FXUS65 KSLC 280945
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
245 AM MST SAT NOV 28 2009
.SYNOPSIS...A SPLITTING PACIFIC STORM SYSTEM WILL SLIDE ACROSS
THE REGION TODAY...WITH THE DEEPENING LOW AFFECTING SOUTHERN UTAH
LATE TODAY THROUGH SUNDAY MORNING. A RIDGE OF HIGH PRESSURE WILL BUILD
OVER THE AREA EARLY NEXT WEEK.
&&
.DISCUSSION...WATER VAPOR LOOP SHOWS AN UPPER LOW DEEPENING OVER
CENTRAL CALIFORNIA...AS IT SPLITS FURTHER FROM A DISTURBANCE MOVING
TOWARD THE UPPER MIDWEST FROM THE NORTHERN ROCKIES. AN UPPER LOW
DEEPENS OVER THE WESTERN GULF OF ALASKA...WITH RIDGING IN PLACE
OVER THE EASTERN PACIFIC. 400-250MB ACARS WIND OBSERVATIONS CONFIRMS
THE PLACEMENT OF THE UPPER LEVEL TROUGH...WHILE SHOWING A 90-115KT
CYCLONICALLY CURVED JET REACHING SOUTHERN CALIFORNIA FROM THE
PACIFIC WATERS. 00Z 700MB ANALYSIS SHOWS THE RIDGE AXIS MOVING EAST
ACROSS THE FOUR CORNERS REGION...AS A COLD FRONT APPROACHES THE
WESTERN GREAT BASIN. ADVECTION HAS TURNED NEUTRAL LOCALLY...WITH 0C
REPORTED AT KSLC ON A SOUTHWEST WIND. 00Z KSLC RAOB INDICATES ABOUT
3C OF WARMING IN THE 775-825MB LAYER...WITH 3-5C OF COOLING
ELSEWHERE IN THE COLUMN DURING THE PAST 24 HOURS. AN INVERSION
REMAINS JUST ABOVE 850MB...BUT HAS STRENGTHENED FROM 4 TO 6C DURING
THE PAST 24 HOURS.
GOES/RUC PRECIPITABLE WATER INDICATE VALUES REMAIN NEAR OR BELOW A
QUARTER INCH ACROSS MUCH OF THE STATE...WITH VALUES INCREASING TO
NEAR A THIRD OF AN INCH ACROSS THE NORTHWEST PORTION OF THE STATE.
MAIN STORY DURING THIS FORECAST CYCLE CONTINUES TO BE THE ROLE OF
THE INVERSION ON SENSIBLE WEATHER AND EXPECTED TRENDS.
AIR QUALITY IMPROVED IN UTAH COUNTY WHERE MIXING WAS REALIZED
YESTERDAY...THOUGH REMAINS ON THE DECLINE ACROSS SALT LAKE COUNTY
NORTH TO OGDEN WHERE MIXING DID NOT OCCUR. COMBINATION OF COPIOUS
MID AND UPPER LEVEL CLOUDS AND APPROACH/EVENTUAL PASSAGE OF THE COLD
FRONT EARLY THIS MORNING SHOULD KEEP VISIBILITIES FROM FALLING
SIGNIFICANTLY ALONG THE GREAT SALT LAKE THIS MORNING. MECHANICAL
MIXING WITH THE PASSAGE OF THE FRONT SHOULD MIX DOWN SOME OF THE
WARMER AIR ALOFT LEADING TO WARMER HIGHS TODAY WHERE THE INVERSION
WAS STRONGEST YESTERDAY (NORTHERN VALLEYS).
MID LEVEL REFLECTION OF THE SYSTEM CONTINUES TO WEAKEN AS IT
APPROACHES NORTHWEST UTAH...WITH THE DEEPENING UPPER LOW SPINNING
OVER CENTRAL CALIFORNIA. SINCE WEAKENING DYNAMICS ARE COMBINED WITH
MEAGER AMBIENT MOISTURE...CONTINUE TO ADVERTISE SLIGHT CHANCE POPS
ACROSS FAR NORTHERN AND WESTERN VALLEYS...TRENDING TO NO MENTION IN
VALLEYS FROM OGDEN SOUTHWARD.
COMBINATION OF ASCENT WITH THE APPROACH OF THE CALIFORNIA UPPER LOW
AND DECREASING STABILITY AS TEMPERATURES COOL ALOFT SHOULD SUPPORT
CONVECTIVE SHOWERS ACROSS SOUTHERN UTAH THIS AFTERNOON INTO SUNDAY
MORNING. 21Z SHORT RANGE ENSEMBLES INDICATE A CHANCE FOR NEGATIVE
LIFTED INDICES AND MUCAPE GREATER THAN 100 J/KG ACROSS FAR SOUTHERN
UTAH THIS AFTERNOON...WITH LIKELY PROBABILITIES ACROSS NORTHERN
ARIZONA. LEFT MENTION OF THUNDER OUT OF THE FORECAST THOUGH IT IS
QUITE POSSIBLE FOR ISOLATED CLOUD TO GROUND LIGHTNING TO SNEAK OVER
THE ARIZONA BORDER INTO FAR SOUTHERN UTAH THIS AFTERNOON.
INCREASING NORTHEASTERLY FLOW AND COOLING TO ABOUT -4 OR -5C AT 700
MB SUNDAY (ADVERTISED COOLER AT -7C YESTERDAY) WILL ATTEMPT TO SCOUR
OUT NORTHERN VALLEYS. SOME IMPROVEMENT IN REDUCTION OF HAZE IS
POSSIBLE AS THE NEW AIRMASS FILTERS IN...THOUGH 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. SO IT IS QUITE POSSIBLE CONDITIONS WILL
DETERIORATE AGAIN EARLY NEXT WEEK AS RIDGING BUILDS IN AND
TEMPERATURES WARM AGAIN AT RIDGETOP LEVELS.
CONFIDENCE CONTINUES TO BE LOWER THAN TYPICAL IN THE LONG
RANGE...MID TO LATE NEXT WEEK.
GFS/CANADIAN/EUROPEAN ALL SHOW NEXT COLD FRONT CROSSING SOUTH INTO
THE PACIFIC NORTHWEST AND NORTHERN ROCKIES MONDAY NIGHT FROM WESTERN
CANADA. THE CANADIAN AND EUROPEAN HAVE TRENDED TOWARD THE GFS
MODEL...INDICATING THAT THE COLD FRONT WILL SURGE SOUTHEAST ACROSS
THE NORTHERN ROCKIES AND UPPER MIDWEST THROUGH MID WEEK. NOT ONLY
DOES THIS SOLUTION SUPPORT CONTINUED DRY WEATHER...IT ALSO SUGGESTS
THAT THE INVERSION REMAINS IN TACT FOR MUCH OF NEXT WEEK.
THE CANADIAN AND GFS INDICATE THE NEXT COLD FRONT CROSSES THE REGION
FROM THE NORTHWEST FRIDAY INTO NEXT WEEKEND. TRENDED TO A SLIGHT
INCREASE IN POPS AND COOLER TEMPERATURES DURING THIS TIME PERIOD.
STILL LOWER THAN TYPICAL CONFIDENCE WITH THE EUROPEAN MODEL
STRUGGLING TO SHOW THE SAME PROGRESSION NEXT WEEKEND.
&&
.AVIATION...SOUTHERLY WINDS AT THE SLC TERMINAL HAVE CONTINUED AS
THE FRONT HAS STALLED TO THE NORTHWEST. THESE WINDS ARE NOW EXPECTED
WILL SHIFT TO THE NORTHWEST BETWEEN 10Z AND 12Z AS THE WEAK COLD
FRONT MOVES THROUGH THE AREA. VFR CONDITIONS ARE EXPECTED TO PREVAIL
THROUGH THE FORECAST PERIOD.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...NONE.
&&
$$
PUBLIC...ROGOWSKI
AVIATION...YOUNG
FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)
