Wasatch Weather Weenies

If you are a skier and you are interested in snow level or snowmaking, you should get to know something called the wet-bulb temperature .   Most of the time when we refer to temperature we are talking about the ambient air temperature or what is known to meteorologists at the dry-bulb temperature .  This is the temperature measured by a thermometer that is exposed to the air but protected from radiation and moisture.  Bulb refers to the rounded end of an old school liquid thermometer and dry bulb indicates that the air temperature recorded is not affected by moisture.   The wet-bulb temperature is the lowest temperature that can be achieved through evaporation under current ambient conditions.  In the past, it was measured by wrapping the bulb of a thermometer in a wet muslin (hence "wet bulb").   Old school dry and wet-bulb thermometer setup.  Source:  https://collection.sciencemuseumgroup.org.uk/objects/co518421/wet-and-dry-bulb-...

Extensive flooding continues along the San Juan River in Colorado, New Mexico, and Utah.   Shiprock, NM.  Source: Navajo Police Department/Handout, via Via Reuters, New York Times Rainfall in the upper San Juan Basin has been remarkable since the start of the water year on October 1st. SNOTEL records in the basin only run back to 1987, but liquid precipitation averaged at sites in the basin is up to 15.9 inches, which is well above the prior record.     Source: NRCS Additionally, the snowpack water equivalent at those sites is only 4.4", so only about a quarter of that precipitation has been retained in the snowpack.   Other headwater basins of the San Juan also received record precipitation, much in the form of rainfall to relatively high elevations.   Meanwhile, the statewide numbers for Utah are also quite remarkable.  At SNOTEL stations, the statewide average precipitation since the start of the water year is  6.5 inch...

A pretty good upper-elevation storm cycle is coming to an end at the upper elevations.  Total water equivalent at Alta-Collins since October 30th is as of 7 AM this morning (Monday, November 2nd) is 2.6 inches.  Total snowfall during the period based on interval measurements is now up to 17 inches with the total snow depth now at 19".   At 9662 ft, Collins received mostly snow in this event.  It's possible that there was rain at that elevation or rain mixed with snow for brief periods as the wet-bulb temperature reached as high as 34°F during a few periods.  The wet-bulb temperature, which is the lowest temperature that can be achieved through the evaporation of water, is a better (but still imperfect) discriminator of precipitation type than normal temperature.  It's a about a 50/50 chance of snow at a wet-bulb temperature of 33°F, so when you go beyond that, it's getting closer to a rain situation.   At the base (8530 feet), yesterday was a...

I woke up this morning refreshed from an extra hour of sleep and excited to check out the storm.  First thing I did was pull up the radar and saw something that one doesn't see all that often. As full and complete coverage of precipitation as you can observe with the KMTX radar.   It's rare to see situations where there is complete coverage of radar echoes here, but there you have it.  Such a situation also allows you to see all of the places where the radar beam is blocked or partially blocked by the topography.  These produce bands of lower reflectivities or no reflectivity "down radial" or beyond the terrain feature as one moves away from the radar. Below is a schematic of this effect. Source: S ecrets of the Greatest Snow on Earth One can also see a ring around the radar that looks a bit like a donut.  This area of higher radar reflectivities is produced where the beam cuts through the melting layer where falling snow is warming, melting, and becoming r...

After many postponements, the Rapid Refresh Forecast System (RRFS) and RRFS Ensemble Forecast System (REFS) are still scheduled to become operational on November 3rd.   The RRFS and REFS are the latest "high resolution" modeling systems developed by NOAA for the National Weather Service.  I have high resolution in quotes because the reality is that many countries are now far ahead of the US National Weather Service in resolution and ensemble design. The RRFS and REFS have 3-km horizontal grid spacing and are based on the Finite-Volume Cubed-Sphere FV3 dynamical core developed by NOAAs Geophysical Fluid Dynamics Laboratory .  A dynamical core is basically the guts of a numerical weather prediction model as it represents the mathematics and numerics used to simulate the motion of the atmosphere on Earth.   In 2016, NOAA decided that the FV3 dynamic core would be the guts of their numerical weather prediction models , starting with the Global Forecast System (...

Early snow often becomes weak snow so the snow-safety cognoscenti often tell me they'd prefer the snow hold off until November and then come in spades.   Right now, the first part of that wish looks like it will come through. Snow in the Wasatch is currently scant and confined to areas near and above 10,000 feet on north aspects.  The 1420 MST Mt. Baldy web cam showing upper Collins Gulch for example show fairly limited snow cover.   Forecasts through Halloween (i.e., the end of October) for the central Wasatch suggest maybe a few periods of precipitation Friday night or Halloween.  Halloween itself is looking warm and windy right now. The GFS forecast for 0000 UTC 1 November (1800 MDT) Saturday shows warm, southerly flow ahead of an approaching upper-level trough with some scattered showers and 700-mb (10,000 ft) free atmosphere temperatures near +1°C.   Thus, I expect to see more snow loss through the end of the month, with snow lingering mainly...