FXUS65 KSLC 271604
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
904 AM MST FRI NOV 27 2009
.SYNOPSIS...A SPLITTING PACIFIC STORM SYSTEM WILL SLIDE ACROSS
THE REGION TONIGHT AND SATURDAY. A RIDGE OF HIGH PRESSURE WILL
BUILD OVER THE AREA EARLY NEXT WEEK.
&&
.DISCUSSION...SOUTHWESTERLY FLOW HAS NOTICEABLY INCREASED ACROSS
ALL BUT THE LOWEST VALLEY AREAS ACROSS THE WESTERN HALF OF THE
STATE THIS MORNING PER LATEST MESOWEST OBSERVATIONS. A QUICK LOOK
AT THE FIRST FEW DAYLIGHT FRAMES IN STATEWIDE CAMERA IMAGERY
INDICATE GENERALLY CLEAR SKIES WITH ALL VISIBLE VALLEY INVERSIONS
RELEGATED TO VALLEY BOTTOM AREAS ONLY ALONG THE WASATCH
FRONT/CACHE VALLEY.
12Z KSLC SOUNDING PAINTS THE PICTURE...VERY STRONG LOW LEVEL
INVERSION IN PLACE WITH ALMOST 20 DEGREE F DIFFERENCE BETWEEN KSLC
AND THE UPPER BENCHES. ALTHOUGH THE TEMPERATURE INVERSION EXISTS
THROUGH ABOUT THE 6500FT LEVEL...GUSTY SOUTHERLIES HAVE PUNCHED TO
WITHIN 300 FT OF THE VALLEY FLOOR GENERATING SIGNIFICANT MIXING AT
THIS TIME. MOISTURE RAPIDLY DECREASES AT THAT LEVEL...LEADING TO A
VERY SHALLOW WEDGE OF TRAPPED SMOG/HAZE. APPROACHING PACIFIC CUT
OFF WILL CONTINUE TO STRENGTHEN SOUTHWESTERLY FLOW ALOFT
TODAY...SO MIXING SHOULD ONLY ENHANCE DURING THE LATE MORNING AND
AFTERNOON HOURS. THAT SAID...THE MAJORITY OF THE WASATCH
FRONT/CACHE VALLEY SHOULD MIX OUT TODAY ALLOWING TEMPS TO TAKE A
NOTICED JUMP INTO THE MID 50S...POSSIBLY MORE. HAVE OPTED TO LEAVE
THE VALLEY BOTTOM AREAS IN NORTHERN UTAH COOLER AS THEY SHOULD
ONLY PARTIALLY MIX IN THIS SCENARIO...BUT THEY SHOULD SEE ABOUT A
5 DEGREE WARM UP AS WELL VERSUS YESTERDAYS HIGHS. ELSEWHERE ACROSS
THE STATE...TEMPS WILL REMAIN UNSEASONABLY WARM WITH VALLEY AREAS
ACROSS CENTRAL/SOUTHERN UTAH COMPLETELY MIXING DUE TO SNOW FREE
GROUND COVER.
UPDATED TO INCREASE HIGH CLOUD COVER ACROSS WESTERN UTAH LATE THIS
MORNING THROUGH THE AFTERNOON HOURS. OUTSIDE OF THIS...PACKAGE
REMAINS IN FINE SHAPE AND NO FURTHER UPDATES ARE PLANNED.
PREVIOUS DISCUSSION FOLLOWS...
WATER VAPOR LOOP SHOWS A SHEARING TROUGH ALONG THE
PACIFIC NORTHWEST COAST...AS AN UPPER LOW ENTERS THE GULF OF ALASKA.
400-250MB ACARS WIND OBSERVATIONS SHOWS LIGHT ANTICYCLONIC FLOW
ALOFT...WITH A 100-125KT ANTICYCLONICALLY CURVED JET FROM THE
PACIFIC NORTHWEST TOWARD LAKE WINNIPEG. 00Z 700MB ANALYSIS PLACED
THE RIDGE ACROSS ARIZONA WITH A COLD FRONT CUTTING ACROSS THE
PACIFIC NORTHWEST. ADVECTION HAS TURNED NEUTRAL LOCALLY...WITH +4C
AT BOTH KSLC AND UPSTREAM AT KNKX. 00Z KSLC RAOB INDICATES 3-5C OF
WARMING BELOW 650MB WITH LITTLE THERMAL CHANGE ALOFT DURING THE PAST
24 HOURS. AN INVERSION REMAINS JUST ABOVE 850MB.
GOES/RUC PRECIPITABLE WATER INDICATE VALUES HAVE FALLEN TO BETWEEN A
TENTH AND A QUARTER INCH ACROSS THE STATE.
AIR QUALITY HAS BEEN ON THE DECLINE DURING THE PAST SEVERAL DAYS
ACROSS THE NORTHERN VALLEYS AS THE INVERSION SET IN. WHILE HAZE HAS
BEEN VISIBLE...VISIBILITIES HAVE BEEN BEHAVING SO WILL LEAVE OUT
MENTION IN THE FORECAST.
SAME INVERSION HAS BEEN LIMITING AFTERNOON WARMING ACROSS THE
NORTHERN VALLEYS. AS THE NEXT FRONT APPROACHES FROM THE NORTHWEST
TODAY...PRESSURE GRADIENT SHOULD START TO INCREASE AND PROMOTE
BETTER MIXING OF THE STRENGTHENING SOUTHERLY FLOW AT 700MB. HAVE
THEREFORE GONE A LITTLE WARMER FOR TODAY. EXPECT THE MOUNTAINS TO BE
A BIT COOLER TODAY AS THE RUC ANALYSIS ALREADY SHOWS 700MB
TEMPERATURES COOLING FROM +4C TO +2C OVERNIGHT.
MODEL SUITE CONSISTING OF NAM/GFS/CANADIAN/EUROPEAN ALL SHOW THE
NEXT SYSTEM ARRIVING TOMORROW...WITH THE MID LEVEL REFLECTION
SPLITTING SOUTHWEST TOWARD SOUTHERN CALIFORNIA. THIS LEAVES THE
GREAT BASIN WITH WANING DYNAMICS MEETING UP WITH MEAGER AMBIENT
MOISTURE. THEREFORE LOWERED POPS ACROSS THE NORTHERN AND CENTRAL
VALLEYS SATURDAY...LEAVING SALT LAKE VALLEY...UTAH COUNTY AND
RICHFIELD LOCALES WITHOUT MENTION.
INCREASING FRONTOGENESIS SATURDAY AFTERNOON AND NIGHT ACROSS
SOUTHERN UTAH AHEAD OF THE SPLIT FEATURE WILL BE THE BEST FOCUS OF
POPS FROM THIS SYSTEM. 21Z SHORT RANGE ENSEMBLES INDICATE A CHANCE
OF NEGATIVE LIFTED INDICES AND MUCAPE GREATER THAN 50 J/KG
SATURDAY AFTERNOON. HAVE MENTION OF CONVECTIVE WEATHER SATURDAY
AFTERNOON AND NIGHT...BUT HAVE NOT SEEN ENOUGH INSTABILITY THIS FAR
NORTH TO MENTION THUNDER AT THIS POINT.
INCREASING NORTHERLY FLOW AND COOLING TO ABOUT -7C AT 700MB SUNDAY
WILL ATTEMPT TO SCOUR OUT NORTHERN VALLEYS...THOUGH CONFIDENCE IS
NOT HIGH AT THAT AT THIS TIME THAT IT WILL BE ENOUGH TO DO SO. 00Z
KSLC NAM BUFKIT FORECAST SOUNDING SHOWS MIXING UP TO 825MB SUNDAY
AFTERNOON WITH ENOUGH RELATIVELY WARM AIR AT 750MB TO PREVENT
COMPLETELY MIXING OUT THE INVERSION.
GUIDANCE SUITE SHOWS AN AMPLIFIED RIDGE BUILDING IN FROM THE WEST
COAST SUNDAY AND MONDAY...BRINGING TRANQUIL WEATHER BACK TO THE
REGION.
GUIDANCE BEGINS TO DIVERGE HEADING INTO MID WEEK.
GFS/CANADIAN/EUROPEAN ALL SHOW NEXT COLD FRONT CROSSING SOUTH INTO
THE PACIFIC NORTHWEST MONDAY EVENING FROM WESTERN CANADA...THOUGH
THE CANADIAN MODEL IS FASTER. THE CANADIAN SHOWS A COLD FRONTAL
PASSAGE FOR THE AREA TUESDAY...THE EUROPEAN ON WEDNESDAY. THE GFS
MODEL CONTINUES TO BE AN OUTLIER TAKING THE COLD AIRMASS INTO THE
MIDWEST. OPTED TO CONTINUE TO SUPPORT A CANADIAN/EUROPEAN TRACK
LEANING CLOSER TO THE EUROPEAN FOR TIMING.
PATTERN IS DIFFICULT TO RESOLVE BEYOND MIDWEEK...SO CONFIDENCE IS
LOWER THAN TYPICAL IN THE LONG RANGE.
&&
.AVIATION...LIGHT SOUTHEAST WINDS AT KSLC TERMINAL ARE EXPECTED TO
SHIFT TO THE NORTHWEST BETWEEN 19 AND 20Z BUT REMAIN BELOW 6 KTS.
WINDS A FEW HUNDRED FEET ABOVE THE KSLC TERMINAL WILL INCREASE OUT
OF THE SOUTHWEST DURING THE DAY TODAY. THERE IS A 20 PERCENT CHANCE
THAT THESE WINDS WILL MIX DOWN TO THE SURFACE AND SHIFT WINDS TO THE
SOUTH BETWEEN 21 AND 00Z. OTHERWISE...VFR CONDITIONS ARE EXPECTED.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...NONE.
&&
$$
MERRILL/MYRICK/ROGOWSKI
FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)
