803
FXUS07 KWBC 311901
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT WED JUL 31 2024
30-DAY OUTLOOK DISCUSSION FOR AUGUST 2024
THE UPDATED MONTHLY TEMPERATURE AND PRECIPITATION OUTLOOKS FOR AUGUST 2024 ARE
BASED ON OFFICIAL FORECASTS AND OUTLOOKS FROM WPC (WEEK-1), CPC (WEEK-2, WEEKS
3-4), AND DYNAMICAL MODEL GUIDANCE FROM THE GEFS AND EUROPEAN ENSEMBLE SUITE. A
WEIGHTED GEFS-CFSV2 30-DAY FORECAST FOR BOTH TEMPERATURE AND PRECIPITATION IS
ALSO USED, WHERE WEIGHTING IS BASED ON RECENT 500-HPA HEIGHT ANOMALY
CORRELATION SCORES. THE UPDATED OUTLOOKS ALSO CONSIDER THE LATEST SOIL MOISTURE
ANOMALIES, COASTAL SEA-SURFACE TEMPERATURES (SSTS), 14-DAY PRECIPITATION
DEFICITS, INITIAL CONDITIONS, CLIMATOLOGY, LONG-TERM TRENDS, AND EXPECTED
TROPICAL CYCLONE ACTIVITY IN THE ATLANTIC AND EAST PACIFIC BASINS.
THE UPDATED TEMPERATURE OUTLOOK FOR AUGUST 2024 FAVORS ABOVE-NORMAL
TEMPERATURES ACROSS MUCH OF THE CONTIGUOUS U.S. (CONUS) AND MOST OF THE
NORTHEAST HALF OF THE ALASKA MAINLAND. MAXIMUM PROBABILITIES EXCEED 60 PERCENT
OVER THE MIDDLE AND SOUTHERN ATLANTIC COAST STATES, AND 70% OVER CENTRAL
PORTIONS OF THE INTERIOR WEST. THIS BROAD EXPANSE OF FAVORED WARMER-THAN-NORMAL
TEMPERATURES IS SUPPORTED BY THE 30-DAY EUROPEAN ENSEMBLE FORECAST, 30-DAY
WEIGHTED GEFS-CFSV2 TEMPERATURE FORECAST, AND IS CONSISTENT WITH MOST OF THE
DYNAMICAL MODEL GUIDANCE AND OFFICIAL TEMPERATURE OUTLOOKS NOTED IN THE FIRST
PARAGRAPH. THE 30-DAY EUROPEAN ENSEMBLE FORECAST DEPICTS 500-HPA HEIGHTS TO BE
ABOVE-NORMAL ACROSS PRACTICALLY ALL OF THE CONUS, WITH THE LARGER HEIGHT
DEPARTURES PREDICTED OVER THE WEST AND NORTHEAST. THIS LEAVES THE GENERAL
VICINITY OF THE MISSISSIPPI VALLEY OPEN TO A WEAK MEAN TROUGH AND EXPECTED
COOLER SURFACE TEMPERATURES. THIS WEAK TROUGH, AND THE FACT THAT THIS PORTION
OF THE LOWER 48 STATES HAS SEEN A LARGE AMOUNT OF TEMPERATURE AND PRECIPITATION
VARIABILITY OVER THE PAST MONTH, ARE THE MAIN REASONS UNDERPINNING THE FORECAST
OF EQUAL CHANCES (EC) OF BELOW-, NEAR-, AND ABOVE-NORMAL TEMPERATURES. THIS IS
ALSO THE BASIS FOR REDUCING THE PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES
RELATIVE TO THE REST OF THE CONUS. BELOW-NORMAL TEMPERATURES ARE FAVORED OVER
MOST OF THE SOUTHWESTERN HALF OF THE ALASKA MAINLAND, THE ALASKA PENINSULA, AND
THE EASTERN ALEUTIANS. THIS IS SUPPORTED BY THE LAST 9 RUNS OF THE CFSV2 MODEL,
ANOMALOUSLY COLD SSTS NEAR THE WESTERN AND NORTHERN COASTS OF ALASKA, THE
30-DAY EUROPEAN ENSEMBLE FORECAST, AND THE WEIGHTED GEFS-CFSV2 TEMPERATURE
FORECAST. SOME OF THESE TOOLS, BUT NOT ALL, SUPPORT ABOVE-NORMAL TEMPERATURE
CHANCES OVER THE NORTHEAST HALF OF THE MAINLAND. IN AREAS WHERE TEMPERATURE
TOOLS WERE AT ODDS, OR WHERE TEMPERATURE SIGNALS WERE WEAK, EC IS INDICATED.
THE UPDATED PRECIPITATION OUTLOOK FOR AUGUST 2024 FAVORS ABOVE-NORMAL
PRECIPITATION FOR THE EASTERN DAKOTAS, UPPER MISSISSIPPI VALLEY, GREAT LAKES
REGION, ATLANTIC COAST STATES, THE GULF COAST AREA, SOUTHERN TEXAS, AND INTO
THE FOUR CORNERS REGION. THIS IS BASED ON SOME OF THE OBJECTIVE TOOLS AND
CONSIDERS A VERY ACTIVE HURRICANE SEASON IN THE ATLANTIC BASIN THAT IS
FORECASTED. RELATIVELY WARM SSTS ARE OBSERVED ALONG MOST OF THE GULF AND
ATLANTIC COASTS, WHICH WOULD BENEFIT ANY TROPICAL CYCLONES PASSING OVER THEM.
THE LATEST EXTENDED-RANGE (OUT TO 2 WEEKS) RUNS OF THE EUROPEAN ENSEMBLE AND
GEFS DEPICT A SIGNIFICANT CHANCE OF A TROPICAL SYSTEM APPROACHING THE SOUTHEAST
COAST SOMETIME AROUND AUGUST 8TH AND 9TH. IF THIS SCENARIO MATERIALIZES,
PORTIONS OF THE SOUTHERN AND MIDDLE ATLANTIC COASTS COULD EASILY RECEIVE ENOUGH
RAIN TO EXCEED THEIR MONTHLY NORMAL PRECIPITATION FOR AUGUST. OVER THE VICINITY
OF THE UPPER MISSISSIPPI VALLEY AND GREAT LAKES REGION, THE FAVORED
ABOVE-NORMAL PRECIPITATION, WHICH IS PREDICTED BY MANY (BUT NOT ALL) OF THE
TOOLS, IS CONSISTENT WITH THE IDEA OF A WEAK MONTHLY MEAN TROUGH OVER OR JUST
UPSTREAM OF THIS REGION. WEAK TO MODERATE MID-LEVEL RIDGING CENTERED OVER THE
NORTHWESTERN CONUS FAVORS A SLIGHT TILT IN THE ODDS TOWARDS ABOVE-NORMAL
PRECIPITATION FOR PORTIONS OF THE SOUTHERN FOUR CORNERS STATES, IN THE DEEPER
EASTERLY FLOW SOUTH OF THE MEAN RIDGE AXIS. THEREFORE, A SLIGHTLY ENHANCED
MONSOON IS FAVORED ACROSS THIS PORTION OF THE SOUTHWEST. THIS SAME RIDGE, ALONG
WITH NEGATIVE SOIL MOISTURE ANOMALIES, FAVORS BELOW-NORMAL PRECIPITATION ACROSS
MUCH OF THE NORTHWESTERN QUARTER OF THE CONUS, WITH A SOUTHEASTWARD EXTENSION
ACROSS SOUTH-CENTRAL PORTIONS OF THE GREAT PLAINS AND MISSISSIPPI VALLEY, AND
INTO WESTERN TENNESSEE. ELSEWHERE ACROSS THE CONUS, EC IS FAVORED. FOR ALASKA,
ABOVE-NORMAL PRECIPITATION IS FAVORED ACROSS MOST OF THE STATE, WITH THE
EXCEPTION OF EC OVER SOUTHEAST ALASKA AND THE WESTERN ALEUTIANS. THIS IS
PRIMARILY BASED ON THE 30-DAY EUROPEAN ENSEMBLE, AND TO A LESSER EXTENT, THE
GEFS-CFSV2 PRECIPITATION FORECAST, THE LAST SEVERAL RUNS OF THE CFS, AND
EXTENDED-RANGE PRECIPITATION OUTLOOKS.
—------- THE PREVIOUS MONTHLY DISCUSSION FOR AUGUST IS SHOWN BELOW —---------
THE AUGUST 2024 MONTHLY TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON
VARIOUS CLIMATE FACTORS. THESE INCLUDE THE PHASE OF ENSO, THE MADDEN-JULIAN
OSCILLATION (MJO), DYNAMICAL AND STATISTICAL MODEL GUIDANCE, AND BOUNDARY
CONDITIONS SUCH AS COASTAL SEA-SURFACE TEMPERATURES (SSTS) AND RECENT SOIL
MOISTURE ANOMALIES. HISTORICAL TEMPERATURE AND PRECIPITATION TRENDS WERE ALSO
CONSIDERED, AS WERE RECENT OBSERVATIONS AND THE LATEST WEEKS 3-4 TEMPERATURE
AND PRECIPITATION OUTLOOKS WHICH EXTEND THROUGH THE 9TH OF AUGUST.
CURRENTLY, ENSO-NEUTRAL CONDITIONS ARE OBSERVED BUT LA NIñA IS FAVORED TO
EMERGE DURING AUGUST-SEPTEMBER-OCTOBER (ASO) 2024 (70% CHANCE) AND PERSIST INTO
THE NORTHERN HEMISPHERE WINTER (79% CHANCE) DURING NOVEMBER-DECEMBER-JANUARY
(NDJ) 2024-25. THE LATEST WEEKLY NIñO 3.4 INDEX WAS +0.3 DEG C. MOSTLY
NEAR-NORMAL SSTS PREVAILED ACROSS THE NEAR-EQUATORIAL EASTERN AND EAST-CENTRAL
PACIFIC, WHILE TEMPERATURES BELOW THE SURFACE IN THESE REGIONS WERE
BELOW-NORMAL. CONVECTION WAS NEAR-NORMAL TO SLIGHTLY ABOVE NORMAL ACROSS
INDONESIA AND THE VICINITY OF THE DATE LINE. COLLECTIVELY, THESE
OCEAN-ATMOSPHERE INDICATORS REFLECTED ENSO-NEUTRAL. THE MJO SIGNAL SHOWED
LITTLE EASTWARD PROPAGATION THIS PAST WEEK BETWEEN THE INDIAN OCEAN AND
MARITIME CONTINENT REGIONS, AND THE OLR PLOTS DISPLAYED CONSIDERABLE
DISORGANIZATION. IMPACTS FROM BOTH ENSO AND THE MJO FOR THE MONTH OF AUGUST ARE
EXPECTED TO BE MINOR.
THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) AND COPERNICUS CLIMATE CHANGE
SERVICE (C3S) MULTI-MODEL, ALSO KNOWN AS THE INTERNATIONAL MULTI-MODEL
ENSEMBLE, AND THEIR CONSTITUENT MODEL INPUTS SERVED AS THE DYNAMICAL BASIS FOR
THE MONTHLY OUTLOOKS. THE CONSTRUCTED ANALOG ON SOIL MOISTURE TOOL (CA-SMT),
ENSO COMPOSITES AND REGRESSIONS, AND HISTORICAL TRENDS SERVED AS THE
STATISTICAL BASIS FOR THE OUTLOOKS. THREE CONSOLIDATION TOOLS WERE USED THAT
SKILL-WEIGHTED AND CALIBRATED THE DYNAMICAL MODELS (NMME-CON), THE STATISTICAL
MODELS (STAT-CON), AND A FINAL-CON WHICH CONSOLIDATED THE OTHER TWO CONS.
BOUNDARY CONDITIONS (COASTAL SSTS AND RECENT SOIL MOISTURE ANOMALIES) WERE ALSO
CONSIDERED IN THE CONSTRUCTION OF THE MONTHLY TEMPERATURE AND PRECIPITATION
OUTLOOKS FOR AUGUST 2024. SSTS WERE BELOW-NORMAL NEAR THE COASTS OF NORTHERN
AND WESTERN ALASKA, MOSTLY NEAR-NORMAL NEAR THE WEST COAST, AND ABOVE-NORMAL
ALONG THE GULF AND ATLANTIC COASTS. RECENT AREAS OF RELATIVELY LOW SOIL
MOISTURE INCLUDE THE OHIO AND TENNESSEE VALLEYS, THE CENTRAL AND SOUTHERN
APPALACHIANS, PORTIONS OF THE MID-ATLANTIC REGION, THE CAROLINAS, THE RIO
GRANDE VALLEY OF TEXAS, AND LARGE PORTIONS OF THE NORTHWESTERN LOWER 48 STATES.
IN CONTRAST, RECENT AREAS OF RELATIVELY HIGH SOIL MOISTURE INCLUDE FROM THE
NORTH-CENTRAL STATES TO THE CENTRAL GREAT LAKES REGION (DUE TO FRONTAL ACTIVITY
AND THUNDERSTORM CLUSTERS), AND EASTERN TEXAS AND MUCH OF THE LOWER MISSISSIPPI
VALLEY, PRIMARILY DUE TO THE PASSAGE OF FORMER HURRICANE BERYL ON JULY 8-9.
NOAA’S ATLANTIC SEASONAL HURRICANE OUTLOOK CALLS FOR A WELL-ABOVE AVERAGE
SEASON THIS YEAR, WHICH PUTS THE GULF AND EAST COASTS AT AN INCREASED RISK OF
IMPACTS FROM TROPICAL STORMS AND HURRICANES.
THE TEMPERATURE OUTLOOK FOR AUGUST 2024 FAVORS ABOVE-NORMAL MEAN TEMPERATURES
OVER NEARLY ALL OF THE CONTIGUOUS U.S. (CONUS). THIS IS SUPPORTED BY THE THREE
CONSOLIDATION (CON) TOOLS, CFS, AND THE C3S. A MAJORITY OF THE TOOLS, INCLUDING
THE NMME PAC, DEPICT A RELATIVE WEAKNESS AND/OR BREAK IN THE FAVORED WARMTH
ACROSS PORTIONS OF THE GREAT PLAINS AND MISSISSIPPI VALLEY, WHICH IS CONSISTENT
WITH SIGNIFICANT CLIMATE VARIABILITY OBSERVED SO FAR THIS SUMMER. MAXIMUM
PROBABILITIES FAVORING ABOVE-NORMAL TEMPERATURES EXCEED 70% OVER PORTIONS OF
THE NORTH-CENTRAL ROCKIES, SUPPORTED BY MUCH OF THE MODEL GUIDANCE AND THE
EXPECTED LATE-SEASON INFLUENCE OF DRY SOILS. THIS IS A RELATIVELY DRY TIME OF
THE YEAR FOR THIS AREA. FOR THE SOUTHWEST, THE C3S AND ITS INPUTS ARE CONFIDENT
OF SIGNIFICANTLY ABOVE-NORMAL TEMPERATURES AND BELOW-NORMAL TOTAL
PRECIPITATION. DEPENDING UPON THE SPEED OF THE ANTICIPATED TRANSITION OF
ENSO-NEUTRAL TO LA NIñA LATER THIS SUMMER, SOME OF THE FAVORED DRYNESS ACROSS
THE SOUTHWEST MAY BE RELATED TO THE TYPICALLY DRY LA NIñA FOOTPRINT OVER THIS
REGION. WITH OTHER MODEL SOLUTIONS NOT BEING QUITE AS CONFIDENT AS THE C3S,
SUGGESTING LOWER PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES WOULD BE PRUDENT
ACROSS THE SOUTHWEST. HISTORICAL TRENDS ALSO SUPPORT ELEVATED PROBABILITIES FOR
WARMER-THAN-NORMAL TEMPERATURES OVER THIS REGION AND THE SOUTHERN HIGH PLAINS
DURING AUGUST. ACROSS THE NORTH-CENTRAL STATES, ODDS ARE ONLY SLIGHTLY TILTED
TOWARDS ABOVE-NORMAL TEMPERATURES DUE TO SEVERAL FACTORS. THESE FACTORS INCLUDE
ADEQUATE MODEL AND TOOL SUPPORT, THE EXPECTATION OF SIGNIFICANT VARIABILITY
CONTINUING IN THE FUTURE, AND THE ANTICIPATED CONTINUED PRESENCE OF VERY MOIST
SOILS. OVER THE EASTERN CONUS, THERE IS PLENTY OF DYNAMICAL MODEL SUPPORT FOR
THE FAVORED ABOVE-NORMAL TEMPERATURES, WITH LIMITED STATISTICAL SUPPORT.
RELATIVELY WARM WATER SURROUNDS THE FLORIDA PENINSULA AND ENHANCES THE CHANCES
FOR ANOMALOUS WARMTH. ODDS SURPASS 60% OVER AN AREA CENTERED ON THE CENTRAL
APPLACHIANS, IN PART DUE TO LOW SOIL MOISTURE. NEAR THE IMMEDIATE WEST COAST,
EQUAL CHANCES (EC) OF BELOW-, NEAR-, AND ABOVE-NORMAL TEMPERATURES ARE FAVORED
IN AUGUST, ATTRIBUTED TO THE INFLUENCE OF THE MARINE LAYER.
FOR ALASKA, ODDS ARE TILTED TOWARDS BELOW-NORMAL TEMPERATURES OVER SOUTHWESTERN
SECTIONS OF THE STATE, LARGELY DUE TO THE NEARBY BERING SEA AND ITS UNUSUALLY
COLD WATER FOR THIS TIME OF YEAR. THE FAVORED BELOW-NORMAL TEMPERATURES ARE
ALSO BACKED BY A REGRESSION TOOL WHICH REGRESSES TEMPERATURE ANOMALIES AGAINST
THE STANDARDIZED NIñO 3.4 INDEX FOR THE JULY-SEPTEMBER SEASON (WITH THE CENTRAL
MONTH, AUGUST, BEING OUR TARGET PERIOD). FOR THE REMAINDER OF THE STATE, A
SUBJECTIVE CONSENSUS OF MODELS AND TOOLS SUGGESTS A WEAK TILT TOWARDS
ABOVE-NORMAL TEMPERATURES FOR THE NORTHEAST PORTION OF THE MAINLAND AND EC
ELSEWHERE.
THE PRECIPITATION OUTLOOK FOR AUGUST 2024 FAVORS ABOVE-NORMAL PRECIPITATION FOR
THE SOUTHEASTERN THIRD OF TEXAS, MUCH OF THE LOWER MISSISSIPPI AND TENNESSEE
VALLEYS, SOUTHERN OHIO VALLEY, THE SOUTHEAST, SOUTHERN APPALACHIAN MOUNTAINS,
AND FROM MUCH OF THE MID-ATLANTIC REGION TO SOUTHERN AND CENTRAL NEW ENGLAND.
THIS IS SUPPORTED IN LARGE PART BY THE THREE CON TOOLS, CA-SMT, CFS, AND C3S.
MAXIMUM PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION CHANCES SURPASS 50% FOR
MOST OF THE GULF COAST AND SOUTHEAST COAST STATES. THE LAST 9 RUNS OF THE CFS
MODEL FAVOR ABOVE-NORMAL PRECIPITATION OVER MUCH OF THE SAME GENERAL AREA. THIS
ANTICIPATED RELATIVELY WET PATTERN IS ALSO DEEMED JUDICIOUS GIVEN NOAA’S
SEASONAL HURRICANE OUTLOOK WHICH FAVORS A VERY ACTIVE ATLANTIC HURRICANE SEASON
IN 2024. IN CONTRAST, BELOW-NORMAL PRECIPITATION IS FAVORED FOR MUCH OF THE
WESTERN HALF OF THE CONUS. MOST OF THE SUPPORT FOR THE RELATIVELY DRY OUTLOOK
COMES FROM THE THREE CONSOLIDATION TOOLS, C3S, CFS, METEO-FRANCE MODEL, AND THE
UKMO MODEL. FOR SEVERAL OF THE LAST 9 DAILY CFS RUNS, WETTER-THAN-NORMAL
CONDITIONS HAVE BEEN PREDICTED BY THE CFS MODEL OVER THE NORTHWESTERN CONUS,
WHICH IS A SIGNIFICANT DEVIATION FROM MOST OTHER TOOLS AND WAS THEREFORE
DISCOUNTED. MINIMAL PROBABILITIES FAVORING BELOW-NORMAL PRECIPITATION AMOUNTS
ARE INDICATED ACROSS MOST OF ARIZONA AND NEW MEXICO, GIVEN THE EARLY AND
CONSISTENT START TO THE SOUTHWEST MONSOON AND POTENTIAL BACKDOOR COLD FRONT
ACTIVITY THAT OFTEN AFFECTS NEW MEXICO IN PARTICULAR.
IN ALASKA, THERE IS A TILT IN THE ODDS TOWARDS ABOVE-NORMAL PRECIPITATION FOR
THE SOUTHWESTERN MAINLAND, THE ALASKA PENINSULA, AND THE EASTERN ALEUTIANS.
THIS HAS THE SUPPORT OF MANY OF THE C3S INPUTS, INCLUDING THE GERMAN AND
CANADIAN MODELS (DWD AND CMCC, RESPECTIVELY), TO NAME A FEW. THE LATEST 3 RUNS
OF THE CFS ALSO LEND SOME SUPPORT TO THE FAVORED ABOVE-NORMAL PRECIPITATION
CHANCES ACROSS SOUTHWESTERN ALASKA. ELSEWHERE ACROSS ALASKA AND THE LOWER 48
STATES, EC IS FAVORED.
FORECASTER: ANTHONY ARTUSA
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1991 AND 2020, FOLLOWING
THE WORLD METEOROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3
COMPLETE DECADES AS THE CLIMATE REFERENCE PERIOD. THE PROBABILITY ANOMALIES
FOR TEMPERATURE AND PRECIPITATION BASED ON THESE NEW NORMALS BETTER REPRESENT
SHORTER TERM CLIMATIC ANOMALIES THAN THE FORECASTS BASED ON OLDER NORMALS.
THE NEXT MONTHLY OUTLOOK...FOR SEP ... WILL BE ISSUED ON THU AUG 15 2024
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1991-2020 BASE PERIOD.
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