Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 290838
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
338 AM CDT SAT AUG 29 2015

.SHORT TERM /TODAY/...
ISSUED AT 338 AM CDT SAT AUG 29 2015

MAIN CONCERNS TODAY WILL BE CLOUDS...FOG AND TEMP TRENDS. MID
LEVEL TROUGH IS CURRENTLY MOVING THROUGH SERN FORECAST AREA WITH
ASSOCIATED LIFT INTO MO AND IL LEADING TO A DRY FORECAST. 08Z
SURFACE ANALYSIS PLACES SURFACE LOW JUST NE OF DES MOINES WITH
ASSOCIATED FRONTAL BOUNDARIES FROM NW OF LAMONI...THROUGH DES
MOINES...TO JUST SE OF WATERLOO. VISIBILITIES HAVE DROPPED ALONG
AND NW OF THIS LINE WITH AREAS OF FOG...SO THIS MENTION WILL BE
KEPT THROUGH 13Z AND SAGGING JUST A BIT MORE SOUTH AND EAST WITH
THE FRONT.

HIGHER RES RAP/HRRR/NMM/ARW RUNS SEEM TO BE HANDLING STRATUS WELL
AND SUGGEST GRADUALLY SOUTH AND EAST MOVEMENT TO THE BACK EDGE
THROUGH THE DAY. CLEARING LIKELY WILL NOT REACH SERN SECTIONS
HOWEVER SO HAVE UNDERCUT EVEN THE COOLEST GUIDANCE THERE...TOWARD
OTTUMWA FOR INSTANCE. THIS MAY RESULT IN FAIRLY HOMOGENEOUS HIGHS.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 338 AM CDT SAT AUG 29 2015

MOST OF THE LONG TERM FORECAST PERIOD WILL BE CHARACTERIZED BY A
MID/UPPER LEVEL BLOCKING PATTERN WITH A LARGE HIGH PRESSURE RIDGE
EXTENDING FROM THE FOUR CORNERS REGION NORTHEASTWARD ACROSS THE
MIDWESTERN STATES...WHILE A PERSISTENT LONGWAVE TROUGH PERSISTS
FROM BRITISH COLUMBIA DOWN THE PACIFIC U.S. COAST. THIS WILL
GENERALLY RESULT IN WARM...DRY...AND MOSTLY CLEAR WEATHER ACROSS
OUR FORECAST AREA FOR THE MAJORITY OF THE WEEK. HAVE THUS
MAINTAINED A WARMING TREND INTO MONDAY FOLLOWED BY HIGHS IN THE
MID TO UPPER 80S THROUGH THE END OF THE FORECAST PERIOD.
HOWEVER...WITHIN THIS GENERALLY QUIET FORECAST THERE ARE A FEW
ITEMS OF NOTE AND LOW CHANCES FOR RAINFALL.

FIRST...IT SEEMS LIKELY THAT THERE WILL ONCE AGAIN BE FOG LATE
TONIGHT INTO EARLY SUNDAY. FOG HAS BEEN FAIRLY WIDESPREAD ACROSS
THE AREA THE PREVIOUS TWO NIGHT...AND TONIGHT A SURFACE HIGH
PRESSURE RIDGE WILL DRAPE ACROSS IOWA WITH FORECAST SOUNDINGS
SHOWING A FAIRLY STRONG SURFACE INVERSION DEVELOPING AS ONE WOULD
EXPECT. HAVE INTRODUCED PATCHY FOG AREAWIDE AFTER MIDNIGHT
TONIGHT...BUT IT IS POSSIBLE THAT IT MAY BECOME MORE WIDESPREAD
THAN THAT.

SECOND...THERE IS CONSENSUS THAT A WEAK 500 MB TROUGH WILL CROSS
THE REGION BETWEEN LATE TUESDAY AND WEDNESDAY BRIEFLY SEVERING THE
RIDGE AND SLIGHTLY INTERRUPTING THE WARMING TREND. THE PASSAGE OF
THIS TROUGH MAY PROVIDE SUFFICIENT IMPETUS TO GENERATE A FEW
SHOWERS AND THUNDERSTORMS...MAINLY TUESDAY NIGHT INTO WEDNESDAY
MORNING...AND HAVE MAINTAINED SLIGHT CHANCE POPS TO ACCOUNT FOR
THIS.

FINALLY...BY NEXT WEEKEND THE MID/UPPER PATTERN WILL BEGIN TO
SHIFT SLIGHTLY EASTWARD WITH THE LARGE RIDGE LAYING ACROSS THE
SOUTH CENTRAL U.S. AND THE LONGWAVE TROUGH CENTERING OVER THE
NORTHERN ROCKIES. THIS WOULD PLACE US CLOSER TO THE PERIPHERY OF
THE CYCLONIC FLOW AROUND THE TROUGH...AND RESULTS IN A
REINTRODUCTION OF LOW POPS ACROSS OUR NORTHERN AND WESTERN
COUNTIES BY SATURDAY. IT WILL BE A WHILE YET BEFORE THE RIDGE
FULLY BREAKS DOWN HOWEVER...AND NO SIGNIFICANT COOLING OR
WIDESPREAD RAINFALL CHANCES ARE SEEN AT LEAST THROUGH NEXT
WEEKEND.

&&

.AVIATION...29/06Z
ISSUED AT 1139 PM CDT FRI AUG 28 2015

SFC LOW STILL HAS SHIFTED TO SCEN IA AND WILL CONTINUE TO SHIFT EAST
THROUGH 12Z. LIGHT PRECIP WILL CONTINUE OVER THE FAR EASTERN TAF
LOCATIONS FOR A COUPLE MORE HOURS. MAIN CONCERN OVER IS IFR/LIFR
CIGS AND FOG POTENTIAL WITH HALF MILE VSBYS AND LOCALLY A QUARTER
OR LESS VSBY POSSIBLE. LOW CLOUDS AND FOG WILL SLOWLY BURN OFF
THROUGH LATE MORNING. A COUPLE MODELS HINT AT THE COLD FRONT
DEVELOPING STORMS DURING PEAK HEATING MAINLY AFFECTING KOTM BUT
CONFIDENCE IN THIS OCCURRING AT THIS POINT IS LOW.

&&

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

&&

$$

SHORT TERM...SMALL
LONG TERM...LEE
AVIATION...FAB


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