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982 NOUS41 KWBC 191757 PNSWSH TECHNICAL IMPLEMENTATION NOTICE 05-80 NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC 100 PM EST MON DEC 19 2005 TO: FAMILY OF SERVICES /FOS/ SUBSCRIBERS...NOAA WEATHER WIRE SERVICE /NWWS/ SUBSCRIBERS...EMERGENCY MANAGERS WEATHER INFORMATION NETWORK /EMWIN/ SUBSCRIBERS... OTHER NATIONAL WEATHER SERVICE /NWS/ CUSTOMERS AND PARTNERS...NWS EMPLOYEES FROM: PAUL HIRSCHBERG CHIEF...SCIENCE PLANS BRANCH OFFICE OF SCIENCE AND TECHNOLOGY /OST/ SUBJECT: NEW CALCULATION OF CAPE IN NCEP NAM MODEL: EFFECTIVE FEBRUARY 7 2006 AT 1200 UTC EFFECTIVE FEBRUARY 7 2006...BEGINNING WITH THE 1200 COORDINATED UNIVERSAL TIME /UTC/ RUN...THE NATIONAL CENTERS FOR ENVIRONMENTAL PREDICTION /NCEP/ WILL CHANGE THE COMPUTATION OF THE SURFACE- BASED CONVECTIVE AVAILABLE POTENTIAL ENERGY /CAPE/ AND CONVECTIVE INHIBITION /CIN/ PARAMETERS IN THE NORTH AMERICAN MESOSCALE /NAM/ MODEL. THE CURRENT FORMULATION SEARCHES THE LOWEST 70 MILLIBARS /MB/ FOR THE LEVEL WITH THE HIGHEST EQUIVALENT POTENTIAL TEMPERATURE /THETA-E/. THIS PARCEL IS THEN LIFTED TO GENERATE VALUES FOR CAPE AND CIN. VARIOUS NWS OFFICES AND THE NCEP STORM PREDICTION CENTER HAVE SUGGESTED THIS FORMULATION OCCASIONALLY RESULTS IN A PARCEL BEING LIFTED THAT IS NOT REPRESENTATIVE OF TRUE SURFACE CONDITIONS. SEVERAL CASES HAVE BEEN IDENTIFIED IN WHICH CONDITIONS AT THE SURFACE WERE NOT UNSTABLE...HOWEVER THE CALCULATION GENERATED A HIGH VALUE OF CAPE BY LIFTING A PARCEL WELL ABOVE THE GROUND. BECAUSE THE NAM OFFERS SEVERAL CAPE/CIN COMPUTATIONS TO REPRESENT ELEVATED INSTABILITY...NWS DECIDED THE CURRENT DETERMINATION OF A SURFACE-BASED PARCEL SHOULD BE REVISED TO MORE ACCURATELY REPRESENT LOW-LEVEL CONDITIONS. THE REVISED COMPUTATION WILL SEARCH FOR THE HIGHEST THETA-E AT EACH GRID POINT OVER A DEPTH SMALLER THAN THE 70 MB CURRENTLY USED. THE PRECISE DEPTH WILL BE BASED ON THE SURFACE PRESSURE TO MAKE SURE THAT A LEVEL CLOSE TO THE GROUND IS USED AT LOW ELEVATIONS...WHILE ABLE TO SEARCH OVER A LARGER DEPTH AT HIGHER ELEVATIONS WHERE THE FIRST MODEL LEVEL ABOVE THE GROUND IS OFTEN MUCH HIGHER ABOVE THE SURFACE. THIS FORMULATION LEADS TO A RANGE OF DEPTHS FROM ABOUT 10 MB AT SEA LEVEL TO AS MUCH AS 50 MB OVER THE HIGHEST TERRAIN. PLEASE NOTE THAT THERE ARE CURRENTLY FOUR SETS OF CAPE/CIN COMPUTATIONS IN THE NAM. 1. THE SURFACED-BASED FIELDS 2. BEST CAPE/CIN COMPUTED BY FINDING THE HIGHEST THETA-E IN THE SIX MIXED 30 MB DEEP LAYERS CLOSEST TO THE GROUND 3. MIXED LAYER CAPE/CIN COMPUTED BY TAKING THE AVERAGE THERMODYNAMIC PROPERTIES IN THE LOWEST 90 MB 4. BEST CAPE/CIN COMPUTED BY FINDING THE LEVEL IN THE LOWEST 300 MB WITH THE HIGHEST THETA-E THIS CHANGE WILL AFFECT ONLY THE FIRST ITEM IN THE LIST ABOVE. DAILY PLOTS OF ALL OF THESE FIELDS CAN BE VIEWED AT /USE LOWER CASE LETTERS/: HTTP://WWW.EMC.NCEP.NOAA.GOV/MMB/NAMSVRFCST IF YOU HAVE QUESTIONS CONCERNING THIS CHANGE...CONTACT: DR. GEOFF DIMEGO CHIEF... NCEP...MESOSCALE MODELING BRANCH CAMP SPRINGS MARYLAND PHONE: 301 763 8000 X7221 EMAIL: GEOFF.DIMEGO@xxxxxxxx OR GEOFF MANIKIN NCEP... MESOSCALE MODELING BRANCH CAMP SPRINGS MARYLAND PHONE: 301 763 8000 X7263 EMAIL: GEOFFREY.MANIKIN@xxxxxxxx THIS AND OTHER NWS TECHNICAL IMPLEMENTATION NOTICES ARE AVAILABLE ONLINE AT /USE LOWER CASE LETTERS/: HTTP://WWW.NWS.NOAA.GOV/OM/NOTIF.HTM $$ NNNN ---------- End Forwarded Message ----------
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