Area Forecast Discussion
Issued by NWS Twin Cities, MN

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KMPX 272016
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
316 PM CDT MON JUL 27 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 314 PM CDT MON JUL 27 2015

FAIRLY CHALLENGING FORECAST THROUGH TUESDAY EVENING. A SEASONABLY
POTENT SHORTWAVE WILL LIFT NORTHWEST ALONG THE INTERNATIONAL
BORDER OVERNIGHT INTO TUESDAY. THIS WILL LEAD TO A 990MB SURFACE
LOW THAT WILL TRACK FROM CENTRAL NORTH DAKOTA TO NORTHERN ONTARIO.
A TRAILING COLD FRONT WILL MOVE EASTWARD ACROSS THE REGION LATE
TONIGHT INTO TUESDAY. GIVEN THE STRENGTH AND MAGNITUDE OF THIS
SYSTEM...TOGETHER WITH THE CONVECTION WHICH WILL INEVITABLY
DEVELOP...HAVE DIFFICULTY TRYING TO PIN DOWN THE LOCATION AND
TIMING OF PRECIPITATION. IN ADDITION...HIRES MODELS ARE SLOW TO
CATCH ON TO THE MCS ACROSS IOWA...WHICH DECREASES THE CONFIDENCE
IN THEIR SOLUTIONS GOING FORWARD.

THERE ARE TWO FEATURES THAT ARE DIFFICULT TO TRACK. THE FIRST TRYING
TO DETERMINE WHERE THE CONVECTION WILL DEVELOP LATER TONIGHT. GIVEN
THE STORMS ACROSS IOWA...ONE WOULD THINK THAT THE OVERNIGHT
CONVECTION...WHICH WILL BE DRIVEN BY THE LOW LEVEL JET...WILL BE
FARTHER SOUTH THAN THE NUMERICAL GUIDANCE SUGGESTS...SO HAVE PUSHED
BACK THE TIMING AND DECREASED POPS OVER THE NORTHERN HALF OF THE
CWA. MEANWHILE...THE CONVECTION WHICH DEVELOPS ALONG THE COLD FRONT
SHOULD BECOME ORIENTED INTO A NORTH/SOUTH LINE...AND MOVE EASTWARD
DURING THE EARLY MORNING HOURS. THE CR-NAM NEST ILLUSTRATES THIS
SCENARIO NICELY. CAPE AND SHEAR SHOULD BE SUFFICIENT FOR A FEW
STRONG STORMS ESPECIALLY AS THE LOW LEVEL JET STRENGTHENS
OVERNIGHT...CAUSING DAMAGING WIND TO BE THE PRIMARY THREAT EARLY
TUESDAY MORNING.

IN RETROSPECT...THE LAST FEW NOCTURNAL/EARLY MORNING SYSTEMS HAVE
CAUSED THE PARENT BOUNDARY TO MOVE THROUGH THE REGION FASTER THAN
ANTICIPATED...AND THE NEXT DAYS CONVECTIVE THREAT HAS BEEN FORECAST
TOO FAR WEST. THIS IS IMPORTANT FOR TUESDAYS CONVECTION...SINCE THE
SYNOPTIC COLD FRONT WILL BE THE FOCUS FOR CONVECTIVE INITIATION.
HOWEVER...THE DIFFERENCE BETWEEN THIS SYSTEM AND THE PAST FEW IS THE
NOTABLE STRENGTH OF THE UPPER LEVEL WAVE DRIVING THE SURFACE
FEATURES. GIVEN THE UPPER LEVEL FORCING FOR ASCENT...ANOTHER LOW
LEVEL BOUNDARY (AREA OF CONVERGENCE) SHOULD DEVELOP IN THE WAKE OF
THE MORNING CONVECTION...AND THIS COMBINED WITH MID LEVEL LAPSE
RATES OF 7-8 C/KM...TOGETHER WITH INCREASING DEEP LAYER SHEAR SHOULD
SUPPORT SEVERE STORMS TUESDAY AFTERNOON/EVENING. THE EXACT LOCATION
REMAINS UNCERTAIN...BUT AT THIS TIME EXPECT THE BEST THREAT FOR
STORMS TO BE ALONG AND EAST OF A LINE FROM ALERT LEA MN THROUGH RICE
LAKE WI.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 314 PM CDT MON JUL 27 2015

THE LARGE SCALE PATTERN THROUGH THE EXTENDED PERIOD LOOKS TO BE
DOMINATED BY NORTHWEST UPPER FLOW AS THE STRONG SHORTWAVE MOVING
THROUGH OVER THE NEXT 36 HOURS CLOSES OFF OVER HUDSON BAY AND
REMAINS NEARLY STATIONARY THROUGH THE BALANCE OF THE FORECAST
PERIOD. THE 12Z GUIDANCE IS IN FAIRLY GOOD AGREEMENT ON THIS
SCENARIO. OVERALL... THIS RESULTS IN A FAIRLY DRY PATTERN FOR OUR
AREA THROUGH THE PERIOD AS THE MORE SIGNIFICANT
MOISTURE/INSTABILITY WILL BE DISPLACED SOUTH OF THE AREA.

LINGERING STORMS THAT REDEVELOP TOMORROW AFTERNOON SHOULD EXIT THE
EASTERN PORTION OF THE AREA DURING THE EVENING HOURS... WITH MUCH
DRIER AIR WORKING IN OVERNIGHT. DRY NORTHWEST FLOW AND HIGH
PRESSURE SHOULD THEN KEEP THINGS FAIR AND DRY WITH NEAR NORMAL
TEMPERATURES THROUGH FRIDAY. A WEAK SURFACE THROUGH DOES LOOK TO
DROP THROUGH THE AREA LATE THURSDAY/EARLY FRIDAY... BUT GIVEN
MINIMAL MOISTURE RETURN AHEAD OF IT AND MEAGER MID-UPPER LEVEL
SUPPORT... IT LOOKS LIKE IT SHOULD MOVE THROUGH DRY. PCPN CHANCES
RETURN SATURDAY AND SATURDAY NIGHT AS A MORE HEALTHY UPPER WAVE
AND SURFACE FRONT MOVE THROUGH THE REGION. THE GFS AND ECMWF
DIFFER A BIT ON TIMING AND POSITION OF THE UPPER WAVE... WITH THE
ECMWF BRINGING THE UPPER SUPPORT FARTHER SOUTH/EAST THAN THE GFS.
BUT... THE DIFFERENCES DON/T IMPACT THE OVERALL POPS TOO MUCH AT
THIS POINT... WITH CHANCES LOOKING WARRANTED FOR SATURDAY AND
SATURDAY NIGHT THEN DRYING OUT FOR MOST OF THE AREA FOR SUNDAY. WE
COULD SEE PCPN TRY TO WORK BACK NORTH ON MONDAY AS THE BAROCLINIC
ZONE LIFTS NORTHWARD... SO INCLUDED SOME CHANCE POPS FOR THAT
POSSIBILITY. AT THIS POINT... THERE ARE NO SIGNALS THROUGH PERIOD
FROM WEDNESDAY THROUGH MONDAY FOR ANY WIDESPREAD SIGNIFICANT PCPN
OR SEVERE WEATHER ACROSS THE AREA.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1231 PM CDT MON JUL 27 2015

TIMING OF CONVECTION REMAINS ON TRACK FOR LATE TONIGHT...SO DID
NOT MAKE SIGNIFICANT CHANGES TO THE PREVIOUS TAF. MORNING CLOUDS
SHOULD CONTINUE TO BURN OFF BY EARLY AFTERNOON. STORMS SHOULD LIFT
UP FROM THE SOUTHWEST AS THE WARM FRONT MOVES ACROSS THE REGION
TONIGHT. THIS SHOULD EVENTUALLY DEVELOP INTO A NORTH/SOUTH
ORIENTED LINE THAT WILL MOVE EASTWARD ACROSS THE REGION WITHIN THE
10-14Z TIMEFRAME.

KMSP...
THE WARM FRONT CONVECTION IN THE 06-08Z TIMEFRAME SHOULD BE
SOUTHWEST OF KMSP...AND THE MAIN THREAT FOR CONVECTION WILL BE
WITH A NORTH/SOUTH ORIENTED LINE THAT WILL AFFECT THE METRO
AROUND 12Z TUESDAY MORNING. LOW CLOUDS WILL LIKELY DEVELOP IN THE
WAKE OF THIS LINE. COULD SEE SOME THUNDERSTORM REDEVELOPMENT IN
THE AFTERNOON...BUT THIS SHOULD BE EAST OF KMSP. WESTERLY WINDS
WILL DEVELOP LATE TUESDAY EVENING AS THE COLD FRONT PASSES
THROUGH.

/OUTLOOK FOR KMSP/
WED...VFR. WINDS W AT 20G30KT.
THU...VFR. WINDS W AT 10-15 KT.
FRI...VFR. WINDS W AT 5 KT.

&&

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

$$

SHORT TERM...JRB
LONG TERM...99
AVIATION...JRB



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.