Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 231134
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
634 AM CDT SAT APR 23 2016

.SHORT TERM.../TODAY/
ISSUED AT 330 AM CDT SAT APR 23 2016

CONCERNS EARLY TODAY RANGE FROM FOG TO STRATUS OVER THE EAST AND
HIGH TEMPERATURES THIS AFTERNOON. LINGERING HIGH PRESSURE TO THE
EAST AND EARLIER LAYER OF CLOUDS ALOFT HAVE LEFT SOME RESIDUAL
MOISTURE ACROSS THE REGION...AT THE SFC DEW POINTS LINGERING IN
THE 40S WITH MINS DROPPING TO SAME HAS CREATED AREAS FOG OVER THE
IOWA AND CEDAR RIVER VALLEYS...BACK TOWARD I-35 EARLY TODAY. WILL
GO WITH A DENSE FOG ADVISORY OVER THE SOUTHEAST AND EAST.
SOUTHEAST WINDS MAY INCREASE TOWARD DAWN CENTRAL AND WEST WHILE
WINDS REMAIN LIGHT SE OVER THE EAST. STRATUS IS ALSO DEVELOPING
EAST BUT WILL LIFT OVER AS WINDS AND MIXING INCREASE THIS
AFTERNOON. H850 TEMPERATURES WILL WARM TO AROUND 14C WEST BY 00Z
WITH 9-10C EAST. THIS WILL EASILY SUPPORT A RATHER WARM AFTERNOON
WITH BREEZY CONDITIONS DEVELOPING AS WELL. HIGHS WILL WARM INTO
THE MID TO UPPER 70S OVER THE WEST HALF WHILE THE EAST WILL REACH
THE LOWER 70S BY AFTERNOON. IF CU REMAIN... MAINLY SCT FOR THE
AFTERNOON HOURS WITH MOSTLY SUNNY SKIES. DEW POINTS WILL BE ON THE
INCREASE THROUGH EVENING IN RESPONSE TO INCREASING SOUTHEAST FLOW.
OVERALL QUIET TODAY BUT CHANCES FOR MORE SIGNIFICANT WEATHER
RAMPING UP FOR SUNDAY AND NEXT WEEK AS WELL. EXTENDED DISCUSSION
WILL COVER THOSE CONCERNS.

.LONG TERM.../TONIGHT THROUGH FRIDAY/
ISSUED AT 330 AM CDT SAT APR 23 2016

THE LONG TERM PERIOD WILL BE ACTIVE...WITH THREE OPPORTUNITIES FOR
SEVERE WEATHER. TEMPERATURES WILL BEGIN THE PERIOD ABOVE
NORMAL...COOLING TO NEAR TO BELOW NORMAL BY THE MIDDLE OF THE WEEK
AND THEN RECOVERING BY THE END OF THE PERIOD.

TONIGHT...THE CWA WILL BE IN A WAA REGIME. THE CLOSED UPPER-LEVEL
LOW/PV ANOMALY WILL MIGRATE EASTWARD RAPIDLY TOWARD THE MID-MISSOURI
RIVER VALLEY...WITH COMBINATION OF BEST DYNAMIC AND THERMODYNAMIC
FORCING JUST WEST OF THE CWA FROM CENTRAL KS INTO EASTERN NE. CANNOT
RULE OUT SHRA/TSRA ESPECIALLY ACROSS THE NORTHWEST HALF OF THE
CWA DURING THIS TIME.

ON SUNDAY...CWA CONTINUES IN THE WAA REGIME AS THE UPPER LOW
CONTINUES SLIDING EASTWARD. SURFACE LOW WEAKENS SLIGHTLY DURING
THIS TIME...AND WILL RIDE ALONG A QUASI-STATIONARY BOUNDARY
EXTENDING FROM EAST-CENTRAL SD EASTWARD INTO CENTRAL/SOUTHERN WI.
DRYLINE WILL MIGRATE EASTWARD FROM EASTERN NEBRASKA INTO IOWA
DURING THE AFTERNOON AND EVENING HOURS. SEVERE WEATHER STILL LOOKS
POSSIBLE ESPECIALLY WEST OF LINE FROM LAMONI TO MASON CITY.
EFFECTIVE BULK SHEAR WILL BE SUFFICIENT FOR ROTATING UPDRAFTS AND
EVEN SOME SUPERCELLS. THERE WILL BE A BRIEF PERIOD WHERE ALL
SEVERE MODES WILL BE POSSIBLE...DUE TO JUXTAPOSITION OF FAVORABLE
INSTABILITY...LOW-LEVEL SHEAR AND LCLS...MAINLY WEST OF A LINE
FROM CRESTON TO ALGONA. AFTER THIS BRIEF PERIOD ENDS...LARGE HAIL
AND DAMAGING WINDS WILL CONTINUE TO BE POSSIBLE. EXPECT ANY
DISCRETE STORMS TO GROW UPSCALE INTO A LINE THAT WILL PROGRESS
EASTWARD DURING THE EVENING...BUT THE SEVERE WEATHER THREAT WILL
DIMINISH.

DRY SLOT MOVES THROUGH THE CWA LATER SUNDAY NIGHT INTO MONDAY...WITH
POTENTIAL FOR LINGERING PRECIP FROM NORTHERN INTO EASTERN PORTIONS
OF THE STATE. THE AFOREMENTIONED QUASI-STATIONARY BOUNDARY WILL PUSH
SOUTH AS A COLD FRONT...AS THE UPPER-LEVEL LOW AND SURFACE LOW
DEPART THE REGION. THE COLD FRONT WILL SWEEP THROUGH THE CWA DURING
THE DAY ON MONDAY...WITH TEMPERATURES FALLING NOTICEABLY DURING THE
AFTERNOON.

ATTENTION THEN TURNS TO TUESDAY NIGHT AND WEDNESDAY...AS ANOTHER
APPROACH TROF/PV ANOMALY FROM OUR WEST RESULTS IN A WAA REGIME.
SURFACE LOW REFLECTION WILL LIFT ENE ACROSS IOWA AND WEAKEN SLIGHTLY
WITH TIME. THETA-E ADVECTION LATE TUESDAY NIGHT INTO WEDNESDAY WILL
BRING RENEWED CHANCES OF ELEVATED SHRA/TSRA. ONE QUESTION ON
WEDNESDAY IS HOW FAR NORTH THE WARM FRONT WILL RETURN. MODELS
SUGGEST THAT IT WILL AT LEAST PUSH INTO SOUTHWEST AND SOUTHERN IOWA.
LOW-LEVEL MOISTURE AND INSTABILITY WOULD BE SUFFICIENT FOR
SURFACE-BASED STORMS. SEVERE WEATHER WILL AGAIN BE POSSIBLE...THIS
TIME IN MORE OF A LOW-CAPE / HIGH SHEAR ENVIRONMENT...WITH ALL
MODES OF SEVERE WEATHER POSSIBLE. MODELS DO SHOW TIMING
DIFFERENCES... HOWEVER...WHICH WOULD HAVE POTENTIAL SIGNIFICANT
IMPACTS ON POTENTIAL FOR SEVERE WEATHER.

A THIRD TROF AND PV ANOMALY THEN APPROACH THE CWA FROM THE WESTERN
U.S. LATE IN THE LONG TERM PERIOD. THETA-E ADVECTION WITHIN THE WAA
REGIME WILL BRING CHANCES OF SHRA/TSRA BEGINNING DURING THE DAY ON
FRIDAY. SURFACE LOW LIFTS NORTHEAST ACROSS NEBRASKA INTO SATURDAY
WITH A WARM FRONT TRYING TO LIFT NORTHEAST INTO IOWA AGAIN. ONCE
AGAIN...HOW FAR NORTH THIS BOUNDARY MAKES IT WILL HAVE A BEARING ON
SEVERE WEATHER POTENTIAL. PRESENT SOLUTIONS SUGGEST IT WILL PUSH
INTO FAR SOUTHERN IOWA. INSTABILITY...SHEAR AND LCL PARAMETERS
SUGGEST ALL MODES OF SEVERE WEATHER WOULD AGAIN BE POSSIBLE ON
SATURDAY.

&&

.AVIATION.../FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING/
ISSUED AT 631 AM CDT SAT APR 23 2016

IFR/LIFR FOG REMAIN WITH AREA OF MVFR STRATUS REPLACING THE DENSE
FOG THE MAIN CONCERN THIS PACKAGE...WIND A BIT LATER TODAY.
OVERNIGHT WIDESPREAD SHALLOW FOG CONTINUES UNTIL 15Z WITH VSBY
IMPROVING SLOWLY ALL SITES AS ST DECK ADVECTS NORTH AND SUNSHINE
WARMS LAYER. SE WINDS INCREASE AFT 18Z WEST TO EAST WITH GRADUAL
VFR CONDITIONS RETURNING ALL AREAS AFT 19-20Z. AFT 00Z MID TO HIGH
CLOUDS RETURN WITH SUSTAINED SOUTH 11-14KT WIND THRU END OF
PERIOD. /REV

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY UNTIL 7 AM CDT THIS MORNING FOR APPANOOSE-
BLACK HAWK-BREMER-BUTLER-CERRO GORDO-DAVIS-FRANKLIN-GRUNDY-
HAMILTON-HANCOCK-HARDIN-JASPER-LUCAS-MAHASKA-MARION-MARSHALL-
MONROE-POLK-POWESHIEK-STORY-TAMA-WAPELLO-WARREN-WAYNE-WINNEBAGO-
WRIGHT.

&&

$$

SHORT TERM...REV
LONG TERM...ZOGG
AVIATION...REV



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