Area Forecast Discussion
Issued by NWS Tucson, AZ
FXUS65 KTWC 271531
Area Forecast Discussion
National Weather Service Tucson AZ
830 AM MST WED JUL 27 2016
.SYNOPSIS...Adequate moisture will provide scattered mainly afternoon
and evening thunderstorms into this weekend. Perhaps some decrease
in coverage will occur around Thursday. Expect hotter than average
daytime temperatures through Thursday followed by moderating
temperatures by early next week.
Mid morning water vapor imagery reveals abundant moisture across the
area this morning with the center of the mid/upper level anticyclone
positioned over northwest Arizona. 12Z KTUS sounding revealed just
over 1.6 inches of precipitable water, modest northeast flow around
10-15kts, and quite a bit of elevated CAPE above 600mb (600mb-
surface looks quite a bit worked over from last night`s storms). Not
surprisingly, a few showers have tapped into this elevated CAPE
although lightning has been minimal as of 15Z.
Looking at some of the incoming 12z model guidance, it still looks
plausible that terrain driven storms will develop on the Mogollon
Rim after noon and dive southwestward through eastern Arizona and
eventually into the Tucson metro by late afternoon/early evening.
Operational models including GFS and ECMWF both indicate anywhere
from 500-750 J/KG of MLCAPE with 850-700mb mixing ratios around 10-
12 g/kg across southeast Arizona. Hi-res models from the UofA as
well as the HRRR and HRRRx indicate storms developing on the Rim by
early afternoon and descending into the lower deserts around 00z.
This is also supported to some extent by the NCAR ensemble and the
HRRR-TLE. The inherited PoPs appear to be in decent shape through
early afternoon although I will more than likely nudge values upward
a bit after 21Z (especially northwest of Tucson as parts of Pinal Co
could be active).
.AVIATION...VALID THRU 28/12Z.
Remnant debris cloudiness above 10k ft agl will gradually diminish
as the morning progresses. Isolated to scattered showers and
thunderstorms will develop again starting this afternoon and
continue into the evening with the main focus area being across the
mountains and locations from Tucson south and eastward. Brief wind
gusts to 45 kts and MVFR conditions are possible with the stronger
TSRA. Otherwise, sfc wind mainly less than 10 kts. Aviation
discussion not updated for TAF amendments.
.FIRE WEATHER...Scattered mainly afternoon and evening thunderstorms
will continue into early next week. Expect the storms later today to
develop over the White mountains and move SW off the higher terrain
into valley locations mainly south and east of Tucson. Perhaps a bit
less areal coverage of thunderstorms Thursday and Friday before
increased moisture moves in this weekend into early next week.
Afternoon temperatures will remain a bit warmer than average through
Friday, then drop to near normal by early next week.
Upper high centered over southern Nevada early this morning with the
steering from the northeast already in place. Radar was still
detecting a few flareups of showers and thunderstorms early this
morning. Most of this activity should continue to move south of
Tucson from the northeast to southwest. Latest HRRR solutions keep
this activity going through about 15Z before diminishing. Then after
a brief break in the activity, the model showed it redeveloping in
the mountains east of Tucson and eventually tracking southwest into
the lower deserts. This scenario looked reasonable based on recent
trends and the flow pattern in place today. Latest GFS showed the
upper high remaining over southern Nevada through at least Friday,
then shift it to a position over northern New Mexico by Monday. The
model showed a significant upswing in rainfall coverage this
weekend. At any rate, will keep similar POP values going in the
forecast and delay the cooler daytime temperatures until Sunday into
early next week.
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