Area Forecast Discussion
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FXUS64 KLUB 272327
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
627 PM CDT Mon Mar 27 2017

.UPDATE...
A surge of moisture on a strengthening low level jet will introduce
the potential for both low level wind shear and stratus late
tonight with the stratus potential lingering through Tuesday morning.
Lift ahead of a strong storm system over western Arizona during the
morning will act on elevated instability with possibility of TS
developing before 18Z. Think best chances will come east of KPVW
and KLBB, but it will be close. Will keep TS mention out of those
two TAFs but will insert a PROB30 group at KCDS for better chances
there during the afternoon.

&&

.PREV DISCUSSION... /issued 325 PM CDT Mon Mar 27 2017/

SHORT TERM...

Today`s ridge will quickly be a thing of the past as our next
weather maker is coming ashore the Pacific Coast.  NWP shows a
slightly faster progression of the associated trough axis than the
past several days.  Wind fields to the east of the trough will
experience increased cyclonic curvature as the trough closes off
along the AZ/NM state line by about 12Z.  NWP appears to have
initialized this feature reasonably well though some divergence
occurs fairly rapidly.  The GFS representation of H3 winds looks a
bit wonky and prefer the ECM`s solution based on conceptual models
of cyclogenesis and deepening.

Overall, would expect that we`ll see low stratus across the area
before sunrise Tuesday as rapid moisture return develops.  However,
not as rapidly as the GFS (which has a distinct high bias in these
regimes) would suggest.  Therefore this forecast will make the
assumption that the dryline will set up near the TX/NM state line
early Tuesday morning.  The dryline will then begin its eastern move
shortly after daybreak with a well defined bulge across our CWFA.

Precipitation continues to be indicated during the morning hours
(though more pronounced in NWP) than in recent days.  Normally, one
would expect some streamer showers during the morning though the
dynamical forcing associated with this system could lead to more
vigorous activity.  With the assumption that some clearing will
occur during the early afternoon (modest confidence) and dynamical
cooling (high confidence) will help to aid in destabilization, we
will probably see severe convection break out east of the dryline.
Granted, the location of the dryline during the afternoon has much
uncertainty with the range of likely possibilities from US385 on the
west to US83 in the east.  The threats include all varieties of
severe induced weather.  With CAPE of 2k-3kj/kg and bulk shear of 40-
60 kts, strong rotating updrafts are likely.  The tornado/heavy rain
threat looks to be greatest in our northeast where low level shear
and backed winds will provide for the greatest low level turning.

To the west of the dryline breezy southwesterlies look quite likely
and combined with the very dry dewpoints expected, fire weather
conditions are still looking favorable for rapid spread.  Have added
Hale county to the fire weather watch given the increasing likelihood
that the could see the 180 mins of red flag conditions.

Finally, some comments about uncertainty.  Models have been all over
the place as to the evolution of the mesoscale features such as the
dryline.  The last system with this trajectory saw moisture make it
much further into NM than the models indicated.  The westward extent
of the low level moisture is one of the key uncertainties in this
forecast.  What we do have confidence in is storms east of the
dryline and fire weather to the west.  As such, watch the dryline as
it it shouldn`t be hard to pick out and adjust expectations
accordingly.

LONG TERM...

By the start of this forecast period, a dry slot will most likely be
forming across much of the forecast area as the dry line will have
moved well into the Rolling Plains and Big Country. There is still
some uncertainty on the timing of this feature developing as the
convection in the morning will be a driving force in wringing out
the atmosphere for the afternoon. Have left slight and chance POPs
in for the forecast area attm for the 0-6Z time period, but then
rapidly erode those POPs eastward during the 6-12Z time period as
dry air is circulated into the area. Another chance of showers with
some thunder will exist as the low translates the area during the
day Wednesday and drags a cold front into the region. Mid and upper
levels look to be well saturated to support this activity, at least
across the northern half of the area. As the meandering low finally
pulls away from the Panhandle on Thursday morning, precipitation
chances end quickly, and skies should briskly clear.

The next feature of interest will be an upper low to impact the
region this weekend. Models are in good agreement on the strength
and track of this storm through Saturday 0Z, and then there is an
abrupt split on solutions. Prior to that, a closed low is forecast
to be roughly positioned over the Four Corners region by Friday
afternoon. South-southwesterly winds and low RH values will combine
ahead of the system to possibly elevate fire weather concerns across
the western portions of the forecast area. Past 0Z on Saturday, the
GFS puts the brakes on and digs the system south while strengthening
it before sending it plowing eastward towards West Texas late on
Sunday. The ECMWF, however, takes a sudden turn north and sends the
system on a similar track to the storm system we just dealt with at
the end of last week that gave us a brief bout of thunderstorms and
lots of wind. A very narrow axis of moisture appears to be available
on Saturday as the dryline looks to set up well east, but moisture
return on Sunday is much better. With so much uncertainty in model
output, kept with the Blend output for now. Both models are now
showing another low developing which would affect the area early
week, and oddly, they seem to agree early on for this one.
Unfortunately, early runs are showing this one to be a wind event
for the area.

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Tuesday afternoon through Tuesday
evening for TXZ027>029-033>035-039>041.

&&

$$

07



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