318
FXUS63 KBIS 312359
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
659 PM CDT SUN MAY 31 2020
UPDATE
ISSUED AT 647 PM CDT SUN MAY 31 2020
THE FORECAST FOR THIS EVENING REMAINS ON TRACK. SEVERE
THUNDERSTORM WATCH NUMBER 238 REMAINS IN EFFECT FOR THE
SOUTHWEST.
THUNDERSTORMS CONTINUE TO MOVE NORTHEAST ACROSS SOUTHEASTERN
MONTANA, AND ARE PROJECTED TO ENTER SOUTHWEST ND BETWEEN 00-01Z.
AT THIS TIME, ONE SEVERE STORM TRACKING EAST OF MILES CITY,
SHOWING SIGNS OF BEING SUPERCELLULAR, TAKING A RIGHT MOVER TRACK
MORE EASTERLY VERSUS NORTHEAST. STILL SOME UNCERTAINTY ON THE
OVERALL STORM COVERAGE ACROSS WESTERN ND WITH FORCING ALOFT NOT
THAT IMPRESSIVE.
WILL MAINTAIN THE WIND ADVISORY AS IS BUT SHOULD BE ABLE TO LET IT
EXPIRE WITHIN THE NEXT HOUR.
UPDATE
ISSUED AT 511 PM CDT SUN MAY 31 2020
SEVERE THUNDERSTORM WATCH NOW IN EFFECT FOR PORTIONS OF SOUTHWEST
NORTH DAKOTA. WILL UPDATE ALL PRODUCTS TO REFLECT THIS.
SHORT TERM
(THIS EVENING THROUGH MONDAY)
ISSUED AT 247 PM CDT SUN MAY 31 2020
THE MAIN CONCERN FOR THE SHORT TERM PERIOD IS THE POTENTIAL FOR
STRONG TO SEVERE THUNDERSTORMS IN WESTERN NORTH DAKOTA THIS EVENING.
AN UPPER LEVEL RIDGE AXIS SITS OVER THE NORTHERN PLAINS EARLY THIS
AFTERNOON, WITH A 30-40 KT LOW LEVEL JET UNDERNEATH. SURFACE
ANALYSIS SHOWS HIGH PRESSURE OVER THE GREAT LAKES AND A DEEPENING
LOW IN SOUTHERN ALBERTA. THIS SETUP HAS RESULTED IN WINDY CONDITIONS
ACROSS THE REGION. THE STRONGEST WINDS HAVE BEEN IN NORTHWEST NORTH
DAKOTA, WHERE SUSTAINED WIND SPEEDS OVER 30 MPH HAVE ROUTINELY BEEN
REPORTED. A WIND ADVISORY IS IN EFFECT FOR THAT AREA UNTIL 8 PM CDT.
MID LEVEL SHORTWAVE TROUGHING WILL MOVE INTO EASTERN MONTANA LATE
THIS AFTERNOON AS A SURFACE TROUGH SHARPENS ATTENDANT TO THE
SOUTHERN ALBERTA SURFACE LOW. THE PRESENCE OF ADDITIONAL FORCING IN
THE FORM OF LOW LEVEL FRONTOGENESIS IS FORECAST ACROSS EASTERN
MONTANA. MOST GUIDANCE AGREES THAT CONVECTIVE INITIATION WILL OCCUR
IN EASTERN MONTANA LATE THIS AFTERNOON, THOUGH SOME OF THE FORCING
MECHANISMS APPEAR A BIT DISJOINTED SPATIALLY. ADDITIONALLY, RECENT
GUIDANCE SUGGESTS CONVECTIVE INHIBITION WILL BE MUCH WEAKER ACROSS
EASTERN MONTANA THAN ORIGINALLY THOUGHT, OWING TO A GREATER
LIKELIHOOD OF CONVECTIVE INITIATION GIVEN THE FORCING THAT IS
FORECAST TO BE PRESENT. THERE IS STILL SOME ON UNCERTAINTY ON
EXACTLY WHERE CONVECTIVE INITIATION MAY OCCUR, BUT THERE IS A
NOTABLE TREND IN MORE RECENT GUIDANCE TO SHIFT LOW LEVEL FORCING AS
FAR EAST AS THE ND/MT BORDER BY LATE AFTERNOON. THIS CAN BE SEEN,
FOR EXAMPLE, IN RAP 0-1 KM MOISTURE FLUX DIVERGENCE AND THETA-E
FIELDS. HOWEVER, THERE IS GREATER CONVECTIVE INHIBITION AND LESS MID
LEVEL FORCING THE FARTHER EAST YOU GO. THIS FURTHER CONTRIBUTES TO
THE UNCERTAINTY IN THE OVERALL OUTCOME OF THIS EVENT.
SURFACE BASED STORMS THAT DEVELOP WILL BE IN AN ENVIRONMENT
CHARACTERIZED BY DEWPOINTS AROUND 60 F, CAPE AROUND 2000 J/KG, AND
30-40 KTS OF EFFECTIVE BULK SHEAR, ACCORDING TO THE HREF ENSEMBLE
MEAN. SHEAR VECTORS ORIENTED NEARLY PERPENDICULAR TO THE SURFACE
TROUGH SUGGEST A DISCRETE MODE WILL BE FAVORED INITIALLY, THOUGH
COLD POOL PROCESSES AND SUSTAINED FORCING MECHANISMS MAY EVENTUALLY
LEAD TO UPSCALE GROWTH INTO LINEAR CLUSTERS DOWNSTREAM. A LARGE HAIL
THREAT IS SUPPORTED BY THE AFOREMENTIONED INSTABILITY AND SHEAR,
STORM MODE, AND RELATIVELY DRY MID LEVELS. A DAMAGING WIND THREAT IS
SUPPORTED BY HIGH LCLS AND INVERTED-V THERMODYNAMIC PROFILES, AS
WELL AS BY ANY TRANSITION TO A LINEAR MODE.
THERE IS GENERAL MODEL CONSENSUS THAT AT LEAST ISOLATED SHOWER AND
THUNDERSTORM ACTIVITY WILL CONTINUE TO MOVE ACROSS NORTH DAKOTA
OVERNIGHT AS THE SURFACE TROUGH AND MID LEVEL SHORTWAVE TRACK
EASTWARD, THOUGH SOME OF THE MORE RECENT CAM RUNS HAVE BACKED OFF ON
THIS SOLUTION, LIKELY DUE TO INCREASING MLCIN. QUIET AND WARM
WEATHER IS EXPECTED ON MONDAY AS SUBSIDENCE REBOUNDS OVER THE
NORTHERN PLAINS. HIGHS WILL MAINLY BE IN THE 80S.
LONG TERM
(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 247 PM CDT SUN MAY 31 2020
ANOTHER MID LEVEL SHORTWAVE WILL APPROACH WESTERN NORTH DAKOTA
MONDAY NIGHT. THERE IS DECENT MODEL CONSENSUS FOR OVERNIGHT SHOWER
AND THUNDERSTORM DEVELOPMENT AHEAD OF THIS WAVE, WITH FORCING
POSSIBLY BEING AIDED BY INCREASING LOW TO MID LEVEL MOISTURE
TRANSPORT. IF UPDRAFTS CAN TAKE ADVANTAGE OF 1000-2000 J/KG MUCAPE
OVER SOUTHWEST NORTH DAKOTA, ALONG WITH AT LEAST 40 KTS EFFECTIVE
BULK SHEAR, STORMS COULD BECOME SEVERE, WITH LARGE HAIL BEING THE
MAIN THREAT. THERE IS UNCERTAINTY ON HOW MUCH MLCIN WILL BE PRESENT
THOUGH, WHICH WILL BE LARGELY DEPENDENT ON INFLOW LAYER RH. THIS
CONDITIONAL SEVERE THREAT MAY EXPAND INTO SOUTH CENTRAL NORTH DAKOTA
TUESDAY MORNING AS THE SHORTWAVE CONTINUES TO PROPAGATE EASTWARD,
BUT INSTABILITY LOOKS MORE MARGINAL THERE. FARTHER NORTH, SCATTERED
SHOWERS ARE POSSIBLE TUESDAY MORNING IN ASSOCIATION WITH STRONGER
HEIGHT FALLS, BUT THERE IS EXPECTED TO BE LITTLE TO NO INSTABILITY.
MODEL GUIDANCE HAS TRENDED AWAY FROM BROAD UPPER LEVEL RIDGING TO
MORE OF A ZONAL FLOW PATTERN LATE TUESDAY THROUGH THURSDAY, WITH
VARIOUS DISTURBANCES PASSING THROUGH. THIS PATTERN SHIFT HAS
RESULTED IN A SLIGHTLY COOLER TEMPERATURE FORECAST THROUGH
THURSDAY, THOUGH STILL NEAR TO ABOVE NORMAL. LONG RANGE GUIDANCE
APPEARS TO BE CONVERGING ON A SOLUTION THAT QUICKLY BUILDS UPPER
LEVEL RIDGING OVER THE NORTHERN PLAINS HEADING INTO THE WEEKEND
AHEAD OF DEEPENING LONGWAVE TROUGHING OVER THE PACIFIC COAST. THIS
COULD SIGNAL THE BEGINNING OF AN ACTIVE PERIOD NEXT WEEKEND,
THOUGH DETERMINISTIC MODELS ARE EXHIBITING THEIR KNOWN BIASES IN
THE PROGRESSIVENESS OF THE PATTERN, WITH THE GFS BEING MUCH
QUICKER TO BRING SHORTWAVE ENERGY INTO THE NORTHERN PLAINS THAN
THE ECMWF.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 647 PM CDT SUN MAY 31 2020
VFR CONDITIONS ARE EXPECTED THROUGH THE FORECAST PERIOD. THERE IS
A CHANCE OF THUNDERSTORMS IN WESTERN ND THIS EVENING. THIS
POTENTIAL SHIFTS INTO CENTRAL ND OVERNIGHT, BUT WITH DECREASING
PROBABILITY. LEFT VCTS IN THE FOR KDIK, BUT OPTED TO REMOVE AND
GO WITH VCSH FOR KXWA, KMOT, KBIS AND KJMS. IF A STORM DOES
HAPPEN TO PASS OVER A TERMINAL, A BRIEF PERIOD OF MVFR/IFR
VISIBILITY AND SPORADIC WIND GUSTS WOULD BE POSSIBLE. STRONG
SOUTHEAST WINDS AROUND 20-25 KTS GUSTING TO 30-40 KTS WILL
GRADUALLY DECREASING THIS EVENING AND OVERNIGHT, WITH WINDS
SHIFTING TO THE NORTHWEST FOR MONDAY.
BIS WATCHES/WARNINGS/ADVISORIES
WIND ADVISORY UNTIL 8 PM CDT /7 PM MDT/ THIS EVENING FOR NDZ001-
002-009-010-017.
UPDATE...NH
SHORT TERM...HOLLAN
LONG TERM...HOLLAN
AVIATION...NH
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