Calibrating the forecast

[w5afw]

I need help. My forecast says it will rain, yet the national weather service confirms that we are in a drought and rain is not expected for at least another seven days. Now either my forecast is clairvoyant, or I have something screwed up. I understand the forecast calibration has to do with the highs and lows of barometric pressure, and I have set my highs and lows according to the historic highs and lows for my city. What have I done wrong? Lex

[beteljuice]

I've checked your current conditions:

Wind Speed (gust): 0.0 mph Wind Speed (avg): 0.0 mph
Wind Bearing: 0 ° --- Beaufort: F0 Calm

Pressure Barometer: 30.01 in Rising slowly +0.01 in /hr

Against the 'standard' range of the forecaster, and it says "Fine Weather", although your baro is lowish and the forecast is on 'the edge' of which way to jump.

So I would imagine that one of your tweaked range values needs changing, but I am a little surprised you are in a drought situation with the baro at that value.

[w5afw]

thanks for looking; just now the forecast says: Showery, bright intervals. the barometric pressure is consistent with other station reports throughout my neighborhood. I guess our Gulf coast temp, pressure and humidty combinations are sometimes extreme. yes, we are officially in drought conditions. by the way, disregard my rain history as those data have been corrupted and I haven't had time to fix them. so which end of my pressure range should I tinker with and which direction should I try moving it?

[beteljuice]

Sorry about the delay in replying .......

I don't know which end you tweaked which way !

The overall effect has been to 'raise' the threshold of decisions, but that could simply mean that you raised your upper limit, or lowered your lower limit, more likely it is the combination, which may have raised or lowered, which may have expanded or contracted your 'range' window - but the result has 'lifted' that window (whatever size it has now become) so that the 'rain' decision is now lower than you expect. (but I would have thought it's pretty close, I'm only a short baro from you and it's raining ... for days !)

You don't say why you tweaked in the first place, were there problems ?

Put back the defaults: High 1050 mb / 31 in and low 950 mb / 28 in.

Use this (metric only I'm afraid) to play with:

http://www.dickie.webfusion.co.uk/zambr ... ecast.html

Short term, regard rising / falling slowly as 'steady'

[w5afw]

Thank you for the reply. I went in and tinkered a little bit with the low side baseline. I lowered it about three tenths and it seems to be more consistent with reality now. It is my opinion that showers in the forecast show up too frequently, but I guess since it is a forecast, one could always say showers are in the future -- it's just a question of how far in the future isn't it? Cheers, Lex

[w5afw]

Local weather bulletin today: Rainfall deficit in southeast Texas -
It has been more than three months since widespread soaking showers have fallen in Houston and Galveston. Some communities near the coast haven't had heavy rain since last September when Hurricane Ike made landfall.

We pray the showers forecast by Cumulus come sooner rather than later, but not in the form of another hurricane.

Perhaps instead of trying to reduce the forecast chance of rain, I should actually be tweaking the forecast calibration to increase the likelihood of rain! Rain dancing, cloud seeding and car washing have proved useless thus far. Smile, cheers, lex

[beteljuice]

You still haven't said why you tweaked, or what values you have

Local weather bulletin today: Rainfall deficit in southeast Texas -
It has been more than three months since widespread soaking showers have fallen in Houston and Galveston

This would seem to suggest that your entire weather 'range' is lower than the default.

[w5afw]

I lowered the low end baseline about three tenths. My range is based on recorded pressure extremes for the past decade: 28.9-31.1 in hg.

[w5afw]

Following the suggestion to reinsert 28 inchs as the low side baseline, rain has disappeared from the forecast. We'll see if the sensitivity has been reduced too much. Thanks, lex