Area Forecast Discussion
Issued by NWS Des Moines, IA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KDMX 191749
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1247 AM CDT TUE AUG 19 2014

.SHORT TERM /TODAY/...
ISSUED AT 415 AM CDT TUE AUG 19 2014

ALTHOUGH ISOLATED LINGERING CONVECTION MAY JUST BRUSH SWRN SECTIONS
THROUGH SUNRISE THE PRIMARY CONCERN THROUGH THE DAY WILL END UP
BEING TEMPS. IA SHOULD BE BETWEEN INFLUENCES OF WRN GREAT LAKES
SHORT WAVE AND MINOR TRAIN OF WEAK WAVES ASSOCIATED WITH SUBTLE JET
SEGMENT TOPPING THE ROCKIES RIDGE. THIS WILL RESULT IN BROAD
SYNOPTIC SCALE SUBSIDENCE WITH SOMEWHAT LOWER HUMIDITY AND
INSTABILITY.  RECENT NAM RUNS SUGGEST CAPPED ENVIRONMENT SW...AND
WHILE THE CINH ERODES NE WITH MLCAPES REBOUNDING TO AROUND 2000
J/KG...SURFACE WINDS SHOULD BE FAIRLY WEAK WITH LITTLE CONVERGENCE
SO HAVE KEPT FORECAST DRY.  CONVECTION ALLOWING HI RES MODELS DO NOT
DEPICT ANY PRECIP AND SUPPORT THIS THINKING AS WELL.

BIGGEST UNCERTAINTY WILL BE TEMPS WITH FORECAST SOUNDINGS DIFFERING
WITH RESPECT TO THE DEGREE OF MIXING AND LOWEST 2KM TEMPS. NAM AND
RAP ARE ON THE WARM SIDE OF THINGS...AND MAY BE OVERDONE
SOMEWHAT...BUT TYPICALLY HANDLE THESE SITUATIONS BETTER AND WILL
LEAN IN THAT DIRECTION WHICH IS AT OR JUST ABOVE THE WARM SIDE OF
MOS.

.LONG TERM /TONIGHT THROUGH MONDAY/...
ISSUED AT 415 AM CDT TUE AUG 19 2014

MOISTURE PLUME SURGING RAPIDLY NORTH FROM THE GULF OF MEXICO WILL
ARRIVE OVER SOUTHWEST IOWA AFTER 06Z TONIGHT AND WILL BRING
INCREASING CHANCES FOR THUNDERSTORMS. THE PRIMARY CONVERGENCE ZONE
ASSOCIATED WITH THE LOW LEVEL JET WILL BE WEST OF THE STATE IN
NEBRASKA HOWEVER THE THERMODYNAMIC FORCING ASSOCIATED WITH THE
THETA-E ADVECTION SHOULD BE ENOUGH FOR CONVECTIVE DEVELOPMENT. THE
THETA-E ADVECTION WILL CONTINUE TO LIFT THROUGH IOWA ON WEDNESDAY
WHILE SFC LOW PRESSURE CONTINUES TO DEEPEN TO THE WEST. WHILE THE
LOW LEVEL JET DOES WEAKEN A BIT...IT DOES MAINTAIN THROUGH THE DAY
AS A STRONG MID LEVEL SHORT WAVE LIFTS THROUGH THE SOUTHWEST FLOW
AND INTO THE WESTERN DAKOTAS. THIS IS IN ADDITION TO THE
INCREASING INSTABILITY AND STEEPENING MID LEVEL LAPS RATES.
POSSIBLE THUNDERSTORMS WILL FESTER THROUGH CENTRAL IOWA AS THE
WARM ADVECTION LIFTS NORTH THROUGH THE STATE AND HAVE A PROLONGED
PERIOD OF CLOUDS. THE CAP WILL DEVELOP WITH THE ARRIVAL OF THE
ELEVATED MIXED LAYER THEN IT WILL BE HOT AND HUMID THE REMAINDER
OF THE DAY CENTRAL AND SOUTH. AREAS OF FOG...SOME POSSIBLY LOCALLY
DENSE IS EXPECTED TO DEVELOP NORTH OF THE CONVECTIVE ACTIVITY
WHERE CLEAR SKIES...LIGHT WINDS AND A MOIST BOUNDARY LAYER WILL BE
IN PLACE.

ANOTHER ROUND OF THUNDERSTORMS IS LIKELY OVER NORTHERN IOWA
WEDNESDAY NIGHT AS THE LOW LEVEL JET VEERS INTO THE STATE. SOME
UNCERTAINTY AS TO HOW FAR NORTH THE SYSTEM AND FOCUS FOR
THUNDERSTORMS WILL BE BUT THE GREATEST POTENTIAL WILL BE NEAR THE
MINNESOTA BORDER TO NEAR HIGHWAY 20. THURSDAY IS EXPECTED TO BE
MOSTLY DRY...HOT AND HUMID WITH HIGHS IN THE UPPER 80S TO LOWER
90S AND HEAT INDEX VALUES APPROACHING 100. FRIDAY SHOULD BE MOSTLY
DRY AND HAVE FAVORED THE DRIER SOLUTIONS. THE GFS IS MORE
CONVECTIVE HOWEVER IT IS PUSHING A STRONG SHORT WAVE RAPIDLY
THROUGH THE FLOW WHILE OTHER GUIDANCE IS HOLDING IT OVER THE
DESERT SOUTHWEST.

THE PRIMARY BOUNDARY ARRIVAL IS EXPECTED LATE IN THE WEEKEND OR
EARLY NEXT WEEK AS THE WESTERN LONG WAVE TROUGH SQUASHES THE SUB
TROPICAL HIGH TO THE SOUTH. GUIDANCE VALUES ARE PUSHING HIGHS
DOWN INTO THE 70S. IT WILL BE DIFFICULT FOR TOO MUCH COOL AIR TO
DROP SOUTH AS THE HIGH DOES NOT SHIFT TO FAR SOUTHEAST RESULTING
IN RETURN SOUTHWEST FLOW DEVELOPING.

&&

.AVIATION...19/18Z
ISSUED AT 1247 PM CDT TUE AUG 19 2014

WARMER AIR WILL MOVE INTO CENTRAL IOWA FROM THE SW...ALONG WITH SOME
MOISTURE AND INSTABILITY AS A WARM FRONT TRIES TO ESTABLISH ITSELF
OVER NEB AND KS THEN LIFT INTO IA LATER THIS EVENING/OVERNIGHT.
SOME SHOWERS/TSRA ARE POSSIBLE MAINLY FM KDSM-KOTM BUT MAY MAKE IT
AS FAR NORTH AS KFOD.  WITH LOW LEVEL MOISTURE INCREASING...COULD
ALSO SEE SOME FOG...ESPECIALLY NORTHEAST AFT 08Z.  MVFR VSBYS
POSSIBLE IN THE FOG.  VFR CONDITIONS SHOULD AGAIN PREVAIL AFTER 13-
15Z.

&&

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

&&

$$

SHORT TERM...SMALL
LONG TERM...DONAVON
AVIATION...FAB



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.