Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 211021
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
421 AM MDT THU MAY 21 2015

.SYNOPSIS...SEVERAL WEATHER DISTURBANCES WILL CROSS THE GREAT
BASIN THROUGH THURSDAY NIGHT. THE NEXT STORM WILL CROSS THE GREAT
BASIN FRIDAY THROUGH TUESDAY.

&&

.SHORT TERM (THROUGH 12Z SUNDAY)...
WATER VAPOR LOOP SHOWS A CLOSED LOW OFF THE CALIFORNIA
COAST...WITH RIDGING SHIFTING INTO THE CENTRAL ROCKIES. AMDAR
400-250MB WIND OBSERVATIONS SHOW A 75-115KT CYCLONIC JET FROM THE
EASTERN PACIFIC INTO THE FOUR CORNERS. GOES/GPS/RAP/00Z SLC RAOB
INDICATE THE PRECIPITABLE WATER VALUE RANGES BETWEEN 0.25"-0.50"
MOUNTAINS...TO 0.45"-0.75" ACROSS THE VALLEYS.

A LULL IN ACTIVITY WILL OCCUR THROUGH MID MORNING...AS A PASSING
WAVE LIFTS NORTH INTO IDAHO LEAVING SUBSIDENCE IN ITS WAKE.
CONVECTION WILL GET GOING ALONG THE MOUNTAINS DURING THE MID TO LATE
MORNING HOURS. ANOTHER DISTURBANCE WILL LIFT OUT OF THE BASE OF THE
TROUGH OVER UTAH FROM SOUTH TO NORTH TODAY. THIS FEATURE SHOULD
ORGANIZE CONVECTION LEADING TO AN INCREASE IN COVERAGE. OTHER
SUPPORT FOR CONVECTION INCLUDE INCREASING DIFFLUENCE ALOFT AND THE
UPPER LEVEL JET NOISING INTO EASTERN UTAH.

SINCE LOW LEVELS HAVE DRIED OUT AS FORECAST...GUSTY DRY MICROBURST
WINDS WILL BECOME MORE LIKELY WITH CONVECTION TODAY. OTHER THREATS
INCLUDE CLOUD TO GROUND LIGHTNING...SMALL HAIL...AND A BRIEF HEAVY
RAIN.

FRIDAY AN AREA OF DEFORMATION NORTH OF THE CLOSED LOW WILL BEGIN TO
IMPACT THE STATE...LEADING TO AN INCREASE IN CONVECTIVE COVERAGE. THE
BEST COVERAGE OF RAIN IS LIKELY SOMETIME SATURDAY OR SATURDAY NIGHT
WHEN WRAP-AROUND PRECIPITATION DUE TO MID LEVEL WARM ADVECTION
ARRIVES FROM THE NORTHEAST. BY THIS TIME GLOBAL MODELS ARE BEGINNING
TO DIVERGE ON TIMING/PROGRESSION OF LARGE SCALE
FEATURES...CONFIDENCE AT THIS TIME. HAVE CUT POPS BACK TO LIKELY IN
THE VALLEYS AS ITS HARD TO PIN DOWN A PERIOD OR TWO FOR THE MOST
WIDESPREAD ACTIVITY GIVEN MODEL SPREAD.

.LONG TERM (AFTER 12Z SUNDAY)...
ALTHOUGH THERE IS A BASIC TROUGH OVER THE GREAT BASIN SUNDAY INTO
MONDAY...THE DETAILS ARE QUITE DIFFERENT BETWEEN MODELS WITH THE
GFS SHOWING MULTIPLE CIRCULATIONS WHILE THE EC HAS ONE
CONSOLIDATED SYSTEM. ALTHOUGH THE DETAILS ARE YET TO SHAKE OUT ON
WHERE THE MOST LIKELY AND HEAVIEST PRECIP WILL OCCUR IT SEEMED
REASONABLE TO BOOST POPS DUE TO THE TROUGH OVERHEAD AND THE
PRECIPITABLE WATER FORECAST TO BE AT THEIR HIGHEST LEVELS DURING
THE SEVEN PERIOD NEAR 0.60-0.75 OF AN INCH.

THE PW AMOUNTS GRADUALLY LOWER THROUGH THE WEEK AS THE TROUGH
WEAKENS AND A RIDGE BUILDS IN FROM THE SOUTHEAST. DUE TO THE STILL
RELATIVELY MOIST AIR MASS HAD TO KEEP SCATTERED SHOWERS BY DAY AND
ISOLATED BY NIGHT TUESDAY BUT TAILED OFF THE PROBABILITY WEDNESDAY
INTO THURSDAY. THE FORECAST WAS MAINLY BASED ON THE GFS BUT SOME
CONSIDERATION WAS GIVEN TO THE EC. THEREFORE THE CONTINUATION OF
SHOWERS INTO THURSDAY AS THE EC SHOWS A FEATURE MOVING THROUGH UTAH
WHILE THE GFS KEEPS THE TROUGH OVER THE WESTERN GREAT BASIN INTO
CALIFORNIA AREA.

DUE TO RIDGE MOVING IN...THE 700 MB TEMPS ACTUALLY WARM TO LEVELS OF
PLUS 8-10 ON WEDNESDAY AND 8-12 ON THURSDAY ACCORDING TO THE GFS
WHILE THE EC IS SEVERAL DEGREES COOLER DUE TO THE FEATURE MOVING
THROUGH. HAVE LEANED TOWARDS THE GFS SOLUTION ONCE AGAIN AND
THEREFORE RAISED TEMPERATURES IN THE EXTENDED BY A FEW DEGREES.

&&

.AVIATION...A LULL IN CONVECTION IS EXPECTED AT THE SLC TERMINAL
THROUGH AT LEAST 19-20Z. THEN STORMS ARE EXPECTED TO MOVE THROUGH IN
THE 20Z-03Z PERIOD WITH BRIEF HEAVY RAIN...GUSTY WINDS TO OVER 30
MPH...AND CIGS AOB 5000FT AGL DURING STORM ACTIVITY AND VSBY DOWN TO
MVFR LEVELS ARE ALL POSSIBLE. WINDS WILL BE SOUTHERLY THROUGHOUT THE
TAF PERIOD BUT WILL BECOME ERRATIC DURING CONVECTION.

&&

.FIRE WEATHER...TODAY WILL BE THE WARMEST AND DRIEST DAY ACROSS THE
REGION THROUGH THE HOLIDAY WEEKEND. STILL...THERE IS ENOUGH MOISTURE
IN PLACE AHEAD OF THE NEXT STORM SYSTEM TO FOSTER THE DEVELOPMENT OF
SCATTERED SHOWERS AND THUNDERSTORMS DURING THE MID MORNING THROUGH
THE EVENING HOURS. 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 TOMORROW AND PERSISTS THROUGH THE
HOLIDAY WEEKEND. SHOWERS AND THUNDERSTORMS WILL GROW MORE NUMEROUS
ACROSS THE REGION...WITH THE GREATEST COVERAGE IN ACTIVITY EXPECTED
SATURDAY. TEMPERATURES WILL TREND COOLER AND HUMIDITY WILL TREND
HIGHER. SNOW LEVELS WILL BE BETWEEN 8-9KFT...FALLING TO 7KFT UNDER
THE HEAVIEST ACTIVITY.

&&

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

$$

SHORT TERM/FIRE WEATHER...ROGOWSKI
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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