20190218 TEP

Another highly unusual weather event is expected to impact SE Arizona and eastern Pima county starting early Friday morning.  A very cold low-pressure system moves slowly through the state bringing widespread precipitation along with a strong cold front.  This system is much drier and colder than the previous system but has much stronger atmospheric forcing thus lower elevations will see as much or more precipitation.  The really important part of this storm is the very low snow levels and right now, it's likely that the lower elevations of eastern Pima County will see significant snow accumulations with 2-4 inches with more at the higher elevations, near the mountains, maybe in the 4-8 inch range.  Mt Lemmon snowfall is expected to be extreme with 2-4 feet possible.  I've included TEP in on this email as there may be enough heavy wet snow to bring tree limbs down on power lines in parts of Tucson.


Precipitation amounts are generally .5" to over 1 inch in the lower elevations with 2-4 inches in the mountains which will all be snow.  It will be cold in the mountains so the snow to liquid ratio will be above 10:1. 


I do not normally send out a forecast this far in advance but confidence is fairly high in the model forecast as all the runs have been quite consistent recently plus this is such an unusual and high impact event, I thought it important to alert Pima County and TEP well in advance.   The set up for snow in Tucson is excellent as the forecast has the cold front coming through around 4-6am, right at the coolest part of the day.  Rain should rapidly change over to snow and continues through the morning. Note that the station model on the below plot shows rain as I never programmed in snow.



Tomorrow, the event will be within the range of the ensemble prediction system thus I'll have a better idea of what may actually happen.