Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 122030
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
330 PM CDT SAT JUL 12 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 326 PM CDT SAT JUL 12 2014

MAIN CHALLENGE THIS PERIOD WILL BE EXTENT OF CONVECTION AND SEVERE
THREAT. MOST OF THE SYNOPTIC SCALE MODELS CONTINUE TO INDICATE
CONVERGENCE AND INSTABILITY SHOULD BE SUFFICIENT TO INITIATE
CONVECTION BETWEEN 3 TO 5 PM OVER CENTRAL IOWA BETWEEN US 20 AND US
30 THIS AFTERNOON...THEN SWINGING ACTIVITY OVER THE REMAINDER OF
THE  AREA BETWEEN 5 PM AND 3 AM. SOME OF THE MESO MODELS AT ODDS
WITH MORE FOCUS ON BANDING SHOWERS/ISO THUNDER NORTH OF US 20 AND
SOME ADDITIONAL DEVELOPMENT OVER THE FAR SOUTH... ESPECIALLY
NEARER 06Z ALONG THE IA/MO BORDER WHEN LOW LEVEL JET INCREASES
ACROSS EXITING BOUNDARY. CURRENT MESO ANALYSIS SHOWS THE SOUTH
HALF NEARLY UNCAPPED WITH 3000 TO 3500 J/KG SBCAPE AND INCREASING
SFC CONVERGENCE ALONG BOUNDARY DRIFTING SOUTH AND CURRENTLY
LOCATED FROM EAST OF MASON CITY SOUTHWEST TO ABOUT OMAHA. H700
TEMPS SUGGEST WEAK CAP OF 10C AT THAT LEVEL FOR NOW...BUT EXPECT
THAT TO WEAKEN YET BY LATE AFTERNOON. EFFECTIVE BULK SHEAR
SUFFICIENT FOR SUPERCELL DEVELOPMENT. SOUNDINGS ACROSS THE SOUTH
SHOW SOME DRYING AROUND H700 SO EXPECT THAT WIND WILL REMAIN THE
GREATER THREAT THIS AFTERNOON/EVENING ALONG WITH AN ISOLATED
TORNADO. 0-3KM CAPE ALREADY NEAR 125 J/KG WITH LCL HTS NEAR 1000
TO 1250 M OVER THE SOUTH AS WELL. WITH WARM CLOUD DEPTHS
APPROACHING 15 KFT AND PRECIPITABLE WATER QUITE HIGH AT 2 TO 2.25
INCHES AVAILABLE THROUGH THE EVENING SOUTH HALF THERE WILL BE A
POTENTIAL FOR A QUICK RAINFALL TOTAL OF +2 INCHES WITH ANY OF THE
STRONGER STORMS. ALONG WITH THAT...A POTENTIAL FOR LOCALIZED WATER
ISSUES AND POSSIBLE FLASH FLOODING REMAINS. CONFIDENCE ON
WIDESPREAD HEAVY RAINFALL COVERAGE REMAINS TOO LOW FOR A FLASH
FLOOD WATCH. WITH RATHER WEAK CONVERGENCE AND THUNDERSTORM
DEVELOPMENT CONDITIONAL ON CAP BREAKING...WILL KEEP THUNDER
CHANCES AT SLIGHT/CHANCE CATEGORY THROUGH MID AFTERNOON SOUTH AND
THEN INCREASE POP THROUGH 23-03Z TIME FRAME. ACROSS THE NORTH
ACTIVITY SHOULD BE NEARING AN END AROUND 00Z-02Z. LOOKING AT ALL
THE DATA...FEEL THE HRRR AND HOP WRF MAY BE TOO PESSIMISTIC WITH
LACK OF THUNDER DEVELOPMENT ACROSS THE WARM SECTOR. LATEST 4 KM
WRF SHOWS INCREASING COVERAGE FROM US 20 SOUTH THIS
AFTERNOON...MATCHING UP BETTER WITH THE SYNOPTIC SCALE SOLUTIONS.
LOWS TONIGHT WILL DROP TO NEAR 60 NORTH AND IN THE UPPER 60S SOUTH
AS COOLER AIR FILTERS INTO THE REGION BY SUNDAY MORNING.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 326 PM CDT SAT JUL 12 2014

MAIN CONCERN REMAINS FOCUSED ON UNSEASONABLY COLD TEMPERATURES TO
FILTER INTO THE STATE MONDAY THROUGH WEDNESDAY...AND THEN MILD
AND DRY CONDITIONS THROUGH THE END OF THE WORK WEEK.

SUNDAY INTO MONDAY...SECONDARY TROUGH/COLD FRONT LOOKS TO PUSH
ACROSS THE STATE ON SUNDAY AND MAY BRING A FEW LIGHT SHOWERS AND
AN ISOLATED THUNDERSTORMS IN THE AFTERNOON WITH SOME MARGINAL
INSTABILITY RECOVERING FROM CONVECTION TONIGHT. SURFACE DEWPOINTS
LOOK TO BE ABOUT 10 DEGREES LESS THAN TODAY BUT ENOUGH MOISTURE
AVAILABLE COMBINED WITH WEAK FORCING WITH BOUNDARY MOVING
THROUGH...SO KEPT SLIGHT POPS GOING IN THE AFTERNOON SUNDAY.
ANOTHER STRONGER COLD FRONT TO BRING THE WELL ANTICIPATED
UNSEASONABLY COOL TEMPERATURES WILL PUSH THROUGH THE STATE DURING
THE DAY MONDAY. GOOD MIXING BEHIND THE FRONT BY THE AFTERNOON AND
TWEAKED UP WINDS SLIGHTLY. LOW CONFIDENCE WITH MENTION THE NON-
DIURNAL TEMP TREND ON MONDAY WITH THE CAA AS SUN ANGLE STILL HIGH
ENOUGH TO WARM TEMPS UP IN THE AFTERNOON.

TUESDAY THROUGH SATURDAY...VERY COLD AIRMASS FOR THIS TIME OF YEAR
TO FILTER INTO THE STATE AS 850MB TEMPS DROP TO +5C TO +6C BY EARLY
TUESDAY MORNING. KEPT MENTION OF NEAR RECORD LOWS FOR TUESDAY
MORNING AS SURFACE RIDGE LOOKS TO BE CENTERED OVER EASTERN IOWA INTO
THE WESTERN GREAT LAKES BY 12Z TUESDAY AND EXPECTING DECENT
RADIATIONAL COOLING TO DEVELOP. SURFACE DEWPOINTS DROP TO AROUND 50F
BY TUESDAY MORNING AND WITH THE RADIATION COOLING EVENT...COULD SEE
SOME SHALLOW FOG DEVELOP IF WINDS DROP OFF ENTIRELY. SOMETHING TO
CONSIDER WITH NEXT FORECAST PACKAGE.

COOL AIRMASS REMAINS IN PLACE THROUGH MUCH OF THE WORK WEEK BEFORE
IT BEGINS MODERATE BACK TO NORMAL TEMPERATURES BY FRIDAY INTO
SATURDAY OF NEXT WEEK. NO SIGNIFICANT SYSTEM TO BRING PRECIPITATION
TO CENTRAL IOWA FROM MID TO LATE WEEK NEXT WEEK.

&&

.AVIATION...12/18Z
ISSUED AT 105 PM CDT SAT JUL 12 2014

FRONTAL BOUNDARY DRIFTING SOUTH THIS AFTERNOON AND EVENING. SHRA
CONTINUE ALONG THE BOUNDARY OVER NORTHERN IOWA WITH GENERALLY
UNSTABLE CONDITIONS DEVELOPING ACROSS THE SOUTH. EXPECTING LINE
OF SHOWERS TO BECOME MORE CONVECTIVE THIS AFTERNOON WITH POTENTIAL
FOR BRIEF PERIOD OF HEAVIER RAINFALL AND MVFR VSBY. TIMING FOR
NORTHERN AREAS BETWEEN 19 AND 00Z...FROM US 20 SOUTH TO HIGHWAY
30...22Z THROUGH 03Z AND SOUTH OF HIGHWAY 30 FROM 23Z THROUGH 06Z.
BEST CHANCES FOR SVR CONVECTION WILL BE FOR KDSM AND KOTM AS MAX
INSTABILITY EXPECTED THERE FROM 21Z THROUGH 03Z. SVR THREAT MOST
LIKELY WIND GUSTS ABOVE 45 TO 50 KTS. HAVE NOT ADDED TO TAFS AT
THIS TIME...DUE TO TIMING/UNCERTAINTY CONSIDERATIONS...BUT WILL
MONITOR/ADD AS NEEDED WHEN TRENDS BECOME MORE EVIDENT. AFT 06Z
MOST AREA WILL BE VFR WITH LIGHT NW WINDS BECOMING 10-15KTS AFT
15Z SUNDAY... ESPECIALLY NORTH HALF. /REV


&&

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

$$

SHORT TERM...REV
LONG TERM...PODRAZIK
AVIATION...REV



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