Area Forecast Discussion
Issued by NWS Midland/Odessa, TX

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FXUS64 KMAF 020515

1215 AM CDT Sat Aug 2 2014


VFR conditions will prevail next 24 hours.


.PREV DISCUSSION... /ISSUED 830 PM CDT Fri Aug 1 2014/

Convection has mostly dissipated within the flash flood watch area
across the Trans Pecos. Mesoscale models including RUC13/NAM12/TTU
WRF suggest that there will be little development thru 06Z.
Thereafter these mesoscale models redevelop convection across
Presidio and Culberson Counties. Looking closely at water vapor
there is a shrtwv trof that will be moving NW into and thru
Chihuahua, MX thus providing a source for forcing overnight. Sufficient
mstr is place with PWs of 1-2 standard deviations above normal and
steering flow is 10kts or less. As such we will give the watch the
overnight hours to "pan out". May make some minor adjustments to
PoPs before local 10 PM news, but the integrity of the fcst will
remain as is for the most part.


00Z TAF issuance...
No major aviation concerns for the next 24 hours, VFR conditions
expected at all TAF sites. Currently have light easterly winds at
all terminals this evening with some light showers south of CNM
and in/near the Davis Mountains. Could see an increase in
SHRA/TSRA coverage tonight but best chances will be confined to
the far west, possibly affecting CNM, PEQ and FST at some point.
Not expecting any vis restrictions at this time therefore will not
include mention of SHRA in the TAF. However, will need to amend
if TSRA develops. Otherwise, light easterly winds will continue
through Saturday with best TSRA chances remaining to the west of
most terminals.



An elongated and fractured upper ridge extending from SoCal to the
Mexican states of Chihuahua/Coahuila is aiding monsoonal moisture in
staying over Arizona and New Mexico, and over the western half or so
of the forecast area this afternoon.  A shortwave trough translating
slowly east/southeastward between the ua ridge and an ua trough over
the eastern ConUS is the reason for the fracture, and also playing a
hand in fairly widespread convection we`ve seen last night and so
far today.  There also appears to be at least two Mesoscale
Convective Vortices (MCVs), from earlier convection, spinning near
the Guadalupe Mountains, and the other near El Paso.  A surface
ridge over eastern portions of the forecast area is fostering a more
stable atmosphere, although showers have been able to move into the
central Permian Basin early this afternoon.

Cloud cover over the higher terrain of West Texas is beginning to
thin this afternoon as showers and thunderstorms from earlier are
moving into the PB and west central Texas.  This will allow the
atmosphere to destabilize before nightfall, and along with
persistent upslope flow and close proximity to the mentioned ua
features, result in additional shower and thunderstorm development.
Will continue to carry the highest PoPs over these areas tonight and
Saturday.  Precipitable Water is fairly high over the western third
of the forecast area, around 1.5 inches, while the soil is wet, and
flash flood guidance low.  The steering flow around/under the ua
ridge is weak so slow moving thunderstorms, some strong, could drop
1-2 inches of rain per hour.  Considering all this, will issue a
Flash Flood Watch (FFA) for locations along and west of a Guadalupe
Mountains, to Alpine to Presidio line tonight and Saturday.  Also
have concerns about Eddy County in southeast New Mexico where
rainfall amounts of 1 to 3 inches have occurred in the last couple
of days.  It doesn`t appear the atmosphere will destabilize there
quite as much through the rest of the day, so have not included them
in the FFA.  Subsequent shifts will have to monitor and adjust
accordingly.  There could also be additional rises along the Rio
Grande River tonight and Saturday due to runoff from heavy rainfall
over the forecast area, in addition to the potential for heavy rain
over eastern Chihuahua and more water flowing into the Rio Grande
from the Rio Conchos.

Saturday night and thereafter, the eastern ConUS ua trough will
translate eastward, allowing the ua ridge to expand eastward back
over the region.  We should see a gradual decrease in monsoonal
moisture over the region as a result, more subsidence, lower rain
chances and temperatures warming back to normal levels as early as
Tuesday.  There still could be heavy rain concerns along the western
fringe of the forecast area Saturday night, if not Sunday.  Later
shifts will have to monitor the progress of the ua features to see
whether an extension of the FFA is needed.  Rain chances may be few
and far between from Sunday until Wednesday, but there are
indications another ua trough will flatten the ridge mid next week
and allow for more rain chances.  For now, will just keep a slight
chance of thunderstorms mainly over the western half of the forecast
area for mid to late next week.


NM...FLASH FLOOD WATCH through Saturday afternoon FOR THE FOLLOWING
     ZONES... Guadalupe Mountains of Eddy County.

      Davis/Apache Mountains Area...Guadalupe Mountains...Marfa
     Plateau...Presidio Valley...Van Horn and Highway 54



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