Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 191217
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
517 AM MST MON JAN 19 2015

.SYNOPSIS...A WEAK PACIFIC WEATHER DISTURBANCE WILL IMPACT FAR
NORTHERN UTAH AND SOUTHWEST WYOMING TODAY. HIGH PRESSURE ALOFT WILL
BECOME ESTABLISHED ACROSS THE WESTERN STATES FOR THE LATTER HALF OF
THE WEEK.

&&

.SHORT TERM (THROUGH 12Z THURSDAY)...A WEAK SHORTWAVE DISTURBANCE
PASSING WELL NORTH OF THE FORECAST AREA MANAGED TO PUSH A WEAK COLD
FRONT INTO NORTHERN UTAH OVERNIGHT. PER SURFACE PRESSURE TRENDS AND
WIND SHIFTS...THE SURFACE BOUNDARY HAS MADE IT INTO UTAH
COUNTY...BUT IS EXPECTED TO MAKE LITTLE ADDITIONAL PROGRESS FOR THE
REST OF THE MORNING. A SMALL BAND OF PRECIPITATION WAS ASSOCIATED
WITH THE FRONT AND IMPACTED FAR NORTHERN UTAH AND SOUTHWEST WYOMING.
THIS HAS MOSTLY TAPERED OFF NOW...BUT SOME LOW/MID CLOUDS LINGER
NORTH OF THE FRONT.

A SECOND AND SLIGHTLY STRONGER SHORTWAVE TROUGH...CURRENTLY SEEN ON
SATELLITE OVER WASHINGTON STATE...WILL GRAZE NORTHERN UTAH AND
SOUTHWEST WYOMING LATER THIS AFTERNOON AND THIS EVENING. THIS WILL
PUSH A REINFORCING COLD FRONT THROUGH NORTHERN UTAH THIS AFTERNOON
AND THROUGH THE REMAINDER OF THE STATE BY LATE TONIGHT. THE
COMBINATION OF THE TWO COLD FRONTS TODAY WOULD SUGGEST COOLER
TEMPERATURES TODAY FOR NORTHERN AND CENTRAL UTAH...ALTHOUGH THE
CURRENTLY INVERTED EASTERN VALLEYS MAY TREND STEADY OR WARMER DUE TO
INCREASED MIXING BEHIND THE FRONT. REGARDING MIXING...H7
TEMPERATURES FALL TO AROUND -7 TO -9C ACROSS NORTHERN ZONES...SO
INVERSIONS SHOULD WEAKEN CONSIDERABLY. HOWEVER...NAM BUFR SOUNDINGS
SUGGEST FULL MIXING STILL ELUSIVE AS A SHALLOW STABLE/INVERTED LAYER
LINGERS. LIGHT PRECIPITATION IS POSSIBLE ACROSS THE NORTH AGAIN WITH
THIS SECOND FRONT. HOWEVER...THE BULK OF THE UPPER SUPPORT WILL
REMAIN NORTH OF THE AREA...SO HAVE NO COMPELLING REASON TO GO WITH
HIGHER POPS THAN SLIGHT CHANCE TO CHANCE WORDING.

A NORTHWESTERLY TO NORTHERLY FLOW WILL REMAIN IN PLACE BEHIND THE
TROUGH THROUGH THE MIDWEEK PERIOD...KEEPING THE COOLER AIRMASS IN
PLACE. THIS PATTERN WILL ALLOW THE NEXT SYSTEM TO ENTER THE GREAT
BASIN...ALBEIT AS A WEAK SPLITTING SYSTEM WITH THE BULK OF ITS
ENERGY CONFINED TO THE SOUTHERN BRANCH WAVE WHICH IS PROGGED TO
CROSS THE DESERT SOUTHWEST TUESDAY NIGHT THROUGH WEDNESDAY NIGHT.
SOUTHWESTERLY FLOW DEVELOPING AHEAD OF THIS TROUGH WILL CONVERGE
WITH THE EXISTING BOUNDARY NEAR THE UTAH/ARIZONA BORDER. LATEST
GFS/EC/NAM ALL KEEPING THIS CONVERGENCE ZONE AND ASSOCIATED
PRECIPITATION JUST SOUTH OF THE BORDER. LOWERED POPS SLIGHTLY AS A
RESULT...KEEPING ONLY SLIGHT CHANCE MENTION IN THE ZONES ALONG THE
ARIZONA BORDER FOR TUESDAY NIGHT AND WEDNESDAY. AS THE STORM
CONTINUES TO TRACK SOUTHEAST OUT OF THE AREA...HIGH PRESSURE WILL
BUILD BACK INTO THE AREA...SETTING UP FOR STRONGER VALLEY INVERSIONS
ONCE AGAIN.

&&

.LONG TERM (AFTER 12Z THURSDAY)...A RIDGE AXIS WILL MOVE OVER THE
REGION THURSDAY BRINGING DRY AND SOMEWHAT WARMER TEMPERATURES ALOFT.
HAVE ADJUSTED MOUNTAIN TEMPERATURES UP A FEW DEGREES AS THE H7 TEMPS
INCREASE BY ABOUT 3-4 DEGREES C ACCORDING TO THE EC...CANADIAN AND
GFS ACROSS NORTHERN UTAH AND A COUPLE DEGREES ACROSS SOUTHERN UTAH.
THE NORTHEAST H7 FLOW IS MODERATELY STRONG ACROSS SOUTHWEST UTAH
THURSDAY SO THE IDEA OF ENHANCED CANYON OR GAP WINDS ACROSS DIXIE
LOOKS REASONABLE.

VERY WEAK DISTURBANCES BRUSH BY NORTHERN PART OF THE CWA FRIDAY AND
SATURDAY WITH A SLIGHT INCREASE IN THE H7 TEMPERATURES BUT SKIES ARE
EXPECTED TO BE PARTLY CLOUDY WHICH SHOULD CAUSE TEMPERATURES IN THE
MOUNTAINS NOT TO CHANGE MUCH AS WELL AS IN THE VALLEYS WHERE AN
INVERSION SHOULD REMAIN IN PLACE. THE CANADIAN MODEL HAS A SLIGHTLY
STRONGER DISTURBANCE MOVING ACROSS UTAH SUNDAY COMPARED TO EITHER
THE EC OR GFS. HAVE NOT ADJUSTED FORECAST TO INCLUDE THIS
DISTURBANCE AS THE CANADIAN HAS YET TO PROVE ITSELF. BOTTOM LINE IS
THAT THE PATTERN REMAINS RATHER STAGNANT FOR THE FORESEEABLE FUTURE.

&&

.AVIATION...CEILINGS AT THE SLC TERMINAL ARE EXPECTED TO REMAIN
ABOVE 7000 FT AGL...WITH A 30 PERCENT CHANCE OF LOWERING TO NEAR
6000 FT AGL BETWEEN 15 AND 20Z. SURFACE WINDS SHOULD GENERALLY BE
SOUTHEAST THROUGH ABOUT 17Z THEN SHIFT TO NORTHERLY...ALTHOUGH THERE
IS A 30 PERCENT CHANCE THAT SWITCH BETWEEN 15 AND 16Z.

&&

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

$$

CHENG/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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