Area Forecast Discussion
Issued by NWS Tucson, AZ
FXUS65 KTWC 290435
Area Forecast Discussion
National Weather Service Tucson AZ
935 PM MST SUN AUG 28 2016
.SYNOPSIS...Isolated thunderstorms will be confined to mainly near
the New Mexico border Monday afternoon and evening. Some increase in
moisture will then provide isolated to scattered afternoon and
evening thunderstorms areawide Tuesday through Thursday. Drier
conditions will return again by next weekend.
.DISCUSSION...Clear skies prevail across southeast Arizona at this
time except for a few cumuloform clouds near the New Mexico border.
The dry regime was noted via the 29/00Z KTWC sounding total precip
water value of 0.64 inch, nearly identical to 24 hours ago.
Dewpoints at lower elevations valid 8 PM MST generally ranged from
the upper 30s-lower 40s, and these temps were mostly a couple of
degs lower versus 24 hours ago.
The official forecast was updated to remove the mention/depiction of
PoPs the rest of tonight. The 29/00Z NAM12 depicted measurable rain
amounts Monday afternoon/evening to be mainly near the New Mexico
border, and within this forecast area especially across the White
Mountains northeast of Safford, and the Chiricahua Mountains in
eastern Cochise County.
If this solution is reality, the precip Monday afternoon/evening
would be further west versus earlier today when showers/tstms were
east of the area across southwest New Mexico. Would be very
surprised to have measurable precip as far west as the Catalina/
Rincon Mountains near Tucson as depicted via the official forecast.
However, will defer to subsequent shifts to make any adjustments in
this regard. High temps Monday are expected to be quite similar to
temps achieved this afternoon, or perhaps just a degree-or-two
warmer depending upon the location.
Please refer to the additional sections for further detail.
.AVIATION...VALID THRU 30/06Z.
Isolated -TSRA/-SHRA mainly east of a KSAD-KDUG line Monday
afternoon and evening. Otherwise, clear skies across much of the
area into Monday morning, then a few to scattered clouds around 10k-
15k ft msl after about 17Z Monday and continuing into Monday
evening. Surface wind the rest of tonight variable in direction less
than 10 kts, then surface wind Monday into Monday evening generally
easterly at 5-15 kts. Aviation discussion not updated for TAF
.FIRE WEATHER...A few thunderstorms will occur Monday afternoon and
evening mainly near the New Mexico border. The coverage of showers
and thunderstorms will spread further west Tuesday followed by
isolated to scattered thunderstorms Wednesday into Thursday. A
drying trend will then occur from west-to-east Friday into next
weekend, and dry conditions may prevail area-wide next Sunday. 20-
foot winds Tuesday and Wednesday will be mainly from the east at 5-
15 mph with gusts perhaps of 20-25 mph at times. Otherwise, 20-foot
winds will be terrain driven and less than 15 mph.
.PREV DISCUSSION /205 PM MST/...Water vapor imagery and 28/12Z upper-
air plots show the upper low spinning over the four corners region.
Meanwhile, high pressure resides over the eastern Pacific waters
several hundred miles west of the south central Baja peninsula.
Plenty of dry mid to upper level air can be seen over a large part
of the eastern Pacific, all of Baja, southern California, northern
Mexico and southern Arizona. Visible and IR satellite imagery shows
cloudiness associated with the low covering parts of southeast Utah,
eastern Arizona as well as Colorado and New Mexico. The latest radar
mosaic shows isolated showers and thunderstorms over southwestern
parts of New Mexico and along the Mogollon Rim and the White
mountains but this activity is mostly east and north of my forecast
area and is moving northeast.
The 28/12Z KTWC sounding revealed a PW of 0.67 inches which was down
0.43 inches from 24 hours ago. In addition, surface dewpoints
currently range from the mid 30s to the mid 40s. That said, the
latest run of the Univ of AZ WRF/NAM & GFS models show very little
activity today, mainly some isolated activity near the New Mexico
border and areas to our north. That said, the threat for this
evening and again Monday afternoon should be minimal and mostly
along the border with New Mexico.
Through Monday, the upper low currently over the four corners region
will slowly move east into northern New mexico before weakening in
the process. By Tuesday the flow aloft will transition to more of an
easterly component bringing the moisture that is to our east back
into Arizona. Therefore, expect increasing rain chances beginning
Tuesday, but especially into Wednesday and continuing on Thursday
before decreasing significantly by late in the week and into the
weekend as high pressure to our east retrogrades to a position to
the south of Arizona and a trough approaches from the west coast
bringing in drier air from the west and southwest.
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