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Storm Prediction Center Forecast


RSS Mesoscale Discussions from Storm Prediction Center

SPC - No watches are valid as of Sat Apr 21 16:35:02 UTC 2018

No watches are valid as of Sat Apr 21 16:35:02 UTC 2018.


SPC - No MDs are in effect as of Sat Apr 21 16:35:02 UTC 2018

No Mesoscale Discussions are in effect as of Sat Apr 21 16:35:02 UTC 2018.


SPC Apr 21, 2018 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
0751 AM CDT Sat Apr 21 2018

Valid 211300Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
NORTHWEST AND NORTH-CENTRAL TEXAS TO WESTERN LOUISIANA...

...SUMMARY...
Isolated severe thunderstorms are possible from
northwest/north-central Texas this afternoon to southeast Texas and
southwest Louisiana tonight.

...Synopsis...
A progressive, split-flow pattern will persist in mid/upper levels
this period.  The main feature for this forecast is a synoptic-scale
cyclone initially centered over south-central/southeastern CO, with
trough south-southwestward over far west TX to Chihuahua.  By 00Z,
the associated 500-mb low should move to the OK/KS border region
between ICT-GAG, with trough southward across west-central/southwest
TX.  The mid/upper low should reach northeastern OK overnight, with
the trough becoming somewhat negatively tilted, extending across the
Arklatex and TX/LA border area by 12Z.

At the surface, 11Z analysis showed a frontal-wave low near PVW,
with cold front arching southwestward across the Llano Estacado and
over extreme southeastern NM.  A warm front was drawn southeastward
across the SAT area then eastward over the upper TX coast and Gulf
waters south of LA.  The low should move east-southeastward across
northwest/north-central TX today as the warm front shifts/redevelops
northward across the Hill Country and into parts of north-central
TX.  By 00Z, the cold front should extend from the low over north-
central TX southwestward across parts of the Hill country to the
lower Pecos Valley.  By 12Z, the cold front will have crossed most
of southeast and south-central TX, extending southwestward from the
low near the LA/AR state line.

...TX/LA...
Isolated to widely scattered strong/severe thunderstorms are
expected to develop this afternoon over portions of northwest/
north-central TX, in a zone of maximized low-level convergence/lift,
close to the surface low.  This activity should move east-
southeastward to eastward across parts of north-central or central
TX through the rest of the afternoon into the evening, offering the
potential for hail and isolated severe gusts.  The initial activity
will be supported by a pocket of diurnal/warm-sector diabatic
heating and related boundary-layer destabilization, behind an area
of clouds, precip and non-severe thunderstorms now moving across
parts of OK and north TX.  That increasing low-level instability,
along with surface dew points generally upper 50s to mid 60s F, will
be juxtaposed with cooling temperatures aloft as areas of DCVA pass
through the southeastern quadrant of the mid/upper cyclone. 
Forecast soundings accordingly depict MLCAPE 1000-1500 J/kg over
parts of north-central TX in the 21Z-00Z time frame.  Effective-
shear magnitudes around 45-55 kt and curved low-level hodographs
suggest potential for a supercell or two in the first few hours,
followed by upscale development of a near-frontal convective band
that would cross parts of north-central and east TX, reaching
western LA overnight.  Isolated severe hail and gusts will be
possible in that convective band as well.

Coverage and boundary timing/placement uncertainties with respect to
the convection are the main concerns precluding greater
unconditional severe probabilities at this time, but a small area of
greater risk may be added as the event gets closer and presumably
better-focused on the mesoscale.

..Edwards/Peters.. 04/21/2018

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SPC Apr 21, 2018 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
1049 AM CDT Sat Apr 21 2018

Valid 211630Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A SMALL PART
OF NORTH TX...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF TX AND NORTHERN LA...

...SUMMARY...
Isolated severe thunderstorms are possible from
northwest/north-central Texas this afternoon to east Texas and
northern Louisiana tonight.

...TX/LA...
An upper low is centered today over eastern CO/western KS, with 
band of strong westerly flow around the south side of the low across
TX.  A large area of showers and thunderstorms is affecting much of
OK and north-central TX within the strong low-level advection
regime.  This activity should spread northeastward and away from
north TX by mid afternoon.

In the wake of the morning activity, some heating/destabilization is
expected west of FTW, leading to an area of sufficient CAPE and
low-level convergence for isolated thunderstorm development. 
Low-level shear will decrease through the day as winds veer/weaken,
but the consensus of 12z CAM solutions suggests 1 or 2 strong/severe
storms will develop in this small area, capable of large hail.  The
threat should focus in the 22-02z period.  After that, storm
intensities are expected to diminish but overall mesoscale
organization may increase as storms become oriented into a line.  A
marginal risk of gusty winds or hail will persist through much of
the night as storms spread into east TX and northern LA.

..Hart/Broyles.. 04/21/2018

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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
1130 AM CDT Sat Apr 21 2018

Valid 211700Z - 221200Z

No changes to the ongoing forecast are needed. See below for more
details.

..Picca.. 04/21/2018

.PREV DISCUSSION... /ISSUED 0150 AM CDT Sat Apr 21 2018/

...Synopsis...
An upper low over the southern/central Rockies early this morning
will continue eastward across the southern/central Plains today,
with enhanced mid-level winds confined to mainly parts of the
southern Plains. A weak surface low will develop from west TX to
north-central TX through this evening as a trailing cold front moves
eastward across the TX Hill Country and Edwards Plateau. A
secondary, reinforcing cold front attendant to this low will move
southward across the southern High Plains through the period.

...Portions of Far Southern NM to the Edwards Plateau of TX...
Behind the initial cold front passage but ahead of the reinforcing
cold front, elevated conditions are expected this afternoon for
parts of far southern NM into west TX, including the Edwards Plateau
region. Sustained winds of 15-20 mph will become common along with
RH values lowered into generally the 10-20% range given the
antecedent dry low-level airmass. Very isolated thunderstorms
developed across far west TX yesterday into early this morning. Per
MRMS gauge-corrected precipitation estimates, the spotty and
generally light rainfall associated with this convection should not
greatly reduce fuel receptiveness across a vast majority of the
elevated delineation. The lack of even stronger forecast winds
continues to preclude the introduction of a critical area.

...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
1131 AM CDT Sat Apr 21 2018

Valid 221200Z - 231200Z

...NO CRITICAL AREAS...

No changes to the ongoing forecast are needed. See below for more
details.

..Picca.. 04/21/2018

.PREV DISCUSSION... /ISSUED 0152 AM CDT Sat Apr 21 2018/

...Synopsis...
An upper low should develop east-southeastward across the Southeast
on Day 2/Sunday. Farther west, an upper trough is forecast to move
eastward across the Pacific Northwest to the northern Rockies
through the period. Beneath shortwave upper ridging, a warm/dry
low-level airmass will remain confined to portions of the Great
Basin and Southwest Sunday afternoon. Light winds across these
regions will preclude any elevated or critical conditions.

...Portions of Eastern ND into Northern MN...
A modestly enhanced surface pressure gradient should exist across
parts of eastern ND into northern MN Sunday afternoon ahead of a
cold front, with sustained southwesterly winds around 15-20 mph
possible. A lack of meaningful precipitation over the past week
could allow for some receptiveness of fine fuels. Diurnal heating
and mixing of a dry low-level airmass may result in RH values
becoming lowered into the 25-30% range for a couple hours Sunday
afternoon. For now, these forecast meteorological conditions appear
too marginal to include an elevated area, but trends will continue
to be monitored.

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

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