Area Forecast Discussion
Issued by NWS Rapid City, SD

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KUNR 220442
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
942 PM MST SAT FEB 21 2015

.UPDATE...
ISSUED AT 936 PM MST SAT FEB 21 2015

00Z KUNR SOUNDING SHOWED STEEP LOW LEVEL LAPSE RATES WITH A LAYER
OF MOISTURE AT THE TOP OF THE BOUNDARY LAYER. WEAK SHORTWAVE OVER
SOUTHEAST MT TAPPING INTO THIS INSTABILITY NORTH/EAST OF THE BLACK
HILLS THIS EVENING. HAVE UPDATED FORECAST AGAIN FOR EXPANDING AREA
OF SCATTERED -SHSN. ACCUMULATIONS WILL BE MINOR. AS SHORTWAVES
SHIFTS SOUTH OVERNIGHT...ACTIVITY SHOULD COME TO AND END AS DRIER
AIR/SUBSIDENCE TAKES OVER.

&&

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT
ISSUED AT 122 PM MST SAT FEB 21 2015

THE LATEST WATER VAPOR IMAGES AND SHORT-TERM MODEL GUIDANCE
INDICATED A LARGE TROUGH COVERING MOST OF THE CONUS WITH A SHARP
RIDGE JUST OFF THE WRN NOAM COAST. THIS HAS ALLOWED ARCTIC AIR TO
SPILL SOUTH ACROSS ALL OF THE NRN PLAINS. A SHORT-WAVE TROUGH WAS
LOCATED FROM WRN MT TO NRN MN AND WAS MOVING SOUTHEAST TOWARD THE
FORECAST AREA. AHEAD OF THIS TROUGH THERE WERE SNOW SHOWERS OVER
MUCH OF THE REGION...AIDED BY STEEP SURFACE-BASED LAPSE RATES AND
SOME INSOLATION. SNOW SHOWERS ALSO WERE ENHANCED NEAR THE BLKHLS
WHERE UPSLOPE...DOWNSTREAM CONVERGENCE...AND FRONTOGENESIS WERE
LOCALLY ENHANCED.

FOR TONIGHT...THERE WILL BE A DOWNWARD TREND IN COVERAGE OF THE SNOW
SHOWERS...ALTHOUGH THEY WILL PERSIST MOST OF THE NIGHT ACROSS NERN
WY AND SWRN SD AHEAD OF THE UPPER TROUGH. ACCUMULATIONS WILL BE
LIGHT BUT THE MODELS ARE CONSISTENT WITH THE QPF SIGNAL IN THIS
AREA. OTHERWISE...SKIES WILL BE CLEARING SOMEWHAT FROM NORTH TO
SOUTH...AND THIS WILL ALLOW TEMPERATURES TO DROP TO NEAR OR BELOW
ZERO...ESPECIALLY OVER NWRN SD. WIND CHILLS WILL DROP TO -15 TO -25
OVER NWRN SD...CLOSE TO ADVY CRITERIA. FORTUNATELY...THE WINDS WILL
BE DIMINISHING OVERNIGHT...WHICH WILL HELP OFFSET THE DROP IN TEMPS.

A DRY DAY IS EXPECTED SUNDAY AS THE UPPER TROUGH AXIS WASHES OUT
JUST SOUTH OF THE CWA AND UPPER HEIGHTS BUILD SLIGHTLY. IT WILL BE
QUITE COLD AS A 1048-MB HIGH SETTLES OVER THE ERN DAKOTAS. MODELS DO
INDICATE A 100-MB THICK UNSTABLE LAYER AT THE SURFACE...WITH TEMPS
FAVORABLE FOR SNOW GROWTH OVER THE BLKHLS. HOWEVER...GIVEN THE
RELATIVELY DRY AIR...SUBSIDENCE ALOFT...AND SHALLOW DEPTH TO THIS
LAYER IT SEEMS UNLIKELY THAT SNOW SHOWERS WILL DEVELOP OVER THE
BLKHLS...AND THUS HAVE MAINTAINED A DRY FORECAST FOR TOMORROW.

SUNDAY NIGHT WILL CONTINUE TO BE DRY AND COLD...ALTHOUGH SOME
LOW-LEVEL WARM ADVECTION WILL COMMENCE LATE AS A LEE SURFACE TROUGH
DEVELOPS. THIS COULD FORCE THE HIGHER ELEVATIONS OF NERN WY AND THE
BLKHLS TO SEE RISING TEMPS AFTER MIDNIGHT...WITH MORE NOTABLE
WARMING ON MONDAY.

.LONG TERM...MONDAY THROUGH SATURDAY
ISSUED AT 122 PM MST SAT FEB 21 2015

PERSISTENT NW FLOW WILL REMAIN IN PLACE THROUGH THE PERIOD...WITH
A LL BAROCLINIC ZONE WAVERING BACK AND FORTH ACROSS THE REGION. A
MORE PRONOUNCED CP/MODIFIED ARCTIC INTRUSION STILL ON TRACK LATE
NEXT WEEK AS ADVERTISED IN BOTH THE ECMWF AND GFS. THE WESTERN
NOAM RIDGE WILL SHIFT WEST AS A STRONG RIDGE-TOPPING TROUGH SHIFTS
SE ACROSS THE ROCKIES...WITH THE RIDGE THEN BUILDING NORTH INTO
THE HIGH LATITUDES. THIS WILL ALLOW A MUCH DEEPER COLD AIR MASS TO
SHIFT WEST OVER THE REGION...WITH A LONGER RESIDENCE TIME...AS SIG
TROUGH LOADING OCCURS INTO THE WEST SIDE OF THE RIDGE. THE WESTERN
BIAS TO THE EASTERN PAC RIDGE LOOKS TO LINGER INTO NEXT WEEKEND...
SUGGESTING THAT COLD CONDS WILL PREVAIL INTO THE WEEKEND AND
BEYOND.

A BRIEF WARM UP EXPECTED IN THE MON-TUE PERIOD AS SERIES OF WEAK
IMPULSES SHIFT THE LL FRONTAL ZONE EAST. HAVE WARMED TEMPS...ESP TUE
AS A DECENT WAA SURGE IS EXPECTED AHEAD OF WED/S SYSTEM. DRY
WEATHER EXPECTED THROUGH EARLY NEXT WEEK...WITH A DECENT CHANCE FOR
SNOW TUE NIGHT-WED AS THE AFOREMENTIONED IMPULSE DIVES SE ACROSS
THE ROCKIES AND A COLD FRONT SLIDES SOUTH. ATTM MOST OF THE LSA AND
ASSOCIATED LIFT CONTINUES TO BE PROGGED SW OF THE FA...WITH
GENERALLY LIGHT ACCUMS /1-3 INCHES/ EXPECTED PER FGEN PROCESSES.
COLD AIR WILL SETTLE INTO THE REGION THUR...WITH TEMPS AVERAGING
10-20 DEGREES BELOW SEASONAL NORMS. SOME MODERATION IN TEMPS LOOKS
POSSIBLE FRI-SAT WITH WEAK RIDGING AHEAD OF ANOTHER POTENTIAL STRONG
NW FLOW UPPER TROUGH. HAVE KEPT MOST PLACES DRY THUR-SAT. HOWEVER...
LINGERING LL FGEN AND WAA PROCESS MAY SUPPORT LIGHT SNOW ACROSS
THE SOUTHERN HALF AT TIMES. LOW CONFIDENCE AND HIGH UNCERTAINTY
SUPPORT ONLY SLIGHT CHANCE MENTIONS ATTM.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 936 PM MST SAT FEB 21 2015

MVFR CIGS WITH LOCAL IFR CIGS WILL SLOWLY IMPROVE TO VFR BY
SUNDAY AFTERNOON. ISOLATED/SCATTERED -SHSN WILL OCCUR TONIGHT OVER
NORTHEAST WY/SOUTHWEST SD WITH LOCAL IFR VSBYS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

UPDATE...HELGESON
SHORT TERM...BUNKERS
LONG TERM...JC
AVIATION...HELGESON






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.