Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 210926
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
426 AM CDT SUN SEP 21 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 425 AM CDT SUN SEP 21 2014

TODAY-TONIGHT...SFC ANALYSIS SHOWS A CDFNT PUSHING ACRS LAKE MI INTO
LOWER MI WITH A SECONDARY CDFNT DRAPED FROM CENTRAL MANITOBA
PROVINCE THRU THE NRN GREAT LAKES INTO QUEBEC PROVINCE. THE FIRST
CDFNT WAS RESPONSIBLE FOR THE STRONG/SEVERE TSTMS THAT PASSED THRU
THIS REGION YDA...WHILE THE SECOND CDFNT IS MORE REFLECTIVE OF THE
UPR LVL VORT MAX DROPPING SEWD FROM S-CENTRAL CANADA. CYCLONIC FLOW
ARND THIS UPR VORT WITHIN COLD AIR ALOFT AND LINGERING DEEP MOISTURE
WILL PRODUCE SCTD SHWRS OVER WRN WI INTO FAR ERN MN THRU THE FIRST
HALF OF TDA. NO SEVERE WX WILL COME FROM THIS...AND HIGHLY LIKELY
THAT NO TSTMS WILL DEVELOP WITH A MUCH MORE STABLE ATMOS IN PLACE.
SO...HAVE KEPT POPS NO HIGHER THAN CHC CATEGORY FROM DAYBREAK ON AS
COVERAGE NOT EXPECTED TO BE ALL THAT GREAT...AND QPF WILL BE QUITE
LIGHT...GENERALLY ONLY UP TO A FEW HUNDREDTHS TO BE RECEIVED. ANY
AND ALL PRECIP SHOULD DISSIPATE AND SHIFT OFF TO THE E BY MIDDAY
WITH GRADUAL CLEARING EXPECTED THEREAFTER AS HIGH PRES SLOWLY
ARRIVES FROM THE W. DEEP DRY NW FLOW FROM THE SFC UPWARD WILL
PROMOTE CLEARING SKIES THIS EVENING THRU THE OVERNIGHT HRS. THE ONLY
QUESTION WILL BE THE COVERAGE OF FOG OVERNIGHT AS CAA KICKS INTO
HIGH GEAR WHILE WINDS DROP OFF UNDER THE CLEARING SKIES. CROSSOVER
TEMPS ARE CLOSE SO IT MAY WELL BE A MATTER OF HOW MUCH MOISTURE CAN
BE SCOURED OUT BEFORE THE NIGHTLY INVERSION SETS IN. HAVE OPTED TO
INCLUDE PATCHY FOG FOR NRN AND ERN PORTIONS OF THE CWFA WHERE WINDS
ARE MOST LIKELY TO GO CALM AND WHERE COLDEST TEMPS ARE EXPECTED.
WITH RESPECT TO THE CAA...HIGHS TDA WILL BE NOTICEABLY COOLER THAN
SATURDAY WITH HIGHS RANGING FROM THE LWR 60S IN WRN WI TO THE UPR
60S TO ARND 70 IN WRN MN. FOR TNGT...LOWS OUTSIDE THE TWIN CITIES
METRO WILL DROP TO THE LOW-MID 40S...WITH MIN TEMPS CLOSE TO 50
WITHIN THE TC METRO.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 425 AM CDT SUN SEP 21 2014

THE UPPER MIDWEST WILL FIND ITSELF ON THE WARM SIDE OF A HIGHLY
AMPLIFIED UPPER LEVEL PATTERN WHICH WILL LEAD TO TEMPERATURES THAT
WILL BE WELL ABOVE THE SEASONAL AVERAGE FOR LATE SEPTEMBER. DRY
WEATHER IS EXPECTED ASIDE FROM SCATTERED SHOWERS LATE TUESDAY
THROUGH WEDNESDAY.

EARLY MORNING WATER VAPOR IMAGERY WITH GFS 21.00 500MB HEIGHTS AND
WINDS SHOWED A DIGGING TROUGH OVER THE NORTHWEST PACIFIC WITH A
RIDGING OVER THE CANADIAN ROCKIES. MEANWHILE A WEAKENING OCCLUDED PV
ANOMALY WAS SITUATED ACROSS SOUTHERN CALIFORNIA...AND THIS WILL BE
THE FOCUS FOR PRECIP CHANCES EARLY IN THE PERIOD. FORECAST SOUNDINGS
SHOW DRY AIR IN THE LOWER LEVELS...SO MAY SEE MORE MID-LEVEL
SATURATION/CLOUDS THAN ACTUAL PRECIP. THEREFORE BROKE UP THE POPS
INTO 6HR BLOCKS TO INCREASE THE TEMPORAL RESOLUTION. ALSO...FORECAST
SOUNDINGS DO NOT SHOW ELEVATED INSTABILITY...SO HAVE LOW CONFIDENCE
IN UPRIGHT CONVECTION AND AS RESULT REMOVED THE THUNDER MENTION FROM
THE WEATHER GRIDS.

LOOKING AHEAD...WARM AIR MOVES ACROSS THE REGION AS THE UPPER LEVEL
PATTERN AMPLIFIES. WAS TEMPTED TO INCREASE POPS WELL ABOVE
GUIDANCE...BUT THERE ARE TWO VAIRABLES THAT PREVENTED THIS. FIRST OF
ALL...FORECAST MODELS HINT AT A WEAK WAVE CUTTING OFF OVER THE CORN
BELT...AND THIS COULD LEAD TO MID/UPPER LEVEL CLOUDS WHICH WILL
SEVERELY LIMIT AFTERNOON HEATING. SECONDLY...SURFACE WINDS MAY
CONTAIN A SLIGHT EASTERLY COMPONENT. FORECAST SOUNDINGS SHOW
AFTERNOON MIXING WITH WINDS EVENTUALLY BECOMING 180-190DEG...BUT IF
CLOUDS MOVE IN THEN THE BOUNDARY LAYER MIXING WILL BE LESS THAN
CURRENTLY FORECAST. SINCE IT IS ONLY SUNDAY...HAVE PLENTY OF TIME TO
RAISE TEMPERATURES FOR THE LATTER HALF OF THE WEEK...SO WAS CONTENT
TO STICK WITH THE HIGHER END OF GUIDANCE...RATHER THAN EXCEEDING IT.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1045 PM CDT SAT SEP 20 2014

A SMALL BAND OF SHOWERS WILL PASS BETWEEN KRWF AND KMSP BEFORE THE
START OF THE 06Z TAFS. OVERNIGTH...CYCLONIC LOW LEVEL FLOW WILL
INCREASE ACROSS THE REGION IN RESPONSE TO AN UPPER LEVEL LOW
PRESSURE SYSTEM MOVING SOUTHEAST. MVFR CEILINGS WILL BECOME
WIDESPREAD ACROSS EASTERN MN AND WESTERN WI ALONG WITH LIGHT RAIN
OR DRIZZLE. THERE WILL ALSO BE IFR CIGS FOR A FEW HOURS LATE IN
THE NIGHT AND SUNDAY MORNING AT KEAU. CEILINGS AT KRNH AND KEAU
WILL SLOWLY IMPROVE TO VFR BY SUNDAY AFTERNOON WITH CLR-SCT CONDITIONS
ARRIVING AT ALL SITES BY SUNSET. NORTHWEST WINDS NEAR 10 KNOTS
THROUGH THE PERIOD WITH GUST TO 18 KNOTS ON SUNDAY.

KMSP...A VFR CEILING WILL ARRIVE EARLY IN THE TAF PERIOD WITH A
PERIOD OF MVFR CIGS LIKELY FROM 14-17Z. THIS COULD COME AN HOUR OR
TWO EARLIER THAN FORECAST AND A FEW SPRINKLES ARE ALSO POSSIBLE.
VFR CEILING RETURN FOR THE AFTERNOON ALONG WITH CLEARING BY EVENING.

/OUTLOOK FOR KMSP/

MON...VFR. WINDS W 5-10 KTS.
TUE...VFR. WINDS S 10 KTS.
WED...VFR WITH MVFR/SHRA/TSRA POSSIBLE. WINDS S 10-15 KTS.


&&

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

$$

SHORT TERM...JPC
LONG TERM...JRB
AVIATION...RAH






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