Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 220209
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
809 PM MDT TUE APR 21 2015

.SYNOPSIS...HIGH PRESSURE ALOFT OVER THE GREAT BASIN WILL SLOWLY
SHIFT EAST OF THE STATE BY LATE WEDNESDAY. A WEAKENING LOW
PRESSURE SYSTEM OVER SOUTHERN CALIFORNIA WILL TURN NORTH AND SEND
MOISTURE NORTH ACROSS UTAH...WHICH WILL RESULT IN PRECIPITATION
ACROSS MUCH OF THE STATE THROUGH THE REMAINDER OF THE WEEK.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A RIDGE OVER THE GREAT
BASIN AND NORTHERN ROCKIES...WITH A CLOSED LOW OVER SOUTHERN
CALIFORNIA AND A TROUGH ENTERING THE PACIFIC NORTHWEST. AMDAR
400-250MB WIND OBSERVATIONS SHOW A 75-100KT ANTICYCLONIC JET OVER
WESTERN CANADA. A 100-125KT SOUTHWESTERLY JET WAS LOCATED OVER
NORTHERN MEXICO ACROSS THE SOUTHEAST CONUS. GOES/GPS/RAP/00Z SLC
RAOB INDICATE THE PRECIPITABLE WATER VALUE RANGES BETWEEN
0.15"-0.20" NORTHERN MOUNTAINS...TO 0.35"- 0.45" ACROSS SOUTHERN
AND FAR NORTHWEST VALLEYS. BLENDED TOTAL PRECIPITABLE WATER
PRODUCT INDICATES MUCH LOWER THAN TYPICAL VALUES ACROSS THE WEST
COAST/SOUTHWEST CONUS...WITH HIGHER THAN NORMAL VALUES ACROSS
WESTERN CANADA AND SIERRA MOUNTAINS.

DEFORMATION AXIS OVER SOUTHERN UTAH IS THE FOCUS FOR ISOLATED TO
SCATTERED CONVECTION. SINCE THERE IS SYNOPTIC FORCING...BELIEVE
ACTIVITY WILL PERSIST THROUGH THE OVERNIGHT HOURS. LITTLE
PRECIPITATION...MORE OF A WIND GUST THREAT DUE TO DRY MICROBURSTS.
HAVE SEEN SOME IN-CLOUD LIGHTNING WITH THIS ACTIVITY SO WILL LEAVE A
MENTION IN FOR THE REMAINDER OF THE EVENING. THE AXIS IS SHOWN BY
THE RAP TO REMAIN FAIRLY STEADY IN POSITION OVERNIGHT.

GOING FORECAST IN GREAT SHAPE. JUST EXPANDED ISOLATED POPS INTO
SEVERAL MORE CENTRAL/SOUTHERN ZONES PER RADAR TRENDS. THIS IS ALSO
WHERE MOST CLOUD COVER WILL BE FOUND...LOWERED SKY COVER ACROSS FAR
NORTH. WARMED UP OVERNIGHT LOWS SEVERAL DEGREES ESPECIALLY UNDER THE
GREATER SKY COVER ACROSS CENTRAL AND SOUTHERN ZONES. HOURLY CURVE
UPDATED WITH LAMP GUIDANCE THROUGH EARLY MORNING HOURS.

&&

PREVIOUS DISCUSSION...
THE UPPER RIDGE SQUARELY OVER THE GREAT BASIN
THIS AFTERNOON WILL SLOWLY WORK EAST ALONG THE SPINE OF THE ROCKIES
BY LATE WEDNESDAY. BEHIND THIS RIDGE AXIS THE UPPER LOW OVER
SOUTHERN CALIFORNIA THIS AFTERNOON WILL TURN NORTH INTO EXTREME
SOUTHERN NEVADA EARLY WEDNESDAY. MOISTURE ASSOCIATED WITH THIS
FEATURE WILL EJECT NORTH ACROSS SOUTHWEST UTAH TONIGHT...THEN ACROSS
MAINLY WESTERN UTAH WEDNESDAY.

THE DEFORMATION AXIS TO THE NORTH OF THE APPROACHING UPPER LOW WILL
BE THE FOCUS FOR CONVECTION AS IT MOVES NORTH THROUGH SOUTHERN AND
CENTRAL UTAH TONIGHT/EARLY WEDNESDAY. POCKETS OF CONVECTION WILL
ALSO LINGER ACROSS FAR SOUTHERN UTAH NEAR THE CENTER OF THE LOW. IN
GENERAL THE DYNAMIC FORCING IS ON THE WEAK SIDE WITH AVAILABLE
MOISTURE ADEQUATE FOR CONVECTION /PWAT VALUES AROUND .45 TO.55
INCHES/. SUSPECT THAT MUCH OF THE CONVECTION WILL REMAIN TIED TO THE
HIGHER TERRAIN OR CONCENTRATED ALONG THE DEFORMATION AXIS THROUGH
WEDNESDAY EVENING.

THE LATTER PORTION OF THE WEEK WILL SEE A WEAK TROUGH COVERING MUCH
OF THE INTERIOR WEST ALONG WITH THE STILL ADEQUATE MOISTURE TO
MAINTAIN SCATTERED CONVECTION THROUGH AT LEAST FRIDAY. A SHORTWAVE
MOVING EAST ACROSS THE NORTHERN ROCKIES ON THURSDAY WILL NUDGE A
SURFACE BOUNDARY INTO NORTHWEST UTAH WEDNESDAY NIGHT...THEN ACROSS
SOUTHWEST WYOMING THROUGH WEST-CENTRAL UTAH THURSDAY. THIS BOUNDARY
WILL LIKELY SEE ORGANIZED CONVECTION DURING THE DAY...WITH THE HIGH
TERRAIN TO THE SOUTH AND EAST OF THE BOUNDARY ALSO REMAINING
ACTIVITY IN DIURNAL CONVECTION. THURSDAY WILL BE THE BETTER OF THE
TWO DAYS IN TERMS OF MEASURABLE PRECIP...WITH SOME SNOW POSSIBLE
ACROSS THE HIGHER NORTHERN AND CENTRAL MOUNTAINS. INCREASING CLOUD
COVER AND PRECIP WILL BRING A MODEST COOLING TREND TO MAINLY
NORTHERN AND CENTRAL UTAH HEADING INTO THE WEEKEND.

GLOBAL MODELS IN AGREEMENT THAT A SHORTWAVE TROUGH WILL SWING
THROUGH THE GREAT BASIN FRIDAY NIGHT WITH THE LONGWAVE TROUGH TO
MOVE THROUGH SATURDAY NIGHT INTO SUNDAY. ALTHOUGH THE FIRST SHORT
WAVE IS WEAK IT WILL BE ACTING ON A MORE MOIST AIR MASS...THEREFORE
HAVE BOOSTED POPS ABOVE 35 PERCENT ACROSS THE NORTHWESTERN HALF OF
THE CWA WITH SOME LIKELY POPS IN THE MOUNTAINS. THE NAM12...GFS AND
EC ALL SHOW A BAND OF QPF IN THE 0.25 TO 0.40 OF AN INCH RANGE FOR
THE 6 HR PERIOD BETWEEN 00Z AND 06Z SATURDAY...GENERALLY IN A SWATH
FROM WEST CENTRAL UTAH TO THE WASATCH FRONT FRIDAY NIGHT. CHANCES
ARE THAT SOME PLACE WITHIN THIS SWATH WILL RECEIVE SOME GOOD RAIN
BUT TOO EARLY TO PINPOINT WHERE AT THIS TIME...BUT DID INCREASE QPF
SOME.

HAVE LOWERED SOME TEMPERATURES FOR SATURDAY ACROSS NORTH AND WESTERN
AREAS AS CLOUDS AND RAIN LIKELY TO IMPACT AMOUNT OF INCOMING
INSOLATION.

THE LONG WAVE TROUGH IS FORECAST BY BOTH THE EC AND GFS TO ACTUALLY
BE OVER EASTERN UTAH BY SUNDAY MORNING BUT THE GFS HOLDS BACK LOW
LEVEL MOISTURE UNDER NORTHWEST FLOW INTO SUNDAY NIGHT. ALTHOUGH NOT
CONVINCED ANY SHOWERS WILL OCCUR FELT IT BEST TO KEEP THE LOW POPS
IN FOR NOW. THE EC AND GFS DIVERGE ON THEIR SOLUTIONS WITH THE EC
MAINTAINING A RIDGE OVER THE WESTERN GREAT BASIN ABOUT 5-10 DEGREES
LONGITUDE FARTHER WEST THAN THE GFS. THIS PLACES UTAH UNDER AN
ANTICYCLONIC NORTHWEST FLOW THROUGH TUESDAY VERSES THE GFS IDEA OF A
PROGRESSIVE RIDGE WITH SOUTHWEST FLOW ALREADY OVER UTAH BY TUESDAY.
PLAYED THE DRIER EC SOLUTION AS THE EC HAS BEEN MORE CONSISTENT IN
ITS FORECAST PAST FEW RUNS.

&&

.AVIATION...NORTHWEST WINDS AT SLC TERMINAL WILL SHIFT TO SOUTHEAST
BETWEEN 02-04Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...NONE.
&&

$$

PUBLIC...ROGOWSKI/CONGER/STRUTHWOLF
AVIATION...KRUSE

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)


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