172 
fxus65 kpsr 191627 
afdpsr 


Area forecast discussion 
National Weather Service Phoenix Arizona 
925 am MST Wednesday Nov 19 2008 


Synopsis... 
strong high pressure aloft will yield mostly clear cool nights and 
sunny warm days through Friday...with another day of near record 
high temperatures expected today. The high will weaken and move well 
east of our area by this weekend. As it does so...high temperatures 
will slowly lower and clouds will increase. Next week forecast 
models are indicating the weather pattern will continue to shift 
..with a low pressure system possibly moving into the western 
states. 


&& 


Discussion... 
upper level ridge has already begun to weaken...with 12z 500 mb heights 
down slightly and ridge axis northern Mexico to kslc area. Soundings 
were all very dry...and quite warm above the boundary layer. Overall 
temperature profile similar to yesterday morning...and morning temperatures 
around the greater Phoenix area were running close to those of 
Tuesday morning...with the exception of Deer Valley. Very sharp surface 
based inversion will likely redevelop again tonight. 


Latest model trends still show the erosion of the ridge across the 
southwestern states as a major short wave moves onshore well north 
of our County Warning Area. NAM is just a bit slower than GFS and heights slightly 
lower through Thursday night and into Friday. This remains a very dry 
pattern for southwest Arizona and southeast California...and MOS 
guidance shows little change from older runs. 


Previous discussion... 
over the weekend...the GFS and European both forecast a split in the 
flow to develop...with the main storm track riding well north of our 
area...and a weak southern branch to form south of the Arizona/mex 
border. Weak baggy trough to form off the Baja California coast...which will 
slowly drift eastward with time...and this feature should not bring 
any precipitation to our area. Rather...it will continue to spread mainly 
high clouds across the County Warning Area...leading to partly cloudy conditions. 
Thickness values should continue to slowly lower...and coupled with 
partly cloudy skies...temperatures are expected to lower a bit more...but 
remain above seasonal normals. 


For the remainder of the extended...into early next week...models 
continue to show quite a bit of inconsistency both run to run and 
between themselves. However...it does seem more and more apparent 
that there is a shift in the weather pattern brewing...with the 
strong upper ridge over the west being replaced by troffing...but 
exactly when and where the trough sets up...and the details regarding 
the short waves moving through it remain to be seen. HPC/NCEP extended 
period discussions tend to favor the European model (ecmwf) over the GFS...and given 
the still large degree of uncertainty in the forecast at such long 
ranges...will favor the European model (ecmwf) but will keep probability of precipitation in the climatology range 
Monday into Tuesday. On Tuesday...will increase probability of precipitation a bit...enough 
to introduce slight chance for showers in the higher terrain zones 
ca030 and az024. Maximum temperatures will continue their downward trend...but 
even so...by Tuesday readings will still be above seasonal normals. 
Highs next Tuesday over the warmer deserts are forecast to be in the 
middle to upper 70s. 


&& 


Aviation... 
generally clear skies and light winds...under 10kts...will continue 
through 12z Thursday under high pressure aloft. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
temperatures will begin to cool as the high pressure...that has been 
dominating of late...begins to weaken by the end of the week. As 
this occurs...high clouds should spread over the area at times while 
winds remain light and minimum relative humidity values reach the middle teens by 
early next week. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


National Weather Service Phoenix is on the internet at 


Weather.Gov/Phoenix 


Discussion...Sipple/cb 
aviation...paddock/estle 
fire weather...paddock