Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 211906
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
206 PM CDT THU AUG 21 2014

.UPDATE...
ISSUED AT 131 PM CDT THU AUG 21 2014

UPDATED TO INCLUDE 18Z AVIATION DISCUSSION BELOW.

&&

.SHORT TERM...(TODAY AND TONIGHT)

UPDATE ISSUED AT 738 AM CDT THU AUG 21 2014

GIVEN THE SHOWER AND THUNDERSTORM ACTIVITY IS MOVING OUT RATHER
QUICKLY THIS MORNING...DECIDED TO HOIST A HEAT ADVISORY WHERE IT
IS LIKELY THE THERMAL RIDGE WILL BUILD IN EARLY THIS AFTERNOON AND
THE THREAT FOR ADDITIONAL STORM DEVELOPMENT IS RATHER LOW. THIS
THERMAL RIDGE WILL ALLOW FOR TEMPS TO REACH THE 90S IF MIXING CAN
OCCUR TO 925 MB. IN ADDITION...DEW POINTS WILL BE RISING STEADILY
THROUGH THE DAY INTO THE MID 70S WHICH WILL PUT HEAT INDICES IN
THE 95 TO 105 DEGREE RANGE.

ISSUED AT 411 AM CDT THU AUG 21 2014

IT IS SHAPING UP TO BE A VERY BUSY DAY WEATHERWISE WITH MULTIPLE
THREATS TO BE CONCERNED ABOUT. THE FIRST IS SEVERE WEATHER AND
FLASH FLOODING. AT 4 AM...DEEP MOISTURE CONTINUES TO ADVECT INTO
THE AREA...AIDED BY A TROPICAL CONNECTION TO LARGE TROPICAL STORM
LOWELL IN THE EASTERN PACIFIC. TWO THUNDERSTORM COMPLEXES ARE
BEGINNING TO CONGEAL OVER ERN SODAK AND WRN MN ON THE NOSE OF A
40-50 KT LLJ. IN ADDITION...OBSERVATIONS INDICATE A POTENT
MESOSCALE AREA OF LOW PRESSURE IS DEVELOPING OVER SOUTHEASTERN
SODAK AS THESE TWO COMPLEXES MERGE. THE HEAVIEST THUNDERSTORMS ARE
OCCURRING TO THE NORTH AND EAST OF THIS LOW WHERE MOISTURE
CONVERGENCE IS MAXIMIZED. THERE IS A RELATIVELY GOOD RISK FOR
FLASH FLOODING IN THIS DEFORMATION ZONE REGION AS THUNDERSTORMS
CONTINUE TO DEVELOP AND TRAIN OVER THE SAME AREAS. THE MESO LOW
WILL CONTINUE PUSHING EAST AS THE LLJ VEERS EARLY THIS
MORNING...WITH THE HEAVY RAIN AND FLASH FLOODING THREAT SHIFTING
FROM WRN MN TO CENTRAL AND ERN MN AND FAR WESTERN WI DURING THE
NEXT FEW HOURS. WIDESPREAD RAINFALL OF 1 TO 3 INCHES ARE
EXPECTED...WITH HIGHER TOTALS OF 3 TO 6 INCHES POSSIBLE IN THE
DEFORMATION BAND/TRAINING CELL REGION EXTENDING ALONG A LINE FROM
NEAR MORRIS TO WILLMAR...THE TWIN CITIES...AND RED WING MN. SHOULD
THE HIGHER END TOTALS FALL IN THE TWIN CITES PROPER...SERIOUS
FLASH FLOOD CONCERNS COULD DEVELOP. LUCKILY...THE CONVECTION SEEMS
SOMEWHAT DISORGANIZED AND CONTINUOUS TORRENTIAL RAIN HAS NOT YET
MATERIALIZED. HOWEVER...IT WILL CONTINUE TO BE MONITORED. TO THE
NORTH AND EAST OF THIS MAX POTENTIAL REGION...A LARGE AREA OF
MODERATE TO OCCASIONALLY HEAVY STRATIFORM RAIN WILL CONTINUE WITH
A LESSER THREAT FOR FLASH FLOODING. SEVERE THREAT EARLY THIS
MORNING IS DIMINISHING AS THUNDERSTORMS BECOME MORE WIDESPREAD AND
DESTRUCTIVE INTERFERENCE OCCURS. STILL...SOME OF THE MORE DISCRETE
CELLS COULD PRODUCE MARGINALLY SEVERE HAIL. THE AREA MOST
SUSCEPTIBLE TO THIS IS SOUTH OF THE MN RIVER AND ALONG I-90.

THE LLJ WILL WEAKEN BY MID MORNING AND THE LARGE AREA OF SHOWERS
AND THUNDERSTORMS WILL BEGIN TO DIMINISH. THERMAL RIDGING WILL
BUILD NORTHEAST THIS AFTERNOON AND SET UP AT LEAST ACROSS SRN MN.
TOUGH TO SAY HOW FAR NORTH AND EAST THIS WILL REACH GIVEN THE
ONGOING CONVECTION WHICH WILL IMPACT IT TO SOME DEGREE...AND THE
POTENTIAL FOR REDEVELOPMENT THROUGH THE DAY. TEMPERATURES UNDER
THE THERMAL RIDGE WILL LIKELY REACH THE 90S. IN ADDITION...AND
PERHAPS MORE IMPORTANTLY...DUE TO THE JUICY AIRMASS THE BOUNDARY
LAYER WILL HAVE A HARD TIME MIXING AWAY DEW POINTS AND VALUES MAY
REMAIN IN THE LOW TO MID 70S THROUGHOUT THE AFTERNOON. THIS WOULD
SEND HEAT INDICES INTO THE LOW 100S. HOWEVER...HELD OFF ON A HEAT
ADVISORY FOR NOW UNTIL THE IMPACTS FROM MORNING THUNDERSTORMS
BECOME CLEARER.

A COLD FRONT WILL SAG SOUTH TONIGHT AND TAKE WITH IT THE RESIDUAL
THUNDERSTORM CHANCES.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 411 AM CDT THU AUG 21 2014

FRIDAY LOOKS LIKE A CONTINUED WARM AND HUMID DAY...BUT THE MAIN
THERMAL RIDGING WILL BE DOWN TO THE SOUTH. ALSO LOOKS DRY UNTIL
OVERNIGHT WHEN THE FRONT LIFTS BACK NORTH AND A 40-50 KT LLJ
DEVELOPS ANOTHER ROUND OF THUNDERSTORM ACTIVITY ALONG IT. MOST OF
THIS WILL BE SOUTH OF MN FRIDAY NIGHT...BUT WILL EXPAND NORTHWARD
SATURDAY ACROSS MUCH OF THE REGION AS LOW PRESSURE DEVELOPS OVER
THE CENTRAL PLAINS. ANOTHER NEARLY STATIONARY BOUNDARY...WHICH THE
LOW WILL TRACK NORTH ALONG...WILL BE THE FOCUS FOR CONTINUED
THUNDERSTORM DEVELOPMENT THROUGH SUNDAY NIGHT. SUNDAY COULD BE A
RATHER WARM DAY IF SUNSHINE CAN MAKE AN APPEARANCE WITH THE LOW
PASSING TO THE WEST. AS THE LOW PASSES BY TO THE WEST...THE FRONT
WILL BEGIN TO MAKE EASTWARD PROGRESS AND MONDAY CURRENTLY LOOKS
DRY POST FRONTAL.

BY THE MIDDLE OF NEXT WEEK...MODELS STILL HINT AT THE FRONT
STALLING AND LIFTING BACK AS A WARM FRONT AS ANOTHER LOW FORMS
OVER THE PLAINS. THIS MAY BRING ANOTHER ROUND OF HEAVY RAIN
PRODUCING THUNDERSTORMS IN THE TUESDAY/WEDNESDAY TIME FRAME.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 131 PM CDT THU AUG 21 2014

WITH AN AREA OF LOW PRESSURE PROGGED TO SLIDE ACROSS SOUTHERN MN
INTO SOUTHERN WI THRU THIS EVENING...ASIDE FROM SOME CLEARING OVER
SOUTHERN MN...MUCH OF THE AREA WILL REMAIN CAUGHT UNDER LOW MVFR
TO IFR CEILINGS. VERY LITTLE PRECIPITATION TO SPEAK OF...ALTHOUGH
SHORT-TERM MODELS CALL FOR SCATTERED SHOWERS AND ISOLATED TSTMS TO
DEVELOP OVER ERN MN INTO WRN WI THIS AFTN INTO EVENING. THE WI
SITES MAY WELL BE SUSCEPTIBLE TO FLIGHT CONDITION REDUCTION BUT AM
NOT LOOKING FOR SUCH IN MN. AFTER SOME PARTIAL CLEARING THIS
EVE...COOLER TEMPERATURES OVER A HIGHLY MOIST AIRMASS LOOKS TO BE
VERY CONDUCIVE TO FOG DEVELOPMENT OVERNIGHT THRU DAYBREAK FRI
MRNG. HAVE BROUGHT DOWN CIGS AND VSBYS AT ALL SITES TO IFR-AND-
LOWER OVERNIGHT AS CONFIDENCE IS RATHER HIGH SUCH CONDITIONS WILL
BE SEEN. THERE MAY BE SOME DIFFERENCES IN THE TIMING COMPARED TO
WHAT IS CURRENTLY ADVERTISED...BUT GENERALLY 08Z-14Z WILL BE THE
BEST TIMEFRAME TO SEE THE DEGRADED CONDITIONS.

KMSP...MVFR-TO-VFR CONDS EXPECTED THRU THIS AFTN...WITH POSSIBLY A
FEW STRAY -SHRA AS THE LOW PRES CENTER MOVES THRU. WINDS THEN
DIMINISH LATE AND CONDS DROP INTO MVFR IN THE 06Z-08Z RANGE...
FOLLOWED BY IFR CONDS FROM EARLY MRNG THRU DAYBREAK BEFORE CONDS
IMPROVE LATE TMRW MRNG INTO TMRW AFTN.

/OUTLOOK FOR KMSP/
SAT...MVFR WITH IFR/+TSRA POSSIBLE. WINDS E AT 10G15 KTS.
SUN...VFR WITH MVFR/TSRA POSSIBLE. WINDS NW 10 KTS.
MON...VFR. WINDS VARIABLE 5 KTS.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR MNZ060-062-065>070-
     073>077-082>085-091>093.

WI...NONE.
&&

$$

UPDATE...JPC
SHORT TERM...BORGHOFF
LONG TERM...BORGHOFF
AVIATION...JPC





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