Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 251602
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
902 AM MST Sun Jun 25 2017

.SYNOPSIS...Very hot temperatures will continue today, but the
end is near for this historic heat wave. An ongoing moisture
increase will bring an increase in shower and thunderstorm chances
today and Monday. Some drying will limit thunderstorms the second
half of the week, with temperatures closer to normal for late
June as we back away from the record heat.

&&

.DISCUSSION...A very warm start this morning with a low in
Tucson of 87 degrees. If this holds through midnight, it will easily
break the previous high min record of 83 from 2015. Most of
Southeast Arizona is more moist this morning largely in part to
convective outflows overnight. Surface dewpoints are now in the 40s
and 50s areawide with derived PWAT values from satellite hanging
around 1 inch and the 12Z KTWC sounding depicting PWAT values just
over 1 inch. The sounding did depict the bulk of the moisture below
850 mb and above 525 mb with drier air between. Meanwhile, the
subtropical ridge remains over the forecast area today which will
continue to result in very hot temperatures. As far as convective
development today, satellite is showing some debris clouds but
considerable clearing is already taking place. Our latest thinking
is storms will develop around midday or early afternoon across the
sky islands from Tucson eastward and largely move towards the east
to southeast. Most of the storms will continue to be on the drier
side with only isolated spots of significant rain. Gusty outflow
winds and more dry lightning will be the main threats today. We`ve
made a few tweaks to the PoP forecast this afternoon and this
evening to nudge down PoPs in the Tucson metro as this area will be
dependent on outflows for convective initiation given the steering
flow will be pushing thunderstorms away.

A fairly similar scenario is on tap Monday with the bulk of the
showers and thunderstorms once again from the Tucson area eastward.
Thereafter, as a more active higher latitude pattern sets up, the
flow aloft becomes more westerly as the subtropical high weakens and
pushes south of the area. This will bring our temperatures down to
more normal late June temperatures as the weak progresses. However,
with the cooler temperatures, drier air will make its way into just
about the entire area with just some slight chances of thunderstorms
by Wednesday or Thursday along the international border into next
weekend.

&&

.AVIATION...Valid thru 26/18Z.
SCT-BKN clouds at 8k-15k ft AGL thru the forecast period, though
occasional OVC skies can`t be ruled out E of KTUS. Isolated-
scattered SHRA/TSRA from KTUS/KOLS eastward this afternoon and
evening. SFC wind ELY at 8-12 kts this morning, though stronger
speeds of 15-20 kts are possible near KSAD. Wind becoming WLY/NWLY
this afternoon at less than 12 kts. A few of the stronger SHRA/TSRA
may produce wind gusts to 40 kts and brief MVFR conditions. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Scattered thunderstorms generally from Tucson
eastward and southward through Tuesday. Expect decreasing coverage
of thunderstorms Wednesday, with isolated to scattered thunderstorms
mainly east to south of Tucson. Precipitation will be confined to
near the Mexico border on Thursday and Friday. A slight increase in
moisture will then increase thunderstorm coverage northward next
weekend.

Morning southeasterly winds and afternoon northwesterly winds will
be periodically gusty through the Gila River Valley again today.
Additionally, any convection which develops will be capable of
producing gusty outflow winds in excess of 40 mph. Otherwise, 20-
foot winds will then exhibit diurnal trends with speeds mainly less
than 15 mph, although some elevated afternoon gusts may occur due to
strong daytime heating.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 7 PM MST this evening for
AZZ501>507-509-515.

Heat Advisory until 7 PM MST this evening for AZZ514.

&&

$$

GL

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