Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 281711
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1211 PM CDT THU AUG 28 2014

.UPDATE...
FOR 18Z AVIATION DISCUSSION BELOW

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 340 AM CDT THU AUG 28 2014

THE UPPER LEVEL PV ANOMALY WHICH WILL BRING HEALTHY RAINFALL
TOTALS ACROSS THE UPPER MIDWEST CONTINUES TO TREND SLOWER WITH
TIME. AS A RESULT HAVE DELAYED THE NORTHERN EXTEND OF THE SMALLER
CHANCE POPS...BUT CONTINUED WITH THE HIGHER PROBABILITIES ALONG THE
I-90 CORRIDOR. THE MAIN AREA OF PRECIP SHOULD EXIT THE REGION EARLY
FRIDAY MORNING WHILE ANOTHER AREA DEVELOPS SOUTHWEST ON FRIDAY.

EARLY MORNING WATER VAPOR IMAGERY WITH GFS 28.00 500MB HEIGHTS AND
WINDS SHOWED THE CUTOFF UPPER LEVEL LOW SLOWLY SPINNING EAST
NORTHEAST ACROSS THE CONTINENTAL DIVIDE TO ITS CURRENT LOCATION OVER
THE FOOTHILLS OF CO/WY. AN AREA OF THUNDERSTORMS DEVELOPED AHEAD OF
THIS WAVE IN EASTERN NE...WHERE RADAR ESTIMATED Q2 6HR RAINFALL
TOTALS OF 4-6 INCHES HAD FALLEN ACROSS SOUTH CENTRAL NE. THIS MOIST
TROPICAL AIRMASS WILL OVERSPREAD THE UPPER MIDWEST AS THE SYSTEM
LIFTS NORTHEAST...BUT THESE RAINFALL TOTALS ARE NOT EXPECTED OVER
THE CWA FOR A COUPLE OF REASONS. FIRST OF ALL...THE CUTOFF UPPER
LEVEL WAVE IS SLOWLY FILLING AS THE LATENT HEAT WARMS THE MID
LEVELS. THIS TIES INTO THE SECOND POINT...WHICH IS THE MOIST
ADIABATIC PROFILE ABOVE 750MB IN THE 28.00Z MPX RAOB...WHICH CARRIES
THROUGH TO FRIDAY MORNING IN THE BUFR FORECAST SOUNDINGS. THIS
PROFILE IS BY DEFINITION IS WITHOUT CAPE...SO DEEP CONVECTION AND
HIGH RAINFALL RATES WILL BE UNLIKELY ACROSS MN/WI. WITH THAT
SAID...THE TROPOPAUSE WILL BE AROUND 150MB AND COULD GET A SMALL
AMOUNT OF ELEVATED INSTABILITY SO RAINFALL TOTALS OF 2-3 INCHES ARE
STILL EXPECTED ACROSS SOUTHERN MN...BUT THESE SHOULD FALL OVER
MULTIPLE HOURS WHICH WILL MITIGATE THE RUNOFF AND FLOODING THREAT.
TRIMMED THE BACK EDGE OF POPS EARLY FRIDAY TO BETTER MATCH UP WITH
THE HIRES MODELS BUT KEPT THEM ACROSS THE SOUTH AND EASTERN CWA.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 340 AM CDT THU AUG 28 2014

A PROGRESSIVE LONG WAVE PATTERN WILL CONTINUE THROUGH THE EXTENDED
WITH A COUPLE TROUGHS MOVING THROUGH THE UPPER MISSISSIPPI RIVER
VALLEY IN THE COMING WEEK.

THE FRONTAL SYSTEM RESPONSIBLE FOR THE AFOREMENTIONED RAIN TODAY
AND TONIGHT WILL STILL BE CLOSE TO THE FORECAST AREA ON FRIDAY
/LIKELY LOCATED ALONG THE EASTERN EDGE OF THE FORECAST AREA
FRIDAY MORNING/. THERE IS GOOD MODEL CONSENSUS AMONG THE 28.00Z
NAM/GFS/ECMWF IN THE PLACEMENT OF THE SURFACE FRONTS...ALTHOUGH
THERE STILL REMAINS SOME DISAGREEMENT ON THE EVOLUTION OF THE WEAK
SURFACE LOW/TROUGH INTO SATURDAY MORNING. THE RESULTING QPF
PATTERNS ARE ALSO A LITTLE DIFFERENT...BUT THERE SEEMS TO BE
ENOUGH AGREEMENT AND CONSISTENCY IN RUNS TO CARRY "LIKELY" WORDING
FOR PRECIP IN EASTERN MN AND WESTERN WI ON FRIDAY. THE HIGHEST
TOTALS ON FRIDAY SHOULD BE IN CENTRAL WI...UNLESS THE WHOLE SYSTEM
SLOWS ANYMORE /IT HAS ALREADY DONE SO OVER THE PAST COUPLE DAYS/.

PREVIOUS DISCUSSIONS HAVE MENTIONED AND THE CURRENT FORECAST
HIGHLIGHTS THE EXPECTED STRONG COLD FRONT AND TROUGH EXPECTED TO
PASS THROUGH THE FORECAST AREA SUNDAY NIGHT. THIS SYSTEM HAS A
MUCH STRONGER UPPER JET AND THE TROUGH EVEN TRANSITIONS FROM
POSITIVE TO NEGATIVE TILT AS IT SWINGS THROUGH THE PLAINS AND
FORECAST AREA. UNLIKE THE SYSTEM EXPECTED TODAY...THE SUNDAY NIGHT
EVENT WILL HAVE DECENT MUCAPE OF 1000-2000J/KG AND THERE WILL ALSO
BE GOOD CONVERGENCE AND TEMPERATURE ADVECTION ALONG/BEHIND THE
FRONT. WE ALREADY HAVE 60-75% RAIN IN THE FORECAST AND THE
GUIDANCE SUGGESTS WE COULD EVEN GO HIGHER. BEYOND THE WEEKEND...THE
TROUGH FLATTENS OUT AND WE`RE LEFT WITH A RELATIVELY DRY AND COOL
WESTERLY FLWO PATTERN THROUGH AT LEAST MID WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1212 PM CDT THU AUG 28 2014

RAIN WILL CONTINUE TO GRADUALLY OVERSPREAD THE AREA THIS
AFTERNOON...ALTHOUGH CIG/VSBY DEGRADATION TO THE MVFR/IFR CATEGORY
WILL LAG PRECIPITATION ONSET AT SITES BY A FEW HOURS. EXPECT TO
SEE NOTABLE CIG REDUCTION BETWEEN 00Z AND 06Z...WITH PREVALENT IFR
CIGS OVERNIGHT ALONG WITH AREAS OF DRIZZLE AND MVFR VSBYS. LOW
CLOUDS LINGER ON FRIDAY...WITH SHOWERS AND ISOLATED THUNDERSTORMS
REMAINING POSSIBLE...ESPECIALLY FOR EASTERN SITES /KMSP-KRNH-
KEAU/. EAST/SOUTHEAST WINDS AT 7-14KTS TODAY VEER TO
SOUTH/SOUTHWEST IN DIRECTION ON FRIDAY.

KMSP... PRECIP SHOULD SNEAK INTO KMSP BETWEEN 19Z AND
20Z...ALTHOUGH THE INTENSITY WILL BE LIGHT AND THE THUNDER
POTENTIAL IS LOW. CIGS DEGRADE TO MVFR THIS EVE THEN IFR BY 06Z.
PERIODS OF PRECIPITATION PERSIST THROUGH FRIDAY.

/OUTLOOK FOR KMSP/
SAT...VFR. WIND NNE AT 5-10 KTS.
SUN...VFR WITH MVFR/TSRA LATE. WINDS SSE AT 10KTS.
MON...VFR WITH MVFR/TSRA EARLY. WINDS W 10-15KTS.

&&

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

$$


SHORT TERM...JRB
LONG TERM...CLF
AVIATION...LS





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