Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 241104
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
604 AM CDT SUN AUG 24 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 253 AM CDT SUN AUG 24 2014

1003 MB SFC LOW THIS MORNING WAS LOCATED NEAR BISMARK. ITS WARM
FRONT WAS SURGING NORTH INTO SRN MN...WITH A COLD FRONT BEGINNING
TO TAKE SHAPE AT 3AM ACROSS CENTRAL SODAK THROUGH CENTRAL NEB. AHEAD
OF THIS WARM FRONT...WE HAVE SEEN A CLUSTER OF TSRA COME OUT OF
SODAK AND INTO CENTRAL MN AT THE NOSE OF AN H85 WARM TONGUE...WHICH
IS CHARACTERIZED BY 20-22C TEMPS THAT HAVE ALREADY MOVED INTO SOUTH
CENTRAL MN. THIS ACTIVITY WAS HESITANT TO MOVE EAST EARLIER THIS
EVENING UNTIL IT FINALLY MANAGED TO GENERATE A STRONG ENOUGH COLD
POOL AROUND 6Z TO ADD AN ERLY COMPONENT TO ITS NRLY MOTION. HAD A
SEGMENT OF THE LINE THAT BOWED OUT MOVING ALONG AT 55 MPH...BUT THIS
LINE IS QUICKLY WEAKENING AS IT ENCOUNTERS COOLER/MORE STABLE AIR TO
ITS NORTHEAST. FOR THE REST OF THE MORNING...WE MAY CONTINUE TO SEE
A FEW ISOLATED SHOWERS/STORMS POP UP ON THE NRN EDGE OF THE WARM
TONGUE...BUT WITH MAIN UPPER FORCING GOING INTO NW MN...EXPECT ANY
ADDITIONAL ACTIVITY THIS MORNING TO BE ISOLD/SCT IN NATURE.

FOR THE REST OF TODAY...THERE WILL BE TWO CONCERNS...THUNDERSTORM
REDEVELOPMENT ON THE COLD FRONT AND HOW HIGH WILL HEAT INDICES GET.
ONLY MINOR DIFFERENCES EXIST WITH THE TIMING OF THE FRONT...BUT A
MODEL BLEND BRINGS IT JUST INTO WRN MN BY 18Z...A LITTLE WEST OF
I-35 BY 00Z...AND EXITING THE MPX CWA BY 12Z MON. BY THE
AFTERNOON...TEMPS NEAR 90 COMBINED WITH LOWER 70S DEWPS WILL ALLOW
MLCAPE VALUES TO BUILD TO BETWEEN 3K AND 4K J/KG. HOWEVER...FORECAST
SOUNDINGS ALSO SHOW THE WARM TONGUE AT H85 RESULTING IN A FAIRLY
STOUT CAPPING INVERSION FORMING AS WELL. GENERALLY LIKE THE IDEA OF
THE NMM/ARW/MPX WRFS...WITH STORMS DEVELOPING ALONG THE COLD FRONT
NEAR THE US-71 CORRIDOR AROUND 21Z...AND WORKING EAST WITH THE COLD
FRONT THROUGH THE EVENING. ALTHOUGH SHEAR WILL BE MARGINAL /BULK
SHEAR 30-35 KTS/...THE DEGREE OF INSTABILITY WILL MORE THAN MAKE UP
FOR THE WEAKER SHEAR. SHEAR/INSTABILITY PARAMETERS WOULD INDICATE WE
WILL LIKELY SEE SOME FORM OF SUPERCELLULAR STRUCTURE
INITIALLY...BEFORE STORMS CONGEAL INTO A LINE. HAIL AND WIND WILL
LIKELY BE THE MAIN THREATS...BUT A TORNADO OR TWO CERTAINLY CAN NOT
BE RULED OUT IN THE FIRST COUPLE OF HOURS AFTER STORM INITIATION.
CENTRAL MN CURRENTLY APPEARS TO BE THE MOST FAVORABLE AREA FOR
HAVING A TORNADO THREAT THIS AFTERNOON.

THIS FRONTAL TIMING WILL ALSO PUT A WARM SECTOR WITH H925 TEMPS
INCREASING TO AROUND 25C OVER ERN MN DURING PEAK HEATING.
HOWEVER...DID CUT BACK ON FORECAST HIGHS TODAY BY A DEGREE OR TWO
FOR A COUPLE OF REASONS. ONE...WE WILL AGAIN SPEND MUCH OF THE
MORNING CLEANING LAYERED CLOUD COVER OUT OF THE AREA...AND TWO WITH
DEWPOINTS UP IN THE LOWER 70S...IT OFTEN MAKES IT DIFFICULT TO WARM
TEMPERATURES MUCH BEYOND 90. NOT TO MENTION THIS SUMMER...90 DEGREES
HAS BEEN A TOUGH NUT TO CRACK. GIVEN THE CLOUDY SKIES THIS
MORNING...A NARROW 4 HOUR WINDOW FOR GETTING HEAT INDICES AROUND 100
THIS AFTERNOON...FOLLOWED BY THE PASSAGE OF A COLD FRONT TONIGHT
SIGNALING THE ARRIVAL OF DRIER AIR...DECIDED TO STAY AWAY FROM
ISSUING A HEAT ADVISORY IN A MARGINAL SITUATION. WITH THAT
SAID...HEAT WILL BE MENTIONED IN THE HWO...GRAPHICAST...AND THE
FORECAST READS HIGHS NEAR 90...SO ITS NOT LIKE WE WILL NOT BE
GETTING THE WORD OUT ABOUT THE HEAT IN OTHER WAYS.

FOR TONIGHT...IT WILL BE FAIRLY UNEVENTFUL OUTSIDE OF THE
THUNDERSTORMS WORKING ACROSS WRN WI WITH THE COLD FRONT. THIS
ACTIVITY WILL BE PROGRESSIVE...BUT PWATS PUSHING 2" SHOULD BE ABLE
TO GET 0.5"-1.5" OF RAIN OUT OF MOST LOCATIONS IN WI. FOR WRN
MN...THE NATURAL AIR CONDITIONING WILL BE KICKING IN WITH THE WEST
WINDS BEHIND THE COLD FRONT...WITH DEWPS FALLING BACK INTO THE LOWER
50S AND TEMPS DROPPING INTO THE MID 50S.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 253 AM CDT SUN AUG 24 2014

THE LARGE SCALE PATTERN STILL LOOKS TO BECOME LESS AMPLIFIED FOR
THE LONGER TERM PORTION OF THE FORECAST WITH THE UPPER FLOW
BECOMING FAIRLY ZONAL ACROSS THE CONUS. THERE REMAINS SOME
DISAGREEMENT IN THE DETAILS WITH THE DETERMINISTIC SOLUTIONS OF
THE GFS... ECMWF... AND GEM... WITH THE RESPECTIVE ENSEMBLES
SHOWING AN UNDERSTANDABLE DEGREE OF SPREAD. SO... THERE REMAINS
SOME UNCERTAINTY ON PCPN CHANCES TIED TO SHORTWAVES MOVING THROUGH
THE ZONAL FLOW AS WELL AS CONVECTION FORCED NEAR THE BAROCLINIC
ZONE/FRONTAL BOUNDARY THAT WILL LINGER NEARBY FOR AT LEAST THE
FIRST PART OF THE WEEK. CONTINUED TO STICK CLOSE TO THE GEFS MEAN
IN TERMS OF THE LARGE SCALE MASS FIELDS... WHILE BLENDING IN THE
DETERMINISTIC ECMWF TO ACCOUNT FOR SOME OF THE UNCERTAINTY AND
FORECAST DETAILS.

COLD ADVECTION AND SUBSIDENCE SHOULD BE IN PLACE ACROSS THE ENTIRE
AREA ON MONDAY AS LOW PRESSURE LIFTS TOWARD HUDSON BAY AND A
SURFACE RIDGE NOSES IN FROM THE NORTHERN HIGH PLAINS. CHANCES FOR
PCPN COULD RETURN TO THE SOUTHERN PORTION OF THE AREA MONDAY
NIGHT THEN LINGER INTO WEDNESDAY AS THE STALLED BOUNDARY NEAR THE
MINNESOTA/IOWA BORDER BECOMES MORE ACTIVE AS INSTABILITY POOLS
ALONG IT AND WE SEE SOME WEAK ISENTROPIC ASCENT RE-ESTABLISH
ITSELF OVER IT. THERE REMAINS QUITE A BIT OF UNCERTAINTY ON HOW
FAR NORTH PCPN MIGHT OCCUR... AND IF THERE HAS BEEN A TREND IT HAS
BEEN FOR A BIT OF A SOUTHWARD SHIFT IN THE PAST FEW MODEL CYCLES.
MEAN LAYER WIND WOULD GENERALLY TAKE ANY ACTIVITY EAST OR EAST-
NORTHEAST... SO WOULDN/T EXPECT THINGS TO MOVE TOO FAR NORTH FROM
WHERE ANYTHING INITIATES... AND WITH THE BEST COMBINATION OF
INSTABILITY AND ISENTROPIC ASCENT AND/OR CONVERGENCE LOOKING TO BE
OVER NORTHERN IOWA THE SOUTHWARD SHIFT IN GUIDANCE MAKES SENSE.
ADJUSTED POPS A BIT SOUTH... AND WOULDN/T BE SURPRISED IF
SUBSEQUENT SHIFTS ARE ABLE TO PUSH THINGS FARTHER SOUTH AND/OR
TIGHTEN THE POP GRADIENT ON THE NORTHERN EDGE. LOW CHANCE POPS
LOOK NECESSARY FOR MUCH OF THE AREA DURING THE THURSDAY-FRIDAY
TIME FRAME WITH AT LEAST SOME OF THE GUIDANCE... NAMELY THE
ECMWF... SUGGESTING AN INVERTED SURFACE TROUGH AND RENEWED WARM
ADVECTION WILL WORK INTO THE SOUTHERN PORTION OF THE AREA DURING
THAT TIME FRAME. HOWEVER... THE LACK OF MODEL AGREEMENT PRECLUDES
INCLUDING MUCH MORE THAN LOW CHANCE POPS AT THIS POINT IN TIME. BY
SATURDAY IT LOOKS LIKE WE SHOULD HAVE DECENT SURFACE RIDGING
ACROSS MUCH OF THE AREA... SO ALLOWED FOR A POP-FREE PERIOD GIVEN
THE LACK OF ANY STRONG SIGNAL IN ANY OF THE SOLUTIONS OTHER THAN
THE IDEA FOR SOME WIDELY SCATTERED DIURNAL SHRA.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 544 AM CDT SUN AUG 24 2014

DRY SLOT COMING UP FROM ERN NEB/WRN IA WILL QUICKLY SQUASH
SCATTERED ACTIVITY ACROSS MN THIS MORNING...ALONG WITH ALLOWING
FOR MOSTLY CLEAR SKIES BY 18Z. INCREASED MIXING FROM STORMS HAS
PUNCHED QUITE A FEW HOLES IN THE STRATUS FIELD THIS MORNING AND NOT
EXPECTING MUCH OF AN EXPANSION IN WHAT IS CURRENTLY OUT. LOOKING
AHEAD...COLD FRONT WILL BE MOVING THROUGH AXN/RWF BETWEEN 18Z AND
20Z...WITH AFTERNOON/EVENING TSRA CHANCES EXISTING EAST OF THESE
TERMINALS. STILL A BIT OF SPREAD IN HI-RES CAMS IN COVERAGE/TIMING
OF TSRA...BUT ENOUGH CONFIDENCE EXISTS IN THEIR TIMING/EXISTENCE
TO INCLUDE TEMPO/PROB30 GROUPS FOR TSRA AT STC/MSP/EAU/RNH. ONCE
THE MORNING STRATUS LIFTS...THE REST OF THE TAF PERIOD WILL BE VFR
OUTSIDE OF ANY TSRA.

KMSP...STORMS THAT QUICKLY POPPED UP OVER THE WEST METRO WILL BE
MAINLY EAST OF THE FIELD BY 12Z...WITH NO ADDITIONAL ACTIVITY
EXPECTED UNTIL COLD FRONT ARRIVES THIS EVENING. CAMS RANGE FROM
00Z ON THE EARLY END TO 4Z ON THE LATE END OF THINGS FOR BRINGING
TSRA INTO THE VCNTY. GIVEN CAPPING AND FRONTAL TIMING...LEANED
MORE TOWARD THE SLOWER TIMING FOR THE TSRA THREAT THIS AFTERNOON.
MAY BE SOME SEVERE WEATHER WITH THIS ACTIVITY AS WELL...SO COULD
BE A BUSY EVENING FOR CONTROLLERS DEPENDING ON THE COVERAGE OF
STORMS...WHICH LOOKS TO BE GREATEST OVER TOWARD WRN WI THIS
EVENING.

/OUTLOOK FOR KMSP/
MON NIGHT...VFR. WINDS W 5-10 KTS.
TUE-THU...MAINLY VFR. CHANCE OF MVFR IN OCNL SHRA/TSRA. WINDS N TO
          NE 5-10 KTS.

&&

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

$$

SHORT TERM...MPG
LONG TERM...
AVIATION...MPG






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