Area Forecast Discussion
Issued by NWS Tucson, AZ

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

FXUS65 KTWC 110415

Area Forecast Discussion
National Weather Service Tucson AZ
915 PM MST Sat Mar 10 2018

.SYNOPSIS...A few showers will occur this evening followed by
decreasing coverage of showers late tonight and especially Sunday.
Most rainfall amounts will be quite light with snow levels above
most mountain peaks. A few showers may linger Monday mainly across
the White Mountains, then dry conditions return Tuesday into
Thursday. A colder system will bring a chance of valley rain and
mountain snow by next weekend.


.DISCUSSION...Overcast skies continued this evening across
southeast Arizona with shortwave troughing approaching from the
west. Moisture ahead of this disturbance was evident through the
column, with the 11/00z KTWC RAOB measuring 0.47" PWAT and surface
dewpoints 20 to 30 degrees higher compared to 24 hours ago. The
first batch of showers have dissipated quite a bit since earlier
this evening. The latest runs of Hi-Res models including the RAP and
HRRR weren`t terribly impressive with regard to measurable precip
continuing overnight. That said, can`t say for certain that the rain
has ended for the night as the upper forcing associated with the
aforementioned shortwave could still pop off some showers as it
nears the region. A few updates were made to the forecast, namely
PoPs were trended downward just slightly into tomorrow morning and
hourly temps/RHs were adjusted to match the current conditions.
Please see the remaining sections for additional details.


.AVIATION...Valid thru 12/06Z.
Decreasing coverage of -SHRA into Sunday morning. Scattered -SHRA
Sunday afternoon limited mainly northeast of KSAD. MVFR conditions
to occur especially across higher terrain. Cloud decks lowering to
4k-8k ft AGL early this evening and continuing into Sunday
afternoon. SFC wind variable in direction mainly less than 12 kts
into Sunday morning. A WLY/NWLY component will develop Sunday
afternoon, but speeds will remain less than 12 kts. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...Decreasing coverage of showers late tonight and
especially Sunday. A few showers may linger Monday across the White
Mountains. Otherwise, dry conditions Monday into Thursday.
Thereafter, a chance of valley rain and mountain snow exists as
early as Friday, but more likely by next Saturday. Winds will mainly
be less than 15 mph Sunday, then gusty east to southeast winds at
times Monday into early Tuesday. Less wind Wednesday followed by
gusty southwest afternoon winds Thursday through Saturday.


.PREV DISCUSSION...KEMX WSR-88D detected scattered 30-40 dBZ echoes
mainly in an area from the Tohono O`odham Nation southeastward into
western/central Santa Cruz County at this time. These echoes were
moving eastward generally around 10-15 mph. IR/water vapor satellite
imagery depicted an extensive area of colder-topped clouds
representing subtropical moisture extending from Arizona/southeast
California well southwestward to between 130W-140W and between 20N-
30N. This fetch of moisture will provide widespread showers across
southeast Arizona this evening.

If the high resolution models such as the HRRR and the Univ of AZ
WRF-NAM and WRF-GFS are reality, showers should decrease in coverage
especially from about 10 pm MST or so and during the late night
hours. At any rate, for this forecast issuance have maintained
numerous showers across much of this forecast area this evening,
then coverage decreasing to scattered showers mainly from Tucson
eastward by around daybreak Sunday. Scattered showers will continue
Sunday afternoon mainly across the White Mountains. There appears to
be enough residual moisture to maintain a slight chance of showers
across the White Mountains Monday.

For this short-term precip event, appears that generally less than
0.10 inch of rainfall for the valleys, and 0.10 - 0.50 inch across
the mountains. Snow levels will mostly be above mountain tops,
although 1-3 inches of snow may accumulate across the highest peaks
of the White Mountains.

Various NWP models then depict the bulk of deeper moisture to be
south of the area Monday night and through at least the middle of
the upcoming week. Thus, have opted for precip-free conditions area-
wide Monday night through Thursday. Thereafter, the focus of
attention will turn toward a deepening upper trough/closed upper low
near the northern California coast Friday. The 10/12Z GFS has
trended slower with the onset of precip versus previous GFS
solutions, as is now closer to several ECMWF solutions. This
translates into reduced PoPs for Friday, essentially a slight chance
of showers mainly west-to-north of Tucson. A chance of valley rain
and mountain snow showers now exists Friday night and especially
next Saturday.

Cooler temps will occur Sunday before a warming trend starts Monday
and continues through Wednesday. Increased moisture and precip
chances will translate into another cooling trend next Friday and





Prev Discussion...Francis

Visit us on Facebook...Twitter...YouTube...and at is the U.S. government's official web portal to all federal, state and local government web resources and services.