Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 122202

Area Forecast Discussion
National Weather Service Tucson AZ
300 PM MST Mon Nov 12 2018

.SYNOPSIS...Dry conditions with colder temperatures through the
middle of the week. A Hard Freeze is expected Tuesday morning across
the valleys south and east of Tucson. Gusty winds will also persist
this evening into Tuesday. Warmer temperatures with less wind will
return later in the week.


.DISCUSSION...After warming up from a chilly morning, temperatures
around southeast Arizona at 12/21Z were in the 50s to low 60s, or 5
to 9 degrees cooler than the same time yesterday. Additionally,
dewpoints have continue to fall with values mainly in the single
digits, or anywhere from 9 to as much as 22 degrees cooler than 24
hours ago. Visible satellite imagery revealed clear skies across the
region, save for a few cu which have popped up over the White
Mountains. Surface winds have also begun to make their turn toward
the northeast, with a more due easterly component expected later on
this evening and overnight.

Breezy winds overnight will be one result of a dry shortwave
tracking south along the AZ/NM border into Tuesday morning. This
occurrence will also introduce additional cool/dry air to the same
valleys which froze this morning, inducing a hard freeze for those
spots. There is some trickiness to this forecast though; locations
which are shielded well from the easterly winds could experience low
temperatures Tuesday morning 3 to 6 degrees colder compared to this
morning. On the other hand, locales which are well exposed to
easterly breezes may only freeze to the same degree as this morning,
or potentially warm a degree or two. Regardless, there remains high
confidence that low temperatures will have noticeable impacts, and
so the Hard Freeze Warning remains in effect from 2 AM MST to 8 AM
MST Tuesday morning. Also want to note that wind speeds are not
expected to meet or exceed wind advisory criteria for an extended
period of time.

The trough moves out of the picture during the day Tuesday, but a
surface pressure gradient will remain in place, allowing for
easterly breezes to continue in the favored locations. Daytime
temperatures will be 2 to 5 degrees cooler compared to today behind
the departed trough. Heading into Wednesday, expect another cold
morning as less wind will allow more of a radiational cooling
process to take place, and for some this could be the coldest
morning of the fall so far. We should start to see temperatures
begin their rebound by Wednesday afternoon though, with high
pressure building in from the west.

A slow warming trend under northwesterly and eventually westerly
flow aloft will continue into Friday, with daytime temperatures
within a degree or two of mid-November averages. Morning lows should
also begin to creep out of the bitter cold during this period.
Seasonable conditions will persist this weekend into early next week
with some passing high clouds, less wind and no rain.


.AVIATION...Valid through 14/00Z.
Generally SKC thru the valid period. SFC wind nely 8-18 kts with
gusts near 25 kts increasing to ely 10-25 kts with gusts near 35 kts
this evening through much of Tuesday. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Very low humidity levels and gusty northeast to
east winds of 15-25 mph will continue tonight through Tuesday. Wind
speeds late tonight into early Tuesday will be highly variable
depending on topographic shadowing and where inversions are able to
setup despite the general wind. While the overall fire danger is
low, the wind and very low RH conditions could result in challenging
dead grass fires during the afternoon hours. Easterly winds will
persist on Wednesday, but at lesser speeds. Cool temperatures
expected through Wednesday with a moderating trend into the weekend
with humidity levels remaining low. Going to be awhile before there
is a good chance of wetting rains, at least seven days.


Hard Freeze Warning from 2 AM to 8 AM MST Tuesday for AZZ503-507>509.




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