Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 210447
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1147 PM CDT SUN JUL 20 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 241 PM CDT SUN JUL 20 2014

IT SHOULD BE ANOTHER RELATIVELY QUIET NIGHT ACROSS CENTRAL IOWA
AS WARM ADVECTION CONTINUES OVER MUCH OF THE MIDWEST. GFS DEVELOPS
SOME ISOLATED CONVECTION LATE TONIGHT AS DOES THE EURO TOWARD
DAYBREAK IN THE WEST...ASSOCIATED WITH AN 850MB FRONT AND MOISTURE
PUSH ARRIVING FROM THE WEST. HOWEVER...HEIGHTS WILL BE RISING
DURING THIS TIME WITH WARMER MID LEVEL AIR ALSO SPREADING INTO THE
STATE WHICH SHOULD LIMIT THE ABILITY TO REALIZE THE INCREASING
INSTABILITY IN THE LOWER LEVELS AND HAVE LEFT OUT ANY MENTION.
OTHERWISE...WITH THE INCREASE IN LOW LEVEL MOISTURE AND CONTINUING
SOUTH FLOW...TEMPERATURES WILL GAIN A FEW DEGREES OVER LAST NIGHT
WITH LOWS NEAR 70 IN THE WEST WITH COOLER READINGS IN THE EAST
WHERE SURFACE FLOW AND DEWPOINTS ARE LOWER.

.LONG TERM /MONDAY THROUGH SUNDAY/...
ISSUED AT 241 PM CDT SUN JUL 20 2014

THE LONG TERM FORECAST CONTINUES TO BE MARKED BY VARIABLE WEATHER
PATTERNS WITH SWINGS IN TEMPERATURE AND INTERMITTENT THUNDERSTORM
CHANCES. FROM MONDAY THROUGH MOST OF TUESDAY OUR WEATHER WILL BE
DOMINATED BY THE 500 MB HIGH PRESSURE DOME BUILDING FROM THE
SOUTHERN HIGH PLAINS UP INTO THE MIDWEST AND OVER IOWA. THIS WILL
LEAD TO INCREASINGLY HOT AND HUMID CONDITIONS IN A SOLID WARM
AIR/MOISTURE ADVECTION REGIME. MEANWHILE A MID LEVEL SHORTWAVE
TROUGH WILL MOVE ACROSS THE UPPER MIDWEST LATE MONDAY AND MONDAY
NIGHT...LIKELY GENERATING A SEVERE CLUSTER OF THUNDERSTORMS ACROSS
MINNESOTA AND BRINGING A SURFACE COOL FRONT INTO THE NORTHWESTERN
CORNER OF IOWA BY TUESDAY MORNING. THE AFOREMENTIONED CLUSTER OF
STORMS MONDAY NIGHT SHOULD MOVE TO OUR NORTH ACROSS
MINNESOTA...BUT MAY JUST SCRAPE OUR FAR NORTHERN COUNTIES AFTER
MIDNIGHT. THERE IS ALSO SOME POTENTIAL FOR A FEW STORMS TO DEVELOP
LATE MONDAY NIGHT ACROSS THE REMAINDER OF THE FORECAST AREA WITHIN
THE WARM AIR ADVECTION ZONE AND ALONG THE NOSE OF THE NOCTURNAL
LOW LEVEL JET...HOWEVER A RELATIVE LACK OF FORCING AND WARM
TEMPERATURES ALOFT SHOULD LIMIT THIS POTENTIAL AND HAVE MAINTAINED
JUST SLIGHT CHANCE POPS ON TUESDAY MORNING TO ACCOUNT FOR IT.

OTHERWISE...ONCE THE SUN COMES UP TUESDAY IT SHOULD BE OFF TO THE
RACES ONCE AGAIN FOR TEMPERATURES UNTIL THEY ARE CUT SHORT BY THE
GRADUALLY ADVANCING COOL FRONT FROM NORTHWEST TO SOUTHEAST. THE
TIMING OF FRONTAL PASSAGE WILL BE CRITICAL IN DETERMINING HIGH
TEMPERATURES...BUT IT IS LIKELY THAT MUCH OF OUR AREA WILL REACH
HEAT ADVISORY CRITERIA ON TUESDAY AFTERNOON. WHILE MONDAY WILL NOT
BE QUITE SO HOT...THE CURRENT FORECAST DOES BRING HEAT INDEX
VALUES UP TO RIGHT AROUND OR JUST OVER 105 DEGREES ACROSS SOME OF
OUR WESTERN COUNTIES. GIVEN THE MARGINAL ADVISORY CRITERIA
FORECAST FOR MONDAY BUT AFTER A SPELL OF UNSEASONABLY COOL
WEATHER...FOLLOWED BY WARM TEMPERATURES THROUGH MONDAY NIGHT AND
AN EVEN HOTTER DAY ON TUESDAY...FELT IT PRUDENT TO ISSUE A HEAT
ADVISORY FOR THE ENTIRE FORECAST AREA FROM NOON MONDAY THROUGH
TUESDAY EVENING. THE ENDING TIME WILL LIKELY NEED TO BE REFINED
LATER AS THE HEAT WILL BREAK A BIT SOONER IN THE NORTH WITH THE
FRONT MOVING THROUGH.

THE NEXT FORECAST ISSUE IS THE CONVECTIVE POTENTIAL ASSOCIATED
WITH THE COOL FRONT PASSAGE FROM TUESDAY INTO TUESDAY NIGHT. WHILE
THE TIMING OF THE FRONT IS FAIRLY CONSISTENT AMONG THE VARIOUS
PROGNOSTIC MODELS...THE QPF FIELDS ARE VARYING WILDLY AS A RESULT
OF VERY STRONG INSTABILITY MITIGATED BY AN IMPRESSIVE CAPPING
INVERSION. FORECAST SOUNDINGS INDICATE CAPE VALUES IN THE
NEIGHBORHOOD OF 6000 BY LATE TUESDAY AFTERNOON/EVENING...BUT WITH
AN INVERSION OF ABOUT 1.2 OR 1.3 C WHICH SHOULD BE SUFFICIENT TO
SQUELCH ANY THUNDERSTORM DEVELOPMENT FOR MOST OF THE DAY. IT IS
UNCLEAR AT WHAT POINT THE CAP WILL BREAK...IF AT ALL...AS THE
FRONT MOVES ACROSS OUR AREA. HOWEVER...IT WOULD SEEM MOST LIKELY
FROM AROUND 22Z UNTIL AFTER SUNSET AND ROUGHLY ACROSS THE
SOUTHEAST HALF OF THE CWA SO HAVE CONCENTRATED POPS ACCORDINGLY.
IF STORMS DO DEVELOP THEN GIVEN THE INSTABILITY IN PLACE THERE
WILL CERTAINLY BE SOME POTENTIAL FOR SEVERE WEATHER.

THE COOL FRONT AND ANY ASSOCIATED THUNDERSTORMS WILL CLEAR OUT TO
THE SOUTH ON TUESDAY NIGHT...USHERING IN RELATIVELY COOLER AND
QUIETER WEATHER FOR AT LEAST A COUPLE OF DAYS WITH A SURFACE HIGH
PRESSURE RIDGE SLIDING BY. ANOTHER 500 MB SHORTWAVE IS STILL
PREDICTED TO CROSS THE AREA AND BRING MORE THUNDERSTORM CHANCES
SOMETIME BETWEEN FRIDAY AFTERNOON AND SATURDAY MORNING...THEN FROM
LATE SATURDAY THROUGH SATURDAY NIGHT A HUGE 500 MB LOW PRESSURE
GYRE WILL MOVE ACROSS MINNESOTA AND TOWARD THE GREAT LAKES
BRINGING ANOTHER OUTBREAK OF UNSEASONABLY COOL WEATHER ACROSS IOWA
FROM AROUND SUNDAY INTO EARLY NEXT WEEK.

&&

.AVIATION...21/06Z
ISSUED AT 1147 PM CDT SUN JUL 20 2014

BAND OF VFR STRATUS STILL MOVING A EAST ACROSS NORTH CENTRAL IOWA
THIS EVENING AND WILL MAINLY IMPACT ONLY KMCW. SOME POTENTIAL FOR
VSBY RESTRICTIONS LATE TONIGHT DUE TO FOG WITH MOISTURE ADVECTING
IN. POTENTIAL STILL NOT HIGH ENOUGH TO INCLUDE AT THIS TIME.
BREEZY SOUTHERLY WINDS AND VFR CONDITIONS WILL PREVAIL ON MONDAY.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY FROM NOON MONDAY TO 7 PM CDT TUESDAY FOR ADAIR-
ADAMS-APPANOOSE-AUDUBON-BLACK HAWK-BOONE-BREMER-BUTLER-CALHOUN-
CARROLL-CASS-CERRO GORDO-CLARKE-CRAWFORD-DALLAS-DAVIS-DECATUR-
EMMET-FRANKLIN-GREENE-GRUNDY-GUTHRIE-HAMILTON-HANCOCK-HARDIN-
HUMBOLDT-JASPER-KOSSUTH-LUCAS-MADISON-MAHASKA-MARION-MARSHALL-
MONROE-PALO ALTO-POCAHONTAS-POLK-POWESHIEK-RINGGOLD-SAC-STORY-
TAMA-TAYLOR-UNION-WAPELLO-WARREN-WAYNE-WEBSTER-WINNEBAGO-WORTH-
WRIGHT.

&&

$$

SHORT TERM...COGIL
LONG TERM...LEE
AVIATION...DONAVON


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