wxgeek's weather-Early August Forecast-Update 8/8

Update Fri Aug 8

Our daily showers and thunderstorms are rolling across the mountain and foothills and into the plains. Atmosphere remains fairly moist and slightly unstable so storms will persist through sunset, then die down. Storm motion today from the west at 15-25 mph, so faster motion will limit flood potential, but brief heavy rain along with small hail and lightning will be possible.

For the weekend, pattern will remain very similar with abundant surface moisture, monsoon flow and ripples in the flow aloft that will aid in afternoon and evening showers and thunderstorms. Flow likely to be from the west and storm motion of 10-20 mph expected, so fast enough to limit substantial flooding, but some storms will be strong and capable of dropping a quick 0.50 - 1.0 inches of rain quickly, along with small hail and frequent lightning. All in all, fairly typical August pattern for CO with temps near seasonal norms.

For next week, medium range models differ. ECMWF drops a another cutoff low over CA by late next week and keeps a ridge over CO, while the more progressive GFS swings an upper trough across the Rockies. Preference is to go with the ECMWF which would keep our daily monsoon pattern in tact through most of next week. If the GFS solution wins, then we could expect cooler temps and some pretty heavy rain at times by late next week. Either way our wet summer pattern will continue, and longer range models suggest this will likely persist into late August which will keep CO looking and feeling more like the Pacific Northwest for a while.

_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

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Update Wed Aug 7

Strong to severe band of thunderstorms passed through the foothills and Urban Corridor now heading onto the plains. This band dropped a nice layer of hail and up to an inch of rain in many areas, causing some localized flooding. SPC has issues a Severe Thunderstorm Watch for eastern CO (east of I-25) through 7 pm this evening. This activity is related to a moist and unstable surface environment aided by a weak upper level disturbance moving across CO today. A second disturbance is now moving into northwest CO and will move east across eastern Co this evening, so a new round of showers and thunderstorms will be possible late this afternoon into this evening across the foothills and into the plains.

For Friday, models indicate a slightly drier and more stable air mass will be in place, so expect fewer storms, but there will still be isolated activity with some storms capable of producing brief heavy rain during the afternoon and evening hours from the mountains to the plains.

For the weekend, expect more isolated to scattered showers and thunderstorms in the afternoon and evening hours from the mountains to the plains. Upper level pattern suggest a decent monsoon flow both days, so potential for brief heavy rainfall will exist.

By next week, models indicate upper ridge will retrograde westward to our west, creating a more northwesterly flow aloft over CO. This would indicate a slightly drier pattern, but I believe there will be enough surface moisture and instability to fuel afternoon and evening showers and thunderstorms pretty much every day next week. Mostly of the isolated variety, but heavy if they happen to move over you. Upper level pattern does not appear to be changing anytime soon, so expect more of this type of pattern into mid August. Temps will remain close to seasonal norms through the period as well.

Hurricane Iselle is currently located about 200 miles east southeast of Hilo, Hawaii. Iselle is a category 1 hurricane with maximum sustained winds to 75 mph and is expected to make landfall just south of Hilo on the Big Island around 10 pm Hawaii local time tonight. Biggest impacts will be very large surf up to 30 ft, heavy rainfall of 5-10 inches and a storm surge of 3-5 feet. It has been a while since a hurricane made landfall on the big Island, none since 1950 and 22 years since any hurricane has hit Hawaii, which was hurricane Iniki on the island of Kuai. Hurricane Julio, which is a category 2 hurricane with max sustained winds to 100 mph is located 900 miles east southeast of the big island, but is forecast to track north of the Hawaiian islands on Sunday and Monday, but may still provide large surf and high winds.

Lastly, the activity near Hawaii is likely connected to warmer than usual waters in the Pacific, due to a building El Nino. However, the latest El Nino advisory issued today suggests waters have cooled some since June, so the probability of an El Nino this Fall and Winter has reduced to a 65% chance, and most models now indicate only a weak El Nino is likely. This change may have significant impacts to pattern that develop this winter across the U.S. The weaker the El Nino, the less defined the pattern becomes. El Nino normally means higher than average snowfall for eastern CO, especially in the foothills, but the weaker the intensity, the less confident this correlation becomes. We will know more by October and how this El Nino will actually evolve and the implications for our upcoming snow season.

_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

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Update Wed Aug 6

Upper level low now currently over central CA and upper ridge axis along the Continental Divide through CO. This will bring a slightly drier flow to CO today with storm motion from the west at 10-20 mph. Precip today looks to be confined to the mountains this afternoon and the far northeast plains this evening. Could be a stray shower or two over the foothills, but not expecting much.

On Thursday, the upper ridge axis shifts eastward into eastern CO and NM, while upper trough over CA ejects into the Great Basin. This pattern will allow for a better monsoon flow up from Mexico and as upper trough moves across CO Thursday evening, it will create some additional instability, thus better precip chances across CO on Thursday. Storm motion Thursday will be from the southwest at 5-15 mph, so flood potential will be higher, and storms could persist into nighttime hours over the plains. Similar pattern expected for Friday as upper ridge axis remains over eastern CO, so similar precip chances to Thursday.

By Saturday, models move upper ridge axis back over central CO, so precip will be more confined to areas along and west of the Divide, with a few showers and thunderstorms possible into the foothills and Urban Corridor. Similar pattern expected for Sunday with most precip remaining west of the Divide, only isolated showers and thunderstorms for the foothills.

For early next week, upper ridge expected to shift eastward into west Texas, which will allow for a better monsoon flow into all of CO, hence better precip chances statewide Monday into Wednesday and as weak upper trough moves over CO Tuesday into Wednesday, so slightly cooler temps as well. By late next week, upper ridge moves farther west so slightly drier pattern expected. This ebb or pulse in the monsoon pattern is quite normal, especially in August as weak upper level disturbances begin to become more frequent and slide farther south, impacting CO.

Since our record precipitation in July, we don't need too much more in August to keep fire danger low. However, September is the month we typically need to be more concerned about for fire danger. As grasses begin to dry out, September tends to be our second fire season in CO that can extend into October depending on precip. The good news this year is that an El Nino pattern typically brings in early storms in September and October which would limit fire danger.

_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

Bump for 8/7 update

Bump for 8/8 update