Area Forecast Discussion
Issued by NWS Bismarck, ND

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000
FXUS63 KBIS 200622
AFDBIS

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

.UPDATE...
ISSUED AT 103 AM CDT WED AUG 20 2014

THE MAIN FOCUS THIS MORNING IS ON PRECIPITATION AMOUNTS AND THE
FLOOD RISK. THE 00 UTC HIRES ARW AND WRF AND HRRR ARE IN GOOD
AGREEMENT THAT THE PREVIOUS FORECAST IS TOO FAST WITH THE ONSET OF
CONVECTION. THERE HAS ALSO BEEN A TREND TOWARD PUSHING CONVECTION
FURTHER NORTH...WHICH WOULD SPARE MUCH OF THE SOUTHWEST FROM
HEAVIER AMOUNTS. DECISIONS WILL NEED TO BE MADE THIS MORNING
REGARDING ANY FLOOD OR FLASH FLOOD WATCHES.

UPDATE ISSUED AT 953 PM CDT TUE AUG 19 2014

A FEW MINOR ADJUSTMENTS TO SKY COVER FOR THE LATE EVENING UPDATE.
LATEST RADAR IMAGERY SHOWS ISOLATED CONVECTION LIFTING THROUGH
SOUTH CENTRAL MONTANA...WHICH SHOULD MOVE INTO NORTH DAKOTA LATE
TONIGHT. THIS IS CURRENTLY HANDLED WELL. ALSO WEAK CONVECTION
CONTINUES TO FIRE OVER FAR NORTHEAST MONTANA INTO SOUTHERN
SASKATCHEWAN. MODELS DO SHOW AN INCREASING JET OVER WESTERN NORTH
DAKOTA TONIGHT IN AN AREA OF WEAK UPPER LEVEL DIVERGENCE AND
INSTABILITY ALOFT. COULD POSSIBLY BE SOME ELEVATED CONVECTION
ACROSS THE NORTHWEST INTO THE NORTH CENTRAL LATE TONIGHT SO
EXTENDED SOME SLIGHT POPS EAST ACROSS THESE AREAS AFTER MIDNIGHT.

UPDATE ISSUED AT 639 PM CDT TUE AUG 19 2014

A COUPLE OF THUNDERSTORMS DEVELOPED OVER SOUTHWEST NORTH DAKOTA
LATE THIS AFTERNOON IN AN AREA OF CAPES AROUND 2000 J/KG AND 25-35
KNOTS OF BULK SHEAR. ONE HAS DISSIPATED AS IT MOVED FROM BOWMAN
INTO ADAMS COUNTY. THE SECOND IS STILL HOLDING TOGETHER OVER
CENTRAL SLOPE. WILL MAINTAIN OUR SLIGHT CHANCE POPS OVER THE
SOUTHWEST. A FEW CELLS TRIED TO FIRE OVER THE NORTHWEST BUT WITH
LESS LUCK IN A LOW SHEAR ENVIRONMENT. SCATTERED CONVECTION OVER
NORTHEAST MONTANA CONTINUES TO LIFT NORTHEAST BUT IS HAVING A HARD
TIME MAINTAINING ITS STRENGTH AS IT APPROACHES NORTHWEST NORTH
DAKOTA. WILL HOLD OFF ON BRINGING ANY SLIGHT CHANCE POPS INTO THE
FAR NORTHWEST. OTHERWISE QUIET ACROSS MOST OF WESTERN AND CENTRAL
NORTH DAKOTA WITH NO CHANGES NEEDED TO THE GOING FORECAST.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)

ISSUED AT 327 PM CDT TUE AUG 19 2014

THE MAIN CONCERN IN THE SHORT TERM FORECAST PERIOD IS EXPECTED
WIDESPREAD SHOWERS AND THUNDERSTORMS WEDNESDAY AND WEDNESDAY NIGHT.
THE PROBLEM IS LOW CONFIDENCE ON WHERE THE HEAVIEST RAINFALL TOTALS
CAN BE EXPECTED.

CURRENTLY...SURFACE LOW PRESSURE WAS OVER SOUTHWESTERN SASKATCHEWAN
AND NORTH CENTRAL MONTANA AHEAD OF AN UPPER LEVEL LOW/TROUGH OVER
UTAH. SURFACE DEWPOINTS WERE IN THE MID 50S WEST AND IN THE 60S OVER
EASTERN NORTH DAKOTA.

TONIGHT THE UPPER LOW LIFTS NORTHEASTWARD AND APPROACHES
SOUTHWESTERN NORTH DAKOTA. IN RESPONSE...THE SURFACE LOW/TROUGH
SHOULD DEVELOP EASTWARD SO THAT BY DAYBREAK WEDNESDAY IT IS ALONG
THE MONTANA/DAKOTAS BORDER. SOME MODELS ARE DEPICTING SOME ISOLATED
SHOWERS/THUNDER BEFORE DAYBREAK IN THE WEST...AND HAVE KEPT
ISOLATED/SMALL CHANCE PROBABILITIES FOR THE WESTERN QUARTER OF THE
STATE THROUGH DAYBREAK.

MODELS ARE IN GOOD AGREEMENT THAT SHORTLY AFTER/AT DAYBREAK THE
UPPER LEVEL ENERGY IMPULSES WILL BE SUFFICIENT FOR INCREASING
CHANCES OF SHOWERS AND THUNDERSTORMS THROUGH THE DAYLIGHT MORNING
HOURS. AROUND/AFTER NOON SHOWERS AND THUNDERSTORMS SHOULD BE
WIDESPREAD AND NUMEROUS ACROSS WESTERN AND CENTRAL NORTH DAKOTA.
WEDNESDAY EVENING MOST OF THE PRECIPITATION FROM THE THUNDERSTORMS
SHOULD BE IMPACTING ALL BUT THE FAR WESTERN PORTION OF NORTH
DAKOTA...WITH DECREASING CHANCES FROM WEST TO EAST LATE WEDNESDAY
NIGHT.

THE MAIN PROBLEM IS THAT THE VARIOUS MODELS ARE NOT COMING TO A GOOD
CONSENSUS REGARDING PLACEMENT OF THE HEAVIEST PRECIPITATION. THE NAM
MODEL IS FARTHEST NORTH WITH THE PLACEMENT OF HEAVY
PRECIPITATION...WITH WESTERN AND NORTH CENTRAL NORTH DAKOTA (SOURIS
RIVER BASIN) TAKING THE BIGGEST HIT. THE GFS/ECMWF WANT TO SPLIT THE
ENERGY - AND HENCE RESULTING IN TWO HEAVIER PRECIP BULLS-EYES - WITH
ONE OVER THE SOURIS BASIN...AND ANOTHER OVER CENTRAL NORTH DAKOTA.
THE OTHER SHORT TERM HIGH RESOLUTION MODELS ARE FAVORING SOUTH
CENTRAL NORTH DAKOTA.

FINAL PRECIPITATION FORECAST INVOLVES A SECTION OF SOUTH CENTRAL
NORTH DAKOTA INCLUDING THE JAMES RIVER VALLEY OF 1 TO 1.5 INCHES OF
RAIN...AND AROUND 0.75 TO 1 INCH OVER THE NORTHWEST/NORTH CENTRAL.

A HYDROLOGIC OUTLOOK (ESF) HAS BEEN ISSUED TO ADDRESS THIS FIRST
WAVE OF PRECIPITATION WEDNESDAY THROUGH WEDNESDAY NIGHT...THEN ALSO
ADDRESSES THE LONG TERM PERIOD EXPECTED PRECIPITATION THURSDAY NIGHT
THROUGH THE WEEKEND.

.LONG TERM...(THURSDAY THROUGH TUESDAY)

ISSUED AT 327 PM CDT TUE AUG 19 2014

A VERY ACTIVE/WET PATTERN THROUGH THE WEEKEND WILL HIGHLIGHT THE
EXTENDED FORECAST PERIOD.

WILL NOTE 12Z MODELS STILL SHOW CONSIDERABLE SPREAD IN REGARDS TO
PRECIPITATION...TIMING/PLACEMENT/AMOUNTS...FRIDAY NIGHT THROUGH
SUNDAY. BETTER AGREEMENT THURSDAY THROUGH FRIDAY.

FOR THURSDAY...SHOWERS/THUNDERSTORMS WILL BE IN THE PROCESS OF
LIFTING OFF TO OUR NORTHEAST DURING THE MORNING AS A MID LEVEL S/WV
IMPULSE EJECTS INTO CANADA AND ITS ASSOCIATED SFC TROUGH PUSHES EAST
INTO THE UPPER MISSISSIPPI VALLEY. CONVECTIVE REDEVELOPMENT WILL BE
VERY POSSIBLE THURSDAY AFTERNOON/EVENING AS WE REMAIN IN
SOUTHWESTERLY FLOW ALOFT ALONG WITH AMPLE INSTABILITY AND DECREASING
CIN AS THE DAY PROGRESSES.

MAIN AREA OF PRECIPITATION WILL ENTER WESTERN NORTH DAKOTA THURSDAY
NIGHT AS ANOTHER EMBEDDED WAVE LIFTS NORTHEAST ACROSS EASTERN
MONTANA INTO FAR SOUTH CENTRAL CANADA...ALONG WITH FORCING
ASSOCIATED WITH THE UPPER LEVEL JET NOSING INTO THE REGION RESULTING
IN DIVERGENCE ALOFT OVERSPREADING THE NORTHERN PLAINS. BASED ON THE
PROJECTED TRACK OF THE MID LEVEL S/WV DEPICTED BY BOTH THE 12Z
GFS/ECMWF...MOST FAVORABLE AREAS FOR HEAVY PRECIPITATION WILL BE
OVER THE WESTERN HALF OF THE STATE AND INTO THE NORTH CENTRAL THURS
NIGHT-FRIDAY MORNING.

UPPER LEVEL TROUGH DIGS ACROSS THE WESTERN CONUS
FRIDAY-SATURDAY...THEN LIFTS NORTH AND EAST ACROSS THE DAKOTAS SAT
NIGHT-SUN NIGHT. MODEL SPREADS RATHER HIGH IN REGARDS TO
PRECIPITATION DURING THE FRIDAY/SATURDAY TIMEFRAME...WITH LEAD S/WV
IMPULSES DIFFICULT FOR MODELS TO KEY IN ON AT THIS TIME. SOME
LOCATION DIFFERENCES AS WELL SAT NIGHT INTO SUNDAY WITH THE TRACK OF
THE MAIN UPPER LEVEL WAVE WHEN IT MOVES ACROSS THE LOCAL REGION.
LOOKS TO BE WET MOST LOCATIONS.

WE REMAIN IN A QUASI-ACTIVE FLOW PATTERN INTO EARLY NEXT WEEK AS
WELL WITH A BROAD TROUGH IN PLACE ALOFT MONDAY AND TUESDAY.

TEMPERATURES WILL COOL SIGNIFICANTLY FROM FRIDAY INTO SUNDAY WITH
THE PRECIPITATION EXPECTED AND STRONG CAA ON SUNDAY IN THE WAKE OF A
STRONG SURFACE LOW AND UNDERNEATH THE UPPER WAVE. HIGHS SUNDAY WILL
BE IN THE 60S COMPARED TO UPPER 70S AND MID 80S ON THURSDAY. A
SLIGHT MODERATION IN HIGHS FORECAST NEXT WEEK MONDAY AND
TUESDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 103 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 327 PM CDT TUE AUG 19 2014

THERE WILL BE POTENTIALLY SIGNIFICANT RAINS ACROSS MUCH OF WESTERN
AND CENTRAL NORTH DAKOTA FROM WEDNESDAY MORNING THROUGH EARLY
THURSDAY...AND THEN AGAIN THURSDAY NIGHT THROUGH SUNDAY. THOSE AREAS
OF THE STATE WHICH RECEIVE MULTIPLE PASSES OF HEAVY RAINS OF HEAVY
RAIN WILL LIKELY EXPERIENCE EXCESSIVE RUNOFF AND A HIGHER LIKELIHOOD
OF OVERLAND AND SMALL STREAM FLOODING.

WHILE THE SOURIS RIVER BASIN OF NORTH DAKOTA HAS BEEN RELATIVELY DRY
TO NEAR NORMAL THE PAST FEW WEEKS...SOME OF THE MODELS DEPICT
WIDESPREAD RAINS BETWEEN TWO AND FOUR INCHES ACROSS THE UPPER
PORTIONS OF THE SOURIS IN NORTH DAKOTA AND SASKATCHEWAN. AREAS THAT
RECEIVE AN INITIAL WETTING DURING THE EARLIER EVENT ARE MORE LIKELY
TO EXPERIENCE EXCESSIVE RUNOFF DURING THE LATTER RAINS. SEVERAL
MISSOURI RIVER TRIBUTARIES WERE PARTICULARLY HARD HIT BY HEAVY RAINS
LAST WEEKEND, INCLUDING THE KNIFE AND HEART RIVERS ALONG WITH APPLE
CREEK. THESE RIVERS WILL STILL BE RUNNING WELL ABOVE NORMAL AS THE
NEXT FEW WEATHER SYSTEMS MOVE INTO THE STATE.

THE JAMES AND PIPESTEM CREEK BASINS HAVE NOT BEEN PARTICULARLY
AFFECTED BY RECENT HEAVY RAINS. HOWEVER...THERE HAS BEEN ENOUGH RAIN
TO KEEP THE SOIL MOISTURE LEVELS AT OR ABOVE NORMAL FOR THIS TIME OF
YEAR.

&&

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

$$

UPDATE...SCHECK
SHORT TERM...JV
LONG TERM...NH
AVIATION...SCHECK
HYDROLOGY...AJS





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