In Brief:

Today (Friday) will be quite hot (upper 80sF) then a cold front arrives around 3pm and the temperatures start to sink a bit. We are 10F cooler than today through Tuesday. Rain, severe thunderstorm chances (high winds primarily), and normal thunderstorm chances pick up with the front and continue- mainly each midday to early evening through Tuesday. We warm up and dry out after that.

2:30 pm Update:

The SPC (Storm Prediction Center, Norman OK) has trimmed the western edge of our Marginal Risk off so it now begins about 10-20 miles east of I-25. It does include DIA but not Longmont at this time. General thunderstorms are the most likely storm effects we’ll feel for the rest of the afternoon.

Figure 2 update shows the redrawn extent of the Marginal Risk and the first showers firing off.

Figure 2 update: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Friday for Friday overlay on a radar may from MyRadar app IOS.

End 2:30 pm Update.

9:30am Update:

There is a marginal risk of severe weather for Longmont today (Figure 1 update) – a 1 on a scale of 1-5. Some better moisture, a Denver cyclone, upper air energy (cold air), and serious daytime heating will come together to allow a few cells to reach severe limits today – high winds and large hail are now the primary threats. There is a slight risk (2 on a 1-5 scale) further to the southeast on the Plains. The western edge of the marginal risk runs from just south of Ft. Collins and includes Loveland to Boulder and western Denver southward. Peak thunderstorm time should run from 2pm to 6pm.

Figure 1 update: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Friday for Friday overlay on a radar may from MyRadar app IOS.

End 9:30am Update.

Forecast Discussion:

There is a front approaching today, as that happens that happens we’ll have, maybe, the warmest day of the year so far, more atmospheric moisture, and a much better chance of afternoon thunderstorms (Figure 1). We will also be on the edge of a Marginal Risk (1 on a scale of 1-5) with the primary threat being powerful downburst winds (Figure 2).

The Longer Range Forecast:

Oops, I forgot to mark features on Figure 3, but the front looks timed with the point where the black line bottoms out and winds peak on Friday around 2-3pm. Rain chances are highest with the front as well. By early Saturday morning, the front is down the Front Range and into Oklahoma (Figure 4). The amount of water we’ll receive over the next 5 days is pretty substantial, now, over much of the northern and eastern parts of the state (Figure 5). This run gives Longmont 3/4th inch of water, but nearby locations get up to 2 inches.

Now to the much longer range forecast:

Some of the U.S. models (GFS!) have not been doing well in temperature and precipitation forecasts over the long range. The CFS has been doing a pretty good job.

Figure 6 is the temperature departure for normal averaged over 5 days June 13-18 from the CFS. Longmont is quite a bit colder than normal.

Figure 7 is the same but for June 18-23. We are colder than normal even compared to the previous 5 days.

Figure 8 is June 23-28 – still quite a great deal below normal.

Figure 9 is June 28-July 3 and we are somewhat below normal.

As for precipitation June 12 to 30 from the NCEP CFSv2 model – we are a good deal above normal (200%) for the amount of precipitation normally seen over the last half of June. Cool and Wet is our future.

Figure 1: The forecast surface map for Friday night from NCEP.
Figure 2: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Thursday for Friday.
Figure 3: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 4: The forecast surface map for Saturday morning from NCEP.
Figure 5: the forecast accumulated precipitation map from the GFS and weather5280.com for Colorado,over the next 5 days.
Figure 6: the CFS model surface temperature anomaly (departure from normal – blues to greens are below and much below normal, oranges to reds are above to much above normal). For the period June 13-18. From weatherbell.com
Figure 7: the CFS model surface temperature anomaly (departure from normal – blues to greens are below and much below normal, oranges to reds are above to much above normal). For the period June 18-23. From weatherbell.com
Figure 8: the CFS model surface temperature anomaly (departure from normal – blues to greens are below and much below normal, oranges to reds are above to much above normal). For the period June 23-28. From weatherbell.com
Figure 9: the CFS model surface temperature anomaly (departure from normal – blues to greens are below and much below normal, oranges to reds are above to much above normal). For the period June 28- July 3. From weatherbell.com
Figure 10: the NCEP CFSv2 model surface temperature anomaly (departure from normal – blues to greens are below and much below normal, oranges to reds are above to much above normal). For the period June 12 to 30. From weatherbell.com
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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 – 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.

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