020
FXUS07 KWBC 311929
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300 PM EDT MON MAR 31 2008
30-DAY OUTLOOK DISCUSSION FOR APRIL 2008
MODERATE LA NINA CONDITIONS CONTINUE THROUGHOUT THE TROPICAL PACIFIC AND WILL
CONTINUE TO FORM THE UNDERLYING BASIS FOR THIS MONTHLY FORECAST. BELOW AVERAGE
SEA SURFACE TEMPERATURES (SSTS) ARE OBSERVED ACROSS THE CENTRAL AND
EAST-CENTRAL EQUATORIAL PACIFIC. SSTS MORE THAN 1 DEGREE CENTIGRADE BELOW
AVERAGE WERE OBSERVED BETWEEN 160E AND 120W AND THE LATEST WEEKLY NINO 3.4
REGION INDEX VALUE IS NOW -1.0 DEGREES C WHICH REPRESENTS A NOTABLE WEAKENING
OF THE NEGATIVE DEPARTURES FROM ONE MONTH AGO. IN ADDITION THE LOW LEVEL
EQUATORIAL EASTERLY WINDS HAVE BEEN STRONGER THAN AVERAGE ACROSS THE CENTRAL
EQUATORIAL PACIFIC... STRONGER THAN AVERAGE UPPER LEVEL WESTERLY WINDS HAVE
BEEN OBSERVED... AND CONVECTION HAS BEEN SUPPRESSED OVER THE CENTRAL PACIFIC.
COLLECTIVELY, THESE ATMOSPHERIC AND OCEANIC CONDITIONS ARE SIMILAR TO THOSE
ACCOMPANYING THE LAST STRONG LA NINA EPISODE IN 1998-2000. SST FORECASTS FROM
THE CFS AND A SUITE OF OTHER STATISTICAL AND DYNAMICAL MODELS INDICATE THAT LA
NINA SHOULD REMAIN MODERATELY STRONG THROUGH BOREAL SPRING. THEREFORE, THE
APRIL TEMPERATURE AND PRECIPITATION FORECASTS ARE STILL BASED TO A SIGNIFICANT
DEGREE ON LA NINA COMPOSITES FOR THE MARCH - APRIL - MAY SEASON.
INTRASEASONAL (MJO) ACTIVITY HAS BEEN RATHER PERSISTENT SINCE MID-NOVEMBER, AND
HAS MODULATED LA NINA IMPACTS ACROSS THE CONUS AT VARIOUS TIMES DURING THE
WINTER. DURING MID-MARCH, THE MJO SIGNAL WEAKENED CONSIDERABLY WITH ANOMALOUS
CONVECTION FOCUSED OVER THE EASTERN INDIAN OCEAN AND INDONESIA, AND SUPPRESSED
CONVECTION AT THE DATE LINE. VARIOUS MODEL FORECASTS ARE INDICATING INCREASING
UNCERTAINTY REGARDING THIS MJO, ESPECIALLY DURING THE TWO TO THREE WEEK TIME
FRAME. THEREFORE, THE MJO DOES NOT HAVE A SIGNIFICANT INFLUENCE ON THIS
MONTHLY FORECAST.
THE UPDATED TEMPERATURE OUTLOOK FOR APRIL FAVORS ABOVE AVERAGE TEMPERATURES
ACROSS MOST OF THE FAR SOUTH FROM EASTERN NEW MEXICO TO SOUTHERN PARTS OF NORTH
CAROLINA. BELOW-AVERAGE TEMPERATURES ARE MOST LIKELY FROM SOUTHERN SECTIONS OF
THE ALASKA PANHANDLE THROUGH THE PACIFIC NORTHWEST, IN ADDITION TO COASTAL
AREAS OF SOUTHERN CALIFORNIA. THE LATTER COLD AREA IS ATTRIBUTED TO ANOMALOUSLY
COLD SEA SURFACE TEMPERATURES RECENTLY OBSERVED NEAR THE COAST. SOME OF THE
TOOLS, SUCH AS THE SKILL-MASKED CFS HAD A BROAD AREA OF COLD PREDICTED OVER THE
EAST- CENTRAL CONUS, AND OTHER TOOLS ALSO CAUTIONED AGAINST EXPANDING WARMTH
NORTHWARD ACROSS THE EAST. ELSEWHERE, WHICH INCLUDES MUCH OF THE CONUS AND ALL
OF ALASKA, EQUAL CHANCES OF BELOW-, NEAR-, AND ABOVE NORMAL TEMPERATURE ARE
FORECAST.
THE UPDATED PRECIPITATION FORECAST FOR APRIL (MADE MARCH 31ST) USED THE
0.5-MONTH LEAD PRECIPITATION FORECAST ISSUED ON MARCH 20TH AS THE STARTING
POINT, WHICH WAS MODIFIED ACCORDING TO THE LATEST NUMERICAL MODEL GUIDANCE.
THE RELATIVELY WET AREAS DEPICTED OVER THE PACIFIC NORTHWEST, UPPER MISSISSIPPI
VALLEY, AND FROM THE SOUTH-CENTRAL PLAINS EASTWARD TO THE OHIO AND TENNESSEE
VALLEYS ARE BASED PRIMARILY ON EXTENDED RANGE (8-14 DAY) GUIDANCE. THIS
INCLUDED THE CPC AUTO PRECIPITATION PROG AND THE CDC REFORECAST PRECIPITATION,
IN ADDITION TO THE SKILL-MASKED MONTHLY CFS FORECAST FOR APRIL. THE HPC
QUANTITATIVE PRECIPITATION FORECASTS FOR DAYS 1-5 WERE ALSO CONSIDERED, WHICH
HAD UP TO 0.5" OF RAIN ALONG THE SOUTHERN CALIFORNIA COAST, AS WELL AS A
MAXIMUM OF 7 INCHES CENTERED OVER SOUTHWEST MISSOURI. RELATIVELY DRY
CONDITIONS ARE ANTICIPATED OVER PARTS OF THE SOUTHWEST AND SOUTHEAST.
ELSEWHERE, WHICH INCLUDES MUCH OF THE CONUS AND ALL OF ALASKA, EQUAL CHANCES OF
BELOW-, NEAR-, AND ABOVE NORMAL PRECIPITATION ARE 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 MAY 2008...WILL BE ISSUED ON THU APR 17 2008
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1971-2000 BASE PERIOD.
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