Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 152356
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
556 PM MDT WED APR 15 2015

.SHORT TERM...(TONIGHT THROUGH FRIDAY NIGHT)
ISSUED AT 348 PM MDT WED APR 15 2015

12Z H5 HAND ANALYSIS SHOWED THE LOW HAD CLOSED OFF OVER THE NORTHERN
ROCKIES AND CENTRAL GREAT BASIN WITH THE CENTER OF THE CIRCULATION
PEGGED OVER SOUTHEAST IDAHO. SIGNIFICANT HEIGHT FALLS WERE SEEN
OVER THE GRAND FLATS AREA AND LATEST SATELLITE IMAGERY AND RADAR
SUGGEST THE LOW HAS DROPPED INTO NORTHEAST UTAH THIS AFTERNOON.
SNOW HAS BEEN FALLING OVER THE NORTHERN MOUNTAINS OF THE CWA AND
INTO THE LOWER ELEVATIONS OF THE NORTHERN CWA AT TIMES TODAY.
MUCH OF THIS IS INSTABILITY DRIVEN WITH THE COLD CORE ALOFT
EXPANDING OVER OUR EASTERN CWA. ISOLATED SHOWERS POPPING UP
FARTHER SOUTH LATE THIS AFTERNOON WITH SOME ACTIVITY IN THE
SOUTHEAST UTAH MOUNTAINS AS WELL. EXTREMELY DRY AIR STILL IN PLACE
TO THE SOUTH SO NOT EXPECTING MUCH TO REACH THE GROUND...BUT A
FLURRY MAY REACH SOME OF THE CENTRAL VALLEYS THROUGH EARLY EVENING
DUE TO THE EXTREMELY DRY AIR IN THE PBL. THE FOCUS FOR THIS STORM
WILL BE SHIFTING FROM THE NORTH TO THE SOUTH BY TOMORROW WITH
NORTHEAST UTAH TERRAIN BEING FAVORABLE FOR COLLECTING MORE SNOW
OVERNIGHT IN THE NORTHEAST FLOW ALOFT. ISENTROPIC SURFACES NEAR
300K SHOW WEAK UPGLIDE AND MOISTENING ACROSS THE WEST CENTRAL CWA
TOWARD SUNRISE AS THE NOSE OF THE CYCLONIC JET PUSHES ACROSS
EASTERN COLORADO. THIS WILL SPREAD CLOUDINESS WESTWARD FOR SURE
WITH SOME POSSIBLE LIGHT PRECIPITATION IN THE EASTERN HILLS.
CLOUDS COULD HELP MODERATE TEMPERATURES OVERNIGHT BUT WHERE THIS
OCCURS IS DIFFICULT AT BEST TO PREDICT ATTM. DO FEEL WITH SUNSET A
GOOD AMOUNT OF THE CONVECTIVE DEBRIS WILL DISSIPATE SO HAVE STAYED
TOWARD THE COOLER SIDE OF GUIDANCE.

VERY TRICKY FORECAST EVEN IN THE SHORT TERM PERIOD AS MODELS ARE
HAVING A DIFFICULT TIME HANDLING THE DETAILS ON FOCUS AREAS FOR BEST
PRECIPITATION.  THE ONE THING THE MODELS AGREE UPON IS THAT THE LOW
PRESSURE SYSTEM WILL MOVE TOWARDS THE FOUR CORNERS AND WOBBLE AROUND
SOUTHWEST COLORADO ON THURSDAY BEFORE SHIFTING EAST OF THE DIVIDE ON
FRIDAY.  MOISTURE WRAPS AROUND THIS LOW IN EASTERLY FLOW WHICH WOULD
BENEFIT THE EASTERN SLOPES OF THE FRONT RANGE IN UPSLOPE FLOW AND IS
NOT AS FAVORABLE FOR THE MOUNTAINS OF WESTERN COLORADO TO SEE
SIGNIFICANT SNOWFALL...WITH THE EXCEPTION OF THE EASTERN UINTAS THAT
BENEFIT IN NORTHEAST FLOW WHERE ADVISORY IS IN EFFECT AND LOOKS ON
TRACK. IT DOES LOOK LIKE THE FOCUS FOR THE BEST PRECIPITATION WILL
BE THURSDAY EVENING THROUGH FRIDAY AFTERNOON...SO DECIDED TO
INCREASE POPS ACROSS THE AREA FAVORING THE NORTHERN AND CENTRAL
PORTIONS FOR BEST PRECIP DURING THAT TIMEFRAME AS VORT LOBES ROTATE
AROUND THE LOW AND THE ISENTROPIC FLOW LOOKS BEST OVER THOSE AREAS.
THAT BEING SAID...THE FLOW STILL TENDS TO FAVOR THE EASTERN AND
NORTHEAST SLOPES FOR BEST SNOWFALL ACCUMULATIONS.

TEMPERATURES WILL BE WARMER ON THURSDAY THAN TODAY WITH A WARMING
TREND THROUGH THE END OF THE WEEK INTO THE WEEKEND AND THIS WILL
ALSO LIMIT SNOW ACCUMULATIONS.  MOISTURE IS ALSO NOT AS PREVALENT
WITH PRECIPITABLE WATER VALUES BELOW 0.4 INCHES.  THE TREND TODAY
ACCORDING TO WEBCAMS IS THAT ANY SNOW THAT IS FALLING IS MELTING DUE
TO THE ROADS BEING WARM FROM RECENT ABOVE NORMAL WARMTH. SO THINKING
THAT WITH TEMPERATURES BEING WARMER ON THURSDAY AND FRIDAY...ANY
SNOW THAT DOES FALL WOULD MELT AS IT FALLS.  THERE MAY BE PERIODS OF
HEAVY SNOW IN SOME AREAS AS SHOWERS LOOK TO BE CONVECTIVE WITH SOME
ISOLATED THUNDER POSSIBLE.  ALTHOUGH THERE IS SOME POTENTIAL FOR
SOME MOUNTAIN AREAS TO PICK UP A FEW INCHES OF SNOW...CONFIDENCE IS
LOW ON WHICH AREAS TO FOCUS ON FOR BEST ACCUMULATIONS SO DID NOT
ISSUE ANY ADDITIONAL WINTER WEATHER HIGHLIGHTS.  THIS WILL BE
SOMETHING FOR FUTURE SHIFTS TO CONSIDER DEPENDING ON WHERE THE
CENTER OF THE LOW ENDS UP TRACKING AND WHERE CONVECTION AND PRECIP
BANDS DEVELOP.

.LONG TERM...(SATURDAY THROUGH WEDNESDAY)
ISSUED AT 348 PM MDT WED APR 15 2015

MODELS SHOW THE UPPER LOW FINALLY EJECTING INTO THE PLAINS TOWARD
THE GREAT LAKES LATE SATURDAY...EVENTUALLY PHASING WITH THE TROUGH
MOVING ACROSS SRN CANADA TOWARD MONDAY MORNING. 300K ISENTROPIC
SURFACE SHOWED MOISTURE CONTINUING TO WRAP AROUND THE NORTH SIDE
OF THE LOW AND BACK INTO THE ERN UINTAS AND WRN CO SAT. WILL KEEP
CLOUDS AND A CHANCE OF RAIN/SNOW IN THE FORECAST SATURDAY.

ADDITIONAL EMBEDDED WAVES THEN FOLLOW IN THE NW FLOW SUNDAY AND MONDAY.
THE MOST SIGNIFICANT WAVE LOOKS TO BE SUNDAY NIGHT INTO
MONDAY...BUT MOISTURE WILL LIKELY BE LIMITED WITH THE LONG
UPSTREAM FETCH OVER LAND. TEMPS WILL BE NEAR SEASONAL LEVELS.

GFS AND ECMWF DIVERGE HANDLING A WEAK UPPER LOW OFF THE CA COAST
MONDAY AND A PACIFIC TROUGH TRYING TO PUSH INLAND TUE-WED. ECMWF
SWINGS THE CA LOW ACROSS NRN BAJA AND TO THE EAST EARLY NEXT
WEEK WITH A THE PAC LOW EJECTING A WAVE INTO THE GREAT BASIN WED.
GFS...ON THE OTHER HAND...IS MUCH SLOWER WITH THE CA LOW AND HAS
THE PAC TROUGH DIRECTING MORE ENERGY DOWN THE COAST THAN INLAND.
WITH CONFIDENCE BELOW AVERAGE ON THE DETAILS AND TIMING...WILL
KEEP JUST A SLIGHT CHANCE TO CHANCE OF SHOWERS MAINLY OVER MTNS
MON-WED FOR NOW.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 528 PM MDT WED APR 15 2015

PLENTY OF CLOUDS AROUND THIS EVENING AND THEY WILL CONTINUE
THROUGH TOMORROW AS THE CLOSED LOW CONTINUES TO DROP SOUTHWARD.
MID LEVEL CLOUDS BETWEEN 5K TO 10K FEET WILL LIFT SOME TONIGHT BUT
EXPECT A RETURN TOMORROW. AS MOISTURE INCREASES...ANTICIPATED
CLOUDS WILL THICKEN AND LOWER THROUGH THE DAY WITH TAF SITES
SEEING OVC CIGS FROM GENERALLY 5K TO 10K FEET. SOME PRECIP IS
POSSIBLE AT TAF SITES AFTER 18Z TOMORROW BUT CONFIDENCE NOT VERY
HIGH AS TO WHERE PRECIP WILL FALL...THUS...LEFT MENTION OUT FOR
MOST SITES. THIS UNSETTLED WX WILL CONTINUE FOR THE NEXT 24 HOURS.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM MDT THURSDAY FOR
     COZ001-006-011-021.

     FREEZE WATCH FROM LATE THURSDAY NIGHT THROUGH FRIDAY MORNING FOR
     COZ021.

UT...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM MDT THURSDAY FOR
     UTZ022-024-027-029.

     WINTER WEATHER ADVISORY UNTIL 6 PM MDT THURSDAY FOR UTZ023.

&&

$$

SHORT TERM...15/MDA
LONG TERM...JAD
AVIATION...TGR



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