Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 141132
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
532 AM CST SUN DEC 14 2014

.UPDATE...
ISSUED AT 519 AM CST SUN DEC 14 2014

UPDATED TO INCLUDE 12Z AVIATION DISCUSSION BELOW.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 332 AM CST SUN DEC 14 2014

CURRENT CONDITIONS SYNOPSIS...
THE LARGE SCALE PATTERN CONTINUES TO SLOWLY EVOLVE... BUT THE
SENSIBLE WEATHER ACROSS THE FORECAST AREA REMAINS THE SAME... WITH
WIDESPREAD LOW CLOUDS... FOG OF VARYING DENSITY... AND AREAS OF
DRIZZLE. SOUTHERLY BOUNDARY LAYER FLOW AHEAD OF LOW PRESSURE IN THE
LEE OF THE ROCKIES CONTINUES TO FEED WARM MOIST AIR NORTH INTO THE
REGION... WHICH IS WORKING TO KEEP CONDITIONS AS DESCRIBED GIVEN THE
SATURATED CONDITIONS... WITH THE COLD/FROZEN GROUND HELPING THE
PROCESS. WATER VAPOR IMAGERY SHOWS THE TROUGH/RIDGE/TROUGH PATTERN
OVER THE CONUS INTO THE ATLANTIC... WITH THE MAIN SOUTHERN STREAM
SHORTWAVE OVER THE SOUTHWEST JUST STARTING TO MAKE THE TURN
NORTHEAST. THERE IS SOME DEEP LAYER MOISTURE EVIDENT IN THE WATER
VAPOR IMAGERY... AND AS THIS EVENTUALLY WORKS INTO THE AREA LATER
TODAY AND TONIGHT WE/LL LIKELY SEE A BIT MORE IN THE WAY OF LIGHT
RAIN VS DRIZZLE.

FORECAST ITEM/S/ OF CONCERN...
NOTHING ESPECIALLY HAZARDOUS IN THE SHORT TERM... WITH DRIZZLE/FOG
BEING THE PRIMARY ISSUES... BUT WITH TEMPERATURES STAYING ABOVE
FREEZING THROUGH TONIGHT ANY ISSUES WITH MIXED PCPN SHOULD GENERALLY
HOLD OFF UNTIL MONDAY. SOMEWHAT HEAVIER PCPN SHOULD START TO DEVELOP
LATER TONIGHT... BUT PROFILES FROM SURFACE THROUGH ALOFT LOOK TO BE
ABOVE FREEZING ACROSS ALL BUT THE VERY FAR WEST JUST PRIOR TO 12Z.

MODEL DISCUSSION/PREFERENCES...
THE RAP... NAM... GFS... ECMWF... AND ASSORTED CAMS ARE ALL IN
FAIRLY GOOD AGREEMENT ON THE OVERALL PROGRESSION OF THINGS TODAY AND
TONIGHT... AND LINE UP WITH THE GOING FORECAST. SO... KEPT THINGS
CLOSE TO THE GOING FORECAST... AND GENERALLY BLENDED WITH A
RAP/NAM/GFS CONSENSUS FOR ANY ADJUSTMENTS TO THAT.

SENSIBLE WEATHER EXPECTATIONS...
AREAS OF FOG AND DRIZZLE LOOK TO PERSIST TODAY AS WE SEE CONTINUED
WARM MOIST SOUTHERLY FLOW ACROSS THE AREA... BENEATH THE STRONG
INVERSION. THE INVERSION WILL ERODE TONIGHT AS DEEP LAYER FORCING
WORKS IN AHEAD OF THE UPPER SHORTWAVE. THIS SHOULD HELP TO MITIGATE
THE LOW CLOUDS/DRIZZLE... BUT WILL LEAD TO MORE IN THE WAY OF STEADY
LIGHT RAIN AS THE NIGHT PROGRESSES. SOME MIXED PCPN COULD WORK INTO
THE VERY FAR WEST PRIOR TO DAYBREAK... WITH LIGHT SLEET OR FREEZING
RAIN BEING POSSIBLE.

DETAILED DISCUSSION FOR ITEM/S/ OF CONCERN...
WEAK ISENTROPIC LIFT APPARENT IN THE 290-295K LAYER LOOKS TO PERSIST
THROUGH THE DAY TODAY... WITH CONDENSATION PRESSURE DEFICITS AOB
10MB. THIS SHOULD PROVIDE ENOUGH LIFT TO KEEP AREAS OF DRIZZLE OR
VERY LIGHT RAIN GOING ACROSS MUCH OF THE AREA TODAY. WE/LL START TO
SEE SOME MID-LEVEL FORCING WORK INTO THE AREA TONIGHT ALONG WITH
SOME UPPER DIVERGENCE AS THE JET STRENGTHENS TO OUR NORTH. THE LARGE
SCALE LIFT WILL WORK TO ERODE THE PERSISTENT INVERSION WE/VE HAD IN
PLACE FOR SEVERAL DAYS... AND AS THE PROFILE SATURATES THROUGH ITS
DEPTH OVER THE COURSE OF THE NIGHT WE/LL EVENTUALLY SEE A TRANSITION
FROM AREAS OF DRIZZLE TO MORE IN THE WAY OF OF A STEADY LIGHT
RAIN... PARTICULARLY OVER THE NORTHERN AND WESTERN PORTION OF THE
AREA.

FORECAST CONFIDENCE/UNCERTAINTY...
CONFIDENCE IN CONTINUED CLOUDY SKIES AND AREAS OF FOG/DRIZZLE
THROUGH TODAY IS HIGH. CONFIDENCE IS ALSO HIGH IN SEEING WELL ABOVE
NORMAL TEMPERATURES... WITH HIGHS EXCEEDING 50 OVER MUCH OF THE AREA
SOUTH OF I-94. CONFIDENCE IS MODERATE IN A TRANSITION TO STEADIER
LIGHT RAIN VS DRIZZLE OCCURRING TONIGHT... AND CONFIDENCE IS LOW ON
TIMING/TYPE OF ANY MIXED PCPN OVER THE FAR WEST LATE TONIGHT.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 332 AM CST SUN DEC 14 2014

BY MONDAY MORNING...THE NEARLY STACKED LOW PRESSURE SYSTEM WILL BE
MOVING NORTHEAST ACROSS EASTERN KANSAS WITH A LARGE PRECIPITATION
SHIELD TO THE NORTHWEST OF THE LOW IN THE BAROCLINIC ZONE. MODELS
HAVE COME IN TO GOOD AGREEMENT IN THE POSITIONING AND MOVEMENT OF
THE LOW...SO HIGHLY CONFIDENT IN PRECIPITATION ACROSS THE FA
MONDAY AND MONDAY NIGHT AS THE LOW LIFTS THROUGH EASTERN IOWA
TOWARD SOUTHERN LAKE MICHIGAN. THE PRE-EXISTING WARM AIR WILL
OBVIOUSLY MAKE FOR RAIN INITIALLY WITH A POTENTIALLY MESSY
TRANSITION TO SNOW EVENTUALLY. 850MB TEMPS WILL GENERALLY RANGE
FROM +4 NEAR AXN...TO +6 NEAR MSP AND SLIGHTLY WARMERS AREAS EAST
AT 6AM MONDAY. AS THE LOW PUSHES EAST COLD AIR ADVECTION WILL
ENSUE. AN EVALUATION OF MODEL FORECAST SOUNDINGS INDICATES THAT IN
NORTHWEST MN...THERE IS A CONCERN THAT THE SURFACE WILL COOL
FASTER THAN THE 850MB LEVEL...MEANING A PERIOD OF FREEZING RAIN IS
POSSIBLE. AS THE COLD AIR ADVECTION CONTINUES
SOUTHEAST...SOUNDINGS INDICATE A THE SURFACE WILL REMAIN WARM
SLIGHTLY LONGER...ALLOWING THE 850MB LAYER TO SUFFICIENTLY COOL TO
REALLY LIMIT FREEZING RAIN POTENTIAL...SO EXPECT RAIN TO
TRANSITION TO SNOW WITH A VERY BRIEF MIX IN BETWEEN FOR THE
EASTERN HALF OF THE FA. THE WESTERN HALF WILL LIKELY SEE THAT
SLIGHTLY LONGER PERIOD OF FREEZING RAIN. FORECASTING SNOW RATIOS
IS A CHALLENGE WITH THIS EVENT AS TIMING OF INCREASING THE RATIOS
WITH THE QPF AS IT WORKS ACROSS THE FA IS CRITICAL IN DETERMINING
EXPECTED AMOUNTS. THE EC AND NAM ARE IN PRETTY GOOD AGREEMENT IN
THE AXIS OF PRECIP/SNOW AND THE GFS IS EVER SO SLIGHTLY TO THE
NORTHWEST OF THIS AREA. THE ONSET OF THE MAIN PRECIP WITH THIS
EVENT IS NOW WITHIN RANGE OF THE HI-RES ARW AND NMM...AND THEY DO
INDICATE A DECENT SNOW BAND WORKING ACROSS THE FA MONDAY NIGHT AND
GIVEN MODEL SOUNDINGS...A COUPLE HOURS OF ACCUMULATING SNOW LOOKS
LIKELY OVERNIGHT INTO TUESDAY...SO DID UP SNOWFALL ACCUMULATIONS
GENERALLY IN THE 1-3" RANGE FOR MUCH OF SOUTHERN AND CENTRAL
MN...WITH LESS TO THE EAST. AS THE PREVIOUS DISCUSSION
STATED...TIMING IS KEY IN THE AMOUNTS SO AGAIN...IF PRECIP
SWITCHES TO SNOW MORE QUICKLY THAN CURRENTLY ANTICIPATED...THERE
IS POTENTIAL FOR WIDESPREAD 2-4" AMOUNTS. CONFIDENCE IN TIMING THE
CHANGEOVER IS AVERAGE AT THIS POINT GIVEN MODEST AGREEMENT IN THE
THERMAL PROFILE.

PRECIPITATION WILL END ON TUESDAY AS A SURFACE HIGH BUILDS IN
THROUGH MID WEEK. TEMPERATURES WILL BE MUCH MORE SEASONAL FOR MID-
DECEMBER THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE GFS/EC
INDICATE A SYSTEM MOVING THROUGH THE SOUTHERN CONUS TOWARD THE
WEEKEND...WITH CONTINUED DRY AND SURFACE HIGH PRESSURE LINGERING
FROM THE UPPER MIDWEST THROUGH THE NORTHERN GREAT LAKES.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 519 AM CST SUN DEC 14 2014

WILL CONTINUE TO SEE LITTLE CHANGE IN AVIATION CONDITIONS THROUGH
MOST OF THE PERIOD... WITH LOW CLOUDS AND REDUCED VISIBILITIES
STICKING AROUND ALONG WITH OCCASIONAL DRIZZLE. WE WON/T SEE MARKED
IMPROVEMENT UNTIL THE MOIST SOUTHERLY FLOW ENDS AND WINDS SHIFT
AROUND TO THE WEST AND EVENTUALLY NORTHWEST BEHIND THE FRONT ON
MONDAY. THERE HAS BEEN AND WILL LIKELY CONTINUE TO BE SOME
VARIABILITY IN CEILINGS AND VISIBILITIES AS WEAK DISTURBANCES RIDE
NORTH-NORTHEAST THROUGH THE MEAN FLOW AND WORK TO BRIEFLY MIX OUT
SOME OF THE LOWER CEILINGS AND WORST VISIBILITIES. HOWEVER...
THOSE VARIATIONS LOOK TO BE SHORT-LIVED GIVEN OBSERVED CONDITIONS
UPSTREAM AND GUIDANCE WHICH CONTINUES TO SHOW CONSISTENTLY HIGH
LOW LEVEL RH VALUES AND NO MEANINGFUL CHANGES IN ADVECTION THROUGH
THE PERIOD.

KMSP...IFR AND LIFR CONDITIONS APPEAR LIKELY TO CONTINUE GIVEN
ABUNDANT LOW LEVEL MOISTURE TRAPPED BENEATH THE INVERSION WITH
EXTENSIVE LOW CEILINGS AND VISIBILITIES UPSTREAM. COULD SEE SOME
BRIEF FLUCTUATIONS AND IMPROVEMENT AT TIMES... BUT VERY TOUGH TO
TRY AND PIN DOWN MUCH OF THAT AT THIS POINT IN TIME. WILL REMAIN
PESSIMISTIC OVERALL... WITH AMENDMENTS HANDLING ANY IMPROVEMENT
SHOULD IT START TO SHOW UP.

/OUTLOOK FOR KMSP/
MONDAY AFTERNOON...IFR EXPECTED WITH RAIN CHANGING TO SNOW LATE.
NORTHEAST WIND 10 TO 20 KT BECOMING NORTH.
MONDAY NIGHT...IFR EXPECTED... GIVING WAY TO MVFR. LIGHT SNOW
ENDING. NORTHWEST WIND 10 TO 20 KT.
TUESDAY...MVFR EXPECTED. CHANCE OF LIGHT SNOW EARLY. NORTHWEST
WIND 5 TO 15 KT.
TUESDAY NIGHT...MVFR CEILINGS POSSIBLE. NORTHWEST WIND 10 KT OR LESS.
WEDNESDAY THROUGH ...VFR. NORTHWEST WIND LESS THAN 10 KT BECOMING
VARIABLE LESS THAN 5 KT THURSDAY.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR MNZ041>045-047>053-
     055>063-065>070-075>078-083>085-091>093.

WI...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR WIZ014>016-023>028.

&&

$$

UPDATE...
SHORT TERM...
LONG TERM...SPD
AVIATION...






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