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Jamie was at HWT for the last week (5) of the testbed (31 May - 3 June)

Notes from Day 1 overview:

  • CAPS radar assimilation ended up not running so there will be no GSD vs. CAPS comparison
  • Plan to continue controlled experiment (CLUE) in future HWT - has been successful but also had a few "lessons learned" in this inaugural year that can be improved upon next year
  • CAM hail size evaluation a focus for this year
    • Three hail algorithms: HAILCAST, directo output from the mp scheme (developed by G. Thompson), and machine learning (statistical) technique  (Gagne)
  • Ensemble sensitivity (Texas Tech work - Brian Ancell)
    • Features in flow early in the forecast that impact the ensemble response later (predictability)
  • So far they have noticed if the CAMs don't handle overnight convection well they have problems the next day
    • There are a lot of solutions between the CAMs in this type of pattern
  • Week 5 had a more of weaker shear/multi-cell storm pattern - this is a challenge for CAMs
  • This blog entry is a good overview of what we did each day (

Notes from sitting with forecasters each day

  • opHRRR tends to have
    • PBL too warm/dry
    • too much convection
  • parallel HRRR (going operational in early July)
    • has been decent during HWT
  • 5-day MPAS
    • performance is region dependent
    • strongly forced systems easier
    • general temporal/spatial coverage OK but not specific storm location
  • Thompson mp
    • less aggressive cold pools to slow propagation (this was an intentional design based on feedback from previous experiments
    • see the result of this in the statistics
  • For verification (subjective during the experiment) they used LSRs (local storm reports), WFO warnings (especially in rural areas where no reports are received), and MESH (maximum estimated size of hail - MRMS hail product)
    • Forecasters generally like the MESH - seems to be pretty accurate
  • If we draw a 5% poly we would want 5 reports for each 100 grid box (at 80 km resolution) area
  • General comment from HWT coordinators over the past 4 weeks
    • ARW (HRRR) generally has (incrementally) better performance than NAMRR - but on cases when NAMRR is better, it tends to be much better
  • When evaluating probabilities of 40 dBZ or greater they used reflectivity > 40 dBZ as the comparison field
  • In operations, NAM has poor sounding structure near convective initiation
  • Forecasters need to be aware of the CWAs they issue
    • Don't want to change their poly just enough to include a CWA if it wasn't in there previously (unless warranted) 
    • They joke that they could put so-and-so's house in a slight risk!
  • There is no reward to the forecaster for keeping the poly smaller (to reduce FAR) but they are punished if the area is too small and they miss reports
    • Every bust makes them draw larger poly's
    • Only need a handful of reports to verify
  • Don't care so much about FARs
  • Hard to decrease probabilities once they are issued to the public ("Thou shalt not downgrade...")
    • They tend to err on the side of too low early on to avoid this problem
  • How do you evaluate hail forecast if storms are in the wrong spot?! 
  • To start eh SFE2016 this post talks a bit about CLUE (; the final blog entry to wrapup SFE2016 is here (

A few of the days they took ~ 2-5 minutes to show some objective statistics from the experiment

  • Aggregated ROC for SFE2016 to-date (3-hrly ROC area by forecast lead time)
    • Assess mixed core vs. single core - In general, mixed (ARW+NMMB) beats core beats any single (ARW or NMMB) core; for single core, ARW generally beats NMMB
  • When looking at FSS: mixed (ARW+NMMB) beats core beats any single (ARW or NMMB) core; for single core, NMMB generally beats ARW at shorter lead times and ARW beats NMMB at longer lead times
    • When they compute FSS they do the following:
      • Make obs 0/1 and apply smoother to get continuous values between 0-1 in obs
      • Apply a 40 km radius to forecast field
      • Difference forecast probabilities from the observations and look at the squared difference
  • Does influence of DA extend longer when looking at probabilities rather than deterministic?
  • They compared PQPF to observations by using the same threshold for a single case
  • This blog entry has an example of the ROC curves and PQPF comparison that we looked ( I can't seem to find a link to these plots on the testbed webpage (, however.


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