496
FXUS65 KREV 122008
AFDREV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
1208 PM PST MON JAN 12 2026
KEY MESSAGES
* DRY WEATHER FIRMLY IN PLACE THIS WEEK WITH NEAR AVERAGE DAYTIME
TEMPERATURES EARLY THIS WEEK, WARMING TO ABOVE AVERAGE FROM
MIDWEEK ONWARD.
* LIGHT WINDS AND VALLEY INVERSIONS WILL ALLOW HAZY SKIES AND AIR
QUALITY REDUCTIONS TO BUILD OVER VALLEYS THIS WEEK. OVERNIGHT
VISIBILITY MAY BE REDUCED BY AREAS OF FREEZING FOG IN VALLEYS.
* SIERRA RIDGES CAN EXPECT PERIODIC GUSTY EAST WINDS THIS WEEK,
WITH THE BEST CHANCES BY LATE THURSDAY.
DISCUSSION
FOGGY SKIES LINGERED OVER SOME VALLEYS THIS MORNING, SUCH AS NEAR
LEE VINING AND MONO LAKE, BRINGING REDUCED VISIBILITIES ALONG
ROADWAYS SUCH AS US-395 THIS MORNING. THE FOG IS A FREEZING FOG,
WHICH CAN DEPOSIT UPON SURFACES SUCH AS ROADS AND SIDEWALKS,
CAUSING POTENTIALLY SLICK SPOTS DURING THE EARLY MORNING COMMUTE.
WE EXPECT THE INVERSIONS THAT ARE SETTLING OVER VALLEYS TO
CONTINUE UNDER THIS HIGH PRESSURE DOME THAT FEATURES LIGHT WINDS
AND OVERALL WARMING TEMPERATURES. THE INVERSIONS WILL WORK TO KEEP
COLD AIR TRAPPED IN VALLEYS SINCE THE WINDS ALOFT HAVE YET TO MIX
DOWN, WHICH WOULD BE THE NECESSARY MECHANISM TO SCOUR THE
AIRMASS. AND SO THIS WILL BE THE TREND INTO THIS WEEK, WITH
NIGHTLY AREAS OF FREEZING FOG OVER VALLEYS, ESPECIALLY VALLEYS
CONTAINING BODIES OF WATER OR STRONG SNOW MELT CAUSING A HIGHER
VAPOR PRESSURE AT THE SURFACE. WINDS ALOFT ARE JUST THAT, ALOFT,
AND WAY UP THERE. IN MODEL SOUNDINGS, WIND SPEEDS GREATER THAN 20
KTS ARE WELL-ABOVE 500MB, WITH LIGHT AND VARIABLE WINDS AT THE
SURFACE. WITH THIS TYPE OF SHEER PROFILE, LITTLE TO NO MIXING WILL
TAKE PLACE IN VALLEYS. EXPECT FREEZING FOG TO DEVELOP IN THE
SIERRA AND MARTIS VALLEYS AS WELL AS OVER MONO LAKE/LEE VINING
TUESDAY MORNING. OTHER AREAS THAT COULD DEVELOP FREEZING FOG ARE
THE WALKER LAKE/HAWTHORNE AREA, THE SMITH AND MASON VALLEYS, AND
POSSIBLY BRIDGEPORT AND EVEN TOPAZ LAKE/COLEVILLE. IF YOUR
TRAVELS BRING YOU THROUGH ANY OF THESE VALLEYS, KEEP THIS FREEZING
FOG POTENTIAL IN MIND.
ON THIS INVERSION NOTE, HAZY SKIES WILL RETURN EACH AFTERNOON AS
INVERSIONS HANG AROUND AREA VALLEYS. THE FIRST OPPORTUNITY TO SEE
WINDS THAT MAY BE CAPABLE OF MIXING DOWN AND CLEARING THE VALLEYS
WILL BE THURSDAY NIGHT, WHEN RIDGE GUSTS WILL APPROACH 45-55 MPH,
WHICH COULD TRANSLATE TO VALLEY FLOORS WITH WINDS OF 5-10 MPH.
THIS COULD BE JUST ENOUGH TO CLEAR SOME OF THE HAZE AND SURFACE
MOISTURE-INDUCED FOG, BUT TIMING IS EVERYTHING IN THESE SETUPS.
THE BEST TIME TO EXPECT FREEZING FOG TONIGHT WILL BE AROUND 3 TO 4
AM, AND LINGERING WELL AFTER DAYBREAK AND INTO THE LATE MORNING
FOR SOME AREAS, SUCH AS IN AND AROUND TRUCKEE.
WINDS WILL INCREASE LATE THURSDAY AND REMAIN ELEVATED INTO THE
OVERNIGHT HOURS, BUT WILL IT MAKE A DIFFERENCE IN DEEPER, COLDER
VALLEYS? IF THE RIDGE GUSTS DO NOT MIX DOWN AND CLEAR THE VALLEYS,
WE COULD SEE DENSE EARLY MORNING FOG DEVELOP. THE LONGER THE
WINDS ARE ABSENT, THE HIGHER THE CHANCES TO SEE FOG DEVELOP AND
HAZE RETURN, AND THE POTENTIAL FOR DENSER PATCHES OF FOG TO
DEVELOP INCREASES LIKEWISE. THIS BALANCING ACT WILL DETERMINE THE
'WHERE' AND 'HOW MUCH' ANSWERS TO THE ABOVE QUESTION.
OUR WARMER TREND LOOKS TO REMAIN FIRMLY IN PLACE THROUGH AT LEAST
EARLY NEXT WEEK, PROMISING A BENIGN WEATHER PATTERN OVER THIS
WEEKEND, FOR THOSE MAKING PLANS. SIGNALS OF A STORM ON THE HORIZON
SHOW UP IN THE GFS AND ECMWF AROUND TUESDAY OR WEDNESDAY NEXT
WEEK. HOWEVER, THERE EXISTS A DISCREPANCY ON THE SOURCE REGION OF
THIS INCOMING SYSTEM, WITH THE GFS SUGGESTING A SUBTROPICAL
MOISTURE FEED, WHILE THE ECMWF SUGGESTS A MORE NORTHERLY TRACK
FROM WHENCE THIS WILL EMANATE. CONFIDENCE IS THEREFORE LOW AT THIS
TIME, PENDING MORE CLARITY LATER THIS WEEK. HRICH
AVIATION
* VFR CONDITIONS WITH LIGHT SURFACE WINDS TODAY AND TOMORROW.
GUSTS ALONG SIERRA RIDGES OVER MONO COUNTY WILL INCREASE TO 30
KTS TONIGHT. SIMILAR WIND GUSTS WILL REAPPEAR TUESDAY NIGHT.
* INVERSIONS OVER VALLEY TERMINALS WILL KEEP HAZE DURING THE DAY,
IMPACTING SLANTWISE VISIBILITY EACH DAY. FREEZING FOG WILL
SETTLE OVER KTRK, KMMH AND KNFL AS COLD VALLEYS DEVELOP EACH
NIGHT, BRINGING OVERNIGHT AND EARLY MORNING IFR TO LIFR
CONDITIONS FOR IMPACTED TERMINALS. HRICH
REV WATCHES/WARNINGS/ADVISORIES
NV...NONE.
CA...NONE.
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