NWS Storm Prediction Center - Day 1 Convective Outlook

Apr 19, 2018 1300 UTC Day 1 Convective Outlook
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 Forecast Discussion - Day 1 Convective Outlook


   SPC AC 191246

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0746 AM CDT Thu Apr 19 2018

   Valid 191300Z - 201200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
   CENTRAL AND SOUTHERN NEW MEXICO AND FAR WEST TEXAS...

   ...SUMMARY...
   Isolated severe thunderstorms may impact parts of central and
   southern New Mexico and far west Texas late this afternoon and
   evening with a risk for downburst winds and hail.

   ...Synopsis...
   In mid/upper levels, a complex cyclone will shift eastward across
   the Northeast and Canadian Maritimes through the period, while a
   progressive/split-flow pattern will dominate the western U.S.  A
   large cyclone -- now apparent in moisture-channel imagery over much
   of CA/NV -- will move eastward to UT/AZ and western parts of CO/NM
   by the end of the period, with the 500-mb low over UT at 12Z.  

   At the surface, a large, continental/polar anticyclone will spread
   across much of the central/eastern U.S. in the wake of a low-level
   cold front related to the departing Northeastern cyclone aloft. 
   This will preclude substantial moisture return or destabilization
   except for a narrow corridor over and near the mountains of northern
   Mexico, around the western part of the residual frontal zone now
   stalled across northern portions of Coahuila and Chihuahua.  

   ...Central/southern NM, far west TX...
   Widely scattered thunderstorms are expected to develop over northern
   Chihuahua and then southern NM this afternoon into early evening,
   shifting eastward to northeastward over the outlook area.  While
   storms are surface-based or very nearly so, isolated severe gusts or
   large hail may occur. 

   The aforementioned ribbon of convectively favorable moisture return
   through northern MX should extend northward over the marginal-severe
   outlook area this afternoon and evening, juxtaposed with surface
   heating of the desert valleys and higher terrain.  The air mass over
   the region is quite dry at this time; however, some lower-elevation
   surface dew points in the 30s to low 40s F should result from moist
   advection by mid/late afternoon.  This process will start sooner in
   northern Chihuahua this afternoon, where stronger heating and
   somewhat higher PW will combine with low-level convergence and
   orographic forcing to erode MLCINH and boost MLCAPE to near 1000
   J/kg.  Buoyancy should diminish gradually northward across southern
   NM, while becoming less surface-based eastward over the Trans-Pecos
   and Big Bend regions.  

   Storms will have little room to access favorable boundary-layer
   parcels before moving atop a more stable/lower-theta-e air mass this
   evening, even though a general thunder risk may persist eastward
   toward the Pecos Valley.  Within the narrow zone of favorable
   MLCAPE, however, well-mixed subcloud layers beneath that buoyancy
   will support maintenance of any hail to the surface, as well as some
   downburst potential.  Deep shear should be increasingly favorable,
   with the juxtaposition of surface southeasterlies under
   strengthening mid/upper gradient winds ahead of the cyclone. 
   Forecast soundings show effective-shear magnitudes 45-55 kt, along
   with sufficiently straight hodographs to support splitting cells
   with both right- and left-moving offspring.

   ..Edwards/Goss.. 04/19/2018

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z



Data courtesy the Storm Prediction Center
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