Date: Sun, 04 Aug 2002 19:24:31 +1000
From: elly spark
To: laps <laps_feedback@BoM.GOV.AU>, Synoptic <synoptic_discussion@BoM.GOV.AU>
Subject: [synoptic_discussion] rain from 400-300 hPa cloud in GASP

Hi folks,

Can someone please explain WHY the 00Z run of GASP today (Sunday 4th)
[as well as last night's 12z run] has rain falling in the SW of NSW when
the RH forecasts in this area are:
700 hPa: 10%
600 hPa: 10%
500 hPa: 20-30%
400 hPa: 90%
300 hPa: 90%

It seems most unlikely.

I suppose GASP smears out fields because of the low resolution, but any
rain likely to result from 700hPa moisture is  along way to the
southwest, so that's not a real explanation. Also recent LAPS/MesoLaps
runs have had similar behaviour (although in those cases producing rain
from 500 hPa 90%RH - refer previous email to laps_feedback, no reply
received). There must be something in the rainfall algorithms that is
causing this to happen, and it would be nice to know what it is.

thanks.

--
Elly Spark
Senior Meteorologist
NSW Regional Forecasting Center

Lawrie Rikus

Elly,

I had a look at the 0312 forecast from gasp. There is a rain spot which
develops right from the analysis - see the first gif attached. It
continues to grow for about 2 hours then stops. An area averaged precip
time series is shown in the second attachment. Is this the event you were
worried about?

When you look at the time series for the relative humidity averaged over
the same area you can see why it is raining. (see attachment 3)

The relative humidity seems to be flipped in levels relative to the values
you have given. Is your visualization package correct for GASP? (note that
laps levels run in the other direction!)

Peter Steinle has looked into the assimilation and has found that the
analysis agrees quite well with 03 12Z soundings of 70-80% RH over the
southwest of Australia.

Lawrie

Peter Steinle

Subject: sonde printout

Just for info ...(over south EAST Aust.)

A few sondes from 12Z August 3, 2002
Moisture values are percentage relative humidity

 Station
 47582     Lat. =   -39.717  Long. =   140.100
           Day = 20020803  Time =   1200
           Level  Temp.     Geop.     Moisture
         1000.00   25.4      55.1     0.81E+02
          925.00   19.8     736.3     0.92E+02
          850.00   17.6    1462.3     0.72E+02
          700.00    7.6    3098.1     0.95E+02
          500.00   -5.7    5809.6     0.42E+02
          400.00  -17.9    7519.8     0.58E+02

 47590     Lat. =   -38.267  Long. =   140.900
           Day = 20020803  Time =   1200
           Level  Temp.     Geop.     Moisture
         1000.00   22.0      67.3     0.86E+02
          925.00   19.2     741.4     0.94E+02
          850.00   17.4    1469.5     0.80E+02
          700.00    9.2    3110.3     0.78E+02
          500.00   -4.9    5819.8     0.19E+02
          400.00  -17.3    7540.2     0.20E+02

 47646     Lat. =   -36.050  Long. =   140.133
           Day = 20020803  Time =   1200
           Level  Temp.     Geop.     Moisture
         1000.00   22.8      63.2     0.90E+02
          925.00   23.4     744.4     0.68E+02
          850.00   18.0    1476.6     0.86E+02
          700.00    9.0    3118.4     0.90E+02
          500.00   -5.1    5830.0     0.46E+02
          400.00  -16.9    7550.4     0.27E+02
          300.00  -32.9    9639.9     0.76E+02