Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 260952
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
452 AM CDT TUE AUG 26 2014

.UPDATED FOR 12Z AVIATION DISCUSSION...
ISSUED AT 447 AM CDT TUE AUG 26 2014

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 251 AM CDT TUE AUG 26 2014

EARLY MORNING WATER VAPOR IMAGERY TOGETHER WITH 500MB HEIGHTS AND
WINDS IDENTIFIED THE NORTHERN STREAM ACROSS SOUTHERN CANADA...WITH A
FEW EMBEDDED SHORTWAVES THE POLEWARD SIDE OF THE JET. MEANWHILE A
POSITIVELY TILTED TROUGH WAS DIGGING ACROSS THE SOUTHWESTERN
US...AND THIS WILL EVENTUALLY BECOME CUTOFF OVER THE 4 CORNERS
REGION BY WEDNESDAY. IN THE MEAN TIME...A POSITIVELY TILTED
SHORTWAVE CURRENTLY LOCATED ON THE LEE SIDE OF THE ROCKIES OVER
ALBERTA WILL QUICKLY TRAVERSE THE INTERNATIONAL BORDER OVER THE NEXT
24 HOURS. THE NAM AND ECMWF 26.00 DEVELOP PRECIP ACROSS THE NORTHERN
CWA TIED TO THIS WAVE. FORECAST SOUNDINGS SHOW MORE OF MID LEVEL
CLOUD DECK...BUT A 20 PERCENT POPS IS WARRANTED MAINLY NORTH OF I-94
TUESDAY NIGHT.

A SECOND AREA OF POPS WILL LIFT UP FROM THE SOUTH ALONG THE I-90
CORRIDOR AS ANOTHER ROUND OF NOCTURNAL THUNDERSTORMS WILL DEVELOP.
THE THUNDERSTORMS ONGOING EARLY TUESDAY MORNING MATCH UP WITH THE
H850 THETA_E GRADIENT. THIS GRADIENT WILL SLOWLY SHIFT NORTHWARD AND
BE ORIENTED EAST/WEST ACROSS NORTHERN IOWA. THEREFORE THE HEAVIEST
RAIN WILL REMAIN SOUTH OF THE CWA. TEMPERATURES WILL RUN ABOUT 5
DEGREES BELOW NORMAL AS SEASONABLY COOL/DRY AIR REMAINS ACROSS THE
UPPER MIDWEST.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 251 AM CDT TUE AUG 26 2014

FORECAST EXPECTATIONS AND REASONING HAVEN/T CHANGED MUCH FROM THE
PAST SEVERAL DAYS. THE LARGE SCALE PATTERN STILL LOOKS TO BECOME
FAIRLY ZONAL BY MIDWEEK... WITH THE BAROCLINIC ZONE CURRENTLY
BOTTLED UP TO OUR SOUTH LIFTING BACK NORTH AND BRINGING INCREASED
CHANCES FOR SHRA/TSRA. THE CUTOFF LOW OVER THE SOUTHWEST WILL
SLOWLY MOVE EAST INTO THE PLAINS AND MISSISSIPPI VALLEY DURING THE
LATER HALF OF THE WEEK. ALTHOUGH IT DOESN/T LOOK TO DIRECTLY
IMPACT OUR AREA... IT WILL HAVE AN INDIRECT EFFECT BY HELPING TO
DRAW DEEPER MOISTURE NORTHWARD FROM THE WESTERN GULF OF MEXICO...
WHICH WILL BE ADVECTED NORTHWARD OVER THE WARM FRONTAL BOUNDARY
AND BRING SOME POTENTIAL FOR SIGNIFICANT RAINFALL AMOUNTS WHEREVER
IT WINDS UP PRECIPITATING IN OUR AREA DURING THE LATE WEDNESDAY
THROUGH FRIDAY TIME FRAME. THE 00Z DETERMINISTIC RUNS OF THE ECMWF
AND GFS ARE IN REMARKABLY GOOD AGREEMENT ON THE LARGE SCALE
PATTERN AND MASS FIELDS THROUGH THE FORECAST PERIOD... EVENTUALLY
EVOLVING TOWARD A MORE AMPLIFIED PATTERN BY EARLY NEXT WEEK AS AN
UPPER TROUGH WORKS ACROSS THE ROCKIES AND TOWARD OUR AREA.
ALTHOUGH THEIR SOLUTIONS COULD BE WRONG IT IS TOUGH TO FABRICATE
AN IDEA WHICH WOULD BE MORE LIKELY TO BE CORRECT... SO WILL STICK
CLOSE TO A BLEND OF THEIR GUIDANCE. IN SUPPORT OF THAT NOTION IS
DECENT AGREEMENT IN THE GEFS... WHICH IS ALSO SIMILAR TO THE GFS.

WILL CONTINUE TO KEEP POPS CONFINED TO THE FAR SOUTH WEDNESDAY
INTO WEDNESDAY NIGHT AS THE BAROCLINIC ZONE AND INSTABILITY REMAIN
WELL SOUTH OF THE AREA. HOWEVER... THINGS WILL QUICKLY CHANGE
WEDNESDAY NIGHT INTO THURSDAY AS AN INVERTED SURFACE TROUGH LIFTS
NORTH FROM THE CENTRAL PLAINS TOWARD SOUTHERN MINNESOTA COINCIDENT
WITH THE NORTHWARD SURGE IN 850MB THETA-E VALUES AND CONVECTIVE
INSTABILITY PER THE 850-500MB DIFFERENTIAL THETA-E. SHOULD SEE
SUFFICIENT FORCING FROM ISENTROPIC ASCENT ALONG WITH SOME
FRONTOGENESIS TO GET SHRA/TSRA INTO THE SOUTHERN HALF OF THE AREA
BY THURSDAY MORNING. CONDITIONS FOR PCPN LOOK TO REMAIN FAVORABLE
INTO THURSDAY NIGHT... PARTICULARLY OVER THE SOUTHEAST HALF OR SO
OF THE FORECAST AREA. BY FRIDAY IT LOOKS LIKE WE/LL FIND OURSELVES
IN A BIT OF A LULL AS THE SURFACE TROUGH AND FORCING FROM THURSDAY
SHIFTS SOUTHEAST AND THE NEXT FRONTAL BOUNDARY REMAINS UPSTREAM
OVER THE DAKOTAS. THIS FEATURE IS PROGGED TO DROP THROUGH THE AREA
FRIDAY NIGHT INTO SATURDAY... BUT DOESN/T APPEAR TO WARRANT MORE
THAN LOW CHANCE POPS AT THIS POINT AS THE BETTER LARGE SCALE
FORCING PASSES BY TO OUR NORTH AND THE BETTER INSTABILITY AND LOW
LEVEL FORCING IS OFF TO OUR SOUTH/EAST. APPEARS WE/LL SEE A BETTER
CHANCE FOR MORE WIDESPREAD SHRA/TSRA LATE SUNDAY NIGHT AND MONDAY
AS WE GET A WINDOW OF DECENT RETURN FLOW/WARM ADVECTION AHEAD OF
THE NEXT FRONTAL BOUNDARY... WHICH WILL MOVE THROUGH AHEAD OF AN
WELL DEFINED UPPER TROUGH MOVING EAST FROM THE NORTHERN ROCKIES
AND HIGH PLAINS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 447 AM CDT TUE AUG 26 2014

MVFR CLOUDS WERE BEGINNING TO SCATTER OUT AS THEY SAGGED SOUTHWARD
ACROSS KAXN AND KSTC. ONCE THESE CLOUDS COMPLETELY DIMINISH EXPECT
VFR CONDITIONS THROUGHOUT. ANVIL CIRRUS FROM THE IOWA
THUNDERSTORMS WILL ALSO DIMINISH THIS MORNING. A MID LEVEL CLOUD
DECK WILL MOVE ACROSS THE REGION THIS EVENING. THE WINDS WILL BE
LIGHT...BUT SHOULD MAINTAIN A NORTHERLY COMPONENT.

KMSP...
VFR CONDITIONS THROUGHOUT. NO CHANGES FROM GENERAL DISCUSSION.

/OUTLOOK FOR KMSP/
WED...VFR. WINDS E AT 5KTS.
THU...VFR WITH MVFR SHRA/TSRA LIKELY. WINDS E AT 5-10KTS.
FRI...VFR WITH LOW CHANCE MVFR SHRA/TSRA. WINDS VRB AT 5KTS.

&&

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

$$

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





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