Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 250538
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1038 PM MST TUE FEB 24 2015

UPDATED AVIATION SECTION

.UPDATE...
ISSUED AT 751 PM MST TUE FEB 24 2015

OBSERVATIONS AT THE CORTEZ AIRPORT HAVE SHOWN STEADY 1/4 MILE
VISIBILITY FOR THE PAST HOUR SO WENT AHEAD AND ISSUED DENSE FOG
ADVISORY FOR SERN UT AND SWRN CO. SO FAR DURANGO AND PAGOSA
SPRINGS CONTINUE TO SHOW SOME LOW CLOUDS BUT NO FOG...WILL
CONTINUE TO KEEP AN EYE ON THINGS.

UPDATE ISSUED AT 638 PM MST TUE FEB 24 2015

ADDED SOME FOG FOR THE SOUTHERN VALLEYS OVERNIGHT AND ALSO
SOUTHEASTERN UTAH FOR THE OVERNIGHT HOURS. RECENT OBS SHOW
VISIBILITY FLUCTUATING FROM 1 1/2 MILES TO 1/4 MILES AT TIMES FOR
THE CORTEZ AREA SO WILL KEEP AN EYE ON THINGS AND ISSUE DENSE FOG
ADVISORY AS NEEDED. SOME CLOUDS STILL HANGING ON FOR DURANGO AND
PAGOSA WHICH WILL KEEP FOG FORMATION AT BAY...FOR NOW. WITH SO
MUCH MOISTURE IN THE ATMOSPHERE WOULD NOT BE SURPRISED TO SEE SOME
PATCHY DENSE FOG FOR THAT AREA TOO.

&&

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 339 PM MST TUE FEB 24 2015

CLOUDS WILL CONTINUE CLEARING TONIGHT OVER THE SAN JUAN MOUNTAINS
AND LOWER ELEVATION OF THE FOUR CORNERS. THE SMALL ECHOES SEEN ON
RADAR THE CLOUDS ON SATELLITE ARE ALL MOVING TOWARD THE SOUTH AND
SOUTHWEST AS THE LOW CENTER MOVES FROM EASTERN AZ INTO WESTERN NM.
NEARLY CLEAR SKIES EXIT OVER THE REST OF THE FORECAST AREA. OVER
NIGHT MID AND HIGH CLOUDS WILL MOVE OVER NORTHERN CO AND UT AS THE
NEXT SERIES OF SHORTWAVES APPROACH.

THURSDAY AND THURSDAY NIGHT A SERIES OF WEAK SHORTWAVE TROUGHS
WILL TRAVEL DOWN THE FRONT RANGE AND INCREASE THE CHANCE OF SNOW
OVER THE MOUNTAINS GENERALLY EAST OF HAYDEN...EAGLE AND ASPEN.
MOST OF THE SNOW IS EXPECTED TO FALL EAST OF THE CONTINENTAL
DIVIDE SO THE AREA OF 5 PLUS INCH SNOW ACCUMULATIONS IN THE GJT
FORECAST AREA SHOULD AFFECT ONLY THE A SMALL AREA NEAR THE
CONTINENTAL DIVIDE.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 339 PM MST TUE FEB 24 2015

AGAIN TODAY A COOL AND WET PATTERN CONTINUES TO BE ADVERTISED BY
GLOBAL MODELS FOR THE LONG TERM PERIOD. CONFIDENCE IS INCREASING
THAT A SIGNIFICANT AMOUNT OF PRECIPITATION WILL ONCE AGAIN BE
FOCUSED NEAR THE 4 CORNERS...INCLUDING AT LEAST THE SOUTHERN THIRD
OF OUR CWA LATE THIS WEEK INTO EARLY NEXT WEEK. ON EITHER END OF
THIS WEEKEND STORM...LIGHT SNOWFALL WILL BE CENTERED OVER THE
DIVIDE MOUNTAINS ON THURSDAY AND ON TUESDAY THE MODELS ARE HINTING
AT ANOTHER TROUGH SWINGING INTO THE GREAT BASIN. THIS TREND ON
THIS LATTER STORM APPEARS TO HAVE MORE IMPACT TO THE NORTHERN CWA
ATTM...BUT DETAILS ABOUT THIS SCENARIO ARE VERY FUZZY ATTM. WHAT
IS IN FOCUS THROUGH THE PERIOD IS THAT BELOW NORMAL TEMPERATURES
WILL BE IN PLACE...WITH HIGHS RUNNING 10 TO 15 DEGREES BELOW
NORMAL FOR LATE FEBRUARY.

SO THE RECENT TREND OF PACIFIC ENERGY AND MOISTURE DROPPING OVER THE
EAST PACIFIC RIDGE INTO THE WESTERN GREAT BASIN CONTINUES THIS
FRIDAY. A CLOSED CIRCULATION LOOKS TO FORM OVER NEVADA BY SATURDAY
PM...WHICH THEN DIGS TOWARD SOUTHERN CALIFORNIA BY SUNDAY PM. THE
LOW THEN MIGRATES EASTWARD AND OPENS AS A WAVE AS IT CROSSES THE 4
CORNERS REGION BY MONDAY PM. THIS TROUGH IS INITIALLY PHASED WITH
THE HIGH LATITUDE VORTEX OVER EASTERN CANADA WHICH SUPPLIES THE COLD
AIR FOR THIS SYSTEM. THE RESULT IS THE BULK OF THE PRECIPITATION
THAT FALLS WILL BE IN THE FORM OF SNOW. THE GEM/NAEFS ARE THE
OUTLIERS THIS RUN DUE TO A DISPLACEMENT IN THE NORTHERN STREAM
TROUGH WHICH SUPPRESSES A DOWNSTREAM RIDGE OVER THE PLAINS. THIS
KEEPS THE FLOW AROUND THE WESTERN TROF MORE ZONAL AND THE HEAVY
PRECIPITATION STAYS FOCUSED TO OUR SOUTH THOUGH SATURDAY. THE
GFS/EURO ARE IN LINE...PRODUCING A STRONGER DOWN STREAM PLAINS
RIDGE...PRODUCING SOUTHWESTERLY ACROSS THE 4 CORNERS INTO
SOUTHERN COLORADO. THIS FLOW GRABS ONTO ADDITIONAL PACIFIC
MOISTURE PER THE 300K THETA SURFACES AND PUSHES PWATS NEAR 0.40 OR
NEAR 150 PERCENT OF NORMAL. UNLIKE THE LAST STORM ANY SUBTROPICAL
MOISTURE LOOKS TO ENTRAIN AS THE STORM BEGINS TO FOCUS TO OUR
SOUTH LATER SUNDAY INTO MONDAY. DOES THIS MEAN SNOW TOTALS WILL
NOT BE AS HIGH AS THE LAST STORM...POSSIBLY BUT NOT PROBABLY. GFS
BUFKIT FILES FOR DURANGO HAVE DROPPED THE AVERAGE SNOW
AMOUNTS(BOTH COBB AND SLR AMOUNTS)FROM 14 TO 12 TO NOW 9 INCHES ON
THE 24/12Z RUN. A FALLING TREND BUT STILL A SIGNAL THAT HEAVY
SNOW CENTERED ON FRIDAY NIGHT THROUGH SATURDAY IS A STRONG
POSSIBILITY FOR OUR SOUTHERN CWA CENTERED OVER THE SAN JUANS. WHAT
IS NOT AS APPARENT WITH ONLY LIMITED SYNOPTIC SCALE MODELS IS A
HEAVY BAND OF SNOW SIMILAR THIS PAST EVENT SETTING UP. THE GFS
DOES SHOW A WARM FRONT FEATURE LINING UP OVER THE SAN JUANS AS A
SURFACE LOW FORMS NEAR THE PARADOX VALLEY. MID LEVEL FRONTAL BAND NEAR
650MB OVER THIS FRONT DUE TO THE INCOMING UPPER JET MAX AND
STEEPENING LAPSE RATES WOULD ALL SIGNAL IMPRESSIVE SNOW RATES. ALL
BIG IF/S FOR NOW BUT WORTH WATCHING THE TRENDS. LASTLY IF THIS
FRONT DOES FORM PTYPE COULD BE AN ISSUE IN THE LOWER VALLEYS NEAR
THE 4 CORNERS AND ALONG THE SOUTHERN COLORADO BORDER. WILL OPT TO
START THE HEADS UP FOR THIS STORM WITH AN SPS AS THE STORM IS AT
LEAST 3 DAYS OUT AND HOPEFULLY NARROW SOME AREAS AND ELIMINATE
OTHER TOMORROW FOR FUTURE HEADLINES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1036 PM MST TUE FEB 24 2015

A WEAK WEATHER DISTURBANCE IS ENTERING NE UTAH AND NW COLORADO AND
WILL DROP CIGS AT AIRPORTS IN THESE AREAS OVERNIGHT. A STRONGER
PUSH OF MOISTURE MOVES IN MIDDAY AND IS EXPECTED TO REDUCE VIS AT
KASE AND KEGE IN THE AFTERNOON. GUSTS UP TO 20 MPH ARE EXPECTED
AT THE NORTHERN TAF SITES TOMORROW AFTERNOON AS THIS WEAK SYSTEM
BLOWS THROUGH.

VALLEYS ACROSS SE UTAH AND SW COLORADO ARE EXPECTED TO DEVELOP
PATCHY DENSE FOG THROUGH 17Z WEDNESDAY. PATCHY FOG IS POSSIBLE AT
KMTJ AS WELL THROUGH LATE WED MORNING.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...DENSE FOG ADVISORY UNTIL 10 AM MST WEDNESDAY FOR COZ021.

UT...DENSE FOG ADVISORY UNTIL 10 AM MST WEDNESDAY FOR UTZ022.

&&

$$

UPDATE...TGR
SHORT TERM...CC
LONG TERM...15
AVIATION...JAM



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