Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 230418

Area Forecast Discussion
National Weather Service Tucson AZ
918 PM MST Tue May 22 2018

.SYNOPSIS...Dry conditions will continue into the upcoming
holiday weekend and likely through the end of the month. Gusty
winds will weaken tonight and should return again this weekend as
a couple of low pressure systems move north of the area. High
temperatures will warm above seasonal normals later this week
before cooling a few degrees this weekend.


.DISCUSSION...Winds are diminishing after sunset this evening as
anticipated. Seasonably dry conditions continue with precipitable
water on the 00Z KTWC sounding measured under 1/2 inch and
surface dew points ranging from the upper teens to lower 30s.
These values are actually up slightly with the sustained
southwesterly fetch due to the proximity of the low over eastern
Nevada and western Utah. At any rate, western Mexico is also dry,
all the way south of Sinaloa and Durango. Any significant
moisture will remain east of our area to finish off a typically
dry month in a manner to which we`ve become accustomed.

Please see the previous discussion below for additional details.


.AVIATION...Valid through 24/06Z.
Clear. Winds weakening overnight to under 10kts. Breezy southwest
to west winds will return by late morning, or 23/18Z.

Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Winds will weaken Wednesday through Friday but
sustained speeds up to 15 mph will still be possible each
afternoon. Another low pressure system will approach our area this
weekend bringing another round of breezy/windy conditions on
Saturday, elevating fire danger across our CWA. Dry conditions
will continue, with afternoon humidities below 10 percent. No
precipitation is expected through the end of the month.


.PREV DISCUSSION...An upper level low is currently centered over
southern Nevada this afternoon generating clouds and thunderstorms
over much of the Great Basin. Just to the south, the Desert SW
sits under dry southwesterly flow with PWs around 0.4 inches. In
response to this low pressure system moving to our north, breezy
winds have developed this afternoon with gusts ranging from 20-30
mph across much of our CWA. Given the dry and breezy conditions, a
Red Flag Warning remains in effect from noon to 7 PM MST today
for the White Mountains.

Models are in excellent agreement of rapidly moving this low
pressure circulation into Montana by Wednesday afternoon while
Arizona remains under weak and dry southwesterly flow. Looking
beyond this, heights will gradually build through this work week
warming temperatures a few degrees each day with upper 90s
forecast by Friday. However, this warming trend will come to a
halt on Saturday as yet another upper level low pressure system
approaches our area. Temperature gradients associated with this
approaching low will tighten surface pressure gradients  and
bring more breezes to our area come Saturday. Models agree that
modestly cooler air will also begin infiltrating our area come
Saturday and Sunday knocking high temperatures down by a few
degrees each day. Given the dry nature of this system, elevated
fire danger will also be of concern on Saturday.

Models and ensembles are in surprisingly good agreement of
lingering this upper low over our area through at least the
beginning of next week. During this period, temperatures could be
near to even slightly below normal. One caveat is that the
position of this low will really dictate our temperatures in the
extended. Previous model runs have positioned this system further
north continuing the above normal temperatures into the weekend.
However, given the latest model consensus of a more southerly
track we have trended temperatures down for the weekend as
confidence grows in this particular solution.






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