Special Weather Statement, NWS Twin Cities, MN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
750 PM CDT SAT MAY 16 2015

.UPDATE...
ISSUED AT 720 PM CDT SAT MAY 16 2015

UPDATED TO INCLUDE 00Z AVIATION DISCUSSION BELOW.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 351 PM CDT SAT MAY 16 2015

WATER VAPOR IMAGERY THIS AFTERNOON INDICATES A STRONG UPPER LEVEL
CIRCULATION PUSHING EAST THROUGH NORTHERN NEW MEXICO...WITH
CONVECTIVE INITIATION IMMEDIATELY DOWNSTREAM OF THE WAVE ACROSS
THE TEXAS PANHANDLE. MEANWHILE...A WARM FRONT HAS LIFTED INTO
SOUTHERN MN AND DEW POINTS HAVE RISEN WELL INTO THE 60S.
ADDITIONAL THUNDERSTORM DEVELOPMENT ACROSS WESTERN MN INTO EASTERN
SD WILL CONTINUE AS DESTABILIZATION HAS OCCURRED. A SUBTLE WAVE
ADVANCING NORTH WILL HELP INITIATE STORM DEVELOPMENT IN THIS AREA.
EFFECTIVE BULK SHEAR VALUES OF AROUND 30-40 KNOTS MAY PRODUCE
MULTICELL CLUSTERS WITH ISOLATED EMBEDDED SUPERCELLS CAPABLE OF
PRODUCING ISOLATED SEVERE WEATHER ACROSS WESTERN MN THIS EVENING.
EASTERN MN AND WESTERN WI SHOULD GENERALLY REMAIN DRY THROUGH THE
EVENING...BEFORE SCATTERED SHOWERS AND WEAK THUNDERSTORMS MOVE IN
LATE TONIGHT THROUGH SUNDAY MORNING.

ON SUNDAY...THE AFOREMENTIONED UPPER LEVEL SHORTWAVE WILL ADVANCE
NORTH AND A DEEPENING SURFACE LOW WILL ADVANCE FROM KANSAS
NORTHWARD THROUGH NEBRASKA AND EVENTUALLY INTO EASTERN SOUTH
DAKOTA. WITH A MOIST AND UNSTABLE AIRMASS PRESENT...MUCH BETTER
SHEAR AND SURFACE ENERGY WILL COME TOGETHER THROUGH EARLY
AFTERNOON...ESPECIALLY ACROSS EASTERN MN AND WESTERN WI...WHERE
THE SEVERE WEATHER RISK HAS BEEN UPGRADED TO THE ENHANCED
CATEGORY. 0-6KM EFFECTIVE SHEAR APPROACHING 60 KNOTS COMBINED WITH
BETTER SURFACE HEATING ACROSS THIS AREA WILL ALLOW SURFACE BASED
CAPE VALUES OF 1000-2000 J/KG. CONFIDENCE IS RELATIVELY LOW THOUGH
IN THE SEVERE DEVELOPMENT POTENTIAL DUE TO MORNING CONVECTION AND
ITS POSSIBLE AFFECT ON DESTABILIZATION BY EARLY AFTERNOON. GIVEN
SUFFICIENT HEATING THOUGH...EXPECT BY EARLY AFTERNOON THE
POSSIBILITY OF DISCRETE SUPERCELL THUNDERSTORMS INITIATING IN
EASTERN MN AND WESTERN WI WHICH WOULD BE CAPABLE OF PRODUCING
SEVERE HAIL...WIND...AND A FEW TORNADOES.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 351 PM CDT SAT MAY 16 2015

SFC LOW OVER N-CENTRAL MN WILL HAVE ITS PROGRESS SLOWED AS IT
RUNS INTO HIGHER PRES FROM THE N. MEANWHILE...THE DEEP UPR LVL LOW
WILL THEN RUN ATOP THE SFC LOW...MAKING FOR A DEEPLY STACKED LOW
PRES AREA CENTERED OVER NERN MN COME DAYBREAK MON MRNG. THE BULK
OF THE SHWRS/TSTMS WILL BE IN ERN PORTIONS OF THE WFO MPX CWFA BY
SUN EVE...PARTICULARLY ANYTHING OF A STRONG/SEVERE NATURE...
LEAVING MAINLY RESIDUAL SHOWERS AND ISOLD TSTMS IN THE WAKE OF THE
PASSING CDFNT. WHILE THE FRONTAL PRECIP COVERAGE WANES SUN NIGHT
INTO MON...THE DEEP COLD LOW MOVING OVER THE REGION MAY BRING
ADDITIONAL LIGHT RAIN SHOWERS TO NRN-CENTRAL MN AND NWRN WI DURG
THE DAY ON MON. THIS LOW WILL THEN PULL AWAY FROM THE AREA MON
NIGHT INTO TUE...BEING REPLACED BY SFC HIGH PRES THAT WILL REMAIN
IN PLACE TUE THRU FRI...MAKING FOR A PROLONGED DRY PERIOD FOR THE
REGION. HOWEVER...AT THE SAME TIME...THE NW-SE ORIENTATION OF THE
SFC HIGH COMBINED WITH A LONGWAVE TROF SETTING UP OVER ERN NOAM
WILL ALLOW A PERSISTENT PATH OF MUCH COLDER CANADIAN AIR TO TAKE
RESIDENCE OVER THE REGION THRU AT LEAST THE FIRST HALF OF THE
WEEK. THIS POTENT SURGE OF CAA WILL DROP TEMPS NEARLY 30 DEGREES
FROM SUN INTO MON AS HIGHS ON MON WILL RANGE FROM THE LOWER 40S TO
THE LOWER 50S. TEMPERATURES WILL THEN SLOWLY MODERATE THROUGH THE
REST OF THE WEEK...WITH HIGHS RETURNING TO THE UPPER 60S BY THE
END OF THE WEEK. FROST MAY BE A CONCERN ON MON AND TUE NIGHTS AS
LOWS DIP INTO THE LOW/MID 30S ACROSS PARTS OF CENTRAL MN/WI.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 720 PM CDT SAT MAY 16 2015

VERY TRICKY CONVECTIVE FORECAST OVER THE NEXT 24 HOURS SO THERE IS
POTENTIAL FOR FREQUENT UPDATES TO ROUTINE TAFS ALONG WITH
AMENDMENTS. A SFC LOW MOVG FROM SD IN WRN MN OVERNIGHT INTO TMRW
MRNG WILL SHOVE A WMFNT NWD FROM SWRN MN INTO N-CENTRAL MN.
ONGOING CONVECTION CURRENTLY ON KMPX RADAR IS ROUGHLY INDICATIVE
OF THE WMFNT LOCATION...WITH CONVECTION CROSSING OVER THE WMFNT
WITHIN AN ENVIRONMENT FAVORABLE FOR STRONG/SEVERE TSTMS... MAINLY
AFFECTING KRWF-KAXN AND POSSIBLY KSTC OVER THE NEXT 3-4 HRS. THE
LOSS OF DAYTIME HEATING SHOULD MITIGATE FURTHER DEVELOPMENT BUT
ADDITIONAL STORMS FIRING OVER FAR S-SE MN WILL ALSO MOVE NEARLY
DUE N AND MAY IMPACT ERN MN AND WRN WI TAF SITES. SHORT-TERM
MODELS INDICATE THIS CONVECTION WILL ONLY LAST UNTIL ABOUT 04Z OR
SO...GIVE OR TAKE AN HOUR...THEN ANOTHER ROUND OF BETTER COVERAGE
RAIN WILL SPREAD OVER MUCH OF THE AREA OVERNIGHT. WITH ADDITIONAL
HEATING AND INSTABILITY TMRW ALONG WITH AN APCHG UPPER LEVEL
LOW...THE TABLE IS BEING SET FOR A MORE ORGANIZED STRONG/SEVERE
TSTM THREAT MID-TO-LATE AFTN...ALTHOUGH A NARROW BAND OF
CONVECTION IS POSSIBLE MID-TO-LATE MRNG. SO OVERALL...QUITE THE
COMPLICATED PICTURE. CEILINGS ARE EXPECTED TO DROP TO NO LOWER
THAN MID-MVFR RANGE WHILE VSBY MAY HAVE A WIDE VARIANCE DEPENDING
ON POCKETS OF HVY RAIN.

KMSP...AM CONCERNED WITH CONVECTIVE BREAKING OUT WELL S OF MSP
/WHICH IS ALREADY NOTED IN THE OBS WITH THE CB/ ALONG WITH THE
EVER-SO-SLIGHT EWD MOVEMENT OF THE MAIN LINE IN WRN MN. FROM
EITHER SOURCE...A MORE PERSISTENT MENTION OF CB/TS LOOKS MORE
LIKELY FOR MSP OBS AFTER 02Z SO HAVE ADDED THIS MENTION TO THE 00Z
TAF VIA A 02Z-06Z TEMPO GROUP. AM NOT THINKING CEILINGS WILL DROP
BELOW UPPER-END MVFR BUT VSBY MAY BE HIGHLY VARIABLE IF HEAVY RAIN
MOVES OVER THE FIELD. MORE PERSISTENT SHWRS/TSTMS LOOK TO DEVELOP
OVERNIGHT THEN BREAK BY MIDDAY BEFORE ADDITIONAL ROUNDS DEVELOP
TMRW. WILL MONITOR AND AMEND AS NEEDED ALONG WITH KEEP IN TOUCH
WITH MSP OPS.

/OUTLOOK FOR KMSP/
MON...MVFR CIGS. SCT -SHRA. WINDS NW AT 15-25 KTS.
TUE...MVFR CIGS EARLY. WINDS N AT 10 KTS.
WED...VFR. WINDS NNE 5 KTS.

&&

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

UPDATE...JPC
SHORT TERM...SPD
LONG TERM...JPC/CLF
AVIATION...JPC

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