Area Forecast Discussion
Issued by NWS Duluth, MN

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000
FXUS63 KDLH 202330
AFDDLH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DULUTH MN
630 PM CDT WED AUG 20 2014

.UPDATE...
ISSUED AT 630 PM CDT WED AUG 20 2014

LATEST SHORT TERM HIRES MODEL GUIDANCE...AS WELL AS 18Z NAM12 HAVE
BACKED WAY OFF WITH THE ONSET OF RAIN UNTIL CLOSER TO 12Z THURSDAY.
HAVE DIALED BACK THE POPS TO START AT 09Z...WHICH IS A BIT OF A
COMPROMISE BETWEEN PREVIOUS FORECAST AND LATEST GUIDANCE. ADDED
SOME MENTIONS OF FOG AS ATMOSPHERE OVER THE FA HAS NOT CHANGED ALL
THAT MUCH. HOWEVER...CLOUD COVER MAY PREVENT IT FROM FORMING AND
OVERALL COVERAGE. MADE SOME OTHER MINOR TWEAKS AS WELL.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 321 PM CDT WED AUG 20 2014

AT 315PM...THERE WAS WEAK SURFACE HIGH PRESSURE OVER NW ONTARIO AND
THE WESTERN LAKE SUPERIOR REGION. THERE WAS SURFACE LOW PRESSURE
OVER THE NORTHERN AND NORTHERN HIGH PLAINS. A WARM FRONT STRETCHED
FROM A SURFACE LOW IN CENTRAL SOUTH DAKOTA TO IOWA. MUCH OF THE
NORTHLAND HAD PARTLY TO MOSTLY CLOUDY SKIES WITH LIGHT EASTERLY
WINDS. TEMPERATURES WERE PRIMARILY IN THE UPPER 60S AND LOWER 70S.
THE COOLER TEMPERATURES WERE CLOSER TO LAKE SUPERIOR.

THROUGH TONIGHT...THERE WILL LIKELY BE SOME CLEARING LATE THIS
AFTERNOON AND EARLY THIS EVENING. THE WARM FRONT IN IOWA WILL
GRADUALLY LIFT NORTHWARD INTO MINNESOTA AND WISCONSIN. THE
INCREASING LOW LEVEL JET OVER THE REGION WILL BRING A SURGE OF
MOISTURE ALOFT AND AHEAD OF THE WARM FRONT. THIS WILL BRING
INCREASING CHANCES OF SHOWERS AND STORMS FROM THE SOUTH. WHILE
MOST OF THE 12Z MODEL RUNS DELAYED THE TIMING WITH WHICH PCPN
MOVES INTO OR DEVELOPS OVER THE FORECAST AREA FROM THE SOUTH...I
DID NOT BACK OFF ON PCPN CHANCES TOO MUCH SINCE THE INCREASING
LOW LEVEL JET AND MOISTURE COULD HELP FIRE OFF STORMS...DESPITE
THE SURFACE AND MID LEVEL WARM FRONT REMAINING SOUTH OF THE
FORECAST AREA. THERE WILL BE INCREASING MOST UNSTABLE CAPE FROM
THE SOUTH LATE TONIGHT...AND DEEP LAYER (0-6 KM) WIND SHEAR COULD
INCREASE TO AROUND 30 KNOTS. THERE IS A LIMITED RISK OF STRONG
STORMS ACROSS THE FAR SOUTHERN FORECAST AREA LATE TONIGHT WITH THE
POTENTIAL FOR SMALL HAIL AND HEAVY RAIN.

THURSDAY...THE MODELS ARE NOT IN THAT GOOD OF AGREEMENT...BUT IT
GENERALLY STILL LOOKS LIKE THE SURFACE WARM FRONT WILL STALL OVER
SOUTHERN MINNESOTA AND SOUTHERN WISCONSIN. THE SOUTHERLY FLOW WILL
CONTINUE TO PUMP MOIST AIR INTO THE NORTHLAND. THE PRECIPITABLE
WATER VALUES COULD REACH AROUND 1.75 INCHES. THE COOLER EASTERLY
FLOW OFF LAKE SUPERIOR COULD SET UP A BAROCLINIC ZONE OVER THE
SOUTHERN FORECAST AREA...WITH INLAND AREAS GETTING WARMER THAN
AREAS NEAR LAKE SUPERIOR. SHOWERS AND STORMS ARE LIKELY...BUT THE
MODELS HAVE BACKED OFF ON THE AMOUNT OF PCPN COMPARED TO PREVIOUS
RUNS. IT STILL LOOKS LIKE SIGNIFICANT RAINFALL IS LIKELY FOR MUCH
OF THE FORECAST AREA...PROBABLY BETWEEN 0.25 AND 0.50 INCHES. SOME
AREAS COULD SEE EVEN HIGHER AMOUNTS. THE MODELS SUGGEST MOST OF
THE INSTABILITY WILL BE OVER THE SOUTHERN AND WESTERN FORECAST
AREA...SO I ATTEMPTED TO DOWNPLAY THE STORM THREAT CLOSER TO LAKE
SUPERIOR AND OVER THE NORTHERN FORECAST AREA.

THURSDAY NIGHT...A WEAK MID LEVEL LOW WILL LIKELY MOVE NEAR THE
SOUTHERN FORECAST AREA. THE CHANCES OF SHOWERS AND STORMS WILL
LIKELY BEGIN TO DIMINISH FROM WEST TO EAST.

FRIDAY...THE WEAK MID LEVEL WILL LIKELY CONTINUE MOVING EAST JUST
SOUTH OF THE FORECAST AREA. THE MORNING LOOKS CLOUDY WITH
LINGERING CHANCES OF SHOWERS AND STORMS...BUT THE AFTERNOON LOOKS
PRIMARILY DRY WITH PARTIAL CLEARING.

.LONG TERM...(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 321 PM CDT WED AUG 20 2014

THE VARIOUS DETERMINISTIC AND ENSEMBLE MODEL DATA APPEARS TO BE
CONVERGING TOWARD A POTENTIALLY VERY ACTIVE AND WET PERIOD OF
WEATHER ACROSS MUCH OF THE NORTHLAND FROM LATER FRIDAY NIGHT INTO
SUNDAY. THERE APPEARS TO BE AT LEAST SOME POTENTIAL FOR TRANSIENT
SEVERE STORMS..BUT A MUCH BIGGER THREAT APPEARS TO BE FOR HEAVY
RAINFALL.

LEAD SHORT WAVE TROF IS PROGGED TO EJECT NEWD ACROSS THE REGION
FRIDAY NIGHT/SATURDAY..ACCOMPANIED BY RATHER COPIOUS LOW LEVEL
MOISTURE ADVECTION AS A STRONG SLY LOW LEVEL JET DEVELOPS IN THE
WARM SECTOR AND INTERACTS WITH BAROCLINIC ZONE IN THE SURFACE TO
850 LAYER. THIS WILL ACT TO TRY AND PUSH A WARM FRONTAL ZONE
SLOWLY BUT STEADILY NORTHWARD ACROSS THE REGION FROM LATE FRIDAY
NIGHT INTO SATURDAY NIGHT. SOME OF THE SOLUTIONS SUGGEST THAT MEAN
1000-850 LAYER MIXING RATIOS IN EXCESS OF 18 G/KG MAY BE LURKING
IN THE TROPICAL AIRMASS TO THE SOUTH OF THE WARM FRONTAL ZONE..SO
THERE WILL BE AMPLE MOISTURE AVAILABLE FOR TSTORMS AND THE
POTENTIAL FOR HEAVY RAINFALL.

THE MAIN UPPER LEVEL TROF AXIS WILL THE EJECT/AMPLIFY SATURDAY
NIGHT/SUNDAY SOMEWHERE IN THE VICINITY OF THE RED RIVER
VALLEY..WHICH WOULD ALSO PLACE THE DLH CWA IN A CONTINUED RISK FOR
TSTORMS AND ADDITIONAL HEAVY RAINFALL. THE OVERALL SYNOPTIC SET UP
SEEMINGLY ALSO WOULD FAVOR AT LEAST SOME POTENTIAL FOR SEVERE
WEATHER..ESPECIALLY WITH SUCH HIGH BOUNDARY LAYER MOISTURE CONTENT
IN PLACE. HOWEVER..LATE SUMMER CHARACTERISTIC WARMER TEMPS ALOFT
AND WEAKER LAPSE RATES MAY LEAD TO TALL/SKINNY CAPE PROFILES THAT
COULD LIMIT THE OVERALL SEVERE POTENTIAL AND FOCUS THE THREAT MORE
ON HEAVY RAIN DUE TO DEEP WARM CLOUD LAYERS IN ADDITION TO VERY
HIGH PRECIPITABLE WATER VALUES THAT WILL PUSH 2 INCHES IF THE
NAM/ECM FORECASTS ARE EVEN REMOTELY IN THE BALLPARK.

IN THE WAKE OF DEEP LAYER CYCLOGENESIS ON SUNDAY/MONDAY..WESTERLY
LOW LEVEL FLOW WILL TRY TO SCOUR OUT..OR AT LEAST REDUCE THE
DEPTH OF..THE EXTREMELY MOIST BOUNDARY LAYER. HOWEVER..THE MAIN
PUSH ON THE DRY SLOT APPEARS TO BE DIRECTED FROM THE RED RIVER
VALLEY INTO NW ONTARIO..SO THE PRIMARY SYNOPTIC FRONTAL BOUNDARY
MAY NOT GET PUSHED TOO FAR EAST/SOUTHEAST WITH MUCH SPEED
SUNDAY/MONDAY UNTIL IT GETS ANOTHER PUSH FROM THE NEXT DISTURBANCE
AT THE END OF THIS 7 DAY FORECAST PERIOD. THUS..CHANCES FOR
SHOWERS/TSTORMS HAVE BEEN RETAINED FOR THIS TIME FRAME DUE TO
UNCERTAINTY ABOUT HOW FAR/FAST SOUTHEAST THE FRONT WILL ACTUALLY
BE ABLE TO PUSH.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 630 PM CDT WED AUG 20 2014

VFR OVER THE TERMINALS AT THE BEGINNING OF THIS FORECAST CYCLE.
MADE ONLY SOME SLIGHT CHANGES FROM PREVIOUS FORECAST IN REGARDS TO
BR FORMATION. CLOUD COVER MAY PLAY A ROLE. BACKED OFF ON THE
MENTION OF VCSH AS LATEST MODEL GUIDANCE SUPPORTS THIS THINKING.
WENT WITH PREDOMINATE -TSRA AT BRD AT 19Z...VCTS AT HYR.
THUNDERSTORMS MAY TAKE A BIT LONGER TO REACH DLH/HIB. LEFT OUT THE
MENTION OF PCPN AT INL THIS FORECAST.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  57  69  60  73 /  10  50  60  20
INL  56  72  59  76 /   0  60  60  30
BRD  63  80  62  79 /  50  60  30  10
HYR  60  80  64  80 /  20  70  60  10
ASX  56  74  61  74 /  10  50  60  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
LS...NONE.
&&

$$

UPDATE...GSF
SHORT TERM...GROCHOCINSKI
LONG TERM...MILLER
AVIATION...GSF





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