Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 160408

Area Forecast Discussion
National Weather Service Tucson AZ
908 PM MST Thu Mar 15 2018

.SYNOPSIS...Lighter winds and cooler tonight as a passing weather
system exits to the northeast. Another system will increase winds
again this weekend and bring a better chance of valley rain and
mountain snow to southeast Arizona Saturday night into Sunday.
Cooler temperatures will prevail through this weekend, followed by
a warm-up next week.


.DISCUSSION...For the short term, things are going as expected
with the first low lifting well northeast of the area this
evening. The gradient is relaxing enough for easy decoupling of
the boundary layer, with winds diminishing and surface
temperatures running 8 to 12 degrees cooler compared to 24 hours
ago. We`ll start to see some thin cirrus filtering in from the
west, otherwise drier with surface dewpoints in the teens to 20s
and our 00Z KTWC sounding coming in with 1/3 of an inch
precipitable water.

Our next weather of significance is still expected to be
associated with a system over the weekend. We`re starting to see a
better hint of a partial split into Arizona from a busy mean
trough positioned across much of the west. We may be a little
underdone with our current probability of precip forecast,
especially just ahead of and with a potential frontal passage
sometime Sunday morning or so. Still not looking at significant
storm totals though. Please see the previous discussion below for
more on this.


.AVIATION...Valid through 17/06Z.
Clearing from the west this evening followed by increasing cirrus
Friday. Strong westerly winds will ease this evening below 10
kts. Winds restrengthen Friday afternoon, southwesterly 10-15 kts
with 15-20 kts in the far southeast such as at KDUG. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...Winds will continue to ease this evening, but
breezes still pick up every afternoon into the weekend as another
weather disturbance arrives on Sunday. This will also bring a
better chance of precipitation area-wide, primarily Sunday
morning with the frontal passage. Drier and warmer weather then
builds back in early next week.


.PREV DISCUSSION...The next system currently off the Pacific NW
coast will rotate southeast across the Four Corners states this
weekend. The GFS and ECMWF are now in better agreement with the
timing and placement of this system. Chances for rain and mountain
snow Saturday night and Sunday look better than recent runs
indicated and PoPs have been raised correspondingly. If this model
agreement continues, confidence to raise PoPs will likely
increase with subsequent forecasts. This system will have colder
air associated with it than the one that passed through a few days
ago and the timing appears to be focused on the late night
Saturday/Sunday morning time frame. Thus, it should be more
efficient at squeezing out precipitation and snow accumulation
levels could drop down to around 5000 feet.

Temperatures will remain close to normal until Sunday behind this
next weather system. Expect colder than average temperatures for
highs Sunday and lows Sunday night. Fairly robust ridging of
high pressure is then indicated early next week which will cause a
decent temperature rebound by Tuesday.






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