Scientific Forecaster Discussion
fxus65 ktwc 172108
Area forecast discussion
National Weather Service Tucson Arizona
210 PM MST Wed Jul 17 2019
Synopsis...daytime temperatures will experience a decreasing trend
through the weekend and into next week. A more favorable steering
flow for daily thunderstorms will become established today. This
flow pattern will become even more favorable early next week.
satellite imagery continues to show the decaying complex of storms
south of the border in Sonora, mex. A well developed mesoscale convective vortex is making
its way across the Gulf of California. The complex moistened the
lower levels of the atmosphere with widespread dewpoints in the 60s
(and even 70s in spots) across the deserts. 12z ktus sounding came
in with pw's around 1.3 inches which is in the 80th percentile
(approx) along with decent mixing just above the surface.
Latest hi-res deterministic and probabilistic guidance (hrrr, href,
nbm, and upper air wrfs) still indicative of a busy afternoon with
initiation in the usual mountain spots south and east of Tucson.
Good ensemble agreement showing the bulk of the activity across
Cochise, Graham, and Greenlee counties after 21z, but outflow driven
convection can't be entirely ruled out either in/around Tucson in
the afternoon and early evening hours. There isn't spectacular
steering flow in place today (5-10 kts), which will result in nearly
stationary storms throughout the rest of the afternoon. Locally
heavy rain/gusty winds/lightning are the primary threats.
Steering flow is poised to become more favorable into the weekend
and early next week, allowing for greater storm organization and
rates of motion. Per the GFS and European model (ecmwf) 500 hpa height anomaly
forecasts, the monsoonal ridge is expected to be in its prime
location by late in the weekend/early next week, transporting much
more impressive moisture values into Arizona. We can reasonably say
that the monsoon flow and moisture pattern is here to stay.
With dewpoints on the rise, temperatures will be less hot. Ktus has
yet to reach the 100 degree mark today, a Stark difference from the
110 degree day achieved yesterday. As the monsoonal pattern
continues settling into its most favorable position, coupled with
higher atmospheric moisture content, temperatures can be expected to
top off between the upper 90s and low 100s.
Aviation...valid through 19/00z.
Scattered to numerous rain showers/thunderstorms and rain are expected to develop initially
across the higher terrain south and east of tus, then spreading into
valley locations during the later afternoon into evening. The
greatest rain showers/thunderstorms and rain coverage will be along the international border
including kols/kdug with lower confidence of impacts for ktus.
Surface winds generally southeasterly 10-15 kts with gusts to 20 kts
in the afternoon before diminishing in the evening by 18/07z. Gusty
and erratic outflow winds are expected with shra/tsra. Otherwise,
generally scattered-overcast clouds mainly 7-10k ft above ground level through the forecast
period. Aviation discussion not updated for taf amendments.
Fire weather...more abundant moisture will result in greater
shower and thunderstorm coverage with the potential for locally
heavy rain, especially from Tucson south and eastward. Any storms
that develop will have the potential to produce locally heavy
rainfall, as they are also slow movers. Thereafter, a fairly typical
monsoon pattern with enhanced moisture will continue into next week
with isolated to scattered mainly afternoon and evening showers and
thunderstorms. Expect brief strong, gusty and erratic winds near
thunderstorms. Otherwise, 20-foot winds will be mainly under 15 mph.