Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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657
FXUS65 KSLC 200947
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
347 AM MDT WED MAY 20 2015

.SYNOPSIS...THE NEXT STORM SYSTEM WILL ARRIVE LATE IN THE WEEK
AND IMPACT MUCH OF UTAH THROUGH THE HOLIDAY WEEKEND.

&&

.SHORT TERM (THROUGH 12Z SATURDAY)...
WATER VAPOR LOOP SHOWS RIDGING BUILDING OVERHEAD BETWEEN THE LAST
SYSTEM NOW OVER THE NORTHERN PLAINS...AND THE NEXT CLOSED LOW OFF
OF THE CENTRAL CALIFORNIA COAST. AMDAR 400-250MB WIND OBSERVATIONS
SHOW A 75-100KT CYCLONIC JET FROM SOUTHERN CALIFORNIA INTO THE
NORTHERN PLAINS. GOES/GPS/RAP/00Z SLC RAOB INDICATE THE
PRECIPITABLE WATER VALUE RANGES BETWEEN 0.25"-0.50" MOUNTAINS...TO
0.50"-0.75" ACROSS THE VALLEYS.

GIVEN THAT TODAY WE HAVE PLENTY OF RESIDUAL MOISTURE AND ARE IN
BETWEEN SYSTEMS...CAN EXPECT CONVECTION TO BE MORE TIED TO THE
TERRAIN ALONG AND EAST OF THE THE WASATCH MOUNTAINS...AND FAR
NORTHWEST UTAH THIS AFTERNOON. LESS COVERAGE IN THE VALLEYS EXCEPT
UINTA BASIN AND SOUTHWEST WYOMING WHICH ARE FAVORED DUE TO STORM
MOTION OFF THE TERRAIN.

HAVE INCREASED POPS AFTER 00Z AS GUIDANCE SHOWS A LEAD WAVE PIVOTING
AROUND THE UPSTREAM CLOSED LOW INTO WEST CENTRAL UTAH THIS EVENING.
THIS SHOULD SUPPORT BETTER CONVECTIVE COVERAGE AS IT PIVOTS
NORTHWARD THROUGH AT LEAST MIDNIGHT.

A LULL IN ACTIVITY IS EXPECTED LATER TONIGHT INTO TOMORROW MORNING
DUE TO COMBINATION OF DIURNAL INSTABILITY TRENDS...SUBSIDENCE BEHIND
AFOREMENTIONED WAVE AND RIDGING ALOFT.

CONVECTIVE COVERAGE WILL INCREASE FRIDAY AS UPPER LEVEL DIFFLUENCE
AND LEFT EXIT OF THE JET STREAM ARRIVE ACROSS THE EASTERN GREAT
BASIN. DUE TO COOLING ALOFT SHOULD BE ABLE TO SUSTAIN CONVECTION
OVERNIGHT INTO SATURDAY.

.LONG TERM (AFTER 12Z SAT)...
THE NEXT IN THE SERIES OF MOIST CLOSED UPPER LOWS WILL BE
PROGRESSING THRU THE CWA ON SAT WITH FAIRLY WIDESPREAD CONVECTIVE
SHOWERS AND THE POTENTIAL FOR AN AREA OF MORE STRATIFORM WRAP
AROUND PRECIP INTO THE NWRN CWA LATE SAT INTO SAT NIGHT.

MODELS CONTINUE TO STRUGGLE WITH THE EVOLUTION OF AN UPSTREAM CLOSED
LOW WITH TIMING AND TRACK DIFFERENCES THAT ARE FAIRLY SIGNIFICANT.
CONFIDENCE IN THE GUIDANCE IS EVEN LOWER DUE TO INTERNAL RUN TO RUN
INCONSISTENCIES AS WELL. REGARDING THIS...THE 18Z GFS WENT BACK TO
THE IDEA THAT THE TRAILING UPPER LOW WOULD REMAIN OVER THE PACNW AND
HEAD NORTH WITH WEAK RIDGING MOVING INTO THE ERN GREAT BASIN SUN
INTO MON...THEN THE 00Z RUN WENT COMPLETELY AWAY FROM THIS AND
MIMICKED THE EARLIER EC DROPPING THIS TRAILING LOW INTO THE WRN
GREAT BASIN SAT NIGHT AND TRACKING IT EVEN MORE SLOWLY EWD THRU TUE.
THE 00Z EC WENT AWAY FROM THIS SOLUTION AND TOWARDS LAST NIGHTS GFS
KEEPING THE CLOSED LOW FARTHER NORTH AND TRACKING IT THRU SRN ID
THRU TUE. EITHER SOLUTION WOULD KEEP A THREAT OF SHOWERS OVER THE
CWA RIGHT THRU THE WEEKEND AND INTO TUE...BUT AT THIS TIME THE EC
IDEA WOULD KEPT CONVECTION MORE DIURNAL AND TERRAIN BASED THAN THE
WETTER GFS.

CONFIDENCE IS HIGHER HOWEVER THAT OVERALL THE GENERAL MOIST WEAK
FLOW PATTERN WILL REMAIN IN PLACE REGARDLESS OF THE DETAILS SO THERE
SHOULD BE A THREAT OF PRECIP EACH DAY THRU THE FIRST PART OF THE
WEEK AND HAVE LEANED TOWARDS THE IDEA OF A WETTER SOLUTION. SO
TRENDED POPS HIGHER IN THE GRIDS FOR THE ENTIRE DAY 4-7 PERIOD.

&&

.AVIATION...VFR CONDITIONS WILL PREVAIL AT THE KSLC TERMINAL THROUGH
THE TAF PERIOD. CIGS SHOULD GENERALLY REMAIN ABV 6000 FT BUT COULD
DIP BELOW THAT AT TIMES IN RAIN SHOWERS THIS AFTERNOON THROUGH THIS
EVENING. SOUTHEASTERLY WINDS SHOULD SWITCH TO NORTHWESTERLY AROUND
19Z BUT THE CONFIDENCE IN THE WIND FORECAST DROPS OFF QUICKLY ONCE
SHOWERS DEVELOP AROUND THE SALT LAKE VALLEY THIS AFTERNOON.

&&

.FIRE WEATHER...A WARMING AND DRYING TREND IS FORECAST FOR TODAY AND
TOMORROW. MAINLY AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS WILL BE
MOST WIDESPREAD ALONG AND EAST OF THE WASATCH MOUNTAINS. CLOUD TO
GROUND LIGHTNING...GUSTY/ERRATIC WINDS...A BRIEF HEAVY
DOWNPOUR...AND SMALL HAIL ARE ALL POSSIBLE WITH THE STRONGER
ACTIVITY.

THE NEXT STORM SYSTEM ARRIVES FRIDAY THROUGH THE HOLIDAY WEEKEND.
EXPECT ANOTHER COOL AND WET PERIOD ACROSS THE ENTIRE REGION. SNOW
LEVELS BETWEEN 8-9KFT TODAY AND TOMORROW WILL FALL OVER THE
WEEKEND.

&&

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

$$

SHORT TERM/FIRE WEATHER...ROGOWSKI
LONG TERM/AVIATION...WILENSKY

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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