Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 200438
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1138 PM CDT TUE AUG 19 2014

.SYNOPSIS...
ISSUED AT 305 PM CDT TUE AUG 19 2014

WEAK HIGH PRESSURE OVER IOWA WILL MOVE EAST AS A WARM FRONT
DEVELOPS TO THE SOUTH AND BEGINS TO LIFT NORTH TONIGHT. THE FRONT
WILL LIFT NORTH OF THE STATE ON WEDNESDAY NIGHT. STRONG S/WV WILL
MOVE UP THE BACK SIDE OF THE UPPER LEVEL RIDGE AND PUSH A COLD
FRONT ACROSS THE STATE THIS WEEKEND.

&&

.SHORT TERM /TONIGHT/...
ISSUED AT 305 PM CDT TUE AUG 19 2014

A SURFACE LOW DEVELOPING OVER NORTHEAST COLORADO WILL SHIFT INTO
NORTHWEST NEBRASKA OVERNIGHT.  AN ASSOCIATED WARM FRONT WILL EXTEND
FROM THE LOW THROUGH EASTERN NEBRASKA AND INTO SOUTHWEST IOWA AND
NORTHERN MISSOURI BY 12Z WEDNESDAY BEFORE SURGING NORTH THROUGH THE
DAY WEDNESDAY.  STRONG THETA-E ADVECTION IS FORECAST TO LIFT ACROSS
CENTRAL IOWA DURING THE OVERNIGHT HOURS...ESPECIALLY AFTER 06Z.
FORCING IS WEAK BUT DOES IMPROVE OVERNIGHT AS A LOW LEVEL JET
FOCUSES INTO SOUTHWEST IOWA.  ALOFT A WEAK SHORTWAVE IS PROGGED TO
MOVE ACROSS EASTERN NEBRASKA/SOUTHWEST IOWA.  THIS SHOULD BE ENOUGH
TO PRODUCE SHOWERS AND THUNDERSTORMS ACROSS SOUTHWEST INTO CENTRAL
IOWA.  STORMS SHOULD MAINLY BE ELEVATED AS LOW LEVEL CONVERGENCE IS
WEAK TO NON EXISTENT.  THERE IS ALSO SOME WEAK SHEAR...PERHAPS
ENOUGH FOR AN ISOLATED STORM TO BRIEFLY PRODUCE SOME MARGINALLY
SEVERE TO SEVERE HAIL. THE HIGH RES AND NAM12 MODELS ARE NOT AS
IMPRESSIVE WITH DEVELOPING STORMS ACROSS THE AREA BUT THE SREF DOES
AS DOES PREVIOUS RUN OF THE HI-RES MODELS.  THE HRRR IN PARTICULAR
IS FAIRLY BULLISH ON BRINING PRECIP INTO THE SW WHILE THE MEMBERS OF
THE HOPWRF ARE A LITTLE MORE RESERVED...AT LEAST THROUGH 09Z.

SOME POTENTIAL FOR FOG ACROSS THE NORTHEAST OVERNIGHT AS REMAINING
CLOUDS ACROSS THE AREA DISSIPATE WITH SUNSET AND SURFACE RIDGING
MOVES OVERHEAD PRODUCING LIGHT WIND.  NOT LOOKING AT DENSE FOG AT
THIS POINT GIVEN THE VERY SHALLOW NATURE OF THE MOISTURE MOVING IN.
GENERALLY WENT WITH PATCHY FOG WORDING HOWEVER ALO/MCW WILL BE EAST
OF THE RIDGE AXIS AND MOISTURE COULD BE ENOUGH FOR A LITTLE MORE
WIDESPREAD FOG SO I MENTION AREAS OF FOG OVER THESE LOCATIONS.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 305 PM CDT TUE AUG 19 2014

A BREAK IN THE CONVECTION IS EXPECTED ON WED AS THE FIRST ROUND OF
THETA-E ADVECTON LIFTS OUT OF THE STATE. A RENEWED THREAT OF
THUNDERSTORMS WILL COME AS THE WARM FRONT LIFTS NORTH AND STRONG
THETA-E ADVECTION TAKES PLACE WED NIGHT. THE H8 SHOWS GOOD SPEED
CONVERGENCE AND THERE IS DIVERGENCE ALOFT...THE FLY IN THE
OINTMENT WILL BE IF THE ATMOSPHERE CAPS OFF OR NOT. AN EML IS IN
PLACE...BUT IT IS NOT ALL THAT STRONG.

WARM AND HUMID WEATHER WILL HOLD INTO THE WEEKEND WITH AFTERNOON
HEAT INDICES IN THE LOW TO MID 90S NORTH...AND 95 TO 105 SOUTH
TUE-THU AFTERNOON. BELOW CRITERIA...BUT WILL MENTION IN THE HWO
WITH ALL THE SCHOOL ACTIVITIES GOING ON.

COOLER WEATHER WILL MOVE IN OVER THE WEEKEND...FIRST DUE TO THE
INCREASED CLOUD COVER...THEN DUE TO THE FRONTAL PASSAGE SAT. COOL
AIR WILL SETTLE IN SLOWLY WITH TEMPS FALLING BELOW NORMAL; FOR MON
AND TUE.

&&

.AVIATION...20/06Z
ISSUED AT 1134 PM CDT TUE AUG 19 2014

BOUNDARY WILL LIFT ACROSS IOWA THROUGH WEDNESDAY...THIS WILL BRING
CHANCES FOR SHRA/TSRA TO SITES...PRIMARILY SOUTHERN SITES
THROUGHOUT THE PERIOD. BEST CHANCES WILL COME BEFORE 12Z...BEFORE
DECREASING. HAVE INCLUDED VC MENTION AT KFOD/KDSM/KOTM. NORTHERN
SITES WILL LIKELY SEE BR/FG NEAR 12Z GIVEN AMPLE LOW LEVEL
MOISTURE. MVFR...IFR OR LOWER CEILINGS AND VISIBILITIES WILL BE
POSSIBLE AT TIMES AT SITES THROUGH 12Z BEFORE IMPROVING QUICKLY
AFTER 12Z. WINDS WILL BECOME SOUTHERLY AND CONDITIONS WILL REMAIN
VFR THROUGH REMAINDER OF PERIOD.

&&

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

&&

$$

SYNOPSIS...MS AUG 14
SHORT TERM...FAB
LONG TERM...MS AUG 14
AVIATION...AWB



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