Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 260500 AAB
AFDMPX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1200 AM CDT SUN JUL 26 2015

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 415 PM CDT SAT JUL 25 2015

A COUPLE OF MCVS FROM CONVECTION EARLIER IN THE DAY OVER SODAK ARE
NOW DRIFTING OVER MN...BUT ENCOUNTERING DRY HIGH PRESSURE AT THE SFC
AS THEY DO SO...SO THEY HAVE BEEN ABLE TO PRODUCE LITTLE MORE THAN
AN INCREASE IN MID/UPPER CLOUDS. THE AREA TO WATCH THIS AFTERNOON
THOUGH IS CENTRAL SODAK OUT BY MILLER AND CHAMBERLAIN WHERE SEVERAL
SEVERE WEATHER PARAMETERS ARE LINING UP. THIS REGION IS ALSO AT THE
EDGE OF A CAPPING EML. CURRENT EXPECTATIONS ARE THAT THUNDERSTORMS
WILL RAPIDLY DEVELOP IN THIS REGION AROUND 21/22Z AND WILL LIKELY BE
SEVERE GIVEN STRONG INSTABILITY...VERY STEEP MID LEVEL LAPSE RATES
AND DEEP LAYER SHEAR IN EXCESS OF 50 KTS. H85 THETA-E GRADIENT...H7
THERMAL FIELDS AND H85-H3 THICKNESSES ALL POINT TO THIS ACTIVITY
BUILDING SE THROUGH THE NIGHT...WORKING DOWN TO OR EVEN SW OF DES
MOINES THROUGH THE NIGHT. WHAT THIS MEANS FOR THE MPX CWA IS THAT WE
ARE LIKELY TO GET NOTHING MORE THAN A GRAZING FROM THIS
ACTIVITY...WITH THE BEST CHANCES FOR SEEING RAIN BEING SW OF THE MN
RIVER IN SW INTO SC MN. THIS IDEA IS GENERALLY SUPPORTED BY THE NSSL-
WRF AND THE HOP-WRF MEMBERS. THE HRRR SHOWS SOMETHING SIMILAR AS
WELL...THOUGH THINK IT BRINGS ACTIVITY TOO FAR NORTH THROUGH THE
NIGHT.

FOR THE MPX AREA...OUR BEST SHOT AT SEEING PRECIP TONIGHT WILL BE
WITH SOME WEAK ELEVATED THETA-E ADVECTION THAT MAY BE ABLE TO SPARK
SOME ACCAS TYPE ACTIVITY IN WRN MN...BUT WITH THE AMOUNT OF
ACTIVITY EXPECTED TO HEAD FOR IOWA...DO NOT THINK WE WILL SEE MUCH
DEVELOPMENT UP HERE.

FOR SUNDAY...CONFIDENCE IS BEGINNING TO INCREASE THAT WE WILL NOT
SEE ANY ADDITIONAL CONVECTION DURING THE AFTERNOON. THOUGH MOISTURE
AND INSTABILITY SHOULD BE PLENTIFUL WITH DEWPS INCREASING BACK INTO
THE 70S FOR THE SRN HALF OF THE MPX CWA...FORCING WILL BE DECIDEDLY
LACKING. THE BIGGEST ISSUE FOR US IS THAT IN THE WAKE OF ACTIVITY TO
OUR SOUTH OVERNIGHT INTO SUNDAY MORNING...WE WILL HAVE RISING H5
HEIGHTS ALL DAY. IN ADDITION TO THAT...ANY SORT OF WEAK/DIFFUSE WARM
FRONT WILL REMAIN DOWN IN IOWA...SO WE WILL NOT HAVE THAT TO HELP
WITH FORCING DEEP CONVECTION EITHER. IN THE END...RETAINED SOME 30
POPS OR LESS...BUT TRIMMED THAT MENTION DOWN TO ALONG AND SOUTH OF
THE MN RIVER. IN GENERAL THOUGH...SUNDAY LOOKS LIKE A GOOD...THOUGH
WARM/HUMID SUMMER DAY ACROSS THE MPX CWA.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 415 PM CDT SAT JUL 25 2015

THE EVOLUTION OF THE LARGE-SCALE PATTERN THROUGH MONDAY IS THAT OF
BUILDING HEIGHTS AND THE CONTINUATION OF A WARM AND HUMID AIR
MASS THAT SHOULD LINGER INTO TUESDAY...ALTHOUGH THE TEMPERATURE
FORECAST TUESDAY IS COMPLICATED BY THE POSSIBILITY OF CONVECTION.
THE MAIN SURFACE WARM FRONT WILL BE SOUTH AND WEST OF THE FORECAST
AREA ON MONDAY. LOCALLY MN/WI BE SITTING UNDER THE UPPER RIDGE
WITH A MOIST SOUTH-SOUTHEAST BL FLOW BUT NO PRONOUNCED TRIGGER
FOR CONVECTION. 700MB TEMPS AREN`T OVERLY WARM...SO THE CAPPING
ISN`T OVERLY STRONG...THIS IS WHY WE THINK THE GFS TRIES TO
INITIATE CONVECTION OVER THE FORECAST ARE ON MONDAY. THE NAM/ECMWF
ARE DRIER IN MID-LEVELS...SO WE THINK THE POP SHOWERS SHOULD BE
LIMITED MONDAY...ALTHOUGH NOT IMPOSSIBLE EITHER.

ON MONDAY NIGHT INTO TUESDAY MORNING A WARM FRONT LIFT NORTHEAST
INTO THE AREA. THE GUIDANCE SHOWS SCATTERED SHOWERS AND STORMS
ALONG THE FRONT AS IT LIFTS THROUGH. THIS ACTIVITY WILL LIKELY BE
ELEVATED BASED ON FORECAST SOUNDINGS...HOWEVER...PWATS THAT
APPROACH 2" - 2000 J/KG OF MLCAPE - A 13500FT WARM LAYER - AND
FAVORABLE LOW LEVEL SHEAR VECTORS...SUGGEST HEAVY RAIN AND THE
THREAT FOR FLASH FLOODING IS PROBABLY THE BIGGEST HAZARD. THE
925-700MB MOISTURE TRANSPORT LEANS OVER THE FORECAST AREA DURING
THE DAY TUESDAY WITH THE SURFACE TROUGH PASSING THROUGH.
THEREFORE...WE COULD KEEP SHOWERS/STORMS MOST OF THE DAY AND AT
THE VERY LEAST CLOUD COVER COULD MEAN HIGHS ARE CLOSER TO 80 THAN
THE UPPER 80S CURRENTLY IN THE FORECAST. THE SPEED OF THE WARM
FRONTAL PASSAGE IS STILL SOMEWHAT UNCERTAIN...BUT THE MOISTURE
TRANSPORT IS SOLID BY TUESDAY MORNING AT LEAST OFF TODAY`S MODEL
RUNS. THE PRONOUNCED UPPER TROUGH AND BEST DYNAMICS ARE NORTH OF
THE AREA. THE COLD FRONT SHOULD FINALLY CLEAR THE FORECAST AREA
TUESDAY NIGHT...BRINGING IN LESS HUMID AIR WED-FRI.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1159 PM CDT SAT JUL 25 2015

MUCH OF THE THUNDERSTORM ACTIVITY IS SOUTHWEST OF RWF...WITH A
LARGE AREA OF LIGHT TO MODERATE RAIN EXTENDING NORTHEAST ACROSS
THE MN RIVER INTO CENTRAL MN. THIS AREA WILL DROP SOUTHEAST
OVERNIGHT...LIKELY ERODING ON THE NORTHERN EDGE SOMEWHAT AS IT
DOES SO. REGARDLESS...VFR CONDITIONS EXPECTED THROUGH THE PERIOD.

KMSP...IT APPEARS MSP SHOULD SEE A PERIOD OF LIGHT RAIN LATE
TONIGHT...BUT VFR CONDITIONS EXPECTED TO PREVAIL AND AMOUNTS WILL
BE A FEW HUNDREDTHS OR LESS.

/OUTLOOK FOR KMSP/
MON...VFR. CHC OF TSRA LATE. WINDS SE 5-10 KTS.
TUE...MAINLY VFR. CHC MVFR/IFR IN TSRA. WINDS S 10-15 KTS.
WED...VFR. WINDS W 15-20 KTS.

&&

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

$$

SHORT TERM...MPG
LONG TERM...CLF
AVIATION...BORGHOFF


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