGEST CHANGES ARE IN THE WESTERN
CONUS. WITH A MUCH STRONGER MID-LEVEL RIDGE DEVELOPING AND DISPLACING THE
THROUGH THAT HAD BEEN FORECAST ACROSS THE WEST, TEMPERATURES ARE FAVORED TO BE
ABOVE-NORMAL ACROSS THE WEST COAST WHILE INTERIOR PORTIONS OF THE WEST THROUGH
THE HIGH PLAINS ARE FAVORED TO BE NEAR TO BELOW-NORMAL. MEANWHILE, ACROSS THE
EAST, ABOVE-NORMAL TEMPERATURES REMAIN FAVORED DURING THE 6 TO 10 DAY PERIOD,
ALTHOUGH PROBABILITIES ARE SIGNIFICANTLY REDUCED RELATIVE TO YESTERDAY. IN
ALASKA, BELOW-NORMAL TEMPERATURES ARE STILL FAVORED ACROSS MUCH OF THE STATE.
HOWEVER, CHANCES ARE REDUCED ACROSS SOUTHEAST AND THE COPPER RIVER BASIN
RELATIVE TO YESTERDAY AS MORE ONSHORE FLOW IS FAVORED, PARTICULARLY BY THE END
OF THE PERIOD. OVERALL, TOOLS ARE IN RELATIVELY FAIR AGREEMENT TODAY ACROSS THE
COUNTRY, BUT THEY ARE QUITE DIFFERENT RELATIVE TO YESTERDAY.
PRECIPITATION LIKEWISE SEES BIG CHANCES RELATIVE TO YESTERDAY, WITH LITTLE
CONFIDENCE IN THE EVOLUTION OF THE PATTERN. THE STRONGEST PROBABILITIES FOR
ABOVE-NORMAL PRECIPITATION ARE IN PORTIONS OF TEXAS WHERE REFORECAST AND RAW
GUIDANCE ARE IN THE BEST AGREEMENT WITH THE POTENTIAL FOR A STATIONARY FRONT TO
BE DRAPED ACROSS THIS REGION. NORTH OF THIS AREA, WHEREAS YESTERDAY THE HIGH
PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION STRETCHED INTO THE NORTHERN
PLAINS, NEAR-NORMAL PRECIPITATION IS NOW FAVORED OVER THIS REGION AS A DRYING
TREND IS LIKELY. THE NEWLY ESTABLISHED HIGH PRESSURE ACROSS THE WEST, IS LIKELY
TO LIMIT THE AMOUNT OF MOISTURE AVAILABLE ACROSS THE NORTHERN AND CENTRAL
PLAINS. SIMILAR TO THE TEMPERATURE PATTERN, THE FORECAST FOR PRECIPITATION
UNDERGOES A LARGE SHIFT, FROM ABOVE-NORMAL FORECAST YESTERDAY, TO BELOW-NORMAL
FORECAST ACROSS MUCH OF THE WEST TODAY WITH STRONG POSITIVE 500-HPA HEIGHT
ANOMALIES FORECAST ACROSS THE WEST COAST LIMITING ONSHORE FLOW AND PUSHING THE
STRONGEST MOISTURE FLOW FURTHER NORTH. IN THE EASTERN CONUS, REFORECAST TOOLS
AND RAW GUIDANCE ARE MIXED AS POSITIVE 500-HPA HEIGHT ANOMALIES CONTINUE TO BE
FAVORED BUT AS THE PATTERN BECOMES MORE PROGRESSIVE THERE ARE MORE CHANCES FOR
PRECIPITATION TO DEVELOP. A SMALL AREA OF ELEVATED ABOVE-NORMAL PRECIPITATION
PROBABILITIES IS FAVORED IN THE NORTHERN GREAT LAKES WHERE AN EXITING STORM MAY
BRING INCREASED PRECIPITATION DURING THE PERIOD. ALONG THE MID-ATLANTIC COAST,
A SMALL AREA OF ABOVE-NORMAL IS FAVORED WHERE A COASTAL STORM SYSTEM MAY
DEVELOP.
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 15% OF TODAY'S 0Z GFS
ENSEMBLE MEAN CENTERED ON DAY 8, 25% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED
ON DAY 8, 40% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN 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: BELOW AVERAGE, 2 OUT OF 5, LARGE
CHANGES IN THE 500-HPA HEIGHT PATTERN RELATIVE TO YESTERDAY SIGNIFICANTLY
REDUCE CONFIDENCE. THIS IS OFFSET SLIGHTLY BY FAIR AGREEMENT AMONG TODAY’S
FORECAST GUIDANCE.
8-14 DAY OUTLOOK FOR OCT 06 - 12 2023
AS WITH THE 6 TO 10 DAY FORECAST, THE WEEK-2 FORECAST HAS LARGE DIFFERENCES
BETWEEN THE FORECAST GUIDANCE FROM YESTERDAY AND TODAY. THE GEFS, ECMWF, AND
CMCE ARE ALL IN GOOD AGREEMENT ON THE 500-HPA HEIGHT PATTERN ACROSS NORTH
AMERICA, HOWEVER, THEY WERE ALSO IN GOOD AGREEMENT YESTERDAY. AS DISCUSSED IN
THE 6 TO 10 DAY FORECAST, THE CASCADING DIFFERENCES IN WEEK-1 IMPLY A MORE
PROGRESSIVE PATTERN DURING THE FORECAST PERIOD. THE MANUAL HEIGHT BLEND FOR
TODAY, THEREFORE INDICATES MEAN TROUGHING ACROSS THE EASTERN CONUS, WHEREAS
YESTERDAY MEAN RIDGING WAS FORECAST. MEAN RIDGING IS FORECAST ACROSS THE
WESTERN CONUS, WITH POSITIVE 500-HPA HEIGHT ANOMALIES. MEANWHILE, IN ALASKA,
POSITIVE 500-HPA HEIGHT ANOMALIES REMAIN FORECAST, HOWEVER, THE ORIENTATION OF
THE RIDGE AXIS HAS SHIFTED AND BECOME MORE AMPLIFIED BRINGING STRONGER ONSHORE
FLOW INTO SOUTHEAST ALASKA. CONFIDENCE IN THIS FORECAST HEIGHT PATTERN IS LOW
DUE TO THE RAPID CHANGES RELATIVE TO YESTERDAY.
THE WEEK-2 TEMPERATURE FORECAST CONTINUES TO SEE LARGE DIFFERENCES RELATIVE TO
YESTERDAY. ACROSS THE WESTERN CONUS, ABOVE-NORMAL TEMPERATURES ARE NOW FAVORED
WITH STRONG AGREEMENT AMONG THE FORECAST TOOLS TODAY IN THIS REGION DESPITE
LARGE DIFFERENCES RELATIVE TO YESTERDAY. IN THE NORTHEAST, ABOVE-NORMAL
TEMPERATURES REMAIN SLIGHTLY FAVORED WITH STRONG POSITIVE 500-HPA HEIGHT
ANOMALIES PROGRESSING FURTHER EAST AND NOW CENTERED SOUTH OF GREENLAND. IN THE
SOUTHEAST, ABOVE-NORMAL TEMPERATURES ARE ALSO STILL SLIGHTLY FAVORED WITH
NEAR-NORMAL HEIGHTS FORECAST. MEANWHILE, A LARGE AREA OF NEAR-NORMAL
TEMPERATURES ARE FAVORED FROM THE PLAINS TO THE MID-ATLANTIC WITH TOOLS MIXED.
IN ALASKA, BELOW-NORMAL TEMPERATURES REMAIN FAVORED ACROSS MUCH OF THE STATE.
HOWEVER, ACROSS SOUTHEAST ALASKA, TEMPERATURES ARE NOW FAVORED TO BE
ABOVE-NORMAL AS ONSHORE SOUTHERLY FLOW BECOMES ESTABLISHED.
IN ALASKA, AS ONSHORE FLOW BECOMES MORE ESTABLISHED, NEAR TO ABOVE-NORMAL
PRECIPITATION IS FAVORED IN SOUTHEAST, THE COPPER RIVER BASIN, AND
SOUTH-CENTRAL ALASKA DURING WEEK-2. MEANWHILE, ALONG THE WEST COAST, BELOW
NORMAL PRECIPITATION BECOMES MORE FAVORED AS THE POSITIVE 500-HPA RIDGE AXIS
SHIFTS THE STORM TRACK. THAT SHIFTING STORM TRACK ALSO IMPACTS PRECIPITATION
ACROSS THE CONUS. BELOW-NORMAL PRECIPITATION IS LARGELY FAVORED ACROSS THE
NORTHWESTERN AND NORTH-CENTRAL CONUS AS POSITIVE 500-HPA HEIGHT ANOMALIES BUILD
IN ACROSS MUCH OF THE WESTERN AND CENTRAL CONUS. THIS SHIFTS THE STORM TRACK SO
THAT THERE ARE SLIGHT CHANCES FOR ABOVE-NORMAL PRECIPITATION NOW FAVORED ACROSS
THE MID-ATLANTIC AND NORTHEAST. ABOVE-NORMAL PRECIPITATION IS SLIGHTLY FAVORED
IN PORTIONS OF SOUTHERN TEXAS WHERE LINGERING CHANCES FOR PRECIPITATION FROM A
STATIONARY FRONT MAY BRING ABOVE-NORMAL PRECIPITATION.
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 10% OF TODAY'S 0Z GFS
ENSEMBLE MEAN CENTERED ON DAY 11, 25% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED
ON DAY 11, 35% 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: WELL BELOW AVERAGE, 1 OUT OF 5,
LARGE DIFFERENCES BETWEEN THE MODEL GUIDANCE FROM YESTERDAY AND TODAY ALONG
WITH WEAK AGREEMENT ACROSS MUCH OF THE COUNTRY IN THE GUIDANCE GREATLY REDUCES
CONFIDENCE.
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
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:
20010928 - 20071009 - 20081006 - 19620930 - 19841012
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:
20010927 - 20071009 - 19621003 - 19841011 - 19680921
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR OCT 04 - 08 2023
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON A B OREGON A B NRN CALIF A B
SRN CALIF A N IDAHO N B NEVADA N B
W MONTANA N B E MONTANA N N WYOMING N N
UTAH N B ARIZONA N N COLORADO N N
NEW MEXICO N N N DAKOTA N N S DAKOTA N N
NEBRASKA N N KANSAS N A OKLAHOMA A A
N TEXAS A A S TEXAS A A W TEXAS N A
MINNESOTA A N IOWA A N MISSOURI A N
ARKANSAS A A LOUISIANA A A WISCONSIN A A
ILLINOIS A N MISSISSIPPI A N MICHIGAN A A
INDIANA A N OHIO A N KENTUCKY A N
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 N S CAROLINA A N GEORGIA A N
FL PNHDL A N FL PENIN A N AK N SLOPE B N
AK ALEUTIAN N B AK WESTERN B N AK INT BSN B A
AK S INT B A AK SO COAST B A AK PNHDL B N
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR OCT 06 - 12 2023
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 N B WYOMING N B
UTAH A B ARIZONA A N COLORADO N B
NEW MEXICO N N N DAKOTA N B S DAKOTA N B
NEBRASKA N B KANSAS N B OKLAHOMA N B
N TEXAS N N S TEXAS N A W TEXAS N N
MINNESOTA N B IOWA N B MISSOURI N B
ARKANSAS N B LOUISIANA A N WISCONSIN N B
ILLINOIS N B MISSISSIPPI A B MICHIGAN N N
INDIANA N B OHIO N N KENTUCKY N N
TENNESSEE N N ALABAMA A N NEW YORK A A
VERMONT A A NEW HAMP A A MAINE A A
MASS A A CONN A A RHODE IS A A
PENN N N NEW JERSEY A A W VIRGINIA N N
MARYLAND N N DELAWARE N A VIRGINIA N N
N CAROLINA N N S CAROLINA N N GEORGIA A N
FL PNHDL A N FL PENIN A N AK N SLOPE B A
AK ALEUTIAN N N AK WESTERN B N AK INT BSN B A
AK S INT B A AK SO COAST B A AK PNHDL A 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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