Deutscher Wetterdienst Welcome to Session 5, part 2 "Diagnosis of precipitation types from radar (practise)"

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Outline Diagnosis of precipitation type: Practical rules Technical limitations (base: DWD Radar Network) Examples Sections of radar reflectivities in accordance to model temps / sections? Bright band in relation to observations and AMDAR Doppler wind:  Cold air near surface, warmer above Additional remarks Questions and answers

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Radar beam's width and height distance Radar not applicable for diagnosing preciptiation types near the surface!

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), General Z-R–relation (DWD) Fixed values (independend in the season!) a = 256 and b= 1,42! In the meanwhile new radar products at DWD oimproved Z/R-relation oadjusted to measurements (RADOLAN)

Deutscher Wetterdienst Thresholds for precipitation types and intensities (DWD-products) dBZ mm/h(general Z/R-relation)Precipitation type and intensity 1 – 60,02negligible precipitation, drizzle, light snow ,06 - 0,4 light rain, snow (partly moderate) ,4 - 1,9light to moderate rain, moderate to heavy snow ,9 - 8,1moderate rain / shower, Winter: Thunderstorms, heavy snow ,1 - 35,0Summer: Heavy rain, shower, thunderstorm, Winter: heavy rain (seldom) and sleet , ,0Summer: Hazardous rain, heavy shower, thunderstorm, Winter: Sleet, graupel > 56 > 150,0Summer: Heavy thunderstorm (hail) Winter: Heavy sleet

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), General rules (Winter, middle latitudes) Snow of same intensity as rain: about 7 dBZ less Snow almost not possible : above 37 dBZ Rain seldom: above 37 dBZ  sleet? Rain not possible: above 46 dBZ  sleet  graupel Be careful: Attenuation possible (e.g., due to sleet) Low stratus Negative dBZ-values: only snow grains possible Positive dBZ-values, below 7 dBZ: (freezing) drizzle possible

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), , 14 UTC, Heavy snow (75) International composite (2x2 km): Violet, in that case hint to heavy snow, one green pixel ( ≥ 37 dBZ) DWD - Composite (1x1 km): partly even 37 to 40 dBZ Red elipse: Area of Bad Vilbel (our flat), Visibility about 100 m and 10 cm snow within 30 minutes!

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), , 00 UTC, Sleet – Bright band: Model temp correct Kassel Bavarian Forrest model-analysis: wet bulb temperature +1°C:1345 m  sleet (near snow line)

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), , 01 UTC: Clearly sleet 43 – 47 dBZ: Sleet (1000 m) Frankfurt (100 m): moderate rain (63) Automatic cell evaluation: Marker of significant summer convection ?!

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Bright band – snow line - significant weather – precipitation amount ( , 07 UTC) Precipitation amount derived from standard Z/R-relation: above 5 mm/h (in accordance to high reflectivities, below) (measurements less than 1 mm/h) Questions for you: 1.Please consider the lower image. Where do you expect sleet? Mark by using 2.In which height do you expect the transition from snow to rain? Please use again about 100 m about 1000 m about 2000 m

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Answers Up to 41 dBZ (in 1 km height): Sleet AMDAR Frankfurt: T = 1°C (similar to wet bulb temperature during preciptiation) in 800 m ( ≈ 1 km)

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Indirect technique: Doppler, synops (800 and 2 m) Rhein-Main-Area, ) surface m: Wind from north to east above: Wind with west component  near surface cold, above warmer , 04 UTC Wind direction: 1000 m west component, near surface north,  thin layer of cold air , 07 UTC Kleiner Feldberg: 805 m , 07 UTC 10 UTC: 2m-wind now with south component 2km 12 km 1 km 805 m

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Coincidence of mild and cold air over Germany to

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Situation ( , 06 UTC) COSMO-EU-6h-forecast: ps, T850, Sig weather, wind 10m

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Situation ( , 18 UTC) COSMO-EU-6h-forecast: ps, T850, Sig weather, wind 10m

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Situation ( , 18 UTC) COSMO-EU-6h-forecast: ps, T850, Sig weather, wind 10m

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Situation ( , 12 UTC) COSMO-EU-analysis: ps, T850, Sig weather, wind 10m

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Situation ( , 12 UTC) COSMO-EU-12h-forecast: ps, T850, Sig weather, wind 10m

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Precipitation type: Radar in context with other data sources , 19 UTC COSMO-DE-1h-forecast: Warmer air above colder air near surface Lower levels E-wind component Higher levels: westerly wind Snow Radar: Sleet, freezing rain, heavy snow (violet pixel) ? In contect of model section: be aware of freezing rain and as long as easter wind component freezing rain possible! West wind, however around 0°C, fluid precipitation according to radar Further to the west: Not critical, moderate rain and mild air 3° 2° 0° freezing rain? -2° height [hPa]

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Precipitation type: Radar in context with other data sources , 19 UTC COSMO-DE-1h-forecast: Warmer air above colder air near surface Lower levels E-wind component Higher levels: westerly wind Snow Radar: Sleet, freezing rain, heavy snow? In contect of model section: be aware of freezing rain and as long as eastern wind component freezing rain possible! Orange and red pixels: Sleet West wind, however around 0°C, fluid precipitation according to radar Further to the west: Not critical, moderate rain and mild air 3° 2° 0° freezing rain? -2° height [hPa ]

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), COSMO-DE-1h-forecast: T2m, sections (T, wind) / radar section / radar composite + significant weather/ ( , 11 UTC) > 60 dBZ 1 km above sea level! 1,5°C ≈ wet bulb temperature  sleet

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), COSMO-DE-analysis: T2m, sections (T, wind) / radar section / radar composite + significant weather/ ( , 18 UTC) 55 dBZ, in the meanwhile 1.8 km above sea level! 1,5°C ≈ wet bulb temperature  slee

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Question: Where do you expect the snow line? Please mark , 20 UTC

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Answer T ≈ 1.5°C

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Additional remarks Preciptiation types can be derived only indirectly from radar with polarimetric radar possible no information near the surface General synoptic situation should be taken into account General precipitation intensity  interpretation of radar images surface temperatures, wind and observations should be considered, too model data for the forecaster's sensibilisation useful Is freezing rain likely? Pixels of higher dBZ embedded in areas of lower dBZ  danger to freezing rain, other However, clutter in radar should be taken into account Is freezing rain not likely? Pixels of higher dBZ embedded in areas of lower dBZ  sleet or "normal" rain Again, clutter in radar should be taken into account

Deutscher Wetterdienst EUMeTrain-snow-week: Session 5 b), Thank you! Questions?