Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 222341
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
541 PM MDT FRI MAY 22 2015

.SYNOPSIS...A SLOW MOVING LOW PRESSURE SYSTEM WILL TRACK NORTHEAST
ACROSS THE SOUTHERN AND EASTERN GREAT BASIN THIS WEEKEND.

&&

.SHORT TERM (THROUGH 06Z TUESDAY)...THE UPPER LOW CURRENTLY OVER
NORTHWEST ARIZONA WILL CONTINUE ON A SLOW STEADY NORTHEAST TRACK
THROUGH SOUTHERN AND EASTERN LATER TONIGHT THROUGH THE DAY
SATURDAY. SCATTERED CONVECTION THAT FIRED UP LATE THIS MORNING
OVER CENTRAL UTAH CONTINUED SLOWLY NORTH INTO NORTHERN UTAH DURING
THE AFTERNOON. WEAK MEAN LAYER FLOW ALLOWED THESE SLOW-MOVING
SHOWERS/STORMS TO PUT DOWN BRIEF HEAVY RAIN AND SMALL HAIL THIS
AFTERNOON. THE CONVECTION HAS BEEN WEAKENING THE PAST HOUR OR SO
AS IT MOVES INTO MARGINALLY MORE STABLE AIR AND LESS DYNAMIC
FORCING.

SOUTHERN UTAH WILL SEE AN INCREASE IN CONVECTION THIS EVENING AS
THE UPPER LOW MOVES NORTHEAST INTO THE STATE. SOLID SYNOPTIC-
SCALE AND A FAVORABLE MOISTURE WILL PRODUCE POCKETS OF HEAVY
PRECIP OVERNIGHT ALONG THE NORTH AND WEST FLANKS OF THE LOW.

PRECIP WILL SHIFT INTO NORTHERN AND FAR WESTERN UTAH EARLY
SATURDAY. THE HEAVIEST PRECIP WILL REMAIN IN CLOSE PROXIMITY TO
THE UPPER LOW OVER NORTHEAST UTAH...WITH A SECONDARY AREA ACROSS
NORTHWEST UTAH IN ASSOCIATION WITH WARM ADVECTION GENERATED LIFT.
THIS THERMALLY DRIVEN LIFT WILL SLIDE SOUTH ALONG THE UTAH/NEVADA
BORDER DURING THE DAY...THEN FOCUS ON SOUTHWEST UTAH LATE
SATURDAY THROUGH EARLY SUNDAY. LOOKING AT ANOTHER ROUND OF
SIGNIFICANT PRECIP FOR THE SOUTH...ESPECIALLY DURING THE OVERNIGHT
HOURS SATURDAY.

RESIDUAL MOISTURE AND A COUPLE OF WEAK TRAILING SHORTWAVES BEHIND
THE EXITING UPPER LOW SHOULD PRODUCE ADDITIONAL SCATTERED
CONVECTION ACROSS NORTHERN AND WESTERN UTAH ON SUNDAY
AFTERNOON/EVENING. A TRAILING SHORTWAVE RIDGE WILL REACH UTAH ON
MONDAY...LIMITING THE AREAL COVERAGE OF ANY CONVECTION AND
CONFINING THIS TO MAINLY THE HIGHER TERRAIN THROUGH EARLY MONDAY
EVENING.

.LONG TERM (AFTER 06Z TUESDAY)...FEATURES TO FOCUS ON THROUGH THE
LONG TERM PERIOD ARE THE TRACK OF A REMNANT LOW AS IN MEANDERS
SOUTH AND EAST FROM BRITCOL INTO THE PACNW/NORTHERN ROCKIES...AND
WEAK SHORT WAVES TRANSLATING THROUGH THE DESERT SOUTHWEST
ASSOCIATED WITH THE SOUTHERN BRANCH JET. IN GENERAL THE
COMBINATION OF BOTH WILL MAINTAIN A GENERAL TROUGH OVER THE
EASTERN GREAT BASIN THROUGH THURSDAY...THIS ALLOWING UNSETTLED
CONDITIONS TO CONTINUE THROUGH LATE WEEK /ESPECIALLY ACROSS
NORTHERN AND CENTRAL PORTIONS/.

A COMBINATION OF CONDITIONAL INSTABILITY...MAINTENANCE OF DEEP LAYER
MOISTURE AND WEAK LARGE SCALE FORCING IS EXPECTED TO MAINTAIN
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS FOCUSED OVER THE
NORTHERN 2/3RDS OF THE AREA EACH DAY THROUGH WEDNESDAY. EXPECTING
COVERAGE OF THESE TO BE GREATEST ACROSS THE NORTH DUE TO CLOSER
PROXIMITY TO THE WEAK UPPER LOW TRANSLATING FROM THE PACNW INTO THE
NORTHERN ROCKIES. NOCTURNAL SHOWERS WILL REMAIN POSSIBLE DUE TO WEAK
FORCING AIDED BY PASSAGE OF WAVES ASSOCIATED WITHIN THE SOUTHERN
BRANCH.

GFS/ECMWF CONTINUE TO SLIGHTLY DIFFER IN DOWNSTREAM EVOLUTION OF THE
LOW TO THE NORTH...BUT DO BOTH SUGGEST THE MEAN TROUGH AXIS WILL
SWEEP EAST OF THE FORECAST AREA THURSDAY ALLOWING BUILDING STABILITY
AND NET DRYING FROM THE WEST. A MORE NOTED WARMING TREND LOOKS
LIKELY LATE WEEK DUE TO THIS AND ADJUSTED TEMPS UP A BIT TO ACCOUNT
FOR THIS.

&&

.AVIATION...ANTICIPATING THAT PERIODS OF ERRATIC WINDS DUE TO
PASSING SHOWERS WILL BE THE PRIMARY OPERATIONAL WEATHER CONCERN AT
THE KSLC TERMINAL THROUGH THIS EVENING. PREVAILING WINDS ARE
EXPECTED TO REMAIN GENERALLY LIGHT FROM THE WEST/NORTHWEST THROUGH
01/02Z...BUT OUTFLOWS FROM SHOWERS APPROACHING FROM THE SOUTHEAST
WILL LIKELY ALLOW SOUTHERLY WINDS TO RETURN EARLIER THAN NORMAL
AROUND 01/02Z.

&&

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

$$

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