Areal Flood Warning 2, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
630 AM CDT SAT JUL 11 2015

...UPDATED FOR 11/12Z AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
ISSUED AT 337 AM CDT SAT JUL 11 2015

FORECAST CHALLENGES FOR THE SHORT TERM PERIOD OF THE FORECAST WILL
BE POPS AND THEIR PLACEMENT.

SHRA/TSRA IS BLOSSOMING ACROSS THE SWRN CWA ATTM...IN AN AREA OF
ISENTROPIC LIFT OWING TO WAA ALONG WITH RELATIVELY WEAK LLJ. THIS
CONVECTION STRETCHES WEST-NORTHWESTWARD TO EASTERN NEBRASKA WHERE IT
MEETS AN EASTWARD-MOVING ELEVATED MCS...BEING FORCED BY AN EASTWARD-
ADVANCING SHORTWAVE AS WELL AS FED BY NORTH EXTENT OF LLJ. EXPECT
THE CONVECTION TO CONTINUE DEVELOPING AND EXPANDING TOWARD SUNRISE
AS MOISTURE TRANSPORT AND FORCING PERSIST. ANY RAINFALL WILL BE
LOCALLY HEAVY GIVEN THE RELATIVELY HIGH PWATS OF AROUND 2 INCHES
ALONG WITH WARM CLOUD DEPTHS OF 4 KM OR MORE.

CONVECTION WILL SLIDE EASTWARD DURING THE DAY IN CONJUNCTION WITH
BEST FORCING AND PERSISTING RELATIVELY WEAK LLJ. 700 MB CAP BUILDS
IN FROM THE WEST DURING THE DAY HELPING TO LIMIT THE WESTWARD EXTENT
OF ORGANIZED PCPN. EVEN SO...AIRMASS WILL BE QUITE UNSTABLE
UNDERNEATH THE STRENGTHENING CAP...WITH MUCAPES AS HIGH AS 2500 TO
3000 J/KG BY LATE AFTERNOON. THUS THERE MAY BE SOME POCKETS OF
SHRA/TSRA IN LOCAL WEAKNESSES OF THE CAP...AND HAVE CARRIED SLIGHT
CHANCE POPS ACROSS ALL BUT THE FAR WESTERN CWA FOR THAT REASON.
WOULD NOT EXPECT LARGE COVERAGE OF ANY CONVECTION THAT DEVELOPS
GIVEN THE STRENGTHENING CAP AS WELL AS LACK OF COHERENT FORCING
ASIDE FROM THE SURFACE INSTABILITY. HIGH-RES MODELS SEEM TO SUPPORT
THIS IDEA. ANY STORMS THAT DO MANAGE TO DEVELOP THIS AFTERNOON WILL
BE CAPABLE OF PRODUCING LOCALLY HEAVY RAINFALL...AS WELL AS
LOCALLY STRONG WINDS AND POSSIBLE HAIL.

&&

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 337 AM CDT SAT JUL 11 2015

PRETTY TYPICAL SUMMER PATTERN THROUGH THE PERIOD WITH IA BETWEEN
WESTERLIES AND SRN PLAINS RIDGE. THIS LEAVES MAINLY SUBTLE
CONVECTIVE TRENDS ONE OF THE PRIMARY CONCERNS...WITH THE OTHER BEING
BUILDING HEAT INTO MONDAY. CONFIDENCE IS CERTAINLY NOT HIGH
INITIALLY WITH CAP COMING INTO PLAY AND ANY CONVECTIVE FOCUS
SOMEWHAT NEBULOUS. NAM AND GFS BOTH BUILD STRONG INSTABILITY INTO IA
WITH 4000 PLUS J/KG MLCAPES.  ASSOCIATED MLCINHS ARE ONLY
SUFFICIENTLY REDUCED IN SMALL POCKETS HOWEVER...SO WITH WEAK LOW
LEVEL CONVERGENCE DO NOT EXPECTED ANYTHING WIDESPREAD TO BE ONGOING
IN THE EVENING AT ONSET. HOWEVER MODELS ARE ALL FAIRLY SIMILAR
BRINING CURRENT FAR WRN CO SHORT WAVE...WHICH CONTINUES TO GENERATE
CONVECTION AT THIS HOUR...INTO THE MO VALLEY DURING THE EVENING.
AREAL COVERAGE MAY NOT BE WIDESPREAD...BUT WOULD EXPECT AT LEAST A
FEW SMALL CONVECTIVE CLUSTERS TO BE GENERATED...AND THEN FADE WEST
TO EAST INTO THE NIGHT. DEGREE OF INSTABILITY MAY SUPPORT A FEW PULSE
STORMS...BUT LACK OF DEEP SHEAR SHOULD LIMIT POTENTIAL.

HEAT CONCERN WILL THEN INCREASE SUN INTO MON. LOOKING AT FORECAST
SOUNDINGS...THE GFS SEEMS OVERLY MIXED AND DRY BASED ON RECENT ECMWF
RUNS. NAM THERMAL PROFILE MAY BE MORE REALISTIC...BUT LIKELY A
TAD OVERDONE ON BOUNDARY LAYER MOISTURE/DEWPOINTS. SUBJECTIVE
MODIFICATION AND BLEND OF THOSE SOUNDINGS SUPPORTS HIGHS NEAR NAM/GFS
MOS CONSENSUS SUN...AND AT OR JUST BELOW THE WARMER GFS MOS
VALUES MON. RAW GFS BUFR SOUNDINGS SUGGEST 100 IN SPOTS MON...BUT
THAT SEEMS OVERDONE. HEAT INDICES LOOK TO EXCEED 100F IN MANY
SPOTS SUN...BUT NOT QUITE TO ADVISORY CRITERIA /105F/. THE HEAT
MON WILL BE MORE PROBLEMATIC WITH HEAT INDICES TO 105F OR MORE
SOUTH AND EAST. HEADLINE MAY EVENTUALLY BE NEEDED DEPENDING ON
CONVECTIVE TRENDS.

SUN NIGHT MAY BE ONE OF THE TWO MORE LIKELY PERIODS FOR MCS
DEVELOPMENT WITH SHORT WAVE CROSSING THE NRN PLAINS INTO THE UPPER
MS VALLEY INTO THE NIGHT.  THETA-E ADVECTION SEEMS TO BE MAXIMIZED
INTO NERN IA...ESPECIALLY IN THE GFS...SO HAVE HIGHER END CHANCES
POPS IN THIS AREA.  LOW CONFIDENCE IN PEAK HEATING CONTINUES INTO
MON. INSTABILITY WILL AGAIN BE EXTREME WITH ONLY PATCHY CINH REDUCTIONS.
LARGE SCALE LIFT IS LACKING WITH SUBTLE SUBSIDENCE ON THE BACK
SIDE OF AFOREMENTIONED SHORT WAVE. HOWEVER THE PASSAGE OF A
SURFACE TROUGH DURING THE AFTERNOON AND EVENING MAY BE SUFFICIENT
TO AID INITIATION. FLOW IS WEAK AND CONFIDENCE NOT HIGH...SO
NOTHING MORE THAN LOW END POPS NORTH AND EAST ON THE EDGE OF THE
THERMAL RIDGE. IF ANYTHING DOES FORM SEVERE POTENTIAL WOULD BE
HIGHER HOWEVER WITH INCREASING MID LEVEL WINDS AND RESULTANT DEEP
SHEAR ACCOMPANYING SHORT WAVE. THE HEAVY RAIN POTENTIAL IS
SEASONALLY BUT NOT ANOMALOUSLY HIGH...AND WIDESPREAD MCS
DEVELOPMENT IS NOT ANTICIPATED SO NO FLASH FLOOD HEADLINES FOR
NOW. IA HAS HAD A CHANCE TO DRY OUT RECENTLY AND WE ARE AT OUR
CLIMATOLOGICAL INSOLATION AND CROP DRAWING PEAK WINDOW.

SHOULD SEE A FEW DRY PERIODS INTO TUE WITH TEMPS AND HUMIDITIES BACK
TO LESS EXTREME VALUES. NEXT APPRECIABLE PRECIP WINDOW WILL BE
SOMEWHERE AROUND WED OR THU WITH 00Z ECMWF AND GFS BOTH SHOWING
DECENT SHORT WAVE AND LARGE SCALE FORCING WITH H85/H7 BAROCLINIC
ZONE PUSHING SW-NE THROUGH THE AREA. MODEL CONSENSUS DIMINISHES
INTO FRI BUT FLOW REMAINS ACTIVE ENOUGH THAT LOW END POPS ARE
STILL WARRANTED THROUGH THE END OF THE EXTENDED.

&&

.AVIATION...11/12Z
ISSUED AT 630 AM CDT SAT JUL 11 2015

AREA OF SHRA/TSRA WILL CONTINUE MOVING EAST-NORTHEAST ACROSS THE
STATE...BRINGING MVFR TO BRIEF IFR/LIFR FLIGHT RULES. THE SHRA/TSRA
WILL END FROM WEST TO EAST BY MIDDAY TODAY...WITH RESIDUAL SLIGHT
CHANCES OF SHRA/TSRA THIS AFTERNOON AS WELL AS LATER THIS EVENING.
CONFIDENCE WAS NOT HIGH ENOUGH TO INCLUDE PREVAILING THUNDER LATER
THIS EVENING...ONLY INCLUDED VCTS AT THE TERMINALS. BETTER CHANCES
OF TSRA WILL INCREASE TOWARD THE EAST. OTHERWISE MVFR FLIGHT RULES
EXPECTED DUE TO CIGS THRU THIS EVE.

&&

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

&&

SHORT TERM...ZOGG
LONG TERM...SMALL
AVIATION...ZOGG

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
452 AM CDT SAT JUL 11 2015

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-121100-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN-
WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-CARROLL-GREENE-
BOONE-STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-
POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-
CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-
APPANOOSE-DAVIS-
452 AM CDT SAT JUL 11 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS ARE POSSIBLE TODAY AND
TONIGHT...ESPECIALLY DURING THE MORNING HOURS. A FEW MAY BE STRONG
TO SEVERE LATER IN THE DAY WITH LARGE HAIL...DAMAGING WIND...AND
LOCALLY HEAVY RAINFALL.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

HOT AND HUMID WEATHER WILL RETURN SUNDAY AND MONDAY. HEAT INDICES
WILL REACH 100 OR JUST ABOVE BY SUNDAY AFTERNOON...AND UP TO 105
TO 110 SOUTH AND EAST BY MONDAY.

THUNDERSTORM CHANCES WILL REMAIN IN THE FORECAST OFF AND ON
THROUGH THE NEXT WORK WEEK...ESPECIALLY SUNDAY NIGHT NORTHEAST AND
AREA WIDE LATE WEDNESDAY INTO THURSDAY. A FEW STORMS MAY BE
SEVERE WITH LOCALLY HEAVY RAINS...WITH THE GREATEST SEVERE WEATHER
POTENTIAL SUNDAY NIGHT OVER NORTHEAST AND EAST CENTRAL IOWA. LARGE
HAIL...DAMAGING WINDS AND A FEW TORNADOES WOULD ALL BE POSSIBLE
DURING THIS PERIOD.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED SUNDAY NIGHT NORTH AND EAST.
OTHERWISE SPOTTER ACTIVATION CHANCES ARE FAIRLY LOW.

SMALL

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