PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EST THU DEC 20 2001 6-10 DAY OUTLOOK DEC 26 - 30 2001 . . . . . . . . MODEL COMPARISONS: MODELS CONTINUE TO SHOW A RIDGE BUILDING OVER THE WEST COAST DURING THE NEXT 7 DAYS ALONG WITH THE ATLANTIC RIDGE BUILDING INTO THE DAVIS STRAIGHT. THE SHORT WAVE NOW COMING INTO THE PNW WILL COMBINE WITH LOW PRESSURE OVER HUDSON BAY TO FORM A LARGE VORTEX OVER THE ONTARIO AND QUEBEC REGION BY DECEMBER 25. THIS POSITIVE PNA AND NEGATIVE NAO PATTERN WILL PERSIST INTO THE NEW YEAR. ALL THE MODELS ARE IN GENERAL AGREEMENT ON THIS EVOLUTION ALTHOUGH...AS ALWAYS...THERE ARE DIFFERENCES IN THE DETAILS. THE MRF WANTS TO DIG THE TROUGH TOO FAR INTO THE SOUTHWESTERN U.S. AND THE ECMWF APPEARS TO RETROGRESS THE CUTOFF LOW TOO MUCH IN THE MIDWEST. MRF ENSEMBLE MEMBERS ARE IN EXCELLENT AGREEMENT ON THE BASIC FEATURES OUT TO 2 WEEKS. FORECAST MAPS ARE QUITE SIMILAR TO YESTERDAY. AS IT APPEARS THE COLD AIR WILL SPREAD VIRTUALLY NATIONWIDE...THE PREVIOUS AREA OF FORECAST WARMTH HAS SHRUNK AGAIN IN THE WEST. THE CONFIDENCE FOR DRYNESS IS ALSO LESS TODAY IN THE WEST AS MUCH DEPENDS ON THE STRENGTH AND LOCATION OF THE RIDGE AXIS. A POWERFUL STORM WILL HIT ALASKA AT THE START OF THE FORECAST PERIOD AND ABUNDANT MOISTURE ON RELATIVELY MILD SOUTHERLY FLOW WILL CONTINUE TO AFFECT THE STATE. ELSEWHERE...THE CENTRAL U.S. STORM WILL TRACK ACROSS THE GREAT LAKES REGION SATURDAY-SUNDAY...WITH COASTAL DEVELOPMENT OFF THE NORTHEAST COAST ON MONDAY. THERE IS A POTENTIAL FOR A MUCH BIGGER STORM A FEW DAYS LATER AS A LOBE OF VORTICITY RAPIDLY SWINGS SOUTHWARD FROM THE GREAT BASIN ON SUNDAY AND PHASES WITH THE EASTERN TROUGH ON MONDAY-TUESDAY. A SURFACE LOW SHOULD DEVELOP OFF THE SOUTHEAST COAST ON WEDNESDAY AND TAKE A NORTHERLY PATH THAT COULD BRING SIGNIFICANT SNOW AND RAIN TO THE EAST COAST ON WEDNESDAY AND THURSDAY. THE LATEST AVNX IS QUITE CONSISTENT WITH LAST NIGHTS MRF ON THE TIMING AND TRACK OF THIS SYSTEM. THE WET AREA SHOWN ON THE PRECIPITATION FORECAST MAP ALONG THE EAST COAST IS BASED ON THIS STORM. . . . . . . . . CONFIDENCE IN TODAYS FORECAST IS ABOVE AVERAGE - RATED AS A 4 ON A SCALE OF 1 TO 5. THE OFFICIAL 500-HPA HEIGHT PROG USES 50 PERCENT OF THE MRF ENSEMBLE MEAN CENTERED ON DAY 8...30 PERCENT OF THE OPERATIONAL MRF CENTERED ON DAY 8 AND 20 PERCENT OF THE ECMWF CENTERED ON DAY 8. MODEL OF THE DAY: THE OPERATIONAL MRF THE TEMPERATURE OUTLOOK IS BASED MOSTLY ON THE KLEIN SPECIFICATIONS FROM THE OFFICIAL HEIGHT PROG AND MODEL OUTPUT STATISTICS FROM THE SAME PROG. ANALOGUES AND 850-HPA TEMPERATURE ANOMALIES ARE CONSISTENT WITH THESE FORECASTS. THE PRECIPITATION OUTLOOK IS BASED MAINLY ON ANALOGUES...THE MRF ENSEMBLE OUTPUT... AND THE NEURAL NET. . . . . . . . . 8-14 DAY OUTLOOK FOR DEC 28 2001 - JAN 3 2002 THE OPERATIONAL MRF AND MRF ENSMBLE MEAN REMAIN IN VERY GOOD AGREEMENT ON THE BROAD FLOW PATTERN...WITH THE STRONGLY NEGATIVE NAO AND POSITIVE PNA FAVORING COLD AIR FOR MUCH OF THE CENTRAL AND EASTERN CONUS AND A DRY PATTERN ALMOST NATIONWIDE. THE OPERATIONAL MRF DOES TRY TO BUILD A TROF INTO THE SOUTHWEST WHICH COULD LATER BRING PRECIPITATION TO THE GULF COAST OR SOUTHERN PLAINS... BUT NO LARGE STORMS ARE ANTICIPATED AT THIS TIME. CONFIDENCE IN TODAYS FORECAST IS ABOVE NORMAL FOR THE SEASON...RATED 4 ON A SCALE OF 1 TO 5. THE OFFICIAL 500-MB HEIGHT PROG USES 75 PERCENT OF THE MRF ENSEMBLE CENTERED ON DAY 11 AND 25 PERCENT OF THE MRF OPERATIONAL MEAN CENTERED ON DAY 11. THE TEMPERATURE PROG IS BASED LARGELY ON THE MRF ENSEMBLE 850 HPA TEMPERATURE ANOMALIES...HISTORICAL ANALOGUES...AND THE KLEIN SPECIFICATIONS FROM THE 500-HPA BLEND. THE PRECIPITATION PROG IS BASED MOSTLY ON THE MRF ENSEMBLE MEAN ANOMALIES. . . . . . . . . FORECASTER: D. LE COMTE NOTES: NOTE: A WEB PAGE WITH FORECAST TOOLS ON IT IS AVAILABLE EACH DAY AT 3PM AT: WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/SHORT_RANGE AUTOMATED FORECASTS ARE ISSUED ON SATURDAY AND SUNDAY. OTHERWISE - FORECASTS INCORPORATE FORECASTER INPUT. MODEL OF THE DAY - FOR 6-10 DAYS - IS THE MODEL WHOSE SOLUTION IS CONSIDERED TO BE MORE RELIABLE THAN USUAL - AND MAY BE GIVEN HIGHER THAN TYPICAL WEIGHT IN THE BLEND. NO MODEL OF THE DAY IS CHOSEN FOR 8-14 DAYS. 500 MB HEIGHT IS THE HEIGHT - IN METERS - ABOVE MEAN SEA LEVEL - AT WHICH ABOUT HALF OF THE MASS OF THE ATMOSPHERE LIES ABOVE AND BELOW - AS MEASURED BY THE PRESSURE. UPPER AIR STORM SYSTEMS TEND TO BE STEERED IN THE DIRECTION OF THE WINDS AT 500 HPA. 500-HPA SYSTEMS CORRELATE STRONGLY WITH SURFACE WEATHER. ANOMALY - THE ARITHMETIC DIFFERENCE BETWEEN THE VALUE OF A VARIABLE AT A GIVEN PLACE AND TIME AND THE LONG-TERM AVERAGE OF THAT VARIABLE AT THAT PLACE AND TIME OF YEAR. . . . . . . . . TELECONNECTIONS GIVE THE HISTORICAL RELATIONSHIP BETWEEN THE 500-HPA HEIGHT AT A GIVEN POINT AND ALL OTHER POINTS ON A MAP FOR A GIVEN TIME OF YEAR. WE AVERAGE THE TOP/BOTTOM 10% OF DAILY MAPS FROM 1950-1999 FOR THE SAME TIME OF YEAR HAVING THE HIGHEST/LOWEST 500-HPA HEIGHT AT THE SPECIFIED POINT. KLEIN AND NEURAL NETWORK SPECIFICATIONS GIVE THE HISTORICAL RELATIONSHIP BETWEEN 500-HPA HEIGHT ANOMALIES AND SURFACE TEMPERATURE AND PRECIPITATION. KLEIN SPECIFICATIONS TEND TO EMPHASIZE REGIONAL TELECONNECTIONS - WHILE THOSE FROM THE NEURAL NETWORK WORK FROM GLOBAL TELECONNECTIONS. DAVA MEANS DIVERGENT ANOMALY VORTICITY ADVECTION MODEL. THIS IS A BAROTROPIC MODEL WITH DIVERGENCE IN IT TO ALLOW MORE ACCURATE PREDICTION OF LONG WAVES THAN A NON-DIVERGENT BAROTROPIC MODEL. REFERENCE: QIN J. AND H.M. VAN DEN DOOL - 1996: SIMPLE EXTENSIONS OF AN NWP MODEL. MON. WEA. REV. - VOL 124 - PP 277-287. THE NOTATION FOR THE CATEGORICAL FORECAST INDICATED ON THE MAPS IS THE SAME AS THAT IN THE TABLES: A-ABOVE N-NEAR NORMAL B-BELOW IN THE SOUTHWEST AND OTHER CLIMATOLOGICALLY DRY REGIONS - THERE WILL BE A GREATER THAN 33.3% CHANCE OF NO PRECIPITATION AND OCCASIONALLY EVEN A NORMAL (I.E. MEDIAN) VALUE OF ZERO - ESPECIALLY DURING THE DRY SEASONS. IN SUCH CASES A FORECAST OF NEAR NORMAL IS EFFECTIVELY A FORECAST OF LITTLE OR NO PRECIPITATION. THE NARRATIVE DESCRIPTION OF THE FORECAST PATTERNS FOR TEMPERATURE AND PRECIPITATION FOR BOTH THE 6-10 OR 8-14 DAY PERIODS HAS BEEN DISCONTINUED. THE STATE TABLES FOR BOTH THE 6-10 AND 8-14 DAY PERIODS ARE NOW CONTAINED IN THIS MESSAGE...AVAILABLE AS PMDMRD ON AWIPS. EFFECTIVE THURSDAY MAY 17 2001...THE CLIMATE PREDICTION CENTER HAS SWITCHED TO 1971-2000 BASE PERIOD MEANS FOR TEMPERATURE...PRECIPITATION...AND 500-HPA HEIGHTS AS REFERENCE IN THE CLIMATE OUTLOOKS. THE 1971-2000 BASE PERIOD MEANS HAVE REPLACED THE 1961-1990 BASE PERIOD MEANS. THE NEXT MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON THURSDAY JANUARY 17. . . . . . . . . 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A N OREGON A B NRN CALIF A B SRN CALIF N B IDAHO N N NEVADA N B W MONTANA N N E MONTANA N A WYOMING N N UTAH N N ARIZONA B B COLORADO N N NEW MEXICO B N N DAKOTA N A S DAKOTA B A NEBRASKA N A KANSAS B N OKLAHOMA B B N TEXAS B B S TEXAS B N W TEXAS B N MINNESOTA N N IOWA B N MISSOURI B B ARKANSAS B B LOUISIANA B B WISCONSIN B N ILLINOIS B B MISSISSIPPI B B MICHIGAN B N INDIANA B B OHIO B N KENTUCKY B B TENNESSEE B B ALABAMA B N NEW YORK B N VERMONT B A NEW HAMP B A MAINE N A MASS B A CONN B A RHODE ISL B A PENN B N NEW JERSEY B A W VIRGINIA B N MARYLAND B N DELAWARE B A VIRGINIA B N N CAROLINA B N S CAROLINA B N GEORGIA B N FL PNHDL B A FL PENIN B A AK N SLOPE A N AK ALEUTIAN N A AK WESTERN N A AK INT BSN A A AK S INT A A AK S COAST A A AK PNHDL A A 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A N OREGON N B NRN CALIF A B SRN CALIF A B IDAHO N N NEVADA N B W MONTANA N N E MONTANA N A WYOMING N N UTAH N N ARIZONA N B COLORADO N N NEW MEXICO B N N DAKOTA N A S DAKOTA N A NEBRASKA B N KANSAS B N OKLAHOMA B B N TEXAS B N S TEXAS B A W TEXAS B N MINNESOTA N N IOWA B N MISSOURI B B ARKANSAS B B LOUISIANA B B WISCONSIN B N ILLINOIS B B MISSISSIPPI B B MICHIGAN B N INDIANA B B OHIO B N KENTUCKY B B TENNESSEE B B ALABAMA B B NEW YORK B N VERMONT B B NEW HAMP B B MAINE B N MASS B B CONN B B RHODE ISL B B PENN B N NEW JERSEY B B W VIRGINIA B B MARYLAND B B DELAWARE B B VIRGINIA B B N CAROLINA B B S CAROLINA B B GEORGIA B B FL PNHDL B N FL PENIN B A AK N SLOPE A A AK ALEUTIAN B A AK WESTERN N A AK INT BSN A A AK S INT A A AK S COAST A A AK PNHDL A A LEGEND TEMPS WITH RESPECT TO NORMAL PCPN WITH RESPECT TO MEDIAN A - ABOVE N - NEAR NORMAL A - ABOVE N - NEAR MEDIAN N - NEAR NORMAL B - BELOW B - BELOW THE FORECAST CLASSES REPRESENT AVERAGES FOR EACH STATE. NORMAL VALUES - WHICH MAY VARY WIDELY ACROSS SOME STATES - ARE AVAILABLE FROM YOUR LOCAL WEATHER SERVICE FORECAST OFFICE. FOR ADDITIONAL INFORMATION SEE MESSAGE FXUS06 - ON AFOS AS NFDPMDMRD. NNNN NNNN