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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
815 PM MDT SUN MAR 29 2015

.SYNOPSIS...A WEAK WEATHER DISTURBANCE WILL MOVE EAST INTO
NORTHWEST ARIZONA LATE MONDAY. HIGH PRESSURE ALOFT WILL RETURN TO
THE AREA EARLY IN THE WEEK...FOLLOWED BY A SERIES OF COLD PACIFIC
WEATHER DISTURBANCES FOR THE LATTER HALF OF THE WORK WEEK.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A RIDGE OVER THE REGION
WITH AN APPROACHING DISTURBANCE OVER CENTRAL CALIFORNIA. AMDAR
400-250MB WIND OBSERVATIONS SHOW A 95-125KT WESTERLY JET OVER
WESTERN CANADA. GOES/GPS/RAP/00Z SLC RAOB INDICATE THE
PRECIPITABLE WATER VALUE RANGES BETWEEN 0.10"-0.20" NORTHERN
UTAH...TO 0.33"-0.40" ACROSS THE SOUTHEAST VALLEYS. BLENDED TOTAL
PRECIPITABLE WATER PRODUCT INDICATES A PACIFIC TAP INTO THE
PACIFIC NORTHWEST...AND AN ABNORMALLY DRY AIRMASS OVER THE EASTERN
GREAT BASIN.

BASED ON LACK OF LIGHTNING AND SHORT RANGE ENSEMBLE 
GUIDANCE...REMOVED MENTION OF THUNDER FOR THE REMAINDER OF THE 
EVENING. REDUCED POPS TO 20 PERCENT COVERAGE FOR THE SOUTHERN 
MOUNTAINS. WITH SREF INDICATING NIL MOST UNSTABLE CAPE AFTER 
MIDNIGHT...REMOVED ANY POPS AS CONVECTION SHOULD DECAY QUICKLY THIS 
EVENING.

REST OF FORECAST IN FINE SHAPE WITH MINIMAL CHANGES. 

PREVIOUS DISCUSSION FOLLOWS... 

CONVECTION HAS FIRED UP OVER THE SOUTHERN MOUNTAINS NORTH OF THE OLD 
SURFACE BOUNDARY AT MID-AFTERNOON. THIS CONVECTION APPEARS TO BE 
ALIGNED WITH A WEAK NEAR 700MB CONVERGENCE ZONE AND SUPPLEMENTED BY 
DIFFERENTIAL HEATING OVER THE HIGHER TERRAIN. THIS CONVECTIVE 
ACTIVITY WILL LIKELY PERSIST OR EVEN INCREASE SLIGHTLY THROUGH THE 
BALANCE OF THE AFTERNOON...THEN DECREASE WITH THE LOSS OF HEATING 
AND THE DISSIPATION OF THE CONVERGENCE ALOFT.

THE VORTICITY MAX HUNG UP OVER THE CENTRAL SIERRAS STILL PROGGED TO 
DRIFT EAST-SOUTHEAST INTO SOUTHERN NEVADA MONDAY...THEN TRACK EAST 
INTO NORTHWEST ARIZONA MONDAY EVENING. THIS FEATURE WILL LIKELY 
WEAKEN AS IT ENTERS ARIZONA WITH ONLY A MINIMAL IMPACT ON CONVECTION 
ACROSS THE SOUTH DURING THE LATE AFTERNOON AND EVENING. 

A LOW AMPLITUDE RIDGE WILL MOVE WEST TO EAST ACROSS THE GREAT BASIN 
MONDAY NIGHT THROUGH EARLY TUESDAY. ONCE THIS FEATURE CLEARS UTAH 
LOOK FOR AN INCREASINGLY WARM SOUTHWEST FLOW TO DEVELOP AHEAD OF A 
SERIES OF COLD PACIFIC TROUGHS MOVING INTO THE BASIN FOR THE LATTER 
HALF OF THE WEEK. VERY WARM AND WINDY CONDITIONS WILL EXIST TUESDAY 
AFTERNOON AHEAD OF THE LEADING COLD FRONT SCHEDULED TO REACH 
NORTHWEST UTAH TUESDAY AFTERNOON. VERY WARM TEMPS AHEAD OF THE FRONT 
ALONG WITH RATHER COLD AIR TRAILING THE FRONT WILL LEAD TO A 
SIGNIFICANT INCREASE IN THE PRESSURE GRADIENT ACROSS EASTERN NEVADA 
AND WESTERN UTAH DURING THE AFTERNOON. STRONG WINDS WILL DEVELOP 
WITH THE POSSIBILITY OF WIND RELATED HAZARDS ACROSS WESTERN UTAH 
DURING THE LATE AFTERNOON AND EARLY EVENING HOURS. CONVECTION WILL 
LIKELY HOLD OFF UNTIL TUESDAY EVENING WHEN THE MID-LEVEL COLD AIR 
AND DYNAMIC SUPPORT FOR LIFT REACHES NORTHWEST UTAH.

THE SECOND AND SIGNIFICANTLY COLDER SECONDARY TROUGH WILL REACH THE 
WESTERN GREAT BASIN LATE WEDNESDAY. THIS FEATURE WILL LIKELY CARVE 
OUT A BROAD COLD TROUGH ACROSS MUCH OF THE BASIN HEADING INTO THE 
EXTENDED PERIOD OF THE CURRENT FORECAST PACKAGE. 
 
AFTER THE INITIAL COLD FRONTAL PUSH ON WEDNESDAY...THE COLDER LOW 
LEVEL AIR WILL LINGER ACROSS THE NORTHERN TWO THIRDS OF THE CWA 
WEDNESDAY NIGHT...BEFORE A STRONGER AND DEEPER SYSTEM MOVES OVER 
UTAH THURSDAY. THE SOUTHERN TIER OF THE CWA WILL LIKELY SEE MODERATE 
TO STRONG WINDS THURSDAY AS 700MB WINDS INCREASE TO 35-45 KTS ALONG 
WITH A FAVORABLE WEST TO EAST SURFACE GRADIENT. DEPENDING ON FUEL 
STATUS THIS MAY BECOME THE FIRST RED FLAG WARNING DAY OF THE SEASON. 
IN ADDITION THE EC IS FASTER THAN THE GFS AND IF THIS SOLUTION COMES 
TO BE THEN THE WINDS WILL NOT BE AS STRONG EITHER. THE GFS HAS BEEN 
MORE CONSISTENT SO LEANED IN THAT DIRECTION.

DUE TO THE GFS BEING SLOWER AND DEEPER IT HAS A BETTER ORGANIZED 
BAROCLINIC ZONE FARTHER NORTH STRETCHING FROM ABOUT SLC SOUTHWARD TO 
CEDAR CITY. HAVE INCREASED POPS SOME TO ACCOMMODATE THIS SOLUTION. 
WITH TEMPERATURES DOWN TO -10 DEGREES C AT 700MB FROM ABOUT NEPHI 
NORTHWARD HAD TO GO WITH ALL SNOW IN THE FORECAST FOR VALLEYS AND A 
MIXTURE OF RAIN AND SNOW OVER THE WESTERN VALLEYS SOUTH OF THERE. 
AMOUNTS DO NOT LOOK TO BE SIGNIFICANT AS DYNAMICS ALOFT ARE NOT 
COHESIVE. TEMPERATURES WILL BE BELOW NORMAL FOR THE FIRST TIME IN  
ALONG TIME SO THEY MAY FEEL COLDER THAN OTHERWISE FOR THE END OF 
MARCH.

THE SYSTEM PULLS OUT RAPIDLY FRIDAY BUT STILL COULD SEE SOME SHOWERS 
OVER THE HIGHER TERRAIN OF NORTHERN UTAH INTO FRIDAY AFTERNOON AS A 
FINAL WEAK WAVE CLIPS THE CWA. THE 700MB TEMPS REMAIN QUITE COLD AT 
MINUS 10 DEGREES C THROUGH NOON FRIDAY SO DON'T EXPECT MUCH WARMING 
YET ON FRIDAY. TEMPERATURES WARM ANOTHER 4 TO 6 DEGREES C AT 700MB 
SATURDAY SO TEMPERATURES WILL CLIMB ABOVE NORMAL ONCE AGAIN BY 
SATURDAY.

ANOTHER SYSTEM APPROACHES ON SUNDAY BUT IT APPEARS TO BE TRENDING A 
LITTLE SLOWER SO HAVE BACKED OFF ON THE POPS FOR NORTHERN UTAH FOR 
SUNDAY. SOUTH WINDS WILL HELP GET THE TEMPS BACK INTO THE 60S SUNDAY 
OVER MOST VALLEYS BEFORE THE NEXT COLD FRONT.

&&

.AVIATION...THE ONLY OPERATIONAL WEATHER CONCERN AT THE SLC TERMINAL 
IS THE SURFACE WIND FORECAST. WINDS ARE EXPECTED TO BE LIGHT 
NORTHWEST THROUGH 02-04Z THEN SHIFT TO SOUTHEAST. 

&&

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

$$

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

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