Area Forecast Discussion
Issued by NWS Aberdeen, SD

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552
FXUS63 KABR 160941
AFDABR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
441 AM CDT SAT MAY 16 2015

.SHORT TERM...(TODAY THROUGH MONDAY AFTERNOON)
ISSUED AT 435 AM CDT SAT MAY 16 2015

AN ACTIVE WEATHER PATTERN EXPECTED OVER THE SHORT TERM PERIOD!
INITIAL CONCERNS ARE SEVERE WEATHER AND HEAVY RAIN POTENTIAL TODAY
AND TONIGHT. ADDITIONAL PRECIPITATION /AND SNOW?/ ALONG WITH
POSSIBLE FREEZING TEMPERATURES FOLLOW ON SUNDAY AND MONDAY.

TODAY AND TONIGHT...FORECASTER CONFIDENCE: MODERATE

UPPER AIR ANALYSIS AND WATER VAPOR IMAGERY CLEARLY DEPICTED A STRONG
CLOSED LOW SPINNING OVER THE INTERMOUNTAIN WEST.  SEVERAL SHORTWAVES
ARE EXPECTED TO MOVE THROUGH THE REGION THE NEXT DAY OR
SO...PROVIDING THE IMPETUS FOR SEVERAL ROUNDS OF THUNDERSTORM
DEVELOPMENT. INITIAL ROUND OF SHOWERS AND STORMS IS CURRENTLY MOVING
NEWD ACROSS THE CWA PER STOUT LLJ. NOTHING SEVERE WITH THIS
ACTIVITY...ALTHOUGH BRIEF HEAVY RAINFALL AND GUSTY WINDS ARE
POSSIBLE. IN FACT...SEVERAL OBS HAVE NOTED A WEAK "WAKE LOW"
ACROSS WESTERN SD.

IN THE WAKE OF THIS MORNING ACTIVITY...THERE IS STILL A FAIR AMOUNT
OF UNCERTAINTY FOR THE AFTERNOON...MAINLY WITH REGARDS TO
DESTABILIZATION.  SEVERAL MODEL SOLUTIONS KEEP PERSISTENT CLOUDS AND
ELEVATED...WEAK THUNDERSTORMS IN THE AREA THROUGHOUT THE DAY. THIS
OUTCOME WOULD LIMIT ANY SEVERE THUNDERSTORM THREAT.  OTHER SOLUTIONS
INDICATE A LULL IN PCPN...WITH AT LEAST PARTIAL SUNSHINE AND MORE
SIGNIFICANT INSTABILITY.  AT THIS TIME...TRENDED THE FORECAST MORE
TOWARD THE LATER SOLUTION AND FEEL AT LEAST POCKETS OF MLCAPE OF 500-
1500 J/KG WILL DEVELOP IN CONCERT WITH WITH DEEP LAYER SHEAR VALUES
OF 30-40KTS BY 18Z. THUS...BELIEVE WE WILL SEE SCATTERED CONVECTION
RE-DEVELOP BETWEEN 18Z AND 21Z /PER LATEST HRRR SOLUTIONS/ WITH SOME
OF THESE STORMS BECOMING STRONG TO SEVERE.  MAIN THREAT WOULD BE
HAIL AND DAMAGING WINDS...ALTHOUGH ANY OUTFLOW BOUNDARIES OR BACKED
SFC FLOW COULD ALSO PROVIDE ENOUGH SRH FOR AN ISOLATED TORNADO.
CORFIDI VECTORS ARE ALSO INDICATING RELATIVELY SLOW STORM
MOVEMENT...SO KEPT THE MENTION OF LOCALLY HEAVY RAINFALL AS WELL.  A
STRONGER SHORTWAVE/PV ANOMALY WILL EJECT ACROSS THE NRN PLAINS
TONIGHT...LIKELY MAINTAINING OR INITIATING NEW TSTMS. SPC MAINTAINED
A SLIGHT RISK FOR THE ENTIRE AREA IN THE DAY 1 OUTLOOK...AND THIS
APPEARS REASONABLE.

SUNDAY THROUGH MONDAY...FORECAST CONFIDENCE: MODERATE

AS MENTIONED PREVIOUSLY...THE TRACK OF THIS SYSTEM HAS IN FACT
SLOWED DOWN SUCH THAT A LINGERING SEVERE THREAT WILL CONTINUE ON
SUNDAY...MAINLY ALONG AND EAST OF THE JAMES RIVER VALLEY /IN THE
WARM SECTOR/.  ALTHOUGH DEEP LAYER SHEAR WILL BE MARGINAL...SFC
VORTICITY INVOF OF THE SFC LOW COULD YIELD ANOTHER ROUND OF STRONG
TO SEVERE STORMS...AND POSSIBLE LANDSPOUT TYPE STORMS. DEFORMATION
ZONE PCPN IS EXPECTED NW OF THE SFC CYCLONE...WITH 00Z SUITE OF
MODELS INDICATING THE POTENTIAL FOR ADDITIONAL SIGNIFICANT
RAINFALL. FINALLY...IN THE WAKE OF THIS SYSTEM...A UNSEASONABLY
COLD AIRMASS WILL FILTER IN FROM THE NORTHWEST. 850MB/925MB TEMPS
ARE FORECAST TO FALL BELOW ZERO CELSIUS...WITH THE POSSIBILITY OF
A RAIN/SNOW MIX ACROSS N-CENTRAL SD. YES...I SAID A RAIN/SNOW MIX ON
MAY 16TH...UGH. PLENTY OF TIME TO FINE TUNE THIS FORECAST.

.LONG TERM...(MONDAY EVENING THROUGH FRIDAY)
ISSUED AT 435 AM CDT SAT MAY 16 2015

COOL CANADIAN HIGH PRESSURE WILL BE BUILDING SOUTH OVER THE REGION
MONDAY NIGHT INTO TUESDAY MORNING TO START OFF THE EXTENDED PERIOD.
LOOKING FOR RATHER COOL OVERNIGHT LOWS MONDAY NIGHT/TUESDAY MORNING
WITH READINGS AROUND FREEZING OR SLIGHTLY COOLER. ITS LOOKING LIKE
IT MAY NOT BE QUITE AS COLD AS PREVIOUSLY THOUGHT AS THERE IS STILL
A PRESSURE GRADIENT OVERHEAD BY 12Z TUESDAY WHICH WILL KEEP A BIT OF
A BREEZE GOING. NONETHELESS...THREAT FOR FROST/FREEZE CONDITIONS
STILL POSSIBLE TUESDAY MORNING AND STILL POSSIBLE FOR SFC HIGH TO BE
MORE OF AN INFLUENCE WITH WEAKER WINDS BEING THE CASE.

THE HIGH PRESSURE LINGERS OVER THE NORTHERN PLAINS DURING THE FIRST
PART OF THE EXTENDED...KEEPING COOL TEMPS OVER THE REGION THROUGH
MID WEEK. HIGHS ARE ONLY EXPECTED TO BE IN THE 50S TO LOW 60S WHICH
IS WELL BELOW NORMAL FOR THIS TIME OF YEAR. MODELS ALSO SHOWING SOME
SHORTWAVE ENERGY WORKING ACROSS THE CENTRAL/NORTHERN PLAINS TUESDAY
NIGHT THROUGH WEDNESDAY NIGHT...BUT IT WILL BE RUNNING INTO DRIER
AIR ASSOCIATED WITH THE HIGH. APPEARS BEST CHANCES FOR PRECIP WILL
BE OVER THE WEST/SOUTHWEST CWA.

MODELS SHOW WARMING TEMPS BY THE END OF THE UPCOMING WEEK WITH HIGHS
RETURNING CLOSER TO NORMAL BY FRIDAY. LOOKING WAY OUT...MODELS
TRYING TO SHOW ANOTHER SIGNIFICANT STORM SYSTEM POSSIBLY AFFECTING
THE REGION NEXT WEEKEND AS THE ACTIVE WEATHER PATTERN CONTINUES.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 435 AM CDT SAT MAY 16 2015

TWO WAVES OF SHOWERS AND THUNDERSTORMS ARE EXPECTED TO AFFECT ALL
TERMINALS TONIGHT AND AGAIN SATURDAY AFTERNOON. A STRONG WARM
FRONT/LLJ SURGING NORTH ALONG WITH AN UPPER LEVEL TROUGH/JET STREAK
WILL CONTINUE TO SPREAD THE FIRST ROUND OF SHOWERS AND THUNDERSTORMS
ACROSS ALL OF THE AREA INTO SATURDAY MORNING. EXPECT MAINLY MVFR
CEILINGS AND VISIBILITIES TONIGHT. THE RAIN AND STRATUS ARE EXPECTED
TO LIFT NORTH WHILE NEW SHOWER AND THUNDERSTORM DEVELOPMENT IS
EXPECTED SATURDAY AFTERNOON. SOME OF THESE COULD BE SEVERE.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
&&

$$

SHORT TERM...FOWLE
LONG TERM...TMT
AVIATION...TMT



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