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  Sunday June 25, 2017

RSS Mesoscale Discussions from Storm Prediction Center

SPC - No watches are valid as of Sun Jun 25 17:06:01 UTC 2017

No watches are valid as of Sun Jun 25 17:06:01 UTC 2017.


No Mesoscale Discussions are in effect as of Sun Jun 25 17:06:01 UTC 2017.

SPC Jun 25, 2017 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0800 AM CDT Sun Jun 25 2017

Valid 251300Z - 261200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
EAST-CENTRAL NEW MEXICO...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK AND EXTENDING TO PARTS OF WEST-CENTRAL/SOUTHWESTERN
NEW MEXICO...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ELSEWHERE FROM
SOUTH-CENTRAL COLORADO TO THE LLANO ESTACADO OF TEXAS...AND
BORDERLANDS OF FAR WEST TEXAS AND SOUTHERN NEW MEXICO...

...SUMMARY...
Severe thunderstorms with damaging wind and isolated large hail are
expected across parts of central and eastern New Mexico this
afternoon and evening.  Isolated severe storms are possible
elsewhere from southern Colorado to southern New Mexico and far west
Texas.

...Synopsis...
The upper-air pattern will be dominated by:
1.  Mean troughing and broadly cyclonic flow over much of the
central and eastern U.S., and
2.  A persistent high over southern AZ/northern Sonora region. 
Associated synoptic ridging will move eastward across the Northwest
and Great Basin as substantial shortwave perturbations over the
Pacific move onshore in western Canada, and approach the CA coast,
late in the period.  A weak shortwave trough, close to the center of
the mid/upper anticyclone, was evident in moisture-channel imagery
over portions of central and western AZ.  This feature should pivot
northeastward then southeastward today into western and perhaps
central NM, as it becomes entrained in the northwest flow aloft
associated with the eastern U.S. mean trough.

At the surface, a complex area of low pressure was analyzed at 11Z
from the St. Lawrence Valley of southern QC to Georgian Bay, with an
occluded front arching southeastward to a triple point near NYC.  A
cold front was drawn from there southwestward across southeastern
VA, central SC, southwestern AL and southeast TX, becoming a
quasistationary front over central/northwest TX.  This front became
ill-defined amidst outflow from an area of scattered to widely
scattered thunderstorms across much of the TX Panhandle and
adjoining extreme eastern areas of NM.  The aggregate outflow
boundary from that convection is acting as the effective frontal
zone between TCC-CQC in eastern NM, and should become
quasistationary in a NW-SE alignment today from the southernmost
Sangre de Cristos southeastward through the area between CVS-ROW.

...NM, southern CO, west TX...
In general, scattered thunderstorms are expected to develop in the
higher elevations of south-central CO and northern/central/western
NM this afternoon, as heating of high terrain removes already-weak
MLCINH.  Activity is expected to assume a mix of multicell and
supercell modes early, with large hail and damaging gusts likely.  A
tornado cannot be ruled out, though this threat is very conditional
on storm mode, timing/character of storm/boundary interactions, and
storm-scale modulations to ambient kinematic fields.  With time
through the afternoon, activity should move generally southeastward
across central, eastern and perhaps southern NM, coalescing into one
or two dominant storm clusters or MCSs.  Accordingly, the main
threat should evolve to damaging wind, with isolated large hail
possible.  The easternmost of this convection may reach parts of
west TX tonight before diminishing with the loss of inflow-layer
instability.

With the outflow-enhanced baroclinic zone expected to stall SE-NW
across eastern NM today, a corresponding instability gradient and
related corridor of enhanced low-level lift, vorticity, moisture,
deep shear, and storm-relative boundary-layer flow should set up and
focus severe potential, including a most-favored corridor for
potential forward propagation and merging convection.  Multiple
short-fused synoptic-scale (i.e., RAP and parallel RAP) as well as
convection-allowing models reasonably depict this scenario in recent
runs -- both in terms of explicit convection and fields of
environmental parameters.  Forecast soundings along and near the
boundary show weak (generally 10 kt or less) surface flow but strong
directional shear in low levels, beneath about 30 kt of northwest
flow around 500 mb, contributing to effective-shear magnitudes 40-45
kt.  Strong heating near and south of the boundary, along with moist
advection and favorable midlevel lapse rates, will contribute to
MLCAPE exceeding 2000 J/kg over much of eastern NM, with well-mixed
subcloud layers supporting wind potential.  Even deeper mixing,
beneath weaker but still supportive buoyancy, is expected into the
central/southern NM mountains and valleys, in support of some
organized wind potential there as well.  The 15% outlook therefore
has been extended somewhat southwestward.

..Edwards/Picca.. 06/25/2017

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SPC Jun 25, 2017 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1131 AM CDT Sun Jun 25 2017

Valid 251630Z - 261200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
NEW MEXICO...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
NM/FAR WEST TX...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS NEW
MEXICO AND THE SOUTHERN HIGH PLAINS...

...SUMMARY...
Severe thunderstorms with damaging wind and large hail are expected
across parts of central and eastern New Mexico this afternoon and
evening. Isolated severe storms are possible elsewhere from southern
Colorado to southern New Mexico and far west Texas.

...NM/southern CO/far west TX...
A very moist air mass exists across the region today within a
post-frontal upslope flow regime reinforced by prior convective
outflows. In fact, 12Z RAOB-observed precipitable water values are
in the upper 5-15% of daily climatological values. A gradual
thinning of prevalent low-level clouds has begun to occur across
eastern NM as of late morning per visible satellite imagery and this
same general trend will continue through the afternoon. Storms
should initially develop near mountains/higher terrain of
south-central CO and interior NM this afternoon. Heating/orographic
lift aside, such development should be aided by a ridge-peripheral
weak mid-level disturbance moving east/southeastward from northern
AZ into NM per water vapor imagery.

Steep lapse rates/moderate buoyancy in the presence of 30-40 kt
effective shear (especially across east-central/northeast NM) will
some support initial supercells capable of large hail. Storms should
gradually congeal, grow upscale, and progress south-southeastward
through late afternoon into evening across eastern NM and eventually
toward parts of far west TX, with a corresponding increase in
damaging wind potential.

...Coastal GA/Carolinas...
A few stronger storms could occur this afternoon within a moist
environment near/east of the cold front, but the potential for
organized/sustained storms currently appears low.

..Guyer/Gleason.. 06/25/2017

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SPC Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook
          
Day 1 Fire Weather Outlook Image
Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1159 AM CDT Sun Jun 25 2017

Valid 251700Z - 261200Z

No changes have been made to the ongoing forecast.

..Cohen.. 06/25/2017

.PREV DISCUSSION... /ISSUED 0230 AM CDT Sun Jun 25 2017/

...Synopsis...
Shortwave trough currently moving through central CA will continue
moving north-northeastward into northern CA and southern OR, ahead
of a stronger shortwave trough farther off the northern CA coast.
Increased mid-level moisture and forcing for ascent will contribute
to thunderstorm development across northern CA and central OR
(discussed in more detail below). Farther east, upper troughing
currently extending from the northern Rockies to the Northeast and
covering much of the central and eastern CONUS will persist
throughout the day while gradually shifting eastward.

...Northern CA/Central OR...
Antecedent dry airmass and deep boundary-layer mixing will
contribute to highs in the upper 90s/low 100s and afternoon RH
values in the teens. Despite these dry low levels, aforementioned
lead shortwave trough is expected to move through the region during
the afternoon, helping to moisten the mid levels. Resulting modest
instability coupled with forcing for ascent and favorable orographic
circulations will result in isolated to widely scattered
thunderstorms during the afternoon and evening. Storm motions will
not be particularly fast but the warm and dry boundary-layer and
high cloud bases will contribute to significant sub-cloud
evaporation of any precipitation, resulting in low precipitation
totals at the surface. These dry thunderstorms amidst modestly dry
fuels will support an increased fire weather threat.

...Northern Plains...
Anomalously dry fuels exist across the region due to the
below-average rainfall and dry conditions the area has experienced
for the past 30 days. Northwesterly winds near 15 mph and minimum RH
values around 20-25% will contribute to locally elevated fire
weather conditions this afternoon over the region. Below-average
temperatures should keep RH values above critical values except on a
spotty/localized basis.

...Please see www.spc.noaa.gov/fire for graphic product...

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SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook
          
Day 2 Fire Weather Outlook Image
Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1159 AM CDT Sun Jun 25 2017

Valid 261200Z - 271200Z

...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF NORTHWEST NV...
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF EAST-CENTRAL/SOUTHERN
NV...SOUTHWEST UT...NORTHWEST AZ...

No changes have been made to the ongoing forecast.

..Cohen.. 06/25/2017

.PREV DISCUSSION... /ISSUED 0239 AM CDT Sun Jun 25 2017/

...Synopsis...
Upper ridge in place from the Southwest into the northern Rockies is
expected to breakdown on Monday as a shortwave trough moves from
northern CA through the northern Rockies. Farther east, a shortwave
trough will move from the northern Plains/upper Midwest
southeastward into the upper Great Lakes/OH valley, contributing to
an eastward shift of its parent upper trough. At the surface, lower
pressures associated with the northern CA shortwave trough will
contribute to a tightening of the surface pressure gradient across
much of the Intermountain West as well as over the northern Plains.

...Great Basin/AZ...
Aforementioned tightening of the surface pressure gradient along
with modestly enhanced mid-level flow will contribute to gusty
southerly/southwesterly winds in the vicinity of the NV/UT/AZ border
intersection. Very warm and dry conditions are also expected in this
area with minimum RH values in the single digits. Combination of
warm, dry, and windy conditions with dry fuels will support a
critical fire weather threat. Critical fire weather conditions are
also anticipated across northeast NV where winds around 20 mph are
anticipated amidst single-digit RH values and dry fuels.
Above-average temperatures and RH values in the single digits are
anticipated across much of the remainder of the region but winds are
expected to be less than 20 mph, precluding critical fire weather
conditions.

Shortwave trough resulting in the breakdown of the upper ridge will
also support an increase in mid-level moisture across portions of
central/eastern OR and western ID. This mid-level moisture will
exist atop a warm and dry antecedent airmass, contributing to an
environment favorable for dry thunderstorms. Development of these
thunderstorms amidst dry fuels will result in increased fire danger.

...Northern Plains...
Previously discussed tightening of the surface pressure gradient
across the region will result in gusty southeast winds from 20-25
mph from early Monday afternoon through the evening. Above-average
temperatures (i.e. in the upper 80s and low 90s) are also expected,
supporting afternoon RH values around 15-20 percent. While there
will be some dissociation (both spatial and temporally) between the
strongest winds and low RH values, enough overlap exists to support
an elevated to locally critical fire weather threat. A critical
delineation may be needed in subsequent outlooks if guidance
suggests stronger winds will persist farther east.

...Please see www.spc.noaa.gov/fire for graphic product...

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