Area Forecast Discussion
Issued by NWS Midland/Odessa, TX

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FXUS64 KMAF 270545

1145 PM CST Fri Dec 26 2014



A cold front has moved into the northern CWA and will continue
pushing through the area overnight. Winds will remain out of the
N/NE at speeds around 10kts with some gusts to 20kts. Light rain
over SE NM currently changing over to snow. This will continue
through the morning changing back to rain by Saturday afternoon.
Expect cigs and vsbys overnight to fall to MVFR with occasional


PREV DISCUSSION... /ISSUED 437 PM CST Fri Dec 26 2014/


  * Arctic cold front moving across west Texas and southeastern
    New Mexico tonight...

  * Chance of accumulating light snows tonight through Saturday
    night from the Guadalupe south across the Davis Mountains...

  * Much stronger arctic cold front expected Monday night with
    good chances of rain and/or snow Tuesday through New Years Day
    over much of west Texas and southeastern New Mexico...

Summary: A weakening upper level storm system over the Four
Corners this afternoon will move across the central Rockies
tonight. An associated cold front will move across west Texas and
southeastern New Mexico tonight, bringing much cooler
temperatures. There will be a slight chance of rain and/or snow
late tonight along and north of the I-20 corridor, with little to
no accumulations expected. Better chances for accumulating snows
will extend from the Guadalupe Mountains south across the Davis
Mountains tonight and Saturday. As the source moisture for this
system is slight to begin with, accumulations of one to two inches
of snow are possible in the higher elevations of the Davis
Mountains by Saturday afternoon.

Temperatures will moderate Sunday and Monday as high pressure
slips eastward and winds return to the southwest. This will all
change beginning Monday night as a strong surge of arctic air
(likely the strongest we`be seen so far this winter) plunges
southward across west Texas and southeastern New Mexico. Highs
Tuesday through New Years Day will struggle to get above the
freezing mark along and north of the I-10 corridor. Meanwhile,
a strong winter storm system will organize over the desert
southwest Tuesday. This system will then track east across the
southern Rockies and out across west Texas and southeastern New
Mexico. Right now the best chances for snow will be along and
north of the Pecos Tuesday through Thursday. However, confidence
in the amount of moisture this storm will have is low. Thus
we have low confidence of snow amounts which may impact travel
around New Years Day. Best guess we have now is that snow
accumulations of one to maybe two inches will occur over the Davis
Mountains as well as the eastern Permian Basin and western Low
Rolling Plains of west Texas. Conditions are expected to moderate
as we start 2015, with highs expected to be in the mid 40S across
the mountains to near 60 along the Rio Grande.

Technical stuff: We`re seeing a distinct pattern change developing
in the next 6-10 days. The AO is forecast to become positive as
strong height anomalies develop over Alaska, pinching off a good
chunk of the circumpolar vortex and sending it to northern ON by
the middle of next week. In response an area of strong positive
PMSL anomalies (+2 to +3 s.d.) develops along the lee slopes of
the Canadian Rockies this weekend. This arctic high has no place
to go other than south across the CONUS plains. Meanwhile the
cyclonic flow over the western hemisphere buckles in response to
an increase in jet energy over the northern Pacific. A shortwave
trough quickly digs southeastward and intensifies, then closes off
over central CA Tuesday night. This closed low then translates
southeastward and intensifies further over AZ before being picked
up by the polar westerlies Wednesday.

There is relatively low confidence in the exact track of this low,
and as a result there`s dicey confidence in the magnitude and
timing of deep layer lift ahead of the low. Gulf moisture likely will
not be in play with this system as the first arctic front should
take out the western Gulf. Thus whatever moisture we`ll see will
be of Pacific origin. This setup generally favors a top-down
moistening of the column, making precipitation phase forecasts
even harder. It is specious to infer mid-level frontogenesis and
mesoscale precip phasing out at synoptic time scales, so while
there could be mixed phase precip along and north of the I-20
corridor beginning Tuesday night, exact placement and timing of
impacts for New Years Day activities and travel plans is fuzzy
right now. Forecast model blends are of little use during pattern
changes. However, analog forecasts may make a stronger argument
here, and indeed the CIPS analogs are indicating heightened
probabilities of mixed phase/freezing rain along the I-20
corridor from maybe Big Spring east to Ranger Hill by New Years
Eve. So, to put this screed to bed, we`d be a little concerned
about travel impacts going into 2015. We`ll know more as
additional deterministic and ensemble model data are processed.
Stay tuned.





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