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Official 90-day Outlooks are issued once each month near mid-month at 8:30am Eastern Time. Please consult the schedule of 30 & 90-day outlooks for exact release dates.

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HOME> Outlook Maps>Seasonal Forecast Discussion
 
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK 
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830 AM EDT THU AUG 16 2018


30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2018

AS WE ENTER THE AUTUMN MONTHS, FORECAST PREDICTABILITY OFTEN DECREASES
ESPECIALLY FOR THE MONTHS OF SEPTEMBER AND OCTOBER. THESE ISSUES ARE FURTHER
ENHANCED WHEN CONSIDERING A HALF-MONTH LEAD MONTHLY FORECAST SUCH AS THE
SEPTEMBER TEMPERATURE AND PRECIPITATION OUTLOOK PRESENTED HERE AS INFORMATION
ACROSS TIME SCALES (THE EXTENDED RANGE, SUBSEASONAL, AND SEASONAL PERIODS) CAN
INFLUENCE THE EVENTUAL OBSERVED FINAL MONTHLY TEMPERATURE AND PRECIPITATION
PATTERNS. THESE CONSIDERATIONS RESULT IN RATHER SIZABLE AREAS DEPICTING EQUAL
CHANCES (EC) FOR THE THREE FORECAST CATEGORIES.

THE SEPTEMBER OUTLOOK DEPICTS ELEVATED ODDS OF ABOVE-NORMAL MONTHLY MEAN
TEMPERATURES FOR MOST OF ALASKA BASED ON SIGNIFICANTLY ABOVE-AVERAGE SSTS OFF
THE WEST COAST OF THE STATE (LOCATION OF THE GREATEST PROBABILITIES) AND THE
MAJORITY OF DYNAMICAL MODEL GUIDANCE. FAVORED ABOVE-NORMAL TEMPERATURES ARE
ALSO NOTED FOR THE FAR WESTERN CONUS AS SUBSEASONAL AND SEPTEMBER MONTHLY
INTEGRATED FORECAST GUIDANCE ARE CONSISTENT IN DEPICTING WARMER THAN NORMAL
CONDITIONS IN THESE AREAS.

THE FORECAST FOR THE SOUTHWEST CONUS INDICATES ONLY SLIGHTLY INCREASED
PROBABILITIES FROM CLIMATOLOGY FOR ABOVE NORMAL TEMPERATURES DUE TO CONFLICTING
INFORMATION. STRONG POSITIVE LONG TERM TRENDS ARE OFFSET BY FORECAST GUIDANCE
FAVORING ABOVE NORMAL RAINFALL AND BELOW NORMAL TEMPERATURES IN SOME AREAS.

MOVING EASTWARD TO THE INTERIOR CONUS, EC IS FORECAST FOR THIS REGION DUE TO
COMPETING FACTORS. THESE INCLUDE EARLY IN THE MONTH SUBSEASONAL FORECAST
GUIDANCE FAVORING BELOW NORMAL TEMPERATURES, HIGH FORECAST UNCERTAINTY AND
LIKELY LARGE VARIABILITY DURING THE SECOND HALF OF THE MONTH, AREAS OF DRY SOIL
MOISTURE CONDITIONS AND LOW-FREQUENCY IMPACTS SOME OF WHICH WOULD TEND TO
SUPPORT WARMER THAN NORMAL CONDITIONS IN SOME AREAS. STRONG POSITIVE LONG TERM
TRENDS AND SOME FORECAST GUIDANCE INFORMATION PRIMARILY FAVOR ELEVATED ODDS OF
ABOVE NORMAL TEMPERATURES ALONG THE GULF COAST AND IN THE NORTHEAST CONUS.

THE SEPTEMBER PRECIPITATION OUTLOOK FAVORS ABOVE NORMAL TOTAL MONTHLY
PRECIPITATION AMOUNTS FOR WESTERN ALASKA ASSOCIATED WITH POTENTIAL ELEVATED
MOISTURE DUE TO LARGE POSITIVE SST DEPARTURES FROM CLIMATOLOGY IN COASTAL AREAS
AS WELL AS SIGNATURES FROM MODEL FORECAST GUIDANCE.

THE SOUTHWEST MONSOON IS ANTICIPATED TO REMAIN NEAR TO ABOVE AVERAGE DURING ITS
FINAL MONTH AS ABOVE NORMAL SSTS OFF THE WESTERN COAST OF NORTH AMERICA ARE
LIKELY TO MAINTAIN, ON AVERAGE, AN ACTIVE EAST PACIFIC OCEAN ITCZ AND TROPICAL
CYCLONE SEASON RESULTING IN POTENTIAL MOISTURE SURGES INTO THE SOUTHWEST
PORTION OF THE CONUS.

STRONG SUBTROPICAL ATLANTIC RIDGING AND ASSOCIATED MEAN FLOW TO THE SOUTHEAST
AND MID-ATLANTIC COAST FAVORS ENHANCED ODDS OF ABOVE NORMAL PRECIPITATION IN
THESE AREAS. FORECAST GUIDANCE FAVORS BELOW NORMAL PRECIPITATION IN THE PACIFIC
NORTHWEST WHILE CONDITIONS ACROSS THE CARIBBEAN AND ATLANTIC MAIN DEVELOPMENT
REGION (MDR) LOWER THE ODDS FOR MOISTURE TRANSPORT TO THE GULF COAST AND LONG
TRACK TROPICAL SYSTEMS TO ENTER AND PERSIST IN THE GULF OF MEXICO. THESE
FACTORS FAVOR BELOW NORMAL MONTHLY PRECIPITATION AMOUNTS FOR THE TEXAS AND
LOUISIANA COAST.

FORECASTER: JON GOTTSCHALCK

THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, 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.

AN UPDATED MONTHLY OUTLOOK... FOR SEP WILL BE ISSUED ON FRI AUGUST 31 2018

THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.
$$

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