Saturday, 1 September 2012
WALCHA FROST CHASE
From: Walcha area, Written by: Grant Burgess
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)|
Here is my travel log & observations along the way.
|LOCATION||TIME||ELEVATION (m)||AIR TEMPERATURE (°C)||DISTANCE TRAVELLED (km)|
|Weather was cool with patchy cloud & isolated moderate coastal showers|
|Some dry patches on the road but back under cloudy skies|
|Temperature peaked at 11°C at ~2330|
|Sky still overcast but road is continuing to dry|
|Was stopped by police & breath tested passing through Gloucester|
|Only patchy cloud remains, roads are now dry|
|200m Above Sea Level (ASL)||0019||200||7||109.7|
|Cloud thinning; Salisbury Plains was -5.4°C at 0005|
|Carson Memorial Lookout||970||4|
|Nowendoc / Taree turnoff||0125||862||-1||174.6|
|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 -1°C the temperature then dropped straight to -3°C within minutes (-2°C was skipped completely). The thermometer then continued to fall at regular intervals|
|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 -6°C doesn't feel as cold as I thought it would!. I have however experienced temperatures down to -2°C 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|
|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) -5.1°C; GRASS - (glass*5) -9.6°C, (templec*6) -8.1°C|
|0410||-5.2||-10.2||Mostly clear (1 oktas)|
|0440||-5.5||6.2||-6.8||Distant cloud (1 oktas)|
|0500||-5.3||5.7||-8.6||Patchy cloud (2 oktas). AIR - (glass*7) -5.0°C, (templec) -5.0°C; GRASS - (glass) -8.6°C, (templec) -7.2°C|
|0530||-5.6||4.8||-11.8||Clear, first faint light to the east|
|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|
|0625||-6.1||2.9||-11.3||Clear, sun now visible|
|0810||5.0||Distant low cloud south of town|
|MINIMUMS||-6.1||2.6||-12.5||AIR - (glass) -6.0°C, (templec) -5.9°C; GRASS - (glass) -12.0°C, (templec) -10.5°C|
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 Ap||-3.0||Inverell RC||-1.2|
|Glen Innes Ag||-4.0||Salisbury Plains*||-7.8|
|Glen Innes Ap||-8.0||Tenterfield||-5.8|