Scientific Forecaster Discussion
fxus65 ktwc 281600
Area forecast discussion
National Weather Service Tucson Arizona
900 am MST Wed Jun 28 2017
Synopsis...seasonably hot daytime temperatures will prevail into
early next week. Dry conditions will also occur through Friday
followed by isolated to scattered afternoon thunderstorms mainly
south of Tucson late in the weekend into early next week.
mid morning water vapor imagery continues to reveal very dry air
across most of the southwestern United States this morning. Despite
this, low level moisture made its way northward from Mexico into
southern Arizona overnight and most locales are currently looking at
surface dewpoints in the upper 50s to lower 60s as of 16z. 12z ktus
sounding reveals just how shallow the moisture was/is with abundant
dry air above 650mb. Surface dewpoints will slowly mix out through
the day today and should be in the 30s by late afternoon.
Conflicting signals from the ncar ensemble this morning as a few
members are suggesting scattered showers across far southern
Arizona, meanwhile the past few runs of the hrrr and upper air WRF models
are completely dry. Given the shallow nature of the aforementioned
moisture and strong subsidence, i'm inclined to lean heavily toward
the dry solution. Thus, no changes are necessary to the inherited
pops/wx forecast. Outside of T/TD adjustments, no significant
changes are necessary through tonight or through the rest of the
week for that matter.
Aviation...valid thru 29/18z.
Clear to few clouds 13-15k ft above ground level. Surface wind this aftn wly/nwly 10-20
kts with gusts to near 30 kts. Strongest speeds NE of ktus and
particularly near ksad. Surface wind vrbl in direction less than 12 kts
at other times. Aviation discussion not updated for taf amendments.
Fire weather...dry conditions through Friday. Isolated afternoon
and evening thunderstorms are forecast to return this weekend into
early next week. The bulk of these thunderstorms will be east to
south of Tucson. West to northwest winds at 10-15 mph Wednesday and
Thursday afternoons, with the strongest speeds northeast of Tucson
and especially in vicinity of Safford. 20-foot winds will then be
mainly less than 15 mph Friday into early next week.
Previous discussion...with high pressure now in a blocking position to
our south and southwest, a dry westerly flow is pushing moisture
back out of the area over the next few days. Other than a complex in
Sonora pushing a shallow outflow into southeast Cochise County
overnight, dew points are in the 30s to lower 40s (down 10 to 20
degrees compared to 24 hours ago). Precipitable water has also
dropped back into the .5 to .6 inch range as per latest sounding and
GOES estimates. So, dry with temperatures falling back a few degrees
(but still a little above average) through Friday.
By Saturday or Sunday, a weaker flow and a modest push of moisture
from the south will bring a few buildups back to the mountains with
isolated thunderstorms possible near the international border.
Monday and Tuesday high pressure will be in a more favorable
position to import deeper moisture into the area from the east and
south. Don't be surprised if current model moisture fields are a bit
underdone for next week. Our pop values are a little higher than
model ensemble suggestions.