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

FXUS65 KTWC 170254

Area Forecast Discussion
National Weather Service Tucson AZ
753 PM MST Fri Feb 16 2018

.SYNOPSIS...Light showers, drizzle and areas of fog can be
expected into early Saturday morning. Dry and warmer conditions will
then return Saturday, before another system passes through the
region. This next system will bring scattered showers to parts of
southeast Arizona Sunday into early next week.


.DISCUSSION...KEMX radar continues to indicate scattered showers
across the eastern half of southeast Arizona, roughly from Tucson
eastward. The area of precipitation is likely more widespread than
what current radar imagery indicates as the areas of drizzle are not
fully being picked up by the radar. KTWC 180217/00Z sounding
continues to indicate record moisture across the area, with a PW
value of 1.07". Blended Total Precip Water Satellite Imagery
indicates PW values over 1" across much of the forecast area, with
lesser amounts (values around 0.60") over far western Pima county
and in far northeastern portions of Graham/Greenlee counties.

Expect precipitation to come to an end by the mid evening hours
across the Tucson metro area, with far east/southeastern areas to
have precipitation end during the overnight hours tonight. Satellite
imagery indicates clearing skies already taking place over far
western Arizona attm, with the back edge of the cloud shield just
west of the far western Pima county line. Expect a general west to
east clearing later tonight, although do suspect clearing skies from
Tucson eastward will be difficult until after sunrise Saturday with
copious amounts of surface/atmospheric moisture in place.

Main concern tonight will be fog development and corresponding
reduced visibilities. Current/ongoing forecast package already has
patchy fog wording in for much of southeast Arizona. Amount of fog
development and corresponding visibility restrictions will be based
partly upon the amount of clearing that takes place later tonight.
If skies are able to clear more than anticipated, then areas of
dense fog will be able to form. This is something we will be keeping
a close eye on as we work into the overnight and early morning hours
on Saturday.

Forecast package looks to be in good shape. No updates this evening.
For more information on the latter periods of the forecast, please
refer to the additional sections below.


.AVIATION...Valid thru 18/00Z.
Generally MVFR-IFR conditions through the late evening hours south
and east of Tucson due to -RA, with visibilities 2-5SM and clouds
SCT-BKN 1-2k ft AGL and BKN-OVC 2-5k ft AGL with BKN-OVC layers
above. From KTUS north and west, SCT-BKN clouds 1-3k ft AGL and BKN-
OVC 3-6k ft AGL into the late evening with much more limited rain
chances. Areas of -DZ and BR/FG possible overnight and early
Saturday morning with ceilings less than 1k ft AGL possible but
confidence is too low to include in forecast. Otherwise, light and
variable SFC wind less than 10 kts into Saturday. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...Showers will decrease in coverage tonight into
Saturday morning. Saturday is expected to be dry everywhere, with a
slight chance of showers returning to the forecast Sunday afternoon
through Monday night.

Light winds are expected through Saturday, then an increase in SW
winds should occur Sunday and even more so on Monday. Monday 20-foot
winds will be between 15-20 mph and gusts up to 30 mph with the
highest wind speeds east of Tucson. Despite the winds, fuel moisture
levels will be much improved and humidity levels will remain
relatively high.


.PREV DISCUSSION...A weather disturbance continued to pass through
southeast Arizona with more showers flaring up this afternoon.
Models maintain the trend of showers diminishing tonight as the
disturbance exits the area. Expect patchy fog overnight with
possibly pockets of dense fog early Saturday morning. Models showed
a break in systems tomorrow, but this will be rather brief as a weak
upper low off the Baja coast ejects northeast through southern
Arizona Sunday. This feature combined with the tail end of a system
moving through the Great Basin will bring another round of rainfall
Sunday into early next week. This next rain event will not be as
heavy or widespread as the one this week. Thereafter, medium range
models continued to show a couple of system impacting the area late
next week into next weekend.






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.