Alert archive / Louisiana / Dense Fog Advisories in 2021

Dense Fog Advisory 41, NWS New Orleans, LA

December 17, 202115 parishes in Louisiana; 5 counties in Mississippi

NWS New Orleans, LA issued this dense fog advisory at Dec 17, 2021, 7:00 PM CST for 15 parishes in Louisiana; 5 counties in Mississippi. It took effect at Dec 17, 2021, 9:00 PM CST. It was in force for 13 hr.

The area

The counties it named.

The facts

Issued: Dec 17, 2021, 7:00 PM CST (01:00 UTC)
In effect from: Dec 17, 2021, 9:00 PM CST
Expired: Dec 18, 2021, 10:00 AM CST
In force: 13 hr
Issued by: NWS New Orleans, LA

Counties Assumption Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Iberville Parish, LA, Orleans Parish, LA, Pointe Coupee Parish, LA, Saint Bernard Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Amite County, MS, Pearl River County, MS, Pike County, MS, Walthall County, MS, Wilkinson County, MS

The nearest sounding before it

Jackson, MS (KJAN), launched 00:00Z, 1.0 hours before the alert went out and 200 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 251 J/kg
Mixed-layer CIN: -14 J/kg
Mixed-layer LCL: 722 m above ground
0-6 km bulk shear: 26 kt
0-1 km storm-relative helicity: 82 m²/s²
0-3 km storm-relative helicity: 95 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.4

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this dense fog advisory went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS New Orleans, LA wrote its last area forecast discussion before this dense fog advisory went out at Dec 17, 5:10 PM CST, 1 hour 50 minutes earlier.

Area forecast discussion, Dec 17, 5:10 PM CST, 1 hour 50 minutes before

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

The office that day

Everything else NWS New Orleans, LA issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 17, 6:59 PM CST	Marine Dense Fog Advisory	LIX		15 hr
Dec 18, 2:35 PM CST	Small Craft Advisory	LIX		3 days
Dec 18, 4:49 PM CST	Special Weather Statement	LIX	Iberville	56 min
Dec 18, 5:19 PM CST	Special Weather Statement	LIX	Ascension, Livingston	56 min
Dec 18, 5:54 PM CST	Special Marine Warning	LIX		66 min
Dec 18, 4:06 PM CST	Special Weather Statement	LIX	Pearl River	39 min

Nearby

Dense Fog Advisories in Louisiana, 2021 Dense Fog Advisories in Mississippi, 2021 Every dense fog advisory in 2021

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive.