Saturday, 1 September 2012

 

WALCHA FROST CHASE

 

From: Walcha area, Written by: Grant Burgess

http://www.raymondterrace.hunterweather.com/

 

Accompanied by Trevor

 

 

The anticipation of a moderate southerly change on Friday had me planning this trip seriously from days out. I was tossing up either a Barrington Tops snow chase on Friday or a frost chase Saturday. As the models withdrew the forecast moisture from the area, snow chances also diminished some what.

 

With some reasonable coastal showers pushing inland in the hours before we left, I was thinking if they pushed far enough north, then a flake or two might be possible when climbing up onto the tablelands. Regular checks of the private Automatic Weather Station (AWS) at Salisbury Plains (~20km north of Walcha & slightly lower in elevation) had me excited. Here is some of the data I collected:

 

TIME AIR TEMP (C) DEW-POINT (C)
1725 7.2 -6.2
1800 3.9 -7.0
1900 2.2 -7.5
2005 -0.1 -7.3
2205 -3.8 -7.6

 

 

 

 

 

 

 

Here is my travel log & observations along the way.

 

LOCATION TIME ELEVATION (m) AIR TEMPERATURE (C) DISTANCE TRAVELLED (km)
Home (left) 2240 8 10 0.0
Weather was cool with patchy cloud & isolated moderate coastal showers
Booral 2309 23 10 40.4
Some dry patches on the road but back under cloudy skies
Stroud 2315 39 9 47.8
Wards River 2336 84 10 72.1
Temperature peaked at 11C at ~2330
Craven 2342 150 7 79.9
Stratford 2346 131 6 84.6
Sky still overcast but road is continuing to dry
Gloucester 2355 115 8 96.3
Was stopped by police & breath tested passing through Gloucester
Barrington 0013 140 6 104.0
Only patchy cloud remains, roads are now dry
200m Above Sea Level (ASL) 0019 200 7 109.7
Rookhurst 0024 167 5 115.7
Cloud thinning; Salisbury Plains was -5.4C at 0005
Tibbuck 0030 143 4 121.2
300m ASL 0051 300 4 142.7
400m ASL 0052 400 5 143.7
500m ASL 0053 500 5 144.6
600m ASL 0054 600 6 145.2
700m ASL 0055 700 6 146.2
800m ASL 0057 800 5 147.5
900m ASL 0100 900 4  
Carson Memorial Lookout   970 4  
Nowendoc / Taree turnoff 0125 862 -1 174.6
900m ASL 0133 900 -3 185.9
1000m ASL 0136 1000 -3 189.2
1100m ASL 0137 1100 -1 191.0
1200m ASL 0139 1200 0 193.2
1300m ASL 0141 1300 0 195.4
20km south of Walcha 0204 1184 -5 226.3
The temperature drop coming onto the high plains was incredible, after the drop from 0 to -1C the temperature then dropped straight to -3C within minutes (-2C was skipped completely). The thermometer then continued to fall at regular intervals
Walcha 0219 1070 -6 244.5
Walcha (Apsley St) 0223 1055 -6 246.3
Upon shining the car lights into the park whilst turning the car around, the sparkles of frost on the grass was evident - something I never saw the whole drive here

 

*NOTE: All temperatures here were taken from the car thermometer on the run.

 

Took this pic soon after the temperature went into the minuses for the first time

 

Soon after arriving I began setting up my equipment. Before opening my boot, just as a test, I drizzled a few drips of water on my car spoiler, these to my surprise froze almost instantly. For the next half hour or so I remained outside to experience such cold temperatures for the first time in my life, I did this without gloves! My feeling so far was -6C doesn't feel as cold as I thought it would!. I have however experienced temperatures down to -2C in the Barrington Tops during the whiteout of 18/07/2004.

 

 

Weather observations from Apsley St, Walcha

 

TIME AIR TEMP*1 CAR TEMP*2 GRASS TEMP*3 GENERAL OBSERVATIONS
0330 -3.5 7.8 -11.8 Sky clear, frost evident & instruments still equilibrating
0340 -4.4 7.5 -10.9 Clear
0350 -4.7 7.1 -8.0 Broken strato cumulus cloud (5 oktas)
0400 -5.0 6.9 -8.6 Mostly clear (1 oktas). AIR - (templec*4) -5.1C; GRASS - (glass*5) -9.6C, (templec*6) -8.1C
0410 -5.2   -10.2 Mostly clear (1 oktas)
0420 -5.5 5.2 -11.9 Clear
0430 -5.6 5.4 -8.3 Clear
0440 -5.5 6.2 -6.8 Distant cloud (1 oktas)
0450 -5.3 6.1 -7.7  
0500 -5.3 5.7 -8.6 Patchy cloud (2 oktas). AIR - (glass*7) -5.0C, (templec) -5.0C; GRASS - (glass) -8.6C, (templec) -7.2C
0530 -5.6 4.8 -11.8 Clear, first faint light to the east
0546 -6.0 4.0 -12.4 Clear
0600 -5.7 3.4 -11.0 Clear, light Westerly wind 4.5/1.0km/h, air pressure 902hPa
0615 -6.1 2.9 -11.9 Clear, sun rising behind a hill
0620 -6.1 2.9 -11.9 Clear
0625 -6.1 2.9 -11.3 Clear, sun now visible
0630 -6.0 3.6 -10.9 Clear
0810 5.0     Distant low cloud south of town
MINIMUMS -6.1 2.6 -12.5 AIR - (glass) -6.0C, (templec) -5.9C; GRASS - (glass) -12.0C, (templec) -10.5C

 

NOTES: (All temperatures recorded in C)

*1 Air temp recorded with a wireless Oregon Scientific sensor (non-cabled version) located in my home-made mobile Stevenson Screen.

This was monitored remotely from the car with the receiving unit being inside the car.

*2 Car temp recorded with a wireless Oregon Scientific (main unit) located on the dash inside my car.

*3 Grass temp recorded with a wireless Oregon Scientific sensor (cabled version) located with the sensor cable resting on top of short grass.

*4 Air temp recorded with the 'IN' setting of my templec thermometer.

*5 Grass temp recorded with a BoM standard glass thermometer (without wood back) on top of short grass.

*6 Grass temp recorded with the 'OUT' setting of my templec thermometer & the cable resting on top of short grass.

*7 Air temp recorded with a BoM standard glass thermometer (with wood back) laying on the floor of my screen.

I believe this should still be an accurate measurement however as the glass part of the sensor was elevated above the floor & not touching anything.

 

 

Some Pics in the morning...

 

       

 

       

 

 

 

Other Minimum temperatures (C) recorded on the Northern Tablelands (2/9)

 

Armidale -5.9 Inverell -5.0
Armidale Ap -3.0 Inverell RC -1.2
Glen Innes Ag -4.0 Salisbury Plains* -7.8
Glen Innes Ap -8.0 Tenterfield -5.8
Guyra -1.9 Woolbrook -6.2