The Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – June 23, 2018

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Figure 5: The snapshot of precipitation type and intensity with surface pressure features from the GFS and for Sunday AM.

Forecast Discussion:

An early upper level wave creted cloudy skies midday yesterday and some virga (rain that evaporates before hitting the ground due to low levels of atmospheric moisture in the lower levels – called Devils Rain in the desert southwest). There were gusty winds that went along with the virga.  Our afternoon thunderstorms fired about 1pm and passed Longmont around 2:30pm with some showers around town.  They became stronger east of I-25 as predicted yesterday.

Today is a mostly dry day with very low chances of afternoon storms.  A small upper level ridge will make the air sink a bit today, inhibiting convection. Our next system is visible to our northwest in Figure 1.

Checking on the smoke forecast today, Figure 2 shows us with very clear skies and most fire sources remaining fairly tame around the state. That is a relief. (FYI, the 416 fire is 37% contained as of Friday morning.) With a ground level convergence line and some deeper moisture to our east, there is a marginal risk of severe weather fairly far east of I-25, not impacting Longmont.  We may see a cell or two punch through the atmosphere in the afternoon, but, just to our west it, should remain rain free (Figure 3).


Figure 1: The forecast surface map for this afternoon. From NCEP.
Figure 3: The HRRR model forecast for smoke at all levels for Saturday afternoon. From
Figure 3: the day 2 SPC thunderstorm and severe weather forecast made Friday (valid Saturday).

The longer range forecast:

Another upper level trough approaches early on Sunday behind the short wave ridge that is departing. It will usher that cold front, from Figure 1, down across the state – (Figure 4). A run of the GFS model from Friday showing a sunrise snapshot of weather conditions illustrates frontal precipitation pushing into the mountains and NE Colorado plains (Figure 5). We remain in the 70’sF again this day.  Between the morning showers and afternoon scattered thunderstorms, we might see some rain again. The SPC (Figure 6) paints us with a marginal risk (1 on a scale of 1-5) of severe weather Sunday – primarily for hail again.

We warm to the 80’s and dry out some on Monday- then dry out more and return to the 90’sF for most of the week.  See you tomorrow!

Figure 4: The forecast surface map for tomorrow afternoon. From NCEP.
Figure 5: The snapshot of precipitation type and intensity with surface pressure features from the GFS and for Sunday AM.
Figure 6: the day 3 SPC thunderstorm and severe weather forecast made Friday (valid Sunday).
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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 – . 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.

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