650
FXUS65 KSLC 170951
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
351 AM MDT WED OCT 17 2018
SYNOPSIS
AN UPPER LEVEL LOW OVER NORTHERN ARIZONA WILL MOVE
SLOWLY NORTH ACROSS UTAH THROUGH THURSDAY. HIGH PRESSURE ALOFT
WILL BUILD IN BEHIND THE EXITING LOW PRESSURE FRIDAY THROUGH THE
UPCOMING WEEKEND.
SHORT TERM (UNTIL 00Z SUNDAY)
THE UPPER LOW CURRENTLY
POSITIONED OVER NORTHERN ARIZONA WILL TAKE A SLOW NORTH-NORTHEAST
TRACK ACROSS UTAH THROUGH THURSDAY. A COUPLE OF VORTICITY LOBES
ROTATING AROUND THE LOW ALONG WITH FAVORABLE THERMAL ADVECTION
WILL LEAD TO SUFFICIENT SYNOPTIC-SCALE LIFT AND WIDESPREAD PRECIP
ALONG THE NORTHERN AND EASTERN FLANKS OF THE LOW AS IT MOVES
THROUGH THE STATE.
A VORTICITY LOBE ROTATING WEST-NORTHWEST ACROSS SOUTHERN UTAH
ALONG WITH WEAK LOW-LEVEL WARM ADVECTION HAS SPAWNED AREAS OF
LIGHT PRECIP OVERNIGHT. THIS FIRST SURGE OF PRECIP WILL LIKELY
REMAIN ON THE LIGHT SIDE BEFORE DISSIPATING AS THE VORTICITY LOBE
MOVES OUT OF THE STATE.
THE BAROCLINIC STRUCTURE OF THE ADVANCING LOW WILL BECOME MUCH
IMPROVED THIS AFTERNOON/EVENING. INCREASING LOW AND MID-LEVEL WARM
ADVECTION IN THE EASTERN/NORTHERN FLANKS OF THE LOW ALONG WITH
INCREASING DYNAMIC SUPPORT FOR LIFT SHOULD PRODUCE WIDESPREAD
LIGHT/MODERATE PRECIP ACROSS MAINLY CENTRAL/EASTERN UTAH THIS
AFTERNOON THROUGH THE OVERNIGHT HOURS. CAN NOT RULE OUT EMBEDDED
CONVECTION WITH BRIEF HEAVY PRECIP NEAR THE MID-LEVEL COLD POOL
AT THE CENTER OF THE LOW LATE THIS AFTERNOON THROUGH THIS EVENING.
HEADING INTO THURSDAY THE UPPER LOW WILL BEGIN TO WIND DOWN AS IT
DRIFTS INTO NORTHEAST UTAH. THERMAL ADVECTION LOOKS TO BE LESS OF
DRIVING FORCE FOR LIFT AS IT TOO WEAKENS DURING THE MORNING.
SUSPECT THAT PRECIP WILL BEGIN TO TAKE ON A MORE CONVECTIVE NATURE
AS COLD AIR INSTABILITY NEAR THE CENTER REMAINS A FACTOR. BY LATE
AFTERNOON/EVENING THE REMNANT OF THE UPPER LOW BEGINS TO SHEAR TO
THE EAST AS IT BECOME ABSORBED BY THE FAIRLY STRONG SHORTWAVE
DIVING SOUTHEAST INTO THE NORTHERN PLAINS STATES LATE THURSDAYS
NIGHT/FRIDAY.
THE REX BLOCK SETTING UP ALONG THE WEST COAST FRIDAY WILL LEAVE
MOST OF UTAH UNDER DRY/STABLE CONDITIONS THROUGH SATURDAY. THE
BLOCKING PATTERN LOOKS TO BE SHORT-LIVED AS THE RIDGE SHIFTS INTO
THE INTERIOR WEST LATE SATURDAY AND THE LOW PORTION OF THE OLD
BLOCK GRADUALLY STRENGTHENS ALONG THE CALIFORNIA COAST. THIS LOW
COULD PUMP SOME MOISTURE NORTH INTO SOUTHWEST UTAH, LEADING TO A
FEW CONVECTIVE SHOWERS LATE IN THE DAY SATURDAY.
LONG TERM (AFTER 00Z SUNDAY)
GLOBAL MODELS HAVE ALL TRENDED
TOWARD A MUCH MORE ACTIVE SOLUTION WITH THE 00Z RUNS FOR THE LONG
TERM FORECAST PERIOD. A RELATIVELY WEAK BUT SLOW MOVING UPPER LEVEL
LOW WILL BE LOCATED OFF THE SOUTHERN CALIFORNIA COAST SATURDAY
EVENING. DIFFLUENT FLOW AHEAD OF THIS LOW COMBINED WITH A DECENT
MOISTURE TAP SHOULD PROVIDE AN IMPETUS FOR PRECIPITATION ACROSS THE
DESERT SOUTHWEST THROUGH THE TIME THIS LOW...AND THEN OPEN WAVE
CROSS THE INTERIOR WEST (THROUGH LATE TUESDAY, EARLY WEDNESDAY).
MUCH OF THE GLOBAL MODEL GUIDANCE FOCUS ON A PERIOD OF MODERATE RAIN
ACROSS SOUTHWEST UTAH AS EARLY AS SUNDAY MORNING, WITH PRECIPITATION
CONTINUING TO MOVE NORTH AND EAST INTO MUCH OF THE REST OF THE STATE
THROUGH THE DAY SUNDAY INTO MONDAY. IT SHOULD BE NOTED THAT MUCH OF
YESTERDAY'S GUIDANCE WAS FAR LESS BULLISH WITH THIS SYSTEM. STARTED
MARKEDLY INCREASING POPS THROUGH THE LONG TERM FORECAST PERIOD, BUT
REMAIN BEHIND WHAT THE 00Z GLOBAL MODEL CONSENSUS WOULD SUGGEST DUE
TO A NOTORIOUSLY POOR PERFORMANCE IN CLOSED LOW/EJECTING LOW ACROSS
THE SOUTHWESTERN UNITED STATES.
BOTTOM LINE: WIDESPREAD PRECIPITATION IS POSSIBLE LATE THIS WEEKEND
INTO EARLY NEXT WEEK. THIS SYSTEM WOULD BE RELATIVELY WARM...WITH
HIGH SNOW LEVELS AND NEAR NORMAL TEMPERATURES ACROSS THE STATE.
AVIATION
EXPECT SOUTHERLY WINDS TO CONTINUE AT THE SLC TERMINAL
INTO THE MORNING...WITH A NORTHERLY WIND DEVELOPING BETWEEN 18-19Z.
SLC WATCHES/WARNINGS/ADVISORIES
UT...NONE.
WY...NONE.
SHORT TERM...CONGER
LONG TERM/AVIATION...KRUSE
FOR MORE INFORMATION FROM NOAA'S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY
FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP
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