Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 180046
AFDMPX

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

.UPDATE...
FOR 00Z AVIATION DISCUSSION BELOW

&&

.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 NIGHT THROUGH SUNDAY)
ISSUED AT 407 PM CDT SUN AUG 17 2014

THE BACK EDGE OF THE AFOREMENTIONED COMPLEX WILL BE HEADED EAST
ACROSS ERN MN AND WRN WI AT THE BEGINNING OF THE PERIOD...WITH THE
POSSIBILITY OF RESIDUAL SHOWERS CONTINUING THROUGH MUCH OF THE
NIGHT...ESPECIALLY OVER WI. KEPT POPS IN THE CATEGORICAL RANGE
DURING THE EVENING WITH A GRADUAL TAPERING OVERNIGHT AS THE BEST
CHANCES SHIFT EAST. THE TROUGH WILL BECOME MORE NEGATIVELY TILTED
TUESDAY OVER THE WESTERN GREAT LAKES. DIURNAL SHOWER DEVELOPMENT
APPEARS LIKELY WITHIN A SOMEWHAT MOIST CYCLONIC FLOW EXTENDING
WEST INTO MN AND NORTHEASTERN IA.

SKIES WILL CLEAR TUESDAY NIGHT WITH THE SURFACE RIDGE AXIS ALIGNED
OVER THE EASTERN CWA. EXPECTING AREAS OR WIDESPREAD FOG TO DEVELOP
FROM CENTRAL TO SERN MN EASTWARD INTO WI. THERE MAY BE ENOUGH
RETURN FLOW DEVELOPING LATE TO PRECLUDE FOG FROM BECOMING AS
WIDESPREAD ACROSS SRN AND WRN MN.

MID LEVEL RIDGING WILL BUILD NORTHEASTWARD INTO THE MID MISSOURI
VALLEY DURING THE MIDDLE OF THE WEEK. IT WON/T QUITE REACH THE
CWA...SO THIS REGION OF THE COUNTRY IS LIKELY TO REMAIN UNSETTLED
THROUGHOUT MUCH OF THIS WEEK. THE FIRST WAVE TO RIDE NORTH OF THE
RIDGE WILL ARRIVE LATE WEDNESDAY THRU THURSDAY MORNING. INTRODUCED
LIKELY POPS ACROSS SRN MN WEDNESDAY NIGHT WHERE THE BEST JUXTAPOSITION
OF FORCING AND INSTABILITY WILL RESIDE. THE RESULTANT MCS WILL
DEVELOP OVER SODAK WEDNESDAY AFTERNOON AND TRACK EASTWARD INTO WI
BY MIDDAY THURSDAY.

THE RIDGE WILL RETREAT SOME FRIDAY AS A TROUGH BEGIN TO EJECT
EASTWARD FROM THE PACIFIC NORTHWEST. THE SOUTHWEST FLOW WILL SEND
ANOTHER WAVE INTO THE REGION FRIDAY AND SATURDAY WHEN POPS RETURN
INTO THE HIGH CHC RANGE.

BEYOND SATURDAY...MODELS DIVERGE SIGNIFICANTLY FROM EACH OTHER
AND FROM RUN TO RUN. YESTERDAY THEY SHOWED A STOUT HEAT WAVE OVER
THE MID/UPPER MISSISSIPPI VALLEY AND TODAY THEY SHOW A TROUGH WITH
SUB 560DM HEIGHTS. IF THE REST OF THE SUMMER IS ANY GUIDE...I
WOULD FAVOR THE LATTER SOLUTION FOR NOW.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 747 PM CDT SUN AUG 17 2014

IN THE WAKE OF THE FIRST WAVE OF SHOWERS AND
THUNDERSTORMS...EXPECT A BRIEF RESPITE TO ENSUE BEFORE THE NEXT
ROUND ARRIVES OVERNIGHT. PREFER THE RAP 0.5KM AGL CONDENSATIONAL
PRESSURE DEFICITS AS A GUIDE FOR CIGS IN THE NEAR-TERM. THINK IFR
CIGS WILL PLAGUE ALL BUT KRWF THIS EVE...WITH ALL SITES
EXPERIENCING MVFR CIGS AT A MINIMUM THROUGH MOST OF THE PERIOD.
OCCASIONAL SHOWERS/TS AS THE TROUGH PASSES ACROSS
TOMORROW. HARD TO TIME FOR A PARTICULAR SITE AT THIS POINT.
EAST/SOUTHEAST WINDS AHEAD OF THE WARM FRONT...THEN SHIFT TO
WEST/SOUTHWEST FOR TOMORROW. SPEEDS AROUND OR BELOW 10 KTS THROUGH
THE PERIOD.

KMSP...
CIGS ARE LOOKING MORE AND MORE PESSIMISTIC FOR THE OVERNIGHT
HOURS. PROBABILITIES ARE INCREASING THAT AT LEAST A BKN IFR LEVEL
CIG WILL PERSIST THROUGH THE OVERNIGHT HOURS...THEN LOW-END MVFR
CIGS ON MONDAY. AFTER SHRA/TS ENDS BY 03Z...SHOULD BE A BREAK IN
PRECIP UNTIL MONDAY MORNING. THEN SCATTERED SHRA/TS THROUGHOUT THE
DAY. WIND SPEEDS STAY AOB 10 KTS THROUGH THE PERIOD BUT SHIFT FROM
EAST/SOUTHEAST TO SOUTHWEST ON MONDAY MORNING.

/OUTLOOK FOR KMSP/

TUE...VFR. CHC MVFR WITH AFTERNOON TSRA. WINDS NW 5-10 KTS.
WED...VFR. WIND VRB AT 5KTS.
THU...VFR. CHC MVFR WITH TSRA. WINDS SSE 5-10 KTS.

&&

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

$$


SHORT TERM...CLF
LONG TERM...BORGHOFF
AVIATION...LS






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