Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 171931
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
231 PM CDT SUN AUG 17 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 142 PM CDT SUN AUG 17 2014

TWO ROUNDS OF THUNDERSTORMS EXPECTED OVER THE NEXT 24 HOURS. THE
FIRST IS THIS AFTERNOON AND THE SECOND IS EXPECTED TOMORROW
MORNING IN MN AND AFTERNOON IN WI.

A NEARLY STATIONARY BOUNDARY IS ROUGHLY BISECTING THE FORECAST
AREA THIS AFTERNOON WITH DEWPOINTS IN THE MID TO UPPER 50S IN THE
FAR NORTHERN FORECAST AREA /CENTRAL MN AND NORTHWEST WI/ AND
LOWER 70 DEWPOINTS ACROSS SOUTH. ALONG AND SOUTH OF THE FRONT
THERE IS A PRONOUNCED INSTABILITY GRADIENT WITH SBCAPE VALUES
RANGING FROM 0-3000J/KG OVER THE SPAN OF 40-60 MILES. THE
SIGNIFICANT INCREASE IN SBCAPE WAS AIDED BY A COUPLE HOURS OF
SUNSHINE THIS AFTERNOON AND MOISTURE POOLING NEAR THE FRONT. THE
SHOWERS THIS AFTERNOON ARE STARTING TO UTILIZE THE LARGE CAPE
VALUES AND ARE NOW PRODUCING A FEW LIGHTNING STRIKES. THE 1830Z
LAPS SOUNDING NOW HAS A FREEZING LEVEL OF 15KFT AND PWAT VALUES OF
1.75"...PROVIDING A GREAT ATMOSPHERE FOR WARM RAIN PROCESSES AND
HIGH RAIN RATES FOR RELATIVELY SMALL SHOWERS. WE EXPECT THESE
INTENSE-SMALL SHOWERS TO CONTINUE MOVING EAST ACROSS EASTERN
MN...WITH A SLOW DIMINISHING TREND NEAR SUNSET.

WE INCREASED POPS AND KEPT THE MENTION OF HEAVY RAIN IN THE
FORECAST TOMORROW FROM 09-21Z...WITH THE EXPECTATION OF ANOTHER
COMPLEX OF THUNDERSTORMS EXPECTED TO MOVE OUT OF SOUTH DAKOTA AND
INTO WESTERN MN BEFORE SUNRISE. WE USED A BLEND OF THE 17.12Z GEM-
REG AND NEW AND IMPROVED 17.12Z NAM...WHICH ARE IN VERY GOOD
AGREEMENT WITH ONE ANOTHER. EARLY LOOK AT SOME THE CAM GUIDANCE
FOR TOMORROW IS ALSO TRENDING THIS WAY. THE UPPER LOW WEST OF LAKE
WINNIPEG AND TRAILING TROUGH AND STRONG PV ADVECTION SHOULD BE THE
FOCUS FOR THIS COMPLEX LATE TONIGHT AND TOMORROW. HARD TO IMAGINE THIS
SECOND COMPLEX MISSING THE FORECAST TOMORROW GIVEN HOW CLOSE WE
ARE NOW.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 413 AM CDT SUN AUG 17 2014

PRIMARY CONCERN REVOLVES AROUND STORMS MONDAY AND MONDAY NIGHT.
MODELS ARE IN DECENT AGREEMENT REGARDING SHORT WAVE DRIVING ESE ACROSS
SOUTHERN MN MONDAY MORNING AND INTO WESTERN WISCONSIN LATE MONDAY
AFTERNOON... WITH MAIN TROUGH AXIS ASSOCIATED WITH UPPER LOW
ARRIVING IN WESTERN MN MONDAY AFTERNOON. OF THESE TWO...THE
GREATEST AMOUNT OF MOISTURE THROUGHOUT THE COLUMN WILL BE ON
MONDAY WITH PRECIPITABLE WATER TOTALS GENERALLY AROUND 1.5 TO 1.6
INCHES. INTERESTINGLY...THE HIGH RES MODELS DO NOT PRODUCE TOO
MUCH PRECIP WITH THIS FIRST SURGE MONDAY MORNING AND MIDDAY...BUT
ARE MUCH MORE AGGRESSIVE WITH PRECIP LATER MONDAY AFTERNOON INTO
THE EVENING. MEANWHILE THE DETERMINISTIC ECMWF/NAM/GEM SHOWS MOST
PRECIP ON MONDAY MORNING AND MIDDAY. THERE IS STILL SOME TIME TO
SORT THIS OUT...SO HAVE MAINTAINED MID TO LIKELY POPS AT THIS
STAGE. TEND TO THINK THE GFS/GEM/NAM SOLUTION WILL BE MORE CORRECT
SINCE THE THERMODYNAMICS IN THE HIGH RES MODELS MAY WELL BE MORE
AFFECTED BY THE STORMS TODAY AND TONIGHT.

OTHERWISE...WEAK SHORT WAVE AROUND THE BACK SIDE OF THE UPPER LOW
COULD BRING SOME SHOWERS AND A FEW STORMS TO EASTERN MN AND
WESTERN WISC LATE MONDAY NIGHT AND TUESDAY.

WEAK RIDGING MOVES OVER THE AREA TUESDAY NIGHT AND WEDNESDAY...AND
THIS WILL BE THE ONLY TIME DURING THE WEEK WHEN DRY WEATHER IS IN
THE FORECAST. BROAD SW FLOW ARRIVES WEDNESDAY NIGHT AS LARGE
WESTERN TROUGH DEVELOPS AND AFFECTS MN/WI THROUGH NEXT WEEKEND.
THE ECMWF DOES NOT EXTEND THE WESTERN TROUGH AS FAR SOUTH AS THE
GFS... BUT EVEN IT STILL PICKS UP A COUPLE OF EMBEDDED SHORT WAVES
FROM THE SOUTHWEST AND BRINGS THEM TOWARD THE UPPER MIDWEST. GFS
DEFINITELY SHOWS THIS. THERE ARE TIMING DIFFERENCES WITH THESE...
BUT THE BOTTOM LINE IS LATE THIS WEEK WILL FEATURE A GOOD CHANCE
OF VERY WARM AND HUMID WEATHER ALONG WITH HEAVY RAIN ASSOCIATED
WITH A TROPICAL CONNECTION WITH PRECIPITABLE WATER VALUES
EXCEEDING TWO INCHES.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 142 PM CDT SUN AUG 17 2014

A LOT GOING ON OVER THE NEXT 24 HOURS. IN THE NEXT 6
HOURS...IFR/MVFR CEILINGS WILL CONTINUE TO SLOWLY LIFT...BUT
SHOULD NOT CLEAR ALL OF MN/WI BEFORE SUNSET. SO...WE LIKELY SEE
STRATUS AND LIGHT FOG SPREAD BACK OUT ACROSS THE AREA TONIGHT.
THIS MEANS IFR/MVFR SHOULD ONCE AGAIN BE EXPECTED AT THE TAF SITES
BY MONDAY MORNING /ESPECIALLY ACROSS EAST CENTRAL MN AND NORTHWEST
WI/. THERE HAS BEEN IMPROVEMENT IN SOUTHERN MN. THE OTHER
CHALLENGE IS TIMING THE COUPLE ROUNDS OF THUNDERSTORMS TODAY AND
TOMORROW. THE FIRST ROUND CURRENTLY ON RADAR IN THE FORM OF A SW-
NE ORIENTATED BROKEN BAND WILL CONTINUE IT`S SLOW CRAWL TO THE
EAST. THE SHOWERS ARE LARGELY PAST KAXN/KSTC/KRWF...BUT KMSP AND
KRNH ARE THE NEXT UP TO SEE SHOWERS AND/OR THUNDER. THE SECOND
ROUND ARRIVES EARLY TOMORROW MORNING IN WESTERN MN AND SHOULD
MARCH ACROSS THE AREA DURING THE MORNING AND INTO THE EARLY
AFTERNOON.

KMSP...

SHOWERS ARE NOW WITHIN THE 5-MILE RADIUS OF THE AIRPORT. AT THIS
TIME...THERE IS NOTHING STRONG OR SEVERE...BUT WE COULD STILL SEE
INTENSIFICATION OVER THE NEXT COUPLE HOURS. EXPECT SOME UPDATES AS
WE CONTINUE TO MONITOR THE SHOWER TRENDS. WE THINK THE AIRPORT
COULD SEE A COUPLE GOOD DOWNPOURS BETWEEN NOW AND SUNSET.

/OUTLOOK FOR KMSP/
MON...VFR/MVFR WITH TSRA LIKELY. WINDS S 5-10 KTS.
TUE...VFR/MVFR WITH TSRA POSSIBLE. WINDS NW 5-10 KTS.
WED...VFR. WIND VRB AT 5KTS.

&&

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

$$

SHORT TERM...CLF
LONG TERM...TDK
AVIATION...CLF






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