Winter Storm Warning 12, NWS Salt Lake City, UT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
315 AM MST TUE MAR 28 2006

.SYNOPSIS...MOISTURE WILL CONTINUE TO SPREAD ACROSS THE REGION AHEAD
OF AN APPROACHING PACIFIC STORM SYSTEM. THIS STORM SYSTEM WILL MOVE
THROUGH THE AREA TONIGHT THROUGH WEDNESDAY. HIGH PRESSURE ALOFT WILL
RETURN THURSDAY AFTERNOON FOLLOWED BY A SERIES OF WEAKER WEATHER
DISTURBANCES FRIDAY AND SATURDAY.

&&

.DISCUSSION...WIDESPREAD PRECIPITATION HAS DEVELOPED IN SOUTHWEST
UTAH. THOUGH MOST OF IT IS LIGHT THE 00Z GFS AND NAM COMPLETELY
MISSED THIS ON QPF FIELDS...DESPITE HAVING IT PAST SEVERAL RUNS.
COOLING CLOUD TOPS CONTINUE TO SPREAD OVER WESTERN UTAH THIS MORNING
AS MOISTURE ADVECTION OCCURS. MAIN SYSTEM IS SENDING A BAND OF
PRECIPITATION ACROSS CALIFORNIA WITH A HEALTHY 1.2 INCH
PRECIPITABLE WATER TAP. MOISTURE LEVELS WILL CONTINUE TO INCREASE
TODAY REACHING ABOUT 0.7 INCHES IN SOUTHWEST UTAH. LEADING SHORT
WAVE LOBE AND UPPER DIVERGENCE WILL LIFT NORTHWARD ACROSS UTAH TODAY
AND INCREASE PRECIPITATION IN THE CENTRAL AND NORTHERN AREAS.
INSTABILITY INCREASES TO MARGINAL THIS AFTERNOON. SNOW LEVELS ARE
NEAR 8000 FEET IN THE SOUTHWEST THIS MORNING AND SHOULD HOLD BETWEEN
8000 AND 8500 FEET TODAY OVER THE REGION.

ADDITIONAL WAVES IN CYCLONIC FLOW ARRIVE THIS EVENING THEN STRONGEST
DYNAMICS PUNCH ACROSS NEVADA TONIGHT AND INTO WESTERN UTAH AFTER
MIDNIGHT...REACHING EASTERN UTAH BY WEDNESDAY MORNING. MAIN
MID AND UPPER LEVEL CIRCULATION AND SURFACE REFLECTION STILL PROGGED
TO RIDE INTO NORTHEAST NEVADA BY WEDNESDAY MORNING. THAT WILL BE AN
AREA OF HEAVY PRECIPITATION BUT THE DEEPER MOISTURE AND STEEPEN
LAPSE RATES OVER UTAH COMBINED WITH THE BEST UPWARD MOTION WILL LEAD
TO A LARGE AREA OF HEAVY PRECIPITATION. AREAS THAT FAVOR SOUTHWEST
TO SOUTH FLOW WILL ENHANCE THIS FORCING FROM SOUTHWEST TO NORTHEAST
UTAH. 700 MB WINDS REACH 40 TO 45 KNOTS AHEAD OF THE UPPER TROUGH.
00Z/06Z MODELS LITTLE SLOWER BRINGING COLDER AIR INTO WESTERN UTAH
WITH THE -4C 700 MB ISOTHERM REACHING CEDAR CITY BY 12Z WEDNESDAY.
SNOW LEVELS WILL BEGIN TO COME DOWN LATE TONIGHT IN HEAVY
PRECIPITATION AND COLD AIR ADVECTION FROM THE SOUTHWEST BUT WILL
REMAIN ABOVE 6500 FEET. HEAVIER RAIN SHOULD EXTEND UP INTO THE
WASATCH FRONT LATER TONIGHT AFTER SCATTERED EVENING SHOWERS.

HEAVIEST AREA OF PRECIPITATION WILL SHIFT INTO EASTERN UTAH IN THE
MORNING AND COLD AIR ADVECTION SPREADS ACROSS ALL OF UTAH. MID LEVEL
TROUGH SWINGS THROUGH UTAH WEDNESDAY EARLY AFTERNOON. UPPER TROUGH
LAGS BEHIND PROVIDING ADDITIONAL SYNOPTIC LIFT REGION WIDE WITH A
MOIST AND UNSTABLE AIR MASS IN PLACE. SHOWERS WILL BECOME WIDESPREAD
WITH SNOW MIXING DOWN 5500 FEET. MAIN JET AND BASE OF THE TROUGH
SLIDES ACROSS ARIZONA WHILE UPPER TROUGH AXIS REACHES THE NORTHWEST
DESERTS BY LATE AFTERNOON. PRECIPITATION WEDNESDAY EVENING WILL THEN
BECOME FOCUSED IN NORTHERN UTAH WITH THE UPPER LOW OVERHEAD AND WIND
VEERING TO NORTHWEST WITH TIME. THIS SHOULD BE A HEAVY PERIOD OF
SNOW FOR THE ENTIRE WASATCH RANGE...WITH AIR MASS DROPPING TO -8C AT
700 MB MAKING IT COLD ENOUGH TO CHANGE TO SNOW IN THE VALLEY FLOORS
WITH ACCUMULATIONS...MAINLY ABOVE 4500 FEET.

UPPER RIDGING PROGGED BY ALL MODELS TO ARRIVE OVER WESTERN UTAH
THURSDAY MORNING AND THEN DOMINATE THURSDAY AFTERNOON. SNOW WILL
TAPER OFF IN THE NORTHERN MOUNTAINS BUT LINGERING MOISTURE UNDER THE
SUBSIDENCE WILL KEEP CLOUDS AND SOME FLURRIES INTO THE AFTERNOON.
SOUTHWEST FLOW REDEVELOPS THURSDAY NIGHT AS THE RIDGE AXIS SHIFTS
EAST. MID AND HIGH CLOUDS WILL FOLLOW AND THICKEN THURSDAY NIGHT
INTO FRIDAY. 00Z GFS BRINGS SIGNIFICANT MOISTURE INTO WESTERN UTAH
BY FRIDAY AFTERNOON WITH THE LEADING SHORT WAVE TROUGH IN CYCLONIC
FLOW. THIS WILL BRING SOME PRECIPITATION TO NORTHERN AREAS INTO
FRIDAY NIGHT. A STRONGER WAVE STILL PROGGED BY UKMET...ECMWF AND GFS
FOR LATE SATURDAY SHOULD BRING PRECIPITATION TO MUCH OF THE REGION
FOR SATURDAY AND DROP A COLD FRONT ACROSS THE NORTH. SHORT WAVE
RIDGE AND WARMING PROGGED FOR SUNDAY AND POSSIBLY INTO
MONDAY...HOWEVER 00Z GFS IS STRONGER AND FASTER BRINGING THE LONG
WAVE TROUGH IN THE NORTH PACIFIC INTO THE GREAT BASIN EARLY NEXT
WEEK. HAVE CHANCE WEATHER THIS PERIOD AS TIMING AND AMPLITUDE
UNCERTAIN.

WILL UPGRADE CURRENT MOUNTAIN WATCHES TO WARNINGS FOR WIND AND HIGH
ELEVATION SNOW TODAY AND TONIGHT...WORDING ACCORDINGLY. THE WASATCH
RANGE WILL GET MOST OF ITS SIGNIFICANT SNOW WEDNESDAY AND WEDNESDAY
NIGHT...HOWEVER MOIST CONDITIONALLY UNSTABLE SOUTH FLOW TODAY AND
TONIGHT WILL PRODUCE SIGNIFICANT WETTER SNOWFALL. WILL LIKELY EXPAND
FOR THE NORTHERN WASATCH RANGE FOR THE SECOND HALF OF THIS EVENT TO
BRING AN IMPACT...BUT WIND AND HIGH SNOW LEVELS TODAY AND TONIGHT.

&&

.HYDRO...SNOW LEVELS TODAY WILL BE 8000-8500 FEET WITH MAIN
ACCUMULATION ABOVE THIS AND THEN SLOWLY LOWER TONIGHT. SNOW LEVELS
WILL COME DOWN TO 6000 FEET WEDNESDAY. MAIN CONCERN IS WIDESPREAD
PRECIPITATION IN SOUTHWEST UTAH...AND WITH MODERATELY STRONG
SOUTHWEST FLOW THERE WILL BE LARGE OROGRAPHIC EFFECTS. PINE VALLEY
UPSLOPE AREA SHOULD REACH 4 INCHES OF PRECIPITATION. IN ADDITION
EMBEDDED CONVECTIVE ELEMENTS AND THUNDERSTORMS LATE TODAY...TONIGHT
AND ON WEDNESDAY WILL PRODUCE LOCALLY HEAVY RATES. APPEARS CERTAIN
THAT SLOT CANYONS WILL HAVE PROBLEMS AND SMALLER RIVERS AND STREAMS
WILL RESPOND WITH GOOD RISES...WHILE MAIN STEM RIVERS WILL BE MUCH
LESS OF A CONCERN. WILL CONSIDER FLASH FLOOD WATCH FOR SOUTHWEST
UTAH.

&&

.AVIATION...INCREASING MOISTURE THIS MORNING WILL GRADUALLY LOWER
CEILINGS. UPSTREAM REPORTS INDICATE CIGS IN THE 8-10KFT RANGE...SO
DO NOT EXPECT CLOUD DECKS TO LOWER TO THE CRITICAL 7KFT RANGE UNTIL
LATE AFTERNOON. ONLY EXCEPTION TO THIS IS A 30% CHANCE OF A PASSING
SHOWER...WHICH COULD ALSO MIX DOWN STRONGER WIND GUSTS TO 35KTS.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING THROUGH WEDNESDAY UTZ017-018
     WINTER STORM WARNING THIS AFTERNOON THROUGH WEDNESDAY EVE
     UTZ007>010
     FLASH FLOOD WATCH UTZ016-017-019-020
WY...NONE.

&&

PUBLIC...TARDY
AVIATION...SMITH

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