Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 212211
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
411 PM MDT TUE APR 21 2015

.SYNOPSIS...HIGH PRESSURE ALOFT OVER THE GREAT BASIN WILL SLOWLY
SHIFT EAST OF THE STATE BY LATE WEDNESDAY. A WEAKENING LOW
PRESSURE SYSTEM OVER SOUTHERN CALIFORNIA WILL TURN NORTH AND SEND
MOISTURE NORTH ACROSS UTAH...WHICH WILL RESULT IN PRECIPITATION
ACROSS MUCH OF THE STATE THROUGH THE REMAINDER OF THE WEEK.

&&

.SHORT TERM (THROUGH 00Z SATURDAY)...THE UPPER RIDGE SQUARELY OVER
THE GREAT BASIN THIS AFTERNOON WILL SLOWLY WORK EAST ALONG THE
SPINE OF THE ROCKIES BY LATE WEDNESDAY. BEHIND THIS RIDGE AXIS THE
UPPER LOW OVER SOUTHERN CALIFORNIA THIS AFTERNOON WILL TURN NORTH
INTO EXTREME SOUTHERN NEVADA EARLY WEDNESDAY. MOISTURE ASSOCIATED
WITH THIS FEATURE WILL EJECT NORTH ACROSS SOUTHWEST UTAH
TONIGHT...THEN ACROSS MAINLY WESTERN UTAH WEDNESDAY.

THE DEFORMATION AXIS TO THE NORTH OF THE APPROACHING UPPER LOW
WILL BE THE FOCUS FOR CONVECTION AS IT MOVES NORTH THROUGH
SOUTHERN AND CENTRAL UTAH TONIGHT/EARLY WEDNESDAY. POCKETS OF
CONVECTION WILL ALSO LINGER ACROSS FAR SOUTHERN UTAH NEAR THE
CENTER OF THE LOW. IN GENERAL THE DYNAMIC FORCING IS ON THE WEAK
SIDE WITH AVAILABLE MOISTURE ADEQUATE FOR CONVECTION /PWAT VALUES
AROUND .45 TO.55 INCHES/. SUSPECT THAT MUCH OF THE CONVECTION WILL
REMAIN TIED TO THE HIGHER TERRAIN OR CONCENTRATED ALONG THE
DEFORMATION AXIS THROUGH WEDNESDAY EVENING.

THE LATTER PORTION OF THE WEEK WILL SEE A WEAK TROUGH COVERING
MUCH OF THE INTERIOR WEST ALONG WITH THE STILL ADEQUATE MOISTURE
TO MAINTAIN SCATTERED CONVECTION THROUGH AT LEAST FRIDAY. A
SHORTWAVE MOVING EAST ACROSS THE NORTHERN ROCKIES ON THURSDAY
WILL NUDGE A SURFACE BOUNDARY INTO NORTHWEST UTAH WEDNESDAY
NIGHT...THEN ACROSS SOUTHWEST WYOMING THROUGH WEST-CENTRAL UTAH
THURSDAY. THIS BOUNDARY WILL LIKELY SEE ORGANIZED CONVECTION
DURING THE DAY...WITH THE HIGH TERRAIN TO THE SOUTH AND EAST OF
THE BOUNDARY ALSO REMAINING ACTIVITY IN DIURNAL CONVECTION.
THURSDAY WILL BE THE BETTER OF THE TWO DAYS IN TERMS OF MEASURABLE
PRECIP...WITH SOME SNOW POSSIBLE ACROSS THE HIGHER NORTHERN AND
CENTRAL MOUNTAINS. INCREASING CLOUD COVER AND PRECIP WILL BRING A
MODEST COOLING TREND TO MAINLY NORTHERN AND CENTRAL UTAH HEADING
INTO THE WEEKEND.

.LONG TERM (AFTER 00Z SATURDAY)...GLOBAL MODELS IN AGREEMENT THAT A
SHORTWAVE TROUGH WILL SWING THROUGH THE GREAT BASIN FRIDAY NIGHT
WITH THE LONGWAVE TROUGH TO MOVE THROUGH SATURDAY NIGHT INTO SUNDAY.
ALTHOUGH THE FIRST SHORT WAVE IS WEAK IT WILL BE ACTING ON A MORE
MOIST AIR MASS...THEREFORE HAVE BOOSTED POPS ABOVE 35 PERCENT ACROSS
THE NORTHWESTERN HALF OF THE CWA WITH SOME LIKELY POPS IN THE
MOUNTAINS. THE NAM12...GFS AND EC ALL SHOW A BAND OF QPF IN THE 0.25
TO 0.40 OF AN INCH RANGE FOR THE 6 HR PERIOD BETWEEN 00Z AND 06Z
SATURDAY...GENERALLY IN A SWATH FROM WEST CENTRAL UTAH TO THE
WASATCH FRONT FRIDAY NIGHT. CHANCES ARE THAT SOME PLACE WITHIN THIS
SWATH WILL RECEIVE SOME GOOD RAIN BUT TOO EARLY TO PINPOINT WHERE AT
THIS TIME...BUT DID INCREASE QPF SOME.

HAVE LOWERED SOME TEMPERATURES FOR SATURDAY ACROSS NORTH AND WESTERN
AREAS AS CLOUDS AND RAIN LIKELY TO IMPACT AMOUNT OF INCOMING
INSOLATION.

THE LONG WAVE TROUGH IS FORECAST BY BOTH THE EC AND GFS TO ACTUALLY
BE OVER EASTERN UTAH BY SUNDAY MORNING BUT THE GFS HOLDS BACK LOW
LEVEL MOISTURE UNDER NORTHWEST FLOW INTO SUNDAY NIGHT. ALTHOUGH NOT
CONVINCED ANY SHOWERS WILL OCCUR FELT IT BEST TO KEEP THE LOW POPS
IN FOR NOW. THE EC AND GFS DIVERGE ON THEIR SOLUTIONS WITH THE EC
MAINTAINING A RIDGE OVER THE WESTERN GREAT BASIN ABOUT 5-10 DEGREES
LONGITUDE FARTHER WEST THAN THE GFS. THIS PLACES UTAH UNDER AN
ANTICYCLONIC NORTHWEST FLOW THROUGH TUESDAY VERSES THE GFS IDEA OF A
PROGRESSIVE RIDGE WITH SOUTHWEST FLOW ALREADY OVER UTAH BY TUESDAY.
PLAYED THE DRIER EC SOLUTION AS THE EC HAS BEEN MORE CONSISTENT IN
ITS FORECAST PAST FEW RUNS.

&&

.AVIATION...NORTHWEST WINDS AT SLC TERMINAL SHOULD SHIFT TO
SOUTHEAST AT ABOUT 04Z WITH A 30 PERCENT CHANCE OF SWITCHING BY 03Z.
NO OTHER OPERATIONAL METEOROLOGICAL CONCERNS.

&&


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

$$

SHORT TERM...CONGER
LONG TERM/AVIATION...STRUTHWOLF

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)


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