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weekend storm update

By ccrossen | November 16, 2010

gfs_p60_150m20101116.gif

Weather is coming. See above GFS model run for 150 hours out. At this point in time, the NWS is telling us we’re going to get hit, but due to the variance in model runs, it’s not exactly clear exactly when and exactly how much we’re going to get. The potential is there for a lot of snow due to very cold temps and moderate moisture tap, with the potential for more of a moisture tap. Or a little bit. I tend to favor the former. Forecast for next week looks unclear as well, with some models running stormy, others fair. PacNW is getting slammed all the way over to JH.

From NWS:
241 AM PST TUE NOV 16 2010…SIGNIFICANT WINTER STORM TO IMPACT THE REGION…A VERY COLD LOW PRESSURE SYSTEM DEVELOPING OVER THE GULF OF ALASKA WILL DROP SOUTHWARD TO THE PACIFIC NORTHWEST COAST BY THURSDAY AND INTO NORTHERN CALIFORNIA AND NEVADA THIS WEEKEND. AHEAD OF THIS SYSTEM ON THURSDAY AND FRIDAY WINDS WILL INCREASE AND BECOME STRONG AT TIMES. GUSTS OF 45 MPH OR MORE ARE POSSIBLE IN THE EASTERN SIERRA AND WESTERN NEVADA. RIDGE WIND GUSTS WILL LIKELY EXCEED 90 MPH. OVER THE WEEKEND…THE MAIN PORTION OF THE STORM WILL REACH THE SIERRA AND WESTERN NEVADA WITH SNOW LEVELS FALLING TO ALL VALLEY FLOORS. MOST AREAS WILL RECEIVE ACCUMULATING SNOW WITH A FEW MODELS SUGGESTING A POTENTIAL FOR SIGNIFICANT SNOWFALL.

DETAILS CONTINUE TO CHANGE FROM RUN TO RUN AND MODEL TO MODEL AND THIS IS RESULTING IN LESS CONFIDENCE IN TIMING OF PRECIPITATION AS WELL AS AMOUNTS. AT START OF PERIOD…MODELS SHOW COLD FRONT AND INITIAL PRECIPITATION BAND HANGING UP OVER THE NORTHERN SIERRA AS IT AWAITS UPPER LEVEL JET TO MOVE ACROSS THE PACNW INTO THE NORTHERN ROCKIES LATE FRI. MODELS HAD BEEN TRENDING EVER SO SLOWER FROM PREVIOUS RUNS AND THIS HAS PROMPTED POPS TO BE REDUCED OVER PARTS OF WESTERN NV FRI. ALSO BUMPED TEMPERATURES UP A FEW DEGREES MAINLY FROM I-80 SOUTHWARD. DUE TO THE DELAY IN THE FRONTAL SYSTEM…GUSTY DAYTIME WINDS WILL LIKELY OCCUR ONCE AGAIN FRI AFTERNOON AND EVENING PRIOR TO FRONTAL PASSAGE AS RIDGE WINDS WILL LIKELY STILL BE GUSTING WELL OVER 75 MPH.

ONCE JET IS IN PLACE…FRONTOGENESIS AND LARGE SCALE LIFT WILL INTENSIFY FRONTAL PRECIPITATION BAND AND ALSO HELP PUSH FRONT SOUTHWARD FRI NIGHT/EARLY SAT. THE ECMWF DIFFERS A BIT HERE NOW IN THAT IT PUSHES FRONT QUICKLY THROUGH FRI NIGHT AND SHOWS A DRY SLOT ALOFT AND ROUGHLY A 12 HOUR BREAK IN PRECIPITATION SAT. THE GFS KEEPS THIS DRY AIR FURTHER WEST AND THUS TRANSITIONS QUICKLY TO MOIST UNSTABLE PROFILE UNDER APPROACHING UPPER LOW. ONCE THE UPPER LOW DROPS FURTHER SOUTH AND COLD MOIST AND UNSTABLE PROFILE DEVELOPS OVER THE AREA SAT NIGHT INTO SUN…PRECIPITATION CHANCES SEEM TO BE MORE CERTAIN. DECIDED NOT TO CHANGE POPS/WEATHER OVER THE WEEKEND BECAUSE OF THIS UNCERTAINTY. SNOW LEVELS WILL FALL QUICKLY TO MOST VALLEY FLOORS WITH INITIAL FRONT AND THEREFORE PRECIPITATION TYPE IS MORE CERTAIN. BOTTOM LINE…CONTINUE TO MONITOR FORECASTS AND STATEMENTS AS THIS IS AN UNUSUALLY VIGOROUS SYSTEM AND ALMOST GUARANTEES SOME SNOW AND TRAVEL ISSUES WHILE LEAVING THE POTENTIAL FOR MORE SIGNIFICANT IMPACTS IF HEAVIER SNOW BANDS DEVELOP. TEMPERATURES WILL CERTAINLY BE WELL BELOW NORMAL WITH DAYTIME HIGHS STRUGGLING TO GET OUT OF THE 30S SAT-SUN. MODELS DIVERGE SIGNIFICANTLY MONDAY AND ALL BETS ARE OFF EARLY NEXT WEEK. SOME MODELS SHOW SYSTEM WINDING DOWN WHILE OTHERS BRING A CONTINUED THREAT OF SNOW. FOR NOW WILL MAINTAIN LOW CHANCE POPS DUE TO UNCERTAINTY. TEMPERATURES WILL REMAIN COLD.

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