Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tucson Arizona
235 PM MST Wednesday Jul 23 2014
Synopsis...enough moisture is back in place for a chance of showers
and thunderstorms this afternoon. Hotter temperatures are possible
again today and Thursday. Thunderstorms are expected to increase
this weekend... especially Saturday afternoon and Saturday night.
Discussion...storms are currently forming across central Pima
County and across the rim. Storm motion is pitiful though...with
maybe 10 miles per hour of westerly motion with the faster moving storms. Given
the decent precipitation water values...I am concerned for isolated flood
threat. Latest hrrr seems to have the best handle on the convection
thus far and hints at convection focused mainly across the central
portion of our area...or near the I-10 corridor. Could see some
marginally severe storms today. But the tall skinny cape
profile...also noted with the .05 normalized cape value...suggest
limited parcel acceleration today so it may be difficult to sustain
strong a lasting updrafts.
I increased tomorrows min temperatures in the valleys by a few
degrees based on min temperatures from this morning. The near record warm
lows are again possible unless convective outflows provide localized
cooling. The upper ridge again drops south tomorrow and the models
respond by decreasing the middle level moisture. So convective activity
should be down...but the temperatures will be up again. Moisture slowly
returns Friday and an inverted trough should move across the area
Saturday. So we currently focus the highest probability of precipitation over the next 7
days on Saturday thinking the added lift from the inverted trough
will be enough to overcome the marginal moisture content. Moisture
content starts to dissipate Sunday before a more pronounced drying
trend begins Monday.
Next week...the long wave pattern shows a high amplitude ridge over
the west with a deep trough over the east. This type of blocking
pattern can greatly reduce the precipitation chances and promote warmer
than normal conditions. Certainly can not rule out some isolated
storms next week...but i'm more concerned for the excessive heat
potential. Current guidance is showing similar temperatures as we
experienced this week...but 850-700mb thickness values suggest we
may be a few degrees too cool for maximum temperatures next week.
Aviation...valid through 24/18z.
Fair amount of clearing has occurred this morning which has allow
for some good mixing. The good thing is there isn't much wind in the
low/middle levels to tap into. This should keep most of the gust well
below 20kts. The one caveat to that will be given the inverted v
profile seen in point soundings from across the area all terminals
will have the potential for gusty outflow winds with the convection.
Enough instability exist over the area for convection though there
isn/T much in the hail growth zone which will limit lightning
activity. That being said...once storms develop and modify the
environment this will likely change quickly. However...given the low
confidence in where storms will develop at this time will keep ts
out of all terminals and will handle with amend once development
occurs. Aviation discussion not updated for taf amendments.
Fire weather...moisture has returned to Southeast Arizona with
scattered mainly afternoon and evening showers and thunderstorms
across most of Southeast Arizona. There will be a brief downturn in
storm coverage Thursday before a more typical monsoon pattern moves
in by this weekend. Expect strong...gusty and erratic winds with the
stronger thunderstorms. Potentially hotter temperatures Wednesday
and Thursday with strong high pressure nearby...but with this will
be mitigated somewhat by the moisture back in the picture.
Visit US on facebook...twitter...youtube...and at weather.Gov/Tucson