Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 230555
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1155 PM CST THU JAN 22 2015

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 335 PM CST THU JAN 22 2015

MAIN ISSUE IS THE POTENTIAL FOR VERY LIGHT FREEZING RAIN FRIDAY
MORNING. OTHERWISE THE PATCHWORK OF STRATUS WILL BE GRADUALLY
ERODING LATE THIS AFTERNOON AND EVENING.

WEAK TROUGH APPROACHES IN NORTHWEST FLOW TONIGHT...WITH BEST LIFT
FOR THE FORECAST AREA ARRIVING IN CENTRAL MN AROUND 12Z. WARM
ADVECTION AHEAD OF THE TROUGH WILL RESULT IN TEMPS ALOFT RISING TO
5C AROUND 900MB. THERE WILL BE SOME SLIGHT WARMING AT THE SURFACE
BUT NOT VERY MUCH...AND SURFACE TEMPS SHOULD BE IN THE MID 20S TO
30 DEGREES OR SO THROUGH 12Z-15Z...JUST AS SOME PRECIP DEVELOPS.
PROFILES SUGGEST FREEZING RAIN WILL BE THE MAIN THREAT... BUT
AMOUNTS SHOULD BE VERY LIGHT. MAYBE A BIT OF SLEET TOO BUT MOSTLY
FREEZING RAIN. THERE LOOKS TO BE ABOUT 3000-4000 OF SOMEWHAT DRY
AIR FOR THE PRECIP TO OVERCOME... AND THE PRECIP DURATION SHOULD
BE SHORT ENOUGH AND THESE ARE THE MAIN REASONS FOR THE LIGHT
AMOUNTS. GREATEST POTENTIAL WILL BE IN EAST CENTRAL MN INTO WISC
FRIDAY 12Z-18Z. IF IT TURNS OUT THERE IS MORE MOISTURE THAN
THIS...AN ADVISORY MAY BE NEEDED...BUT THERE ARE ENOUGH
UNCERTAINTIES TO ISSUE ONE AT THIS TIME.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 309 PM CST THU JAN 22 2015

BY FRIDAY NIGHT...THE TROUGH AXIS WILL BE THROUGH OUR AREA...AND
WINDS WILL HAVE TURNED NORTHWEST BY THE EVENING HOURS. ADDITIONAL
LOW LEVEL CLOUDINESS WILL OVERTAKE THE EASTERN HALF OF THE AREA
THROUGH THE NIGHT...WITH WESTERN MN HAVING MORE DRY AIR PRESENT IN
THE LOW LEVELS. ON SATURDAY MORNING...AN INITIAL SUBTLE WAVE AHEAD
OF OUR MAIN CLIPPER SYSTEM THAT IS EXPECTED SATURDAY NIGHT THROUGH
SUNDAY. HOWEVER...THERE IS ESSENTIALLY NO FORCING AT THIS TIME FRAME
AND WHILE LOW LEVEL SATURATION IS FORECAST IN THE MODEL
SOUNDINGS...AT THIS TIME EXPECTATIONS REMAIN GENERALLY FOR LOW CLOUD
COVER.

OUR MAIN CONCERN IN THE LONG RANGE FORECAST IS ON SATURDAY NIGHT
THROUGH SUNDAY AS A STRONG CLIPPER SYSTEM DIVES SOUTH TOWARD OUR
AREA. THERE IS MUCH TO BE SORTED OUT WITH THIS SYSTEM AT THIS POINT.
THE GFS HAS SHIFTED THE MAIN PRECIP AXIS TO THE EAST...AND HAS THE
HEAVIEST PRECIP AXIS RUNNING FROM THE ARROWHEAD TOWARD MILWAUKEE.
THIS SOLUTION WOULD SIDE SWIPE OUR AREA WITH LIGHT SNOW.  THE 12Z
NAM AND THE GEM SHIFTED EAST AS WELL SO CONFIDENCE HAS SLIGHTLY
INCREASED IN A MORE EASTERLY SOLUTION. THE PROBLEM CONFIDENCE WISE
IS THE ECMWF. IT IS HOLDING FIRM AS A WESTERN OUTLIER AND BRINGS THE
HEAVIEST PRECIP DIRECTLY THROUGH OUR CWA. TAKING A LOOK AT THE MID
AND UPPER LEVELS...THE ECMWF HAS A MUCH STRONGER 500MB TROUGH THAT
BECOMES A CLOSED LOW AS IT MOVES THROUGH OUR AREA. THE GFS ON THE
OTHER HAND HAS A FLATTER WAVE THAT DOES NOT CLOSE OFF AT 500MB AND
IS SLOWER.  THE NAM TENDS TO AGREE MORE WITH GFS SOLUTION WHICH IS
REFLECTED IN THE SIMILARITIES OF THE PRECIP FIELD. TAKING A LOOK AT
THE SREF PLUMES SHOWS A LARGE AMOUNT OF SPREAD IN THE VARIOUS
MEMBERS AS WELL.

SO...I DID NOT GET TOO AGGRESSIVE IN REDUCING POPS BASED ON THE
CONSENSUS OF AN EASTERN SHIFT IN MOST OF THE GUIDANCE EXPECT THE
ECMWF. EVEN WITH THE GUIDANCE THAT AGREES ON THE EASTWARD
SHIFT...TIMING DIFFERENCES REMAIN.  BUT THE MAIN HESITATION I HAD
WAS HOW MUCH TO TRIM THE POPS...ESPECIALLY IN WESTERN MN...DUE TO
THE WESTERN SOLUTION OF THE ECMWF.  THE ECMWF HAS BEEN FAIRLY
CONSISTENT...SO I`D LIKE TO SEE THE GFS/NAM/GEM KEEP SHOWING THIS
EASTERLY SOLUTION FOR A FEW MORE RUNS BEFORE GETTING AGGRESSIVE WITH
THE FORECAST. ITS STILL POSSIBLE FOR THE GFS/NAM/GEM CLUSTER TO
START MOVING THE WAY OF THE ECMWF AT THIS STAGE SO THE POINT
IS...EXPECT THIS FORECAST TO BE CHANGED/TWEAKED/FINE TUNED AS
CONFIDENCE IN THE GUIDANCE INCREASES.

BEYOND THE WEEKEND...BOTH THE EC/GFS INDICATE A WEAK CLIPPER MOVING
THROUGH AGAIN ON MONDAY-TUESDAY TIMEFRAME.  THE MAIN DIFFERENCES
THERE ARE TIMING...BUT A LIGHT SNOWFALL EVENT IS POSSIBLE DURING
THAT PERIOD.

AS FAR AS TEMPERATURES ARE CONCERNED...RELATIVELY WARM CONDITIONS
WILL PERSIST AS THE WESTERN RIDGE HOLDS STRONG AND WE REMAIN ALONG
THE UPPER JET EARLY NEXT WEEK. THE WESTERN RIDGE IS FORECAST TO
PUSH THE JET NORTHEAST OF US WEDNESDAY...AND ALLOW EVEN WARMER
TEMPERATURES TO MOVE TOWARD OUR AREA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1142 PM CST THU JAN 22 2015

VFR TONIGHT...WITH A BAND OF LIGHT FREEZING RAIN OR SLEET COMING
THROUGH BETWEEN 12-18Z THIS MORNING...FOLLOWED BY MVFR CEILINGS IN
THE AFTERNOON AND EVENING. THE PRECIP SHOULD BE LIGHT AND AFFECT
AREAS PRIMARILY NEAR AND NORTH OF THE I-94 CORRIDOR.
UNFORTUNATELY...THAT MEANS MOST TAF SITES /BESIDES KAXN AND KRWF/
HAVE A 1-2 HOUR WINDOW WHERE LIGHT SLEET OR LIGHT FREEZING RAIN IS
POSSIBLE. TEMPS ARE EXPECTED TO GET ABOVE FREEZING BY THE LATE
MORNING AND EARLY AFTERNOON. SO...ANY SLICK SPOTS ON RUNWAYS
SHOULD MELT THIS AFTERNOON. THE MVFR CEILINGS SHOULD ARRIVE BEHIND
THE PRECIP FOR THE 2ND HALF OF THE TAF PERIOD.

KMSP...

WE`RE NOT 100% CONFIDENT IN FREEZING RAIN OR SLEET AT THE
AIRPORT...BUT IF IT MISSES KMSP...IT WILL NOT BE BY MUCH. WE THINK
THE CHANCE IS HIGH ENOUGH TO INCLUDE THE FREEZING PRECIP IN THE
TAF AT THIS POINT. THIS PRECIP...HOWEVER...SHOULD COME AFTER THE
HIGHER TRAFFIC THIS MORNING. THERE WILL DEFINITELY BE MORE STUFF
SHOWING UP ON RADAR TO THE NORTH AND EAST OF THE AIRPORT. KMSP
WILL BE ON THE SOUTHERN END OF THE PRECIP.

/OUTLOOK FOR KMSP/
SATURDAY...VFR. WIND W 5-10 KTS.
SUNDAY...MVFR WITH -SN/IFR POSSIBLE. WIND NW 10G20 KTS.
MONDAY...VFR. WIND SW 5-10 KTS.

&&

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

$$

SHORT TERM...TDK
LONG TERM...SPD
AVIATION...CLF



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