Area Forecast Discussion
Issued by NWS Midland/Odessa, TX

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FXUS64 KMAF 232319

Area Forecast Discussion
National Weather Service Midland/Odessa TX
619 PM CDT FRI SEP 23 2016

See aviation discussion below.


VFR conditions are expected the next 24 hours at the majority of
the west Texas and southeast New Mexico terminals. The exception
is KMAF where tempo MVFR ceilings are expected in the 13z to 16z
Saturday timeframe. An upper level disturbance will combine with
a surface trough to produce scattered thunderstorms mainly across
west Texas near the end of the TAF period later Saturday afternoon.
Will likely address in more detail in the next issuance. Mainly
south to southeast winds of 5 to 15 mph are expected the next 24



.PREV DISCUSSION... /issued 200 PM CDT FRI SEP 23 2016/


Some big changes are on the way, but just how much change will
depend on the formation and subsequent movement of a cutoff low.
Presently, the evolution is for a cutoff low over the Great Basin
will open a bit and translate northeast over the Northern Plains
while another short wave trough develops to its south.  This trough
then evolves into a closed upper low over New Mexico.  Given the
uncertainty inherent with forecasting closed upper features, further
adjustments to the forecast are likely.  However, confidence is high
that much cooler temperatures along with heavy rainfall are in the
cards for Sunday, with well below normal temperatures persisting
through the early part of next week.

As it stands now, an upper level ridge, which has been over the
Southern Plains for several days, will be shunted eastward in the
next 24-36 hours as a large upper low currently over the Great Basin
eases northeastward.  A short wave trough within this upper low will
eject northeastward over the central Rockies and out over the Northern
Plains Saturday afternoon.  In response to increasing surface
frontogenesis associated with the passing of the aforementioned short
wave trough over the Northern Plains, a cold front will develop and move
south toward the southern High Plains, with colder air hugging the eastern
slopes of the Rockies down to northeastern New Mexico by Sunday morning.
Meanwhile, additional short wave energy will drop down behind the
Northern Plains system and close off over southern New Mexico/northern
Chihuahua by Sunday morning.  A surface low will develop over the Big
Bend, drawing the colder air deeper over much of west Texas and all of
southeastern New Mexico Sunday afternoon.  Surface cooling will be
augmented further as extensive cloudiness will retard insolation and
widespread precipitation will lead to substantial wet-bulb cooling of
the column.

Although models diverge in their handling of the upper low thereafter,
cooler conditions are expected to prevail over the region through at
least mid next week.  High temperatures Monday and Tuesday could be
20 to 25 degrees below normal, if not more!  Rain chances will increase
over southeastern New Mexico and west Texas Saturday, then stay in the
forecast through at least next Wednesday.  See details below.

For this afternoon and tonight, a surface trough over New Mexico
will develop/move eastward into the forecast area this afternoon as
the above mentioned initial short wave trough aids in lowering
heights over the region.  We will add isolated thunderstorms over the
western half of the CWA this afternoon due to a minor short wave
trough moving north from Coahuila.  There does not appear to
be much mid level support farther west near the surface trough, but
that will change overnight as a shortwave trough sweeps east/
northeastward over New Mexico.  In addition, deep layer lift
associated with the right rear quadrant of an 80kt jet at 250 hPa may
support isolated thunderstorms along the surface trough overnight.
A few storms could be strong with gusty winds and brief heavy rainfall;
however, effective shear is generally less than 25kt, instability is
fairly modest, and lapse rates are close to moist adiabatic.

On Saturday, the upper trough over the west will deepen as additional
short wave energy drops into the base of the long wave trough over New
Mexico.  As a result, lift will increase over the area and as such
thunderstorms are forecast to develop along and east of the surface
trough stretching southwest/northeast across the CWA.  Forecast SBCAPE
will rise to at least 1000-1500 J/Kg, but lapse rates will continue to
be near moist adiabatic and 0 to 6km shear will generally be 25kt or
less.  Therefore, we think a few strong storms could develop, perhaps
reaching severe levels, with gusty winds over 50 mph, large hail and
locally heavy rainfall.  We will include this potential for strong to
severe convection in the Hazardous Weather Outlook.

For Sunday, the cutoff low is expected to reside over southern New
Mexico/northern Chihuahua.  With difluent flow aloft and deep layer
lift further enhanced beneath the right rear quadrant of an 80kt jet
at 250 hPa, isentropic upglide will increase above the frontal surface.
This will in turn tap a subtropical moisture feed and increase deep
layer moisture, a critical factor in heavy rain forecasting.  By Sunday
morning, precipitable water values will rise to between 1.25 and 1.50
inches, or close to the 90th percentile climatologically.  We expect
widespread showers and thunderstorms to develop Sunday morning along
the southward-moving cold front, with signals indicating a good chance
of heavy rainfall.  Behind the front, gap winds through Guadalupe Pass
could increase to 40 to 50 mph sustained.  As stated earlier, surface
cold air advection, low insolation, and diabatic cooling of the column
behind the front will result in temperatures Sunday being well below
normal areawide.  We will make mention in the Hazardous Weather Outlook
for the potential of heavy rainfall and flash flooding along with high
winds through Guadalupe Pass.  If model agreement continues, do not be
surprised if a Flash Flood Watch is issued within the next 24 hours for
Sunday and perhaps Sunday night for much of the forecast area along with
a High Wind Watch for Guadalupe Pass.

We will continue the theme of wet and cool conditions Monday through
Wednesday, but lesser rainfall rates should mitigate heavy rain concerns.
Where the cutoff low meanders to during this time frame will dictate how
cool and how wet, but the details are uncertain.  Best indications
now will be for a warming and drying trend late next week.


Big Spring                     73  90  69  70 /  10  60  70  90
Carlsbad                       65  87  63  69 /  20  10  20  60
Dryden                         72  92  72  75 /  10  30  70  90
Fort Stockton                  71  90  68  70 /  10  40  60  90
Guadalupe Pass                 63  77  60  62 /  20  10  20  60
Hobbs                          66  84  63  68 /  30  30  30  70
Marfa                          60  83  61  65 /  20  50  50  70
Midland Intl Airport           71  88  68  70 /  10  50  70  90
Odessa                         71  88  67  70 /  10  50  70  90
Wink                           71  91  68  72 /  20  30  40  80


.MAF Watches/Warnings/Advisories...



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