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August 2017 Discussion (1 Viewer)


JayF

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PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MON JUL 31 2017

30-DAY OUTLOOK DISCUSSION FOR AUGUST 2017

THE UPDATED MONTHLY TEMPERATURE AND PRECIPITATION OUTLOOKS FOR AUGUST 2017 ARE
BASED ON THE LATEST DYNAMICAL MODEL GUIDANCE, WPC TEMPERATURE AND PRECIPITATION
FORECASTS DURING THE FIRST WEEK OF THE MONTH, THE CPC 6-10/8-14 DAY TEMPERATURE
AND PRECIPITATION OUTLOOKS, CLIMATE LINKAGES TO CURRENT SOIL MOISTURE
CONDITIONS, AND POTENTIAL INFLUENCE FROM AN ATMOSPHERIC KELVIN WAVE (KW).
ALTHOUGH THE MADDEN-JULIAN OSCILLATION (MJO) STRENGTHENED DURING LATE JULY WITH
ITS ENHANCED PHASE OVER THE MARITIME CONTINENT AND WEST PACIFIC, IT IS FORECAST
TO WEAKEN. A ROBUST KW EMERGED FROM THE WEST PACIFIC RECENTLY AND IS CURRENTLY
PROPAGATING EAST ACROSS THE WESTERN HEMISPHERE. THIS KW IS EXPECTED TO PROVIDE
A FAVORABLE ENVIRONMENT FOR TROPICAL CYCLONE (TC) DEVELOPMENT OVER THE EAST
PACIFIC DURING THE FIRST WEEK OF AUGUST. TCS ACROSS THE EAST PACIFIC MAY
ENHANCE MOISTURE ACROSS THE SOUTHWESTERN U.S. DURING EARLY AUGUST.

THE MAJOR REVISION TO THE TEMPERATURE OUTLOOK IS A LARGE REDUCTION IN THE
COVERAGE OF INCREASED CHANCES FOR ABOVE-NORMAL TEMPERATURES ACROSS THE CENTRAL
AND EASTERN U.S. THE GFS AND ECMWF ENSEMBLE MEANS INDICATE AN AMPLIFYING
500-HPA TROUGH DEVELOPING OVER THE EAST-CENTRAL U.S. DURING THE FIRST WEEK OF
AUGUST WITH NEAR- TO BELOW-NORMAL 500-HPA HEIGHTS PERSISTING THROUGH AT LEAST
THE FIRST TEN DAYS OF THE MONTH. BELOW-NORMAL TEMPERATURES ARE MOST LIKELY
ACROSS THE CENTRAL AND SOUTHERN GREAT PLAINS WHERE TEMPERATURES ARE FORECAST TO
AVERAGE NEAR 10 DEGREES F BELOW NORMAL DURING THE FIRST WEEK OF AUGUST AND
WEEK-2 TEMPERATURE TOOLS HAVE THE HIGHEST PROBABILITIES FOR BELOW-NORMAL
TEMPERATURES ACROSS THIS REGION. INCREASED CHANCES FOR ABOVE-NORMAL
TEMPERATURES ARE FORECAST ACROSS THE WESTERN U.S. DUE TO ANOMALOUS RIDGING
EARLY IN THE MONTH ALONG WITH A CONSISTENT SIGNAL AMONG RECENT MONTHLY
TEMPERATURE FORECASTS FROM THE CFS MODEL. PROBABILITIES FOR ABOVE-NORMAL
TEMPERATURES ARE HIGHEST ACROSS THE PACIFIC NORTHWEST SINCE TEMPERATURES ARE
FORECAST TO AVERAGE NEAR 15 DEGREES F ABOVE NORMAL THROUGH THE FIRST WEEK OF
AUGUST. ELEVATED CHANCES FOR ABOVE-NORMAL TEMPERATURES INCLUDE THE NORTHERN
HIGH PLAINS, BASED IN PART ON EXCEPTIONALLY LOW SOIL MOISTURE. AS OF JULY 30,
SOIL MOISTURE IS BELOW THE 5TH PERCENTILE ACROSS EASTERN MONTANA AND WESTERN
NORTH DAKOTA. ACCORDING TO THE U.S. DROUGHT MONITOR VALID ON JULY 25, NEARLY
ALL OF WESTERN NORTH DAKOTA IS DESIGNATED WITH EXTREME (D3) TO EXCEPTIONAL (D4)
DROUGHT.

ENHANCED ODDS FOR ABOVE-MEDIAN PRECIPITATION ARE MAINTAINED ACROSS THE
SOUTHWESTERN U.S. AND EXPANDED TO INCLUDE PARTS OF THE CENTRAL AND SOUTHERN
GREAT PLAINS, GULF COAST, AND SOUTHEASTERN U.S. THE HIGHEST ODDS FOR
ABOVE-MEDIAN PRECIPITATION ARE FORECAST FOR SOUTHEAST NEW MEXICO AND THE RIO
GRANDE VALLEY DUE TO SHORT-TERM RAINFALL AND A CONSISTENT SIGNAL AMONG RECENT
MONTHLY PRECIPITATION FORECASTS FROM THE CFS MODEL. THE EXPANSION OF INCREASED
CHANCES FOR ABOVE-MEDIAN PRECIPITATION ACROSS PARTS OF THE CENTRAL AND SOUTHERN
GREAT PLAINS, GULF COAST, AND SOUTHEASTERN U.S. IS BASED ON LOCALLY HEAVY
RAINFALL EXPECTED DURING THE FIRST WEEK OF AUGUST ALONG WITH GOOD AGREEMENT
AMONG PRECIPITATION TOOLS AT ALL TIME RANGES. AS OF 11AM ON JULY 31, TROPICAL
STORM EMILY IS NEAR TAMPA BAY, FLORIDA. EMILY IS FORECAST TO CROSS THE FLORIDA
PENINSULA AND TRACK AWAY FROM FLORIDA AT THE BEGINNING OF THE MONTH. ALTHOUGH
MOST OF THE RAINFALL ASSOCIATED WITH EMILY IS EXPECTED TO OCCUR BEFORE THE
START OF THE MONTH, THE MOST RECENT DAILY RUN OF THE CFS MODEL INDICATES
ENHANCED ODDS FOR ABOVE-MEDIAN PRECIPITATION ACROSS FLORIDA. LITTLE OR NO
PRECIPITATION IS LIKELY ACROSS THE PACIFIC NORTHWEST, NORTHERN ROCKIES, AND
NORTHERN HIGH PLAINS DURING THE FIRST WEEK OF AUGUST. SINCE THE PAST THREE
DAILY RUNS OF THE CFS MODEL HAVE A DRY SIGNAL, ENHANCED ODDS FOR BELOW-MEDIAN
PRECIPITATION WERE ADDED TO THESE AREAS IN THIS UPDATED OUTLOOK. DUE TO
CONFLICTING OR WEAK PRECIPITATION SIGNALS AT DIFFERENT TIME RANGES, EQUAL
CHANCES FOR BELOW-, NEAR-, OR ABOVE-MEDIAN PRECIPITATION ARE NECESSARY FOR THE
MIDWEST AND NORTHEAST.

ONLY MINOR CHANGES ARE REQUIRED TO THE PREVIOUS TEMPERATURE AND PRECIPITATION
OUTLOOKS ACROSS ALASKA. THE HIGHEST CHANCES FOR ABOVE-NORMAL TEMPERATURES ARE
FORECAST ACROSS NORTHWEST ALASKA WHERE SEA SURFACE TEMPERATURE ANOMALIES ARE
AVERAGING MORE THAN 2.5 DEGREES C ABOVE NORMAL. ENHANCED ODDS FOR ABOVE-MEDIAN
PRECIPITATION ARE EXPANDED TO INCLUDE MORE OF THE ALASKA MAINLAND BASED ON THE
LATEST PRECIPITATION TOOLS.

----------- PREVIOUS MESSAGE (FROM JULY 20) IS SHOWN BELOW ------------
THE AUGUST 2017 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON DYNAMICAL
MODEL GUIDANCE, STATISTICAL TOOLS, CURRENT SOIL MOISTURE CONDITIONS, AND
POTENTIAL INFLUENCES FROM MODES OF TROPICAL VARIABILITY. ENSO IS NOT A FACTOR
IN THESE OUTLOOKS SINCE IT IS IN A NEUTRAL STATE AND IS PREDICTED TO REMAIN
NEUTRAL. PLEASE SEE THE ENSO DIAGNOSTIC DISCUSSION AT:
HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/ANALYSIS_MONITORING/ENSO_ADVISORY/ENSODISC
.SHTML FOR A MORE DETAILED ANALYSIS OF SEA SURFACE TEMPERATURES ACROSS THE
EQUATORIAL PACIFIC. THE MADDEN-JULIAN OSCILLATION (MJO) BECAME MORE COHERENT
DURING MID-JULY WITH ITS ENHANCED PHASE OVER THE WESTERN MARITIME CONTINENT. A
COHERENT MJO SIGNAL IS FAVORED TO PROPAGATE EASTWARD DURING THE NEXT TWO WEEKS,
BUT ITS EFFECTS ON THE EXTRATROPICS ARE EXPECTED TO BE MINIMAL GIVEN THE TIME
OF YEAR. THE CFS MODEL INDICATES AN ATMOSPHERIC KELVIN WAVE (KW) CROSSING THE
WESTERN HEMISPHERE DURING LATE JULY INTO THE BEGINNING OF AUGUST. THIS KW COULD
PROVIDE A FAVORABLE ENVIRONMENT FOR TROPICAL CYCLONE DEVELOPMENT OVER THE EAST
PACIFIC AND CONTRIBUTE TO A CONTINUATION OF ENHANCED MOISTURE ACROSS THE
SOUTHWESTERN U.S.

THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) DEPICTS INCREASED PROBABILITIES
FOR ABOVE-NORMAL TEMPERATURES ACROSS NEARLY ALL OF THE CONTINENTAL U.S. THE
LARGEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES IN THE OFFICIAL OUTLOOK ARE
FORECAST ACROSS THE NORTHERN GREAT PLAINS WHERE CURRENT SOIL MOISTURE VALUES
RANK BELOW THE 10TH PERCENTILE. ALSO, THE GFS, ECMWF, AND CANADIAN ENSEMBLE
MEANS INDICATE THAT THE ANOMALOUS 500-HPA RIDGE IS LIKELY TO PERSIST AT LEAST
THROUGH THE BEGINNING OF AUGUST. ALTHOUGH MANY OF THE DYNAMICAL MODELS FAVOR
ABOVE-NORMAL TEMPERATURES ACROSS THE SOUTHWESTERN U.S., EQUAL CHANCES FOR
BELOW-, NEAR-, OR ABOVE-NORMAL TEMPERATURES ARE FORECAST FOR THIS REGION BASED
ON A CONSISTENT SIGNAL AMONG DAILY RUNS OF THE NCEP CLIMATE FORECAST SYSTEM
(CFS) MODEL, DEPICTING NEAR TO BELOW-NORMAL TEMPERATURES, AND THE ENHANCED ODDS
FOR ABOVE-MEDIAN PRECIPITATION FORECAST IN THE PRECIPITATION OUTLOOK.

THE PROBABILITY ANOMALY CORRELATION (PAC) CALIBRATED PROBABILITY FORECAST FROM
THE NMME FEATURES LITTLE IF ANY SIGNAL THROUGHOUT MOST OF THE FORECAST DOMAIN
WITH ONLY A SLIGHT TILT IN THE ODDS (36 TO 40 PERCENT) FOR THE ABOVE NORMAL
TERCILE FROM THE RIO GRANDE VALLEY NORTH TO THE CENTRAL ROCKIES. THE MOST
CONSISTENT SIGNAL AMONG DAILY CFS MODEL RUNS IS A FAVORED AREA OF ABOVE-MEDIAN
PRECIPITATION OVER THE RIO GRANDE VALLEY AND PARTS OF THE WESTERN U.S. BASED ON
THESE TWO PRECIPITATION TOOLS ALONG WITH POTENTIAL INFLUENCES FROM AN EXPECTED
ACTIVE PERIOD OF EAST PACIFIC TROPICAL CYCLONE ACTIVITY, ABOVE-MEDIAN
PRECIPITATION IS FAVORED FOR THE RIO GRANDE VALLEY, MOST OF THE MONSOON REGION
OF THE SOUTHWESTERN U.S., AND THE CENTRAL ROCKIES. FORECAST CONFIDENCE IN THE
PRECIPITATION OUTLOOK IS LIMITED DUE TO THE LACK OF PREDICTABILITY OF
CONVECTIVE RAINFALL ON A MONTHLY TIME SCALE.





FORECASTER: BRAD PUGH
 
Last edited:

Bob Thompson

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Ashburn, Virginia
Just keep it out for the next 14 days.
Is it my imagination, or has the second half of this summer wimped out big time? I just did a computation of temperature data at IAD (Dulles International Airport) for August, and 20 of the 30 days have been below normal in temperature. The 10 that are at or above are only slightly so. Yesterday's high of 67 was 18 degrees below normal for that date! Furthermore, there is no relief (for summer lovers!) any time seen. Both the 6-to-10 and 8-to-14 day forecast show temperatures almost Biblically below normal for the eastern U.S. Only in week 3-4 do we rebound to even normal temperatures, but by then "normal" is only a high of 75. This is ridiculous!
 

JayF

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AH HA HA HA
 

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