103
FXUS06 KWBC 221903
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EDT FRI SEPTEMBER 22 2023
6-10 DAY OUTLOOK FOR SEP 28 - OCT 02, 2023
THE GEFS, CANADIAN, AND ECMWF ENSEMBLE MEANS ARE IN GOOD AGREEMENT DEPICTING AN
AMPLIFIED 500-HPA TROUGH (RIDGE) OVER WESTERN (EASTERN) NORTH AMERICA. THIS
LONGWAVE PATTERN FAVORS BELOW-NORMAL TEMPERATURES ACROSS THE WESTERN THIRD OF
THE CONTIGUOUS U.S. (CONUS), WHILE ABOVE-NORMAL TEMPERATURES ARE LIKELY FOR
MUCH OF THE CENTRAL AND EASTERN CONUS. PREVAILING SOUTHERLY SURFACE FLOW ALONG
WITH RIDGING ALOFT RESULTS IN LARGE PROBABILITIES (MORE THAN 80 PERCENT) FOR
ABOVE-NORMAL TEMPERATURES ACROSS THE UPPER MISSISSIPPI VALLEY. EASTERLY SURFACE
FLOW FAVORS BELOW-NORMAL TEMPERATURES FROM THE CAROLINAS NORTH TO SOUTHERN NEW
JERSEY ON DAYS 6 AND 7 WITH AN EXPECTED TRANSITION TOWARDS NEAR TO ABOVE-NORMAL
TEMPERATURES BY DAY 10. THIS PREDICTED VARIATION IN TEMPERATURES DURING THE
5-DAY PERIOD SUPPORTS NEAR NORMAL TEMPERATURES FOR PARTS OF THE MID-ATLANTIC
AND SOUTHEAST.
THE AMPLIFIED TROUGH FAVORS ABOVE-NORMAL PRECIPITATION ACROSS THE NORTHERN HALF
OF THE WESTERN CONUS WITH THE LARGEST PROBABILITIES (MORE THAN 50 PERCENT)
ACROSS THE PACIFIC NORTHWEST. DOWNSTREAM OF THIS TROUGH, SURFACE LOW
DEVELOPMENT IS LIKELY ACROSS THE HIGH PLAINS BY DAY 8 OR 9 (SEP 30 OR OCT 1).
THIS SURFACE LOW ALONG WITH A TRAILING COLD FRONT SUPPORTS ELEVATED
ABOVE-NORMAL PRECIPITATION PROBABILITIES ACROSS THE NORTHERN TO CENTRAL GREAT
PLAINS, WITH NEAR NORMAL PRECIPITATION BECOMING MORE LIKELY FOR THE SOUTHERN
GREAT PLAINS. FARTHER TO THE EAST AND CLOSER TO THE AMPLIFIED RIDGE, INCREASED
BELOW-NORMAL PRECIPITATION PROBABILITIES ARE FORECAST ACROSS THE EASTERN GREAT
LAKES, MIDDLE TO LOWER MISSISSIPPI VALLEY, AND OHIO VALLEY. THERE CONTINUES TO
BE MORE UNCERTAINTY IN THE PRECIPITATION OUTLOOK FOR THE EASTERN CONUS DUE TO A
MID-LEVEL TROUGH UNDERCUTTING THE RIDGE TO THE NORTH AND AN INCREASED POTENTIAL
FOR LOW PRESSURE DEVELOPMENT ACROSS OR OFFSHORE OF THE SOUTHEAST AND
MID-ATLANTIC. THE ECMWF REFORECAST TOOL DEPICTS ELEVATED ABOVE-NORMAL
PRECIPITATION PROBABILITIES AS FAR WEST AS THE APPALACHIANS, WHILE THE GEFS
REFORECAST TOOL LIMITS THIS WET SIGNAL TO THE COASTAL SOUTHEAST AND
MID-ATLANTIC. THE 6-10 DAY PRECIPITATION OUTLOOK WAS BASED ON THE CONSOLIDATION
TOOL (SKILL-WEIGHTED GEFS/ECMWF BLEND) WHICH LEANS SLIGHTLY TOWARDS
ABOVE-NORMAL PRECIPITATION FROM THE SOUTHERN MID-ATLANTIC SOUTH TO FLORIDA.
THIS POTENTIAL LOW PRESSURE SYSTEM IS UNLIKELY TO TRACK NORTHWARD WITH THE
STRONG RIDGING ANCHORED OVER SOUTHEASTERN CANADA. THEREFORE, BELOW-NORMAL
PRECIPITATION IS MORE LIKELY ACROSS THE NORTHEAST.
ABOVE NORMAL PRECIPITATION PROBABILITIES ARE SLIGHTLY ELEVATED FOR MUCH OF
ALASKA DUE TO A 500-HPA TROUGH OVER THE EASTERN BERING SEA. THE 6-10 DAY
TEMPERATURE OUTLOOK ACROSS ALASKA WAS BASED MOSTLY ON THE CONSOLIDATION TOOL
WHICH SUPPORTS ELEVATED PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES THROUGHOUT
NORTHEASTERN MAINLAND ALASKA WITH NEAR NORMAL TEMPERATURES MORE LIKELY ACROSS
THE REMAINDER OF THE STATE.
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 25% OF TODAY'S 0Z GFS
ENSEMBLE MEAN CENTERED ON DAY 8, 10% OF TODAY'S OPERATIONAL 0Z GFS CENTERED ON
DAY 8, 30% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8, 10% OF
TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8, AND 25% 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
GOOD AGREEMENT AND CONTINUITY AMONG THE ENSEMBLE MEANS WITH AN AMPLIFIED
TROUGH/RIDGE PATTERN OVER NORTH AMERICA.
8-14 DAY OUTLOOK FOR SEP 30 - OCT 06, 2023
THE GEFS, ECMWF, AND CANADIAN ENSEMBLE MEANS MAINTAIN A BROAD 500-HPA RIDGE
WITH LARGE POSITIVE 500-HPA HEIGHT DEPARTURES OVER THE MIDDLE TO HIGHER
LATITUDES OF EASTERN NORTH AMERICA THROUGH EARLY OCTOBER. HOWEVER, MODEL
GUIDANCE FEATURES A TRANSITION TO A MORE ZONAL FLOW PATTERN UPSTREAM OVER
WESTERN NORTH AMERICA AND THE NORTH PACIFIC. DESPITE THE MORE ZONAL FLOW LATER
IN WEEK-2, THE TEMPERATURE TOOLS REMAIN IN GOOD AGREEMENT WITH BELOW (ABOVE)
NORMAL TEMPERATURES FAVORED ACROSS THE WESTERN (CENTRAL AND EASTERN) CONUS.
BASED ON PREVALENT SOUTHERLY SURFACE FLOW DURING MUCH OF WEEK-2, LARGE
PROBABILITIES (MORE THAN 70 PERCENT) FOR ABOVE-NORMAL TEMPERATURES ARE FORECAST
FOR THE GREAT LAKES. PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES DECREASE
ACROSS THE MID-ATLANTIC AND SOUTHEAST DUE TO EASTERLY SURFACE FLOW EARLY IN
WEEK-2.
THE AMPLIFIED TROUGH OVER THE WEST, EARLY IN WEEK-2, ENHANCES ABOVE-NORMAL
PRECIPITATION PROBABILITIES ACROSS THE INTERIOR PACIFIC NORTHWEST, NORTHERN
CALIFORNIA, AND THE NORTHERN TO CENTRAL ROCKIES. HOWEVER, NEAR NORMAL
PRECIPITATION IS FAVORED FOR COASTAL OREGON AND WASHINGTON AS THE HEAVIER
PRECIPITATION BEGINS TO TIME OFF WITH THE 500-HPA TROUGH AXIS PREDICTED TO
SHIFT INLAND. INCREASED ABOVE-NORMAL PRECIPITATION PROBABILITIES ARE FORECAST
ACROSS THE NORTHERN TO CENTRAL GREAT PLAINS AND THE UPPER MISSISSIPPI VALLEY
SINCE THE ENSEMBLE MEANS DEPICT A LOW PRESSURE SYSTEM AND TRAILING FRONT
CROSSING THESE AREAS AT THE BEGINNING OF OCTOBER. BASED ON THE ECMWF REFORECAST
TOOL AND THE ANALOG TOOL DERIVED FROM THE MANUAL 500-HPA HEIGHT BLEND,
ABOVE-NORMAL PRECIPITATION IS ALSO FAVORED ACROSS THE SOUTHERN GREAT PLAINS.
THE STRONG RIDGE ALOFT, CENTERED OVER SOUTHEASTERN CANADA, INCREASES CHANCES
FOR BELOW-NORMAL PRECIPITATION FOR MUCH OF THE EASTERN CONUS. HOWEVER, NEAR
NORMAL PRECIPITATION IS FAVORED FROM THE COASTAL MID-ATLANTIC SOUTH TO FLORIDA
AS A SHORTWAVE TROUGH AND POTENTIAL LOW PRESSURE SYSTEM MAY LINGER NEAR THE
EAST COAST INTO THE BEGINNING OF WEEK-2.
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 WEEKEND. ALTHOUGH A MAJORITY
OF THE RECENT GEFS AND ECMWF ENSEMBLE MEMBERS RECURVE THIS POTENTIAL TC
NORTHWARD ACROSS THE CENTRAL ATLANTIC EARLY IN WEEK-2, THIS TC COULD APPROACH
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 THE EASTERN TWO-THIRDS OF
ALASKA. SIMILAR TO THE 6-10 DAY PERIOD, THE ALASKA TEMPERATURE OUTLOOK CLOSELY
FOLLOWED THE CONSOLIDATION TOOL.
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 35% OF TODAY'S 0Z 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: AVERAGE, 3 OUT OF 5, DUE TO A
TRANSITION TOWARDS A LESS AMPLIFIED PATTERN OVER THE WEST AND NORTH PACIFIC
LATER IN WEEK-2.
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:
20050903 - 20090929 - 20040919 - 19870915 - 19960919
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:
20050902 - 20090928 - 19870914 - 20040918 - 19940912
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 28 - OCT 02, 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 N N DAKOTA A A S DAKOTA A A
NEBRASKA A A KANSAS A N OKLAHOMA A N
N TEXAS A N S TEXAS A N W TEXAS A N
MINNESOTA A A IOWA A A MISSOURI A B
ARKANSAS A B LOUISIANA A N 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 N B W VIRGINIA A N
MARYLAND N N DELAWARE N N 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 A N
AK ALEUTIAN N N AK WESTERN N A AK INT BSN A A
AK S INT N A AK SO COAST N A AK PNHDL N N
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR SEP 30 - OCT 06, 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 N A WYOMING A A
UTAH B N ARIZONA B N COLORADO A A
NEW MEXICO A A N DAKOTA A A S DAKOTA A A
NEBRASKA A A KANSAS A A OKLAHOMA A A
N TEXAS A A S TEXAS A A W TEXAS A A
MINNESOTA A A IOWA A A MISSOURI A B
ARKANSAS A B LOUISIANA A N 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 N VIRGINIA A B
N CAROLINA A N S CAROLINA A B GEORGIA A B
FL PNHDL A N FL PENIN A N AK N SLOPE A A
AK ALEUTIAN N N AK WESTERN N N AK INT BSN A 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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