Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 202215
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
415 PM MDT WED MAY 20 2015

.SYNOPSIS...SEVERAL WEATHER DISTURBANCES WILL CROSS THE GREAT
BASIN THROUGH THURSDAY NIGHT. SEVERAL AREAS OF LOW PRESSURE WILL
CROSS THE GREAT BASIN FRIDAY THROUGH TUESDAY.

&&

.SHORT TERM (THROUGH 06Z SUNDAY)...THE MEAN POSITION OF THE UPPER
LOW OFF THE CALIFORNIA COAST WILL CONTINUE EJECTING A SERIES OF
VORTICITY LOBES NORTH ACROSS THE GREAT BASIN THROUGH AT LEAST
EARLY FRIDAY. THE FIRST LOBE JUST OFF THE SOUTHWEST CORNER OF UTAH
WILL GENERATE AN INCREASING AREA OF SCATTERED CONVECTION ACROSS
SOUTHERN/CENTRAL UTAH LATE THIS AFTERNOON/EARLY EVENING. THIS LOBE
WILL REACH NORTHERN UTAH AROUND MID-EVENING...WITH DYNAMIC
SUBSIDENCE PRODUCING A DECREASING TREND TO CONVECTION ACROSS THE
SOUTH LATE THIS EVENING.

ACROSS THE NORTH CONVECTION APPEARS A BIT STRONGER UNDERNEATH
INCREASING DIVERGENCE ALOFT. THIS ACTIVITY WILL LIKELY INCREASE IN
INTENSITY AND AREAL COVERAGE OVER MAINLY NORTHWEST UTAH LATE THIS
EVENING AS THE VORTICITY LOBE MOVES NORTH THROUGH THE AREA AND
DIVERGENCE ALOFT PEAKS. SMALL HAIL AND BRIEF HEAVY RAIN THE LIKELY
RESULT IN STRONGER CONVECTION OVER NORTHERN UTAH OVERNIGHT.

THE SECOND VORTICITY LOBE WILL REACH SOUTHERN UTAH EARLY THURSDAY.
THIS SECOND FEATURE SHOULD GENERATE SCATTERED CONVECTION ONCE
AGAIN...WITH THIS ACTIVITY PEAKING ACROSS THE NORTH DURING THE
AFTERNOON HOURS. A THIRD FEATURE WILL FOLLOW EARLY FRIDAY...BUT WILL
BE CAUGHT IN THE ORBIT OF THE UPPER LOW NOW CENTERED INLAND OVER
SOUTHERN CALIFORNIA. THIS THIRD FEATURE WILL TURN EAST TOWARDS
NEVADA DURING THE AFTERNOON...WITH IMPACTS CONFINED TO MAINLY TO
WEST-CENTRAL AND CENTRAL UTAH.

A PROLONGED PERIOD OF COOL/WET CONDITIONS IS ANTICIPATED AS THE
SOUTHERN CALIFORNIA UPPER LOW TURNS NORTH-NORTHEAST AND TRACKS
SLOWLY THROUGH THE GREAT BASIN. PLENTY OF MOISTURE AND SOLID
DYNAMIC LIFT SHOULD SERVE TO PRODUCE WIDESPREAD AND SUBSTANTIAL
VALLEY RAIN AND MOUNTAIN SNOW THROUGH AT LEAST SATURDAY EVENING.
DEEP LAYER AND MOIST NORTHWEST FLOW WARM ADVECTION COULD SET UP
ACROSS NORTHWEST UTAH LATE SATURDAY. THE LATEST GFS IS SHOWS THIS
COMING TO PASS...WITH THE ECMWF MAINTAIN A MORE EASTERLY COMPONENT
TO THE FLOW. FOR NOW WILL FOLLOW THE GFS SOLUTION AND WILL BOOST
POPS/QPFS ACCORDINGLY.

.LONG TERM (AFTER 06Z SUNDAY)...MODEL TO MODEL AND RUN TO RUN
CONSISTENCY ISSUES ARE HAVING A SIGNIFICANT IMPACT ON THE
CONFIDENCE OF ANY PARTICULAR SOLUTION AFTER SATURDAY EVENING. AN
UPPER LEVEL LOW IS EXPECTED TO BE SLOWLY PUSHED SOUTHEASTWARD
SATURDAY EVENING THROUGH THE PACIFIC NORTHWEST INTO THE GREAT
BASIN...THOUGH TIMING OF THIS FEATURE IS SIGNIFICANTLY DIFFERENT
ACROSS THE 12Z MODEL SUITE. ANOTHER SOMEWHAT WEAKER TROUGH IS
FORECAST TO IMPACT THE REGION EARLY NEXT WEEK.

GIVEN THE CONSISTENCY ISSUES...CONFIDENCE IN TIMING/LOCATION OF
THESE FEATURES IS LOW AT BEST. KEPT THE TREND OF THE PREVIOUS
FORECAST WITH ELEVATED POPS THROUGH THE LONG TERM FORECAST. THE
MAIN MESSAGE WILL CONTINUE TO BE...UNSETTLED CONDITIONS WITH THE
POTENTIAL FOR PRECIPITATION WILL PERSIST THROUGH THE END OF THE
WEEKEND...THROUGH MEMORIAL DAY...AND INTO EARLY NEXT WEEK.

&&

.AVIATION...PRIMARY OPERATIONAL CONCERNS AT THE KSLC AIRPORT REMAIN
FOCUSED ON SHOWERS AND ISOLATED THUNDERSTORM IMPACTS THROUGH THIS
EVENING...AND ASSOCIATED WINDS. A LULL IN ACTIVITY THROUGH 01Z IS
EXPECTED BEFORE ADDITIONAL STORMS ARE EXPECTED TO MOVE THROUGH IN
THE 02Z-05Z WINDOW. A SWITCH TO PREVAILING NORTHWEST WINDS IS A
LOW CONFIDENCE FORECAST BUT IS MOST LIKELY IN THE 23-01Z WINDOW.
AFTER THAT PREVAILING SOUTHERLY WINDS ARE EXPECTED WITH PERIODIC
CIGS AOB 6000FT AGL DURING STORM ACTIVITY.

&&

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

$$

CONGER/KRUSE/MERRILL

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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