Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 151540
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
840 AM MST MON DEC 15 2014

.SYNOPSIS...HIGH PRESSURE WILL MOVE EAST ACROSS UTAH TODAY. A
SERIES OF WEATHER SYSTEMS WILL CROSS THE REGION LATE MONDAY NIGHT
THROUGH THURSDAY. HIGH PRESSURE WILL RETURN FOR FRIDAY.

&&

.DISCUSSION...
WATER VAPOR LOOP SHOWS RIDGING BUILDING INTO THE EASTERN GREAT
BASIN...AHEAD OF THE NEXT TROUGH ALONG THE WEST COAST. AMDAR 400-
250MB WIND OBSERVATIONS INDICATE A 75-115KT ANTICYCLONIC JET FROM
CENTRAL CALIFORNIA INTO THE FOUR CORNERS. GOES/GPS/RAP/12Z RAOB
INDICATE THE PRECIPITABLE WATER VALUE RANGES BETWEEN 0.05"
NORTHEAST MOUNTAINS...TO 0.33" DIXIE. BLENDED PRECIPITABLE WATER
PRODUCT SHOWS A WEAK PACIFIC MOISTURE TAP INTO NORTHERN
CALIFORNIA.

A FEW STRATUS CAUGHT ALONG THE TERRAIN OF THE NORTHERN ZONES THIS
MORNING. OTHERWISE BUMPED UP SKY COVER ACROSS THE SOUTHWEST AS
COPIOUS MID AND HIGH LEVEL CLOUDS WILL INVADE AS THE RIDGE AXIS
BUILDS IN.

WITH HIGH PRESSURE SURFACE AND ALOFT...TEMPERATURES WILL STRUGGLE TO
CLIMB ACROSS THE NORTHERN VALLEY ZONES DUE TO INVERTED CONDITIONS.

PREVIOUS DISCUSSION FOLLOWS...
HIGH PRESSURE ALOFT WILL MOVE EAST ACROSS UTAH TODAY...FOLLOWED
BY THE NEXT SERIES OF WEATHER DISTURBANCES OFF THE EASTERN PACIFIC
FOR LATE MONDAY NIGHT THROUGH THURSDAY.

THE UPPER TROUGH CURRENTLY OFF THE CALIFORNIA/OREGON COASTS WILL BE
THE FIRST FEATURE TO IMPACT THE GREAT BASIN LATE TONIGHT AND
TUESDAY. A VORTICITY LOBE EJECTING OUT AHEAD OF THIS TROUGH WILL
TRACK NORTHEAST THROUGH THE WESTERN GREAT BASIN TONIGHT. THIS
FEATURE HAS TAPPED INTO A DECENT AMOUNT OF MOISTURE TO THE SOUTH
WHICH SHOULD ENHANCE PRECIP SOMEWHAT AS THIS FEATURE MOVES THROUGH
NEVADA AND NORTHWEST UTAH OVERNIGHT.

THE MAIN TROUGH WILL FOLLOW THE FIRST FEATURE AND MOVE THROUGH
NORTHEAST THROUGH THE GREAT BASIN AS A WEAKENING OPEN WAVE TUESDAY.
SUFFICIENT DYNAMIC LIFT AND COLD AIR ALOFT WILL STILL EXIST WITH
THIS WEAKENING FEATURE ALONG WITH ADEQUATE DEEP LAYER MOISTURE.
GUIDANCE AT THIS POINT IS FOCUSING THE GREATEST QPFS ACROSS
NORTHEAST UTAH...THOUGH SUSPECT THAT CENTRAL AND EAST-CENTRAL UTAH
WILL ALSO SEE PRECIP LATE TONIGHT OR EARLY TUESDAY.

A SPLITTING TROUGH OVER THE EASTERN PACIFIC WILL SEND AN ENERGETIC
VORTICITY MAX INTO THE SOUTHERN END OF THE OVER CALIFORNIA
WEDNESDAY....THEN INTO THE SOUTHERN GREAT BASIN AS A CLOSED LOW
WEDNESDAY NIGHT. THE GFS AND ECMWF HAVE COME TO AN AGREEMENT ON THIS
SOLUTION...WITH THE GFS MIGRATING TOWARDS THE ECMWF IN THE LATEST
MODEL RUNS. THE CURRENT MODEL SOLUTIONS WOULD BRING ANOTHER
SIGNIFICANT PRECIP EVENT TO THE SOUTHERN HALF OF UTAH...WITH THE
POTENTIAL FOR HEAVY SNOW FOR THE SOUTHERN MOUNTAINS MIDWEEK.
NORTHERN UTAH WILL REMAIN IN A COOL/MOIST BUT WEAKLY FORCED
ENVIRONMENT AS THE UPPER LOW TRACK EAST THROUGH NORTHERN ARIZONA.
PRECIP WILL REMAIN LIGHT ACROSS THE NORTH WITH MINIMAL AMOUNTS OF
SNOW...EVEN AT THE HIGHER ELEVATIONS.

THE ANTI-CYCLONIC NORTHERLY FLOW DEVELOPING BEHIND THE EXITING UPPER
LOW WILL SPREAD DRIER AND MORE STABLE AIR ACROSS THE STATE THURSDAY.
PRECIP WILL END ACROSS THE NORTHERN HALF OF THE STATE EARLY
THURSDAY...THEN ACROSS THE REMAINDER OF THE FORECAST AREA BY
THURSDAY EVENING.

THE GLOBAL MODELS ARE IN AGREEMENT THAT A RIDGE WILL BUILD IN OVER
THE REGION FRIDAY WITH THE EC SHARPER AND STRONGER THAN THE GFS.
EITHER WAY FRIDAY SHOULD BE DRY BUT THE MOUNTAINS WILL BE A COUPLE
OF DEGREES WARMER IF THE EC PANS OUT. WITH THE WEAKER RIDGE SOLUTION
THE GFS IS QUICKER BY 6-12 HRS OVER THE EC IN MOVING IN A WEAK WAVE
ON WESTERLY FLOW ACROSS NORTHERN UTAH FRIDAY NIGHT. HAVE ADDED SOME
POPS ACROSS THE NORTHWEST TO ACCOUNT FOR THIS POSSIBLE SOLUTION BUT
BELIEVE THE SLOWER EC WILL BE THE BETTER FORECAST. THE EC IS MORE
CONSOLIDATED WITH THIS SHORTWAVE WITH BETTER DYNAMICS MOVING INTO
NORTHERN UTAH SATURDAY WHILE THE GFS SHOWS A RATHER BROKEN UP SYSTEM
WITH MULTIPLE WAVES. HAVE LEANED TOWARDS THE EC SINCE IT HAS BEEN
HAVING A SOMEWHAT BETTER TRACK RECORD OF LATE.

THE EC CLOSES THIS SYSTEM OFF JUST AS THE LEADING EDGE MOVES INTO
NORTHERN UTAH AND MOVES IT/REORGANIZES IT OVER WESTERN ARIZONA BY
SUNDAY WHICH LEAVES MOST OF THE DYNAMICS BYPASSING MOST OF THE CWA
TO THE WEST...THAT IS OTHER THAN THE INITIAL SURGE ON SATURDAY
ACROSS NORTHERN UTAH. THE GFS ON THE OTHER HAND...MOVES THE CORE OF
THE SYSTEM ACROSS SOUTH EASTERN MONTANA AND WYOMING WITH IT CLOSING
OFF THEN TRACKING EASTWARD INTO THE HIGH PLAINS.  HAVE LEANED
TOWARDS THE EC AS IT HAS BEEN SOMEWHAT MORE CONSISTENT SO RAISED
POPS ACROSS THE NORTH FOR SATURDAY AND LEFT THEM LINGER INTO
SATURDAY NIGHT DUE TO THE UNCERTAINTY OF THE MODELS. ISOLATED
SHOWERS MAY ALSO CONTINUE INTO SUNDAY BUT MAINLY MOUNTAINS AND THE
SOUTHEAST WHICH WILL BE CLOSEST TO THE EC CLOSED CIRCULATION.

&&

.AVIATION...THE SLC TERMINAL WILL SEE VFR CONDITIONS THROUGH THE
AFTERNOON WITH SOME SCATTERED CLOUDS. SOUTHEAST WINDS ARE EXPECTED
TO SHIFT TO THE NORTHWEST BETWEEN 17Z AND 19Z.

&&

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

$$

PUBLIC...ROGOWSKI/CONGER/STRUTHWOLF
AVIATION...TRAPHAGAN

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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