Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 310406
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
900 PM MST MON MAY 30 2016

.SYNOPSIS...A weak and slow moving low will keep temperatures
around average into Wednesday, with enough moisture for
isolated thunderstorms. Strong high pressure will then build over
the region late in the week into next weekend, resulting in much
hotter daytime temperatures with highs in the triple digits for most
of the lower elevations of southeast Arizona. Highs around 110
degrees possible near and west of Tucson this weekend.

&&

.DISCUSSION...We saw isolated convection this afternoon, primarily
across Cochise and Greenlee counties.  Not much rain in the bucket
anywhere, but dry lightning strikes were plentiful in the Chiricahua
mountains as well as areas around Clifton in southern and central
Greenlee county. Hopefully no new fire starts.

The moisture push up the gulf has gotten relatively shallow north of
Guaymas, with weak pressure differentials and larger scale features
shutting down as the weak low shifts into southwest Arizona.
Considerable moisture through southern and eastern half of Sonora is
still evident on CIRA layered precipitable water estimates, with
even deeper moisture through portions of Chihuahua into New Mexico.
Influences from both gulfs will lead to another modest surface dew
point increase in areas both west and east of Tucson. We will
probably still have enough moisture for a few lightning strikes once
again in Greenlee, Graham and eastern Cochise counties Tuesday
afternoon. It`s unclear if we will be able to say the same for areas
further west, however an early look at the latest NAM suggests our
current forecast with isolated thunderstorms south and west of Tucson
(in addition to eastern areas) is well served.

Please see the previous discussion below for additional details.

&&

.AVIATION...VALID THRU 01/06Z.
Clearing overnight with light winds. Isolated thunderstorms will
develop Tuesday afternoon (after 31/18Z), however VFR conditions are
expected to continue at TAF sites.  Strong and gusty thunderstorm
outflow winds will be possible, otherwise normal diurnal wind trends,
gusty at times in the afternoons. Aviation discussion not updated for
TAF ammendments.

&&

.FIRE WEATHER...We will continue to see just enough moisture
for isolated afternoon thunderstorms Tuesday and Wednesday. Not much
rain with the storms, so dry lightning and gusty outflows will be a
concern with any storm that manages to form. Also, Haines 6
conditions are likely each afternoon through Wednesday across zone
153 and much of zone 152.

Thursday onward a large upper ridge will build over the region
resulting in very hot temperatures, low relative humidities and
generally light winds through next Monday. As a result of the hot
and dry air mass, unstable Haines 6 conditions will develop across
much of southern Arizona from Friday onward through Monday. Cerniglia

&&

.PREV DISCUSSION...May has been an enjoyable month but later
this week it will be a distant memory as summer arrives with gusto.
More on this later in the discussion.

All of today`s activity being driven by an upper level low that was
situated between Phoenix and Lake Havasu City this afternoon. Models
are similar in dropping this upper low SSE over western Pima county
after midnight, then over northwest Sonora Mexico by late Tuesday
morning and then into northwest Chihuahua Mexico on Wednesday. Will
maintain low end PoPs mainly over the mountain with better chances
up in the White mountains. Interesting to see if the models are
correct with some overnight, Tues night into Wed morning, light
showers on back side of low from Tucson west. The below normal high
temperatures that have been the norm for the past week plus will
close out May and start June.

After a second consecutive below normal May, the first full weekend
of meteorological summer will be a rather hot one with record high
temperatures possible as strong high pressure builds over the desert
SW. Based on 12z GFS/ECMWF 850-700 mb thickness values, I went ahead
and upped highs a few degrees Friday thru Sunday. However still may
not be hot enough in spots. May eventually need to an excessive heat
watch for areas from Tucson west this weekend. As the week
progresses these highs will continue to be updated. I went back to
last June when the lower deserts had highs in the 109-113 range
around mid-month. The upper ridge later this weekend will be much
more amplified over the western CONUS versus a year ago. Hello
summer.

&&


.TWC Watches/Warnings/Advisories...None.

&&

$$

Meyer

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