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INTELLIGENT USE OF THE AVN/MRF 2000

INTELLIGENT USE OF THE AVN/MRF 2000. Wes Junker. HYDROMETEOROLOGICAL PREDICTION CENTER. CAMP SPRINGS, MD. E-MAIL ADDRESS: norman.junker@noaa.gov. Presented COMAP Symposim 00-2 Wednesday, 29 March 2000.

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INTELLIGENT USE OF THE AVN/MRF 2000

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  1. INTELLIGENT USE OF THE AVN/MRF 2000 Wes Junker HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS, MD E-MAIL ADDRESS: norman.junker@noaa.gov Presented COMAP Symposim 00-2Wednesday, 29 March 2000

  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. Beware of the initial analysis errors.

  3. MRF 1ST GUESS VERSUS OBSERVATIONS

  4. MRF INITIAL ANALYSIS VERSUS OBSERVATIONS

  5. The T170 version of the Avn does a better job depicting in the West than the T126 but the model still misses much of the detail in the West. NOTE THAT NEITHER THE AVN OR ETA PREDICT A MAX IN THE SISKIYOU MOUNTAINS OF NORTHERN CA. NEED TO KNOW THE TERRAIN 12-36 HR AVN QPF V.T. 22 FEB 2000 VERIFYING ANALYSIS OF QPF V.T. 22 FEB 2000 12-36 HR ETA QPF V.T. 22 FEB 2000

  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. • THE AVN IS NOW AGAIN A T170 VERSION (SINCE JAN 28) AND SOMETIMES EXHIBITS ITS OLD CONVECTIVE FEEDBACK PROBLEM. ITS BIAS HAS ALSO GONE UP. . • ISOLATED PRECIPITATION “BULLSEYES” HAVE BEEN A PROBLEM DURING MARCH. • THIS IS MORE LIKELY WHEN A SYSTEM HAS PLENTY OF MOISTURE WITH IT. • HEAVY PRECIPITATION OFTEN DOES VERIFY BUT NOT WHERE THE MODEL PREDICTS IT.

  8. AVN/MRF Still Has Problems Handling Upslope Events. It generally overforecasts precipitation 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

  9. 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

  10. 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 In the past the MRF has spun-up precipitation bombs and tropical systems erroneously at all time ranges. Improvements have been made that make such marked error less likely. However, a few spin-ups will probably occur. SFC ANALYSIS v.t. 00Z 28 May 1998

  11. When you see a precipitation bulleye. How can you tell when latent heat feedback may be causing problems Look at the convective and total precipitation If there is little or no convective precipitation, beware especially if the mass fields start looking funny

  12. More reasons to suspect a feedback Produced kink in isobars Round bulleye in vertical motion field and pimple that forms at 700 mb. Sometimes will affect surface forecasts

  13. What happened? A 3 inch max near Shreveport, LA. Verifying analyses Note that the kink in the isobars has disappeared. Such a feature can be induced by latent heat. The induced trough may be subtle but can enhance the low level convergence and help lead to a erroneous forecast.

  14. A test. From the following charts try to decide where you would predict the precipitation max 36hr 700 height and vertical velocity forecast v.t. 12Z 23 Mar 2000. 36hr 500 height and vorticity forecast v.t. 12Z 23 Mar 2000.

  15. Do you think, the 3 inch area is correct in NM, Why or Why not?Would you modify the axis of heavy rain in TX. IF so how? 36hr surface and thickness forecast v.t. 12Z 23 Mar 2000. 12-36hr AVN/MRF QPF v.t. 12Z 23 Mar 2000.

  16. How did you do? The axis was east of the model’s forecast. Note that the surface low was weaker. Did the possible feedback cause the lower pressure? Doen’t his case look like the one in 1998? Axis of heaviest rains outlined in red Verifying surface analysis v.t. 12Z 13 March 2000

  17. Despite the low bias for heavy precipitation during most of the winter. During March • The AVN twice forecast 5 inch precipitation maxes that were not observed. • During each case almost all the precipitation was grid scale not convective. • When this occurs other fields, especially the 700h height field will be affected.

  18. AVN PRECIPITATION CHARACTERISTICS. • AVN has a large bias for the lighter precipitation thresholds. • Its bias grows with time. During Feb. 2000, the AVN had a low bias for heavy amounts. In March the model has had a high bias for amounts up to 2.00”

  19. Avn threat score and bias during Feb. 2000 • 12-36 hr forecast • bias for .50”=1.28, for 1.00”=1.06, for 2.00”=.36 • T.S. for .50”=.348, for 1.00”=.233, for 2.00”=.052 • 36-60 hr • bias for .50”=1.5, for 1.00”=1.3, for 2.00”=.60 • T.S. for .50”=.28, for 1.00”=.176, for 2.00”=.04 • 60-84 hr • bias for .50=1.54, for 1.00”=1.3, for 2.00”=1.07 • T.S. for .50=.275, for 1.00”=.178, for 2.00=.054

  20. AVN Bias for various thresholds for the 30 days ending 25 Mar 2000

  21. Note the AVN threat scores are better usually better than the eta during winter and worse in summer

  22. The AVN/MRF had a warm bias at mid levels over the Rocky Mountains and Plains (2 or 3oC at 700 mb). If the eta had lower 1000-500 thickness over Plains in summer but had similar 500h height, it was usually right. 36 hr surface and thickness v.t. 12Z 17 July 1999, <576 (shaded) Verifying surface and thickness analysis v.t. 12Z 17 July 1999, <576 (shaded)

  23. Note how dry AVN/MRF was over the Plains. Also note that it predicted too much rain across the South. This was fairly typical of its summer forecasts. 24 hr precipitation analysis v.t. 12Z 17 July 1999 12-36 hr AVN QPF v.t. 12Z 17 July 1999

  24. For .50” the avn threat scores were lower than the eta during Jan and Feb. Possibly because the AVN overpredicted the threshold.

  25. 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

  26. 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

  27. LOWS TO THE LEE OF THE ROCKIES • THE AVN AND NGM USUALLY PREDICT THEM TO FORM TOO FAR NORTH. USE THE 300 MB UPPER LEVEL JET. THE SURFACE • LOW IS USUALLY FOUND BENEATH THE LEFT EXIT REGION OF THE JET

  28. IN ZONAL FLOW

  29. ANOTHER COMMON ERROR 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.

  30. 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.

  31. HPC IS NOW TRYING VERIFY 500 HEIGHT ERRORS BASED ON REGIME, THIS IS A VERFICATION OF 72 HR FORECASTS

  32. ANOTHER PATTERN. NOTE SIMILARITIES IN WHERE THE BIGGEST ERRORS OCCUR

  33. 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.

  34. 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

  35. 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.

  36. MRF PERFORMACE FOR 3-5 DAY FORECASTS (CONT) • MODEL TENDS TO PHASE SEPARATE STREAMS TOO MUCH. • 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

  37. 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.

  38. 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

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

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

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

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

  43. AVN performance characteristics changed when T170 was implemented • The model now has a high bias for most thresholds at least during Spring. • The model suffers from latent heat feedback • During Summer 1999, the AVN had a warm bias at 700 mb and a low precipitation bias for .50” greater amounts over the Plains and Intermountain region. Suspect the problem is still there but won’t know for sure until Summer. • Whenever a model is changed to correct one problem it often changes the model performance characteristics in other ways.

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