The figure above indicates the forecasted high in orange (with error bar denoting the range of ensemble forecast members), average high for this time of year in orange (dashed line), forecasted low in blue (with error bar), average low this time of year in blue (dashed line), and forecasted wind speed in purple. Note that the wind speed forecast is sustained wind (not gusts), and it is based on only one model (not an ensemble).
** CORRECTION: Regarding my previous e-mail, the NWS has informed me that there was a peak wind gust at the Prescott Airport of 70 mph in Jan. 2010. That was the 2nd strongest wind gust on record and last Friday night would probably have been the 3rd strongest since peak winds have been recorded starting in July 1996. It’s hard to locate these records…
Wow…it’s shaping up to be a wet week! This weather pattern is not typical of the current La Niña conditions in the tropical Pacific ocean, probably because the north-central Pacific is unusually cold for this time of year and the subtropical Pacific Ocean is abnormally warm (see the latest anomalies at https://www.esrl.noaa.gov/psd/map/images/sst/sst.daily.anom.gif warm colors are warmer than normal and cold colors colder than normal). This temperature contrast in the Pacific is likely causing more frequent storm formation than normally expected during La Niña years.
The first of two storms, the cutoff low circulating along the West Coast of the Baja is now expected to open up and move across Arizona tonight and tomorrow, bringing widespread showers and about 1 - 1.5” of rain accumulation across the Prescott area. By tomorrow afternoon, the atmosphere will become weakly unstable, with the possibility for isolated thunderstorms. Any thunderstorms that form will propagate towards the northeast at about 25 mph and be capable of 20-30 mph wind gusts, occasional lightning, locally heavy rain or graupel (or snow pellets). Otherwise, it will be too warm for frozen precipitation, as snow levels will be about 8-9,000’. Winds will otherwise be light southwesterly breezes tomorrow.
On Friday, the weather will remain unsettled as the first system exits the state and a colder and stronger storm approaches. The forecast models are converging on a solution…with the axis of this second storm mostly likely to cross the state on Saturday evening. Expect widespread rain developing during the day on Saturday, with gusty wind of 20-30 mph gusting up to 45 mph. Liquid water equivalent with the second storm will be about 0.75”. With the passage of the cold front on Saturday afternoon (Christmas eve), snow levels will gradually drop to near 4,000’ and rain will change to snow between 2 and 5 pm. The current forecasts are indicating 2”-4” of snow accumulation in Prescott on Saturday afternoon - evening, with lingering snow flurries possible on Christmas morning. Higher snow amounts up to 8” may be possible in the higher mountain locations around town. Looks like it just could be a white Christmas this year! Roads may get snow packed on Christmas eve or icy on Christmas morning, so be prepared.
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