Area Forecast Discussion
Issued by NWS Bismarck, ND

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000
FXUS63 KBIS 200932
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
432 AM CDT WED AUG 20 2014

.SYNOPSIS...
ISSUED AT 432 AM CDT WED AUG 20 2014

A POTENT WEST COAST UPPER LEVEL TROUGH MOVING SLOWLY EASTWARD WILL
BE THE FOCUS FOR WEATHER ACROSS THE NORTHERN PLAINS FOR THE NEXT
WEEK. SOUTHWESTERLY FLOW ALOFT AHEAD OF THE TROUGH WILL DIRECT A
SERIES OF MIDDLE LEVEL SHORTWAVES INTO THE DAKOTAS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 432 AM CDT WED AUG 20 2014

THE MAIN FOCUS THIS MORNING IS ON FLOODING POTENTIAL AS TWO ROUNDS
OF HEAVY RAINFALL THREATEN TO BOTH EXACERBATE ONGOING FLOODING
AND CAUSE NEW IMPACTS.

THE 00 UTC HIRES ARW AND WRF/HRRR HAVE ALL TRENDED SLOWER WITH
ONSET AND NORTHWARD WITH THE HEAVIEST PRECIPITATION AMOUNTS
THROUGH THURSDAY MORNING...BUT THE 00 UTC ECMWF/GFS/GEM GLOBAL AND
WPC HAVE ALL HELD WITH THE IDEA THAT CONVECTION WILL FORM ALONG
THE ENTIRE INSTABILITY AXIS...AND MOVE SLOWLY EAST BEFORE EXITING
THURSDAY MORNING.

SEE THE HYDROLOGY SECTION BELOW FOR MORE DETAILS.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 432 AM CDT WED AUG 20 2014

THE MEDIUM RANGE MODELS ARE FAIRLY CONSISTENT WITH RESPECT TO
SOUTHWESTERLY FLOW ALOFT PERSISTING OVER WESTERN AND CENTRAL NORTH
DAKOTA THROUGH THE PERIOD. DID NOT FAVOR ONE MODEL OVER ANOTHER
WITH RESPECT TO THE DETAILS SO KEPT WITH A BLENDED APPROACH FOR
THE EXTENDED.

THUNDERSTORM CHANCES WILL CONTINUE THURSDAY THROUGH SUNDAY AS
SHORTWAVES IN THE SOUTHWESTERLY FLOW ALOFT CONTINUE TO TRAVERSE
THE REGION. A COLD FRONT WILL ALSO PUSH THROUGH THE STATE THURSDAY
NIGHT WITH WELL BELOW NORMAL HIGHS FORECAST FRIDAY AND SATURDAY
(HIGHS AROUND 70).

THE GFS HAS NOW COME MORE IN LINE WITH THE ECMWF PROGGING
THUNDERSTORM CHANCES CONTINUING SUNDAY. WELL BELOW NORMAL
TEMPERATURES ARE EXPECTED TO CONTINUE WITH HIGHS IN THE MID TO
UPPER 60S. FOR MONDAY...A LITTLE DRIER AIR IS PROGGED TO FILTER
INTO THE REGION. HOWEVER...SOUTHWESTERLY FLOW ALOFT IS PROGGED TO
PERSIST. GIVEN THE PATTERN...WILL INDICATE SLIGHT CHANCES OF
PRECIP MONDAY CONTINUING INTO TUESDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 432 AM CDT WED AUG 20 2014

THUNDERSTORMS WILL INCREASE FROM WEST TO EAST TODAY. THERE IS HIGH
UNCERTAINTY ON TIMING AND PLACEMENT BEYOND THAT TREND...SO THE
TIMING IN TAFS IS A BEST GUESS. THERE COULD BE MVFR VISIBILITIES
AND CEILINGS WITH STRONGER THUNDERSTORMS.

&&

.HYDROLOGY...
ISSUED AT 432 AM CDT WED AUG 20 2014

SOILS ARE NEARLY SATURATED ACROSS MOST OF THE MISSOURI TRIBUTARY
COUNTIES...AND THE MAIN FLOOD THREAT AREA IS HIGHLIGHTED IN THE
HAZARDOUS WEATHER OUTLOOK IN COUNTIES THAT HAVE JUXTAPOSITION OF
NEARLY SATURATED ANTECEDENT SOIL CONDITIONS...INSTABILITY...
CORFIDI VECTORS LESS THAN 5 KNOTS...AND PRECIPITABLE WATER VALUES
2.5 STANDARD DEVIATIONS ABOVE NORMAL.

BECAUSE OF POTENTIAL CONFUSION WITH SUCH AN EXTENDED DURATION
EVENT...AND GREATER UNCERTAINTY WITH LOCATION OF HEAVIER
RAINFALL...NO FLOOD WATCH WAS ISSUED FOR THIS FIRST ROUND OF
CONVECTION.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...SCHECK
SHORT TERM...SCHECK
LONG TERM...TM
AVIATION...SCHECK
HYDROLOGY...SCHECK



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