Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 292357
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
657 PM CDT FRI MAY 29 2015

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 249 PM CDT FRI MAY 29 2015

THE SHORT TERM CONCERNS ARE TIMING OF PRECIPITATION AND THE CLEARING
TREND.

LARGE AREA OF RAIN WITH EMBEDDED THUNDER OVER MOST OF THE AREA.
MORE SCATTERED NATURE OF THUNDER WITH BEST CHANCE LOCATED MAINLY
OVER THE SOUTHEAST THIRD OF THE CWA INTO THE EVENING.  THIS MATCHES
WELL WITH THE 1 HOUR THUNDERSTORM FORECAST FROM THE SREF. SHOULD SEE
THUNDER END THROUGH 03Z ACROSS THE CWA. TIMING CONCERNS AS WELL AS
UPPER TROUGH LIFTING OVER THE AREA AT THIS TIME.  WILL SLOW CLEARING
SOME...BUT STILL ANTICIPATE MAINLY HIGH CLOUDS REMAINING TO THE
SOUTHEAST BY 12Z SAT. RAINFALL RATES STILL RANGING AROUND AN 1 INCH
AN HOUR IN MORE ORGANIZED CONVECTION.  THIS WILL LINGER THROUGH
ABOUT 00Z WITH PRECIPITABLE WATER VALUES AROUND 1.5 INCHES...PER
MODEL TRENDS AND SPC MESOANALYSIS.

WITH SOME CLEARING EXPECTED AND STRONG CAA...TEMPERATURES WILL DROP
OFF INTO THE UPPER 30S OVER THE NORTHWEST CWA. COOLER WEATHER WITH A
FEW CLOUDS EXPECTED TO THE SOUTHEAST AT LEAST EARLY SATURDAY WITH
HIGH PRESSURE BUILDING TO THE SOUTHEAST. HIGH TEMPERATURES REMAINING
IN THE LOWER AND MID 60S MOST AREAS...SOME 10 DEGREES BELOW
NORMAL.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 249 PM CDT FRI MAY 29 2015

IN THE EXTENDED PERIOD THE WEATHER PATTERN WILL TRANSITION FROM
SEEMINGLY EARLY FALL TO EARLY SUMMER AS NORTHWEST FLOW AND COOL HIGH
PRESSURE IS REPLACED WITH ZONAL FLOW AND INCREASING MOISTURE. AS A
RESULT...AFTER A FROSTY MORNING ACROSS THE NORTHWEST...TEMPERATURES
WILL INCREASE WITH PERIODIC CHANCES FOR SHOWERS AND THUNDERSTORMS
FOR MOST OF NEXT WEEK. AT THIS POINT...THE INSTABILITY APPEARS TO BE
IN PLACE...BUT THE LIMITING FACTOR FOR SEVERE WEATHER HINGES ON WIND
SHEAR AND FORCING.

AT THE START OF THE PERIOD...A TEXTBOOK EXAMPLE OF A H500 RISE/FALL
COUPLET ON THE UPSTREAM/DOWNSTREAM SIDE OF A POTENT UPPER LEVEL WAVE
WILL RESULT IN SURFACE HIGH/LOW PRESSURE OVER ONTARIO/NEWFOUNDLAND.
LIGHT WINDS AND CLEAR SKIES WITHIN THIS SURFACE HIGH WILL PROMOTE
RADIATIONAL COOLING...AND A FEW AREAS NORTH AND EAST OF I-94 WILL BE
SUBJECT TO FROST DEVELOPMENT IN THE TYPICAL COLD SPOTS.

MEANWHILE...ZONAL FLOW WILL DEVELOP CAUSING LEE CYCLOGENESIS OVER
THE HIGH PLAINS...AND SOUTHEASTERLY SURFACE WINDS WILL DEVELOP OVER
THE MIDWEST AS THE AFOREMENTIONED SURFACE HIGH DRIFTS EASTWARD.
SHORTWAVES EMBEDDED IN THE ZONAL FLOW WILL LEAD TO SHOWERS AND
THUNDERSTORMS ACROSS THE DAKOTAS...AND FORECAST MODELS INDICATE THIS
AREA OF CONVECTION WILL PROPAGATE EASTWARD AS AN MCS.

THIS HAS TWO IMPLICATIONS ON THE FORECAST. FIRST OF ALL...OVERCAST
SKIES FROM CONVECTIVE DEBRIS COULD LIMIT THE AFTERNOON HEATING...SO
DID NOT STRAY FROM THE BLENDED GUIDANCE DESPITE THE SEASONABLY WARM
TEMPS A H850. ALSO...CONVECTIVE DEBRIS WOULD LIMIT CAPE
DEVELOPMENT/SEVERE WEATHER POTENTIAL. ONE THING THAT IS SUPPORTIVE
OF INSTABILITY IS THE MID LEVEL LAPSE RATES OF 7 TO 8 C/KM ABOVE A
H800 WARM NOSE. FORECAST SOUNDINGS SHOW ROUGHLY 1500 J/KG OF MUCAPE
BY MID AFTERNOON. HOWEVER...THE ENVIRONMENT MAY BE CAPPED OFF BY THE
AFOREMENTIONED WARM NOSE...SO AS OF NOW EXPECT THE BEST CHANCE FOR
SHOWERS AND THUNDERSTORMS ACROSS THE NORTHERN HALF OF MN/WI UNLESS A
SHORTWAVE COMES FARTHER SOUTH ACROSS THE REGION. WIND PROFILES SHOW
90 DEG OF DIRECTIONAL SHEAR...BUT THE MAGNITUDE IS ON THE LOWER END
OF THE SEVERE WEATHER SPECTRUM...ESPECIALLY IN MID AND UPPER LEVELS
WHERE H500 AND H300 WINDS ARE FORECAST TO RANGE FROM 20 TO 35KTS.

IN SUMMARY...EXPECTED PERIODIC SHOWERS AND THUNDERSTORMS NEXT WEEK.
A FEW STORMS COULD BE STRONG TO SEVERE SHORTLY AFTER
INITIATION...BUT THE MORE LIKELY SCENARIO IS AN UNORGANIZED COMPLEX
OF STORMS WITH LOCALIZED HEAVY RAIN AS THE PRIMARY THREAT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 655 PM CDT FRI MAY 29 2015

WHAT YOU SEE IS WHAT YOU GET FOR THE NEXT SEVERAL HOURS.
WIDESPREAD MVFR CEILINGS WITH POCKETS OF IFR WILL CONTINUE THROUGH
06Z AT MOST OF THE TAF SITES. RAIN WILL SLOWLY COME TO AN END IN
EAST CENTRAL MN BETWEEN 01Z-04Z...BUT LINGER IN WI UNTIL 06Z-07Z.
THE CEILINGS WILL SLOWLY CLEAR FROM WEST TO EAST TONIGHT.

KMSP...

LITTLE IMPROVEMENT IN THE CEILING HEIGHT IS EXECTED THROUGH
06Z...BUT THE VISIBILITY SHOULD IMPROVE WITHIN THE NEXT 1-2 HOURS
AS THE RAIN SLIDES EAST OF THE AREA. THE WHOLE SYSTEM IS A BIT
SLOWER THAN EXPECTED...SO WE PUSHED THE CLEARING BACK WITH THE
LATEST FORECAST.

/OUTLOOK FOR KMSP/
SUN...VFR.WINDS SE 5-10 KT.
MON...VFR. WINDS SE 10 KT.
TUE...VFR. CHANCE -TSRA. WINDS 10-20 KT.

&&

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

$$

SHORT TERM...DWE
LONG TERM...JRB
AVIATION...CLF


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