Area Forecast Discussion
Issued by NWS Salt Lake City, UT

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KSLC 300215
AFDSLC

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

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.