507  
FXUS63 KDLH 210539  
AFDDLH  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DULUTH MN  
1239 AM CDT SAT SEP 21 2019  
   
SHORT TERM
 
(THIS EVENING THROUGH SATURDAY NIGHT)  
ISSUED AT 355 PM CDT FRI SEP 20 2019  
 
A MORE ACTIVE WEATHER PATTERN WILL DEVELOP ACROSS THE NORTHLAND,  
WITH INCREASING CHANCES OF SHOWERS AND THUNDERSTORMS LATE TONIGHT,  
AND CONTINUING THROUGH THE DAY SATURDAY AND SATURDAY EVENING. SOME  
STORMS COULD BE STRONG TO SEVERE SATURDAY AFTERNOON.  
 
A MERIDIONAL PATTERN HAS DEVELOPED ACROSS THE CONUS, WITH A  
LONGWAVE UPPER-LEVEL TROUGH OVER THE INTERMOUNTAIN WEST STATES AND  
A RIDGE OVER THE CENTRAL GREAT LAKES REGION. THE LONGWAVE TROUGH  
WILL INCH CLOSER TO THE NORTHLAND THROUGH THE DAY SATURDAY AND  
LIFT NORTHEASTWARD. AHEAD OF THE TROUGH WILL BE A COUPLE OF MID-  
LEVEL SHORTWAVE IMPULSES THAT WILL EJECT INTO THE REGION, ALONG  
WITH A SURFACE WARM FRONT, BRINGING WARM AND HUMID AIR WITH IT.  
UPPER-LEVEL DIVERGENCE ON THE LEEWARD SIDE OF THE UPPER-LEVEL  
TROUGH WILL PROVIDE SOME WEAK LARGE SCALE FORCING OVER THE  
NORTHLAND, BUT A THETA-E RIDGE AXIS WILL TRANSLATE THROUGH THE  
REGION. A STRONG 35 TO 45 KNOT NOCTURNAL LOW-LEVEL JET WILL HELP  
INCREASE MOISTURE TRANSPORT INTO THE REGION, WITH PWAT VALUES IN  
THE BALLPARK OF 1.5 TO 1.9 INCHES, WHICH IS AROUND 99% OF  
CLIMATOLOGY PER THE NAEFS CLIMATOLOGICAL ANOMALIES. CHANCES OF  
THUNDERSTORMS WILL COME IN A FEW WAVES: 1) DURING THE MORNING  
HOURS SATURDAY ALONG A MID-LEVEL IMPULSE, AND 2) DURING THE  
AFTERNOON AND EVENING HOURS OVER NORTH-CENTRAL MINNESOTA AS THE  
MAIN LONGWAVE TROUGH LIFTS NORTHWARD. THE AXIS OF INSTABILITY,  
CHARACTERIZED BY MIXED-LAYER CAPE IN THE 1500 TO 2500 J/KG RANGE,  
WILL MOVE THROUGH SATURDAY AFTERNOON AND EVENING, BUT THE MOST  
FAVORABLE DEEP-LAYER SHEAR SHOULD STAY TO THE WEST. STILL, VALUES  
BETWEEN 35 TO 45 KNOTS OF BULK SHEAR OVER NORTH-CENTRAL MINNESOTA  
WILL LEAD TO THE POTENTIAL FOR STRONG TO SEVERE STORMS IN THAT  
AREA. THE MAIN THREATS WILL BE LARGE HAIL, DAMAGING WIND GUSTS,  
AND FREQUENT LIGHTNING. THERE IS A BIT MORE UNCERTAINTY REGARDING  
THE THREAT FOR FLASH FLOODING AS THE LATEST ROUND OF MODEL  
GUIDANCE KEEPS THE BULK OF THE RAINFALL OVER FAR NORTH-CENTRAL  
MINNESOTA, WITH A STORM TOTAL RAINFALL AMOUNT OF AROUND ONE TO ONE  
AND A HALF INCHES, DESPITE THE LOW-LEVEL JET IN PLACE. IF THESE  
AMOUNTS DO PAN OUT, THEN THEY SHOULD BE BELOW THE AMOUNT TO  
REACHING FLASH FLOOD GUIDANCE IN THESE AREAS, SO THINKING THAT THE  
FLASH FLOOD POTENTIAL HAS DECREASED.  
 
EVENTUALLY, AS THE MID-LEVEL TROUGH LIFTS NORTHEASTWARD, THE  
BETTER FORCING AND INSTABILITY WILL KICK OFF TO THE EAST SATURDAY  
EVENING AND INTO SUNDAY MORNING, LEADING TO A DECREASING TREND IN  
THUNDERSTORM CHANCES. THE REGION WILL REMAIN UNDER THE CYCLONIC  
FLOW AROUND THE TROUGH, WHICH SHOULD BE ENOUGH TO SUPPORT SOME  
RAIN SHOWERS OVER PORTIONS OF THE REGION.  
   
LONG TERM
 
(SUNDAY THROUGH FRIDAY)  
ISSUED AT 322 PM CDT FRI SEP 20 2019  
 
ON THE SYNOPTIC SCALE A FAIRLY ACTIVE PATTERN CONTINUES ACROSS NORTH  
AMERICA THROUGH NEXT WEEK RESULTING IN FREQUENT CHANCES FOR  
PRECIPITATION AND TEMPERATURES STAYING WITHIN TEN DEGREES OF NORMAL.  
LATE WEEKEND A DEEPENING MID/UPPER LEVEL LONGWAVE TROUGH WILL MOVE  
ACROSS THE GREAT PLAINS AND SOUTHERN CANADA, WITH THE RESULTANT  
SURFACE LOW OVER HUDSON BAY AND A COLD FRONT EXTENDING DOWN INTO THE  
UPPER MIDWEST LATE SATURDAY INTO SUNDAY. THIS COLD FRONT WILL BE  
THROUGH THE NORTHLAND BY SUNDAY MORNING, WITH A CHANCE FOR SHOWERS  
IN THE POST-FRONTAL ENVIRONMENT AS COLDER AIR MOVES IN ALOFT AND THE  
LONGWAVE TROUGH BEGINS TO BREAK APART WITH A MID-LEVEL SHORTWAVE  
DEEPENING INTO AN UPPER LOW AS IT TRACKS TOWARDS THE UPPER GREAT  
LAKES, AIDING IN INCREASING BROAD-SCALE LIFT OVER THE NORTHLAND.  
 
MID-LEVEL RIDGING BUILDS IN BEHIND THE TROUGH FOR MONDAY LEADING TO  
SUNNY AND SLIGHTLY MILD CONDITIONS. SOUTHWEST WINDS DEVELOP AT LOW  
LEVELS ON TUESDAY LEADING TO WARMER AIR TO BE ADVECTED INTO THE  
REGION, WITH HIGHS IN THE UPPER 60S TO LOW 70S. A BROAD MID/UPPER  
LEVEL LONGWAVE TROUGH WILL DEVELOP ACROSS MUCH OF THE WESTERN TWO-  
THIRDS OF CANADA INTO NORTHERN GREAT PLAINS AND NORTHERN ROCKIES  
TOWARDS MID-WEEK, WITH A COLD FRONT MOVING SOUTH ACROSS THE GREAT  
PLAINS AND UPPER MIDWEST LATE TUESDAY INTO EARLY WEDNESDAY, LEADING  
TO A CHANCE FOR SHOWERS AND PERHAPS A FEW THUNDERSTORMS TUESDAY  
NIGHT THROUGH WEDNESDAY AFTERNOON AS A SUBTLE TROUGH WITHIN THE  
WESTERLY FLOW ALOFT LEADS TO BROAD-SCALE LIFT ALONG THE FRONT. A  
BREAK IN THE PRECIPITATION CHANCES WEDNESDAY NIGHT INTO EARLY  
THURSDAY AS HIGH PRESSURE BUILDS ACROSS THE MID MISSISSIPPI RIVER  
VALLEY. TEMPERATURES COOLER, HIGHS IN THE 60S WEDNESDAY, UPPER 50S  
TO LOW 60S THURSDAY. PRECIPITATION AMOUNTS WOULD GENERALLY BE LIGHT,  
LESS THAN A HALF INCH IN MOST LOCATIONS, AND THUNDERSTORMS ARE NOT  
ANTICIPATED.  
 
LATE-WEEK THERE IS A BROAD RANGE OF POSSIBILITIES ACROSS THE  
DETERMINISTIC AND ENSEMBLE GUIDANCE WITH AT LEAST A CHANCE FOR  
PRECIPITATION AT SOME POINT LATE THURSDAY THROUGH SATURDAY, WITH A  
POSSIBILITY IN SOME SCENARIOS FOR HEAVY RAINFALL. IN GENERAL, THE  
PATTERN SHIFTS TO FAVOR TOWARDS MILD TEMPERATURES AND A CHANCE FOR A  
STRONGER LOW PRESSURE SYSTEM TO DEVELOP OVER THE SOUTHERN/CENTRAL  
HIGH PLAINS AND LIFT NORTHEAST TOWARDS THE UPPER GREAT LAKES REGION.  
HOWEVER, THE TIMING/STRENGTH/TRACK OF ANY SUCH LOW PRESSURE SYSTEM  
IS UNCERTAIN AT THIS TIME, SO THE FORECAST REFLECTS LOW  
PRECIPITATION CHANCES AND TEMPERATURES NEAR NORMAL.  
 
THERE DOES NOT APPEAR TO BE A WIDESPREAD RISK FOR FROST THROUGH NEXT  
WEEKEND.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)  
ISSUED AT 1237 AM CDT SAT SEP 21 2019  
 
DENSE FOG WILL PERSIST THROUGH THE NIGHT AT DLH WITH AN EASTERLY  
ONSHORE WIND. LOWER CEILINGS HAVE MADE THEIR WAY TO HIB AS WELL  
AND EXPECT MVFR TO IFR CEILINGS OVERNIGHT. ELSEWHERE, SOME LOWER  
VISIBILITIES ARE POSSIBLE DUE TO SOME PATCHY FOG DEVELOPING.  
MAINLY EXPECTING MVFR, BUT BRIEF IFR IS POSSIBLE. SHOWERS AND  
THUNDERSTORM CHANCES DEVELOP FOR MOST AREAS OVERNIGHT INTO  
SATURDAY MORNING. THIS COULD BRING MVFR TO IFR CONDITIONS DUE TO  
REDUCED VISIBILITIES AND CEILINGS. GENERALLY EXPECTING TO HOLD ON  
TO MVFR CEILINGS THROUGH THE DAY AT MOST SITES, THOUGH DLH WILL  
LIKELY REMAIN IFR. MORE SHOWERS AND THUNDERSTORMS MAY DEVELOP  
DURING THE AFTERNOON, ESPECIALLY AT DLH/HYR. LOW LEVEL WIND SHEAR  
WILL BE AN ISSUE OVERNIGHT INTO EARLY SATURDAY MORNING DUE TO A  
SOUTHERLY LOW LEVEL JET. WINDS WILL BECOME BLUSTERY FROM THE SOUTH  
ON SATURDAY WITH GUSTS AROUND 25 KT POSSIBLE.  
 

 
   
MARINE
 
 
ISSUED AT 923 PM CDT FRI SEP 20 2019  
 
WIDESPREAD DENSE FOG WILL AFFECT THE NEARSHORE WATERS THROUGH THE  
MORNING. A MARINE DENSE FOG ADVISORY IS IN EFFECT UNTIL 10 AM  
SATURDAY. OTHERWISE, NORTHEAST WINDS 5 TO 10 KNOTS THROUGH THIS  
EVENING, THEN SOUTH-SOUTHEASTERLY WINDS DEVELOP LATE SATURDAY,  
BECOMING SOUTHWESTERLY 15 TO 20 KNOTS ON SATURDAY NIGHT ACROSS  
WESTERN LAKE SUPERIOR. WINDS PEAK IN STRENGTH ON SUNDAY MORNING AS  
THEY TURN MORE WESTERLY, WEAKENING THROUGH THE REST OF THE DAY.  
THESE STRONGER WINDS COULD LEAD TO A PERIOD OF HAZARDOUS  
CONDITIONS FOR SMALL CRAFT LATE SATURDAY NIGHT INTO SUNDAY  
MORNING. IN ADDITION, THERE IS A CHANCE FOR THUNDERSTORMS ACROSS  
WESTERN LAKE SUPERIOR ON SATURDAY, BUT STORMS ARE NOT EXPECTED TO  
BE SEVERE.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
DLH 58 73 53 66 / 10 70 30 10  
INL 64 73 52 64 / 50 70 70 30  
BRD 67 77 54 67 / 50 60 10 10  
HYR 66 76 55 68 / 10 60 40 10  
ASX 58 77 54 69 / 0 50 40 0  
 

 
   
DLH WATCHES/WARNINGS/ADVISORIES
 
 
WI...NONE.  
MN...NONE.  
LS...DENSE FOG ADVISORY UNTIL 10 AM CDT THIS MORNING FOR LSZ121-  
140>148.  
 

 
 

 
 
SHORT TERM...JTS  
LONG TERM...JJM  
AVIATION...MELDE/JS  
MARINE...JJM/GSF  
 
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