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INTELLIGENT USE OF THE AVN/MRF

INTELLIGENT USE OF THE AVN/MRF. Michael Eckert. HYDROMETEOROLOGICAL PREDICTION CENTER. CAMP SPRINGS, MD. E-MAIL ADDRESS: michael.eckert@noaa.gov. COMAP SYMPOSIUM 00-1 15 December 1999.

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INTELLIGENT USE OF THE AVN/MRF

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  1. INTELLIGENT USE OF THE AVN/MRF Michael Eckert HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS, MD E-MAIL ADDRESS: michael.eckert@noaa.gov COMAP SYMPOSIUM 00-1 15 December 1999

  2. Understanding the performance of an operational model is critical to being able to forecast the sensible weather • All models have strengths and weaknesses. • All have trouble handling smaller scale features. • All have problems with convection. • All do a decent job in handling the short range (0-36 hr) forecast of synoptic scale features.

  3. Why models have forecast problems • Initialization and quality control smoothes data fields. Some of the lost detail may be important. • Lack of data over the oceans and Mexico. • Atmospheric processes are non-linear; small changes in initial conditions can lead to large forecast variations (this is the basis for ensemble forecasting). • Terrain may not have sufficient resolution • Model physics are approximations • for lower resolution models (OUR CURRENT OPERATIONAL MODELS) convection is parameterized • for higher resolution models the micro-physical processes are parameterized

  4. The T126 version of the Avn does not have sufficientresolution to adequately depict the rain shadow east of the Cascades. A forecaster needs to know the climatology of precipitation during certain flow regimes. 12-36 AVN V.T. 12Z 23 FEB 1999 Prism climatological precipitation data. Note the distinct rain shadow to the east of the Cascades PRECIPITATION ANALYSIS AVN V.T. 12Z 23 FEB 1999

  5. The way the physics are approximated can lead to model errors, for example • The Betts parameterization in the eta is handled differently over land and water • this can cause the eta and meso-eta to erroneously strengthen the coastal front. • and to forecast too much rain along the Gulf and Atlantic Coastal regions

  6. AVN/MRF APPROXIMATED PHYSICS • THE AVN/MRF USE A MODIFIED GRELL SCHEME • THIS USES THE CHANGE IN STABILITY TO DETERMINTE WHEN TO RELEASE ENERGY AS CONVECTION. • NO DIRECT MIXING BETWEEN THE CLOUDY AIR AND ENVIRONMENTAL AIR. (except at the cloud top and bottom) • NO CLOUD WATER EXISTS, THEREFORE ALL WATER IS CONVERTED TO RAIN.

  7. A NUMBER OF AVN/MRF PERFORMANCE CHARACTERISTICS HAVE CHANGED IN THE PAST YEAR. • SINCE JUNE THE AVN/MRF AGAIN UNDERPREDICTS HEAVIER PRECIPITATION THRESHOLDS. • THE AVN/MRF NO LONGER “OFTEN UNDERPREDICTS SURFACE LOWS, ESPECIALLY OVER OCEANS” • ISOLATED PRECIPITATION “BULLSEYES” HAVE BEEN A PROBLEM, ESPECIALLY DURING THE WARM SEASON. • THIS WAS MORE LIKELY WHEN THERE WAS SLOW SYSTEM MOVEMENT

  8. LATEST AVN/MRF CHANGES • June 15, 1998: INCREASED HORIZONTAL RESOLUTION TO 170 AND LAYERS TO 42 • THIS LED TO A WARM BIAS AND THE DEVELOPMENT OF SPURIOUS PRECIPIATION BULLSEYES/TROPICAL SYSTEMS • July 21, 1998: EMERGENCY MODEL IMPLEMENTATION TO REDUCE ERRORS IN THE JUNE 15TH CHANGE

  9. AVN/MRF Still Often Has Problems Handling Upslope Events Around 75% of the precipitation predicted by the AVN during this event was grid scale, rather than convective, precipitation. In these cases, the model QPF is often too far to the northwest. The maximum rainfall falls farther to the south along the surface front. $5” $4” $4” $3” $3” 12-36 hr AVN QPF V.T. 12Z 27 APR 98 VERIFYING 24H PRECIPITATION V.T. 12Z 27 APR 98

  10. About 75% of the AVN Rainfall Over the OK Panhandle Was Grid-scale Precipitation (Not Convection). The overprediction of grid-scale precipitation may result in latent heat being released at too low a level in the atmosphere. This tends to cause pressures to lower, often resulting in the lows wrapping up too far to the west or northwest. 36-HR AVN/MRF VERIFYING AVN/MRF V.T. 12Z 27 APRIL 98 V.T. 12Z 27 APRIL 98

  11. Another Case: AVN Wraps Low Too Far North And West. Both Surface and 500 mb Lows Are Too Deep. PRECIPITATION FORECAST IS POOR BECAUSE OF BAD SURFACE AND 500 MB FORECASTS OR VICE-VERSA. AVN 36 HR FCST APR 1998 AVN VERIFYING SURFACE ANALYSIS V.T. 00Z APR 1998 Is this another case with some type of latent heating feedback problem?

  12. Aviation Model handling of 500 mb trough 558 546 546 552 558 558 564 564 564 570 570 576 576 570 06h V.T. 18Z Apr 18 36h V.T. 00Z Apr 20 Analysis V.T. 00Z Apr 20 The vorticity increases as the system lifts northeastward even though it never taps into or phases with any northern stream energy.

  13. 12-36 hr bias 12-36 hr bias Valid 2 Apr - 30 Apr 98 Valid 2 Feb - 28 Feb 98 4.0 MRF GLOBAL 1.2 EARLY ETA 1.0 3.0 0.8 MRF GLOBAL 2.0 BIAS SCORE 0.6 BIAS SCORE EARLY ETA 0.4 1.0 0.2 0.0 0.0 .10 .75 1.50 .01 .25 .50 1.00 2.00 .01 .50 2.00 .10 .25 .75 1.00 1.50 THRESHOLD (INCHES) THRESHOLD (INCHES) BIAS COMPARISON OF 12-36 HR MRF AND EARLY ETA FORECASTS VERIFIED TO AN 80 KM GRID THE MRF AND AVN OVERPREDICT ALL THRESHOLDS ESPECIALLY THE HEAVIER ONES DURING SPRING AND SUMMER

  14. 24-h MRFX v.t. 12Z 27 May 1998 36-h MRFX v.t. 00Z 28 May 1998 10”+ bullseye 24-36-h MRFX v.t. 00Z 28 May 1998 The MRF and MRFX spin-up precipitation bombs and tropical systems erroneously at all time ranges. SFC ANALYSIS v.t. 00Z 28 May 1998

  15. MRF PRECIPITATIONConvective - dashedGridscale - solid green(inches -Vs- time)BEFORE 7/21 AFTER 7/21

  16. MRF RELATIVE HUMIDITY(pressure -Vs- time)BEFORE 7/21 AFTER 7/21 >99% RH >99% RH

  17. >342 <342 <342 >342 <342 >342 MRF THETA-E (pressure -Vs- time)BEFORE 7/21 AFTER 7/21

  18. After the change • Latent heat induced precipitation bombs are less common. Surface lows are less prone to spin up. • The MRF/AVN still has problems initializing tropical wave at low latitudes.

  19. During Oct-Feb 1999, the AVN/MRF now had a bias of • About 1.00 for 1.00” or greater amounts • .47 for 2.00” or greater amounts • .27 for 3.00” or greater amounts The Aviation significantly underpredicted heavier rainfall amounts

  20. During OCT-JAN 1999 4 INCH OR GREATER ISOHYETS • WERE ANALYZED 22 TIMES • WERE PREDICTED 2 TIMES • THE AVIATION FORECAST 3” OR GREATER AMOUNTS 6 TIMES.

  21. 1.2 12-36 hr bias Valid 2 Apr - 30 Apr 98 1.0 4.0 B MRF GLOBAL EARLY ETA I 0.8 A 3.0 S 0 .6 0.4 2.0 BIAS SCORE 0.2 1.0 0.0 .01 .10 .25 .50 .75 1.00 1.50 2.00 THRESHOLD (INCHES) 0.0 .01 .50 2.00 .10 .25 .75 1.00 1.50 THRESHOLD (INCHES) SINCE THE CHANGES INJUNE AND JULY, THE ETA BIAS FOR HEAVY AMOUNTS HAS DECREASED SIGNIFICANTLY 12-36 HR AVN/MRF BIAS VALID 1 AUG - 25 AUG 1998 WILL THE BIAS INCREASE INCREASE IN THE COLD SEASON?

  22. One of the typical errors of the AVN is to predict convective systems too far north 12-36 HR QPF V.T. 1200Z 29 JAN 1999 ANALYSIS V.T. 1200Z 29 JAN 1999 12-36 HR QPF V.T. 1200Z 30 JAN 1999 ANALYSIS V.T. 1200Z 30 JAN 1999

  23. The AVN/MRF may be right onthe synoptic scale features but cannot handle outflow boundaries, etc. 36 HR QPF V.T. 1200Z 29 JAN 1999 ANALYSIS V.T. 1200Z 29 JAN 1999 36 HR QPF V.T. 1200Z 29 JAN 1999 A SLOW MOVING 500 CLOSE LOW AND QUASISTATIONARY FRONT WERE WELL FORECAST BY THE MODEL. HOWEVER, THE EFFECTIVE BOUNDARY REMAINED SOUTH OF THE MODEL FORECAST

  24. Despite these problems, the AVN model was the best model during the winter

  25. LOWS TO THE LEE OF THE ROCKIES • THE AVN AND NGM USUALLY PREDICT THEM TO FORM TOO FAR NORTH. HOWEVER, DURING THE PAST WINTER THE AVN WAS SIGNIFICANTLY BETTER AT HANDLING CYCLONES AND THE ASSOCIATED PRECIPITATION THAN THE ETA. • USE THE 300 MB UPPER LEVEL JET. THE SURFACE LOW IS USUALLY FOUND BENEATH THE LEFT EXIT REGION OF THE JET

  26. The AVN broke continuity on this forecast being much faster than previous runs or models from other centers When systems are digging into the west with no kicker evident upstream, it is usually smart to follow the lead of the slowest model. In this case the AVN was much to fast with the upper low in the west.

  27. If the 500 forecast is poor, the surface forecast will also be corrupted. Note that surface low in the plains is too deep and far north on the forecast. When the avn is in error to the lee of the mountains. This is the typical error.

  28. 36 HR AVN V.T. 00Z APR 09, 1995 THE NGM AND AVN/MRF HAVE SERIOUS PROBLEMS WITH ARCTIC AIRMASSES L 36 HR NGM V.T. 00Z APR 09, 1995 AVN ANALYSIS V.T. 00Z APR 09, 1995 TEMPERATURES ACROSS KANSAS WERE IN THE LOW TO MID 50s WITH STRONG NORTH WINDS. SOUTH OF THE FRONT TEMPERATURES WERE IN THE UPPER 70s TO LOW 90s.

  29. Why models have problems with arctic airmasses • Terrain is averaged • Initialization process sometimes robs shallow airmass of its coldness • Models have problems handling the strength of the inversion • The leading edge of the ETA LI gradient is often the best indicator of the frontal position

  30. MRF PERFORMANCE FOR 3-5 DAY FORECASTS • SHALLOW COLD AIR IS NOT HANDLED WELL. THE MODEL IS SLOW TO TRANSPORT SHALLOW COLD AIRMASSES, ESPECIALLY ARCTIC AIRMASSES JUST TO THE EAST OF THE ROCKY MOUNTAINS OR APPALACHIAN CHAIN. THIS IS DUE TO MODEL TERRAIN ERRORS. • EASTERLY BOUNDARY LAYER WINDS ARE OFTEN OVERPREDICTED ALONG THE FRONT RANGE OF THE ROCKY MOUNTAINS. • MODEL HAS A SLIGHT COLD BIAS, ESPECIALLY OVER THE EASTERN THIRD OF THE COUNTRY, DURING THE COLD SEASON.

  31. MRF PERFORMACE FOR 3-5 DAY FORECASTS (CONT) • MODEL TENDS TO PHASE SEPARATE STREAMS TOO MUCH. POSSIBLY DUE TO RESOLUTION • AT HIGH LATITUTES (NORTH OF 50O), THE MODEL PREDICTS TOO MUCH RETROGRESSION • TENDS TO WEAKEN THE REMAINS OF UPPER LOWS TOO QUICKLY THAT ARE COMING OUT OF THE SOUTHWEST

  32. A VERIFICATION OF THE 500 H FORECASTS FOR DAY 4 MEAN MRF 70.5 90 ECMWF MEAN ECMWF 70.4 80 MEAN UKMET 62.7 ANOMALY CORRELATION MRF 70 60 UKMET 50 40 30 -45 -40 -35 -30 -25 -20 -15 -10 -05 DAY (VALID TIME RELATIVE TO TODAY) DEPICTS MEDIUM RANGE MODEL PERFORMANCE FOR THE PAST 50 DAYS WORTH OF RUNS. NOTE THAT HOW WELL A MODEL PERFORMS APPEARS TO BE REGIME DEPENDENT.

  33. MEAN SCORES HIGH DAILY VARIABILITY IS WEATHER PATTERN DEPENDENT. THE ECMWF IS BEST AT 500 MB BUT CAN HAVE SOME BAD MSLP FORECASTS HPC/MRF/ECMWF MSLP ANOMALY CORRELATIONS

  34. The best ensemble approach is to use various models to assess the possible range of solutions THE MEDIUM RANGE MODELS AVAILABLE AT HPC MODEL RUN HORIZONAL VERTICAL TIMES RESOLUTION LEVELS MRF (00 UTC) 104 KM 28 MRF [1999] (00 UTC) 80 KM 42 CANADIAN (00/12 UTC) 70 KM 28 ECMWF (12 UTC) 40 KM 31 UKMET (00/12 UTC) 60 KM 30 NOGAPS (00/12 UTC) 70 KM 24 *VALUES ARE APPROXIMATED AND UPDATED AS OF DECEMBER 1998

  35. You need to know the characteristics of the MRF MOS guidance. Stations included in MOS How HPC breaks up regional verification of MOS

  36. MOS verification for Northwest (left) and northern Plains (right) MOS POPS ARE USUALLY TOO HIGH

  37. Verification of MOS POPS for Great Lakes Region (top) and Northeast (bottom)

  38. Southwest (left), Southern Plains (right), Southeast (bottom left) and Mid Atantic/Oh Valley (lower right)

  39. NUMBER OF DAYS WHEN THE TEMPERATURE ERROR WAS 8 DEGREES OR GREATER ON DAY 4 HPC MANUAL PROGS USUALLY CUT DOWN ON THE ERRORS DURING THESE TYPE CASES

  40. THE PERCENT OF THE NUMBER OF DAYS (JAN-MAR) HPC FORECASTERS REDUCE THE ERROR BELOW 8 DEGREES F HPC shows improvement for max temperatures through 7 days for all areas

  41. THE AVN HAS PERFORMED MUCH BETTER SINCE GOING BACK TO T126 • During winter its threat scores were higher than those from either the NGM or ETA • The 0-48 hr AVN generally had better mass field forecasts, even to the lee of the Rocy mountains. • The number of spurious lows has been reduced significantly. • The models bias for 2 inch or greater amounts is now considerably below 1.00

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