Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 151121

Area Forecast Discussion
National Weather Service Tucson AZ
420 AM MST Thu Feb 15 2018

.SYNOPSIS...Showers will gradually decrease in coverage into
tonight. However, scattered showers will return Friday afternoon and
evening, especially east and south of Tucson. Dry conditions with
warmer temperatures will then prevail Saturday. Another disturbance
is expected to bring a slight chance of showers to much of the area
early next week.


.DISCUSSION...KEMX WSR-88D depicted numerous showers across much of
southeast Arizona early this morning. Somewhat lesser coverage of
showers was ongoing across western Pima County as well as far
southeast Cochise County.

Several HRRR solutions have been very consistent with depicting
widespread coverage of showers to continue through the rest of this
morning. The HRRR has also depicted an increase in intensity to
occur during about the next 1-3 hours and also continue into the
late morning hours. Thereafter, the HRRR and the 15/00Z Univ of AZ
WRF-NAM and WRF-GFS were quite similar with depicting decreasing
coverage of showers this afternoon and especially this evening.
However, these solutions are somewhat different than the 15/00Z
deterministic GFS/ECMWF that depicted more robust precip potential
especially for locales southeast-to-south of Tucson tonight into
early Friday.

For this forecast issuance, have maintained scattered to numerous
showers across this forecast area today, then PoPs decrease to
slight chance category most sections late tonight and early Friday.
Snow levels are forecast to remain above most mountain tops. Various
models then depict another impulse embedded within the upper trough
that extends well to the west of the Baja California spur to move
northeastward across northern Sonora and into southeast Arizona
Friday afternoon and evening.

PoPs were raised well into chance-category for southern Graham
and central/eastern Cochise County, while a slight chance of showers
exists Friday afternoon and evening further west to include the
Tucson metro area. Decreasing precip chances again late Friday night
followed by dry conditions area-wide Saturday and Saturday evening.
The global models maintain broad upper trough over the western CONUS
Sunday into Monday.

The ECMWF was more robust versus the GFS with the depiction of model
generated rain amounts and higher elevation snow amounts starting
Sunday afternoon, and especially by Monday. Per coordination with
neighboring WFO`s, PoPs were increased versus the inherited
forecast, especially on Monday. Thus, a slight chance of showers
exists east of Tucson Sunday night, then a slight chance of showers
now exists for much of the area Monday. Snow levels by midday Monday
should range from 7000 feet (Tucson area) to around 8000 feet (near
New Mexico border).

Thereafter, mid-level heights are progged to increase as the upper
flow becomes increasingly southwesterly Tuesday into Wednesday. This
is due to deeper troughing progged to occur west of the California
coast. A few snow showers may linger across the White Mountains
Tuesday, then have opted for dry conditions area-wide Wednesday.

High temperatures today will average about 5-10 degrees below
normal. A warming trend will begin Friday with above normal daytime
temperatures returning this weekend. A cooling trend is on tap
Monday into Tuesday with highs next Wednesday remaining slightly
below normal.


.AVIATION...Valid thru 16/12Z.
Cloud layers SCT-BKN 3-6k ft AGL and several BKN-OVC layers above,
with NUM SHRA through today becoming more SCT SHRA tonight.
Occasional MVFR and ISOLD IFR cigs and vsbys with mountains obscd,
especially through noon today. Sfc wind generally south to southwest
at less than 12 kts through the period. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Periods of rain will continue through today
gradually shifting more to eastern areas tonight into Friday.
Significant rains expected all areas by Friday morning. Saturday
is expected to be dry everywhere then a small chance of showers
returns to the forecast late Sunday through Monday night. Light
winds expected through Saturday then an increase in SW winds should
occur Sunday and even more so on Monday, however fuel moisture
levels will be much improved by that point and RH levels will remain
relatively high.





FIRE WEATHER...Cerniglia

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