Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 272106
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
406 PM CDT THU AUG 27 2015

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 405 PM CDT THU AUG 27 2015

CONVECTION CONTINUES TO SLOWLY MEANDER DOWN THE MINNESOTA RIVER
AT MID AFTERNOON...ASSOCIATED PRIMARILY WITH AN MCV THAT PUSHED IN
FROM SOUTH DAKOTA LATE THIS MORNING. SOME OF THE RAINFALL HAS BEEN
HEAVY WITH 1.61 INCHES THIS AFTERNOON AT TRACY. THE ACTIVITY WILL
GRADUALLY DIMINISH WHILE HEADING EASTWARD FOR THE REMAINDER OF THE
AFTERNOON AS IT MOVES AWAY FROM THE BETTER INSTABILITY AND LOW
LEVEL MOISTURE TRANSPORT. SOME SHOWERS AND ISOLATED THUNDERSTORMS
WILL LIKELY CONTINUE ACROSS WEST CENTRAL AREAS INTO THE EVENING AS
MID LEVEL FRONTOGENESIS HOLDS ACROSS THE AREA ALONG WITH
INCREASING LOW LEVEL MOISTURE TRANSPORT.

THE FORECAST FOR TONIGHT AND FRIDAY IS A MESSY ONE. THE
DETERMINISTIC MODELS AND CAMS CONTINUE TO OSCILLATE NORTH AND SOUTH
WITH THE INCOMING LOW PRESSURE SYSTEM AND THE RESULTING AXIS OF
HEAVY QPF...GYRATING BETWEEN SOUTHERN MN AND IA. ONE COMPLICATING
MATTER IS THAT THIS IS A PHASING SYSTEM IN THE UPPER LEVELS. ONE
PART IS OVER SOUTH DAKOTA THIS AFTERNOON WITH THE OTHER OVER
NEBRASKA. THIS IS EVIDENT IN THE REGIONAL RADAR. THESE TWO FEATURES
WILL COME TOGETHER LATE TONIGHT ACROSS SOUTHERN MINNESOTA AND
NORTHERN IA AND THEN MOVE SLOWLY OFF TO THE EAST FRIDAY AND FRIDAY
NIGHT. OUR BELIEF IS THAT THE HEAVIEST RAINFALL FROM THIS SYSTEM
WILL BE ALONG AND SOUTH OF THE I-90 CORRIDOR. THIS IS AT THE NOSE OF
THE LOW LEVEL MOISTURE TRANSPORT AND STRONG DIFFERENTIAL DIVERGENCE.
RAIN AMOUNTS ALONG I-90 MAY REACH 2 INCHES BUT IT WILL BE SPREAD OUT
OVER A 6 TO 9 HOUR PERIOD. HENCE...THE THREAT OF FLASH FLOOD IS LOW
WITH PONDING OF WATER IN LOW AREAS MORE COMMON. STILL...THE RAINFALL
WITH THIS SYSTEM IS DEFINITELY A CONCERN WITH THE UPPER LEVELS
ORIGINATING FROM BAJA/MEXICO SEVERAL DAYS BACK. THE SUBTROPICAL JET
WRAPS ANTICYCLONICALLY ACROSS THE UPPER MISSISSIPPI VALLEY WITH A
RATHER PRONOUNCED RIGHT ENTRANCE REGION LATE TONIGHT AND EARLY
FRIDAY. IN ADDITION...THE PRECIPITABLE WATER VALUES ARE PROGGED TO
REACH 1.75 INCHES ACROSS THE SOUTHERN FA...WHICH IS NEAR THE MAX
MOVING AVERAGE OF 1.83 INCHES FROM THE KMPX SOUNDING CLIMATOLOGY FOR
LATE AUGUST. RAIN AMOUNTS FROM THIS SYSTEM WILL DIMINISH
SIGNIFICANTLY HEADING NORTHWARD...WITH ABOUT A THIRD OF AN INCH
FORECAST FOR THE TWIN CITIES WITH NO PRECIPITATION AT THE FAR
NORTHERN END OF THE FA (STAPLES).

AS FOR THE LOWS AND HIGHS IN THE SHORT TERM...LITTLE CHANGE FOR
TONIGHT WITH AROUND 60 TO THE LOWER 60S. HIGHS ON FRIDAY REMAIN
QUITE COOL ACROSS THE SOUTH AND EAST SECTIONS OF THE FA DUE TO THE
CLOUDS AND RAIN WITH MIDDLE 60S COMMON. HIGHS WILL BE NEAR 75 BACK
TOWARDS KAXN AND KMOX.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 405 PM CDT THU AUG 27 2015

THE MAIN FEATURE DURING THE EXTENDED IS STILL THE ARRIVAL OF AN
UPPER RIDGE OVER THE WEEKEND THAT WILL PERSIST ACROSS MUCH OF THE
ERN CONUS THROUGH NEXT WEEK. AFTER RAIN MOVES OUT FRIDAY
EVENING...IT LOOKS TO BE HARD TO COME BY UNTIL LABOR DAY WEEKEND.
BESIDE THAT...HIGHS IN THE UPPER 80S/LOWER 90S ARE LOOKING MORE AND
MORE LIKELY BY THE MIDDLE OF NEXT WEEK.

THE WAVE HEADING FOR SRN MN WILL BE ON THE WAY OUT FRIDAY EVENING.
THE 27.12 ECMWF HAS COME IN FASTER WITH THE MOVEMENT OF THE PRECIP
WITH THIS SYSTEM...COMING MORE IN LINE ON TIMING WITH THE GFS/NAM.
AS A RESULT...SPED UP THE DEPARTURE OF POPS FRIDAY EVENING...WITH
DRY CONDITIONS NOW FORECAST AFTER 6Z SATURDAY ACROSS THE ENTIRE MPX
AREA.

BEHIND THIS WAVE...NOT MUCH HAS CHANGED WITH WHAT THE GFS/ECMWF HAVE
BEEN SHOWING FOR THE PAST FEW DAYS WITH AN UPPER RIDGE BUILDING UP
ACROSS THE UPPER MS RIVER VALLEY AS DEEP TROUGHING BUILDS DOWN THE
PAC NW COAST. BY MONDAY H5 HEIGHTS ACROSS THE MPX AREA WILL BUILD TO
OVER 588 DM. THE ECMWF EVENTUALLY SHOWS THESE HEIGHTS NUDGING BACK
DOWN SOME BY FRIDAY...BUT THE GFS KEEPS THE HIGH HEIGHTS CENTERED
OVER THE AREA THROUGH SUNDAY.

THIS RIDGE WILL MAKE IT DIFFICULT FOR FRONTS TO GET IN HERE. NOT
UNTIL THE END OF THE WEEK DOES THE ECMWF SHOW A FRONT WORKING INTO
THE AREA...COINCIDENT WITH THE H5 HEIGHTS STARTING TO FALL SOME. DO
HAVE A COUPLE OF SMALL TSRA CHANCES DURING THE OVERNIGHT PERIODS
WED/THU NIGHTS. THE ECMWF HAS A COUPLE OF WEAK WAVES WORKING AROUND
THE PERIPHERY OF THE UPPER RIDGE WITH A WEAK LLJ JUXTAPOSED OVER THE
AREA AS WELL...BUT WE WILL BE DEALING WITH CAPPING ISSUES DUE TO
WARM MID LEVEL TEMPS AND WEAK SFC BASED FORCING. DO NOT THINK WE
REALLY HAVE MUCH OF A CHANCE FOR SEEING PRECIP HERE UNTIL THE RIDGE
STARTS TO BREAK DOWN...WHICH IS FRIDAY ON THE ECMWF AND NOT UNTIL
AROUND LABOR DAY FOR THE GFS...SO IN ALL LIKELIHOOD...WE ARE LOOKING
AT THE HOLIDAY WEEKEND BEFORE APPRECIABLE RAINFALL CHANCES CAN
RETURN.

ON THE TEMPERATURE FRONT...IT CERTAINLY LOOKS WARM...THOUGH THE
WARMEST H85 TEMPS REMAIN JUST TO OUR WEST THROUGH THE COURSE OF THE
WEEK. BY MONDAY...BOTH THE ECMWF AND GFS SHOW H85 TEMPS WARMING INTO
THE MID 20S C...AND WITH SEVERAL DAYS OF SUNNY SKIES AND SRLY
WINDS...WE WILL SEE TEMPERATURES SLOWLY BUILD AND BY THE MIDDLE OF
NEXT WEEK UPPER 80S/LOWER 90S SHOULD RULE THE LANDSCAPE. ONLY CHANGE
MADE TO THE BLENDED FORECAST WAS TO NUDGE HIGHS A FEW DEGREES
HIGHER...GETTING THEM FROM THE LOW/MID 80S INTO THE MID/UPPER 80S.
BESIDE THE WARM HIGHS...DEWPOINT NEXT WEEK LOOK TO REMAIN IN THE
UPPER 60S...SO OVERNIGHT LOWS WILL BE REMAINING UP IN THE MID/UPPER
60S AS WELL...SO DON/T TURN THAT AC OFF JUST YET!

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1250 PM CDT THU AUG 27 2015

THE FIRST 12 HOURS OF THE FORECAST LOOK MAINLY VFR...WITH THE MOST
INTERESTING TIME PERIOD FROM MIDNIGHT AND BEYOND. FOR THE
REMAINDER OF TODAY...EXPECTING HIGH LEVEL CLOUDINESS TO CONTINUE
STREAMING IN...WITH MID LEVEL CLOUDINESS AND SHOWERS PUSHING INTO
SOUTHWESTERN MN. RWF WILL BE THE MOST VULNERABLE TO PRECIP THIS
AFTERNOON. THE SURFACE LOW IS EXPECTED TO REMAIN SOUTH OF THE MN
BORDER...BUT GUIDANCE STILL INDICATES WIDESPREAD MVFR POSSIBLE.
PUSHED BACK THE ONSET SLIGHTLY...MAINLY VERY LATE TONIGHT THROUGH
THE MORNING ON FRIDAY. IN FACT...AT THIS POINT IT LOOKS LIKE THE
CIGS MAY BE LOWEST TOMORROW AFTER DAYBREAK AND WE MAY CARRY MVFR
UNTIL AT LEAST 18Z...POTENTIALLY ALL DAY. SOME GUIDANCE INDICATES
IFR CIGS POSSIBLE...BUT NOT READY TO BITE ON THAT AT THIS TIME
WITH THE LOW BEING SO FAR SOUTH.

KMSP...MOST OF THE PRECIP WILL STAY SOUTH OF MSP...BUT STILL
EXPECT THE POSSIBILITY OF SOME LIGHT RAIN AT MSP EARLY TOMORROW.

/OUTLOOK FOR KMSP/
SAT...VFR. WINDS SE 5-10 KTS.
SUN...VFR. WINDS S 5-10 KTS.
MON...VFR. WINDS S 5-15 KTS.


&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

$$

SHORT TERM...RAH
LONG TERM...MPG
AVIATION...SPD



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