By John Ensworth
50 ways to create rain in Colorado. Ok, maybe there aren’t that many on display, but as we transition from northwest flow/shortwaves/and surface moisture/ and convergence on a frontal boundary, the ridge axis will pass to the east over the end of the weekend/start of the week and monsoon moisture is lurking ready to come up again. Figure 1 shows the still present surface front down the axis of the Rockies with the high out in Kansas/Nebraska sending moisture westward to Longmont and our neighboring communities.
Figure 1: Surface frontal analysis, pressure centers and radar from Wunderground.com.
Figure 2 shows, in dark green on the water vapor satellite image, the returning monsoon moisture to the south even as (light green) Great Plains moisture flows back towards us.
Figure 2: The 500mb map forecast for Friday morning from the GFS model.
With the shortwaves still coming, and more surface heating as the ridge approaches, and with the front nearby, severe weather is still expected for Longmont and the Front Range Saturday and Sunday as southwest flow and warm air and monsoon moisture flows in. It is again a Marginal Risk – a 1 on a scale of 1-5 issued by the Storm Prediction Center in Norman, Oklahoma (the SPC) – again mainly for supercell related large hail and damaging winds. Soils are quite wet many places, so always be aware that local flooding may occur under the bigger storms – Figure 3 and 4.
Figure 3: The SPC forecast Day 2 for Saturday issued on Friday.
Figure 4: The SPC forecast Day 3 for Sunday issued on Friday.
In a look at the longer range:
By Monday morning (Figure 5) the ridge axis is passing and monsoon moisture (green arrow) is flowing back towards Colorado with more warm air. Things stay wet and unsettled into midweek and beyond with an approaching trough and warm moist southwest flow. I’ll include a hydrology update this week when it is issued to see how our drought (or non-drought) conditions are.
Figure 5: The Monday morning upper air pattern, 500mb GFS forecast. The ridge is drawn in blue.
Figure 6: The Wednesday morning upper air pattern, 500mb GFS forecast. The ridge is drawn in blue, the next major trough is in red, and southwest moisture is in green.
*** This feature will run as close to daily as possible in this location on the Longmont Observer. ***
This article will provide a brief discussion concerning the ‘why’ behind the weather with a focus on severe weather, unusual weather, and snow (especially trying to predict snow depth and its human impact in Longmont).
John Ensworth works from Longmont as the Principle Investigator for the NASA Science Mission Directorate Earth and space science education product review through the IGES (The Institute for Global Environmental Strategies – www.strategies.org) . He is in his 14th year running this review. He is an astronomer (from the 2nd grade onward) and became a meteorologist (in the 5th grade) when a thunderstorm in Arizona rained on his telescope when the weather service had only forecasted a 10% chance of rain. He has college degrees in physics and astronomy and climatology and a graduate degree in meteorology and earth science. He lectures at the Little Thompson Observatory in Berthoud, the Estes Park Memorial Observatory in Estes Park, and for a number of online universities. He built and runs a backyard observatory near Pace and 17th in northeast Longmont where he has lived for 8 years with his wife, daughter, son, and two cats. Invitations to open house nights at this observatory, LTO, and EPMO will be posted with future discussions when they are scheduled.
Forecasting severe weather and snow amounts via text lead to this column. He began texting friends about the weather right after the September 2013 flood. The readers of this column will, hopefully, keep him honest in what he ‘thought’ he had forecasted for ‘the most recent’ storm.