Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 191830
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
130 PM CDT FRI SEP 19 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 355 AM CDT FRI SEP 19 2014

THE RAIN THAT WE`VE BEEN TALKING ABOUT ALL WEEK IS FINALLY ON OUR
DOORSTEP...HOWEVER...STRONG WARM ADVECTION WILL ACT TO CAP THE
ATMOSPHERE TODAY AND KEEP DEEP MOIST CONVECTION AT A MINIMUM UNTIL
THIS EVENING ACROSS PORTIONS OF SOUTHERN MN AND WI. THETA-E
ADVECTION IS GOING STRONG IN THE DAKOTAS EARLY THIS MORNING AND
THE RESULT IS A HEALTHY BATCH OF SHOWERS AND THUNDERSTORMS THAT
CONTINUE TO SLOW CREEP EAST WITH TIME. MODEST MUCAPE AND GOOD MID-
LEVEL LAPSE RATES HAVE LEAD TO A COUPLE STRONGER CORES IN THE ABR
FORECAST AREA AND EVEN A LATE NIGHT SEVERE THUNDERSTORM WARNING
FOR ONE PARTICULARLY STRONG ELEVATED THUNDERSTORM. WE THINK THE
SOUTHERN EXTENT OF THESE SHOWERS /ROUGHLY GETTYSBURG-BOWDLE/ WILL
ALSO REPRESENT THE LATITUDINAL SOUTHERN EXTENT IN MN LATE THIS
MORNING AND EARLY AFTERNOON IN WESTERN WI. THEREFORE...NEARLY ALL
OF THE SHOWERS AND EMBEDDED THUNDER SHOULD BE WELL NORTH OF
I-94...CLOSER TO THE UPPER JET AND COOLER MID LEVEL TEMPS. THERE
SHOULD STILL BE PLENTY OF CLOUD COVER...BUT WE REALLY DON`T EXPECT
MUCH IN THE WAY OF RAIN BEFORE 00Z.

AS THE COLD FRONT APPROACHES...THE SHORT RANGE GUIDANCE AND
EXTRAPOLATION OF CURRENT TRENDS SUGGEST WE SHOULD BUILD IN A
TONGUE OF MODEST MLCAPE /800-1500 J/KG/ BETWEEN 21-03Z ACROSS
SOUTHERN MN. THIS INSTABILITY WILL COINCIDE WITH INCREASING
WESTERLY 0-6KM SHEAR VECTORS BY 00Z. THE TEMPERATURE GRADIENT
ACROSS THE ADVANCING COLD FRONT IS NOT VERY GOOD...SO THERE SHOULD
BE LITTLE IN THE WAY OF A FRONTAL CIRCULATION TO HELP INITIATE
CONVECTION. THERE WILL BE MECHANICAL LIFTING ALONG THE FRONT AND
EASTWARD ADVANCING 20-50M 12-HR FALLS WITH THE SHORTWAVE. WE
DEFINITELY THINK THERE IS ENOUGH SUPPORT FOR SCATTERED
THUNDERSTORM DEVELOPMENT...BUT CONFIDENCE IS STILL NOT HIGH THAT
WIDESPREAD OR NUMEROUS STORMS WILL BREAK OUT ALONG THE FRONT. THIS
MORNING`S CAM GUIDANCE SHOWS MORE WIDESPREAD THUNDERSTORM ACTIVITY
AS THE FORCING EXITING THE FORECAST AREA. THIS WOULD SUGGEST
BETTER STORM COVERAGE IN EASTERN IA...SOUTHEAST MN AND SW WI.

THERE REMAINS A MARGINAL HAIL AND WIND THREAT ACROSS SOUTHERN MN
THIS EVENING. SYNTHETIC REFLECTIVITY OF THE CAMS SUGGEST MULTI-
CELL AND/OR LINEAR STORM STRUCTURE FROM 02-06Z ALONG THE
SOUTHERN AND EASTERN FRINGES OF THE FORECAST AREA. GIVEN THE
STRONG WESTERLY FLOW ALOFT...IT`S POSSIBLE A COUPLE OF THESE
STORMS WILL GET STRONG ENOUGH CORES TO TRANSFER SOME OF THIS
MOMENTUM DOWN TO THE GROUND. THE 24-HR CIPS /VALID AT 20.00Z/
ANALOGS FROM THE 19.00Z NAM SUGGEST 30-40% OF AT LEAST ONE SEVERE
REPORT WITH THE TOP ANALOGS FAVORING MARGINALLY SEVERE HAIL IN
WESTERN MN AND THE DAKOTAS...AND MORE WIND REPORTS IN SOUTHERN MN
AND IA. THIS MAKES SENSE BASED ON THE EXPECTED EVOLUTION OF
CONVECTION TODAY. AS MENTIONED ABOVE...WE ALREADY SAW A NICE
ELEVATED IN SD THIS MORNING...SO THAT MATCHES THE CIPS SIGNAL FOR
HAIL OUT WEST. ALL THAT SAID...WOULD DOUBT WE NEED A WATCH TODAY
LOCALLY...BUT WOULDN`T BE TOTALLY SURPRISED TO SEE A WARNING OR
TWO COME OUT OF THIS OFFICE LATER ON THIS EVENING.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 355 AM CDT FRI SEP 19 2014

SATURDAY...THE LONGWAVE TROUGH AXIS WILL PASS THRU THE UPR MISS
RIVER VALLEY SAT MRNG...PUSHING ALONG A SFC CDFNT THRU THE REGION.
MEAGER UPR LEVEL SUPPORT FOR TSTMS BUT THERE MAY WELL BE SOME
LINGERING SHWRS ALONG AND IMMEDIATELY POST-FRONT SHORTLY AFTER
DAYBREAK AS MOISTURE WILL STILL BE FAIRLY DEEP WITH POCKETS OF PVA
INVOF THE CDFNT. ONCE THIS TROUGH AXIS PUSHES THRU...A SHORT BREAK
IN THE ACTION IS EXPECTED THRU MIDDAY BUT THIS IS AHEAD OF A
RAPIDLY-DROPPING SHORTWAVE TROF AXIS FROM CENTRAL CANADA. WITHIN
NW FLOW ALOFT...A CUTOFF LOW ALOFT WILL DEVOLVE INTO AN OPEN WAVE
BUT NOT BEFORE ARRIVING WITH A POST-FRONTAL SFC TROUGH AND
CONTINUED DEEP MOISTURE OVER THE AREA SAT AFTN. DECENT DIVERGENCE
ALOFT WITH WEAK-MODERATE SFC CONVERGENCE LOOKS TO SPARK OFF SOME
ISOLD-SCATTERED SHOWERS SAT AFTN AND EVE FOR NE AND E PORTIONS OF
THE WFO MPX CWFA. THE UPR LEVEL FEATURE WILL DRIVE INTO SRN-ERN WI
SAT NIGHT...ENDING ANY FURTHER CONCERN FOR PRECIP AND HELPING DEEP
DRY NW FLOW TO TAKE HOLD.

SUNDAY THROUGH TUESDAY...A LARGE WRN CONUS RIDGE WILL BUILD
FURTHER SUNDAY AND SPREAD ACRS THE ROCKIES GOING INTO MONDAY WHILE
AN UPR LVL LOW IS SUPPRESSED ON THE WRN FRINGES OF THE RIDGE OVER
CA/NV. THE UPR RIDGE WILL ALLOW COOLER/DRIER CANADIAN SFC HIGH
PRES TO DROP INTO THE NRN-CENTRAL PLAINS SUN...SPREADING EWD MON
INTO THE UPR-MID MISS RIVER VALLEY REGION AND THE OHIO VALLEY
REGION. THE SFC HIGH PRES AND RIDGE ALOFT PATTERN WILL SLOWLY
SHIFT E ACRS THE REGION MON INTO TUE...KEEPING THE AREA WITH
SEASONABLE TEMPERATURES AND NO PRECIP. HOWEVER...THE UPR LVL LOW
OVER THE WRN STATES WILL SLOWLY SHIFT EWD BEHIND THE UPR RIDGE...
BECOMING A SHORTWAVE TROUGH OVER THE N-CENTRAL STATES BY MIDDAY
TUE. ITS SLOW WWD PROGRESS SPELLS NO PRECIP EXPECTED DURING THE
FIRST FEW DAYS OF NEXT WEEK.

WEDNESDAY THROUGH THURSDAY...THE AFOREMENTIONED SHORTWAVE TROUGH
NOW EXPECTED TO TRAVERSE THE NRN STATES DURG THE MIDDLE OF NEXT
WEEK MEANS A PATTERN CHANGE COMPARED TO THE PERSISTENT RIDGING AT
THE SFC AND ALOFT ORIGINALLY EXPECTED THE FAST FEW DAYS. IN TERMS
OF SENSIBLE WX...DESPITE WEAK SFC SUPPORT...FLOW ALOFT WILL SHAKE
THE ATMOS UP ENOUGH SUCH THAT ISOLD TO SCATTERED SHOWERS AND A FEW
TSTMS CAN BE EXPECTED ACRS THE AREA WED INTO THU. NOT LOOKING FOR
A LOT OF COVERAGE NOR QPF ATTM. TEMPERATURES WILL GENERALLY RUN
WITHIN A FEW DEGREES OF NORMAL.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1252 PM CDT FRI SEP 19 2014

ALL SHORT TERM GUIDANCE HAS BEEN PERSISTENT WITH ANY TSRA ACTIVITY
REMAINING SE OF ALL TERMINALS THIS EVENING...SO REMOVED ANY
REMAINING VC MENTIONS WITH THE 18Z TAFS. MEANS ONLY CONCERN IS THE
EVOLUTION OF THE MVFR CIGS THIS AFTERNOON. THESE CIGS HAVE BEEN
RAPIDLY ERODING AWAY FROM THE SOUTH...AND THE RAP LOOKS TO HAVE A
GOOD HANDEL ON HOW THEY ARE ERODING AWAY...SO FOLLOWED IT TO TIME
CIG IMPROVEMENTS IN TAFS. MAY SEE MVFR CIGS TRY TO REFORM THIS
EVENING AS THE PREFRONTAL MOISTURE POOL MOVES INTO WI...BUT THE
HRRR ALONG WITH THE SREF ARE NOT VERY AGGRESSIVE WITH BUILDING
LOWER CIGS BACK IN UNTIL THE DEEPER MOISTURE MOVES OFF TO THE EAST
OF EAU...SO JUST WENT WITH A SHORT WINDOW OF MVFR CIGS...SIMILAR
TO WHAT THE HRRR HAS. WILL LOOSE GUSTY WINDS THIS EVENING AS THEY
VEER OVER TO THE WNW OVERNIGHT. PRECIP IS BEGINNING TO LOOK
LIKELY SATURDAY AFTERNOON...BUT TIMING AFTER 18Z MAKES THEM A
PROBLEM FOR THE 00Z TAF FORECASTER TO FIGURE OUT.

KMSP...
MAY SEE OCCASIONAL MVFR CIGS THROUGH 20Z AS MOISTURE WORKS IN FROM
THE WEST. HOWEVER...AS THESE CLOUDS ARRIVE...THEY ARE BREAKING UP
PRETTY FAST FROM THE SOUTH. AT ANY RATE...WITH THE FIELD
OPERATING ON THE 12S...THERE REALLY IS NOT MUCH OF AN
OPERATIONS IMPACT DIFFERNCE BETWEEN AN 025 AND AN 040 FOR THE CIG.
CONFIDENCE IS HIGH THAT THERE WILL BE NO THUNDER THIS EVENING AT
MSP GIVEN THE STRENGTH OF THE CAPPING INVERSION...WITH IT NOT
LOOKING TO BREAK DOWN UNTIL THE FRONT IS WELL SE OF THE FIELD.
CONFIDENCE IS MUCH HIGHER IN SEEING SHRA/TSRA SAT AFTERNOON. DEBATED
PUTTING IN A -SHRA WITH THE 20/2200 GROUP...BUT AT 28 HOURS
OUT...WE HAVE PLENTY OF TIME TO WORK THAT INTO THE TAF WHEN.

/OUTLOOK FOR KMSP/
SUN...VFR. WINDS NW 10-15 KTS.
MON...VFR. WINDS W 5-10 KTS.
TUE...VFR. WINDS SE 5-10 KTS.

&&

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

$$

SHORT TERM...CLF
LONG TERM...JPC
AVIATION...MPG






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