SPC Forecast Products Storm Prediction Center

  • SPC - No MDs are in effect as of Mon Sep 23 13:46:01 UTC 2019
    on September 23, 2019 at 1:45 pm

    No Mesoscale Discussions are in effect as of Mon Sep 23 13:46:01 UTC 2019.

  • SPC - No watches are valid as of Mon Sep 23 13:46:01 UTC 2019
    on September 23, 2019 at 1:45 pm

    No watches are valid as of Mon Sep 23 13:46:01 UTC 2019.

  • SPC Sep 23, 2019 1300 UTC Day 1 Convective Outlook
    on September 23, 2019 at 12:55 pm

    SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0749 AM CDT Mon Sep 23 2019 Valid 231300Z - 241200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THROUGH LATE EVENING ACROSS A SMALL PART OF SOUTHWEST AZ... ...SUMMARY... Thunderstorms with very large hail and damaging winds will be possible today across parts of southwest and central Arizona. Storms with a few strong wind gusts will be possible in parts of the Northeast. ...AZ through tonight... A transition season severe weather episode is expected today into tonight across AZ. A midlevel shortwave trough over northwest NV this morning will dig south-southeastward toward the lower CO River valley and evolve into a closed low by Tuesday morning. Low-level mass response to the approaching midlevel trough will result in northward transport of moisture from southwest/south central AZ to the rim through the day. Some slightly elevated convection is ongoing along the north edge of the returning moisture, and this convection may persist through the morning and pose a marginal hail threat. The background environment will become favorable for additional thunderstorms through the day as ascent and midlevel cooling develop southeastward into AZ. Daytime heating across southwest AZ will support surface-based thunderstorm development by late morning (17-18z) along a pseudo-dryline near the CO River, and storms will spread eastward near the rim through the afternoon and into this evening. Surface dewpoints have increased to 70-76 F across southwest AZ with a moisture surge from the Gulf of CA. After accounting for some daytime heating/mixing, boundary-layer dewpoints of 65-70 F beneath midlevel lapse rates near 7 C/km will result in MLCAPE of 1500-2500 J/kg and minimal convective inhibition. Effective bulk shear of 40-50 kt and relatively long/straight hodographs will favor splitting supercells capable of producing isolated very large hail near 2 inches in diameter, and there is some potential for clustering of hail events west of Phoenix this afternoon. The stronger supercells, as well as eventual upscale growth into small clusters, will pose a threat for damaging winds. Otherwise, an isolated tornado cannot be ruled out, but this threat will be secondary given relatively weak low-level flow/shear. Convection should persist into the overnight hours, with at least a low-end threat for hail/wind continuing. ...NY and vicinity this afternoon/evening... A midlevel shortwave trough and associated surface cold front will move eastward across NY by late afternoon into early tonight. Clouds and poor lapse rates in the pre-frontal warm sector will limit buoyancy, with MLCAPE likely to remain near 500 J/kg. Still, an increase in midlevel flow with the approach of the shortwave trough could support isolated strong gusts with downward momentum transfer in convection near the front this afternoon/evening. ..Thompson/Leitman.. 09/23/2019 Read mor