Area Forecast Discussion
Issued by NWS Midland/Odessa, TX

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FXUS64 KMAF 211651

1051 AM CST Wed Jan 21 2015


See Aviation Discussion below.



Area radars show a wide swath of convection has developed over the
Stockton Plateau, courtesy of a shortwave ahead of the upper
trough currently over central AZ. This should taper off for a
brief VFR window over the srn terminals this afternoon/evening,
before precip redevelops overnight as the upper trough nears. This
will coincide w/a cold front moving in late tonight. Forecast
soundings suggest precip will begin as RA, but then quickly
transition to SN around 12Z Thursday as the column saturates.
Buffer soundings suggest deteriorating cigs/vsbys overnight, to
LIFR most terminals as early as 06Z. Once precip transitions to
SN, visbys should drop considerably.


PREV DISCUSSION... /ISSUED 351 AM CST Wed Jan 21 2015/

Water vapor shows a well defined shrtwv trof in AZ along with good
model depiction of a 4h speed max coincident with the noted subsidence
(steep LR/s) across nrn Baja. These features will be the impetus
for the development of scattered SHRA/TSRA this PM. Initial development
will be across Trans Pecos around 18Z. Based on said defined speed max
and broad lift in the 7h-5h omega field we will opt to increase PoPs
across the Lower Trans Pecos between 18Z-24Z today. Into Wed night/early
Thur AM mid level flow will begin to reflect a stronger/cold upper low
that develops across the central Rocky Mtns while dropping s thru wrn
NM. Current fcst has much of the area covered by likely PoPs Wed night.
This may be a little aggressive on the swd and wwd extent, thus we will
make some of the PoP gradients a little tighter. By 12Z Thur there is
good agreement in models that precip will have made a transition to
SN across the nrn parts of SE NM and as the column cools with 546
dam 1000-500mb thickness along I-20 and 540 dam thru SE NM/NW PB,
per cooler ECMWF. There is better agreement in 5h soln of the ECMWF
as it now shows a closed 5h contour around the low at 12Z Thur with
NAM still the outlier/weaker soln. Low level cold advection will occur
thru the day with 85h temps of -2C near I-20 by 18Z and 540 thickness
near I-20 around 18Z. This data is colder sooner than the runs of last
night and therefore with the transition to SN earlier the amounts
may be a little higher. Seems like a slam dunk that it will snow with
the tougher question being how much? Referring back to past cases per
CIPS analog data the 2nd highest similarity goes to the 12/11/98 event
which at the time resulted in a daily record snowfall here at MAF of
9.8". In that case the upper low was farther s and the PWs probably
a little higher, on the other hand this event the column is colder and
there is a strong signal in the cross section showing persistent lift
in the dendritic growth region. Even though grids already have 2-6"
of snow we will nudge amounts up a little more, especially across the
Upper Trans Pecos and GDP/Davis Mtns. The watch looks pretty good, but
will opt to include the rest of Brewster Co and Marfa Plateau. The window
for heaviest snow looks to be from 18Z Thur - 06Z Fri in the western
half and 03Z-12Z Fri in the eastern half, although significant snows
will likely have already occurred in nrn parts of SE NM Thur AM. There
is good agreement that the system will move out e fairly quickly Fri
with slowly moderating temps gaining momentum early next week.


NM...WINTER STORM WATCH from this evening through late Thursday night
     FOR THE FOLLOWING ZONES... Central Lea County...Eddy County
     Plains...Guadalupe Mountains of Eddy County...Northern Lea
     County...Southern Lea County.

TX...WINTER STORM WATCH from late tonight through late Thursday night
     FOR THE FOLLOWING ZONES... Andrews...Big Bend Area...
     Borden...Crane...Davis/Apache Mountains Area...Dawson...
     Ector...Gaines...Glasscock...Guadalupe Mountains...Howard...
     Loving...Marfa Plateau...Martin...Midland...Mitchell...
     Pecos...Reagan...Reeves County and Upper Trans Pecos...
     Scurry...Upton...Van Horn and Highway 54 Corridor...Ward...




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