It's not much, but... (the rest of the script is the same)

Yours:

  if (%wu_command == !forecast) || (%wu_command == !forecast5) {
    if (%wu_f1_title != $null) { 
      var %wu_forecast1 $(%wu_f1_title $+ : %wu_f1_fcttext)
      var %wu_forecast2 $(%wu_f2_title $+ : %wu_f2_fcttext)
      if (%wu_f2_title != %wu_P2_weekday ) var %wu_forecast3 $(%wu_P2_weekday $+ : %wu_P2_conditions $+ . High: $+(%wu_P2_highf,$chr(176),F) $chr(47) $+(%wu_P2_highc,$chr(176),C) Low: $+(%wu_P2_lowf,$chr(176),F) $chr(47) $+(%wu_P2_lowc,$chr(176),C)) 
      if (%wu_f2_title == %wu_P2_weekday ) var %wu_forecast3 $(%wu_P3_weekday $+ : %wu_P3_conditions $+ . High: $+(%wu_P3_highf,$chr(176),F) $chr(47) $+(%wu_P3_highc,$chr(176),C) Low: $+(%wu_P3_lowf,$chr(176),F) $chr(47) $+(%wu_P3_lowc,$chr(176),C))
      .timer 1 0 msg %wu_chan %wu_address $+ : %wu_forecast1
      .timer 1 1 msg %wu_chan %wu_forecast2 %wu_space %wu_forecast3 %wu_spaceend 
    }
    if (%wu_f1_title == $null) {
      var %wu_forecast1 $(%wu_P1_weekday $+ : %wu_P1_conditions $+ . High: $+(%wu_P1_highf,$chr(176),F,$chr(40),%wu_P1_highc,$chr(176),C,$chr(41)) Low: $+(%wu_P1_lowf,$chr(176),F,$chr(40),%wu_P1_lowc,$chr(176),C,$chr(41)))
      var %wu_forecast2 $(%wu_P2_weekday $+ : %wu_P2_conditions $+ . High: $+(%wu_P2_highf,$chr(176),F,$chr(40),%wu_P2_highc,$chr(176),C,$chr(41)) Low: $+(%wu_P2_lowf,$chr(176),F,$chr(40),%wu_P2_lowc,$chr(176),C,$chr(41)))
      var %wu_forecast3 $(%wu_P3_weekday $+ : %wu_P3_conditions $+ . High: $+(%wu_P3_highf,$chr(176),F,$chr(40),%wu_P3_highc,$chr(176),C,$chr(41)) Low: $+(%wu_P3_lowf,$chr(176),F,$chr(40),%wu_P3_lowc,$chr(176),C,$chr(41)))
      .timer 1 0 msg %wu_chan %wu_address $+ : %wu_forecast1  
      .timer 1 1 msg %wu_chan %wu_forecast2 %wu_space %wu_forecast3
    }
  }

Mine

 if (%wu_command == !forecast) || (%wu_command == !forecast5) {
    if (%wu_f1_title != $null) { 
      var %wu_forecast1 $(%wu_f1_title $+ : %wu_f1_fcttext)
      var %wu_forecast2 $(%wu_f2_title $+ : %wu_f2_fcttext)
      if (%wu_f2_title != %wu_P2_weekday ) var %wu_forecast3 $(%wu_P2_weekday $+ : %wu_P2_conditions $+ . High: $+(%wu_P2_highf,$chr(176),F) $chr(47) $+(%wu_P2_highc,$chr(176),C) Low: $+(%wu_P2_lowf,$chr(176),F) $chr(47) $+(%wu_P2_lowc,$chr(176),C)) 
      if (%wu_f2_title == %wu_P2_weekday ) var %wu_forecast3 $(%wu_P3_weekday $+ : %wu_P3_conditions $+ . High: $+(%wu_P3_highf,$chr(176),F) $chr(47) $+(%wu_P3_highc,$chr(176),C) Low: $+(%wu_P3_lowf,$chr(176),F) $chr(47) $+(%wu_P3_lowc,$chr(176),C))
      .timer 1 0 msg %wu_chan %wu_address $+ : %wu_forecast1
      .timer 1 1 msg %wu_chan %wu_forecast2 %wu_space %wu_forecast3 %wu_spaceend 
    }
    if (%wu_f1_title == $null) {
      .timer 1 0 .notice %wu_nick 05Error: Try again in a few seconds, also make sure you typed a correct zipcode, city, state or country.
    }
  }

Basically, i just removed/replace the code after the following line:

if (%wu_f1_title == $null) {

Edit: thought I fixed the !forecast5 one too, guess not.