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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