Flash Flood Warning 26, NWS Salt Lake City, UT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
220 PM MDT SAT SEP 11 2004

.SYNOPSIS...MOISTURE WILL CONTINUE TO LIFT ACROSS THE REGION TONIGHT
ASSOCIATED WITH AN UPPER LEVEL DISTURBANCE. SOUTHWEST FLOW WILL
INCREASE ON SUNDAY AHEAD OF A COLD FRONT. THE COLD FRONT WILL PUSH
THROUGH THE NORTHERN HALF OF THE AREA SUNDAY NIGHT.

&&

.DISCUSSION...SCATTERED THUNDERSTORMS HAVE BEEN DEVELOPING SINCE
ABOUT NOONTIME IN SOUTHERN UTAH FROM BRYCE TO NEAR CEDAR CITY AND
CONTINUE TO EXPAND NORTH AND EAST. WELL ADVERTISED BY MODELS OF
LATE. NOW AS FAR NORTH AS NEAR RICHFIELD. STRONG CELLS AND MORE
ORGANIZED ACTIVITY LIFTING NORTH IN NORTHERN ARIZONA WHERE MOISTURE
IS GREATEST AND DYNAMICS FROM THE UPPER CIRCULATION. WATER VAPOR
CLEARLY SHOWING THIS WAVE. GOES SOUNDER DEPICTING THE MOISTURE SURGE
WITH NEAR .90 INCHES OVER ST. GEORGE. WEAK FLOW ALOFT WITH A
DEFORMATION ZONE FROM CENTRAL NEVADA TO NORTH CENTRAL UTAH...AND
TIMING OF PEAK HEATING WILL INCREASE HEAVY RAIN THREAT FOR SOUTHERN
UTAH INTO THIS EVENING. SHORT WAVE TROF STILL ON TRACK TO PINWHEEL
NORTH AND CONTINUE NORTHEASTWARD FROM SOUTHERN NEVADA...SOUTHERN
UTAH AND NW ARIZONA AND SPREAD HIGH PRECIPITABLE WATER UP TO THE GSL
TONIGHT. THIS DISTURBANCE SHOULD CONTINUE ACTIVITY INTO THE NIGHT
HOURS AFTER DIURNAL SHOWERS AND THUNDERSTORMS DISSIPATE. BEST LIFT
AND MOISTURE ADVECTION IS SOUTHERN UTAH THIS EVENING AND THEN OVER
EASTERN UTAH LATER TONIGHT...BUT REACHES TO ABOUT PROVO AND THEN IS
SHUNTED EASTWARD IN THE SOUTHWEST FLOW MOVING ACROSS SOUTHWEST
WYOMING...UINTA MOUNTAINS AND EASTERN UTAH SUNDAY MORNING. CERTAINLY
THE MOISTURE SURGE IN SOUTHERLY FLOW AND SUFFICIENT LIFT COULD
TRIGGER ELEVATED CONVECTION ON THE NORTHERN FRINGE OVER THE GSL INTO
FAR NORTHEAST UTAH. CLOUD COVER SHOULD INCREASE MIN TEMPS TONIGHT
ALONG WITH A LITTLE STRONGER SOUTHERLY SURFACE GRADIENT.

LINGERING ELEVATED MOIST CONVECTION IN THE FORM OF SHOWERS AND
THUNDERSTORMS WILL EXIT NORTHEASTERN AREAS SUNDAY MORNING BUT
RESIDUAL MOISTURE IS SUFFICIENT TO DEVELOP SURFACE BASED CAPE FROM
ABOUT CEDAR CITY TO PROVO TO THE NORTHERN WASATCH AND POINTS
EASTWARD SUNDAY AFTERNOON. SLIGHT DRYING AND NVA SUBSIDENCE
INVERSION FORMING ALOFT COULD SUPPRESS MOST REDEVELOPING ACTIVITY
FROM THE GSL AND NORTHWEST...EXCEPTION BEING NEAR THE IDAHO BORDER
AND NEVADA BORDER IN ADVANCE OF THE NEXT SYSTEM...BUT AGAIN THE SLC
AREA IS IN BETWEEN MOST LIFT. AIR MASS REMAINS WARM WITH INCREASING
SOUTHWEST FLOW ON SUNDAY KEEPING 700 MB TEMPS FROM 12C TO 14C FROM
NORTH TO SOUTH.

APPROACHING STRONGER SYSTEM MOVING THROUGH THE PACNW WILL DEVELOP
SYNOPTIC LIFT OVER NORTHWEST UTAH AND SOUTHEAST IDAHO LATE
SUNDAY...WHICH INCREASES SUNDAY EVENING AND OVERNIGHT AND SPREADS
SOUTHWARD OVER THE GSL. PVA DEVELOPS AS EARLY AS SUNDAY EVENING OVER
THE GSL. PW PLUME WILL BECOME CONFINED AHEAD OF THIS SYSTEM SO
SHOWERS AND THUNDERSTORMS WILL EXIT AND END OVER THE SOUTH...CENTRAL
AND EAST AND THEN BE CONFINED AND INCREASE OVER NORTHERN AREAS
SUNDAY NIGHT. SURFACE COLD FRONT PROGGED TO REACH SLC JUST BEFORE
SUNRISE MONDAY MORNING AND THEN PUSH SOUTH INTO CENTRAL UTAH. UPPER
LEVEL TROF AXIS SWINGS THOUGH MIDDAY AND THE ASSOCIATED 700 MB
THERMAL GRADIENT WILL SAG SOUTHWARD INTO NORTH CENTRAL UTAH. A
LOWERING SUBSIDENCE INVERSION IN THE WAKE OF THIS SYSTEM WILL
DIMINISH/LIMIT DEPTH OF ACTIVITY IN THE NORTH MONDAY
AFTERNOON...LAST IN THE NORTHEAST MOUNTAINS BY EVENING. DRIER AIR
MOVES IN FROM THE WEST ON MONDAY AND THE COMBINATION OF WIND AND
LOWER HUMIDITY AFFECTS THE SOUTHWEST PORTION OF UTAH.

FLOW ALOFT IS FLAT WESTERLY AND STABLE ON TUESDAY WITH THE MID LEVEL
BAROCLINIC ZONE HANGING OVER CENTRAL UTAH. EVEN DRIER AIR MOVES OVER
CENTRAL AND SOUTHERN UTAH ON TUESDAY SO THE MID LEVEL BOUNDARY WILL
LIKELY BE QUIET...WHILE THE SURFACE FRONT SETTLES TOWARD SOUTHERN
UTAH AND SHOULD KEEP IT BREEZY THERE. FLOW ALOFT GENERALLY BECOMES
FLAT WESTERLY REST OF THE WEEK WITH THE MAIN JET TO OUR NORTH. THE
NEXT SHORT WAVE TO INCREASE LIFT AND RIDE ALONG THE BOUNDARY COULD
ARRIVE BY WEDNESDAY NIGHT OR THURSDAY. SLOWER TIMING ALLOWS FOR WARM
AIR ADVECTION ON WEDNESDAY AND LITTLE INCREASE IN PW OVER NORTHERN
AREAS. THREAT FOR PRECIP PROBABLY LIMITED TO THE UINTA MOUNTAINS ON
WEDNESDAY. UPPER TROF DIGS SOME AND RIDES ALONG THE OLD BAROCLINIC.
THIS BRINGS A CHANCE OF SOME PRECIP TO THE NORTHERN HALF OF FORECAST
AREA ON THURSDAY...BUT AGAIN LOOKS MARGINAL. LATEST UKMET AND ECMWF
APPEAR SIMILAR TO THE GFS RUNS. BY NEXT WEEKEND A MORE SIGNIFICANT
SHORT WAVE IS PROGGED TO DIG ACROSS THE WEST PUSHING A COLD FRONT
INTO NORTHERN UTAH. UNTIL THEN AIR MASS NEXT WEEK HOVERS AROUND 6-8C
700 MB TEMPS IN THE NORTH TO AS WARM AS 12-14C IN THE FAR SOUTH.
COOLER MIN TEMPS DUE TO DRIER BOUNDARY LAYER.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...

UT...NONE.
WY...NONE.
ID...NONE.

&&

TARDY