Heavy Rain in Iowa, December 12 to 14, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
554 AM CST SAT DEC 12 2015

.SHORT TERM /TODAY/...
ISSUED AT 348 AM CST SAT DEC 12 2015

TODAY BEGINS THE TRANSITION TO A VERY WET PERIOD AND COOLING TEMPS.
A SURFACE LOW AND INVERTED TROUGH WILL SHIFT INTO SOUTHERN/SOUTHEAST
IOWA TODAY.  SOUNDINGS SHOW A LOT OF LOW LEVEL MOISTURE ACROSS
SOUTHERN IOWA THIS MORNING GRADUALLY WORKING NORTH THIS AFTERNOON
BUT NOT BECOMING DEEPLY SATURATED UNTIL LATE AFTERNOON AND MORE SO
THIS EVENING.  AS A RESULT I THINK WE WILL SEE THE DENSE FOG
CONTINUE ACROSS THE SOUTH THROUGH MID MORNING BEFORE IMPROVING SOME
BUT NOT REALLY MAKING MUCH NORTHWARD PROGRESS.  WE WILL LIKELY SEE
AT LEAST PATCHY FOG ELSEWHERE ACROSS IOWA AS AT LEAST SOME LOW LEVEL
MOISTURE IS PRESENT ACROSS CENTRAL IOWA.  I HELD OFF AN ANY
APPRECIABLE PRECIPITATION UNTIL MID TO LATE AFTERNOON AS A RESULT OF
THE MORE GRADUAL DEEPENING OF MOISTURE.

BETWEEN 20Z AND 22Z HOWEVER SOUNDINGS ACROSS THE SOUTHERN HALF OF
THE FORECAST AREA MOISTEN QUICKLY AND FORCING BEGINS TO INCREASE. AS
A RESULT...LIGHT RAIN SHOULD DEVELOP ACROSS SOUTHERN IOWA AND SPREAD
NORTH/NORTHEAST ACROSS CENTRAL INTO EASTERN IOWA.  IN ADDITION TO
THE FORCING...A COUPLE HUNDRED JOULES OF CAPE PUSH INTO SOUTHERN
IOWA SO WE CANNOT RULE OUT THUNDER AFTER 23Z.  THERE IS DECENT SHEAR
IN PLACE AS WELL AND WITH AS COLD ALOFT AS IT WILL BE...SOME
POTENTIAL FOR GRAUPEL OR HAIL THOUGH WE ARE NOT LOOKING AT ANYTHING
SEVERE AT THIS POINT.  ONCE THE RAIN  STARTS...IT WILL BE WITH US
THROUGH THE WEEKEND.

AS FOR TEMPS...WE HAVE BEEN STEADILY COOLING EACH DAY AND WITH LOW
CLOUD COVER AND PRECIP DEVELOPING...WE WILL SEE TEMPS SEVERAL
DEGREES TO A CATEGORY COOLER TODAY THAN YESTERDAY.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 348 AM CST SAT DEC 12 2015

POTENT STORM SYSTEM STILL ON TRACK TO IMPACT THE STATE THIS WEEKEND
INTO MONDAY. UPPER LEVEL TROUGH DIGGING INTO THE DESERT SOUTHWEST
CURRENTLY WITH MOISTURE BEING DRAWN IN FROM THE PACIFIC. VERY STRONG
FLOW OFF THE GULF AS WELL WITH H85 WINDS OF 30-60KTS PUSHING
MOISTURE NORTHWARD INTO THE STATE TONIGHT INTO SUNDAY. PWAT VALUES
PUSHING 1 TO 1.5 INCHES FOR TONIGHT INTO SUNDAY...WHICH NEAR THE MAX
VALUES EVER RECORDED FOR THIS TIME OF YEAR. THE AVERAGE PWAT FOR MID
DECEMBER IS AROUND 0.3 INCHES. STRONG LIFT ACROSS THE CWA TONIGHT
INTO SUNDAY...WITH DEEP ISENTROPIC LIFT AND THETA-E ADVECTION.
MODELS ALSO ADVERTISING SOME MUCAPE ACROSS MUCH OF THE CWA BY LATE
TONIGHT...SO ISOLATED POSSIBLY EVEN SCATTERED THUNDER STILL
EXPECTED. WITH THE LIFT...INSTABILITY AND DEEP MOISTURE EXPECT
MAJORITY OF THE QPF TO FALL TONIGHT INTO SUNDAY. TOTAL RAINFALL
AMOUNTS COULD PUSH 1.5 TO 2 INCHES ACROSS MUCH OF THE CWA WITH THE
HEAVIEST AMOUNTS EXPECTED IN AREAS THAT SEE THUNDERSTORMS. SFC LOW
TO MOVE INTO SW IOWA BY SUNDAY EVENING...THEN PUSH ENE THROUGH THE
STATE SUNDAY NIGHT. COLD AIR TO WRAP INTO THE BACKSIDE OF THE
SYSTEM...SHOULD ALLOW FOR PRECIPITATION TO CHANGE OVER TO SNOW
ACROSS THE FAR WESTERN CWA SUNDAY NIGHT INTO MONDAY MORNING. WRAP-
AROUND ZONE OF PRECIP TO STILL BE LINGERING ACROSS THE NORTHERN CWA
MONDAY MORNING...WITH PRECIPITATION TAPERING OFF MONDAY AFTERNOON.
MAY SEE AROUND AN INCH OR TWO OF SNOW IN THE FAR NORTHWEST...WITH A
DUSTING FURTHER SOUTH ACROSS THE WEST CENTRAL CWA.

CLOUDS EXPECTED TO LINGER ACROSS THE AREA TUESDAY WITH BRIEF RIDGING
ALOFT...THEN ANOTHER STORM SYSTEM TO LIFT OUT OF THE SOUTHERN
ROCKIES NORTHEASTWARD THROUGH THE STATE TUESDAY NIGHT INTO
WEDNESDAY. THIS SYSTEM MUCH COLDER ALOFT...SO EXPECT MAJORITY OF
PRECIP TO BE SNOW WITH THE GREATEST CHANCES ACROSS NORTHWEST IOWA AS
THE SURFACE LOW EXPECTED TO TRACK THROUGH WESTERN/CENTRAL IOWA
WEDNESDAY WITH THE DRY SLOT PUSHING THROUGH MUCH OF THE REST OF THE
STATE. NORTHWEST FLOW IN PLACE WITH UPPER RIDGING BUILDING ACROSS
THE WESTERN/CENTRAL US BY LATE WEEK INTO THE WEEKEND. THIS SHOULD
ALLOW FOR DRY CONDITIONS AND MODERATING TEMPERATURES...BUT WILL
STILL FEEL COLD AS TEMPERATURES ARE EXPECTED TO BE NEAR THE SEASONAL
AVERAGES LATE IN THE WEEK.

&&

.AVIATION...12/12Z
ISSUED AT 552 AM CST SAT DEC 12 2015

LOW CLOUDS AND DENSE FOG TO AFFECT EASTERN TAF LOCATIONS WITH
IFR CONDITIONS THROUGH 15Z BEFORE IMPROVEMENT.  FOG WILL BE MORE
PATCHY WITH MAINLY MVFR CONDITIONS WEST. A LOW PRESSURE SYSTEM
WILL BEGIN TO LIFT TOWARDS IOWA AFT 21Z AND RAIN WILL BEGIN TO
OVERSPREAD THE SOUTHERN TAF LOCATIONS BY 00Z THEN LIFT NORTH
THROUGH THE REMAINDER OF THE PERIOD.

&&

.HYDROLOGY...
ISSUED AT 350 PM CST FRI DEC 11 2015

AS MENTIONED IN THE LONG TERM SECTION...PWAT VALUES WILL INCREASE
TO IN EXCESS OF 1.25 INCHES ACROSS THE AREA WHICH IS AT LEAST 400
PERCENT OF NORMAL FOR THIS TIME OF YEAR. THIS SYSTEM WILL BE AN
EFFICIENT RAIN PRODUCING SYSTEM WITH CURRENT QPF ACROSS MUCH OF
THE FORECAST AREA IS FROM 1.50-3.00 INCHES THROUGH MIDDAY MONDAY
WHICH WOULD BE NEAR RECORD TO RECORD RAINFALL FOR A TWO DAY PERIOD
FOR DECEMBER AT MANY LOCATIONS. MOST RIVERS ARE RUNNING HIGHER
THAN THE 90TH PERCENTILE FOR THIS TIME OF YEAR...ALBEIT THATS NOT
HORRIBLY BAD IN MID DECEMBER AS FAR AS STAGES ARE CONCERNED...BUT
STILL SHOWS ITS WET. GIVEN DORMANT VEGETATIVE GROWTH AND OPEN
FIELDS...RUNOFF WILL BE DECENT/EFFICIENT AND ANTICIPATE AT LEAST
SOME MINOR FLOODING ON AREA STREAMS AND RIVERS SHOULD QPF
MATERIALIZE.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY UNTIL 9 AM CST THIS MORNING FOR APPANOOSE-
BLACK HAWK-BREMER-CLARKE-DAVIS-DECATUR-GRUNDY-JASPER-LUCAS-
MADISON-MAHASKA-MARION-MARSHALL-MONROE-POWESHIEK-RINGGOLD-TAMA-
TAYLOR-UNION-WAPELLO-WARREN-WAYNE.

&&

SHORT TERM...FAB
LONG TERM...BEERENDS
AVIATION...FAB
HYDROLOGY...COGIL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
500 AM CST SAT DEC 12 2015

IAZ028-038-039-049-050-061-062-072>075-082>086-092>097-131100-
BREMER-GRUNDY-BLACK HAWK-MARSHALL-TAMA-JASPER-POWESHIEK-MADISON-
WARREN-MARION-MAHASKA-UNION-CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-
RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS-
500 AM CST SAT DEC 12 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

A DENSE FOG ADVISORY IS IN EFFECT FOR THE AREA. PLEASE REFER TO
THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR
FURTHER DETAILS.

ISOLATED NON-SEVERE THUNDERSTORM ARE POSSIBLE LATE THIS AFTERNOON
INTO TONIGHT. HEAVY RAINFALL IS ALSO POSSIBLE.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

A LONG DURATION RAINFALL EVENT IS EXPECTED FROM THIS AFTERNOON
INTO EARLY MONDAY MORNING. WIDESPREAD ONE TO THREE INCHES OF RAIN
IS EXPECTED WHICH MAY LEAD TO MINOR FLOODING ALONG STREAMS AND
RIVERS OF CENTRAL IOWA.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED...HOWEVER RAINFALL REPORTS
WILL BE APPRECIATED.

IAZ004>007-015>017-023>027-033>037-044>048-057>060-070-071-081-
131100-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-SAC-CALHOUN-WEBSTER-
HAMILTON-HARDIN-CRAWFORD-CARROLL-GREENE-BOONE-STORY-AUDUBON-
GUTHRIE-DALLAS-POLK-CASS-ADAIR-ADAMS-
500 AM CST SAT DEC 12 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

ISOLATED NON-SEVERE THUNDERSTORMS ARE POSSIBLE BY LATE AFTERNOON
INTO THE OVERNIGHT HOURS. HEAVY RAINFALL IS ALSO POSSIBLE.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

A LONG DURATION RAINFALL EVENT IS EXPECTED FROM THIS AFTERNOON
INTO EARLY MONDAY MORNING. WIDESPREAD ONE TO THREE INCHES OF RAIN
IS EXPECTED WHICH MAY LEAD TO MINOR FLOODING ALONG STREAMS AND
RIVERS OF CENTRAL IOWA.

THE RAIN IS EXPECTED TO TRANSITION TO SNOW ACROSS PORTIONS OF
WEST CENTRAL IOWA INTO NORTHWEST IOWA LATE SUNDAY NIGHT INTO
MONDAY. LIGHT ACCUMULATIONS WILL BE POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED...HOWEVER RAINFALL REPORTS
WILL BE APPRECIATED.

MJB