PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EDT SUN SEP 30 2007 30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2007 DURING AUGUST AND MUCH OF SEPTEMBER 2007 NEGATIVE EQUATORIAL SEA SURFACE TEMPERATURE (SST) ANOMALIES IN THE EASTERN PACIFIC EXPANDED WESTWARD AND NOW EXTEND FROM THE COAST OF SOUTH AMERICA TO THE DATE LINE. THREE OF THE NINO INDICES (EXCLUDING NINO 4) WERE COOLER THAN -0.5 DEG C THROUGHOUT AUGUST... WITH THE NINO 4 INDEX TURNING NEGATIVE IN SEPTEMBER. THE UPPER-OCEAN HEAT CONTENT (AVERAGE TEMPERATURES IN THE UPPER 300 METERS OF THE OCEAN) IN THE CENTRAL AND EAST-CENTRAL EQUATORIAL PACIFIC CONTINUES TO BE BELOW AVERAGE. TEMPERATURES AT THERMOCLINE DEPTH RANGE FROM 1 TO 4 DEG C BELOW AVERAGE. LOW-LEVEL EASTERLY WINDS REMAINED STRONGER THAN AVERAGE IN THE WEST-CENTRAL EQUATORIAL PACIFIC. DURING THE PAST FEW WEEKS, CONVECTION WAS SUPPRESSED THROUGHOUT MOST OF THE TROPICAL PACIFIC, IN PARTICULAR BETWEEN THE EQUATOR AND 10N, AND WAS ENHANCED OVER PARTS OF THE PHILLIPPINES, MALAYSIA, AND INDONESIA. COLLECTIVELY... THE OCEANIC AND ATMOSPHERIC CONDITIONS REFLECT LA NINA CONDITIONS. HOWEVER... LA NINA CONDITIONS ARE NOT EXPECTED TO EXERT MUCH INFLUENCE ON CLIMATE ANOMALIES OVER THE U.S. IN OCTOBER. THE TRADITIONAL STATISTICAL TOOLS... SMLR... CCA... AND OCN ALL HAVE MODEST INDICATIONS FOR ABOVE AVERAGE TEMPERATURES ACROSS MOST OF THE LOWER 48 STATES AND ALASKA FOR OCTOBER. THE LATEST EXTENDED-RANGE GFS MODEL GUIDANCE SUPPORTS A BROAD AREA OF RELATIVE WARMTH ACROSS MUCH OF THE NORTHEASTERN QUARTER OF THE CONUS. IT IS DIFFICULT TO SAY WHETHER OR NOT THIS WARMTH WILL LAST THROUGHOUT A GOOD PORTION OF THE SECOND HALF OF THE MONTH. THE EXTENDED-RANGE GUIDANCE ALSO SUGGESTS NEAR TO BELOW NORMAL TEMPERATURES FOR THE SOUTHWEST, DESPITE THE TREND BASED PREFERENCE FOR WARMTH IN THAT REGION. DUE TO CONSIDERATIONS FROM THE FIRST HALF OF THE MONTH... AVERAGE TEMPERATURES FORECAST ACROSS THE SOUTHWEST IN THE HALF-MONTH LEAD OUTLOOK HAS BEEN REMOVED, BUT WOULD BE PREDICTED (WITH LOW PROBABILITY) FOR THE NORTHEAST U.S. ELSEWHERE... EQUAL CHANCES OF BELOW-... NEAR-... AND ABOVE AVERAGE SURFACE TEMPERATURES ARE PROJECTED FOR OCTOBER. FOR THE PRECIPITATION OUTLOOK... THE SMLR FORECASTS ABOVE AVERAGE PRECIPITATION OVER THE EASTERN GREAT LAKES AND OHIO VALLEY AND BELOW AVERAGE OVER THE DESERT SOUTHWEST. THE CCA TOOL (AND TO A LESSER EXTENT THE OCN) ALSO ANTICIPATES RELATIVE DRYNESS OVER THE SOUTHWEST. WHETHER OR NOT THIS VERIFIES IS LARGELY DEPENDENT UPON LATE SEASON EASTERN PACIFIC TROPICAL CYCLONE ACTIVITY. THE SKILL-MASKED CFS PREDICTS ABOVE AVERAGE PRECIPITATION OVER NORTHERN AND CENTRAL CALIFORNIA... NORTHERN NEVADA... AND ALSO OVER THE UPPER MISSISSIPPI VALLEY. THE CAS TOOL DISAGREES WITH THE WETNESS PREDICTED OVER CALIFORNIA... AND HAS DRYNESS IN THAT REGION INSTEAD. EXTENDED-RANGE MODEL GUIDANCE INDICATES AN INCREASE IN STORM ACTIVITY FURTHER UP THE COAST FOR WASHINGTON AND OREGON, AND ALSO INCLUDES THE POSSIBILITY OF TROPICAL ACTIVITY AND ONSHORE FLOW FOR THE SOUTH ATLANTIC COAST. THE AREA OF ABOVE AVERAGE PRECIPITATION FORECAST OVER THE EASTERN GREAT LAKES DURING THE HALF-MONTH LEAD FORECAST (ISSUED SEPTEMBER 20TH) WAS NOT INCLUDED IN THE UPDATED OUTLOOK BECAUSE IT HAD LITTLE SUPPORT FROM THE GFS EXTENDED-RANGE MODEL RUNS. THE OFFICIAL OUTLOOK FEATURES ABOVE AVERAGE PRECIPITATION ALONG THE GULF AND SOUTH ATLANTIC COASTS FROM THE UPPER TEXAS COAST TO THE VIRGINIA CAPES, INCLUDING FLORIDA, AND BELOW AVERAGE PRECIPITATION OVER THE SOUTHWESTERN STATES. THE WETNESS PREDICTED ACROSS THE GULF AND SOUTH ATLANTIC COASTS IS ALSO BASED UPON THE FACT THAT THE PRIMARY TROPICAL STORM AND HURRICANE DEVELOPMENT AREAS IN OCTOBER ARE THE GULF OF MEXICO AND CARIBBEAN SEA. ELSEWHERE... WHICH INCLUDES MUCH OF THE CONUS AND ALL OF ALASKA... EQUAL CHANCES OF BELOW-... NEAR-... AND ABOVE AVERAGE PRECIPITATION IS FORECAST. FORECASTER: ANTHONY ARTUSA NOTES: AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED AS EC (EQUAL CHANCES). THE NEXT MONTHLY OUTLOOK...FOR NOVEMBER 2007...WILL BE ISSUED ON THU OCT 18 2007 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1971-2000 BASE PERIOD. $$