Severe Thunderstorm Warning 156, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
319 AM CDT THU JUL 23 2009

.SHORT TERM.../TODAY/
S/WV IS CURRENTLY DROPPING SEWD ACRS THE CWA ANDC SONT TO SENT OFF A
FEW TSRA.  MAIN AREA HAS SHIFTED S OF I-80 NOW AND WILL CARRY ISOLD
POPS OVR THE SRN THIRD THIS MRNG AND KEPT A SMALL POP OVR THE FAR
SERN ZNS THIS AFTN.  FEELING IS THAT WELL AVOID A REPEAT OF TSRA
DVLPMT THAT WEVE SEEN THE PAST COUPLE DAYS SINCE THE AMS IS BCMG A
BIT DRIER AND ALSO RDGG ALF IS SLATED TO MOV INTO THE STATE DURG THE
DAY.  RISING HGTS AND H7 TEMPS ARE NOT ALL THAT CONDUCIVE FOR
DVLPMT.  WENT FOR TEMPS SIM TO THOSE OF YDA.

.LONG TERM.../TONIGHT THROUGH WEDNESDAY/
PRIMARY FORECAST ISSUE REMAINS THE LARGE CYCLONE BARRELING SOUTHEAST
FROM SOUTHERN CANADA INTO THE GREAT LAKES REGION FRIDAY AND
SATURDAY. FORECAST THINKING HAS CHANGED VERY LITTLE OVER THE LAST
COUPLE OF DAYS...WITH PROGNOSTIC MODELS STEADILY COMING INTO BETTER
AGREEMENT REGARDING THE DETAILS OF TIMING AND SO FORTH. SURFACE HIGH
WILL MOVE OFF TO THE SOUTHEAST TONIGHT WITH LIGHT SOUTHERLY BREEZES
KICKING IN BY FRIDAY MORNING. COLD FRONT WILL ENTER OUR NORTHERN
COUNTIES FRIDAY AFTERNOON AND MOVE QUICKLY ACROSS OUR AREA THROUGH
THE EVENING. AHEAD OF THE FRONT WINDS WILL VEER TO SOUTH SOUTHWEST
AND SOUTHWEST...ENHANCING WARM AIR ADVECTION. WITH THE FRONT NOT
ENTERING THE MAJORITY OF THE STATE UNTIL AFTER PEAK HEATING HAVE
CONTINUED UPWARD TREND IN MAX TEMP FORECAST FOR FRIDAY...WITH LOWER
90S ACROSS OUR SOUTHWEST NOW. IF SURFACE FLOW IS STRONGER THAN
FORECAST AND/OR CLOUD COVER IS LESS...TEMPS WILL LIKELY HAVE TO COME
UP EVEN MORE AS WE COULD CERTAINLY HIT LOWER 90S IN THE DES MOINES
METRO.

AS THE FRONT PROGRESSES ACROSS OUR AREA FRIDAY AFTERNOON AND EVENING
THE THREAT FOR THUNDERSTORMS WILL INCREASE. AHEAD OF THE FRONT A
GOOD AMOUNT OF LIFT WILL BE MITIGATED BY CAPPING AND LACK OF A FOCUS
MECHANISM...SO AM NOT OVERLY OPTIMISTIC ABOUT POPS MUCH AHEAD OF THE
FRONT. SURFACE CONVERGENCE ALONG THE BOUNDARY WILL BE THE PRIMARY
FOCUS FOR THUNDERSTORM DEVELOPMENT...ESPECIALLY ACROSS THE
NORTHEASTERN HALF OF OUR AREA WHERE DYNAMICS WILL BE MORE FAVORABLE
CLOSER TO THE MID/UPPER LOW. THERE SHOULD BE A GOOD AMOUNT OF
CONDITIONAL INSTABILITY BENEATH THE CAP IN THE AFTERNOON...SO ONCE
STORMS BREAK THROUGH ALONG THE FRONT CONDITIONS MAY BE FAVORABLE FOR
SEVERE WEATHER. SPC HAS PLACED US IN A SLIGHT RISK WHICH SEEMS
APPROPRIATE. FOR NOW HAVE HELD OFF ON INTRODUCING LIKELY POPS FOR
FRIDAY/FRIDAY NIGHT ONLY BECAUSE OF ISSUES REGARDING TIMING OF THE
FRONT/CONVECTION CROSSING THE 00Z THRESHOLD...BUT HAVE INCREASED TO
AROUND 50 POP ACROSS MUCH OF OUR NORTHEAST AND EAST.

BEHIND THE FRONT FROM FRIDAY NIGHT THROUGH AT LEAST SATURDAY NIGHT
WE WILL REMAIN IN NORTHWESTERLY FLOW IN A COLD AIR ADVECTION
REGIME...WITH STRATUS/STRATOCUMULUS CLOUDS BLANKETING AT LEAST
NORTHEASTERN IOWA AND POSSIBLY FURTHER SOUTHWEST INTO OUR AREA. THIS
DEPENDS ON PRECISELY WHERE THE LARGE CYCLONE SETTLES AND IF/WHEN ANY
SUBTLE REINFORCING SHORTWAVES ADVECT AROUND IT ACROSS OUR AREA. IN
ANY EVENT SIGNIFICANTLY COOLER TEMPERATURES ARE ON TAP FOR THE
WEEKEND...ALTHOUGH RAIN CHANCES ARE VERY LOW WITH JUST A FEW LIGHT
SHOWERS POSSIBLE IN THE NORTHEAST. FURTHER OUT IN THE EXTENDED
PERIODS...LONG RANGE MODELS CONTINUE TO TRY TO BRING A WAVE INTO THE
REGION ON MONDAY. GIVEN HIGH DEGREE OF UNCERTAINTY IN THIS
PATTERN...HAVE LEFT THE FORECAST BASICALLY UNCHANGED FOR MONDAY.

&&

.AVIATION...23/06Z
STILL DEALING WITH CONVECTION PERCOLATING FROM NW IA INTO CENTRAL
IA. SEEMS TO BE OCCURRING IN AREA OF WEAK TO MODERATE ELEAVTED
INSTABILITY...WEAK SURFACE CONVERGENCE AND LIFT FROM SHORTWAVE ALOFT
MOVING TOWARD THE REGION. ALL OF THESE FEATURE REMAIN IN PLAY FOR
SEVERAL MORE HOURS...SO WILL CARRY VCSH AND CB AT KFOD AND KDSM.
LATER TONIGHT...MVFR FOG IS A POSSIBILITY AND GENERALLY FOLLOWED
MODEL GUIDANCE FOR SITES WITH THE GREATEST PROBABILITY. AFT ANY FOG
BURNS OFF BY 14-15Z...VFR AND LIGHT WIND CONDITIONS EXPECTED THRU
THE END OF THE FORECAST.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

SHORT TERM...MS JUL 09
LONG TERM...LEE
AVIATION...MOYER

<!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>

<!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>