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6 Days of Winter Weather
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19 January 2017   Dr. Curtis James

Weather will include rain and snow this weekend.

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).

Weather Discussion:

You can be sure that for the next 6 days…we are going to see a series of storms and a lot of cloudiness and precipitation! 

Storm #1 Thursday – Thursday Night, 

Storm #2 Friday afternoon – Saturday noon, 

Storm #3 Sunday night - Tuesday morning (timing of storm #3 is still somewhat uncertain). 

The forecasts are indicating precipitation totals between 1.5” and 2.0” of liquid water equivalent by next Tuesday, which will provide some continued drought relief (California will be getting even more rain than we do). It will also be breezy to windy, with sustained winds 20-30 mph on Friday night and again on Monday, with higher gusts possible both days.

What isn’t certain is exactly what the temperatures will be (especially on Friday night), which affects the snow levels and snow amounts. The attached briefing from the National Weather Service indicates 1-2” of total snow for Prescott by Saturday afternoon. This forecast is strongly weighing the guidance from the GFS model (which is predicting warmer temperatures than the other models). The GFS is only indicating 0.6” of snow for the Prescott Airport by Saturday afternoon and 1.7” total snow through Tuesday. This is because the temperatures in the model indicate that most of the precipitation would fall as rain or rain/snow mixed at the elevation of Prescott. However, another computer model called the NAM is indicating 10.6” of snow for Prescott Airport by Saturday afternoon. Thus, how much snow we receive these next few days will be strongly dependent upon just how low the surface temperatures and the snow levels drop. Snow levels can be affected by many different variables. Evaporation and melting of falling precipitation can cool the air near the ground and help rain or rain/snow mixed to change to snow especially when the precipitation rate is heavier and the air is drier. Also, cold air can get entrenched into certain valleys or low-lying areas, helping the snow levels to lower. At the same time, in advance of each of the storms, there is a warming that takes place as warmer south to southwest wind moves into the area.

Therefore, my prediction is that we will see rain mixed with snow this morning, changing to rain this afternoon, then back to snow late tonight-early tomorrow morning for about 1-2” of accumulation by Friday morning. Then, light snow flurries will linger on Friday morning, change back to rain or rain/snow mixed on Friday afternoon as warmer air comes back into Arizona, then back to snow on Friday night – Saturday. I would expect another 2-4” on Friday night, so a total of say 3-7 inches of snow accumulation by Saturday afternoon. Higher elevations around town will see higher snowfall amounts and more snow will be possible next Monday – Tuesday. The more hazardous times for travel will be Friday morning, Saturday morning, and Tuesday morning, when packed snow or icy roads will be more likely to be present. Travel will be difficult at higher elevations around northern Arizona this weekend and early next week. (Flagstaff will receive 1-2 feet of snow by Saturday afternoon.)

C. James

 


Met Mail is an unofficial weather discussion and forecast transmitted once or twice a week via e-mail by the Embry-Riddle Department of Meteorology (http://meteo.pr.erau.edu/). Embry-Riddle offers an undergraduate bachelor-of-science degree program in Applied Meteorology. Please spread the word to all potential qualified candidates!

Further Information:

ERAU Applied Meteorology degree program

Official National Weather Service forecast

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