Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 270433
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1130 PM CDT SAT JUL 26 2014

.UPDATE...
ISSUED AT 1130 PM CDT SAT JUL 26 2014

WARM FRONTAL BOUNDARY ACROSS SRN IA/NR MO WILL GET PUSHED SOUTH
OVERNIGHT AS A LARGE LOW PRESSURE SYSTEM ACROSS CANADA MOVES
SOUTHEAST INTO THE GREAT LAKES AREA.  ANY STORM CHANCES WITH THIS
BOUNDARY WILL LIKELY REMAIN SOUTH AND EAST.  I HAVE REMOVED MENTION
OF PRECIP ALONG THIS BOUNDARY.

A COLD FRONT ACROSS MN INTO SE SDKTA WILL SINK INTO NW IA OVER NIGHT
AND CONTINUE TO PUSH ACROSS THE STATE ON SUNDAY.  COOLER AND DRIER
AIR WILL WORK INTO THE STATE AND AS THE AFOREMENTIONED UPPER LOW
SWING IN THE GRADIENT WILL TIGHTEN.  WINDS ACROSS THE FAR N/NE WILL
BEGIN TO INCREASE AFT 09Z WITH THE STRONGEST WINDS DEVELOPING
BETWEEN 12-15Z SUNDAY THROUGH MID TO LATE AFTERNOON.  THERE IS SOME
POTENTIAL FOR AN ISOLATED STORM ALONG THE COLD FRONT...ESPECIALLY
ACROSS THE NORTHEAST BUT CONFIDENCE IS LOW AND ALL THE HIGH RES
SHORT TERM MODELS SEEM TO OVERDO THE PRECIP POTENTIAL EXCEPT FOR ONE
OF THE HOPWRF MEMBERS.  THE NAM12 IS ALSO QUITE DRY.  THERE WILL BE
SOME POTENTIAL FOR PATCHY LIGHT FOG UNTIL THE FRONT PUSHES THROUGH
AND SCOURS EVERYTHING OUT BUT IT WILL BE TOO PATCHY TO PUT IN THE
FORECAST.

&&

.SHORT TERM /TONIGHT THOUGH MONDAY/...
ISSUED AT 223 PM CDT SAT JUL 26 2014

WATER VAPOR IMAGERY WAS SHOWING ADVERTISED UPPER TROUGH OVER THE
NORTHERN PLAINS AND SOUTH CENTRAL CANADA MOVING SOUTHEAST TOWARDS TO
THE GREAT LAKES THIS AFTERNOON.  THUNDERSTORMS OVER EASTERN NEBRASKA
EARLY THIS AFTERNOON WERE MOVING AND DEVELOPING SOUTH INTO
INSTABILITY GRADIENT.  AT THE SURFACE...A STATIONARY FRONT EXTENDED
FROM EASTERN NEBRASKA EAST THROUGH FAR SOUTHERN IOWA AT 18Z.  THE
IMMEDIATE FORECAST CONCERN IS THUNDERSTORMS THIS EVENING AND THEIR
IMPACTS. THE AIRMASS OVER CENTRAL AND NORTH CENTRAL IOWA WAS
RELATIVELY STABLE EARLY THIS AFTERNOON WITH AN AREA OF DRY AIR AT
850 MB COUPLED WITH LIGHT NORTHEAST FLOW CENTERED OVER THE STATE
ACCORDING TO THE SPC MESO PAGE. THE POCKET OF DRY AIR IS
COINCIDENT WITH A SMALL SURFACE HIGH OVER NORTHERN IOWA AT 18Z.
SHORT RANGE MESOSCALE MODELS ALONG WITH 12Z NAM/GFS ALL SUGGEST
VERY LITTLE ACTIVITY THIS EVENING. CONVECTION OVER NEBRASKA SHOULD
CONTINUE TO FEED INTO UNSTABLE AIR OVER SOUTHEAST NEBRASKA AND
NORTHERN MISSOURI LATE THIS AFTERNOON. THE AIRMASS OVER SOUTH
CENTRAL IOWA SHOULD DESTABILIZE ALONG A LOW-LEVEL MOISTURE AXIS
NEAR THE IOWA AND MISSOURI BORDER. AT THIS POINT...THE BEST CHANCE
FOR THUNDERSTORMS APPEARS TO BE SOUTHERN IOWA...CLOSE TO THE
MISSOURI BORDER. MUCH OF CENTRAL AND NORTHERN IOWA WILL LIKELY BE
DRY. AS THE VIGOROUS UPPER TROUGH...FOR LATE JULY...MOVES
SOUTHEAST TONIGHT...THE ASSOCIATED COLD FRONT WILL SWEEP ACROSS
IOWA. THE FRONT WILL CLEAN OUT ALL MESOSCALE BOUNDARIES AND IT
WILL USHER IN COOLER AND DRIER AIR.

MODELS ARE IN GOOD AGREEMENT WITH THE MASS FORECAST FIELDS SUNDAY
AND MONDAY CARVING OUT A DEEP UPPER TROUGH OVER THE EASTERN CONUS.
BIG STORY FOR IOWA WILL BE UNSEASONABLY COOL AIR OVER THE STATE. 850
MB TEMPERATURES ARE FORECAST FROM 8-12 DEGREES C ACCORDING TO THE
12Z GFS WHICH APPEARS REASONABLE.  KEPT MENTION OF SHOWER ACTIVITY
IN THE NORTHEAST SUNDAY AFTERNOON...OTHERWISE IT SHOULD BE DRY AND
UNSEASONABLY COOL SUNDAY AND MONDAY.

.LONG TERM /TUESDAY THROUGH SATURDAY/...
ISSUED AT 223 PM CDT SAT JUL 26 2014

EASTERN CONUS UPPER TROUGH REMAINS IN PLACE THROUGH THE EXTENDED
WITH THE 500 MB UPPER RIDGE CENTERED OVER THE ROCKIES. AT THE
SURFACE...A LARGE SURFACE RIDGE REMAINS IN PLACE THROUGH THE
PERIOD. LATE IN THE FORECAST PERIOD...THE 12Z ECMWF/GFS RETROGRADE THE
UPPER LOW ENOUGH TO SUPPORT A SMALL CHANCE OF SHOWERS.
OTHERWISE...DRY AND CONTINUED BELOW NORMAL TEMPERATURES.

&&

.AVIATION...27/06Z
ISSUED AT 1130 PM CDT SAT JUL 26 2014

LOW CLOUDS WILL REMAIN ACROSS SRN TAF LOCATIONS AFFECTING MAINLY
KOTM SO WILL KEEP OVC040-050 DECK IN FOR SEVERAL HOURS OVERNIGHT.
AN ISOLATED THUNDERSTORM IS POSSIBLE WITH FROPA MAINLY NR KMCW AND
KALO BUT DUE TO UNCERTAINTY AND VERY ISOLD COVERAGE TSRA MENTION WAS
LEFT OUT OF TAFS AT THIS TIME.  A COLD FRONT WILL ENTER NW IA AND
PUSH ACROSS TAF LOCATIONS INTO SUNDAY MORNING AS A LARGE UPPER LOW
MOVES SE INTO THE GREAT LAKES.  GRADIENT WILL TIGHTEN ACROSS
NRN/NERN TAF LOCATIONS AFT09Z AND SPREAD ACROSS THE REST OF THE
FORECAST AREA DURING THE MORNING ON SUNDAY.  SFC WIND WILL BE NRLY
AT 15G30KTS THROUGH 21Z BEFORE DIMINISHING.

&&

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

$$

UPDATE...FAB
SHORT TERM...JOHNSON
LONG TERM...JOHNSON
AVIATION...FAB


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