Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 291950 AAC
AFDMPX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
250 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 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1230 PM CDT FRI MAY 29 2015

SURFACE FRONT MOVING SLOWLY SOUTHEAST THROUGH THE FIRST HALF OF
THE FORECAST. SHRA/TSRA LIMITED O MAINLY ALONG/AHEAD OF FRONT INTO
THE EVENING...MAINLY AFFECTING KMSP FOR A COUPLE HOURS...AND
EXITING TO KEAU THROUGH EARLY EVENING. LOW CONFIDENCE ON OVERALL
TIMING OF LOWER CLOD TRENDS INTO THE EVENING. LAGGING UPPER
TROUGH COULD CONTINUE LIGHT RAIN THREAT THROUGH ABOUT 01Z OVER
CENTRAL MN...THEN REFORMING TO THE SOUTHEAST THIS EVENING. WILL
STILL BREAK OUT TO VFR FROM WEST TO EAST IN MN THROUGH ABOUT
04Z...THEN REMAINING VFR INTO WI THROUGH THE NIGHT. MAY SEE VFR
DEVELOP THROUGH THE 12Z-14Z PERIOD THERE. CONFIDENT ON VFR
FORECAST OVER MN THROUGH THE REST OF THE PERIOD...AND INTO WESTERN
WI BY SATURDAY AFTERNOON. NORTHERLY SURFACE WINDS DEVELOPING AND
GUSTING TO 25 KTS OVER THE WEST INTO THE LATE AFTERNOON WITH WIND
GUTS DEVELOPING INTO THE EAST THROUGH 00Z SAT. SHOULD DIMINISH
THIS EVENING WITH GUSTS POSSIBLE DEVELOPING SATURDAY MORNING.

KMSP...
MEDIUM CONFIDENCE ON TREND OF THUNDER FOR THE NEXT COUPLE OF
HOURS...THEN SHOULD MOVE OFF TO THE SOUTHEAST INTO THE EVENING.
LOWER MVFR CIGS/-SHRA THROUGH THE AFTERNOON...WITH FROPA WINDS
BECOMING NORTH AND GUSTY TO 22KTS INTO THE EVENING. EXPECT VFR
CONDITIONS DEVELOPING THROUGH 04Z SAT...WITH LAYERED CLOUDS
EXITING AFTER 06Z. WILL SEE WINDS DIMINISH AGAIN AFTER 06Z AND
BECOME GUTSY AFTER 14Z SAT.

/OUTLOOK FOR KMSP/
SAT...VFR. WINDS NE 10 G20KTS.
SUN/MON...VFR. WINDS SE 10 KT.


&&

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

$$

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


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