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FXUS64 KEPZ 162238
AFDEPZ

Area Forecast Discussion
National Weather Service El Paso Tx/Santa Teresa NM
338 PM MST Sat Dec 16 2017

.SYNOPSIS...
An upper level storm system will bring increasing clouds to the
area overnight, which will help keep temperatures a little warmer
than the past few nights. The approaching storm system will bring
widespread lowland rain and high elevation snow showers to the
area Sunday, with several inches of snow expected in higher
elevations above 7,500 feet, and lesser amounts down to around the
6,000 foot level. A few showers will linger around into Monday,
with dry weather persisting for most of the week ahead. A cooler
airmass will approach the area towards the weekend, along with
more unsettled weather.

&&

.DISCUSSION...
Water vapor satellite imagery shows twin upper lows -- one
ejecting out and moving NE over the Trans-Pecos, soon to be out of
sight/out of mind...and another embedded in a high amplitude
trough digging into northern Baja. Models have come into better
agreement on the track of this low at least until Monday
morning when the low should be over SE Arizona. After that,
things become a little less clear with the low possibly stalling
out and drifting south into Sonora.

In the meantime, it looks like most of the precip should hold off
until around dawn Sunday, after which a strong vortmax moving into
NE Sonora will bring a rapid increase in PVA and larger-scale lift
over SW New Mexico. Mid-level SSW winds will also increase, with
orographic lift helping develop/enhance precip over the Gila.
Precip will spread east towards Las Cruces and El Paso towards
noon or a little after. Precip might be a little more delayed over
Otero county, but still expect orographic lift to lend a hand over
the Sacramento Mountains, with precipitation starting in the
early afternoon.

Snow levels still look to be well-behaved thanks the lack of a
backdoor front and attendant low level cold air mass, and deep
southerly flow aloft. Although precip will hold off most of the
night and winds will remain light, thickening high clouds will
help keep temperatures from bottoming-out over the Gila like they
are apt to do under clear skies. Still, any early-morning precip
could start out as a mix of rain/snow or even snow pellets down to
around 5,000 feet, but snow levels will quickly increase after
sunrise and generally hover between 6500 and 7500 feet throughout
the day both in the Gila Region and the Sacramentos.

Some weak instability and steepening lapse rates ahead of the low
may result in some isolated thunderstorms with the initial round
of precipitation Sunday, mainly in the lowlands in SW New Mexico.

Snowfall amounts...in the Gila: generally looks like 3 to 6
inches above 7500 feet, with localized areas up to 8 inches
(mainly along the crest of the Black Range and perhaps the Pinos
Altos Range). Between 6000 and 7500 feet...expect 1 to 3 inches of
snow, and it`ll be pretty sloppy below 6500 feet. Silver City
(which varies between 5800 and 6200 feet) will be on the lower end
of the scale, with their hopes mostly dependent on keeping precip
around into Sunday night. The heaviest snow will be in
unpopulated areas, with the worst impacts on higher mountain
passes. This includes NM-15 in two spots -- crossing the Pinos
Altos Range, and again near the Copperas Ridge just south of Gila
Hot Springs. Also NM-152 through Emory Pass. Some of these areas
will flirt with Winter Storm Warning criteria (6 inches in 12
hours or 9 inches in 24 hours), but given the relatively limited
impacts (especially in Silver City), we decided to go with a
Winter Weather Advisory for Zone 402 (which covers the southern
Gila region above 6,000 feet).

Snowfall...for the Sacramentos: generally 3 to 5 inches above
7500 feet, with 1 to 3 inches down to 6,000 feet. A little less
confident in this given the tendency of some models and ensemble
members to slow the system down, including the ECMWF which is very
shy about spreading QPF into the Sacramentos. Went with an
Advisory for all 3 Sacramento Mountain zones, starting it a little
later in the day Sunday (18z).

Elsewhere...could be a sloppy inch or so in some of the higher
terrain in the Bootheel. Some rain/snow mix is possible in a few
lowland areas late Sunday night or Monday morning, but with little
to no accumulation. The best chance of this will be north and west
of Las Cruces. For El Paso, expect a healthy rainfall of 0.20 to
0.50 inches.

For Monday, we could see some lingering snow showers in the higher
terrain, especially if the low stalls out, but the amounts will
generally be low since we will dry-slot early Monday, and then the
low rapidly weakens.

Dry conditions with a low warm-up are expected Tuesday into
Thursday. On Friday, a fast-moving shortwave trough may sweep
through, but it looks dry.

Then things get very unclear. There is good agreement on a very
high-amplitude ridge setting up along the West Coast northward
towards the Yukon. This is an ideal pattern for sending an arctic
airmass southwards into the U.S.. The question is with the
strength, orientation, and amplitude of the trough that sets up to
the east of the ridge. The ECMWF continues to favor the less-
amplified solution, with the Arctic air mass mostly deflecting
into the Great Lakes. The 12z GFS pushes the colder air further
south and backs it up into the Rockies, and keeps it around
through next weekend. However, the 12Z GFS Ensembles show there is
a large amount of variation Friday onwards, with most members
preferring a warmer solution. FWIW, the 18Z deterministic GFS has
flopped back to a warm solution.

So, there is some increasing confidence in precip being around
the area Christmas Eve/Christmas (Sun/Mon), but it`s not a slam
dunk (20-30 PoPs seem OK), and precip type remains completely up
in the air.

&&

.AVIATION...
Valid 17/00Z-18/00Z...
VFR conds thru most part of the period. A closed low approaching the
region will start deteriorating conds after 12Z. Widespread lowland
rain showers are possible along with mountain snow showers above
7000 feet. However, some wintry mix and light snow showers could be
possible in lower elevations. Areas near rain and snow showers could
observe lower CIG and VIS, taking flight categories into the MVFR or
even IFR. Winds will start from the SW

&&

.FIRE WEATHER...
A closed low pressure system is going to be moving through the
region tonight and tomorrow. This system brings lowland rain showers
and mountain snow showers. The effects of this system will be felt
until Tuesday morning. Dry and warmer air makes a short come back
between Tuesday and Thursday, before the next system comes to the
Borderland. Temperatures will be around or slightly above normal in
those days and winds will be between 5 to 15 mph. Minimum relative
humidities will be higher than in previous days with peak values
tomorrow between the 50s and 60s, then decreasing into the lower
30s for the rest of the week.

&&

.PRELIMINARY POINT TEMPS/POPS...
El Paso                 39  54  36  54 /   0  40  60  20
Sierra Blanca           40  60  41  55 /   0  20  30  10
Las Cruces              35  48  34  52 /   0  60  50  20
Alamogordo              34  50  34  51 /   0  50  50  20
Cloudcroft              26  33  24  35 /   0  70  70  20
Truth or Consequences   34  47  33  49 /   0  70  50  30
Silver City             34  42  31  45 /  10  80  60  20
Deming                  34  49  36  52 /  10  70  50  20
Lordsburg               39  50  34  52 /  30  80  50  20
West El Paso Metro      41  52  38  53 /   0  50  60  20
Dell City               32  61  39  58 /   0  20  40  20
Fort Hancock            37  62  42  57 /   0  20  30  20
Loma Linda              38  54  35  50 /   0  30  60  20
Fabens                  33  58  36  55 /   0  30  60  20
Santa Teresa            38  50  34  52 /   0  60  60  20
White Sands HQ          38  51  35  52 /   0  60  60  20
Jornada Range           26  51  31  52 /   0  70  50  20
Hatch                   33  48  35  53 /   0  70  50  20
Columbus                37  50  35  53 /  10  70  50  20
Orogrande               35  54  35  53 /   0  40  60  20
Mayhill                 32  43  26  42 /   0  60  60  20
Mescalero               27  42  23  42 /   0  60  70  20
Timberon                26  41  27  42 /   0  50  60  20
Winston                 27  40  21  42 /   0  80  60  30
Hillsboro               32  44  31  49 /   0  80  60  30
Spaceport               28  49  31  50 /   0  70  50  20
Lake Roberts            24  38  23  43 /  10  80  60  30
Hurley                  31  44  31  48 /  10  80  60  20
Cliff                   31  48  27  50 /  20  80  50  20
Mule Creek              31  47  30  48 /  20  80  50  20
Faywood                 33  45  30  49 /  10  80  60  30
Animas                  40  51  36  52 /  30  80  50  20
Hachita                 37  50  36  51 /  20  80  50  20
Antelope Wells          38  48  36  51 /  30  80  50  20
Cloverdale              39  46  36  49 /  30  80  60  20

&&

.EPZ WATCHES/WARNINGS/ADVISORIES...
NM...Winter Weather Advisory from 5 AM Sunday to 11 AM MST Monday for
     NMZ402.

     Winter Weather Advisory from 11 AM Sunday to 11 AM MST Monday
     for NMZ414>416.

TX...None.
&&

$$

25-Hardiman/29-Crespo



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