Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 010255
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
955 PM CDT TUE SEP 30 2014

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY EVENING)
ISSUED AT 954 PM CDT TUE SEP 30 2014

MOST LOCATIONS SHOULD SEE MEASURABLE PRECIP OVER THE NEXT 24
HOURS...ESPECIALLY IN WESTERN WI DURING THE DAY ON WEDNESDAY.

EARLY AFTERNOON VISIBLE SATELLITE IMAGERY TOGETHER WITH SURFACE
OBS AND RAP13 MSL PRESSURE ANALYSIS SHOWED A COMPACT SURFACE
CYCLONE ACROSS CENTRAL SOUTH DAKOTA...WITH THE MASS FIELD
RESPONSE/COUNTER CLOCKWISE WINDS EXTENDING AS FAR EAST AS CENTRAL
WISCONSIN. A WEAKENING LINE OF SHOWERS ARCED DOWN THE LEADING EDGE
OF THE UPPER LEVEL PV GRADIENT ALONG A LINE FROM CENTRAL NORTH
DAKOTA DOWN THROUGH EASTERN NEBRASKA. OVER THE NEXT 12 HOURS THIS
PRECIP WILL CONTINUE TO DISSIPATE AS IT LIFTS INTO MINNESOTA. THE
MOST INTENSE PRECIP WILL SPLIT THE FORECAST AREA WITH THE SOUTHERN
PART MOVING ACROSS IOWA IN THE MORE FAVORABLE THERMODYNAMIC
REGION...AND THE NORTHERN PART CONTINUING ACROSS THE DAKOTAS
CLOSER TO THE BETTER DYNAMICS.

LATER TONIGHT A LOW AMPLIFIED SHORTWAVE TROUGH WILL SWING ACROSS
THE UPPER MIDWEST WHICH WILL INDUCE ISENTROPIC LIFT IN THE
300-305K LAYER. THIS LAYER IS COINCIDENT WITH THE TOP OF THE
STOUT LOW LEVEL INVERSION...SO THEREFORE EXPECTING PRIMARILY
ELEVATED RAIN SHOWERS. FORECAST SOUNDINGS SHOW SOME ELEVATED
CAPE...SO CONTINUED TO INCLUDE ISOLATED THUNDER IN THE WEATHER
GRIDS. ALSO DECREASED HIGH TEMPS ON WEDNESDAY FOR WESTERN WI GIVEN
THE CLOUDS AND RAIN FORECAST.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 311 PM CDT TUE SEP 30 2014

THE PHASING OF THE NORTHERN AND SOUTHERN JET STREAMS WILL BE
CRITICAL IN TERMS OF HOW WIDESPREAD THE PRECIPITATION BECOMES
WEDNESDAY NIGHT THRU FRIDAY MORNING...ESPECIALLY ACROSS WESTERN
AND SOUTHWEST MN.

SEVERAL STRONG SHRTWV/S MOVING INTO THE PACIFIC NW ALONG WITH A
POWERFUL 100-120 KT JET WILL CRAVE OUT A SIGNIFICANT STORM SYSTEM
BY THE END OF THE WEEK ACROSS THE GREAT LAKES REGION. DEPENDING
UPON HOW THE PHASING OF THE SOUTHERN AND NORTHERN JET AND
CONVECTION ACROSS IOWA WEDNESDAY NIGHT...WILL DETERMINE WHETHER
WESTERN MN REMAINS DRY OR BECOMES MUCH WETTER. UPPER LEVEL JET
STRUCTURE REMAINS FAVORABLE FOR A WIDESPREAD RAINFALL EVENT ACROSS
IOWA WEDNESDAY NIGHT...AND TAKING THIS AREA NORTHEAST ACROSS THE
EASTERN 1/4 OF MPX CWA. ALTHOUGH TIME DETAILS REMAIN UNCLEAR...THE
BULK OF THE WET WEATHER WILL OCCUR THURSDAY AFTN/EVENING ACROSS
THE EASTERN 1/4 OF MPX CWA. AS FAR WEST THIS AREA OF PRECIPITATION
EXPANDS IS DEPENDENT ON THE LOCATION OF THE SFC LOW AND HOW MUCH
MOISTURE ADVECTION IS HELD TO THE SE ACROSS EASTERN IA/NORTHERN
IL. THERE HAS BEEN SOME SLOWING OF THE OVERALL PATTERN ONCE THIS
SYSTEM TAKES SHAPE THURSDAY NIGHT. BUT...INCONSISTENCIES AND THE
FACT THE SFC LOW REMAINS MOSTLY SE OF MPX CWA...WILL LEAN TOWARD
ONLY CHC POPS IN THE WEST...WITH LIKELY/CATEGORICAL IN THE FAR
EAST. PRECIPITABLE WATER VALUES DUE INCREASE ENOUGH FOR HEAVY
RAINFALL...ESPECIALLY IF TSRA CAN DEVELOP ABOVE THE BOUNDARY
LAYER. BUT THE BEST CHC/S OF WIDESPREAD ONE INCH RAINFALL TOTALS
WILL BE S/SE OF OUR REGION.

ONCE THIS SYSTEM BEGINS TO ORGANIZE AND DEEPEN ACROSS THE NORTHERN
GREAT LAKES...STRONG WEST/NW WINDS WILL DEVELOP...LEADING TO
WIND CHILL VALUES IN THE 20S/30S FOR FRIDAY EVENING.

PAST FRIDAY...THE OVERALL PATTERN REMAINS FAVORABLE FOR
ISOLD/SCATTERED SHRA AS THE MEAN FLOW BECOMES NW AND EMBEDDED
SHRTWV/S RIDE SE ALONG THIS NW FLOW PATTERN. TIMING AND HOW
WIDESPREAD THIS ACTIVITY BECOMES REMAINS UNCLEAR. THE CLEAR PART
OF THE EXTENDED PERIOD WILL BE COOLER THAN NORMAL FOR EARLY
OCTOBER. ONE OF THE MAIN FACTORS OF THIS COOLER THAN NORMAL
PATTERN IS THE DEVELOPMENT OF THE NEGATIVE /-AO/ ARCTIC
OSCILLATION WHERE THE MEDIUM RANGE MODELS HAVE BEEN ADVERTISING.
IF THIS BECOMES DOMINATE...THE FIRST/SECOND WEEK OF OCTOBER WILL
BE UNSEASONABLY COOL. IN ADDITION TO THE -AO...THE MEAN UPPER
PATTERN IS FORECASTING A STRONG UPPER RIDGE DEVELOPING ACROSS
GREENLAND WHICH LEADS TO A BLOCKING PATTERN AND THE CONTINUATION
OF THE NW FLOW ALOFT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 717 PM CDT TUE SEP 30 2014

DEEP LOW PRES CENTER OVER THE DAKOTAS WILL CONTINUE TO MOVE NWD
INTO CENTRAL CANADA THRU TMRW. IN ADVANCE OF THIS LOW...A WEAK SFC
CDFNT WILL APPROACH WITH SCT SHWRS/ISOLD TSTMS ALONG IT. VERY WEAK
SUPPORT FOR THIS BAND OF PRECIP EARLY ON IN THE TAF PERIOD WILL
MEAN THAT LITTLE TO NO PRECIP CAN BE EXPECTED AT THE TAF SITES
THRU THE EARLY MRNG HOURS. HOWEVER...CONDITIONS ARE AGAIN GOOD FOR
LOW STRATUS DEVELOPMENT OVERNIGHT THRU MUCH OF THE DAY TMRW.
ANOTHER ROUND OF RAIN LOOKS TO DEVELOP AROUND DAYBREAK AND SHORTLY
THEREAFTER...LASTING INTO THE EARLY AFTN HRS. THIS SECOND ROUND OF
PRECIP LOOKS HEAVIER SO HAVE INDICATED SOME VSBY RESTRICTION DUE
TO THE HEAVIER AND STEADIER EXPECTED PRECIP...WHILE ALSO SLIGHTLY
RAISING CEILINGS. ONCE THE PRECIP ENDS...THE LOW CEILINGS WILL BE
DIFFICULT TO ERODE SO WOULD NOT BE SURPRISED IF TAF SITES REMAINED
NO BETTER THAN MVFR THRU LATE AFTN AND POSSIBLY THRU 00Z TMRW EVE.
BREEZY SE WINDS THIS EVE WILL SETTLE DOWN TO CLOSE TO 10 KT...THEN
BECOME BREEZY AGAIN TMRW AFTN.

KMSP...CONDS TO GRADUALLY DETERIORATE THIS EVE THRU OVERNIGHT AS
MVFR CIGS DEVELOP THEN DROP TO IFR LOW STRATUS CEILINGS. NOT
LOOKING FOR FOG WITH WINDS BEING ELEVATED. MAIN BATCH OF RAIN
LOOKS TO HOLD OFF UNTIL AROUND DAYBREAK TMRW...POSSIBLY IMPACTING
THE MRNG RUSH WITH MVFR VSBY...AND POSSIBLY LOWER THAN WHAT IS
CURRENTLY ADVERTISED. RAIN TO LINGER THRU MIDDAY BUT EVEN AFTER
ENDING...IFR CONDS LIKELY TO REMAIN IN PLACE THRU LATE DAY BEFORE
EVENING IMPROVEMENT.

/OUTLOOK FOR KMSP/
FRI...MAINLY MVFR WITH CHC -SHRA. WINDS WNW 20G30 KTS.
SAT...VFR. WINDS NW 10-15 KTS.
SUN...VFR. SLGT CHC -SHRA. WINDS NW 10 KTS.

&&

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

$$

SHORT TERM...JRB
LONG TERM...JLT
AVIATION...JPC





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