Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Phoenix Arizona
350 am MST sun Feb 1 2015
in the wake of an exiting low pressure system...areas of fog...
potentially dense across the south central deserts...will be
possible through the morning hours due to abundant moisture and
clearing skies. High pressure will quickly cover the area today
bringing clearing skies...dry weather...and warmer temperatures. The
dry conditions will persist through the week while a warming trend
allows for highs to reach near 80 degrees across the lower deserts
by the end of the work week.
upper low that brought widespread precipitation to the central
deserts during the past couple of days has finally shifted off to
the southeast...allowing a subsident northeasterly flow aloft to overspread
the area. Strong subsidence aloft has brought considerable clearing
to south central Arizona...and infrared imagery at 2 am showed generally clear
skies from Phoenix westward. A few middle/high clouds persisted well to
the south and east of central Phoenix. Although moisture has started
to thin a bit as seen by the latest soundings which showed precipitable water
values of 0.86 at San Diego and 0.74 inches at tus...boundary layer
moisture remained high after all of the rain that has recently
fallen. Surface dewpoints over the deserts were running mostly in
the upper 40s to around 50 and relative humidity values were 100 percent or close
to it across much of the central deserts. Observed and forecast
soundings for this morning showed a very favorable dense fog profile
and spotter reports as well as webcams have been indicating dense
fog forming across the southeast valley and across northwest Pinal County.
As such a dense fog advisory has been issued for northwestern/north central Pinal
County as well as the greater Phoenix area through 10 am this morning.
We may have to expand the advisory into western Maricopa County
should fog develop or spread westward into that area. Otherwise...
expect fog to dissipate later this morning leaving mostly sunny
skies across the central deserts. Under mostly sunny skies...high
temperatures will be able to climb a handful of degrees and approach
Model guidance remains very consistent in calling for dry and warmer
conditions for the entire week...as a strong upper level high
pressure ridge steadily builds into the Desert Southwest. As the
ridge builds...there will be periods of high clouds spreading
through the ridge and across the deserts...but overall we should see
mostly sunny days and mostly clear nights. High temperatures are forecast
to climb into the middle to upper 70s by Tuesday...then rise further
and into the upper 70s to low 80s across the warmer deserts by
Friday. 500 mb heights are forecast to rise in excess of 585dm over the
southwest Arizona and southeastern California deserts by this weekend and we could see
high temperatures reach into the middle to upper 80s across the warmer lower
deserts as a result. We have raised our forecast high temperatures 2-3
degrees for the latter portion of the week as a result of increased
confidence in the very warm forecast conditions.
south-central Arizona including kphx...kiwa and ksdl...
fog formation well underway across the metropolitan as of 11z and kiwa has
been vlifr for several hours already. Satellite indicating
deteriorating conditions in the north/West Valley and it appears
its only a matter of time before both kphx and ksdl see fog. Going
to introduce a period of 1sm visibilities at both locations from approx
12z-17z today. I expect the worst conditions from daybreak /14z/
until middle morning when bl mixing should help break things up.
Conditions should improve rapidly through the afternoon hours with
minimal impacts forecast beyond 20z. As for winds...light diurnally
driven at all sites. Very light east winds expected Monday morning.
Southeast California and southwest Arizona including kipl and kblh...
no major aviation impacts for southeast California as skies rapidly
clear. Surface winds will retain a light northerly component...though
could become variable at time as the pressure gradient weakens.
Aviation discussion not updated for amended tafs.
Tuesday through Saturday...
warmer temperatures are expected across the region this week along
with drier air. Despite this...afternoon humidities will only drop
into the 15-25 percent range each afternoon with good overnight
recoveries expected. No major wind events are anticipated with winds
following the typical diurnal patterns.
Arizona...dense fog advisory until 10 am MST today for azz021>023-026>028.
Visit US on facebook...twitter...and at weather.Gov/Phoenix