Area Forecast Discussion
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078
FXUS64 KLUB 211107
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
607 AM CDT Tue Mar 21 2017

.AVIATION...
A weak cold front will move through the area though little other
than a change in wind direction is expected initially. This
evening, we may see an increase in low stratus at all sites though
data currently is quite disparate on the spatial and temporal
characteristics. The bottom line is that IFR ceilings may be
possible after 00Z.

&&

.PREV DISCUSSION... /issued 325 AM CDT Tue Mar 21 2017/

SHORT TERM...

A negatively tilted ridge will rotate, pivoting over West Texas, to
become more meridional through late tomorrow.  This occurs as the
next storm system comes ashore the California coast thus resulting
in a return of southwesterly flow. Well to our northwest, a trough
will drop southeasterly across the Great Lakes.  A surface low is
analyzed across the southeastern Panhandle this morning and this
feature will drift eastward.  As it does, the frontal boundary on
the western periphery of the surface low will be allowed to progress
southward in a slow fashion.  It looks like it may take until about
mid-day before the front clears our southwestern zones.  Despite the
wind shift, scant little difference in the post-frontal theta-e is
noted.  As such, high temps should remain quite warm once again
today.  However, lower theta-e air will come in the form of a
secondary frontal surge tonight and at allow Wednesday to be a few
notches cooler.

A number solutions are hinting at a trend (started by the NAM last
night) of light precip behind the frontal boundary.  Forecast
sounding do indicate a thin layer of low level moisture after
sunset.  However, forecast soundings are not overly supportive of
much, if any, meaningful precipitation.  Have kept mention of silent
10% chance mainly SE.  Considered adding sprinkles, but the spatial
uncertainty and limited moisture argues that it is not worth
mentioning.  It is possible, however.

In the fire weather department.  The RH should dip to below 20 SW of
a Dimmitt to Post line.  However, wind speeds should remain below 15
mph especially given the anticipated frontal location.

LONG TERM...

The big news in the long term will be what happens on Thursday and
Friday. A potent upper level low currently circulating over the
Pacific Ocean will begin to split later today with the weaker
portion of the split flow headed north into Canada. The southern
portion of the split is expected to deepen into a strong trough as
it translates into the Desert Southwest by Wednesday night. By
Thursday morning, the system should progress into a closed low
entering the Four Corners region. As for the actual passage of the
system, models are in fairly good agreement on the track and speed
of the system with the center of the low passing just north of the
TX Panhandle Thursday night into Friday and taking a southerly turn
into OK late Friday. This system poses several threats for the
forecast area, so we`ll address each one separately.

First, winds on Thursday. As the system approaches from the west,
the surface gradient will begin to tighten, turning winds southerly.
Support at higher levels will help mix strong winds to the surface.
500mb winds on Thursday will crank at their highest to 90 KT, at
700mb to 50-60 KT and 850 will be consistently around 40-45 KT
(increasing to 55 late in the day). This should make for an
afternoon of near, if not above, Wind Advisory criteria. With the
southerly winds, moisture should be sufficient, though, to keep fire
weather concerns that day at a minimum.
The big news in the long term will be what happens on Thursday and
Friday. A potent upper level low currently circulating over the
Pacific Ocean will begin to split later today with the weaker
portion of the split flow headed north into Canada. The southern
portion of the split is expected to deepen into a strong trough as
it translates into the Desert Southwest by Wednesday night. By
Thursday morning, the system should progress into a closed low
entering the Four Corners region. As for the actual passage of the
system, models are in fairly good agreement on the track and speed
of the system with the center of the low passing just north of the
TX Panhandle Thursday night into Friday and taking a southerly turn
into OK late Friday. This system poses several threats for the
forecast area, so we`ll address each one seperately.

First, winds on Thursday. As the system approaches from the west,
the surface gradient will begin to tighten, turning winds southerly.
Support at higher levels will help mix strong winds to the surface.
500mb winds on Thursday will crank at their highest to 90 KT, at
700mb to 50-60 KT and 850 will be consistently around 40-45 KT
(increasing to 55 late in the day). This should make for an
afternoon of near, if not above, Wind Advisory criteria. With the
southerly winds, moisture should be sufficient, though, to keep fire
weather concerns that day at a minimum.

Second, winds on Friday. As the system exits to the east, strong
west/northwest winds will be dragged across the region (with cooler
air!). This could be yet another afternoon that sees much of the
area near Wind Advisory Criteria. However, more concerning, this
time, we`ll be on the other side of the dryline, meaning RH values
could fall low enough to warrant a fire weather product. It is still
too early to conjecture if that will be an RFD or an RFW, but
suffice to say, fire weather concerns will be elevated on Friday. It
most likely will be dusty, too.

Finally, we have the storm concerns as this system barrels through.
A dryline will set up along the TX/NM border Thursday afternoon and
begin to push eastward early evening. At the same time, lift from
our storm system will be entering the region, providing extra
support for storm development. Though CAPE values aren`t terribly
impressive and we`ll remain capped most of the day, the extra
instability provided by the low pressure system should be enough to
tip the scales. A few storms could go severe with the main threats
being hail and severe gusts.

Past this, another weak trough passes to the north on Sunday,
bringing yet another breezy afternoon. We`ll be watching for the
possible development of another deep low for early next week as well.

Second, winds on Friday. As the system exits to the east, strong
west/northwest winds will be dragged across the region (with cooler
air!). This could be yet another afternoon that sees much of the
area near Wind Advisory Criteria. However, more concerning, this
time, we`ll be on the other side of the dryline, meaning RH values
could fall low enough to warrant a fire weather product. It is still
too early to conjecture if that will be an RFD or an RFW, but
suffice to say, fire weather concerns will be elevated on Friday. It
most likely will be dusty, too.

Finally, we have the storm concerns as this system barrels through.
A dryline will set up along the TX/NM border Thursday afternoon and
begin to push eastward early evening. At the same time, lift from
our storm system will be entering the region, providing extra
support for storm development. Though CAPE values aren`t terribly
impressive and we`ll remain capped most of the day, the extra
instability provided by the low pressure system should be enough to
tip the scales. A few storms could go severe with the main threats
being hail and severe gusts.

Past this, another weak trough passes to the north on Sunday,
bringing yet another breezy afternoon. We`ll be watching for the
possible development of another deep low for early next week as well.

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

99/99/26



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