Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 142350 AAA
AFDMPX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
650 PM CDT SUN SEP 14 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 246 PM CDT SUN SEP 14 2014

ALTHOUGH NOWHERE NEAR AS INTERESTING ON SATELLITE AS HURRICANE ODILE
IN THE ERN PAC...WATER VAPOR IMAGERY WITH RAP H5 ANALYSIS DOES SHOW
A STRONG WAVE CURRENTLY WORKING SOUTH ACROSS MANITOBA. THIS WAVE
WILL DIVE SE ACROSS NODAK AND SRN MN TONIGHT AND ACROSS CENTRAL WI
MONDAY. THIS IS A PRETTY POTENT WAVE...WITH THE NAM SHOWING THE 1.5
PV SFC /APPROXIMATE TROPOPAUSE LEVEL/ GETTING DOWN TO H5. BESIDE THE
PV ADVECTION OUT AHEAD OF THE WAVE...A FAIRLY STRONG BAND OF FGEN
WILL BE SETTING UP ACROSS SRN MN IN THE H7-H6 LAYER.
HOWEVER...CONCURRENT WITH THIS FORCING IN THE H7-H6 LAYER IS A VERY
DRY LAYER OF AIR BETWEEN H8 AND H7 THAT RAP SOUNDINGS SHOW NOW BEING
IN PLACE ACROSS THE AREA. MAJORITY OF SHORT TERM MODELS /BOTH CAMS
AND NON-CAMS/ SHOW THIS DEFORMATION BAND SETTING UP FROM RWF TO THE
SRN TWIN CITIES METRO AND OVER TO EAU. ALTHOUGH WE HAVE THAT DRY AIR
TO WORK WITH...FORCING LOOKS TO BE AROUND LONG ENOUGH TO ALLOW LIGHT
RAIN TO FALL ALONG THE LINE MENTIONED ABOVE. MAY SEE RAIN FOR
SEVERAL HOURS TONIGHT...BUT WILL BE A STRUGGLE TO EVEN GET TO A
TENTH OF AN INCH. WHAT THIS DRY AIR WILL DO IS RESULT IN A VERY
TIGHT PRECIP GRADIENT...WITH POP FORECAST AS OF 3 PM HAVING NEAR 50
POPS DOWN TOWARD LAKEVILLE...WITH NEAR ZERO BY THE TIME YOU GET TO
ANOKA.

AFTER 6Z...A STRONGER BURST OF RAIN LOOKS TO COME INTO SW MN AND
TRACK ACROSS I-90 THROUGH 12Z AND THIS IS ASSOCIATED WITH THE PV
FEATURE MOVING THROUGH. THIS AREA OF PRECIP LOOKS TO BE A BIT MORE
EFFICIENT AT PRODUCING RAIN...SO WENT WITH AN ECMWF/GFS/HPC QPF
BLEND...WHICH RESULTED ABOUT A QUARTER INCH OF RAIN FORECAST BETWEEN
MKT AND THE IOWA BORDER TONIGHT ALONG WITH CATEGORICAL POPS.

FOR TEMPERATURES...DID BOOST LOWS SOME ACROSS SRN MN...WHERE CLOUDS
WILL LIMIT THE AMOUNT OF COOLING...BUT VERY LITTLE CHANGE WAS MADE
TO THE FORECAST TOMORROW...AS SKIES LOOK TO CLEAR OUT IN THE
MORNING...WITH A BEAUTIFUL EARLY FALL DAY ENSUING THEREAFTER WITH
HIGHS IN THE UPPER 50S TO MID 60S...CLOSE TO WHAT A BLEND OF THE
BIAS CORRECTED RAW MODEL GUIDANCE GIVES YOU.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 246 PM CDT SUN SEP 14 2014

A SURFACE HIGH BUILDS IN ACROSS THE FORECAST AREA ON MONDAY AS THE
RAIN AND CLOUD COVER MOVE OUT DURING THE AFTERNOON. A DRY AND COOL
ATMOSPHERIC COLUMN IS EXPECTED TUESDAY THROUGH THURSDAY. TUESDAY
COULD STILL BE QUITE COOL AS MN/WI REMAIN ON THE BACK SIDE OF AN
850MB COLD POCKET STRETCHING EASTWARD TOWARD THE GREAT LAKES.
THERE IS A WEAK SURFACE TROUGH AND INSTABILITY POOLING ALONG A
MOISTURE AXIS STRETCHING FROM THE SOUTHERN PLAINS INTO NORTH
CENTRAL SD TUESDAY/TUESDAY NIGHT...BUT THERE DOESN`T SEEM TO BE
MUCH CONVERGENCE AT THIS TIME AND THE BOUNDARY WOULD REMAIN WELL
SOUTHWEST OF THE AREA ANYWAY. SO...ZERO POPS IT IS TUESDAY AND
WEDNESDAY. THERE IS 925-850MB WARM ADVECTION ON WEDNESDAY AND
THURSDAY...SO THERE COULD BE A LITTLE MORE WARMING THAN WHAT IS
CURRENTLY IN THE FORECAST. WHILE MONDAY AND TUESDAY SHOULD FEATURE
PLENTY OF 60S DURING THE AFTERNOON...THERE IS THE POTENTIAL FOR
LOW 70S IN MN WEDNESDAY AND THURSDAY AFTERNOON. IT ALSO LOOKS LIKE
OVERNIGHT LOWS IN THE COMING WEEK SHOULD BE WELL ABOVE THE
FREEZING MARK...SO THERE IS VERY LITTLE THREAT OF MORNING FROST
THIS COMING WEEK.

THE NEXT CHANCE FOR PRECIP AFTER MONDAY WILL HAVE TO WAIT UNTIL AT
LEAST FRIDAY WHEN BOTH THE 14.12Z GFS/ECMWF DEPICT LIGHT QPF ACROSS
THE FORECAST AREA. THE MODELS DON`T REALLY SHOW MUCH MOISTENING BELOW
700MB BEFORE SHORTWAVE ENERGY MAKES IT INTO THE EASTERN HALF OF
MN...SO MUCH OF THE FORECAST AREA MIGHT END UP WITH VERY LIGHT RAIN
OR VIRGA DURING THE DAY ON FRIDAY /OR NOTHING/.
NONETHELESS...THERE IS GOOD LOW LEVEL SOUTHWEST FLOW AND
TEMPERATURE ADVECTION DURING THE DAY WITH A MODEST INCREASE IN
INSTABILITY...ESPECIALLY IN WESTERN AND SOUTHERN MN. THE TIMING OF
THE WAVE THROUGH THE DAY ON FRIDAY AND INTO SATURDAY IS STILL
UNCERTAIN. THE 12Z ECMWF IS FASTER THAN THE GFS...AND THE GFS ALSO
DEVELOPS A WEAK SECONDARY LOW NEAR THE COLD FRONT AND SATURDAY.
THIS WOULD PROLONG THE PRECIP WELL INTO THE WEEKEND...HOWEVER...THE
LAST 4-5 RUNS OF THE GFS HAVE REALLY LACKED CONSISTENCY. WE ARE
CARRYING CHANCE POPS FOR SHOWERS WITH EMBEDDED THUNDER FOR NOW
WITH THAT THE IDEA THAT A BROKEN BAND OF SHOWERS WILL SWING
THROUGH WITH THE COLD FRONT FRIDAY NIGHT OR SATURDAY MORNING. IF
THERE IS A LESSON TO BE LEARNED OVER THE PAST COUPLE MONTHS...IT`S
THAT THE HEAVIER SHOWERS AND MORE ROBUST THUNDERSTORMS WILL END UP
SOUTH OF THE FORECAST AREA IN IOWA AND PORTIONS OF IL AND SOUTHERN
WI...WHERE THE HIGHEST INSTABILITY IS FORECAST TO BE LOCATED.
STILL SOME TIME TO WORK THIS LATE WEEK SYSTEM OUT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 638 PM CDT SUN SEP 14 2014

A NARROW STRIPE OF VIRGA CURRENTLY EXTENDS EASTWARD ACROSS SRN MN.
AS THE LOWER ATMOSPHERE MOISTENS AND THE BEST FORCING ARRIVES
LATER THIS EVENING...RAIN WILL EXPAND FROM RWF EASTWARD TO RGK AND
SOUTH ALTHOUGH PERIODS OF LIGHT RAIN COULD ALSO DRIFT OVER MSP
FROM TIME TO TIME. REGARDLESS...VFR CONDITIONS AND LIGHT WINDS
EXPECTED THROUGH MONDAY.

KMSP...BEST RAIN CHANCES APPEAR TO BE FROM 03Z-09Z...ALTHOUGH IT
MAY TAKE A BIT LONGER TO ARRIVE GIVEN RADAR TRENDS.

/OUTLOOK FOR KMSP/
TUE...VFR. WINDS SW AT 10 KTS.
WED...VFR. WINDS SSE AT 5 KTS.
THU...VFR. WINDS SE AT 10 KTS.

&&

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

$$

SHORT TERM...MPG
LONG TERM...CLF
AVIATION...BORGHOFF









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